Abstract
This paper studies the mechanism and influencing factors of resonance overvoltage of EHV transmission lines caused by lightning. By analyzing the time domain steady state of the simplified resonance circuit, the physical mechanism of resonance is revealed. The characteristics of resonance transient process and overvoltage waveform are analyzed by using electromagnetic transient simulation. The main influencing factors of overvoltage amplitude are also studied. The results show that: 1) During uneven open-phase conditions, resonant circuit involving shunt inductors and line equivalent capacitor obtains energy from lightning strikes, which may lead to resonance. 2) the transient process of resonance can be divided into three stages, including lightning stage, lightning-resonance conversion stage and steady-state resonance stage, among which the voltage of the first two stages are higher; 3) the lightning strike time, lightning current parameters and subsequent lightning strike affect on the overvoltage amplitude, which leads to the random amplitude in overvoltage.
Highlights
In recent years, China has recorded several faults caused by resonance overvoltage occurred during uneven open-phase conditions in 500kV transmission lines with shunt compensation reactor
Shunt reactors are usually applied to compensate for the effect of distributed line capacitance for long EHV transmission lines
The common method is to install neutral reactor to make the equivalent phase-to-ground impedance of shunt reactor inductance and line capacitance capacitive. This resonance mechanism only considers the energy provided by the system power supply, and does not account for input of energy from external sources
Summary
China has recorded several faults caused by resonance overvoltage occurred during uneven open-phase conditions in 500kV transmission lines with shunt compensation reactor These resonances were stimulated by lightning strikes on the conductor of tripped phase, and differ from typical resonant overvoltage mechanism[1]. The common method is to install neutral reactor to make the equivalent phase-to-ground impedance of shunt reactor inductance and line capacitance capacitive This resonance mechanism only considers the energy provided by the system power supply, and does not account for input of energy from external sources. Combining formula 3 and formula 5, the steady-state expression of reactor voltage is as follows It can be seen from the above formula that even if the comprehensive impedance Z is capacitive, the circuit can resonate due to excessive external injection energy. This paper only considers the case of lightning shielding failure
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