Transformer Pre-Installation and Inspection in Large Power Transformers – Part 1

Transformers are delivered, transported, and energized with the assumption that factory testing is sufficient; however, in real-world conditions, temperature changes, handling, and environmental factors can create potential issues, which is why a structured transformer installation and transformer inspection procedure is essential to ensure operational reliability. This article provides a practical transformer inspection checklist covering visual inspection, bushings, accessories, protection devices, and transformer oil testing.

Transformer Pre-installation Overview

Before any installation, a complete transformer inspection checklist must be performed to confirm that all components are intact and meet installation requirements. Neglecting even minor aspects, such as loose bolts or slight misalignment, can result in operational failures.

Main Body and Visual Inspection

Visual inspection is often underestimated, yet it is crucial to detect potential damage or misalignment. The transformer installation process should always begin with these checks:

• No visible collision damage, deformation, or coating peeling
• The insulation between the iron core and ground remains intact
• Equipment nameplates and warning signs are complete and clearly readable
• All installation metal components are free from corrosion
• Bolts and fastening parts are secure, without looseness

For units equipped with wheels, the wheelbase should match the rail spacing exactly; if any deviation is found, the track gauge must be adjusted before installation proceeds, otherwise alignment problems may affect positioning and long-term stability.

Transformer Sealing Inspection

For transformers transported with gas filling, the sealing condition must be checked carefully, as it directly reflects whether the unit has remained intact during transportation.

Proper sealing prevents moisture ingress and ensures safe transformer operation.

Conservator and Oil Level Check

The conservator plays a key role in transformer oil management, and its inspection is part of any standard transformer inspection checklist.

• The oil level indicator must be clear and easy to read
• The scale should accurately reflect the actual oil level
• The pointer alignment deviation should not exceed 3 mm

A misaligned or unclear oil level indication may lead to incorrect judgment during operation, which is why this step should not be overlooked even if it seems minor.

 

Accessories Inspection

During transformer installation, all accessories must be unpacked and checked one by one against the packing list, ensuring completeness and confirming that no damage has occurred.

• Compare each item with the packing list
• Inspect for visible damage
• Ensure completeness for installation

Proper inspection of accessories is a key step in any transformer inspection checklist.

Bushing Inspection and Electrical Verification

 

 

Transformer bushings are critical insulation components, and their condition directly affects operational safety, which is why transformer inspection procedures always include detailed bushing checks. For a detailed installation process, refer to the transformer bushing installation guide

Visual inspection should confirm:

• No cracks or surface defects on porcelain or epoxy resin
• Clean flange neck and internal surfaces
• No contamination affecting insulation

Because bushings are tested in oil before leaving the factory, a small amount of oil residue may remain on the surface, especially between metal and porcelain parts, which is considered normal.

Electrical verification includes:

• Measuring resistance between the end screen and transformer body (should be zero)
• Checking resistance between the cap and conductor (should also be zero)

During handling and storage, bushings should be kept at an inclined angle of about 30°, and if repackaging is required after testing, the same inclination must be maintained.

Lightning Arrester Inspection

The inspection of lightning arresters focuses on both physical condition and functional performance.

Visual inspection ensures that:

• The composite housing is free of defects
• Support structures are intact

Hydrophobicity testing is carried out by spraying water mist on the insulator surface and observing the wetting condition, which helps evaluate the surface performance.

Additionally, the discharge counter should be tested using a dedicated instrument capable of simulating lightning current and voltage, and its resistance should be measured and compared with standard values.

Protection Device and Accessories Testing

According to standard practices such as GB 50150-2016, key accessories including gas relays, temperature controllers, oil level gauges, and pressure relief devices should be tested or sent for professional inspection.

 

Gas relay testing includes:

Trip contact reliability check

Signal contact verification

Relay characteristic test within 250–300 mL gas volume

Flow velocity ranges depend on the model, and only spring adjustment is permitted during calibration, while other components must remain unchanged.

Temperature indicators must be tested under controlled conditions, ensuring:

• The temperature bulb must be fully immersed in the constant temperature bath, and the instrument body must remain vertical. During testing, all operations (especially switch settings) should be handled carefully and strictly in accordance with the instruction manual.
• No water should enter the thermometer well. Ensure proper sealing and waterproof measures are in place.
• Do not apply external force to turn the temperature controller pointer counterclockwise (toward 0°C). It may only be turned clockwise. Turning it to the left is strictly prohibited, as it may damage the pointer.
• During testing, excess capillary tubing should be coiled into a loop with a diameter of no less than 100 mm. (For fiber optic temperature sensors, the minimum bending radius of the extended fiber should be 20–25 mm.) Avoid bending, twisting, or tension.
• For units equipped with a test handle, the handle should only be pressed downward. Lifting it upward is prohibited, as it may damage the thermometer.

Transformer Oil Testing

Transformer oil condition is one of the most critical factors affecting insulation performance, and therefore transformer oil testing is an essential part of the transformer inspection checklist.

Oil from each batch must have a valid test report; on-site sampling recommended. Filter oil until the dielectric strength meets standards.

FAQ – Transformer Installation and Inspection

Visual check alone? Not enough. You spray water to see hydrophobicity, and you test the discharge counter. Only then you know it’s actually working as it should. Looks can be deceiving.

Conclusion

Following a structured transformer installation and transformer inspection checklist ensures that all aspects from visual checks to oil testing are completed, significantly reducing risk, preventing equipment failures, and improving long-term reliability. Using this guide, engineers and technicians can confidently install while maintaining compliance with industry standards.