In previous vector checking tests of a 220kV substation, primary current could only be applied on the lines, making it impossible to verify the bushing CTs of the main transformer. After thorough communication and research, two test schemes—voltage-current homologous application and voltage-current non-homologous application—are proposed to complete the tests on CTs of each side and the bushing of the transformer.

Voltage-current Homologous Application Test: The test power supply generates power-frequency three-phase voltage with determined amplitude and phase sequence. After voltage boosting, the voltage is applied to the device under test (when the device under test has no impedance or low impedance, it is advisable to connect a test load) to generate current with determined phase relationship.

The test voltage and current are converted into secondary voltage and current through mutual inductors, and then input into the relay protection device. The correctness of CT ratio, polarity, phase and phase sequence of the entire substation is verified through medium-to-high, medium-to-low, high-to-medium and other test modes.

The HTB-8000 New-type Test Device for Primary Current Injection and Voltage Application of Large Power Transformers is jointly developed by Jiangsu Power Transmission & Transformation Co., Ltd. and Wuhan Haomai. Adopting the capacitive compensation method, it greatly increases the output test current and power under the condition of low requirements for the test power supply, realizing the primary-side high-current injection test for large power transformers (500kV and below). It can conduct current injection tests on both sides of the transformer through the transformer (with the opposite side short-circuited), and perform current injection and voltage application tests on the primary circuits of both sides of the transformer. It can complete the primary and secondary circuit vector verification, mutual inductor ratio checking, protection vector verification and other work for transformer differential circuits, bus differential circuits, bus/interval circuits, etc.

1. Current Injection on 220kV Side

This method adopts the voltage method to inject current into the 220kV bus through the 110kV Qiaoyong Line 1522 and the medium and high voltage sides of No. 1 Main Transformer, and forms a loop by grounding through the line-side switch grounding knife of the 220kV Changqiao 44A6 interval.

The test current flows through the Qiaoyong 1522 interval, 110kV Bus I, medium/high voltage sides of No. 1 Main Transformer, 220kV Auxiliary Bus I, 220kV Auxiliary Bus Section, 220kV Auxiliary Bus II, 220kV No. 2 Bus Coupler, 220kV Main Bus and Changqiao 44A6 Line in sequence, and then to ground.

△ Current Flow Path During Current Boosting

Measure the current and angle of the secondary circuits of protection, measurement & control, metering and other equipment related to No. 1 Main Transformer, 220kV No. 2 Bus Coupler, 220kV Bus Coupler Section and 220kV Changqiao 44A6 Line, and judge whether the CT ratio and polarity meet the requirements. Check whether the sampling values and phase angles of the relevant devices are consistent with the actual test conditions. The power values and power directions of the measurement & control devices and the background should be consistent with the actually applied quantities, and record the data. After each test, short-circuit the next interval first, and then open the outgoing line disconnecting switch and the circuit breaker.

2. Current Injection on 35kV Side

Inject current at the 110kV side through No. 1 Main Transformer, and select short-circuit at the 35kV side.

This method adopts the voltage method to inject current into the 35kV bus through the 110kV Qiaoyong Line 1522 and the medium and low voltage sides of No. 1 Main Transformer, and establishes a grounding point through three-phase short-circuit of the 35kV Gaoning 3894 interval to form a grounding loop.

The test current flows through the Qiaoyong 1522 interval, 110kV Bus I, medium/low voltage sides of No. 1 Main Transformer, 35kV Bus II, 35kV Bus Coupler, 35kV Bus I and Gaoning 3894 interval in sequence, and then to ground.

△ Current Flow Path During Current Boosting

Measure the current and angle of the secondary circuits of protection, measurement & control, metering and other equipment related to No. 1 Main Transformer, 35kV Bus Section and 35kV Gaoning 3894 interval, and judge whether the CT ratio and polarity meet the requirements. Check whether the sampling values and phase angles of the relevant devices are consistent with the actual test conditions. The power values and power directions of the measurement & control devices and the background should be consistent with the actually applied quantities, and record the data. After each test, short-circuit the next interval first, and then open the outgoing line disconnecting switch and the circuit breaker.

3. Current Injection on 110kV Side

Inject current at the 220kV side through No. 1 Main Transformer, and select short-circuit at the 110kV side.

This method adopts the voltage method to inject current into the 110kV bus through the 220kV Changqiao 44A6 interval, 220kV Auxiliary Bus I, 220kV Auxiliary Bus Section, 220kV Auxiliary Bus II, 220kV No. 2 Bus Coupler, 220kV Main Bus, and the high and medium voltage sides of No. 1 Main Transformer, and forms a loop by grounding through the line-side grounding knife of the standby 1GQⅠ interval.

The test current flows through the 220kV Changqiao 44A6 interval, 220kV Auxiliary Bus I, 220kV Auxiliary Bus Section, 220kV Auxiliary Bus II, 220kV No. 2 Bus Coupler, 220kV Main Bus, high/medium voltage sides of No. 1 Main Transformer, 110kV Bus I and standby 1GQⅠ interval in sequence, and then to ground.

△ Current Flow Path During Current Boosting

Measure the current and angle of the secondary circuits of protection, measurement & control, metering and other equipment related to No. 1 Main Transformer, 220kV Changqiao Interval, 220kV Bus Coupler 2510, 220kV Section and 110kV 1GQⅠ, and judge whether the CT ratio and polarity meet the requirements. Check whether the sampling values and phase angles of the relevant devices are consistent with the actual test conditions. The power values and power directions of the measurement & control devices and the background should be consistent with the actually applied quantities, and record the data. After each test, short-circuit the next interval first, and then open the outgoing line disconnecting switch and the circuit breaker.

△ Parameter Settings

△ Sampling Values

△ Test Results