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ABB Group March 10, 2015 | Slide 1
Lionel Ng, LPBS - Low Voltage Products
Welcome To ABB Technical Sharing Session
Circuit BreakersStandards Guidelines IEC 60947-2
ABB Group March 10, 2015 | Slide 3
IEC 60947-2
Circuit Breaker Standard, for industrial application
Definitions for MCCBs and ACBs
Choice criteria based on rated and limit values
Agenda
ABB Group March 10, 2015 | Slide 4
International Standard IEC 60947
European Standard EN 60947
IEC 60947-1 Part 1: General rules
IEC 60947-2 Part 2: Circuit breakers
IEC 60947-3 Part 3: Switch disconnectors
IEC 60947-4-1 Part 4: Contactors
IEC 60947-5-1 Part 5: Control circuit devices
IEC 60947-6-1 Part 6: Multifunction devices
IEC 60947-7-1 Part 7: Auxiliary materials
Standard for LV apparatus
IEC 60947 Standard for industrial application
ABB Group March 10, 2015 | Slide 5
A mechanical switching device capable of breaking, carrying and
making currents under normal circuit conditions and also making,
carrying, for a specified time, and breaking currents under specified
abnormal circuit conditions such as those of short-circuit.
BREAKING Breaking Capacity
WITHSTAND Short time withstand
MAKING Making Capacity
IEC Standard definitions
Circuit Breaker - IEC 60947-2
ABB Group March 10, 2015 | Slide 6
A mechanical switching device capable of breaking, making and
carrying currents under normal circuit conditions but only making and
carrying, for a specified time, currents under specified abnormal circuit
conditions such as those of short-circuit.
BREAKING Breaking Capacity
WITHSTAND Short time withstand
MAKING Making Capacity
IEC Standard definitions
Switch Disconnector - IEC 60947-3
ABB Group March 10, 2015 | Slide 7
Moulded case circuit breaker (MCCB): a circuit breaker having a supporting housing of moulding insulating material, forming an integral part of the circuit breaker (Tmax-XT).
IEC Standard definitions
IEC Standard definitions
ABB Group March 10, 2015 | Slide 8
Air circuit breaker (ACB): a circuit breaker having a supporting housing of moulding insulating material and a metallic frame, forming an integral part of the circuit breaker (Emax & Emax 2).
ABB Group March 10, 2015 | Slide 9
A circuit breaker with a break-time short enough to prevent the short-circuit
current from reaching its peak value.
Current limiting circuit breaker
Current limiting circuit breaker (IEC 60947-2 def. 2.3)
A current-limiting circuit
breaker is able to reduce the
stress, both thermal and
dynamic, because it has been
designed to start the opening
operation before the short-
circuit current has reached its
first peak, and to quickly
extinguish the arc between the
contacts.
Current limiting circuit breaker
ABB Group March 10, 2015 | Slide 10
A = Direction of arc due to the magnetic field
R= Repulsion of moving contacts due to the short circuit current
A
I
A
R
R
ABB Group March 10, 2015 | Slide 11
Time
Current
Current limiting circuit breaker
Energy limitation
ABB Group March 10, 2015 | Slide 12
Value of the limited peak
of the short circuit current
according to the value of
the symmetrical short
circuit current Irms.
Current limiting circuit breaker
Peak limitation curves
ABB Group March 10, 2015 | Slide 13
Value of the let-through
energy according to the
value of the symmetrical
short circuit current Irms.
Current limiting circuit breaker
I2t curves
ABB Group March 10, 2015 | Slide 14
Protection against short-circuit (IEC 60364)
To protect a cable against short-circuit, the specific let-through energy of
the protective device must be lower or equal to the withstanding energy of
the cable:
where
I2 t is the specific let-through energy of
the protective device which can be read on
the curves supplied by the manufacturer;
S is the cable cross section [mm2]; in the
case of conductors in parallel it is the
cross section of the single conductor;
k is a factor that depends on the cable
insulating and conducting material.
0.1kA 1kA 10kA 100kA
1E-2MAs
0.1MAs
1MAs
10MAs
100MAs
1E3MAs
Specific let through energy curve LLL
Current limiting circuit breaker
Energy limitation
ABB Group March 10, 2015 | Slide 15
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Rated values (Iu, Ue)
ABB Group March 10, 2015 | Slide 16
the rated uninterrupted current of an equipment is a value of
current, stated by the manufacturer, that the equipment can carry
in uninterrupted duty (at 40 C)
IEC 60947-1 def. 4.3.2.4
Rated value Iu
Rated uninterrupted current Iu
ABB Group March 10, 2015 | Slide 17
Rated value Iu
The rated uninterrupted current Iu is different from the rated
current In, which is the rated current of the thermomagnetic or
electronic trip unit and is lower or equal to Iu.
A new concept
for setting the
current In: the
rating plug
ABB Group March 10, 2015 | Slide 18
XT1 160
XT4 250
Rated uninterrupted current Iu
Some factors may reduce the Iu of a circuit breaker
like temperature, altitude or frequency.
Rated value Iu
ABB Group March 10, 2015 | Slide 19
the rated operational voltage of an equipment is a value of voltage
which, combined with a rated operational current, determines the
application of the equipment and to which the relevant tests and
the utilization categories are referred.
IEC 60947-1 def. 4.3.1.1
Rated value Ue
Rated operational voltage Ue
ABB Group March 10, 2015 | Slide 20
Breaking capacity is always referred to the operational voltage; the
breaking capacity decreases when the voltage increases.
