MV design guide - Schneider Electric
MV design guide - Schneider Electric
MV design guide - Schneider Electric
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Standards<br />
IEC - ANSI comparison<br />
According to ANSI<br />
c The circuit breaker must be able to break:<br />
v the rated short circuit current at the rated maximum voltage<br />
v K times the rated short-circuit current (maxi symmetrical interrupting<br />
capability with K: voltage range factor) at the operating voltage (maximum<br />
voltage/K)<br />
v between the two currents obtained by the equation:<br />
maxi symetrical current<br />
rated short-circuit current<br />
rated maxi voltage<br />
= = K<br />
rated voltage<br />
We therefore have a constant breaking power (in <strong>MV</strong>A) over a given<br />
voltage range. Moreover, the asymmetrical current will be a function of the<br />
following table taking S = 1.1 for Merlin Gerin circuit breakers.<br />
1.8<br />
1.7<br />
1.6<br />
1.5<br />
1.4<br />
1.3<br />
1.2<br />
1.1<br />
1<br />
ratio S<br />
Asymmetrical interrupting capability = S x symetrical interrupting capability.<br />
Both at specified operating voltage<br />
Symetrical interrupting capability at<br />
specified operating voltage = 1.0<br />
0 0.5 1 2 3 4<br />
cycles<br />
0 0.006 0.017 0.033 0.050 0.067 seconds<br />
Example:<br />
c Isc = 40 kA<br />
c % asymmetry = 50%<br />
c Iasym = 1.1 • 40 = 44 kA<br />
44 44<br />
c Isym = = = 36 kA<br />
1 + 2(50%) 2 1,22<br />
Sequence 6 will therefore be tested at<br />
36 kA + 50% asymmetry,<br />
this being 44 kA of total current.<br />
c Rated short-circuit breaking capacity (kA)<br />
Sequence n° current broken % aperiodic component<br />
1 10 50 - 100<br />
2 30 < 20<br />
3 60 50 - 100<br />
4 100 < 20<br />
5 KI to V/K < 20<br />
6 SI to V 50 - 100<br />
7 KSI to V/K 50 - 100<br />
8 electrical endurance<br />
9/10 reclosing cycle at ASI and AKSI<br />
11 C - 2 s - O at KI<br />
12 rated Isc duration = KI for 3 s<br />
13/14 single phase testing at KI and KSI (0.58 V)<br />
Short-circuit breaking testing must comply with the<br />
14 test sequences above, with:<br />
I : symmetrical breaking capacity at maximum voltage<br />
R : reclosing cycle coefficient<br />
(Reclosing factor)<br />
K : voltage range factor:<br />
K = Vmax<br />
Vmin<br />
Iasym<br />
S : asymmetrical factor: = 1.1<br />
Isym<br />
for Merlin Gerin circuit breakers<br />
V : maximum rated voltage<br />
76 Merlin Gerin <strong>MV</strong> Design Guide <strong>Schneider</strong> <strong>Electric</strong>