MV design guide - Schneider Electric
MV design guide - Schneider Electric
MV design guide - Schneider Electric
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Switchgear<br />
definition<br />
Medium voltage circuit breaker<br />
Rated cable-charging breaking current<br />
(cf. § 4 .108 IEC 60 056)<br />
The specification of a rated breaking current for a circuit breaker located<br />
at the head of no-load cables is not compulsory and is considered as not<br />
being necessary for voltages less than 24 kV.<br />
c Normal rated breaking current values for a circuit breaker located at the<br />
head of no-load cables:<br />
Rated voltage<br />
(Ur in kV)<br />
(Ic in kA)<br />
7.2 10<br />
12 25<br />
17.5 31.5<br />
24 31.5<br />
36 50<br />
Rated breaking current<br />
for no-load cables<br />
Rated line-charging breaking current<br />
(cf. § 4.107 IEC 60 056)<br />
The specification of a rated breaking current for a circuit breaker switch<br />
situated at the head of no-load lines is limited to overhead, three-phased<br />
lines and to a rated voltage ≥ 72 kV.<br />
L<br />
A<br />
B<br />
Rated single capacitor bank breaking current<br />
(cf. § 4.109 IEC 60 056)<br />
G<br />
U<br />
Ic<br />
C<br />
The specification of a breaking current for a circuit breaker switch located<br />
upstream of capacitors is not compulsory. Due to the presence of<br />
harmonics, the breaking current for capacitors is equal to 0.7 times the<br />
device's rated current.<br />
Rated current Breaking current for capacitors<br />
(A)<br />
(A)<br />
400 280<br />
630 440<br />
1250 875<br />
2500 1750<br />
3150 2200<br />
By definition<br />
pu =<br />
r<br />
Ur<br />
e<br />
c The normal value of over-voltage obtained is equal to 2.5 pu, this being:<br />
X1<br />
2.5 • Ur r<br />
e<br />
G<br />
U<br />
Rated back-to-back capacitor bank breaking current<br />
(cf. § 4.110 IEC 60 056)<br />
The specification of a breaking current for multi-stage capacitor banks is<br />
not compulsory.<br />
c If n is equal to the number of stages, then the over-voltage is equal to:<br />
C1 C2 C3<br />
2n<br />
2n + 1<br />
• pu with pu =<br />
r<br />
Ur<br />
e<br />
<strong>Schneider</strong> <strong>Electric</strong><br />
Merlin Gerin <strong>MV</strong> <strong>design</strong> <strong>guide</strong><br />
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