Rated value Ue
Rated operational voltage Ue
ABB Group March 10, 2015 | Slide 21
Some factors may reduce the Ue of a circuit breaker
Rated value Ue
ABB Group March 10, 2015 | Slide 22
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Limit values (Icu, Ics, Icw, Icm)
ABB Group March 10, 2015 | Slide 23
Breaking capacity according to a specified test sequence.
Do not include after the short circuit test, the capability of the
circuit breaker to carry its rated current continuously.
- test sequence: O - 3 min - CO
- dielectric withstand at 2 x Ue- verification of overload release at 2.5 x I1
Limit value Icu
Icu = RATED ULTIMATE SHORT
CIRCUIT BREAKING CAPACITY
IEC 60947-2
def. 4.3.5.2.1
ABB Group March 10, 2015 | Slide 24
Breaking capacity according to a specified test sequence.
Include after the short circuit test, the capability of the circuit
breaker to carry its rated current continuously
- test sequence: O - 3 min - CO - 3 min CO
- dielectric withstand at 2 x Ue- verification of temperature rise at Iu- verification of overload release at 1.45 x I1- verification of the electrical life
Ics = RATED SERVICE SHORT
CIRCUIT BREAKING CAPACITY
IEC 60947-2
def. 4.3.5.2.2
Limit value Ics
ABB Group March 10, 2015 | Slide 25
Limit values Icu and Ics
The service breaking capacity Ics can be expressed as
a value of breaking current, in kA;
Standard ratios between Ics and Icu
Relation between Ics and IcuThis relation is always true!!!
Ics Icu
a percentage of Icu, rounded up
to the lowest whole number,
in accordance with the table (for
example Ics = 25% Icu).
When is Icu required?
Where continuity of service is not a fundamental requirement.
For protection of single terminal load.
For motor protection.
Where maintenance work is easily carried out without much
disruption.
Generally for circuit breaker installed on terminals part of
plant.
When is Ics required?
Where continuity of service is a fundamental requirement.
For installation in power center.
Where is more difficult to make maintenance.
When is difficult to manage spare breakers.
Generally for installation in main distribution board
immediately downstream transformer or generator.
ABB Group March 10, 2015 | Slide 28
Main circuit breakers or circuit breakers for which
a long out-of-service period can not be accepted
(for example naval installation)
CB selection
based on
Ics
Icu
circuit breakers tor termlnal circuits or
circuit breakers for economic application
Limit values Icu and Ics
Icu and Ics: selection criteria
Icu or Ics ?
Application of Icu / Ics circuit breakers
When Isc = 100 % of Icu is not necessary ?
When the real short circuit current in the point of
installation is lower than the maximum Ics breaking
capacity.
U LOAD
B
A
Breaker A:
Icu =100 kA
with Ics = 100 % of Icu
Breaker B:
Icu = 100 kA
with Ics = 75 % of Icu
70 kA
50 kA !!!Please also consider
that short circuit current
at the end of the line is
still lower
When Isc = 100 % of Icu is not necessary ?
Motor Protection according to IEC 60947- 4-1
Duty cycle:
O - 3mins - CO at Iq current (maximum short circuit current)
O - 3mins - CO at r current (critical short circuit current depending from the contactor size)
Where:
O: Tripping of the circuit breaker under short circuit condition.
CO: Closing by the contactor under short circuit condition and tripping of the
circuit breaker.
Icu or Ics ? Conclusion
Consider that not always Ics = 100% of Icu for all the employ
voltage range, i.e. (from 220 V a.c. to 690 V a.c.duty, and 250
V d.c.).
Selection of circuit breaker with breaking capacity Icu or Ics
must be done according to the real technical installation
requirement.
Independently from the duty cycle selected the safety of the
plant is strictly dependent from the maximum circuit breaking
capacity (in most of cases Icu).
ABB Group March 10, 2015 | Slide 33
Limit value Icw
Icw = RATED SHORT-TIME
WITHSTAND CURRENT
IEC 60947-2
def. 4.3.5.4
Example of use of category B circuit breakers
in electrical plant
Trafo 630kVA
Ucc%=4%
400V
ACB E1B12
MCCB XT4
22.7kA
MCCB XT3
The upstream circuit
breaker can withstand
the fault current up to 1
sec, thus guaranteeing
an excellent selectivity
with downstream
apparatus
ABB Group March 10, 2015 | Slide 34
Circuit breakers specifically intended for selectivity in short
circuit conditions in relation to other protection devices in
load-side series, that is with an intentional delay (adjustable)
applicable in short circuit conditions.
These circuit breakers have a specified rated short-time
withstand current Icw.
IEC 60947-2
Table 4CATEGORY BCIRCUIT BREAKER
Limit value Icw
ABB Group March 10, 2015 | Slide 35
Circuit-breakers not specifically intended for selectivity under
short circuit conditions with respect to other protection devices
in series on the load side, that is without intentional short-time
delay provided for selectivity under short-circuit conditions.
These circuit-breakers have not a specified rated short-time
withstand current value Icw.
Limit value Icw
IEC 60947-2
Table 4CATEGORY ACIRCUIT BREAKER
ABB Group March 10, 2015 | Slide 36
It is the value of short-time withstand current assigned to the
circuit-breaker by the manufacturer under specified test
conditions. This value is referred to a specified time (usually 1s or 3s).
