To improve the one-time power transmission success rate, CT vector and polarity checking must be performed before a substation is commissioned. Wuhan Haomai's HTA/HTV wireless remote-controlled digital intelligent current/voltage sources can simulate primary-side load operation. By injecting large current into one bay and switching various circuit breakers and disconnecting switches to connect all bays via the busbar, vector and polarity checking of CTs in multiple bays can be completed with a single current injection, greatly improving work efficiency.

△ Primary System Diagram of a Substation (Partial 110kV Bay Lines)

Test Equipment

HTV-6000 Three-phase Digital Intelligent High-voltage Source，HTA-3300 Three-phase Digital Intelligent High-current Source，YD-300 Intelligent Wireless Remote Control Host for Current/Voltage Source / Wireless Telemetry Voltmeter-Ammeter Phase Indicator

1. Test Method

This test is mainly for checking CT vector and polarity during multi-bay current injection. Primary current is injected from the grounding switch 111-7 of bay 111. By closing circuit breaker 111 and disconnecting switch 111-1, the current can flow into the 110kV I# busbar. Then, by closing the disconnecting switches 114-1, 114-2 and circuit breaker 114 of the bus tie bay, the current flows into the 110kV II# busbar. Finally, by closing circuit breaker 112, disconnecting switch 112-1 and grounding switch 112-7, the current flows into the ground, forming a complete primary current loop.

To check the phase angle of the current loop, it is necessary to apply secondary voltage. The HTV-6000 Three-phase Digital Intelligent High-voltage Source outputs rated voltage to the protection device. Taking phase A bus voltage as the reference, the CT secondary amplitude and angle can be viewed on the protection device of each bay, and the correctness of the vector polarity can be judged according to the definition of the CT polarity terminal.

2. Test Wiring

Since the entire substation adopts GIS fully enclosed equipment, before starting the test wiring, it is necessary to remove the short-circuit connection at the grounding switch 111-7 to inject three-phase current. The current flows through the CT of line circuit breaker 111, the CTs on both sides of bus tie circuit breaker 114, and the CT of line circuit breaker 112, then into the ground, forming a current loop.

△ Current Flow Schematic Diagram

The HTA-3300 Three-phase Digital Intelligent High-current Source is used to apply three-phase primary current, the HTV-6000 is used to apply secondary voltage, and the YD-300 Intelligent Wireless Remote Control Host for Current/Voltage Source is used for wireless online connection and synchronous output control.

3. Test Start

After completing the primary loop wiring, connect the secondary wires of the HTV-6000 to the protection device to ensure the protection device has a reference voltage. Then lead phase A voltage to the YD-300 and output a reference voltage in standalone mode. Turn on the YD-300 to search for the HTA-3300. First, output primary currents of 60A, 120A, 180A and a secondary voltage of 50V for phase sequence verification. After confirming no errors, start the formal output.

4. Test Results

After the current is boosted, the current of each bay side can be viewed on the protection panel. The on-site CT ratio is 1200:5. Since the current is injected from P2 of bay 111, the theoretical phase of the outgoing current should be reversed by 180°. For bay 112, the current is injected from P1, so the theoretical phase of the outgoing current should be consistent. The measured CT amplitude and phase values of the two bays are shown in the table below:

The above data is consistent with the data measured by the phase indicator at the front end of the merging unit, and is also consistent with the analyzed CT polarity. Therefore, this CT vector and polarity test method is correct, and the one-time current injection for multi-bay CT vector and polarity verification is completed before commissioning.