Fault resistance causes conventional distance protection to operate incorrectly, threatening the safe operation of power system. The immunity to fault resistance is improved by utilizing fault-point voltage, measured current, and setting impedance to construct the virtual measured voltage. Then, a new distance protection scheme, known as protection scheme I, is presented to identify in-zone and out-of-zone faults by comparing the amplitudes of the original and virtual measured voltages. Then, the original and virtual measured voltages are improved by a special voltage phasor in phase with the fault-point voltage phasor. Based on the improved original and virtual measured voltages, another distance protection scheme is presented, namely protection scheme II. The two proposed protection schemes are immune to fault resistance and load current and operate well under all types of faults. However, protection scheme II has higher sensitivity to fault detection compared with protection scheme I. Simulation results verify the correctness and effectiveness of the two proposed schemes.

中文翻译：

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一种基于改进虚拟测量电压的距离保护新方案

故障电阻导致常规距离保护误动作，威胁电力系统的安全运行。通过利用故障点电压、测量电流和设置阻抗来构建虚拟测量电压，提高了对故障电阻的抗扰度。然后，提出了一种新的距离保护方案，称为保护方案 I，通过比较原始和虚拟测量电压的幅度来识别区域内和区域外故障。然后，通过与故障点电压相量同相的特殊电压相量改进原始和虚拟测量电压。在改进的原始测量电压和虚拟测量电压的基础上，提出了另一种距离保护方案，即保护方案II。这两种提议的保护方案不受故障电阻和负载电流的影响，并且在所有类型的故障下都能很好地运行。但是，保护方案II比保护方案I具有更高的故障检测灵敏度。仿真结果验证了两种方案的正确性和有效性。