It must be stated when the circuit-breaker is classified in
category B and its value must be greater than:
The highest value between 12 Iu and 5 kA for CBs with Iu 2500A
30 kA for CBs with Iu > 2500A
Circuit breakers without Icw value are classified in category A
Limit value Icw
IEC 60947-2
Table 3Icw = RATED SHORT-TIME
WITHSTAND CURRENT
Selectivity Categories
ABB Group March 10, 2015 | Slide 38
IEC 60947-2
def. 4.3.5.1Icm = RATED SHORT-CIRCUIT
MAKING CAPACITY
Making capacity for which the prescribed conditions according
to a specified test sequence include the capability of the circuit
breaker to make the peak current corresponding to that rated
capacity at the appropriate applied voltage.
Limit value Icm
It is always necessary to verify that:
Icm Ipeak
ABB Group March 10, 2015 | Slide 39
Limit value Icm
Icm n x Icu
For a.c. the rated short-circuit making
capacity of a circuit-breaker shall be not
less than its rated ultimate short-circuit
breaking capacity, multiplied by the factor
n of the table.
IEC 60947-2
Table 2
ABB Group March 10, 2015 | Slide 40
16,8kA
50kA
54kA
Peak
Irms
105kA
10kA 100kA
10kA
100kA
T6L800 In800
XT2L 160 In160
Example
Current limiting circuit breaker
ABB Group March 10, 2015 | Slide 41
If the cos of the plant is higher than the standard prescribed
value, it is not necessary to take into account the rated short-
circuit making capacity of the circuit-breakers (Icm).
If the cos of the plant is lower than the standard
prescribed value, usually near to the transformer and/or
generator, it is necessary to verify Icm Ipeak.
Limit value Icm
ABB Group March 10, 2015 | Slide 42
If the cosk of the plant is equal to 0.16 (lower than the standard
prescribed value) the evaluated Ip = 175 kA.
Short circuit current of the plant is Icc = 75kA ;
The used circuit breaker has an Icu = 75 kA;
According to the table 2, cosk=0.2 and n=2,2 so Icm = n x Icu = 165 kA.
Since Ip > Icm the CB selected is not correct. I will use a CB with a greater
value of Icu in order to have an Icm value suitable to the peak current of the
plant.
Sometimes it can happen
Limit value Icm
ABB Group March 10, 2015 | Slide 43
Limit value Icm
ABB Group March 10, 2015 | Slide 44
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Insulation values (Ui, Uimp)
ABB Group March 10, 2015 | Slide 45
IEC 60947-1
def. 4.3.1.2Ui = RATED INSULATION
VOLTAGE
The rated insulation voltage of an equipment is the value
of voltage to which dielectric tests and creepage
distances are referred.
It shall be always verified that:
Ue < Ui
Limit value Ui
ABB Group March 10, 2015 | Slide 46
IEC 60947-1
def. 4.3.1.3Uimp = RATED IMPULSE
WITHSTAND VOLTAGE
The peak value of an impulse voltage of prescribed form and
polarity (1,2/50ms) which the equipment is capable of
withstanding without failure under specified conditions of test
and to which the values of the clearances are referred.
It shall be always verified that:
Uimp > transient overvoltage in the plant
Limit value Uimp
Temperature-rise for terminals and accessible parts
ABB Group March 10, 2015 | Slide 47
IEC 60947- 2
Table 7
Overload protection
ABB Group March 10, 2015 | Slide 48 i
t
IEC 60947- 2
Table 6
Short circuit protection
ABB Group March 10, 2015 | Slide 49
i
S
I
t
IEC 60947- 2
8.3.3.1.2
Type Tests
The tests to verify the characteristics of
circuit breakers are:
type tests carried out on samples:
IEC 60947- 2
8.3
Type Tests
ABB Group March 10, 2015 | Slide 51
Routine Tests
ABB Group March 10, 2015 | Slide 52
routine tests carried out on
all circuit breakers and
including the following tests:
IEC 60947- 2
8.4
Tests of EMC for circuit breakers with electronic overcurrent protection
Immunity
Emission
Electrostatic discharges
Radiated radio-frequency electromagnetic fields
Electrical fast transients/bursts
Surges
Conducted disturbances induced by radio-frequency fields
Harmonics
Voltage fluctuations
Conducted disturbances
Radiated disturbances
Climatic testsDry heat test Damp heat test
Temperature variation cycles at a specified rate of change
Annex F - J
CE Marking
ABB Group March 10, 2015 | Slide 54
According to european directives:
Low Voltage Directive 73/23 EEC
Electromagnetic Compatibility 89/336 EEC
Annex H
Test sequence for circuit-breakers for IT systems
This test is intended to cover the case of a second fault to earth in presence of a first
fault on the opposite side of a circuit breaker when installed in IT systems.
In this test at each pole the applied voltage shall be the phase-to-phase voltage
corresponding to the maximum rated operational voltage of the circuit breaker at which it
is suitable for applications on IT systems.
Circuit BreakersStandards Guidelines IEC 60898
IEC Standard definitions
International Standard References
IEC 60898
Applicable to circuit-breakers for protection of wiring installation
in buildings and similar applications, and designed for use by
uninstructed persons, and for not being maintained.
Part 1: Circuit-breakers for a.c. operation
Part 2: Circuit-breakers for a.c. and d.c. operation (additional requirements)
Miniature Circuit Breakers MCB
Rated values (In, Ue)
Limit values (Icn, Ics)
Rated values (In, Ue)
Choice criteria
Rated uninterrupted current (In):
the rated uninterrupted current of an equipment is a value
of current, stated by the manufacturer, which the equipment
can carry in uninterrupted duty, at a specified reference
ambient air temperature (30 C).
