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ABB Group August 11, 2015 | Slide 1
Lionel Ng, LPBS - Low Voltage Products
Welcome To ABB Technical Sharing Session
Circuit BreakersStandards Guidelines IEC 60947-2
ABB Group August 11, 2015 | Slide 4
IEC 60947-2Circuit Breaker Standard, for industrial application
Definitions for MCCBs and ACBs
Choice criteria based on rated and limit values
Agenda
ABB Group August 11, 2015 | Slide 5
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 August 11, 2015 | Slide 6
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 August 11, 2015 | Slide 7
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 August 11, 2015 | Slide 8
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 & Formula).
IEC Standard definitions
IEC Standard definitions
ABB Group August 11, 2015 | Slide 9
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 August 11, 2015 | Slide 10
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 August 11, 2015 | Slide 11
A = Direction of arc due to the magnetic fieldR= Repulsion of moving contacts due to the short circuit current
A
I
A
R
R
ABB Group August 11, 2015 | Slide 12
Time
Current
Current limiting circuit breaker
Energy limitation
ABB Group August 11, 2015 | Slide 13
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 August 11, 2015 | Slide 14
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 August 11, 2015 | Slide 15
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 August 11, 2015 | Slide 16
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Rated values (Iu, Ue)
ABB Group August 11, 2015 | Slide 17
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 August 11, 2015 | Slide 18
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 August 11, 2015 | Slide 19
XT1 160
XT4 250
Rated uninterrupted current IuSome factors may reduce the Iu of a circuit breakerlike temperature, altitude or frequency.
Rated value Iu
ABB Group August 11, 2015 | Slide 20
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 August 11, 2015 | Slide 21
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 August 11, 2015 | Slide 22
Some factors may reduce the Ue of a circuit breaker
Rated value Ue
ABB Group August 11, 2015 | Slide 23
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Limit values (Icu, Ics, Icw, Icm)
ABB Group August 11, 2015 | Slide 24
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 August 11, 2015 | Slide 25
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 August 11, 2015 | Slide 26
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 Icu This 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 August 11, 2015 | Slide 29
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
X X X X X X
X X X
X
4000A
1600A
630A 630A 630A
Main incoming Board
Sub Dist Board
Icu breaker :Downstream devices
Ics breaker :Incoming / upstream
devices
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
ABreaker A:Icu =100 kAwith Ics = 100 % of Icu
Breaker B:Icu = 100 kAwith Ics = 75 % of Icu
70 kA
50 kA !!!Please also considerthat short circuit current at the end of the line isstill 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 is available for the full range for all the employed 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 Icsmust 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 August 11, 2015 | Slide 34
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 630kVAUcc%=4%
400V
ACB E1B12
MCCB XT4
22.7kA
MCCB XT3
The upstream circuit breaker can withstand the fault current up to 1 or 3 sec, thus guaranteeing an excellent selectivity with downstream apparatus
ABB Group August 11, 2015 | Slide 35
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 4
CATEGORY BCIRCUIT BREAKER
Limit value Icw
ABB Group August 11, 2015 | Slide 36
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 4
CATEGORY ACIRCUIT BREAKER
ABB Group August 11, 2015 | Slide 37
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 d 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 3
Icw = RATED SHORT-TIME WITHSTAND CURRENT
Selectivity Categories
ABB Group August 11, 2015 | Slide 39
IEC 60947-2 def. 4.3.5.1
Icm = 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 t Ipeak
ABB Group August 11, 2015 | Slide 40
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 August 11, 2015 | Slide 41
16,8kA
50kA
54kA
Peak
Irms
105kA
10kA 100kA
10kA
100kA
T6L800 In800
XT2L 160 In160
Example
Current limiting circuit breaker
ABB Group August 11, 2015 | Slide 42
If the cosM 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 cosM of the plant is lower than the standard prescribed value, usually near to the transformer and/or generator, it is necessary to verify Icm t Ipeak.
Limit value Icm
ABB Group August 11, 2015 | Slide 43
If the cosMk 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, cosMk=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 greatervalue 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 August 11, 2015 | Slide 44
Limit value Icm
ABB Group August 11, 2015 | Slide 45
Rated values (Iu, Ue)
Limit values (Icu, Ics, Icw, Icm)
Insulation values (Ui, Uimp)
Choice criteria
Insulation values (Ui, Uimp)
ABB Group August 11, 2015 | Slide 46
IEC 60947-1 def. 4.3.1.2
Ui = 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 August 11, 2015 | Slide 47
IEC 60947-1 def. 4.3.1.3
Uimp = RATED IMPULSE WITHSTAND VOLTAGE
The peak value of an impulse voltage of prescribed form and polarity (1,2/50Ps) 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 August 11, 2015 | Slide 48
IEC 60947- 2 Table 7
Overload protection
ABB Group August 11, 2015 | Slide 49 i
t
IEC 60947- 2 Table 6
Short circuit protection
ABB Group August 11, 2015 | Slide 50
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 August 11, 2015 | Slide 52
Routine Tests
ABB Group August 11, 2015 | Slide 53
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 August 11, 2015 | Slide 55
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. operationPart 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 valueof current, stated by the manufacturer, which the equipmentcan carry in uninterrupted duty, at a specified referenceambient 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 60898-1def. 5.2.4
Icn = 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 60898-1def. 3.5.5.2
Ics = 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
Trip lever
Hammer-impactelectromagnetic coil
Toggle
Switching mechanism
Label
Bi-directional-cylinder-lift-terminal
Thermally-delayedbimetal
Arc quenching chamber
Fixed contact
Moving contactEasy releasesnap-on catch
Bi-directional-cylinder-lift-terminal
Miniature Circuit Breakers
0.5 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
0.5 ms
1 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
1 ms
1.5 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
1.5 ms
2 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
2 ms
2.5 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
2.5 ms
3 ms after short-circuit current is released
Miniature Circuit BreakersTripping of an MCB
3 ms
IEC 60947-2 IEC 60898-1
People Instructed UninstructedMaintenance Possible Not possible
Rated Voltage (Ue)< 1000 Vac
< 1500 Vdc
< 440 Vac
< 220 VdcAmbient
Temperature 40 C 30 C
Rated CurrentNo limits
(Iu < 6300 A)In = 125 A
Short circuit breaking current No 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 t Un Icu or Ics t Ik Icm t Ip
Ue, Icu, Ics, Icm?
