ABB circuit breakers for
direct current applications
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Index
1. Introduction ............................................................................................................2
2. Generalities on direct current ..................................................................... 3 - 4
3. Applications
3.1 Conversion of alternative energies into electrical energy .........................................5
3.2 Electric traction .......................................................................................................7
3.3 Supply of emergency services or auxiliary services ................................................8
3.4 Particular industrial applications ..............................................................................8
4. Generation
4.1 Storage batteries ....................................................................................................9
4.2 Static conversion ...................................................................................................10
4.3 Dynamo ..............................................................................................................11
5. Interrupting direct current ....................................................................... 12 - 13
6. Types of DC networks
6.1 Network insulated from ground .................................................................... 14 - 15
6.2 Network with one terminal grounded ............................................................. 16 - 17
6.3 Network with the middle point of the supply source connected to ground .... 18 - 19
7. Choice of the protective device ............................................................. 20 - 30
8. Use of alternating current equipment in direct current
8.1 Variation of the magnetic field ........................................................................ 31 - 32
8.2 Connection of circuit breaker poles in parallel .......................................................33
9. ABB offering
9.1 Circuit breakers ....................................................................................................34
9.2 Molded case circuit breakers ......................................................................... 35 - 41
Annex A
Direct current distribution systems ............................................................................ 42 - 44
Annex B
Calculation of short-circuit currents ........................................................................... 45 - 47
Annex C
IEC circuit breakers and molded case switches for applications up to 1000 VDC ..... 48 - 51
Glossary ......................................................................................................................52
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1. Introduction
Direct current, which was once the main means of distrib-
uting electric power, is still widespread today in electrical
plants supplying particular industrial applications.
The advantages offered by the use of DC motors and sup-
ply through a single line make direct current supply a good
solution for railway and underground systems, trams, lifts
and other transport means.
In addition, direct current is used in conversion plants (in-
stallations where different types of energy are converted into
electrical direct energy, e.g. photovoltaic plants) and, above
all, in those emergency applications where an auxiliary en-
ergy source is required to supply essential services such as
protection systems, emergency lighting, wards and facto-
ries, alarm systems, computer centers, etc. Accumulators
are the most reliable energy source for these services, both
directly as direct current as well as by means of uninterrupt-
ible power supply units (UPS), where loads are supplied in
alternating current.
This technical application paper is intended to explain the
main aspects of the most important applications in direct
current and to present the solutions offered by ABB prod-
ucts.
This paper also has the goal to give precise information
to provide a rapid choice of the protection/disconnection
device, paying particular attention to the installation charac-
teristics (fault types, installation voltage, grounding arrange-
ment).
There are also some annexes with further information about
direct current such as:
• Information about distribution systems
• Guidelines on the calculation of DC short circuit cur-
rents as per IEEE 551, IEEE 141
• Circuit breakers and molded case switches for applica-
tions up to 1000 VDC
Introduction
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2. Generalities on direct current
Knowing the electrical characteristics of direct current and
its differences with alternating current is fundamental to
understand how to employ direct current.
By definition, direct current has a unidirectional trend con-
stant in time. Analyzing the motion of the charges at a point
crossed by a direct current, the quantity of charge (Q) flow-
ing through a cross section is always the same.
Batteries or dynamos can provide direct current. It is also
possible to convert alternating current into direct current
through a rectifying process.
However, a “pure” direct current, a current which does not
present any periodic fluctuation, is generated exclusively by
batteries (or accumulators). In fact, the current produced by
a dynamo can present small variations which do not make
it constant in time. Nonetheless, from a practical point of
view, this is considered a direct current.
Figure 1
Quantity of charge flowing through the cross section of a conductor
In a DC system respecting the current direction has
a remarkable importance. Therefore it is necessary to
correctly connect the loads by respecting the termi-
nals, as operation and safety problems could arise if
the terminals should be connected incorrectly.
For example, if a DC motor were supplied by switch-
ing the terminals, it would rotate in reverse and many
electronic circuits could suffer irreversible damage.
Generalities on direct current
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half period
10ms
I (A)
t (ms)
period
20ms
I (A)
t (ms)
I
I
max
I
r.m.s
R.m.s. value of a sinusoidal quantity
The r.m.s. value is the parameter which relates alternating
to direct current.
The r.m.s. value of an alternating current represents the
direct current value that causes the same thermal effects
in the same period of time. For example, a direct current of
Figure 2
Periodic waveform
Figure 3
R.m.s. value (value of the equivalent direct current)
The r.m.s. value of a perfectly sinusoidal waveform is equal to:
I
2
max
I
r.m.s
=
(where I
max
is the maximum value of the amplitude of the sinusoidal waveform)
Figure 4
Sinusoidal waveform
Figure 5
R.m.s. value (value of the equivalent direct current)
1
T
∫
i
2
0
T
(
t
)
dt
I
r.m.s
=
(where T is the period)
i (t)
half period
10ms
I (A)
t (ms)
period
20ms
I (A)
t (ms)
I
I
r.m.s
100 A produces the same thermal effects of a sinusoidal
alternating current with the maximum value of 141 A.
Thus the r.m.s. value allows alternating current to be treated
as direct current where the instantaneous value varies in
time.
Generalities on direct current
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3. Applications
Low voltage direct current is used for different applications,
which have been divided into four macrofamilies including:
• conversion into other forms of electrical energy (pho-
tovoltaic plants, above all where accumulator batteries
are used);
• electric traction (tram-lines, underground railways, etc.);
• supply of emergency or auxiliary services;
• particular industrial installations (electrolytic processes,
etc.).
3.1 Conversion of alternative energies into electri-
cal energy
Photovoltaic plants
A photovoltaic plant converts the energy associated with
solar irradiation into DC electrical energy. These plants are
made up of semiconducting panels which can generate
electrical power once exposed to the rays of the sun.
Photovoltaic plants can be grid-connected or supply a
single load (stand alone plant). In this last case an accumu-
lator battery is present to provide power in case of a lack of
solar radiation.
The following figure shows a block diagram of a stand alone photovoltaic plant.
Photovoltaic array
Single module
String
Charge
regulator
DC load
AC load
DC/AC
converter
Battery
Applications
The basic element of a photovoltaic plant is the photovoltaic
cell made of semiconducting material (amorphous silicon or
monocrystalline silicon). Exposed to the rays of the sun, this
cell is able to supply a maximum current I
mpp
at a maximum
voltage V
mpp
, which corresponds to a maximum power
called W
p
. Photovoltaic cells are connected in series to form
a string to raise the voltage level. By connecting several
strings in parallel, the current level is increased.
For example, if a single cell can provide 5A at 35.5 VDC, in
order to reach the level of 100A at 500 VDC, it is necessary
to connect 20 strings in parallel, each one with 15 cells.
Generally speaking, a stand alone photovoltaic plant in-
cludes the following devices:
• Photovoltaic array: photovoltaic cells suitably intercon-
nected and used for the conversion of sunlight energy
into electrical energy;
• Charge regulator: an electronic device able to regulate
charging and discharging of accumulators;
• Accumulator batteries: to provide power supply in case
of lack of solar radiation;
• DC/AC inverter: to turn direct current into alternating
current by controlling it and stabilizing its frequency and
waveform.
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The general diagram of a grid-connected photovoltaic
plant, unlike a stand alone one, may leave out the accumu-
lator battery since the user is supplied by the network when
solar irradiation is unavailable.
A photovoltaic plant of this type is made up of the following
equipment:
• Photovoltaic array: the photovoltaic cells suitably
interconnected and used for the conversion of sunlight
energy into electrical energy;
• DC/AC inverter: to turn direct current into alternating
current by controlling it and stabilizing its frequency and
waveform;
• Interface device: a circuit breaker equipped with an
undervoltage release or a molded case switch able to
guarantee the total separation of the power generation
units from the public utility network;
• Energy meters: to measure and invoice the energy sup-
plied and absorbed by the distribution network.
The following figure shows the block diagram of a grid-connected photovoltaic plant.
Photovoltaic plants can supply currents from a few dozens
of amperes (domestic applications and similar) up to several
hundreds of amperes (service industry and small industry).
Photovoltaic array
Single module
String
User’s
loads
DC/AC
inverter
kWh
kW
h
Meter of
the given
energy
Meter of the
absorbed
energy
To the
distribution
network
Interface
device
Applications
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3.2 Electric traction
The particular torque/speed characteristic curve and the
ease with which the speed itself can be regulated have led
to the use of DC motors for electric traction.
Direct current supply also gives the great advantage of hav-
ing the contact line consisting of a single conductor as the
rails provide the return conductor.
Currently, direct current is used primarily in urban transport
like trolleybuses, trams and underground railways, with a
supply voltage of 600 V or 750 V, up to 1000V.
The use of direct current is not limited only to vehicle
traction. Direct current represents a supply source for the
auxiliary circuits on board vehicles as well. In this case, ac-
cumulator batteries are installed and constitute an auxiliary
power supply source to be used if the external power sup-
ply should fail.
It is very important that this power supply be guaranteed
since the auxiliary circuits may supply essential services
such as air conditioning plants, internal and external light-
ing circuits, emergency brake systems or electrical heating
systems.
The applications of circuit breakers in DC circuits for electric
traction can be summarized as follows:
• Protection and operation of both overhead and rail con-
tact lines;
• Protection of air compressors on board subway and
train cars;
• Protection of distribution plants for services and signal-
ing systems;
• Protection of DC supply sources (accumulator batter-
ies)
• Protection and operation of DC motors.
Applications
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to the load
Converter
Network
UPS
Inverter
Battery
3.3 Supply of emergency services or auxiliary
services
Direct current is used (directly or indirectly through accumu-
lator batteries) in those plants for which service continuity is
fundamental.
Plants that cannot tolerate a power failure caused by a loss
of energy need a ready-to-use supply source which is able
to cover the time needed to start an emergency generating
set.
Here are some examples of this type of user plant:
• industrial applications (process control systems);
• safety and emergency installations (lighting, alarms);
• hospital applications;
• telecommunication;
• applications in the data processing field (data centers,
work stations, servers, etc.).
In these installations energy interruptions cannot be permit-
ted. Therefore it is necessary to include systems to store
energy when supplied that can give it back immediately if
power fails.
Accumulator batteries are the most reliable electric energy
source for the supply of such services, both directly in direct
current (if allowed by the loads) as well as in alternating
current by using an inverter able to develop an outgoing
sinusoidal waveform starting from an incoming continuous
one.
The above is carried out by uninterruptible power supply
units (UPS):
Figure 6
Principle diagram of a UPS
3.4 Particular industrial applications
The use of direct current is often required in many industrial
applications such as:
• arc furnaces;
• electro welding plants;
• graphite manufacturing plants;
• metal production and refining plants (aluminum, zinc,
etc.).
