Test Equipment: HTA-3300 Three-phase Digital Intelligent High-current Source

Test Purpose: Control the intelligent current source to generate high current with controllable phase, inject it into the primary side of the current transformer, simulate the actual load, detect the vector relationship of the entire primary and secondary circuits at one time, and judge whether the CT polarity is correct through bus differential sampling.

1. Wiring Method

1. Current Source Wiring: Connect the HTA-3300 Three-phase Digital Intelligent High-current Source to the phase A/B/C on the line 1 side of the 5008617 disconnecting switch. Close the disconnecting switches 50086, 50081 and 50096, close the circuit breaker 5008, and connect the CT side on the lower side of the 500967 disconnecting switch to the ground bar at the same time to form a loop.

2. Disconnect the isolation disconnecting switches of other bays.

2. Test Process

Power on the HTA-3300 Three-phase Digital Intelligent High-current Source and set it to standalone operation mode. Set the amplitude of each phase current to 60A and check whether the current phase sequence is correct. When applying current to phase C, the display shows open circuit with no sampling, while phase A and B can be boosted to 60A, indicating an open circuit in the phase C loop. After on-site investigation by the staff, it is found that there is a contact problem on the grounding point side. After troubleshooting the problem, continue to apply the current. The HTA-3300 displays normal three-phase sampling, indicating that the loop is normal.

Output three-phase positive-sequence current of 80A on the HTA-3300 device. The sampling information of the two bays viewed on the bus differential protection is as follows:

Based on the above data analysis, when simulating an external fault, the bus differential current should be 0A, while the actual display on the bus differential protection panel shows a differential current of 0.2A, indicating that the CT polarity on one side is reversed. Since the power plant side is a newly commissioned bay, the on-site staff analyze that the CT polarity of this bay is reversed. After rewiring on the power plant side and reapplying the current, the bus differential current displays 0A, indicating that the CT polarity is normal.

△ On-site Protection Sampling

3. Test Result Analysis

The HTA-3300 Three-phase Digital Intelligent High-current Source is used for current injection, and sampling analysis is performed on the bus differential protection device to judge the CT polarity problem of the newly added bay. During the test, the line open circuit and reversed polarity are detected and handled in a timely manner, further ensuring the safe and stable operation of the unit.