Currently, in my country's 220 kV and above high-voltage power grids, before transmission lines are officially put into operation, joint commissioning tests must be conducted on the relay protection and transmission line equipment on both sides of the line. The conventional testing method involves first completing the commissioning of the respective protection equipment on both sides of the line, then the communication department completing the joint commissioning of the transmission lines on both sides, and finally combining the protection devices and transmission lines for protection-communication joint commissioning. However, this testing method can usually only test the transmission time of the protection device after it operates through the fast and slow transmission lines. Because it is impossible to use telephone communication between the two sides of the line to simultaneously apply fault parameters, it is impossible to simulate a real short-circuit fault test. Only by relying on GPS satellite synchronization clocks to control the testing instruments can fault parameters be applied simultaneously on both sides of the line. The world's first synchronous transient test using GPS was conducted in September 1992 on the Taft-Garrison 500 kV transmission line of the Bonneville Power Plant in the United States. In May 1998, the East China Electric Power Administration conducted synchronous transient tests using GPS on two 500 kV transmission lines from the Tianhuangping pumped storage power station to the Pingyao substation. This test was conducted only on the LFCB102 phase current differential protection from GEC (UK). Coordination was handled by the East China Power Dispatch Bureau, with the East China Electric Power Research Institute and Zhejiang Electric Power Research Institute responsible for specific operations on both sides respectively. The test results largely met expectations. [b]1. Introduction to Test Methods[/b] The synchronous transient test using GPS placed certain requirements on the instruments used. Both sides of the test line were equipped with GPS satellite synchronization clocks, and a Doble F2000 series test device with a GPS interface and the Doble Trans II control program were selected. The specific test methods were as follows: a. Fault files recorded by fault recorders on both sides were converted to COMTRADE format and input into their respective Doble Trans II control programs. The programs then controlled the test instruments on both sides to simultaneously play back the faults. b. The electromagnetic transient calculation program calculated the fault quantities under various fault conditions on the line and input them into the Doble Trans II control program in COMTRADE format. The program then controlled the test instruments to simultaneously apply the fault quantities to both sides of the line. c. Without using the Doble Trans II control program, directly input the fault quantity on both sides and set the same fault time. The fault quantity is simultaneously added on both sides of the line by the GPS synchronization clock. Any of the above three methods can be used to conduct a synchronous transient test using GPS. The test system is shown in Figure 1. [img=313,318]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dlxtzdh/dlxtzdh99/dlxtzdh9905/image5/47.gif[/img] Figure 1 Test system 2 Test Introduction The satellite synchronization interface on the Doble F2000 series test instrument receives two signals from the GPS receiver: one is the IRIG-B signal, and the other is a very precise 1 Hz reference frequency. After processing, the IRIG-B signal generates a "test time" command to start each test. The 1 Hz signal, after passing through the phase synchronization circuit, becomes the synchronization signal and replaces the square wave signal of the test instrument. The dual-channel transient waveform generator provides 16-bit 256 KB transient data per channel. Under the control of Doble Trans II, it features digital-to-analog conversion, filtering, control of slave transient sources, generation of logic signals, and control of satellite interface operations. To enable simultaneous transient simulation tests on both sides of the line, the synchronization signals for both tests must be provided at the same time. The satellite synchronization interface on the Doble test instrument primarily performs the following functions: generating a phase synchronization signal using a 1 Hz signal; and providing global coordinate time using a modulated IRIG-B signal. The start time of the test is input on both sides of the line via the Doble Trans II control program. The satellite synchronization interface of the test instrument compares this time with the global coordinate time. When these two times are the same, an interrupt signal is generated simultaneously on both sides of the line, and all test instruments begin synchronously simulating the fault. A schematic diagram of the GPS synchronization test is shown in Figure 2. [img=315,155]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/dlxtzdh/dlxtzdh99/dlxtzdh9905/image5/48.gif[/img] Fig.2 Schematic diagram of the experiment. Since this was the first time GPS was used for a synchronous transient test in the East China Power Grid, the test was not conducted entirely according to the three methods provided by Doble. The method used in this experiment was as follows: First, the East China Power Dispatch Bureau calculated the three-phase voltage and current on both sides of the fault at 5%, 50%, and 95% of the distance from Pingyao within the area, and 5% of the distance from Pingyao outside the area, under various fault types, based on the normal operation mode of the power grid. These values ​​were then input to the Tianhuangping and Pingyao sides respectively. Additionally, the voltage and current values ​​for the two cycles prior to the fault were input, and the fault start time and fault duration cycles were set. Finally, the computer directly operated the test instrument using GPS (without using the Doble Trans II control program), and the test results were all normal. [b]3 Conclusion[/b] The biggest advantage of using GPS for synchronous transient testing is that it can simulate more realistic faults and make more precise adjustments to the protection on both sides of the line, so that technicians can find problems early and deal with them in a timely manner. However, this testing method is still in its infancy in my country and lacks certain experience, and it is not perfect. Especially for fault playback, since the fault recorders currently store file records in the formats of each manufacturer, while the Doble Trans II control program or other test instruments accept COMTRADE format, it is necessary to convert the files of various recorders. Sometimes, due to various reasons, conversion errors occur during the conversion process, making fault playback impossible. In the future, this aspect should be further strengthened to obtain more and better original fault files, accumulate more valuable fault models for future tests, and thus better serve the construction of the power grid. [b]References[/b] ［1］Carr K R. Application of satellite synchronous transient testing in Boniveli grid. USA: Boniveli Power Administration, 1992