The rated current doesnt exceed the 125A.
IEC 60898-1 def. 5.2.2
Rated value In
Rated operational voltage (Ue):
The rated operational voltage of a circuit-breaker is the
value of voltage, assigned by the manufacturer, to which
its performances (particularly the short-circuit
performance) are referred.
The rated operational voltage doesnt exceed the 440Vac
220Vdc.
IEC 60898-1 def. 5.2.1.1
Rated value Ue
Rated values (In, Ue)
Limit values (Icn, Ics) Limit values (Icn, Ics)
Choice criteria
The rated short-circuit capacity is the value of the ultimate
short-circuit breaking capacity for which the prescribed
conditions, according to a specified test sequence, do not
include the capability of the circuit-breaker to carry 0.85 times
its non-tripping current for the conventional time.
The rated short circuit capacity doesnt exceed the
25kA in ac and 10kA in dc
test sequence: O - 3 min - CO
- leakage current at 1.1 Ue (< 2 mA)
- dielectric strength test at 900 V
- verification of overload release at 2.8 x In
IEC 60898-1
def. 5.2.4Icn = RATED SHORT CIRCUIT
CAPACITY
Limit value Icn
The service short-circuit capacity of a circuit-breaker is the
value of the breaking capacity for which the prescribed
conditions according to a specified test sequence include the
capability of the circuit-breaker to carry 0.85 times its non-
tripping current for the conventional time.
IEC 60898-1
def. 3.5.5.2Ics = RATED SERVICE SHORT
CIRCUIT CAPACITY
Limit value Ics
Service Short Circuit capacity (Ics):
- test seq. : O - 3 min - O - 3 min CO (for one or two poles cb)
O - 3 min - CO - 3 min CO (for three or four poles cb)
- leakage current at 1.1 Ue (< 2 mA)
- dielectric strength test
- verification of no tripping at 0,85 x In
A circuit-breaker with a rated short-circuit capacity (Icn) has a corresponding service short-
circuit capacity (Ics) as from this table:
The circuit breaker with
Icn < 6000A Ics is equal to 1xIcn
6000A < Icn < 10000A Ics is equal to 0,75xIcn Minimum value of Ics is 6000A.
Icn > 10000A Ics is equal to 0,5xIcn Minimum value of Ics is 7500A.
Limit value Ics
Ics Test
The main difference between the overload protection curve of the CBs responding to
IEC 60947 or IEC 60898 are referred to the conventional non tripping current.
The prescibed conditions are given in this table:
Overload characteristics
Tripping Curves
The CBs according to IEC 60947 usually have the instantaneous threshold at 5 or 10 times
the rated current with a tolerance of + 20%.
The CBs according to IEC 60898-1 (ac applications) have different instantaneous
threshold referred to the type B , C , D as indicated in the table below:
Magnetic characteristics
Tripping Curves
Tripping Curves
In some cases, the conditions IB < In < IZand I2 < 1.45 IZ do not guarantee complete
protection, e.g. when overcurrents are
present for long periods which are smaller
than I2. They also do not necessarily lead
to an economical solution. It is therefore
assumed that the circuit is designed so
that minor overloads of a long duration will
not occur regularly.
IEC 60364-4-43
Tripping Curves
Tripping Curves
IEC 60947-2 IEC 60898-1
People Instructed Uninstructed
Maintenance Possible Not possible
Rated Voltage (Ue)< 1000 Vac
< 1500 Vdc
< 440 Vac
< 220 Vdc
Ambient
Temperature40 C 30 C
Rated CurrentNo limits
(Iu < 6300 A)In = 125 A
Short circuit
breaking currentNo limits for Icu
Icn = 25 kA (ac)
Icn = 10 kA (dc)
Comparison IEC 60947-2 vs IEC 60898
Generalities about the main electrical parameters Dont forget
Ue Un Icu or Ics Ik Icm Ip
Ue, Icu, Ics, Icm?
Selection of protective Devices
Protection of feeders against overload
Ib In or I1 Iz
against short-circuit
I2t k2S2
In
Iz S
Ib
Selection of protective Devices
The correct circuit breaker must be selected to satisfy the following
conditions:
It must own short circuit breaking power (lcu or eventually lcs) greater or
equal to the short circuit current lcc
It must use a protection release so that its overload setting current ln (l1)
satisfies the relation lB < ln < lZ
The let through energy (l2t) that flows through the circuit breaker must be
lesser or equal to the maximal one allowed by the cable (KS)
Selection of protective Devices
Selection of protective Devices
As far as the verification required by IEC 60364, according to which the
overload protection must have an intervention current lf that assures the
operation for a value lesser than 1,45 lz (lf < 1,45 lz), we must state that it
is always verified for ABB Circuit breakers, since according to IEC 60947-2
the required value is less than 1,3 ln.
Selection of protective Devices
Selection of protective Devices
Protection of generators Ingen I1 I3 or I2 2.5-4 x Ingen
G
Selection of protective Devices
Protection of transformers InT I1 Upstream CB
I3 or I2 Iinrush
Selection of protective Devices
Steps determining the short-circuit
currents
choosing the CB
setting of the MV overcurrent
protection
setting of the LV overcurrent
protection
20kV
400V
Selection of protective Devices
20kV
400V
Selection of protective Devices
20kV
400V
Selection of protective Devices
As to be able to protect LV/MV transformers LV side, we must mainly
take into account:
Rated current of the protected transformer, LV side, from which
the rated current of the circuit breaker and the setting depend on
(In);
The maximum estimated short circuit current in the installation
point which defines the minimal breaking power of the protection
circuit breaker (Isc).
