Large transformers are required to undergo primary current injection and voltage application tests before commissioning or after major maintenance, which mainly conduct load-simulation verification on the entire primary circuit. This test is a critical procedure to ensure the safe and accurate commissioning of transformers and associated high-voltage equipment. It comprehensively verifies the correctness of installation, wiring, polarity, and functions of the primary main circuit as well as the secondary measurement/protection circuit, avoiding issues such as CT open circuit, protection maloperation/refusal to operate, and metering errors after commissioning.

Functional Features of the Test Device

To address the on-site difficulty of directly applying high voltage and large current, the HTB-8000 Large Transformer Primary Current Injection Test Device adopts the capacitance compensation method. It utilizes an adjustable large-capacity voltage regulator and applies a relatively low voltage to the primary side of the transformer through parallel/series combinations of capacitors. Based on the short-circuit impedance characteristics of transformers, even at low voltage, a significant test current can be generated in the primary winding. This method significantly increases the output current and power, and greatly reduces the requirement for test power supply capacity, enabling various key tests on large power transformers under low-power-supply conditions.

△ HTB-8000 Large Transformer Primary Current Injection Test Device

Primary High-current Injection Test for Transformers: Directly inject high current into the primary side.

Through-current Test for Transformers: Apply voltage to one side and short-circuit the other side to achieve current penetration.

Primary Circuit Current Injection and Voltage Application Test on Both Sides of Transformers: Apply current and voltage to the primary circuits on both sides of the transformer.

Through the above tests, the following tasks can be efficiently completed:

Vector verification of primary and secondary circuits for transformer differential protection circuits, busbar protection circuits, and busbar/bay circuits.

Transformation ratio check of current/voltage transformers.

Protection vector (polarity, phase) verification of relay protection devices.

Test Process

After the completion of primary and secondary acceptance for a newly-built 500kV substation, a station-wide simulated load test was conducted to verify the polarity and transformation ratio of mutual inductors, as well as the correctness of primary and secondary wiring of AC circuits such as protection, measurement, metering, fault recording, network analysis, and synchronous phasor measurement. For this test, the current injection point was selected at the medium-voltage side of the main transformer body, and the high-voltage side (or low-voltage side) was three-phase short-circuited and connected to the ground through a specific earthing switch.

Pre-test Preparation：Determine the optimal current injection and voltage application scheme (e.g., high-voltage side to medium-voltage side, medium-voltage side to low-voltage side) according to the transformer nameplate parameters.

Determine the details of the test scheme (e.g., voltage and current values, capacitor configuration) through theoretical calculations.

Check all test equipment and transport it to the test site.

Conduct on-site technical communication and complete safety disclosure.

Primary Wiring：Determine the voltage application and current injection point (e.g., medium-voltage side) and perform wiring.Through switching operations, reliably short-circuit the non-voltage-applied side (e.g., high-voltage side/low-voltage side) in three phases.

Deploy the test equipment and complete the connection between the equipment and the primary system.

After all preparation work is completed, connect the equipment power cable to the maintenance power box, clear the test site, and assign personnel to their respective positions.

Start the equipment and ensure stable operation; on-site personnel perform their respective duties and conduct the test in accordance with the scheme.

Record the primary and secondary data and conclusions of voltage application and current injection between the medium-high voltage sides and medium-low voltage sides of the transformer.

The primary current injection and voltage application test for large transformers is an important means to verify the compatibility between equipment and the system and ensure the safe commissioning of the power grid. The HTB-8000 Large Transformer Primary Current Injection Test Device innovatively adopts capacitance compensation technology, which greatly reduces the on-site requirement for test power supply and solves the problem that traditional current sources cannot perform primary current injection on transformers. It can realize through-current testing, station-wide current injection and voltage application, and primary-secondary vector verification for large transformers, significantly improving the reliability of one-time power transmission.