Test Site: A 500kV Substation in Sichuan Province

Test Equipment: 1 set of HTB-8000 Large Transformer Primary Current Injection Test Device, 1 three-phase voltage regulator, 1 set of isolation power supply, and a full set of test wires.

Test Purpose: Conduct simulated load tests before the commissioning of relay protection equipment after substation renovation, to verify the polarity and transformation ratio of mutual inductors as well as the correctness of protection circuit wiring.

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. Set up enclosures at current injection points and equipment locations.

△ HTB-8000 Large Transformer Primary Current Injection Test Device

The installation and commissioning of the substation main transformer protection device were completed, and all pre-test preparations were confirmed on-site. The person in charge of the test site issued the instruction: Start the main transformer current injection test. According to the test scheme, the current injection point was selected, and the current was boosted to 45A to conduct current injection through the relevant bays from the medium-voltage side to the high-voltage side of the transformer. The safety and anti-misoperation measures, as well as technical and test procedures, were double-confirmed by the test unit and the maintenance person in charge.

Under the overall coordination and guidance of the chief commander, all parties collaborated closely, and the equipment met the scheme requirements. During the medium-to-high voltage side test, the transformer output a current of 45A and a voltage of 380V. It was confirmed that the transformer differential current and phase angle were correct, and all bay tests were completed within 30 minutes.

△ Current and Voltage Application from Medium-voltage Side to High-voltage Side

During the medium-to-low voltage side test, the transformer output a current of 30A and a voltage of 629V. It was confirmed that the differential current, voltage and current phase angles were correct, and all tests were completed within 10 minutes.

△ Current and Voltage Application from Medium-voltage Side to Low-voltage Side

The test report fully and accurately recorded all test data as required and was confirmed by the maintenance person in charge. After the intense work of all staff, a loud announcement was made: "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. It is of great significance for improving the safe operation level of the power grid and the efficiency of commissioning and put-into-operation." The maintenance person in charge said, unable to hide his joy.

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

The test device adopted the series-parallel capacitor compensation method and the homologous voltage and current application test method to generate three-phase power frequency voltage with determined amplitude and phase sequence. After voltage boosting, the voltage was applied to the device under test to generate current with determined phase relationship. The test voltage and current were converted into secondary voltage and current by mutual inductors, which were then input into the relay protection device to complete the protection vector check. This scheme reduces the requirement for the system power supply; when verifying the main transformer differential protection, the injected current can pass through the main transformer to complete the vector check of the main transformer bushing CT.