750kV Transmission Line Protect & Autorecloser Operation For Limiting Over-voltage

The over-voltage of power system is an important project, studied in 750KV &UHV, which not only affects the insulated intension designs of power equipments,such as transformer, switch, and transmission lines, but also is concerned withwhether the power system can operate safely and reliably. Transmission line parameters and system capability features at 750kV & abovevoltage level make the over-voltage be more serious than EHV line. Therefore, over-voltage is the key and decisive factor of insulation in 750KV & UHV power network.And the relay protections of UHV transmission line must consider how limit the over-voltage. In the paper, The Over-voltage and its related elements have been analyzed indetail. Finally, a scheme has been proposed to control and restrain the over-voltagefrom operations of the relay protection and autorecloser. At first, the over-voltage based main frequency and its restraint by using theshunt reactors has been discussed. Since the shunt reactor can compensate groundingcapacity and limit capacitive current, and decrease the capacity effect, the shuntreactor makes the important role to restrain the over-voltage. In the paper, distributing voltage along the line, for single and double sourcesconnected with long line, with the shunt reactor is analyzed. Secondly, the transient over-voltages have been studied. After building thetransmission line model based on lumped parameter with T orπmodel ,this paperbrings forward the over-voltage approximate formulae. Over-voltage has beendivided into three kinds, such as fault over-voltage, trip over-voltage and switch onover-voltage. Considering the effects of induced current in line and capacitive voltage,and carrying on Laplace transform, over-voltage formulae of UHV transmission linewith faults or breaker operations have been given. Finally, after carrying on a great deal of simulations, the validity of analysis hasbeen testified. Basing on the results, a over-voltage restrain and control scheme of750kV transmission line has been put forward.