What inspections are required before the transformer is put into operation?

Before commissioning a transformer, thorough inspection and testing are crucial to ensure its reliability and safety during operation. The following steps and considerations are essential:

1. Inspection

During inspection, the following steps should be carried out:

• Oil Sampling and Chromatographic Analysis: Obtain oil samples for chromatographic analysis to assess oil condition.

• Valve Status Check: Verify that gate and butterfly valves are open and correctly positioned. Ensure oil levels in storage cabinets and bushings meet specified levels.

• Current Transformer Wiring Check: Verify correct wiring of current transformers, ensuring no secondary coil is grounded or left open-circuited.

• Oil Flow Relay Operation Check: Confirm reliable operation of the oil flow relay.

• Air Insulation Distance Check: Ensure air insulation distances between bushings and ground, and between bushings of different voltage levels, comply with relevant standards.

• Grounding System Check: Ensure proper grounding, including grounding of the oil tank and any grounding bushing leads on the iron core (clamp).

• Protection Device and Control Circuit Check: Verify correct wiring of gas relays, pressure relief valves, oil level gauges, thermometers, and current transformers. Ensure proper operation and reliability of protection devices and circuit breakers.

• Desiccant and Breather Check: Inspect desiccant silica gel condition, oil level, and breather functionality.

• Cooling System and Control Box Operation Check: Verify correct and reliable operation of the cooler and control box systems.

• Oil Circulation Direction Check: Confirm correct oil circulation direction based on the submersible oil pump's orientation.

2. Transformer Pre-Installation Testing

Before installation, perform the following tests:

• Bushing Current Transformer Test: Measure insulation resistance of the secondary winding to ground, DC resistance of the secondary winding, conduct excitation characteristics test, and check transformer ratio and polarity.

• Bushing Test: Measure insulation resistance of the bushing main insulation and end screen to ground. Measure dielectric loss tangent (tgδ) and capacitance value of non-porous porcelain bushings.

3. Electrical Testing After Transformer Oil Filling

After oil filling, conduct comprehensive electrical tests:

• Measure DC resistance of winding and bushing at all tap positions.

• Measure voltage ratio of all taps.

• Verify transformer connection group.

• Measure insulation resistance and absorption ratio (polarization index) of winding and bushing.

• Measure dielectric loss tangent (tgδ) of winding and bushing.

• Measure DC leakage current of winding and bushing.

• Perform AC withstand voltage test of low-voltage side winding and neutral point winding on the high-voltage side.

• Conduct partial discharge and winding deformation tests on windings and bushings.

4. Grounding Check

Ensure reliable grounding of the transformer's supply-side neutral point, especially during impact testing.

5. Protection Device Settings

Verify correct settings and synchronization sensitivity of all protection devices and circuit breakers.

6. Gas Relay

During no-load impact testing, connect the gas relay signal contact to the heavy gas action contact for the power trip circuit.

7. On-Site Storage of Transformers

Upon arrival, adhere to the following storage guidelines:

• Check for dampness. Ensure nitrogen pressure is between 0.01-0.03 MPa and oil meets electrical strength, micro water, and tgδ requirements before injecting.

• Store for no more than 6 months under dry air. Conduct twice-daily inspections of box pressure. Promptly address significant leaks to maintain pressure requirements.

• Store disassembled parts (e.g., oil storage cabinets, coolers) with protection against rain, dust, dirt, and rust.

• Store accessories (e.g., measuring instruments, displays, junction boxes) in dry, ventilated rooms post-unpacking.

By meticulously conducting these inspections and tests, the safety, reliability, and long-term performance of the transformer can be ensured before it is put into operation.