Test Equipment: Two HTA-3300 Three-phase Digital Intelligent High-current Sources, Two HTV-6000 Three-phase Digital Intelligent High-voltage Sources, One YD-300E Intelligent Wireless Remote Control Host for Current and Voltage Sources

Pre-test Preparation: No personnel shall conduct line testing work at the test site. The secondary side of PT must not be short-circuited, and the secondary side of CT must not be open-circuited. Power supply shall be available at the equipment access points.

Test Wiring

△ Test Wiring Diagram for 220kV Side of #1 Main Transformer

HTV-6000 Three-phase Digital Intelligent High-voltage Source Test Wiring

Remove the grounding connection point of the grounding switch (280070 switch) in the voltage transformer bay of 220kV Bus I Section B. Connect the output terminals of the voltage source to the voltage application points of the voltage transformer in Bus I Section B respectively, and connect them to the corresponding terminals in the order of Phase A, Phase B, Phase C and Ground. The red lines in the above diagram represent the wiring of the three-phase voltage circuit. The states of switches and disconnecting switches are shown as per the diagram, with disconnecting switch 28007 open. (Short-circuit the auxiliary contact of the intelligent terminal 28007 to enable the protection device to collect the bus voltage). Switch 280070 is in closed position, and disconnecting switch 28007 is in open position.

△ Three-phase Voltage Application Points of the Voltage Transformer in 220kV Bus I Section B

HTA-3300 Three-phase Digital Intelligent High-current Source Test Wiring

Remove the grounding connection point of the grounding switch (488530 switch) in the 220kV Line 4885 bay. Before the test, disconnect the grounding connection points of other current-carrying circuits to ensure that only the grounding connection point of the grounding switch (280130 switch) in the 220kV #1 Main Transformer bay is retained. Connect the test cables to the Phase A, Phase B and Phase C output terminals of the three-phase current source in sequence from the lead at the removal point (488530 switch), and connect the N wire of the current source to the grounding copper bar. (The red lines in the above diagram represent the flow direction of the three-phase current circuit, with the states of switches and disconnecting switches shown as per the diagram). Switches 488530, 4885, 48852, 26002, 2600, 26001, 21002, 2100, 21001, 28011 and 280130 are in closed position; all disconnecting switches connected to the 220kV bus are open; all other disconnecting switches and grounding switches are in open position.

△ On-site Wiring of the Three-phase Current Source

△ Three-phase Current Application Points in the 220kV Line 4885 Bay

△ Test Wiring Diagram for 110kV Side of #1 Main Transformer

110kV Side Three-phase Voltage Source Test Wiring

Remove the grounding connection point of the grounding switch (50150 switch) in the voltage transformer bay of 110kV Bus I Section A. Connect the output terminals of the voltage source to the voltage application points of the voltage transformer in Bus I Section A respectively, and connect them to the corresponding terminals in the order of Phase A, Phase B, Phase C and Ground. The red lines in the above diagram represent the wiring of the three-phase voltage circuit. The states of switches and disconnecting switches are shown as per the diagram, with disconnecting switch 50150 open. (Short-circuit the auxiliary contact of the intelligent terminal 5015 to enable the protection device to collect the bus voltage). Switch 50150 is in closed position, and disconnecting switch 5015 is in open position.

△ Three-phase Voltage Application Points of the Voltage Transformer in 110kV Bus I Section A

110kV Side Three-phase Current Source Test Wiring

The 798 switch bay is selected as the current injection point due to its close proximity to the power supply maintenance box for convenient power access. Remove the grounding connection point of the grounding switch (79830 switch) in the 110kV Line 798 bay. Before the test, disconnect the grounding connection points of other current-carrying circuits to ensure that only the grounding connection point of the grounding switch (50130 switch) in the 110kV #1 Main Transformer bay is retained. Connect the test cables to the Phase A, Phase B and Phase C output terminals of the three-phase current source in sequence from the lead at the removal point (79830 switch), and connect the N wire of the current source to the grounding copper bar. (The red lines in the above diagram represent the flow direction of the three-phase current circuit, with the states of switches and disconnecting switches shown as per the diagram). Switches 79830, 798, 7982, 4002, 400, 4001, 5011, 501 and 50130 are in closed position; all other disconnecting switches connected to the 110kV bus are open; all other disconnecting switches and grounding switches are in open position.

△ Three-phase Current Application Points in the 110kV Line 798 Bay

Parameter Settings

Set the operation mode of the current and voltage sources on both 220kV and 110kV sides to remote control mode. Use the YD-300E Intelligent Wireless Remote Control Host for Current and Voltage Sources to search for the corresponding equipment. After the connection is completed, set the output amplitude and angle, return to the remote control main interface and click "Start" to control the connected devices for output, and apply differential current balance for output.

△ Application Result of Differential Current Balance

The main transformer protection device displays that the differential currents of Phase IA, IB and IC are all 0, and the restraining current is 0.05A.

Then apply differential current superposition for output, i.e., the differential current is twice the current injection value.

△ Application Result of Differential Current Superposition

The main transformer protection device displays that the differential currents of Phase IA, IB and IC are all 0.09A, and the restraining current is 0.05A.

Test Results

The CT ratio on the 220kV side is 2500:1. When a current of 120A is applied on the primary side, the displayed current on the secondary side should be 0.05A. Since the current injection directions on both sides are towards the transformer during the current source wiring, when a current of 240A is applied on the 110kV side with a 180° phase angle reversal, the differential current on both sides reaches balance at 0A, and the restraining current is 0.048A, which is consistent with the results displayed on the protection device. When a current of 240A is applied on the 110kV side with the same phase angle as that on the 220kV side, the differential current is the superposition value of both sides, i.e., 0.096A, and the restraining current is 0.048A, which is consistent with the results displayed on the protection device. It can be concluded that the vectors of the 220kV and 110kV sides of the transformer are correct.