Circuit Breaker Design, Application and Review

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 U_r	PFWV U_d (kV)		LIWV (pk) U_p (kV)		Rated V (kV)	PFWV (kV)		LIWV (pk) (kV)
Rated U_r	Com	Iso	Com	Iso	Rated V (kV)	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 I_t
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.