The Controllable Logic of the UHVAC Switch Type Controllable Metal Oxide Arrester and its Test Verification on UHV AC Test Base

Abstract

The switch type controllable metal oxide arrester (ST-CMOA, shortly) is mainly used to depress the switching overvoltage caused by closing and reclosing. By using it, the closing resistance of the circuit breaker can be canceled, which has shortcomings at economy and reliability. The ST-CMOA mainly consists of a metal oxide arrester (MOA, shortly) body and a controllable unit (CU, shortly). The MOA is divided into a fixed element MOA1 and a controlled element MOA2. The CU is composed of a switch K and a controller. MOA2 and CU are in parallel. During the system closing and single phase reclosing, the CU is closed in advance before closing the circuit breaker on line side in the station to limit the switching overvoltage caused by the closing and single phase reclosing. After switching over voltage, the CU switch is opened, the MOA1 and the MOA2 work together to ensure the reliability of the operation of the arrester. Under power frequency voltage, power frequency overvoltage and lightning overvoltage, CU is opened, MOA1 and MOA2 withstand them together. In order to make the ST-COMA to depress closing switching overvoltage, the controllable unit must cooperate with the circuit breaker control cabinet, substation controllable and protective system. On the one hand, if the CU cannot be closed successful, the circuit breaker on line side cannot issue the closing order. Otherwise, high amplitude switching overvoltage would be generated, which would be harm to system insulation. On the other hand, if the CU cannot be opened successful, the circuit breaker on line side must be opened immediately. Otherwise, the arrester will be at risk. So, the closing and opening reliability of the controlled unit, the correctness of the controllable logic of the CU and the reliability of the controller are very important to the functional realization and reliability operation of the ST-CMOA. Paper put forward the control logic of ST-CMOA. According to the overall design scheme and design requirements of the ST-COMA, the controller needs the following main functions. It can control opening and closing of the circuit break and K by planning controllable sequential, get acquisition and feedback of CB and K position signals, modify the set parameters by man-machine interface, has trigger recording function, record the information, switch action and state of the controlled unit, and so on. Then the controller was developed. Function and working principle of the controller were expounded. Gave the core controller structure design, human computer interaction unit design, controller drive unit design, protection calculation unit design, external interface design. Finally, the overall design of controller was achieved. In order to verify correctness of controllable logic of the controller and the reliability of the controller, tests were carried out in Wuhan UHV test base. On basis of design and reformation of controllable and protective circuit, correct of the controllable logic and reliability of operation were tested by a large number of experiments lasted for 3 months. According to the test results, the adjustment scheme of controllable time was given. In order to guarantee switching of the controllable switch, the delay time would be extended from 110ms to between 120 ms and 150ms, based on fully considering switching on time of the controllable switch and error of delay relay. The test results and adjustment plan have important reference value and reference meaning for improvement of the controllable system of test run of the CMOA.