In particular, many metals such as aluminum are produced
through an electrolytic process. Electrolysis is a process
which converts electric energy into chemical energy. It is the
opposite of what occurs in the battery process. In fact, with
a battery, a chemical reaction is exploited to produce DC
electric energy, whereas electrolysis uses DC electric energy
to start a chemical reaction which otherwise would not oc-
cur spontaneously.
The procedure consists of immersing the metal to be
refined, which acts as an anode, into a conductive solution,
while a thin plate made of the same pure metal acts as a
cathode. By applying a direct current from the rectifiers, it
is possible to observe the metal atoms on the anode dis-
solve in the electrolytic solution and, at the same time, an
equivalent quantity of metal settles on the cathode. In these
applications, the service currents are very high, greater than
3000 A.
Another very common application is represented by gal-
vanizing plants where processes are carried out to obtain
the plating of metallic surfaces with other metals or alloys
(chromium plating, nickeling, coppering, brass coating,
galvanization zinc plating, tinning, etc.). The metallic piece
to be plated usually acts as a cathode: by the current flow,
the ions move from the anode and settle on the surface of
the piece.
Also in these installations, the operations are carried out by
an electrolytic cell with high service currents (up to 3000 A
and over).
Applications
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Structure of a storage battery
A stationary battery in its easiest form is made up of a
recipient containing a sulfuric acid solution with distilled
water (the electrolyte) where the two electrodes, positive
and negative, are immersed. Each of them is formed of one
or more plates connected in parallel. The terminals of these
electrodes, where the loads are connected or where the
connections in series or in parallel are made, are the anode
(+) and the cathode (-).
4. Generation
Direct current can be generated:
- by using batteries or accumulators where the current is
generated directly through chemical processes;
- by the rectification of alternating current through recti-
fiers (static conversion);
- by the conversion of mechanical work into electrical
energy using dynamos (production through rotating
machines).
The following indications are not intended to be an exhaus-
tive tool but are aimed at giving some brief information to
help understand the main technologies for the production of
direct current.
4.1 Storage batteries
A storage battery, or accumulator, is an electrochemical
generator able to convert chemical energy into direct electri-
cal current.
The structure of a storage battery is analogous to that of a
normal battery. The main difference is that the discharging/
charging process for accumulator batteries is reversible. By
using a DC generator, it is possible to restore the initial state
of the electrodes which have been altered during discharge.
This process cannot be carried out with a normal battery.
The main electrical characteristics of storage batteries are:
• Nominal voltage: potential difference existing between
the negative and positive plates immersed in the elec-
trolyte. The voltage value reported is usually related to
each single cell (2V, 4V, 6V, 12V). To obtain the required
voltage it is necessary to use several cells in series.
• Capacity: quantity of electricity which a battery can
deliver for a defined time. Capacity is expressed in
ampere-hours (Ah) and can be obtained by multiply-
ing the value of the intensity of the discharge current
(amperes) by the discharge time (hours).
• Internal resistance: the value of the internal resistance
of the battery. This value is given by the manufacturer.
• Power: power which the battery can deliver. It is ob-
tained from the average discharge voltage multiplied by
the current and it is expressed in watts (W).
The following figure shows the possible structure of three elements
connected in series:
In addition to these components, there are also current col-
lectors and separators. The collectors direct the generated
current towards the electrodes (discharging phase) and vice
versa from the electrodes towards the elements (charging
phase). The separators, usually made of insulating plates,
avoid contact between anode and cathode to prevent
short-circuits.
To obtain the voltage level needed, it is necessary to con-
nect cells in series or in parallel to increase the voltage or
the current level.
The following figure shows the possible structure of three elements con-
nected in series:
single element
with electrolyte
cathode (–)
anode (+)
connection
between elements
Generation
+
–
+
–
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In this diagram it is possible to identify the three forward diodes (1,3,5)
with the cathodes connected and the three backward diodes (2,4,6)
which instead have the anodes connected.
Having established that a diode carries current only if posi-
tively polarized by supplying the bridge circuit with a set of
three-phase voltages:
a) During the first sixth of a period, the line-to-line voltage
V12 is the prevailing voltage; consequently, diodes 1
and 4 shall carry the current.
b) During the second sixth of a period, the line-to-line
voltage V13 is the prevailing voltage; consequently,
diodes 1 and 6 shall carry the current.
The continuous lines represent the three sine waves of the line-to-line
voltages (V
12
; V
23
; V
31
), whereas the dotted lines represent the sine
curves of the same voltages but reversed (V
13
= -V
31
; V
21
= -V
12
; V
2
= -V
23
).
4.2 Static conversion
Direct current can be supplied by using electronic devices
(rectifiers) able to convert alternating current input into
direct current output. These devices are also called static
converters. The operating principle of rectifiers exploits the
properties of the electronic components made of semicon-
ductor materials (diodes, thyristors, etc.), their capacity of
carrying currents only when positively polarized. The oper-
ating principle can be illustrated by the three-phase bridge
rectifier (Graetz rectifier) shown in the figure:
V
R
I
1 3 5
2 4 6
V
1
V
2
V
3
The same occurs in the subsequent fractions of a period.
The voltage U
R
at the terminals of the load R is the voltage
represented by the envelope of the line-to-line voltages as
shown in the figure.
The resulting output voltage (represented by the continuous
black line) takes the waveform of a ripple voltage with aver-
age value greater than zero.
Therefore, the direct current which flows through the resis-
tance R is equal to:
The electronic circuit of a rectifier is more complex than the
circuit just shown. A capacitor which “smooths” the output
voltage is often present to reduce ripple. Thyristors can also
be used instead of diodes. Thyristors, thanks to the possi-
bility of controlling their switching-on time in relation to their
switching instant, allow varying the output voltage value at
the bridge. In this case, this device is referred to as a con-
trolled bridge rectifier.
I =
Vmed
R
0
t1 t2 t3 t4 t5 t6
t
Vmax
Vmed
V
V
13
=-V
31
V
21
=-V
12
V
31
V
32
=-V
23
V
23
V
12
Generation
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4.3 Dynamo
A dynamo is a direct current generator used to convert
kinetic energy into direct electrical current.
As shown in the figure, these devices consist primarily of a
stationary structure (called the inductor system), which gen-
erates a magnetic field, and of a moving part (called the ro-
tor), made up of a system of conductors, which are “struck”
by the magnetic field generated by the inductor.
The following figure shows the structure of a dynamo:
Assume that a straight-line conductor (positioned along
a cylinder rotating at constant speed), cutting the lines of
force of the magnetic field, becomes the seat of an in-
duced electromotive force (emf) variable in time. With more
conductors suitably connected (so that the positive and
negative values of the electromotive forces induced in the
conductors are compensated), it is possible to obtain a
resulting emf of constant value having always the same
direction.
Generation
Stationary structure (inductor system)
Moving part (rotor)
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5. Interrupting direct current
Interrupting direct current presents different problems than
alternating current as the arc extinction is particularly dif-
ficult.
As Figure 7 shows, with alternating current there is natural
passage of current through zero at each half cycle, which
corresponds to the quenching of the arc during the cir-
cuit opening. With direct current there is no such natural
passage and therefore the current must decrease to null
to guarantee arc extinction (forcing the current passage
through zero).
To illustrate, reference the circuit shown in the figure:
Figure 7
Alternating current
Figure 8
Direct current
In this case:
where:
V is the rated voltage of the supply source
L is the inductance of the circuit
R is the resistance of the circuit
Va is the arc voltage.
The formula can be written also as:
To guarantee arc extinction, it is necessary that:
This relationship shall be verified when the arc voltage (Va)
is so high that the first part of the formula (1) becomes
negative. It is possible to conclude that the extinction time
of a direct current is proportional to the time constant of the
circuit T = L/R and to the extinction constant.
The extinction constant is a parameter depending on the
arc characteristic and on the circuit supply voltage.
V = L
di
+ Ri + Va
dt
L
di
= V - Ri - Va (1)
dt
di
< 0
dt
I (A)
t (ms)
current passage through 0
half cycle
10ms
cycle
20ms
I (A)
t (ms)
value constant in time
L R
L
di
dt
iR
V
Va
Interrupting direct current
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Ip = short-circuit making current
Icn = prospective short-circuit current
Va = maximum arc voltage
Vn = network voltage
T = time constant
to = instant of beginning of short-circuit
ts = instant of beginning of separation of the circuit
breaker contacts
ta = instant of quenching of the fault current
When a short-circuit occurs in correspondence to the
instant to, the current starts rising according to the time
constant of the circuit. The circuit breaker contacts begin to
separate, thus an arc starts from the instant ts.
The following figure shows an oscillogram of a short-
circuit test carried out in the ABB power testing
laboratories.
I/V
0
T
t
Ip
Icn
Va
Vn
to ts ta
Interrupting direct current
The current keeps on rising for a short period after the
beginning of contacts opening, then decreases depending
on the increasing value of the arc resistance progressively
introduced in the circuit. As can be seen in the graph, the
arc voltage remains higher than the supply voltage of the
circuit during the interruption. In correspondence of ta, the
current is completely quenched.
As the graph shows, the short-circuit current represented
by the red line is extinguished without abrupt interruptions
which could cause high voltage peaks.
As a consequence, to obtain a gradual extinction (the graph
represents the descent of Ip), it is necessary to cool and
extend the arc, so that increasing arc resistance is inserted
in the circuit (with the consequent increase of the arc volt-
age Va). This extinction involves energetic phenomena
which depend on the voltage level of the plant (Vn) and
require circuit breakers to be connected in series to opti-
mize performance during short circuit conditions. The higher
the number of contacts opening the circuit, the higher the
breaking capacity of the circuit breaker.
This means that when the voltage rises it is necessary to
increase the number of current interruptions in series, so
that a rise in the arc voltage is obtained and consequently a
number of poles for breaking operations proportional to the
fault level.
To summarize: in order to guarantee breaking of a short-cir-
cuit current in a DC system it is necessary to employ circuit
breakers that can ensure:
• rapid tripping with adequate breaking capacity;
• high fault current limiting capacity;
• overvoltage reduction effect.
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Exposed conductive parts
Grounding of exposed
conductive parts
L+
L-
V
6. Types of DC networks
As previously explained, in order to break a short-circuit
current in a DC system, it is necessary to connect the
circuit breaker poles in a suitable way.
To do this, it is necessary to know the grounding type of
the plant.
This information allows any possible fault condition to be
evaluated and consequently the most suitable connection
type to be selected (short-circuit current, supply voltage,
rated current of the loads, etc.).