Protection of Transformers
Sn
In
Isc
U20
Protection of TransformersSwitchboards with one transformer
The rated current of the transformers LV side is defined by the
following expression
where
Sn = rated power of the transformer [kVA]
U20 = rated secondary voltage (no load) of the transformer [V]
ln = rated current of the transformer, LV side [A]
In =Sn x 103
3 x U20
The full voltage three-phase short circuit current immediately after the LV
side of the transformer can be expressed by the following relation once we
suppose infinite power at the primary:
where
Ucc %= short circuit voltage of the transformer [%]
ln = rated current, LV side, [A]
lsc = three-phase rated short circuit current, LV side, [A]
Isc =In x 100
Ucc %
Protection of Transformers
The short circuit current is normally lesser than the preceding deduced
value if the circuit breaker is installed at a certain distance by means of
a cable or bar connection, according to the connection impedance.
Protection of Transformers
The following table shows some possible choices within the SACE Emax
ACB range according to the characteristics of the CB to protect.
Attention
Those indications are valid at the conditions that we declare in the table;
different conditions will lead us to repeat calculations and modify the
choices.
Protection of Transformers
(1) For values of the percent short circuit voltage Ucc% different from the Ucc% values as per table, the rated three-phase short
circuit current Icn becomes:
(2) The calculated values refer to a U20 voltage of 400 V. for different U20 values, do multiply In and Isc the following k times:
Isc =Ucc %
Ucc %
Isc
U20 [V] 220 380 400 415 440 480 500 660 690
k 1.82 1.05 1 0.96 0.91 0.83 0.8 0.606 0.580
Protection of Transformers
Sn [kVA] 500 630 800 1000 1250 1600 2000 2500 3150
Ucc (1) % 4 4 5 5 5 6,25 6,25 6,25 6,25
In (2) [A] 722 909 1154 1443 1804 2309 2887 3608 4547
Isc (2) [kA] 18 22.7 23.1 28.9 36.1 37 46.2 57.7 72.7
SACE Emax E1B08 E1B12 E1B12 E2B16 E2B20 E3B25 E3B32 E4S40 E6H50
Protection of TransformersSwitchboards with more than 1 transformer in Parallel
Circ
uit b
reaker B
I1 I2 I3
1 2 3
Isc2 + Isc3
Isc1 + Isc2 + Isc3
I4 I5
Circ
uit b
reaker A
Isc1
As far as the calculation of the rated current of the transformer is
concerned, the rules beforehand indicated are completely valid.
The minimum breaking capacity of each circuit breaker LV side must be
greater than the highest of the following values: (the example refers to
machine 1 of the figure and it is valid for the three machines in parallel):
lsc 1 (short circuit current of transformer 1) in case of fault
immediately downstream circuit breaker 1;
lsc2 + lsc3 (short circuit currents of transformer 2 and 3) in case of
fault immediately upstream circuit breaker 1;
Protection of Transformers
Circuit breakers l4 and l5 on the load side must have a short circuit
capacity greater than lsc1 + lsc2 + lsc3; naturally every transformer
contribution in the short circuit current calculation is to be lessened by the
connection line transformer - circuit breaker (to be defined case by case).
Protection of Transformers
ABB Group March 10, 2015 | Slide 92
Low voltage selectivitywith ABB circuit breakersSelectivity definitions and Standards
Definitions and Standards
Selectivity techniques
Definitions and Standards
Back-up protection
AgendaLow voltage selectivity with ABB circuit breakers
Selectivity (or discrimination)
is a type of coordination of two or
more protective devices in series.
Selectivity is done between
one circuit breaker on the supply side
and one circuit breaker, or more than
one, on the load side.
A is the supply side circuit
breaker (or upstream)
B and C are the load side circuit
breakers (or downstream)
IntroductionWhat is selectivity?
Better selectivity
FAULT CONTINUITY OF SERVICEDAMAGE REDUCTION
Fast fault elimination
Reduce the stress and prevent damage
Minimize the area and the duration of power loss
IntroductionProtection system philosophy
Selective coordination among devices
is fundamental for economical and technical reasons
It is studied in order to:
rapidly identify the area involved in the problem;
bound the effects of a fault by excluding just the affected zone of the network;
preserve the continuity of service and good power quality to the sound parts of the network;
provide a quick and precise identification of the fault to the personnel in charge of maintenance or to management system, in order to restore the service as rapidly as possible;
achieve a valid compromise between reliability, simplicity and cost effectiveness.
Main purposes of coordinationSelectivity purpose
The definition of selectivity
Trip selectivity (for overcurrent) is a coordination between the
operating characteristics of two or more overcurrent protection
devices, so that, when an overcurrent within established limits
occurs, the device destined to operate within those limits trips
whereas the others do not trip
IEC 60947-1 Standard: Low voltage equipment
Part 1: General rules for low voltage equipment
Standards definitionSelectivity
IEC 60947-1
def. 2.5.23
In occurrence of a fault
(an overload or a short circuit)
if selectivity is provided
only the downstream circuit
breaker opens.
Overcurrent selectivityExample
All the system is out of service!
