MV design guide - Schneider Electric

Standards
IEC - ANSI comparison
The following comparison
is based on
different circuit breaker
characteristics.
Overview of the main differences
Theme ANSI IEC
asymmetrical breaking 50% 30%
capacity on faults with current without derating
across the terminals derating
insulation level:
imposes chopped waves
impulse wave
for outdoor equipment
115% Uw/3 s
129% Uw/2 s
short-time withstand 2.7 Isc 2.5•Isc at 50 Hz
current peak
2.6•Isc at 60 Hz
value
2.7•Isc for special cases
Transient Recovery around twice
voltage (1)
as severe
electrical endurance 4 times K.S.Isc 3 times Isc
mechanical endurance 1 500 to 10 000 2 000
according to Ua and Isc
motor overvoltages no text standard test circuit
(1)
the ANSI peak voltage is 10% greater than the voltage defined by the IEC.
The E2/t2 slope is 50% greater than the Uc/t3 slope.
However, the largest part of the graph is the initial part where the SF6 reconstitutes itself.
The two standards easily allow the SF6 to reconstitute itself.
Rated voltages
According to IEC
c Standardised values for Ur (kV): 3.6 - 7.2 - 12 - 17.5 - 24 - 36 kV
According to ANSI
c The ANSI standard defines a class and a voltage range factor K
which defines a range of rated voltages at constant power.
Standardised values for Ur (kV)
class (kV) Umax (kV) Umin (kV) K
Indoor equipment 4.16 4.76 3.85 1.24
7.2 8.25 6.6 1.25
13.8 15 11.5 1.3
38 38 23 1.65
Outdoor equipment 15.5 1
25 1
38 1
100
90
50
10
Upeak (%)
1.2 µs
50 µs
Standardised wave 1.2/50 µs
t (µs)
Rated installation level
According to IEC
Rated Rated lightning Rated power frequency
voltage withstand voltage withstand voltage
(kV) (kV) 50 Hz 1 mm (kV)
7.2 60 20
12 75 28
17.5 95 38
24 125 50
36 170 70
72 Merlin Gerin MV Design Guide Schneider Electric