Abstract : This paper introduces the operating impedance characteristics of the Type 11 impedance relay and the test method for recording these characteristics. Keywords : Microprocessor protection; Impedance relay; Operating characteristics; Test 1 Introduction Microprocessor protection is widely used in 110-220kV and above transmission lines in the Yunnan power system, especially the Type 11 protection systems from Nanjing Automation Co., Ltd. and Xuji Electric Co., Ltd., which are very popular among operation and commissioning personnel. It is convenient to operate and maintain, and simple to debug. Fault reports are simple and clear, making it easy to analyze the nature and location of faults—something difficult to achieve with conventional distance protection. However, the manufacturer's technical manuals and commissioning procedures only briefly discuss the operating principle and debugging methods of the impedance relay, limiting the understanding of operation and commissioning personnel. Based on several years of commissioning and understanding, this paper analyzes this impedance relay. 2. Setting Principles for Impedance Elements According to the regulations, the impedance relay should be set as follows: 1) a1 Setting: Considering that when a short circuit occurs through the transition resistor, the additional measuring impedance caused by the transition resistor is smaller at the beginning of the fault than at the end, the a1 setting should be slightly smaller than the maximum sensitivity angle of the line. Generally, a1 = 60°. [b][align=center]For details, please click: Operating Characteristics and Tests of Type 11 Microcomputer Protection Impedance Relay[/align][/b]