The following pages shall give the following for each net-
work type:
• Description of the network
• Fault types
(Pole connection and the relevant breaking capacity dis-
cussed in Chapter 7: ”Choice of the protective device”)
Common solution
6.1 Network insulated from ground
This type of network represents the easiest connection to
carry out as no connection between the battery terminals
and ground is provided.
These types of systems are widely used in those instal-
lations where grounding is difficult, but above all where
service continuity is required after an initial ground fault.
However, because no terminals are grounded, the risk with
this connection is that dangerous overvoltages could occur
between an exposed conductive part and ground due to
static electricity. These hazards can be limited by overload
dischargers.
Figure 10
Types of DC networks
Figure 9
Network insulated from ground
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Fault types in a network insulated from ground
Fault A:
The fault between the two terminals is a short-circuit cur-
rent fed by the full voltage U. The breaking capacity of the
circuit breaker shall be sized according to the short-circuit
current relevant to such fault.
Fault B:
The fault between a terminal and ground has no conse-
quences to plant operation since such current has no
reclosing paths and consequently it cannot circulate.
Fault C:
Like fault B, this fault between a terminal and ground has
no consequences to plant operation.
Figure 11
Double fault in a network insulated from ground
Conclusion:
With this type of network, the fault type which af-
fects the version and connection of the circuit breaker
poles is fault A (between the two terminals).
In an insulated network it is necessary to install a
device able to signal the presence of the first ground
fault so that it can be eliminated to avoid any problem
arising from a second ground fault. In fact, in case
of a second ground fault, the circuit breaker could
have to interrupt the fault current with the full voltage
applied to a single terminal and consequently with an
insufficient arc voltage (see figure).
Double fault (fault B + fault C):
In the case of a double fault as shown in the figure,
the current might circulate and find a reclosing path.
Therefore, it is advisable that a device capable of
signaling a ground fault or a decrease of the insula-
tion to ground of a terminal be installed in the plant. In
this way, the fault is eliminated in good time to prevent
the occurrence of a second ground fault on the other
terminal. The consequent total inefficiency of the plant
due to the tripping of the circuit breaker caused by
the short-circuit generated on the two terminals to
ground is also avoided.
V
Fault A
Ik
+
–
Fault B
+
–
no reclosing path
Fault C
+
–
no reclosing path
V
Fault C
Ik
Fault B
+
–
+
–
load
V
Types of DC networks
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V
Exposed conductive parts
Grounding of exposed
conductive parts
L+
L-
System grounding
L+
Gnd
L-
GndN (DC)
Grounding system
Exposed conductive parts
TN-S system
+
–
Common solution
Figure 14
Figure 13
6.2 Network with one terminal grounded
This type of network is obtained by connecting one terminal
to ground.
This connection type allows the overvoltages due to static
electricity to be discharged to ground.
Types of DC networks
Figure 12
Network with one terminal grounded
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Fault types in a network with one terminal grounded
In the following examples the grounded terminal is the
negative one.
Conclusions
With this type of network, the fault type which affects the
version of the circuit breaker and the connection of the
poles is fault A (between the two terminals). However it is
also necessary to take into consideration the fault between
the non-grounded terminal and the ground itself (fault B)
because as described above, a current could flow at full
voltage. For this reason, all the circuit breaker poles nec-
essary for protection must be connected in series on the
non-grounded terminal.
Fault A:
The fault between the two terminals is a short-circuit cur-
rent fed by the full voltage V. The breaking capacity of the
circuit breaker shall be sized according to the short-circuit
current relevant to such fault.
Fault B:
The fault on the non-grounded terminal sets up a current
involving the overcurrent protections as a function of the
soil resistance.
Fault C:
The fault on the grounded terminal sets up a current which
affects the overcurrent protections as a function of the soil
resistance. This current presents an extremely low value
because it depends on the impedance of the soil and the V
is next to zero because the voltage drop on the load further
reduces its value.
V
Fault A
Ik
+
–
Fault B
V
Ik
+
–
Fault C
Ik
+
–
V
Types of DC networks
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V
L+
Gnd
L-
GndN (DC)
Grounding system
Exposed conductive parts
M
L+
M
L-
Exposed conductive parts
Grounding of exposed
conductive parts
Grounding system
6.3 Network with the middle point of the supply
source connected to ground
This type of network is obtained by connecting the middle
point of the battery to ground.
This type of connection reduces the value of static overvol-
tages, which could otherwise be present at full voltage in an
insulated plant.
The main disadvantage of this connection, if compared with
other types, is that a fault between a terminal and ground
gives rise to a fault current at a voltage
V
.
2
Figure 16
Figure 15
Network with the middle point connected to ground
Common solution
Figure 17
Types of DC networks
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Fault A:
The fault between the two terminals is a short-circuit current
fed by the full voltage V. The breaking capacity of the circuit
breaker shall be sized according to the short-circuit current
relevant to such a fault.
Fault types in a network with the middle point connected to ground
Fault C:
In this case, the fault is analogous to the previous
case but it involves the negative terminal.
Fault B:
The fault between the terminal and ground sets up a short-
circuit current lower than the fault between the two termi-
nals as it is supplied by a voltage equal to
V
2
depending
on the soil resistance.
Conclusion
With this type of network, the fault which affects the
version of the circuit breaker and the connection of
the poles is fault A (between the two terminals). How-
ever, the fault between a terminal and ground should
also be taken into consideration because a current
could flow at a voltage equal to:
V
2
In a network with the middle point of the supply con-
nected to ground, the circuit breaker must be con-
nected on both terminals.
V
Fault A
Ik
+
–
Fault B
Ik
+
–
V
2
Fault C
Ik
+
–
V
2
Types of DC networks
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7. Choice of the protective device
For the correct sizing of a circuit breaker in a direct current
network, some electrical parameters which characterize the
device itself must be evaluated.
Here is a short description of these parameters, which are
discussed in the following pages.
Rated operational voltage Ve
This represents the value of the application voltage of the
equipment and to which all the other equipment parameters
are referred.
Rated uninterrupted current Iu
This represents the value of current which the equipment
can carry for an indefinite time (uninterrupted duty). This
parameter is used to define the size of the circuit breaker.
Rated current In
This represents the value of current of the trip unit mounted
on the circuit breaker and determines the protection char-
acteristic of the circuit breaker itself according to the avail-
able settings of the trip unit.
This current is often referred to the rated current of the load
protected by the circuit breaker itself.
Rated ultimate short-circuit breaking capacity Icu
The rated ultimate short-circuit breaking capacity of a circuit
breaker is the maximum short-circuit current value which
the circuit breaker can break twice (in accordance with the
sequence O – t – CO) at the corresponding rated opera-
tional voltage. After the opening and closing sequence the
circuit breaker is not required to carry its rated current.
Rated service short-circuit breaking capacity Ics
The rated service short-circuit breaking capacity of a circuit
breaker is the maximum short-circuit current value which
the circuit breaker can break three times, in accordance
with a sequence of opening and closing operations (O - t
- CO - t – CO), at a defined rated operational voltage (Ve)
and at a defined time constant (for direct current). After this
sequence the circuit breaker is required to carry its rated
current.
Rated short-time withstand current Icw
The rated short-time withstand current is the current that
the circuit breaker in the closed position can carry during
a specified short time under prescribed conditions of use
and behavior. The circuit breaker shall be able to carry this
current during the associated short-time delay in order to
ensure discrimination between the circuit breakers in series.
Choice of the protective device
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Rating plates of the circuit breakers
Tmax molded-case circuit breakers for direct current
Tmax T2L 160
Ue
(V)
Icu
(kA)
Ics
Cat A
(% Icu)
Iu=160A
Ue=690V Ui=800V Uimp=8kV IEC 60947-2
230
150
75 75
85
400/415 440
75
75
50
75
500 690
10
75
250
85
75
500
85
75
Made in Italy
by ABB SACE
2 P 3 P
in series
50-60Hz
Size
1
2
3
4
5
6
7
CIRCUIT BREAKER TYPE
Rated
uninterrupted
current
160 A
250 A
320 A
400 A
630 A
800 A
Rated ultimate short-circuit
breaking capacity at 250 VDC
(with 2 poles in series)
N = 36 kA
S = 50 kA
H = 70 kA
L = 85 kA (for T2)
L = 100 kA
V = 150 kA
Size
1
2
3
4
5
6
Series
T
Rated operational
voltage
Rated uninterrupted
current
Rated insulated voltage
Rated impulse
withstand voltage
Compliance with the reference standard,
in this case, IEC60947-2:
“Low voltage switchgear and
controlgear - Circuit Breakers”
Part relevant to direct current according to the
number of poles connected in series called to
extinguish the fault current, the rated operational
voltage and the breaking capacities (Icu and
Ics) are indicated.
According to the international Standard IEC 60947-2; the circuit breakers can be
divided into:
• Category A, i.e., circuit breakers without a specied short time withstand current rating
• Category B, i.e., circuit breakers with a specied short time withstand current rating
Rated ultimate short-circuit breaking
capacity (Icu) and rated service
short-circuit breaking capacity (Ics)
CE marking afxed on ABB circuit breakers to indicate
compliance with the following CE directives:
• “Low Voltage Directive” (2006/95/EC)
• “Electromagnetic Compatibility Directive (2004/108/EC)
Choice of the protective device
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Emax air circuit breakers for direct current
SACE
E2B 800
Iu=800A Ue=1000V Icw=35kA x 0.5s
IEC 60947-2
made in Italy by
ABB-SACE
Ue
Icu
Ics
(V)
(kA)
(kA)
500
35
35
750
25
25
1000
25
25
+ -
4P
Cat B
Series
E
Size
2
3
4
6
Rated ultimate short-circuit
breaking capacity at 500 Vd.c.
B = 35 kA (E2)
N = 50 kA (E2)
N = 60 kA (E3)
S = 75 kA (E4)
H = 85 kA (E3)
H = 100 kA (E4-E6)
Rated
uninterrupted
current
800 A
1000 A
1250 A
1600 A
2000 A
2500 A
3200 A
4000 A
5000 A
Rated short-time withstand
current (Icw)
Rated ultimate short circuit breaking
capacity (Icu) and rated service
short-circuit breaking capacity (Ics)
Rated operational
voltage (Ue)
Rated uninterrupted
current
Connection modality to the circuit breaker poles:
the connection in series shown in the scheme is
carried out in the factory by ABB SACE
Compliance with reference standard,
in this case, IEC60947-2: “Low voltage
switchgear and controlgear - Circuit
breakers”
+ -
CIRCUIT BREAKER TYPE
According to the international Standard IEC 60947-2, the circuit
breakers can be divided into:
• Category A, i.e., circuit breakers without a specied short
time withstand current rating
• Category B, i.e., circuit breakers with a specied short
time withstand current rating
CE marking afxed on ABB circuit
breakers to indicate compliance with
the following CE directives:
• Low Voltage Directive” (2006/95/EC)
• Electromagnetic Compatibility Directive
(2004/108/EC)
Choice of the protective device
Type of connection grounding
Ve
≥ Vn
Icu
(accord
ing to
t
he num
b
er of poles in
series)
≥ Ik
In
≥ Ib
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Sizing circuit breakers
In the previous pages, the main electrical character-
istics needed to choose the correct circuit breaker
have been defined so that protection of the plant is
guaranteed.
