Use of Surge Arresters in Transmission System
This example shows the use of surge arresters in a series and shunt compensated 735 kV AC transmission system
G. Sybille (Hydro-Quebec)
A 735 kV equivalent transmission systems feeds a load through a 200 km transmission line. The line is series compensated at the middle point and shunt compensated at its receiving end. A fault is applied at the load terminals. The fault is cleared by load breaker opening. For simplification purpose, only one phase of the transmission system is modeled. All parameters correspond to positive-sequence.
The three-phase short circuit level of the transmission system is 15000 MVA. The line is 40% series compensated by a capacitor (26.2 ohms at 60 Hz) and shunt compensated by a 330 Mvar (110 Mvar/phase) inductor at the load end.
The series capacitor and shunt inductor are both protected by metal oxide varistors (MOV). The series capacitor varistor MOV1 consists of 30 columns protecting the capacitor at 2.5 times its rated voltage (rated voltage is obtained for a 2000 kA line rated current). The corresponding protection voltage (defined at 15 kA = 500 A per column) is 2.5*26.2 *2kA*sqrt(2) = 185 kV.
The shunt inductor is protected by a 2-column arrester (MOV2) at 1.8 p.u. of nominal phase-to-ground voltage (424.4 kVrms). The corresponding protection voltage (defined at 1 kA or 500A /column) is 1.8*424.4*sqrt(2) = 1080 kV.
Start the simulation. Observe the MOV voltages and currents on Scope1 and Scope2.
At fault application, the capacitor voltage increases and MOV1 conducts. Peak current reaches 8.4 kA on the 2nd pulse 2 cycles after fault application, the MOV current is symmetric (4.5 kA current pulses at every half cycle).
At fault clearing, the overvoltage produced at bus B2 is limited by the shunt MOV2. The fast transient produces a 850 A current pulse in the MOV.