The HTA/HTV Wireless Remote-controlled Digital Intelligent Current/Voltage Source can simulate primary-side load operation. By injecting large currents into the high-voltage side CT and low-voltage side CT of the transformer to simulate the current during transformer operation, it can complete loop verification, ratio, phase and polarity verification of the entire high-voltage and low-voltage sides, and verification of transformer differential current, etc. This article describes how to use the HTA/HTV Wireless Remote-controlled Digital Intelligent Current/Voltage Source to achieve simultaneous quantity injection testing on both the high-voltage and low-voltage sides via wireless synchronization.

1 Test Method

After disconnecting the high-voltage side CT and low-voltage side CT from the main transformer, perform the wiring. The high-voltage side uses outdoor overhead CTs, which can be directly wired. The low-voltage side uses bushing CTs; since the exposed end of the busbar passing through is inside the cabinet, the test is performed by passing the current wire through the CT.

As the on-site PT is not in operation, the HTV-6000 Three-phase Digital Intelligent High-voltage Source is used to output voltage to the protection device and the YD-300 Wireless Telemetry Voltmeter-Ammeter Phase Indicator as the voltage reference, ensuring the phase of the current output. In this test, one HTA-3300 Three-phase Digital Intelligent High-current Source is used on the high-voltage side, and three HTA-1300 Single-phase Digital Intelligent High-current Sources are used on the low-voltage side.

2 Test Wiring

Before wiring, process the primary circuits of the high-voltage and low-voltage sides respectively: disconnect the high-voltage side CT from the transformer disconnecting switch and the busbar disconnecting switch, then close the grounding disconnecting switch. Since the high-voltage side grounding disconnecting switch is located on the transformer side, current is injected from the homonymous terminal in this test and returns to N via the grounding disconnecting switch.

△ High-voltage Side Wiring

For the low-voltage side, which uses through-type bushing CTs, there is no need to open or close the primary disconnecting switch; the current wire is directly passed through the bushing CT, connected to N, and returned to the device.

Note: When passing the current wire through the CT, pay attention to the direction of current flow to avoid reversal.

△ Low-voltage Side Wiring

3 Test Process

After completing the primary loop wiring, connect the secondary wires of the HTV-6000 Three-phase Digital Intelligent High-voltage Source to the protection device to ensure the protection device has a reference voltage. Then lead phase A voltage to the YD-300 Wireless Telemetry Voltmeter-Ammeter Phase Indicator, and output a reference voltage in standalone mode.

Turn on the YD-300 to search for the digital intelligent high-current sources, output 120A, 160A, 200A on the high-voltage side and 120A, 160A, 200A on the low-voltage side for phase sequence verification. After confirming no errors, start the formal output.

4 Test Results

After the current rises, the high-voltage and low-voltage side currents can be viewed on the protection panel. The high-voltage side ratio is 200:1, and the low-voltage side ratio is 4000:1. Since the current is injected from P2 on the high-voltage side, the theoretical phase of the outgoing current should be reversed by 180°, while the low-voltage side current should have a normal phase.

△ High-voltage Side Amplitude and Phase

The high-voltage side amplitudes viewed on the protection panel are 0.61, 0.79, 0.99, which are consistent with the ratio conversion values. The phases are 177°, 60°, -64°, which are consistent with the theoretical values.

△ Low-voltage Side Protection Panel

The low-voltage side amplitudes are 0.031, 0.041, 0.053, which are consistent with the ratio conversion values. The phases are 0°, -118°, 122°, which are consistent with the theoretical values. The differential current value viewed via the dispatch center is consistent with the theoretical value.