To size the circuit breaker, it is necessary to know the
following characteristics of the network:
• The type of network (see Chapter 6), to define
the connection of the circuit breaker poles ac-
cording to the possible fault conditions;
• The rated voltage of a plant (Vn), to define the
operational voltage (Ve) depending on the pole
connection by verifying the relation: Vn≤ Ve;
• The short-circuit current at the installation point
of the circuit breaker (Ik), to define the circuit
breaker version (depending on the connection of
the poles) by verifying the relation Ik ≤ Icu (at the
reference rated operational voltages Ve);
• The rated current absorbed by the load (Ib), to
define the rated current (In) of the thermal-mag-
netic trip unit or of the DC electronic trip unit by
verifying the relation Ib≤ In.
The following diagram summarizes the choices for a
correct sizing of the circuit breaker in relation to the
characteristics of the plant.
Choice of the protective device
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The values given in the following tables indicate the performance of circuit breakers under the heaviest fault
conditions for the type of network under consideration (see Chapter 6: “Types of DC networks”).
Choice of the protective device
Tables 1-2. Pole connection (for IEC MCBs type S280 UC-S800S UC) in an insulated network
UNGROUNDED NETWORK
Rated voltage (Un) ≤ 440
Protection
+
isolation function
S280 UC
In = 0,5…2 A 50
In = 3…40 A 6
In = 50…63 A 4,5
1
2
3
4
5
6
7
8
-+ -+
1
2
3
4
UNGROUNDED NETWORK
Rated voltage (Vn) ≤ 500 ≤ 750
Protection
+
isolation function
S800S
UC
In = 10…125 A 50 50
1
2
3
4
5
6
7
8
-+
Tables 3-4. Pole connection (for IEC MCBs type S280 UC-S800S UC) in a network with one terminal grounded
1
2
1
2
3
4
1
2
3
4
+ -
+ - + -
NETWORK WITH ONE TERMINAL GROUNDED
Rated voltage (Vn) ≤ 250 ≤ 500 ≤ 750
Protection function
S800S
UC
In = 10…125
A
50 50 50
NETWORK WITH ONE TERMINAL GROUNDED
Rated voltage (Vn) ≤ 220 ≤ 440
Protection function
Protection
+
isolation function
S280
UC
In = 0,5…2 A 50 50 50
In = 3…40 A 6 10 6
In = 50…63 A 4,5 6 4,5
1
2
1
2
3
4
1
2
3
4
5
6
+ - + - + -
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Table 5. Connection of poles (for IEC S280 UC MCBs)
in a network with the middle point grounded
NETWORK WITH THE MIDDLE POINT
CONNECTED TO GROUND
Rated voltage (Vn) ≤ 220
Protection
+
isolation function
S280
UC
In = 0,5…2 A 50
In = 3…40 A 10
In = 50…63 A 6
Table 6. Connection of poles (for IEC Tmax MCCBs) in an insulated network 1
UNGROUNDED NETWORK
Rated voltage (Vn) ≤ 250 ≤ 500 ≤ 750
Protection
+
isolation function
T1
160
B 16 20 16
C 25 30 25
N 36 40 36
T2
160
N 36 40 36
S 50 55 50
H 70 85 70
L 85 100 85
T3
250
N 36 40 36
S 50 55 50
T4
250/320
T5
400/630
N 36 25 16
S 50 36 25
H 70 50 36
L 100 70 50
V 150 100 70
T6
630/800
N 36 20 16
S 50 35 20
H 70 50 36
L 100 65 50
The positive pole (+) can be inverted with the negative pole (-).
1 with these types of pole connection the possibility of a double fault to ground is considered unlikely (see Chapter 6: “Types of DC networks”)
Choice of the protective device
1
2
3
4
+ -
+ -
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
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Table 7. Connection of poles (for IEC Tmax MCCBs) in a network with one terminal grounded (in
the considered connections, the grounded terminal is negative)
NETWORK WITH ONE TERMINAL GROUNDED
Rated
voltage (Vn)
≤ 250 ≤ 500 ≤ 750
Protection
+
isolation
function
Protection
function
T1
160
B 16 20 16
C 25 30 25
N 36 40 36
T2
160
N 36 40 36
S 50 55 50
H 70 85 70
L 85 100 85
T3
250
N 36 40 36
S 50 55 50
T4
250/320
T5
400/630
N 36 25 16
S 50 36 25
H 70 50 36
L 100 70 50
V 150 100 70
T6
630/800
N 36 20 16
S 50 35 20
H 70 50 36
L 100 65 50
Choice of the protective device
+
-
LOAD
+
-
LOAD
+
-
LOAD
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Table 8. Connection of poles (for IEC Tmax MCCBs) in a network with the middle point grounded
1 for the use of three-phase circuit breakers please ask ABB
2 for the use of three-phase circuit breakers (T4-T5-T6) please ask ABB
NETWORK WITH THE MIDDLE POINT CONNECTED TO GROUND
Rated
voltage (Vn)
≤ 250 1 ≤ 500 2 ≤ 750
Protection
+
isolation
function
T1
160
B 20 16
C 30 25
N 40 36
T2
160
N 40 36
S 55 50
H 85 70
L 100 85
T3
250
N 40 36
S 55 50
T4
250/320
T5
400/630
N 36 25 16
S 50 36 25
H 70 50 36
L 100 70 50
V 100 100 70
T6
630/800
N 36 20 16
S 50 35 20
H 70 50 36
L 100 65 50
Choice of the protective device
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1 With these types of pole connection the possibility of a double fault to ground is considered unlikely (see Chapter 6: “Types of DC networks”)
2 For higher voltages please ask ABB
+ -
LOAD
LOAD
+ -
LOAD
+ -
LOAD
Table 11. Pole connection for (ACBs type Emax) in a network
with the middle point grounded
NETWORK WITH THE MIDDLE POINT
CONNECTED TO GROUND
Rated
voltage
(Vn)
< 500 < 750 ≤ 1000
Protec-
tion
+
isolation
function
3-pole circuit breaker 4-pole circuit breaker 4-pole circuit breaker
E2
B 35 25 25
N 50 35 35
E3
N 60 50 35
H 85 65 65
E4
S 75 65 50
H 100 85 65
E6 H 100 85 65
The values given in the following tables indicate the performances of circuit breakers under the heaviest fault
conditions for the type of network under consideration (see Chapter 6: “Types of networks”.)
+ - + -
LOAD
LOAD
+ -
LOAD
LOAD
LOAD
+ -
LOAD
LOAD
INSULATED NETWORK 1
Rated
voltage (Vn)
≤ 500 ≤ 750 ≤ 1000
Protection
+
isolation
function
3-pole circuit
breaker
3-pole circuit
breaker
4-pole circuit
breaker
E2
B 35 25 25
N 50 35 35
E3
N 60 50 35
H 85 65 65
E4
S 75 65 50
H 100 85 65
E6 H 100 85 65
NETWORK WITH ONE
TERMINAL GROUNDED
Rated
voltage (Vn)
< 500 2
Protection
+
isolation
function
3-pole circuit breaker
E2
B 35
N 50
E3
N 60
H 85
E4
S 75
H 100
E6 H 100
Tables 9-10. Pole connection for (ACBs type Emax) in an insulated network and with one terminal
grounded (in the considered connections, the grounded terminal is negative)
Choice of the protective device
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
LOAD
+ - + -
LOAD
LOAD
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Table 12. Pole connection for IEC Tmax molded case switches
Rated
voltage (Vn)
≤ 250 ≤ 500 ≤ 750
Pole connection
T1D 160
■
–
■
–
T3D 250
■
–
■
–
T4D 250/320
■ ■
–
■
T5D 400/630
■ ■
–
■
T6D 630/800/1000
■ ■
–
■
T7D 1000/1250/1600
■ ■ ■ ■
Rated
voltage (Vn)
≤ 500 ≤ 750 ≤ 1000
Pole
connection
X1-E1…E6 / MS
■
– – –
E1…E6 E/ MS
■ ■ ■ ■
The following tables show the pole connections of Tmax molded case switches according to the installation
voltage. The connections shown in the table shall be carried out by the customer.
Table 13. Pole connection for IEC Emax switch disconnectors
Choice of the protective device
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Tmax molded case circuit breakers
Example:
Characteristics of the plant:
• Type of network: one terminal grounded (the negative one)
• Network voltage: Vn = 250 VDC
• Rated voltage absorbed by the loads (Ib): 450 A
• Short-circuit current: 40k A
Choice of the circuit breaker
According to the indications on page 23, to correctly size
the circuit breaker, the following must be complied with:
• Ve ≥ Vn
• Icu ≥ Ik
• In ≥ Ib
With reference to the type of network, the suitable table
shall be identified from tables 6-7-8. In this case, the table
for a network with one grounded terminal (Table 7) shall be
chosen.
The column with the performances for a network voltage
higher than or equal to the plant voltage shall be identified,
in this example Vn≥ 250 VDC.
The load current is used to identify the row of the table for
circuit breakers with uninterrupted rated current Iu higher
than or equal to the load current. In this case, a Tmax T5
with Iu=600 A circuit breaker can be used.
The interrupting rating is chosen according to the relation
Icu≥Ik. In this example, since Ik=40 kA, version S can be
used.
With these limitations, two possible schemes for the pole
connection can be identified. Assuming that the grounded
terminal is to be disconnected also, the connection scheme
to be used is the following:
+ -
LOAD
A 500 A T5S thermal magnetic circuit breaker shall be cho-
sen. To summarize, a three-pole thermal magnetic T5S600
TMA 500 circuit breaker shall be used connected as shown
in the figure, i.e. with two poles in series on the terminal
insulated from ground and the other one connected to the
grounded terminal.
Emax air circuit breakers
Example:
Characteristics of the plant:
• Type of network: insulated
• Network voltage: Vn = 500 VDC
• Rated voltage absorbed by the loads (Ib): 1800 A
• Short-circuit current: 45 kA
Choice of the circuit breaker
According to the indications on page 23, to correctly size
the circuit breaker, the following must be complied with:
• Ve ≥ Vn
• Icu ≥ Ik
• In ≥ Ib
With reference to the type of network, the suitable table
shall be identified from tables 9-10-11. In this case, the
table for an insulated network (Table 9) shall be chosen.
