MV design guide - Schneider Electric

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definition
Medium voltage circuit breaker
c Value of rated TRV
v the TRV is a function of the asymmetry, it is given for an asymmetry of 0%.
Uc
U (kV)
Rated TRV Time Delay Increase
voltage value rate
(Ur in kV) (Uc in kV) (t3 in µs) (td in µs) (Uc/td in kV/µs)
7.2 12.3 52 8 0.24
12 20.6 60 9 0.34
17.5 30 72 11 0.42
24 41 88 13 0.47
36 62 108 16 0.57
td
0
t3
t (µs)
r
Uc = 1.4 • 1.5 • • Ur = 1.715 Ur
e
td = 0.15 t3
v a specified TRV is represented by a reference plot with two parameters
and by a segment of straight line defining a time delay.
Td : time delay
t3 : time defined to reach Uc
Uc : peak TRV voltage in kV
TRV increase rate:
Uc/t3 in kV/µs
X1
A
B
X2
Rated out-of-phase breaking current
(cf. § 4.106 IEC 60 056)
When a circuit breaker is open and the conductors are not synchronous,
the voltage across the terminals can increase up the sum of voltages in
the conductors (phase opposition).
G
U1
U2
G
c In practice, standards require the circuit breaker to break a current
equal to 25% of the fault current across the terminals, at a voltage
equal to twice the voltage relative to earth.
UA - UB = U1 - (-U2) = U1 + U2
si U1 = U2 so UA - UB = 2U
c If Ur is the rated circuit breaker voltage, the recovery voltage (TRV) at
power frequency is equal to:
v 2e Ur for networks with a neutral earthing arrangement
v 2.5e Ur for other networks.
c Peak values for TRV for networks other than those with neutral earthing:
e
Uc = 1.25 • 2.5 • • Ur
r
Rated TRV Time Rate of
voltage value increase
(Ur in kV) (Uc in kV) (t3 in µs) (Uc/td in kV/µs)
7.2 18.4 104 0.18
12 30.6 120 0.26
17.5 45 144 0.31
24 61 176 0.35
36 92 216 0.43
50 Merlin Gerin MV design guide Schneider Electric