After a transformer short circuit fault, a thorough inspection goes far beyond checking main windings, iron cores, and clamps. You must also perform a series of related tests and follow critical precautions. This guide outlines the complete post‑accident inspection process, the necessary measurements, and the essential handling steps to ensure safe repair and long‑term reliability.

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1. Post‑Short‑Circuit Inspection & Testing Checklist

When a transformer experiences a short circuit, perform the following checks and tests:

• Winding inspection – Look for deformation, displacement, or damage.
• DC resistance measurement – Detects open circuits, poor connections, or turn‑to‑turn faults.
• Winding capacitance measurement – Helps identify winding distortion or insulation changes.
• Behind‑the‑hood inspection – Examine internal connections, tap changer, and lead wires.
• Iron core and clamp inspection – Check for looseness, displacement, or overheating.
• Transformer oil and gas analysis – Dissolved gas analysis (DGA) reveals arcing or overheating.

These combined assessments help you accurately determine the nature and extent of the fault.

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2. Key Precautions for Transformer Short Circuit Fault Handling

Follow these six critical precautions when repairing a transformer after a short circuit:

2.1 Ensure Insulating Parts Performance

When replacing any insulating components (paper, pressboard, barriers), verify that the new parts meet original specifications. Poor insulation quality leads to future failures.

2.2 Perform Insulation Test After 24‑Hour Oil Immersion

Do not conduct insulation tests immediately after oil filling. Wait 24 hours with the transformer still oiled. This allows the oil to fully permeate the insulation and eliminates air bubbles, giving accurate readings.

2.3 Pay Attention to Sharp Corners When Reassembling the Core

When restacking iron core laminations, carefully smooth or insulate any sharp corners. Sharp edges can damage winding insulation or create points of high electric field stress.

2.4 Replace Winding Material with Strong Short‑Circuit Resistance

Use winding materials specifically rated for high mechanical strength – such as oxygen‑free copper with reinforced support structures. This upgrade reduces the risk of future deformation under short‑circuit forces.

2.5 Drying of Transformers

After repair, the transformer must be thoroughly dried to remove moisture absorbed during the open‑air repair process. Use vacuum drying or hot oil circulation drying methods according to the insulation class.

2.6 Other Important Considerations

• Clean all internal components before reassembly.
• Replace damaged or degraded transformer oil.
• Perform a full suite of dielectric tests before re‑commissioning.
• Update maintenance records with all findings and repairs.

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3. Comprehensive Fault Analysis Approach

After a short‑circuit accident, do not rely on a single test. Combine multiple results for an accurate diagnosis:

Test	What It Reveals
Dissolved gas analysis (DGA)	Arcing, overheating, partial discharge
Gas relay gas composition	Type and severity of internal fault
Winding DC resistance	Loose connections, broken strands, turn shorts
Winding capacitance	Deformation, insulation degradation
Winding deformation test (Sweep Frequency Response Analysis)	Physical displacement or buckling of coils

By correlating these results, you can determine the exact fault nature. Then, inspect for:

• Winding deformation (buckling, tilting, or collapse)
• Iron core displacement or looseness
• Clamp damage or movement

Finally, develop a treatment plan – from minor repairs to full winding replacement – and implement preventive measures for future operation.

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4. Special Attention When Winding Replacement Is Necessary

If the short‑circuit accident causes severe winding deformation and you must replace the winding, pay extra attention to:

• Reassembly of iron core laminations – Maintain proper alignment, insulation between sheets, and tightness.
• Drying of all insulating parts – All new and remaining insulation must be dried to safe moisture levels.
• Treatment of transformer oil – Filter, degas, and dry the oil. Consider full replacement if contamination is severe.
• Overall transformer drying – Perform a final vacuum drying cycle before oil filling.

Failure in any of these steps can lead to premature insulation failure or reduced short‑circuit withstand capability.

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5. Summary: Your Post‑Short‑Circuit Action Plan

Step	Action
1	Inspect windings, core, clamps, and behind the hood
2	Measure DC resistance, capacitance, and perform winding deformation test
3	Analyze oil and gas (DGA + gas relay)
4	Replace only with high‑quality insulating parts
5	Wait 24 hours after oiling before insulation testing
6	Smooth core corners during reassembly
7	Use short‑circuit‑resistant winding materials
8	Dry transformer and all insulation thoroughly

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