The column with the performances for a network voltage
higher than or equal to the plant voltage shall be identified,
in this example Vn≥ 500 VDC.
According to the column considered, the circuit breaker
which would seem suitable under short-circuit conditions
is an E2N (N=50kA>Ik). However, according to the table of
the rated uninterrupted current (page 39), it is necessary to
pass to an E3N since it has Iu= 2000 A which is higher than
the current absorbed by the loads. In this way, the third
relationship is complied with.
Therefore the suitable circuit breaker is a three-pole E3N
2000 circuit breaker with PR1122-123/DC In=2000 A. The
connection of the poles is carried out in the factory by ABB.
The solution of the table shows the connections between
three-pole circuit breaker, load and supply source.
+ -
LOAD
LOAD
Choice of the protective device
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8. Use of alternating current equipment in direct current
8.1 Variation of the magnetic tripping
The thermal magnetic trip units fitted to AC circuit
breakers are also suitable for use with direct current.
The tripping characteristics of the thermal protection
do not change since the bimetal strips of the trip units
are influenced by the heating caused by current flow.
It does not matter whether alternating or direct. The
bimetal strips are sensitive to the r.m.s. value.
Due to ferromagnetic phenomena, the instantaneous
tripping occurs at a different value than in alternat-
ing current. The green area in the figure shows the
shifting of the magnetic tripping. A coefficient called
km, a function of the circuit breaker and of the con-
nection type of its poles, allows the DC instantaneous
trip threshold to be derived starting from the relevant
value in alternating current. Therefore this coefficient is
to be applied to the threshold I3.
No variation in the
tripping due to
overload
Variation in the
instantaneous
tripping due to
short-circuit
Use of alternating current equipment in direct current
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+ -
LOAD
+
LOAD
-
32 Low Voltage Products & Systems
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There is no derating for IEC Emax equipped with the DC
PR122-PR123/DC electronic trip units because the trip
times comply with the curve set on the electronic trip unit.
Table 14 Coefficient km according to the connection
modality of the circuit breaker poles
The following table reports the coefficient km according to
the circuit breaker type and to the pole connection. The
given diagrams are valid for all types of networks because
the coefficient km depends exclusively on the circuit breaker
characteristics.
Connection
modality
Circuit breaker
T1 T2 T3 T4 T5 T6
1.3 1.3 1.3 1.3 1.1 1.1
1 1.15 1.15 1.15 1 1
1 1.15 1.15 1.15 1 1
- - - 1 0.9 0.9
- - - 1 0.9 0.9
- - - 1 0.9 0.9
- - - - - 1
- - - - - 0.9
Example
With a T2N 100 TMD In=100 circuit breaker (having
the AC magnetic tripping I3=10xIn) and choosing a
pole connection corresponding to the first figure of
Table 14, it is possible to visualize the coefficient km
equal to 1.3; the DC magnetic tripping shall be equal
to:
I3 = 10 x In x km = 10 x 100 x 1.3 = 1300 A
(±20% tolerance)
Use of alternating current equipment in direct current
V
V
+ -
LOAD
+ -
LOAD
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8.2 Connection of the circuit breaker poles in
parallel
Tmax molded case circuit breakers equipped with thermal
magnetic trip units can be used both for alternating current
and for direct current. When used for DC applications, they
are available for rated current from 15 A (T1) up to 800A
(T6).
For applications where higher currents are required, it is
possible to connect the circuit breaker poles in parallel so
that the required current carrying capacity can be obtained.
When choosing a circuit breaker, it is necessary to consider
that the connection of the poles in parallel involves a varia-
tion of the magnetic tripping and also a derating to be ap-
plied to the rated current of the trip unit. This derating varies
based on the number of poles connected in parallel.
The following table reports the correction factors for the
poles connected in parallel. When using a 4-pole circuit
breaker, the neutral conductor shall be always at 100%:
For example, by using a T6N 800 circuit breaker and
connecting two poles in parallel for each terminal, the
rated uninterrupted current shall be equal to:
In = In x n°
no.of poles in parallel
x K = 800 x 2 x 0.9 = 1440 A
However, it is necessary to take into consideration the
likely fault types in relation to the grounding arrange-
ment of the plant.
ABB advises against the connection in parallel be-
cause it is quite difficult to realize a connection which
can guarantee that the currents flowing in the circuit
breaker poles are perfectly balanced. Therefore, for
rated operational currents exceeding 800 A, the use
of air circuit breakers of IEC Emax series equipped
with PR122 - PR123/DC electronic trip units is sug-
gested when possible.
Number of poles in parallel
2 3
4 (neutral at
100%)
Derating
coefficient
0.9 0.8 0.7
Type of
network
Connection of the
poles in parallel
Electrical characteristics
ungrounded network To obtain this connection it is necessary to use a four-pole circuit breaker with the neutral conductor
at 100%.
With a T6 800 circuit breaker, the available settings are:
-maximum line current = 1440 A
-instantaneous tripping = 14400 A
(±20% tolerance)
This application can be obtained with an installation voltage not exceeding 500 VDC
The breaking capacities are (IEC/UL):
N= 36/35 kA with Vn< 250 VDC - 20/20 kA with Vn< 500 VDC
S= 50/50 kA with Vn< 250 VDC - 35/25 kA with Vn< 500 VDC
H= 70/65 kA with Vn< 250 VDC - 50/35 kA with Vn< 500 VDC
L= 100/100 kA with Vn< 250 VDC - 65/42 kA with Vn< 500 VDC
network with one terminal grounded protection function without insulation
function
To obtain this connection it is necessary to use a four-pole circuit breaker with the neutral conductor
at 100%.
With a T6 800 circuit breaker, the available settings are:
-maximum line current = 1440 A
-instantaneous tripping = 12960 A
(±20% tolerance)
This application can be obtained with an installation voltage not exceeding 500VDC
The breaking capacities are (according to the different versions):
N= 36/35 kA with Vn< 250 VDC - 20/20 kA with Vn< 500 VDC
S= 50/50 kA with Vn< 250 VDC - 35/25 kA with Vn< 500 VDC
H= 70/65 kA with Vn< 250 VDC - 50/35 kA with Vn< 500 VDC
L= 100/100 kA with Vn< 250 VDC - 65/42 kA with Vn< 500 VDC
Table 15. Connections of poles in parallel with the relevant derating and performances under short-
circuit conditions referred to the adopted network type:
Use of alternating current equipment in direct current
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9. ABB offering
9.1 Circuit breakers
ABB offers the following range of products for the protec-
tion and disconnection of DC networks.
Circuit breakers
Circuit breakers, devices carrying out the protection func-
tion against overcurrents, are divided into three families
including miniature circuit breakers, molded case circuit
breakers and air circuit breakers.
Miniature circuit breakers
Miniature circuit breakers available for use in direct current
are series S280UC, S800S UC and S800 PV.
Miniature circuit breakers series S280 UC comply with IEC
60947-2 and differ from the standard versions in that they
are equipped with permanent magnetic elements on the
internal arcing chambers. Such elements allow the electric
arc to be broken, up to voltages equal to 440 VDC.
The presence of these permanent magnetic elements
establishes the circuit breaker terminal (positive or nega-
tive). As a consequence, their connection shall be carried
out in compliance with the terminal indicated on the circuit
breakers.
See the tables of Chapter 7: ”Choice of the protective de-
vice” for information on pole connection.
Incorrect connection of the terminals could damage the
circuit breaker.
S280 UC circuit breakers with a special version for DC ap-
plications are available with characteristics B, C, K and Z.
S280 UC
Reference Standard IEC 60947-2
Rated current In [A] 0.5 ≤ In ≤ 40 50 ≤ In ≤ 63
Poles 1P, 2P
Rated voltage Ve
1P [V] 220 VDC
2P, 3P, 4P [V] 440 VDC
Insulation voltage Vi [V] 500
Max. operating voltage Vb max
DC 1P [V] 220 VDC
DC 2P [V] 440 VDC
“Rated breaking capacity IEC 60947-2
1P - 220 VDC, 2P - 440 VDC”
Icu [kA] 6 4.5
Ics [kA] 6 4.5
Rated impulse voltage (1.2/50) Vimp [kA] 5
Dielectric test voltage at industrial
frequency for 1 min.