In occurrence of a fault
(an overload or a short circuit)
if selectivity is not provided
both the upstream and the
downstream circuit breakers
could open
Overcurrent selectivityExample
A and B connected in series:
partial selectivity and total selectivity.
Standards definitionPartial and total selectivity
IEC 60947-2
def. 2.17.2 - 2.17.3
Partial selectivity is an overcurrent selectivity where, in the
presence of two protection devices against overcurrent in series,
the load side protection device carries out the protection up to a
given level of overcurrent, without making the other device trip.
B opens only according to fault current
lower than a certain current value;
values equal or greater than Iswill give the trip of both A and B.
Is is the ultimate
selectivity
value!
Is = ImA
Standards definition Partial selectivity
Only B trips for every current value
lower or equal to the maximum
short-circuit current.
Total selectivity is an overcurrent selectivity where, in the
presence of two protection devices against overcurrent in series,
the load side protection device carries out the protection without
making the other device trip.
B A
Is = Ik
Standards definitionTotal selectivity
Upstream circuit breaker A
T4N 250 PR221DS In = 250 (Icu = 36kA)
Downstream circuit breaker B
S 294 C100 (Icu = 15kA)
Standards definitionPartial and total selectivity
Overload zone
Thermal protection
L protection
Short-circuit zone
Magnetic protection
S, D, I and EF protections
Time-current selectivity
Current, time, energy, zone,
directional, zone directional selectivity
Selectivity analysisTime-current curves
Real currents circulating through the circuit breakers
I>A
B I> I> I>
A
B
I>
I>
I>
I> I>
A
B
I>
I>
IA = IB
IA IB
tA
tB
tA
tB
IAIBIA=IB
tA
tB
IA = IB + Iloads IA = (IB + Iloads) / 2
Selectivity analysisReal currents
ABB Group, BU Breakers and Switches March 10, 2015 | Slide 106
Definitions and Standards
Selectivity techniques Selectivity techniques
Back-up protection
AgendaLow voltage selectivity with ABB circuit breakers
ABB Group, BU Breakers and Switches March 10, 2015 | Slide 107
Current selectivity
Time selectivity
Energy selectivity
Zone (logical) selectivity
IntroductionSelectivity techniques
The ultimate selectivity value
is equal to the instantaneous trip threshold
of the upstream protection device
Other methods are needed to have a total
selectivity
AB
ImB ImA
Current selectivity: closer to the power supply
the fault point is, higher the fault current is
In order to guarantee selectivity,
the protections must be set to different
values of current thresholds
Ultimate
selectivity
value
1kA
3kA
tB
tA
tA
Current selectivityBase concept
A
B
Here the selectivity is a total selectivity,
because it is guaranteed up to the maximum
value of the short-circuit current, 1kA.
Circuit breaker A will be set to a value which does not
trip for faults which occur on the load side of B.
(I3Amin >1kA)
Circuit breaker B will be set to trip for faults which
occur on its load side (I3Bmax < 1kA)
0.1kA 1kA 10kA
10-2s
10-1s
1s
10s
102s
103s
104s
3kA
Is Is = I3Amin
Current selectivityExample
Plus
Easy to be realized
Economic
Instantaneous
Minus
Selectivity is often only partial
Current thresholds rise very quickly
CURRENT SELECTIVITY
Current selectivity Plus and minus
Time selectivity is based on a trip delay of the upstream
circuit breaker, so to let to the downstream protection the
time suitable to trip
B A
Setting strategy:
progressively increase the
trip delays getting closer to
the power supply source
On the supply side
the S function is required
Time selectivityBase concept
0.1kA 10kA 100kA
10-2s
10-1s
1s
10s
102s
103s
104s
1kA
The ultimate selectivity value is:
Is = IcwA (if function I = OFF)
Is = I3minA (if function I = ON)
Ik
A will be set with the current threshold I2adjusted so as not to create trip overlapping
and with a trip time t2 adjusted so that
B always clears the fault before A
B will be set with an instantaneous trip
against short-circuit
BI2
t2
Is
Time selectivityExample
0.1kA 10kA 100kA
10-2s
10-1s
1s
10s
102s
103s
104s
1kA
The network must withstand high values of
let-through energy!
If there are many hierarchical levels, the
progressive delays could be significant!
Ik
Which is the problem of time selectivity?
