Pilot zero-sequence protection is developed on the basis of stage zero-sequence protection with additional communication interfaces and necessary action logic. When the communication channel is out of service or malfunctions during operation, pilot zero-sequence protection will function as a complete stage zero-sequence protection. The remote signal adopted by pilot zero-sequence protection can be either blocking type or permissive type. For the blocking type, the side that identifies a reverse fault is responsible for sending signals to block the protection at both ends; for the permissive type, the side that identifies a forward fault is responsible for sending signals to permit the tripping of protection at both ends. Taking the commissioning of the CSC-101A protection device with the Relaystar-Z70 Handheld Digital-analog Integrated Relay Protection Tester as an example, this paper introduces how to complete the commissioning of both forward and reverse directions of pilot zero-sequence protection in one go through the zero-sequence module.

△ Relaystar-Z70 Handheld Digital-analog Integrated Relay Protection Tester

1 Protection Setting Values and Press Plate Configuration

2 Test Wiring

△ Pilot Zero-sequence Protection Wiring Diagram

Connect the voltage output terminals "Ua", "Ub", "Uc", "Un" of the Relaystar-Z70 to the AC voltage terminals "UA", "UB", "UC", "UN" of the protection device respectively. Connect the current output terminals "Ia", "Ib", "Ic" of the Relaystar-Z70 to the AC current terminals "IA", "IB", "IC" (polarity terminals) of the protection device respectively. Then short-circuit the AC current terminals "IA'", "IB'", "IC'" (non-polarity terminals) of the protection device and connect them to the "IN" (zero-sequence current polarity terminal), and finally connect the "IN'" (zero-sequence current non-polarity terminal) back to the current output terminal "IN" of the Relaystar-Z70. Connect the input contact "A" of the Relaystar-Z70 to the phase-separated trip output contact "Trip A" of the protection device, and connect the "+KM" terminal of the Relaystar-Z70 to the common terminal of the protection device. The switch position corresponding to this line is "closed", so the output wiring is not considered here.

3 Pilot Zero-sequence Function Verification

1. Parameter Configuration

In the zero-sequence protection menu, check Zero-sequence Stage I and Stage II, which are used for simulating forward and reverse fault conditions of pilot zero-sequence protection respectively. Select time trigger as the trigger mode, set the pre-trigger delay to 15s to ensure the TV disconnection alarm is cleared, and choose the phase-separated tripping mode. The relevant setting values in the test interface can be configured according to the setting sheet. The test time is generally set 0.1–0.2s longer than the setting time, and the fault phase voltage can be set to 20V based on empirical values.

△ Zero-sequence Protection Module Parameter Configuration

△ Normal State Duration Setting

2. Test Operation Method

Click the "Run" and "Confirm" buttons on the start screen, and the Relaystar-Z70 will start outputting. It first outputs the no-load state, then switches to the fault state until the protection trips reliably. After the input contact collects the operation time, the Relaystar-Z70 will automatically proceed with subsequent tests until all protection tests are completed. Select whether to save the test results as prompted.

△ No-load State Lasts for 15s and TV Disconnection Alarm Resets

4 Test Results

After the test is completed, the input quantity records the test action information.

△ Pilot Zero-sequence Channel Disconnected and Signal Transmission Stopped

△ Pilot Zero-sequence Protection Operated

△ Automatically Record Zero-sequence Protection Test Results

For pilot zero-sequence protection under forward fault conditions, it operates reliably at 1.05 times the short-circuit multiple and remains inoperative reliably at 0.95 times the short-circuit multiple. Under reverse fault conditions, the protection remains inoperative reliably at both 1.05 and 0.95 times the short-circuit multiple, indicating correct test results. By checking the test report, it can be seen that the action conditions and action time information of various zero-sequence fault types are correct. This test module enables more convenient, fast and efficient completion of various test items.