[kA] 3
Characteristics of the thermomagnetic
release
B: 3In< Im < 5 In
■
C: 5In< Im < 10 In
■
K: 8In< Im < 14 In
■
Z: 2In< Im < 3 In
■
Number of electrical operations 10000
Number of mechanical operations 20000
Table 16. Electrical characteristics of the MCBs type S280 UC:
ABB offering
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Table 17. Tmax IEC 60947-2
T1 1P T1 T2 T3 T4 T5 T6
Rated uninterrupted current, Iu (A) 160 160 160 250 250/320 400/630 630/800
Poles (Nr) 1 3/4 3/4 3/4 3/4 3/4 3/4
Rated service voltage, Ve V 125 500 500 500 750 750 750
Rated impulse withstand voltage, Uimp kV 8 8 8 8 8 8 8
Rated insulation voltage, Vi V 500 800 800 800 1000 1000 1000
Test voltage at industrial frequency for 1 min. V 3000 3000 3000 3000 3500 3500 3500
Rated ultimate short-circuit current, Icu B C N N S H L N S N S H L V N S H L V N S H L
250 VDC - 2 poles in series (kA)
25
(to 125V)
16 25 36 36 50 70 85 36 50 36 50 70 100 150 36 50 70 100 150 36 50 70 100
250 VDC - 3 poles in series (kA) - 20 30 40 40 55 85 100 40 55 - - - - - - - - - - - - - -
500 VDC - 2 poles in series (kA) - - - - - - - - - - 25 36 50 70 100 25 36 50 70 100 20 35 50 65
500 VDC - 3 poles in series (kA) - 16 25 36 36 50 70 85 36 50 - - - - - - - - - - - - - -
750 VDC - 3 poles in series (kA) - - - - - - - - - - 16 25 36 50 70 16 25 36 50 70 16 20 36 50
Utilization category (IEC 60947-2) A A A A A B (400 A) 1 - A (630 A) B 2
Insulation behavior
■ ■ ■ ■ ■ ■ ■
Thermomagnetic releases
T fixed, M fixed TMF
■
- - - - - -
T adjustable, M fixed TMD -
■ ■ ■ ■ (up to 50 A)
- -
T adjustable, M adjustable (5…10 x In) TMA - - - -
■ (up to 250 A) ■ ■
T adjustable, M fixed (3 x In) TMG - -
■ ■
- - -
T adjustable, M fixed (2,5...5 x I) TMG - - - - -
■
-
Interchangeability - - - -
■ ■ ■
Versions F F-P F-P F-P F-P-W F-P-W F-W
1 Icw=5 kA
2 Icw=7.6 kA (630 A) - 10 kA (800 A)
The following tables show the DC electrical performances of Tmax MCCBs
ABB offering
Table 18. Tmax PV IEC 60947-3 MCSs
T1D PV T3D PV T4D PV T5D PV T6D PV T7D PV
Poles 4 4 4 4 4 4
Conventional thermal current, lth [A] 160 250 250 630 800 1600
Rated service current in category DC22 B, le [A] 160 200 250 500 800 1600
Rated service voltage, Ve [V] 1100 VDC 1100 VDC 1100 VDC 1100 VDC 1100 VDC 1100 VDC
Rated impulse withstand voltage, Uimp [kV] 8 8 8 8 8 8
Rated insulation voltage, Vi [V] 1150 VDC 1150 VDC 1150 VDC 1150 VDC 1150 VDC 1150 VDC
Test voltage at industrial frequency for 1 minute [V] 3500 3500 3500 3500 3500 3500
Rated short-circuit making capacity, MCS only, lcm [kA] 1.5 2.4 3 6 9.6 19.2
Rated short-time withstand current for 1s, lcw [kA] 1.5 2.4 3 6 9.6 19.2
Versions F F F F F F
Terminals FC Cu FC Cu FC Cu FC Cu FC CuAl FC CuAl
Mechanical life [no. operations] 25000 25000 20000 20000 20000 10000
Mechanical life [no. hourly operations] 120 120 120 120 120 60
Molded case circuit breakers
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ABB offering
Tmax T1 – Ts3
Table 19. Tmax UL 489
Tmax T1 Tmax T2 Tmax T3 Tmax Ts3 Tmax Ts3
Frame size [A] 100 100 225 150 225
Number of poles [Nr] 3-4 3-4 3-4 2-3-4 2-3-4
Rated voltage DC [V] 500 500 600 500
Interrupting ratings N S H N S N H L N H L
250V DC (2 poles in series) [kA rms] 25 25 35
500V DC (3 poles in series) [kA rms] 25 25 35
500V DC (2 poles in series) [kA rms] 35 50 65 20 35 50
600V DC (3 poles in series) [kA rms] 20 35 50
Trip units TMF
■ ■ ■ ■ ■
TMD/TMA
ELT
■
MA
■ ■ ■ ■
Electronic
■
Dimensions H [in/mm] 5.12/130 5.12/130 5.9/150 6.7/170 6.7/170
W 3p [in/mm] 3/76 3.54/90 4.13/105 4.13/105 4.13/105
D [in/mm] 2.76/70 2.76/70 2.76/70 4.07/103.5 4.07/103.5
Mechanical life [No. operations] 25000 25000 25000 25000 25000
Table 20. Tmax UL 489
Tmax T4 Tmax T5 Tmax T6
Frame size [A] 250
400-600 1
800
Number of poles [Nr]
2-3-4 2 2-3-4 2
3-4
Rated voltage DC [V] 600 600 600
Interrupting ratings N S H L V N S H L V N S H L
250V DC (2 poles in series) [kA rms]
500V DC (3 poles in series) [kA rms]
500V DC (2 poles in series) [kA rms] 25 35 50 65 100 25 35 50 65 100 35 35 50 65
600V DC (3 poles in series) [kA rms] 16 25 35 50 65 16 25 35 50 65 20 20 35 50
Trip units TMF
■
TMD/TMA
■ ■ ■
ELT
MA
Electronic
■ ■ ■
Dimensions H [in/mm] 8.07/205 8.07/205 10.55/268
W 3p [in/mm] 4.13/105 5.51/140 8.26/210
D [in/mm] 4.07/103.5 4.07/103.5 4.07/103.5
Mechanical life [No. operations] 20,000 20,000 20,000
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Table 21. DC rated currents available for the UL 489 Tmax circuit breakers with the different types of trip units
Caption
TMF = thermomagnetic trip unit with fixed thermal and magnetic threshold
TMD = thermomagnetic trip unit with adjustable thermal and fixed magnetic threshold
TMA = thermomagnetic trip unit with adjustable thermal and magnetic threshold
MA = adjustable magnetic only trip unit
ABB offering
In
T1
100
T3
225
Ts3
150/225
T4
250
T5
400
T6
600/800
In
T2
100
Ts3
150/225
TMF TMF TMF TMD TMA TMF TMA TMA MA MA
15
■ ■ ■ ■ ■
3
■
20
■ ■ ■ ■ ■
5
■
25
■ ■ ■ ■ ■
10
■
30
■ ■ ■ ■ ■
20
■ ■
35
■ ■ ■ ■
25
■
40
■ ■ ■ ■ ■
50
■ ■
50
■ ■ ■ ■ ■
100
■ ■
60
■ ■ ■ ■ ■ ■
125
■
70
■ ■ ■ ■ ■ ■
150
■
80
■ ■ ■ ■ ■ ■
175
■
90
■ ■ ■ ■ ■ ■
200
■
100
■ ■ ■ ■ ■ ■
125
■ ■ ■ ■ ■
150
■ ■ ■ ■ ■
175
■ ■ ■ ■ ■
200
■ ■ ■ ■ ■
225
■ ■ ■ ■ ■
250
■ ■ ■
300
■
400
■
600
■
800
■
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Air circuit breakers
IEC Emax air circuit breakers equipped with DC PR122/
DC-PR123/DC electronic trip units are divided into four
basic sizes. They have an application field from 800 A (E2)
to 5000 A (E6) and current breaking capacities ranging from
35 kA to 100 kA (at 500 VDC).
By using the dedicated voltage module PR120/LV, the mini-
mum rated operational voltage is 24 VDC.
Please refer to Chapter 7: ”Choice of the protective device”
for information on pole connection and supply voltage.
Thanks to their exclusive technology, the DC PR122DC-
PR123/DC electronic trip units cover any possible installa-
tion requirement and perform the same protection functions
that were previously available for AC applications only.
The DC Emax circuit breakers keep the same overall dimen-
sions and the electrical and mechanical accessories as the
Emax range for AC applications.
Table 22. Electrical characteristics of DC Emax ACBs
E2 E3 E4 E6
Rated uninterrupted current, Iu
(A) B N N H S H H
(A) 800 1600 800 1600 1600 3200 3200
(A) 1000 1000 2000 2000 4000
(A) 1250 1250 2500 2500 5000
(A) 1600 1600 3200
(A) 2000
(A) 2500
Poles (Nr) 3/4 3/4 3/4 3/4
Rated operational voltage, Ue V < 1000 < 1000 < 1000 < 1000
Rated impulse withstand voltage, Uimp kV 12 12 12 12
Rated insulation voltage, Ui V 1000 1000 1000 1000
Rated ultimate breaking capacity under short-circuit,
Icu
500
VDC
(kA) 35 50 60 85 75 100 100
750
VDC
(kA) 25 35 50 65 65 85 85
1000
VDC
(kA) 25 35 35 65 50 65 65
Rated service breaking capacity under short-circuit,
Ics
500
VDC
(kA) 35 50 60 85 75 100 100
750
VDC
(kA) 25 35 50 65 65 85 85
1000
VDC
(kA) 25 35 35 65 50 65 65
Rated short-time withstand current, Icw (0.5 s)
500
VDC
(kA) 35 50 35 65 75 100 100
750
VDC
(kA) 25 35 35 65 65 85 85
1000
VDC
(kA) 25 35 35 65 50 65 65
Utilization category (IEC 60947-2) B B B B
Insulation behavior
■ ■ ■ ■
Overcurrent protection
PR122/DC
■ ■ ■ ■
PR123/DC
■ ■ ■ ■
ABB offering
L
S
S
I
U
OT
UV
OV
RP
M
G
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In addition to the standard protection functions (i.e. protection against overload and short-circuit), the
PR122-PR123DC trip units offer some advanced protection functions summed up in the following table:
Thanks to a new human-machine interface, the electronic trip units allow complete control over the system.
More precisely, such releases provide the following measuring and control functions:
(1) for PR 123/DC only
(2) with communication module PR120/D-M
Protection functions PR122 PR123
Protection against overload with inverse long time-delay trip
■ ■
Selective protection against short-circuit inverse or definite short time-delay trip
■ ■
Second selective protection against short-circuit inverse or definite short time-delay trip
■
Protection against instantaneous short-circuit with adjustable trip current threshold
■ ■
Protection against ground fault
■
Protection against phase unbalance
■
Protection against overtemperature (check)
■ ■
Protection against undervoltage
■
Protection against overvoltage
■
Protection against reverse active power
■
Thermal memory for functions L and S
■ ■
Table 23. PR122-PR123 Trip unit characteristics
Measurements
PR122/DC-
PR123/DC
Currents
■
Voltage
■ (1)
Power
■ (1)
Energy
■ (1)
Event marking and maintenance data
Event marking with the instant it occurred
■
Chronological event storage
■
Counting the number of operations and contact wear
■
Communication with supervision system and centralised control
Remote parameter setting of the protection functions, unit configuration, communication opt. (2)
Transmission of measurements, states and alarms from circuit breaker to system opt. (2)
Transmission of the events and maintenance data from circuit breaker to system opt. (2)
Watchdog
Alarm and trip for release overtemperature
■
Check of release status
■
Interface with the user
Presetting parameters by means of keys and LCD viewer
■
Alarm signals for functions L, S, I and G
■
Alarm signal of one of the following protections: undervoltage, overvoltage, residual voltage, active reverse of power, phase unbalance, overtemperature
■
Complete management of pre-alarms and alarms for all the self-control protection functions
■
Enabling password for use with consultation in “READ” mode or consultation and setting in “EDIT” mode
■
Load control
Load connection and disconnection according to the current passing through the circuit breaker
■
Zone selectivity
Can be activated for protection functions S, G (1)
■
ABB offering
Table 24.
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9.2 Molded case switches
To carry out the isolating function and to cut off the power supply from all or from a discrete section of the DC installation,
the product range offered by ABB is:
The following tables show the electrical characteristics of the Tmax molded case switches:
Tmax molded case switches keep the same overall dimen-
sions, versions, terminals and accessories as Tmax molded
case circuit breakers. This version only differs from the
circuit breakers in the absence of the trip unit.
These molded case switches can be used up to 750 VDC
(with T4D-T5D-T6D-T7D). The new Tmax PV line of molded
case switches can be applied up to 1100 VDC.
See the tables of Chapter 7: ”Choice of the protective de-
vice” for information on pole connection.