In the case of fault occurring at the busbars,
circuit breaker A takes a delayed trip time t2
B
t2
Time selectivity Example
Plus
Economic solution
Easy to be realized
Minus
TIME SELECTIVITY
Time selectivityPlus and minus
Quick rise of setting levels
High values of let-through energy
Energy selectivity is based on the current-
limiting characteristics of some circuit breakers
A
B
0.1kA 1kA 10kA
10-2s
10-1s
1s
10s
102s
103s
104s
Current-limiting circuit breaker
has an extremely fast trip time,
short enough to prevent the
current from reaching its peak The ultimate current
selectivity values
is given by the
manufacturer
(Coordination tables)
Energy selectivityBase concept
1kA 10kA0.1kA10-2s
10-1s
1s
10s
102s
103s
104s
Circuit breaker A conditions:
I3=OFF
S as for time selectivity
A
B
Is = 20kA
Energy selectivityExample
PLUS
MINUS
ENERGY SELECTIVITY
Energy selectivityPlus and minus
High selectivity values
Reduced tripping times
Low stress and network disturbance
Increasing of circuit breakers size
Zone selectivity is an evolution of the time
selectivity, obtained by means of a electrical
interlock between devices
The circuit breaker which detects a fault
communicates this to the one on the supply side,
sending a locking signal
Fault
locking
signal
Only the downstream circuit breaker opens,
with no need to increase the intentional time
delay
Zone selectivityBase concept
A Does Not Open
B Does Not Open
C Opens
A
B
C
Zo
ne 1
Zo
ne 2
Zo
ne 3
Zone selectivityExample
Is up to 100kA for Tmax
Is up to Icw for Emax
It is possible to obtain zone selectivity between Tmax and Emax
Zo
ne 1
Zo
ne 2
Zo
ne 3
Zone selectivity needs:
a shielded twisted pair cable
an external source of 24V
dedicated trip units
PR223EF for Tmax T4, T5 and T6
PR332/P for Tmax T7 and T8
PR122/P and PR123/P for Emax
PR332/P and PR333/P for X1
Zone selectivitySpecifications
PLUS
MINUS
ZONE SELECTIVITY
Zone selectivityPlus and minus
Trip times reduced
Low thermal and dynamic stress
High number of hierarchical levels
Can be made between same size circuit breakers
Cost and complexity of the installation
Additional wiring and components
ABB Group, BU Breakers and SwitchesMarch 10, 2015 | Slide 122
Definitions and Standards
Selectivity techniques
Back-up protection Back-up protection
AgendaLow voltage selectivity with ABB circuit breakers
Back-up protection (or cascading)
is a type of coordination of two protective
devices in series which is done in electrical
installations where continuous operation is
not an essential requirement.
Back-up protectionWhat is back-up protection?
Back-up protection
excludes the use
of selectivity!!!
The definition of back-up is given by the
Back-up is a coordination of two overcurrent protective
devices in series, where the protective device on the supply
side, with or without the assistance of the other protective
device, trips first in order to prevents any excessive stress on
downstream devices.
IEC 60947-1 Standard: Low voltage equipment
Part 1: General rules for low voltage equipment
Back-up protectionStandards definition
IEC 60947-1
def. 2.5.24
Back-up is used by those who need
to contain the plant costs
The use of a current-limiting circuit
breaker on the supply side
permits the installation of lower performance
circuit breakers on the load side
Both the continuity of service and the selectivity are sacrificed
Back-up protectionBase concept
T4L 250
T1N 160 T1N 160 T1N 160
Ik = 100 kA
T4L 250 T4L 250 T4L 250 Icu = 120kA
Icu = 36kA
Icu (T4L+T1N) = 100kA
Back-up protection Application example
Back-up protection tables
T4L 250
T1N 160 T1N 160 T1N 160
Ik = 100kA
Icu (T4L+T1N) = 100kA
Ik = 100kA
A
B C D
Back-up protection Application example
General power supply
is always lost
Plus
Economic solution
Quick tripping times
Minus
No selectivity
Low power quality
BACK-UP PROTECTION
Back-up protectionPlus and minus
Incoming = T5H 630A (70kA
rating) Outgoing = T3N 160A
(36kA rating)
Results: The co-ordination
resulted in a conditional short-
circuit of 65kA for the T3 mccb!
The discrimination is up to 20kA.
Example of Selectivity
Iz
T5H 630A 70kA
T3N 160A 36kA
65kA
~
Example of Selectivity
Discrimination
Example of Selectivity
Back-Up
T5H 70kA
T3N 36kA
Example of Selectivity Meaning of Selectivity Value
T3N 36kA
T5H 70kA
Y is 20kA
Fault level at Y is 20kA
T3N 36kA
T5H 70kA
T5H
T3N 20kA
Example of Selectivity Meaning of Selectivity Value
5kA
T5H T3N
5kA fault ON Trip
T3N 36kA
T5H 70kA
Example of Selectivity Meaning of Selectivity Value
T5H T3N
5kA fault ON Trip
10kA fault ON Trip
10kA
T3N 36kA
T5H 70kA
Example of Selectivity Meaning of Selectivity Value
T3N 36kA
20kA
T5H 70kA T5H T3N
5kA fault ON Trip
10kA fault ON Trip
20kA fault Trip Trip
Example of Selectivity Meaning of Selectivity Value
T3N 36kA36kA
T5H 70kA T5H T3N
5kA fault ON Trip
10kA fault ON Trip
20kA fault Trip Trip
36kA fault Trip Trip
Example of Selectivity Meaning of Selectivity Value
T3N65kA
T5H 70kA T5H T3N
5kA fault ON Trip
10kA fault ON Trip
20kA fault Trip Trip
36kA fault Trip Trip
65kA fault Trip Trip
36kA
Example of Selectivity Meaning of Selectivity Value
Motor co-ordination ABB offers co-ordination tables
MV/LV Transformer SubstationsSelection of Protective & Control Devices
Co-ordination between CBs and switch-disconnectors
T2S160
T1D160
400V
MV/LV Transformer SubstationsSelection of Protective & Control Devices
ABB Group March 10, 2015 | Slide 142
Power Factor Correction
ABB Group
March 10, 2015 | Slide 143
Power Factor CorrectionGeneralities on Power Factor Correction
In alternating current circuits, current is absorbed by a load which can be represented by two components:
The Active component
In phase with the supply voltage
Directly related to the output
The Reactive component
Quadrature to the voltage
Used to generate the flow necessary for the conversion of powers through the electric or magnetic field
In most installations the presence of inductive type loads, the current lags the active component (IR).
