302 / 2022-03-15 10:18:54

Propagation Characteristics of Electromagnetic Transients of Power Cables in Pumped Storage Power Station

Pumped Storage Power Station, cable, electromagnetic transient

Purpose/Aim

In pumped-storage power stations, cables are often used to connect the above-ground GIS switch station and underground powerhouses, and the cable length is generally hundreds of meters to thousands of meters. It is controversial whether the electromagnetic transient (slow-front overvoltage, fast-front overvoltage or very-fast-front overvoltage) generated by the operation of the circuit breaker or disconnector will cause damage to the insulation of the transformer and other equipment when it propagates along the cable to the main transformer side. This paper studies the propagation characteristics of electromagnetic transients in long cables by carrying out the actual measurement of the overvoltage of the pumped storage power station, and according to this, the electromagnetic transient model of the cable is revised and improved, in order to accurately evaluate the overvoltage level of the pumped storage power station, and put forward a more reasonable insulation coordination.

Experimental/Modeling methods

The built-in electrode-type voltage sensor is installed at both ends of the cable, inside of  bus duct of the above-ground GIS switch station and the underground powerhouse. It is equipped with an optical fiber-triggered synchronous measurement system to measure the entire electromagnetic transient process caused by the operation of the circuit breaker. By comparing the waveforms at both ends of the cable, the propagation characteristics of the overvoltage waveform in the cable are analyzed. Combined with the actual size and connection mode of the cable, the electromagnetic transient model is established in EMTP, then the measured results are compared and improved.

Results/discussion

Through the actual measurement results, it is found that after the propagation of the cable after hundreds of meters, the wave front time of the electromagnetic transient is slowed down by 10%~20%, and the amplitude is reduced by 3%~5%. The simulation establishes a cable electromagnetic transient model considering loss, which is more accurate than the traditional simulation lossless model based on travel time and surge impedance.

Conclusions

In a pumped-storage power station, the electromagnetic transient caused by the operation of the disconnector or circuit breaker of the above-ground GIS switch station can be transmitted to the transformer of the underground powerhouse through the cable. The test shows that the cable of several hundred meters will cause the wave front time to increase, and amplitude will decrease. Compared with the traditional simulation lossless model based on travel time and surge impedance, the cable electromagnetic transient model proposed in this paper is more accurate, which lays the foundation for accurately evaluating the overvoltage level of the pumped storage power station and proposing a more reasonable insulation coordination.