Tmax molded case switches
ABB offering
Table 25.
Tmax
T1N-D
Tmax
T3S-D
Tmax
T3S-D
Tmax
Ts3H-D
150
Tmax
Ts3H-D
225
Tmax
T4N-S-
H-L-V-D
Tmax
T5N-S-
H-L-V-D
Tmax
T6H-D
Tmax
T7H-D
Rating
[A]
100 150 225 150 225 250 400-600 800 1200
Poles
[Nr]
3, 4 3, 4 3, 4 3, 4 3, 4 3, 4 3, 4 3, 4 3, 4
Magnetic
override
[A]
1000 1500 2250 1500 2250 3000 5000 10000 20000
Rated
voltage
AC (50-60 Hz) [V]
600Y/347 600Y/347 600Y/347 600 480 600 600 600 600
DC [V]
500 500 500 600 500 600 600 600 —
Reference
standard
UL489 UL489 UL489 UL489 UL489 UL489 UL489 UL489 UL489
Table 26.
Tmax
T1B-C-N-D
Tmax
T3N-S-D
Tmax
T4N-S-H-L-
V-D
Tmax
T5N-S-H-L-
V-D
Tmax
T6N-S-H-
L-D
Tmax
T7S-H-L-
V-D
Rating [A] 160 250 250-320 400-630 630-800-1000
1000-1250-
1600
Poles [Nr] 3, 4 3, 4 3, 4 3, 4 3, 4 3, 4
Rated
voltage
AC (50-60 Hz)
[V] 690 690 690 690 690 690
DC
[V] 500 500 750 750 750 750
Reference
standard
IEC 60947-2 IEC 60947-2 IEC 60947-2 IEC 60947-2 IEC 60947-2 IEC 60947-2
Table 27. Tmax
PV T1-D
Tmax
PV T3-D
Tmax
PV T4-D
Tmax
PV T5-D
Tmax
PV T6-D
Tmax
PV T7-D
Tmax
PV T7M-D
Rating [A] 160 250 250 630 800 1600 1600
Poles [Nr] 4 4 4 4 4 4 4
Service current
(category DC22B)
160 200 250 500 800 1600 1600
Rated voltage DC [V] 1100 1100 1100 1100 1100 1100 1100
Reference stan-
dard
IEC 60947-3 IEC 60947-3 IEC 60947-3 IEC 60947-3 IEC 60947-3 IEC 60947-3 IEC 60947-3
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E1B/E MS E2N/E MS E3H/E MS E4H/E MS E6H/E MS
Rated current (at 40° C) lu
[A] 800 1250 1250 3200 5000
[A] 1250 1600 1600 4000 6300
[A] 2000 2000
[A] 2500
[A] 3200
Poles 3 4 3 4 3 4 3 4 3 4
Rated service voltage Ve [V] 750 1000 750 1000 750 1000 750 1000 750 1000
Rated insulation voltage Vi [V] 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000
Rated impulse withstand voltage Vimp [kA] 12 12 12 12 12 12 12 12 12 12
Rated short-time withstand current Icw (1s) [kA] 20 20 25 25 40 40 65 65 65 65
Rated making capacity Icm
750 VDC [kA] 20 20 25 25 40 40 65 65 65 65
1000 VDC [kA] — 20 — 25 — 40 — 65 — 65
Reference standard IEC 60947-3
NOTE: The breaking capacity Icu, by means of external protection relay, with 500 ms maximum timing, is equal to the value of Icw (1s).
Emax switch disconnectors maintain the same overall di-
mensions and the same accessories as the Emax air circuit
breakers. This version differs from the circuit breakers only
in the absence of trip units. These switch disconnectors are
available both in fixed and withdrawable versions, three or
Table 28. Electrical characteristics of the Emax switch disconnectors:
four poles and can be used according to utilization category
DC 23A (switching of motors or other highly inductive loads,
e.g. motors in series).
Emax switch disconnectors
ABB offering
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Annex A
Direct current distribution systems
The Standard IEC 60364-1 defines the direct current and alternating current distribution systems analogously:
TT system
a terminal of the system and the exposed conductive-parts are connected to two electrically independent
grounding arrangements. If necessary, the middle point of the supply can be connected to ground.
Figure 18
TT DC system
Figure 19
TT DC system with the middle point of the supply connected to
ground
The choice of grounding either the positive or the negative terminal
is made according to considerations not treated in this Annex.
TT system
A terminal or the middle point of the supply is directly grounded; the exposed-conductive-parts are connected to the same
grounded point. Three types of TN system are defined according to whether the grounded terminal and the protective
conductor are separated or not:
1.TN-S system – the conductor of the terminal connected to ground and the protective conductor Gnd are separated.
Figure 20 TN-S DC distribution system Figure 21 TN-S DC system with the middle point of the supply
connected to ground
L+L+
L-
Exposed conductive parts
Grounding of system Grounding of exposed
conductive-parts
L-
M
Exposed conductive parts
Grounding of exposed
conductive-parts
Grounding of system
L+
L-
Exposed conductive parts
Grounding of system
Exposed conductive-parts
Gnd
L+
L-
M
Gnd
Grounding of system
Annex A
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2.TN-C system – the functions grounded terminal and protective conductor are partially combined in a single
conductor called GndN
Figure 22
TN-C DC distribution system
Figure 23
TN-C DC distribution system with the middle point of the supply
source connected to ground
3.TN-C-S system – the functions of the grounded terminal and of the protective conductor are partially
combined in a single conductor called GndN and partially separated
Figure 24 TN-C-S DC distribution system Figure 25 TN-C-S DC distribution system with the middle point
of the supply source connected to ground
L+
GndN (DC)
L-
Exposed conductive parts
Grounding of system
L+
Exposed conductive parts
Grounding of system
GndN (DC)
Exposed conductive parts
L+
Gnd
L-
GndN (DC)
L+
L-
Gnd
M
GndN (DC)
Grounding of system
TN-C system TN-S system
TN-C-S DC system
Grounding of system
TN-C system TN-S system
TN-C-S DC system
Exposed conductive parts
Annex A
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IT system
The supply source is not grounded; the exposed-conductive-parts are connected to the same grounding point.
Figure 26 IT DC distribution system Figure 27 IT DC distribution system with the middle point of the
supply isolated form ground
Exposed conductive parts
L+
L-
L+
Grounding of exposed conductive-parts
N
L-
Grounding of exposed conductive-parts
Exposed conductive parts
Protection against indirect contact
To protect against direct and indirect contacts, IEC Standard 60364-4 mandates that the protective device shall
automatically disconnect the supply so that in the event of a fault between a live part and an exposed-conduc-
tive-part or a protective conductor, a voltage exceeding 120 VDC does not persist for a sufficient time to cause
harmful physiological effects to a human body 1.
For particular environments, tripping times and voltage values lower than 120 VDC may be required. Further
requirements for DC systems are being studied at present.
1 For IT systems, the automatic opening of the circuit is not necessarily required in the presence of a first fault.
Annex A
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τ
1
τ
2
i
i
1
(t)
i
p
Ik
0
0
t
p
T
k
t
i
2
(t)
t
pB
t
i
pB
i
B
Ik
Annex B
Calculation of short-circuit currents
The study of short-circuit currents is fundamental for correct
sizing of the components included in the plant.
Here are some brief considerations on how to assess the
short-circuit current according to IEEE Std. 1375, “IEEE
guide for the protection of stationary battery systems”,
Annex C.1.1; and IEEE Std. 946, “IEEE Recommended
Practice for the Design of DC Auxiliary Power Systems for
Generating Stations”, Annex C.
This standard provides some calculation methods regarding
the variations of the short-circuit currents relevant to electri-
cal components acting as short-circuit current sources.
We take into consideration only the information about sta-
tionary lead-acid batteries and give the time-current curves
of the other sources (rectifiers in three-phase AC bridge
connection for 60 Hz, smoothing capacitors and DC motors
with independent excitation).
T`he following figure represents the typical curve of a direct
short-circuit current:
Calculation of the short-circuit current provided by
a stationary lead-acid battery
The following figure shows the curve of the short-circuit cur-
rent delivered by a stationary lead-acid battery.
Annex B
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The internal resistance of a cell can be calculated from its discharge characteristic curve. For this example, we
will take the following values:
If we consider 10 positive plates:
The short circuit current at the cell terminals can be calculated as:
where E
c
is the nominal cell voltage (2.00 V)
The short circuit current available at the load terminals of the main/battery circuit breaker, considering a battery of
60 cells, would be:
Where E
b
is the nominal battery voltage
R
b
is the total internal resistance of the battery = (0.0001385) (60) = 0.00831 Ω
R
x
is the total external circuit resistance = 0.0100 Ω
R
t
is the total circuit resistance = R
b
+ R
x
= 0.00831 + 0.0100 = 0.01831 Ω
Annex B
R
p
=
(V
1
- V
2
)
=
(1.7 - 1.52)
(I
2
- I
1
) (345 - 215)
R
p
= 0.001385
Ω
Positive plate
R
t
=
0.001385
= 0.0001385 Ω
10
I
c
=
E
c
R
t
I
c
=
2.0
= 14,440 Amps
0.0001385
I
b
=
E
b
R
t
= (60 cells) (2.00
Volts
) = 120 V
cell
I
b
=
120 V
) = 6554 Amps
0.01831 Ω
i
p
t
p
t
I
k
i
i
p
t
p
t
I
k1
i
I
k2
i
p
t
p
t
i
i
p
t
p
t
i
I
k3
I
k4
The following table summarizes all the variations of the short-circuit currents indicated relevant to the different
equipment acting as short-circuit sources:
Equipment acting as short-circuit
sources
Short-circuit current variations Description
Stationary lead-acid battery
ip = peak short-circuit current
tp = time to peak
Ik = quasi steady-state short-circuit
current
Rectifiers in three-phase AC bridge
connections for 50Hz without (Ik2)
and with smoothing reactor (Ik1)
Smoothing capacitors
DC motors with independent
excitation without additional inertia
mass (Ik4) or with additional inertia
mass (Ik3)
Low Voltage Products & Systems 47
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Annex B
48 Low Voltage Products & Systems
1SXU210206G0201 ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage
Annex C
Annex C
IEC circuit-breakers and molded case switch
disconnectors for applications up to 1000 VDC
The main installations at 1000 VDC are used for traction,
mines, road tunnels, railway applications, photovoltaic and
industrial applications in general.
This high voltage is used in those plants where it is neces-
sary to have distribution lines longer than normal LV lines
or in those applications requiring significant power. In those
circumstances, to keep the rated and the short-circuit cur-
rents lower, it is necessary to increase the rated voltage of
the plant.
