Zhang Jinxiang

Research on Short-Circuit Test of 500kV Hybrid HVDC Circuit Breaker

A test was performed on the short-circuit current of a hybrid HVDC circuit breaker for the first set of flexible DC loop network system with the highest voltage class of ±500kV in the world, and this paper makes an analysis of the breaking function of a DC circuit breaker configured in a distributed manner in a symmetrical bipolar wiring mode. By setting up a four-terminal loop flexible DC power grid which has the same operation mode with that at a site and making a test program fully equivalent to a single LC oscillator supply, this paper analyzes the parameter configuration and simulation difficulties in such mode and obtains the cost and floor area required for such mode. The paper makes a detailed analysis of the equivalent strategy for the capacity reduction test and unit module test of the single LC oscillator supply and points out respective advantages and disadvantages according to the simulation result. The energy consumption process of a ZnO lightning arrester was considered comprehensively, and the transient overvoltage insulation characteristics of the whole circuit breaker was tested. According to specific case tests, the DC breaking capacity of bipolar short circuit in transient and stable states was tested, and the key factors which needs to be considered during equipment research and manufacture processes were given.

Analysis and Study of Resonance Monitoring and Suppression Strategies of EHV Main Transformer

Analysis of waveforms recorded at the site is made with the interferences such as excitation current, etc. excluded, on the basis of analysis of Extra-high Voltage(EHV) main transformer resonance mechanism and via inputting all previous resonance data by using the accuracy and reliability of electromagnetic transient simulation verification and monitoring methods, corresponding figure topology analysis function is configured according to monitoring result and is used to analyze the cause and condition of resonance. Resonance monitoring methods are put forward in combination of Hilbert-Huang Transform (HHT) and peaking pulse time interval and are used to judge the occurrence and mode of resonance. According to the components and harmonic content of monitored main harmonics, the resonance class of main transformer is defined automatically, multi-stage resonance prewarning, slight resonance reliable signaling and warning of background, direct action on series compensation control and protection system after heavy resonance exceeding limits are achieved, and the safety of capacitor is protected with resonance removed at the same time, on the basis of parameter setting, based on commissioning and decommissioning methods for series compensation and the output magnitude of wind generation set at load side by using root-mean-square algorithm. At the same time, automatic series compensation recommissioning and permanent lockout function of many times of heavy resonances are added at fixed time sections, automatic commissioning and switching of series compensation are realized, the occurrence of secondary resonance is avoided, and the safe and steady operation of EHV main transformer resonance is guaranteed effectively.