161 kV電磁感應型比壓器鐵磁共振分析、量測及抑制方法

Abstract

This dissertation presents a successful mitigation experience of ferroresonance (FR) with a Damping Reactor(DR) involving electromagnetic type Potential Transformers(PTs) of a 161 kV Gas Insulated Switchgear(GIS) in Taiwan. PTs have a typically low thermal capacity and high accuracy due to their measuring functions. Low core losses are necessary to obtain high accuracy, but they also reduce its damping ability and therefore increase the possibility of FR. FR happened twice and destroyed PTs for just nine months in the study case. Complete FR waveforms of 161 kV PT were obtained via field tests never conducted before in Taiwan. The first field test had a reappearing FR which sustained up to 22.9 seconds in 11 random operations and the second to fourth field tests confirmed the validity of DR which shortened FR less than 4.36 seconds in 29 random operations which are carried out in thermal power plant, hydro power plant and nuclear power plant. A reliable prediction by EMTP/ATPDraw simulation and a useful mitigation method with a proper DR were proved by both field tests and the following 23 months satisfactory operations for 82 times which extracted from SCADA system in a thermal power plant since Nov., 2008. The five years study would prove valuable for further research in higher voltage level GIS. Although the first paper on FR was published in 1920, FR is still not a fully understood phenomenon. This dissertation focuses on single phase FR in GIS with PT, fed by the circuit breaker grading capacitance. In principle, FR is a forced oscillation in a nonlinear series resonance circuit including a capacitance and nonlinear inductance, which shows significantly distorted voltage and current waveforms. The complex nonlinear behavior of the saturable inductance can cause fundamental FR, subharmonic FR, quasi-periodic and even chaotic oscillations. FR can result in high overvoltage and high overcurrent, which can finally damage the high voltage equipment or PTs due to dielectric and thermal problems. Even if there is the risk of ferroresonance for specific GIS configurations, electromagnetic PTs are used rather than capacitive ones because of their reliability, higher accuracy and stable transformation ratio during the entire lifetime. However, combine the theory, GIS and PT maker’s experiences, this dissertation provides an overview of network configurations, parameters influencing the FR behavior and a number of methods to avoid or suppress FR are discussed. A very comprehensive analysis is performed by detailed modeling using time domain simulation with a digital computer transient analysis program such as the EMTP/ATPDraw and compares them with field tests and measurements. It would be valuable on planning and designing for electrical engineers.