Generalities
ABB Group
March 10, 2015 | Slide 144
In order to generate and transmit active power (P) a certain reactive power (Q) is essential for the conversion of the electrical energy but is not available to the load.
The power generated and transmitted make up the apparent power (S).
Power factor (cos ) is defined as the ratio between the active component (IR) and the total value of current (I).
is the phase angle between the voltage and the current.
Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 145
Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 146
Typical Power Factors of some electrical equipmentPower Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 147
Advantages of Power Factor Correction Power Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 148
Advantages of Power Factor Correction
Better utilization of electrical machines
Generators & transformers are sized according to the
apparent power (S). With the same active power (P),
the smaller the reactive power (Q) delivered, the
apparent power will be smaller.
Better utilization of cables
The reduction in current allows the use of smaller
cables in the installation.
Power Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 149
Reduction in losses
By improving the power factor, power losses is reduced
in all parts of the installation.
Reduction in voltage drop
The higher the power factor the Voltage drop will be
lower at the same level of Active power.
Power Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 150
Economical savings
Power supply utilities apply penalties for energy used
with poor factor. An improved power factor will reduce
such penalties from the utilities.
Power Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 151
Advantages of Power Factor Correction
Improve capacity of transformers and cables
By improving the power factor, you reduce the kVA load on the transformer and the current carried by the cables
Thus additional transformer capacity is available if upgrade or expansion is required in the future
Or new cables might not be needed if new loads are connected to an existing switchboard
Apparent Power (VA)
e.g 2MVA Transformer
At 100% capacity
Real Power (W)
eg. 500kW Load
Reactive Power (VAR)
e.g Motors (inductive)
100kW at 0.7pf = 102kVAR
Reactive Power (VAR)
eg. 50kVAR Capacitors
Power Factor CorrectionGeneralities
ABB Group
March 10, 2015 | Slide 152
Distributed power factor correction
It is achieved by connecting a capacitor bank properly
sized according to the load and is connected directly to
the terminals of the load.
Power Factor CorrectionDifferent Methods
ABB Group
March 10, 2015 | Slide 153
Group power factor correction
It is achieved by connecting a capacitor bank properly
sized according to a group of loads and is connected to
the upstream of the loads to be corrected.
Power Factor CorrectionDifferent Methods
ABB Group
March 10, 2015 | Slide 154
Types of Power Factor correction
Centralized power factor correction
It is achieved by installing an automatic power factor
correction bank capacitor bank directly to the main
distribution boards.
Power Factor CorrectionDifferent Methods
ABB Group
March 10, 2015 | Slide 155
Types of Power Factor correction
Combined power factor correction
This solution is derived from a compromise between a
distributed & centralized power factor correction.
Distributed power factor correction is used mainly
for higher loads and a smaller centralized power
factor correction is used for the small loads.
Power Factor CorrectionDifferent Methods
ABB Group
March 10, 2015 | Slide 156
Switching and Protection
Electrical switching phenomena
The switching of a capacitor bank causes an electric
transient due to the phenomena of electric charging of
the bank.
The overcurrents at the moment of switching depends
greatly on both the inductance of the upstream network
as well as from the number of connected capacitor
banks.
Power Factor CorrectionCapacitor Switching
ABB Group
March 10, 2015 | Slide 157
Switching and Protection
Choice of protective device
Power Factor CorrectionCapacitor Switching
In
Resistance
In
Motor
In
Capacitor
AC-1 AC-3 AC-6b
Power Factor CorrectionCapacitor Switching
Single step capacitor
In
30 times In
Power Factor CorrectionCapacitor Switching
Multi steps capacitor bank
In
> 100 times In
Power Factor CorrectionCapacitor Switching
Ith = 1.3 x 1.15 x Inc = 1.5 Inc
Thermal current
Up to 30% for harmonics and voltage fluctuations on main
Up to 15% for tolerances on capacitor power
Contactor have to support Ith
Contactor sizing: Thermal current + peak current
Power Factor CorrectionContactor Sizing
ABB Group
March 10, 2015 | Slide 162
Example Power Factor CorrectionExample
kVARh is billed if it is higher than the contracted level.
Apparent power (kVA) is significantly higher than the Active power (kW)
The excess current causes losses (kWh) which is billed.
The design of the installation has to be over-dimensioned.
The installation requires 850kW at power factor of 0.75.
The transformer will have to be overloaded to 850k / 0.75 = 1.133MVA.
Current taken by the system is
Losses in the cables
P = I2R
The Transformer, Circuit breaker & Cable has to be increased.
PI =
3 * U * Cos = 1636A
I = 1636A
Cos = 0.75
kVA
kW kVar
Cos = 0.75
850kW Load
1MVA
400V
ABB Group
March 10, 2015 | Slide 163
Example Power Factor CorrectionExample
kVARh is reduced to lower than the contracted level or eliminated.
Apparent power (kVA) is significantly higher than the Active power (kW)
The charges based on the contracted kVA demand is close to the active
power.
The installation requires 850kW at a power factor of 0.9.
The transformer will not be overloaded to 850k / 0.90 = 945 kVA.
Current taken by the system is
Losses in the cables
P = I2R
There is not need to increase the Transformer, Circuit breaker & Cable.
PI =
3 * U * Cos = 1364A
I = 1364A
Cos = 0.90
kVA
kW kVar
Cos = 0.90
850kW Load
1MVA
400V
ABB Group
March 10, 2015 | Slide 164
Technical Application Paper Power Factor Correction