Thus it is possible to use conductors with smaller cross
sectional areas both in the switchboards as well as in the
distribution lines. This causes a consequent reduction in the
initial investment costs and in the running costs due to the
decrease in the power losses caused by the joule effect.
Another advantage is space savings of the cable runs
thanks to the reduction in their cross sectional area. For
further applications, such as installation in mines, the nar-
rowness of the available spaces enormously amplifies the
problem of the arrangement of the run and of the position-
ing of the conductors in relation to air/suction ducts and air
conditioning.
Moreover, with 1000 V, it is possible to reduce the percent-
age voltage drop, thus obtaining longer distribution lines.
This is one reason why this voltage is used in installations
with particular requirements of length.
The increase in voltage also brings better service condi-
tions thanks to the reduction in the short-circuit levels, thus
limiting the consequences of possible faults and improving
safety.
However, 1000 V affects the choice, the availability and the
cost of the switching and protection devices which can be
used. These special 1000 V versions have constructional
characteristics necessary to meet the most severe require-
ments.
ABB offering for use up to 1000 VDC
The range of products offered by ABB for applications up to
1000 VDC include products for the protection or the isola-
tion of circuits. When choosing a circuit breaker, it is neces-
sary to take into consideration the grounding of the plant.
This helps define the number of poles to be connected in
series with the purpose of creating working conditions under
which, if a short-circuit occurs, the current breaking is car-
ried out by the series of the four circuit breaker contacts.
In the following pages, both the electrical characteristics of
the products as well as the pole connection configurations
are reported.
Low Voltage Products & Systems 49
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Annex C
Emax circuit breakers equipped with electronic trip units
Emax circuit breakers for use in direct current up to 1000 VDC can cover installation requirements up to 5000 A.
These circuit breakers have the same dimensions as the standard circuit breakers, and are available in the fixed
and withdrawable versions and can be equipped with PR122-PR123DC electronic trip units. They are compatible
with all the accessories provided for the standard version.
Tmax T4 Tmax T5 Tmax T6
Rated uninterrupted current, Iu [A] 250 400/630 630/800
Poles [Nr.] 4 4 4
Rated service voltage, Ve [V] 1000 1000 1000
Rated impulse withstand voltage, Vimp [kV] 8 8 8
Rated insulation voltage, Vi [V] 1150 1150 1000
Test voltage at power frequency for 1 min. [V] 3500 3500 3500
Rated ultimate short-circuit breaking capacity, Icu V V L
(DC) 4 poles in series [kA] 40 40 40
Rated service short-circuit breaking capacity, Ics
(DC) 4 poles in series [kA] 20 20
Utilization category (IEC 60947-2) A B (400 A) 1 - A (630 A) B 2
Insulation behavior
■ ■ ■
Reference Standard IEC 60947-2 IEC 60947-2 IEC 60947-2
Thermomagnetic trip units
TMD
■
– –
TMA
■ ■ ■
1 Icw = 5 kA
2 Icw = 7.6 kA (630 A) - 10 kA (800 A)
Circuit breakers for use up to 1000 VDC
Tmax circuit breakers equipped with thermal magnetic trip unit
Tmax circuit breakers for use in direct current up to 1000 V have the same dimensions as the standard circuit breakers and
are available in the fixed, plug-in and withdrawable version. They can be fed from the top only and can be equipped only with
adjustable thermomagnetic trip units. They are compatible with all the accessories provided for the standard version except
for the residual current release.
E2 E3 E4 E6
Rated uninterrupted current, Iu (A) B N N H S H H
(A) 800 1600 800 1600 1600 3200 3200
(A) 1000 1000 2000 2000 4000
(A) 1250 1250 2500 2500 5000
(A) 1600 1600 3200
(A) 2000
(A) 2500
Poles (Nr) 3/4 3/4 3/4 3/4
Rated voltage service, Ve V < 1000 < 1000 < 1000 < 1000
Rated impulse withstand voltage, Vimp kV 12 12 12 12
Rated insulation voltage , Vi V 1000 1000 1000 1000
Rated ultimate breaking capacity under short-circuit, Icu 1000 VDC (kA) 25 35 35 65 50 65 65
Rated service breaking capacity under short-circuit, Ics 1000 VDC (kA) 25 35 35 65 50 65 65
Rated short-time withstand current Icw (0.5s) 1000 VDC (kA) 25 35 35 65 50 65 65
Utilization category (IEC 60947-2) B B B B
Insulation behavior
■ ■ ■ ■
Electronic releases
PR122/DC
■ ■ ■ ■
PR123/DC
■ ■ ■ ■
Electrical characteristics at 1000 VDC of Emax circuit breakers equipped with the new PR122-PR123/
DC trip unit
Electrical characteristics of Tmax circuit-breakers for 1000 VDC applications
50 Low Voltage Products & Systems
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Annex C
+ -
LOAD
+ -
LOAD
+
-
LOAD
+
-
LOAD
+ -
LOAD
+ -
LOAD
The table below shows the pole connection configurations with circuit breakers up to 1000 VDC according to the
network connection types. This table is valid for both Tmax MCCBs equipped with thermomagnetic trip units (the
connections shall be carried out by the customers) as well as for Emax ACBs equipped with the DC PR122-P123/DC
electronic trip units (connections carried out in the factory by ABB).
Connection modalities of poles with circuit breakers for applications up to 1000 VDC
Rated
voltage
(Vn)
1000 VDC
Type of
network
INSULATED NETWORK
NETWORK WITH ONE TERMINAL
CONNECTED TO GROUND 1
NETWORK WITH THE MIDDLE POINT OF THE SUP-
PLY SOURCE CONNECTED TO GROUND
Description
With this network type, a fault is considered to be
significant when it occurs between the positive and
the negative terminal which makes the series of the
four circuit breaker poles open the circuit.
The possibility of a double fault to ground (the first
fault on the supply side of the poles of one terminal
and the second one on the load side of the poles of
the other terminal) is not considered. Therefore, it is
suggested the use of a device to monitor the insula-
tion to ground capable of signaling the decrease of
the insulation to ground as a consequence of a first
fault to ground.
With this network type, the poles connected on the
terminal insulated from ground are called to break a
fault current at 1000 V; therefore it is necessary to
provide on this terminal the series of four poles. As a
consequence, the grounded terminal cannot be inter-
rupted and often this is not even necessary since it is
bound to the ground potential.
With this network type, the two poles connected
on one terminal are called to break a fault current at
500 V, whereas in case of a fault between the two
terminals, the voltage supporting it returns to be 1000
V and the proposed diagram allows breaking with four
poles in series.
Tmax
Protection
+
isolation
function
Protection
function
Emax
Protection
+
isolation
function
1 For Emax circuit breakers, please ask ABB.
Low Voltage Products & Systems 51
ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage 1SXU210206G0201
Annex C
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LOAD
+ -
LOAD
LOAD
+ - + -
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Switch disconnectors for applications up to 1000 VDC
ABB has developed a range of switch disconnectors (Emax/E MS family) for applications in direct current up to 1000 V
in compliance with the international Standard IEC 60947-3.
These switch disconnectors are particularly suitable for use as bus ties or main isolators.
These switch disconnectors are available both in fixed and withdrawable, three-pole and four-pole versions.
The switch disconnectors of the Emax/E MS family maintain the same overall dimensions and can be equipped with the
accessories common to the Emax circuit-breakers.
Hereunder are the wiring diagrams suggested by ABB. Also in this case the division of the different connection modalities
is carried out according to the installation voltage. As it can be seen from the table below, by connecting three break-
ing poles in series, it is possible to reach a rated voltage of 750 VDC, while with four poles in series the rated voltage is
1000 VDC.
Connection modalities of poles with Emax/E MS switch disconnectors
for applications up to 1000 VDC
E1B/E MS E2N/E MS E3H/E MS E4H/E MS E6H/E MS
Rated current (at 40°C), Iu [A] 800 1250 1250 3200 5000
[A] 1250 1600 1600 4000 6300
[A] 2000 2000
[A] 2500
[A] 3200
Poles [Nr.] 3 4 3 4 3 4 3 4 3 4
Rated service voltage, Ve (d.c.) [V] 750 1000 750 1000 750 1000 750 1000 750 1000
Rated insulation voltage, Vi (d.c.) [V] 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000
Rated impulse withstand voltage, Vimp [kV] 12 12 12 12 12 12 12 12 12 12
Rated short-time withstand current, Icw (1s) [kA] 20 20 25 25 40 40 65 65 65 65
Rated
voltage
750 VDC 1000 VDC
Poles connection
E1…E6/E MS
■ ■ ■
The performances at 750 V are:
for E1B/E MS Icw=25 kA
for E2N/E MS Icw=40 kA
for E3H/E MS Icw=50 kA
Electrical characteristics of the Emax switch disconnector
52 Low Voltage Products & Systems
1SXU210206G0201 ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage
Glossary
Imax maximum current
Ip short-circuit making current
Icn prospective short-circuit current
Va maximum arc voltage
Vn line voltage
T time constant
In rated current of the trip unit
lr.m.s r.m.s. value of an alternating current
I3 setting of the instantaneous protection against short-circuit
I2 setting of the protection against short-circuit with time delay
I1 setting of the protection against overload
Icu ultimate short-circuit breaking capacity
Ics service short-circuit breaking capacity
Icw rated short time withstand current
Ve rated operational voltage
TMG thermomagnetic trip unit with low magnetic threshold
TMF thermomagnetic trip unit with fixed thermal and magnetic threshold
TMD thermomagnetic trip unit with adjustable thermal and fixed magnetic threshold
TMA thermomagnetic trip unit with adjustable thermal and magnetic threshold
MF magnetic only trip unit, fixed
MA magnetic only trip unit, adjustable
L overload protection
S protection against short-circuit with time-delay trip
I instantaneous short-circuit protection
Ik quasi steady-state short-circuit current
ip peak short-circuit current
Tk short-circuit duration
tp time to peak
ipb peak short-circuit current supplied by a stationary lead-acid battery
tpb time to peak in a stationary lead-acid battery
Ikb quasi steady-state short-circuit current of a stationary lead-acid battery
Glossary
Low Voltage Products & Systems 53
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Notes
54 Low Voltage Products & Systems
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Notes
Low Voltage Products & Systems 55
ABB Inc. • 888-385-1221 • www.abb.us/lowvoltage 1SXU210206G0201
Notes
56 Low Voltage Products & Systems
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Notes
ABB Inc.
Low Voltage Control Products & Systems
1206 Hatton Road
Wichita Falls, TX 76302
Phone: 888-385-1221
940-397-7000
Fax: 940-397-7085
USA Technical help:
888-385-1221, Option 4
7:30AM to 5:30PM, CST,
Monday - Friday
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