Circuit Breaker Specifications, Design and Application Review

Electronic Electrical Devices
The purpose of a circuit breaker is to break the circuit and stop the current flow when the current exceeds a predetermined value without causing damage to the circuit or the circuit breaker. Circuit breakers are commonly used in place of fuses and sometimes eliminate the need for a switch. A circuit breaker differs from a fuse in that it "trips" to break the circuit and may be reset, while a fuse melts and must be replaced. Air circuit breakers (ACBs) are breakers where the interruption of the breaker contacts takes place in an air environment. Oil circuit breakers (OCBs) use oil to quench the arc when the breaker contacts open.

IEEE C37 and IEC 62271 electrical standards govern the ratings, performance, features, and testing of circuit breakers and switchgear. The primary goal is to ensure that the circuit breakers serve the intended purpose of safely protecting the electrical distribution system. The secondary goal is to ensure that circuit breakers are electrically and mechanically interchangeable so that the electrical grid can be interconnected.

Ciruit Breake Insulated Power Frequency and Impulse Withstand Voltages

Rated
Ur
PFWV
Ud (kV)
LIWV (pk)
Up (kV)
Rated
V (kV)
PFWV
(kV)
LIWV (pk)
(kV)
Com
Iso
Com
Iso
Com
Iso
Com
Iso
3.6
10
12
20
40
23
46
-
-
-
-
-
7.2
20
23
40
60
46
70
4.76
19
21
60
66
12
28
32
60
75
70
85
8.75
36
40
95
105
17.5
38
45
75
95
85
110
15
36
40
95
105
24
50
60
95
125
110
145
27
60
66
125
138
36
70
80
145
170
165
195
38
60
88
150
165

Note: IEC also lists the IEEE ratings.
PFWF = Power Frequency Withstand Voltage
LIWV = Lighting Impulse Withstand Voltage
Com = Common
Iso = Isolating Distance

Circuit Breaker Ratings IEC 52271-100 and IEEE C37

Rating IEC 52271-100 IEEE C37
Voltage Ur (kV) 3.6, 4.76, 7.2, 8.25, 12, 15,
17.5, 24, 27, 36, 38
4.76, 8.25, 15, 27, 38
Frequency fr (Hz) 16 2/3, 25, 50, 60 50, 60
Nominal current Ir (A) 630, 800, 1000, 1250, 1600,
2000, 2500, 3150, 4000
1200, 2000, 3000 
Short-circuit current Isc (kA) 10, 12.5, 16, 20, 25, 31.5,
40, 50, 63, 80
Same R10 Series as IEC
Short-time current Ik (kA) Ik = Isc Ik = Isc
Peak withstand current Ip (A) 2.5 x Isc (50 Hz)
2.6 x Isc (60 Hz)
2.5 x Isc (50 Hz)
2.6 x Isc (60 Hz)
Duration of short-circuit tk 1s (option 0.5s and 2s) 2s
Operated sequence
O = Open
C = Close
O°?3m°?CO°?3m°?CO optional:
O°?0.3s°?CO°?3m°?CO
O°?0.3s°?CO°?1m°?CO
O°?0.3s°?CO°?15s°?CO
CO°?15s°?CO
O°?15s°?CO°?3m°?CO
Option:
O°?0.3s°?CO°?3m°?CO
Mechanical operation M1 = 2000
Option M2 = 10,000
1500 to 10,000
Electrical operation Option for E2°?980% min. 800% lt

Circuit Breaker Temperature Limits per. IEC 62271 and IEEE C37

Description
Temperature Limits °C Above a 40°C Ambient
IEC 62271
IEEE C37
Air
SF6
Air
SF6
Bare-copper contacts
75
105
70
90
Silver-coated contacts
105
105
105
105
Bare-copper connections
90
115
70
100
Silver-plated connections
115
115
105
115
Tin-plated connections
105
105
105
105
Bare-copper to silver-plate
115
-
70
-
Normally touched parts
70
-
50
-
Not normally touched parts
80
-
70
-

Reference From Table J.1 of C37.100.1 (most restrictive listed)

Capacitor Switching per IEC 62271-100 and IEEE C37

Capacitors are often applied to the electrical grid to stabilize voltages following power distributions and to improve power quality. The preferred circuit breaker for capacitor switching is one that has a low probability of restrike. If the circuit breaker is unable to successfully interrupt, the transient voltage can escalate on successive re-strikes. Therefore, the standards have set series of test procedures and ratings to help establish the circuit breakers capacitor switching capabilities. The Table below outlines the optional tests that can be conducted on breakers intended for use on capacitor circuits.

Description IEC 62271-100 IEEE C37
Capacitor
switching classes
C1 = low probability of restrike
C2 = very low probability of restrike
CO = 1 restrike/operation OK
C1 same as IEC
C2 same as IEC
Cable charging
breaking current Ic
10, 25, 31.5A
optional
10, 25, 31.5A
mandatory
Single capacitor bank
breaking current
400A 250, 400, 630, 1000, 1600A
Back-to-back
capacitor bank
breaking current
400A 400, 630, 1000, 1600A
Inrush making
Current
20 kA 15, 20, and 25 kA
Frequency of
inrush current
4.25 kHz 1.3, 2, and 4.3 kHz

The requirements of IEEE, for the most part, equal or exceed IEC requirements. The reason for this is user participation at IEEE meetings. Standard voting is based on individual for IEEE and by country for IEC. The Table below provides a current summary of some of the key differences between the standards.

Description IEC C37
Maximum interrupting time Not required 50 and 83 ms
Short time duration 1 second 2 seconds
Operating duty (basic) O-3m-CO-3m-CO O-15s-CO-3m-CO
Electrical endurance Short circuit only 800% of It
Normally touched parts 70°C 50°C
Abnormally touched parts 80°C 70°C
Copper contacts 80°C 75°C
Bare-copper connections 90°C 70°C
Silver connections 115°C 105°C
Silver to bare copper 115°C 70°C
PFWV/rated voltage 1 2.3 3.0
LIWV/rated voltage 1 4.4 7.9
Continuous current ratings R10 series Three listed ratings
Voltages specifically listed World North America
Single-phase asymmetrical test Not required Required
Cable capacitance switching Not required Required
Number of capacitor switch ratings 1 5
Load switching Not required Required
Double earth fault Option Not addressed
RRRV on outdoor breakers Same as indoor 50% higher
Mechanical endurance 2000 1500 to 10,000

1 PFWV and LIWV is the average of all ratings from 3.3 to 38 kV.

Note: C37.20.2°?IEC 62271-1, 100, and 200 comparison.
C37.100.1 bare copper connections are 20°C higher than C37.20.2.

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