电流差动保护在逆变型新能源场站送出线路中的适应性分析

新能源电源通过电力电子装置并网,其故障特性受控制策略影响而发生根本性变化,传统继电保护原理存在适应性问题。送出线路作为新能源场站电力外送的关键通道,其主保护电流差动保护能否正确动作对于新能源高效利用和系统安全运行十分重要。针对逆变型新能源场站,推导了逆变型新能源电源短路电流表达式,分析了各相短路电流之间的相位关系及其影响因素。在此基础上,分析了送出线路发生不对称短路时电流差动保护在并网系统为强、弱两种情形下的动作性能。研究结果表明,送出线路发生两相短路时,差动保护在并网系统为弱系统时存在拒动的风险、为强系统时灵敏性下降但不会拒动;送出线路发生接地故障时,零序电流的存在使得差动保护在并网系统为强、弱系统时均能可靠灵敏动作。实时数字仿真器(RTDS)试验验证了理论分析。研究结论为逆变型新能源场站送出线路主保护配置提供了参考。

Adaptability Analysis of Current Differential Protection of Outgoing Transmission Line Emanating from Inverter-interfaced Renewable Energy Power Plants

Renewable energy generators(REGs)are integrated into the grid via power electronic devices and their fault current characteristics are greatly influenced by the control strategies. This may cause malfunction of the traditional relays. The transmission line emanating from the renewable energy power plant(REPP)is usually the only power transmission channel, so the operation performance of its primary protections such as current differential protection plays an important role in the utilization efficiency of renewable energy and operation safety of the grid. Here an analysis of current differential protection is demonstrated for such transmission lines connected to inverter-interfaced REPPs. The fault current of the inverter-interfaced REGs is calculated and its angular characteristics are analyzed. Based on this, the operation performance of the current differential protection is discussed under asymmetrical faults facing both a strong grid and a weak grid. It is revealed that for internal phase-to-phase faults, line current differential protection may refuse to operate for the weak grid and will operate reliably with a low sensitivity for the strong grid. And for internal ground faults, current differential protection will operate reliably both for the strong and the weak grid owing to the appearance of zero-sequence current. Simulations based on the real-time digital simulator(RTDS)verify the conclusions. The findings of this study can provide advice about protection configuration of transmission lines connected to the inverter-interfaced REPPs. This work is supported by National Key Research and Development Program of China(No. 2016YFB0900503), State Grid Corporation of China(No. 5211JY16000U), and Fundamental Research Funds for the Central Universities(No. 2016ZZD01).