Location: A 220kV Newly-built Substation (with two main transformers) in Jiangsu Province

Test Equipment: 1 set of HTB-8000 New-type Primary Current Injection and Voltage Application Test Device for Large Transformers, 1 three-phase voltage regulator, YD-300E Intelligent Current and Voltage Source Wireless Remote Control Host, a full set of test wires.

Test Purpose: Conduct simulated load tests before the commissioning of substation relay protection equipment to verify the polarity and transformation ratio of mutual inductors, as well as the correctness of wiring in protection, measurement and metering AC circuits.

Pre-test Preparation

1. Conduct a detailed on-site survey, verify the status of the primary system, and select appropriate current boosting test points.
2. Carefully check the status of each outgoing line bay to determine whether the test conditions are met.
3. Formulate a simulated load test scheme.
4. Estimate the primary current for the simulated load test.
5. Prepare recording forms for the simulated load test.
6. Adjust the tap positions of No.2 and No.3 main transformers to the required positions before the test.
7. Set up enclosures at current injection points and equipment locations.

Upon the completion of the installation, commissioning and acceptance of the electrical secondary system of the 220kV newly-built substation, all pre-test preparations were confirmed on-site by the dispatching department. The chief commander of the test site announced via walkie-talkie: Start the test for Bay 49U5. According to the test scheme, the test equipment boosted the current to 100A from the selected current injection point, and conducted current injection through all relevant bays from the medium-voltage side to the high-voltage side of the transformer.

The relevant safety and anti-misoperation measures, as well as technical and test procedures, were double-confirmed by the construction unit and the maintenance person in charge. Under the overall coordination and guidance of the chief commander and the dispatching department, the construction unit and the maintenance person in charge collaborated closely, and the equipment met the requirements of the scheme. The transformer output a current of 100A and a voltage of 1000V. All tests on the bays from the medium-voltage side to the high-voltage side (including standby bays) were completed within 1 hour, and all tests from the medium-voltage side to the low-voltage side were finished within 1 hour. The test from the high-voltage side to the medium-voltage side was completed within 1 hour after replacing the current injection point. After replacing the main transformer, the time consumed for completing the above tests was basically the same. All test data were fully and accurately recorded in the test report as required.

The on-site dispatching department was responsible for coordination and guidance throughout the process, and the construction department participated in the confirmation work. After several hours of intense work by all staff, a loud announcement came over the walkie-talkie: The test is a complete success, thank you all for your full cooperation. "The commissioning efficiency of this test using the new scheme has been doubled at least compared with the previous one, which has greatly reduced the number of switching operations," said the chief commander, unable to hide his joy. The maintenance person in charge added: "The standby bays have also been verified this time, which is of great significance for future expansion and renovation projects, and this test has improved the acceptance efficiency." Finally, the person in charge of the construction department concluded: This test is of great significance for improving the safe operation level of the power grid and the efficiency of commissioning and put-into-operation.

This test scheme was formulated in accordance with the Implementation Guidelines for Simulated Load Tests Before Commissioning of Relay Protection in Jiangsu Power Grid and the Simulated Load Test Scheme Before Commissioning of Relay Protection in Jiangsu Power Grid. Before the commissioning of new equipment, voltage and current injection tests were carried out using a synchronous current and voltage injection tester to verify the correctness of wiring in the AC circuits of mutual inductors and relay protection.

The scheme adopted the series-parallel capacitor compensation method and the homologous voltage and current application test method. The device generates three-phase power frequency voltage with determined amplitude and phase sequence, and applies the voltage to the device under test after boosting, producing current with determined phase relationship. The test voltage and current are converted into secondary voltage and current by mutual inductors, which are then input into the relay protection device to complete the protection vector check. This scheme can be used for vector check of main transformer bushing CTs; when verifying main transformer differential protection, the injected current can pass through the main transformer, while reducing the requirement for the system power supply. At present, it has been promoted in many provinces and cities across the country and achieved remarkable results.