Mv Circuit Breaker Guide - Ansi Vs Iec Comparison

Medium voltage circuit breaker technical guide

Appendix 3:
IEC - ANSI comparison

IEC 56-1987 - ANSI C37-06 1987 COMPARISON

CONTENTS

page

1 - Rated voltage

3

2 - Rated isolating level

3

3 - Rated voltage during normal running

4

4 - Allowable short time current

4

5 - Allowable current peak value and making capacity

4

6 - Rated short-circuit time

57 - Rated voltage supplying closing, opening and
auxiliary circuit devices,

5

8 - Rated frequency

5

9 - Rated operating cycle short-circuit breaking capacity

6

10 - Associated transient recovery voltage

8

11 - Rated operating cycle

9

12 - Rated phase unbalance breaking capacity

10

13 - Rated off-load cable breaking capacity

11

14 - Rated off-load linebreaking capacity

11

15 - Rated unique capacitor bank breaking capacity

12

16 - Rated stage capacitor bank breaking capacity

13

17 - Rated capacitor bank making capacity

13

18 - Rated low inductive current breaking capacity

14

19 - Normal operating conditions

15

20 - Electrical endurance

16

21 - Mechanical endurance

16

22 - Construction

16

23- Derating

17

24 - Coordination of rated values

17/18

date

4

10/9

3•1
- B•

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ed

revis

12/95
page 1

Medium voltage circuit breaker technical guide

Appendix 3:
IEC - ANSI comparison
(cont’d)

The following comparison is based on different circuit breaker characteristics.
Summary of main differences
theme
asymmetric
breaking capacity
on terminalfaults
isolating level:
impact wave

allowable short time current
peak value
Transient Recovery
Voltage (1)
electrical endurance
mechanical endurance
motor overvoltages

ANSI
50% with
current
derating
impose chopped
waves for outdoor
equipment
115% Uw/3 s
129% Uw/2 s
2.7 Isc
approximately
2 times stricter
4 times K.S.Isc
1 500 to 10 000
depending on Ua and Isc
no textIEC
30% without
derating

2.5 Isc

3 fois Isc
2 000
type test
circuit

(1) The ANSI peak voltage is 10% higher than the voltage defined by the IEC.
The E2/t2 gradient is 50% steeper than the Uc/t3 gradient.
On the other hand, the steepest part of the curve is the initial part, where the
SF6 is reconstituted. The two standards easily allow SF6 to be reconstituted.

date

4

10/93•1
- B•

-

ed

revis

12/95
page 2

Medium voltage circuit breaker technical guide

Appendix 3:
IEC - ANSI comparison
(cont’d)

1 - RATED VOLTAGE Un (kV)
According to IEC
Standardized values for Un (kV) : 3.6 - 7.2 - 12 - 17.5 - 24 - 36 kV
According to ANSI
The ANSI standard defines a grade and a “voltage range factor K” which
defines a rated voltage range withconstant power.
K = Umax.
Umin.
Standardized values for Un (kV)
Indoor equipment

Outdoor equipment

grade
(kV)

Umax.
(kV)

Umin.
(kV)

K

grade
(kV)

K

4.16

4.76

3.85

1.24

15.5

1

7.2

8.25

6.6

1.25

25

1

13.8

15

11.5

1.3

38

1

38

38

23

1.65

2 - RATED ISOLATING LEVEL
According to IEC
rated
voltage
(kV)impact wave
withstand
(BIL)
(kV)

industrial
frequency
withstand
(kV rms)

7.2

60

20

12

75

28

17.5

95

38

24

125

50

36

170

70

Upeak (%)
100
90
50
1.2 µs

t (µs)

10
50 µs
standardized wave 1.2/50 µs

According to ANSI
Indoor equipment
grade

Outdoor equipment

4.16

60

19

7.2

95

36

13.8

95

36

38

15080

BIL : Basic Insulation Level
Outdoor equipment is tested with
chopped waves.
The impact wave withstand is equal to:
1.29 BIL for a time tc = 2 µs
1.15 BIL for a time tc = 3 µs

date

4
10/9
3•1
- B•

industrial
frequency
withstand
(kV rms)

grade

(kV)

impact wave
withstand
(BIL)
(kV)

-

ed

revis

12/95

(kV)

impact wave
withstand
(BIL)
(kV)...