Selection of protective Devices
Protection of feeders against overloadIb In or I1 Iz
against short-circuitI2t 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 theoverload protection must have an intervention current lf that assures theoperation for a value lesser than 1,45 lz (lf < 1,45 lz), we must state that itis always verified for ABB Circuit breakers, since according to IEC 60947-2the 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 t 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
whereSn = 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:
whereUcc %= 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 100Ucc %
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.
AttentionThose 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
Circuit breaker B
I1 I2 I3
1 2 3
Isc2 + Isc3
Isc1 + Isc2 + Isc3
I4 I5
Circuit breaker A
Isc1
As far as the calculation of the rated current of the transformer isconcerned, the rules beforehand indicated are completely valid.
The minimum breaking capacity of each circuit breaker LV side must begreater than the highest of the following values: (the example refers tomachine 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 faultimmediately downstream circuit breaker 1;
lsc2 + lsc3 (short circuit currents of transformer 2 and 3) in case offault immediately upstream circuit breaker 1;
Protection of Transformers
Circuit breakers l4 and l5 on the load side must have a short circuitcapacity greater than lsc1 + lsc2 + lsc3; naturally every transformercontribution in the short circuit current calculation is to be lessened by theconnection line transformer - circuit breaker (to be defined case by case).
Protection of Transformers
ABB Group August 11, 2015 | Slide 100
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 devicesis 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 thepresence of two protection devices against overcurrent in series,the load side protection device carries out the protection up to agiven 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 thepresence of two protection devices against overcurrent in series,the load side protection device carries out the protection withoutmaking 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 protectionL 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
tAtB
IAIBIA=IB
tA
tB
IA = IB + Iloads IA = (IB + Iloads) / 2
Selectivity analysisReal currents
ABB Group, BU Breakers and Switches August 11, 2015 | Slide 114
Definitions and Standards Selectivity techniques Selectivity techniques Back-up protection
AgendaLow voltage selectivity with ABB circuit breakers
ABB Group, BU Breakers and Switches August 11, 2015 | Slide 115
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
tAtA
Current selectivityBase concept
AB
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 nottrip for faults which occur on the load side of B.(I3Amin >1kA)
Circuit breaker B will be set to trip for faults whichoccur 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
PlusEasy to be realized
EconomicInstantaneous
MinusSelectivity 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 100kA10-2s
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 overlappingand with a trip time t2 adjusted so thatB always clears the fault before A
B will be set with an instantaneous tripagainst short-circuit
BI2
t2
Is
Time selectivityExample
0.1kA 10kA 100kA10-2s
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
PlusEconomic solutionEasy to be realized
Minus
TIME SELECTIVITY
Time selectivityPlus and minus
Quick rise of setting levelsHigh 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 breakerhas an extremely fast trip time,short enough to prevent thecurrent from reaching its peak
The ultimate current selectivity valuesis 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 valuesReduced 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
Zone
1Zo
ne 2
Zone
3Zone selectivityExample
Is up to 100kA for Tmax
Is up to Icw for Emax It is possible to obtain zone selectivity between Tmax and Emax
Zone
1Zo
ne 2
Zone
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 reducedLow thermal and dynamic stress
High number of hierarchical levels Can be made between same size circuit breakers
Cost and complexity of the installationAdditional wiring and components
ABB Group, BU Breakers and SwitchesAugust 11, 2015 | Slide 130
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 160Ik = 100kA
Icu (T4L+T1N) = 100kA
Ik = 100kA
A
B C D
Back-up protection Application example
General power supply is always lost
PlusEconomic solution Quick tripping times
MinusNo 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 August 11, 2015 | Slide 150
Power Factor Correction
ABB GroupAugust 11, 2015 | Slide 151
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
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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 M) is defined as the ratio between the active component (IR) and the total value of current (I).
Mis the phase angle between the voltage and the current.
Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities
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Generalities on Power Factor CorrectionPower Factor CorrectionGeneralities
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Typical Power Factors of some electrical equipmentPower Factor CorrectionGeneralities
ABB GroupAugust 11, 2015 | Slide 155
Advantages of Power Factor Correction Power Factor CorrectionGeneralities
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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
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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
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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
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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 GroupAugust 11, 2015 | Slide 160
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
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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
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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
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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
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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
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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 currentUp 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
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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 M= 1636A
I = 1636A
Cos M
kVA
kW kVar
Cos M kW Load
1MVA
400V
ABB GroupAugust 11, 2015 | Slide 171
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 M= 1364A
I = 1364A
Cos M
kVA
kW kVar
Cos M kW Load
1MVA
400V
ABB GroupAugust 11, 2015 | Slide 172
Technical Application Paper Power Factor Correction