On-site Analysis and Handling of Common Visible Faults in Transformers

Visible faults in transformers refer to faults with relatively obvious characteristics and manifestations. Based on actual work site conditions, this text describes and analyzes the causes and characteristics of visible faults in large transformers, and introduces common on-site handling methods, which are also relatively simple methods.

When abnormalities and faults occur during transformer operation, they are often accompanied by corresponding external characteristics. Through these simple external phenomena, some defects can be detected, and qualitative analysis of abnormalities and faults can be performed to propose further analysis or treatment plans. Analysis and handling can be conducted from the following aspects:

1. Damage to the explosion-proof tube or pressure relief valve membrane

When the transformer's breathing is obstructed, air entering above the membrane of the transformer's oil conservator expands rapidly as temperature rises, increasing pressure. If the membrane is damaged, it may be accompanied by a large amount of transformer oil spraying out. The main causes and measures are:

1. Breathing device blockage due to excess silica gel, excess oil in the oil seal, or foreign objects in the pipeline. Silica gel should occupy 2/3 of the breather, and 1/3 oil in the oil seal is sufficient. The pipeline can be checked by injecting nitrogen.
2. Over-tightening of bolts or uneven flanges during installation and maintenance, external force damage, or accidental human contact. Replace the damaged membrane.
3. Internal short circuit faults producing large amounts of gas. First, take a gas sample from the gas relay. If it ignites, oil sample chromatography analysis and electrical inspection are needed to determine the nature of the fault. The transformer cannot be put into operation before the fault cause is identified and defects are eliminated.
4. Improper oil filling method for membrane-structure oil conservators during maintenance or installation, failing to exhaust gas from the upper part of the oil conservator as required. Power off, fill the oil conservator with transformer oil, then drain to the appropriate oil level.
5. For capsule-structure oil conservators, low oil levels can cause the capsule to block the connection between the oil conservator and the transformer body. Install a bracket at the pipeline connection to prevent the capsule from directly blocking the connection.

2. Bushing Flashover Discharge

Bushing flashover discharge can cause self-heating and aging, leading to transformer outlet short circuit accidents. The main causes and measures are:

1. Surface contamination leading to discharge in rainy and humid weather due to increased conductivity of the dirt. Power off the transformer to clean the bushings and apply RTV long-lasting coating to improve anti-pollution flashover performance.
2. Defects from installation, maintenance, or manufacturing. If insulation indicators like dielectric loss angle exceed standards or porcelain parts are incomplete during testing, replace the bushing.
3. Insufficient external creepage distance in design for transformers operating in highly polluted areas. Replace with bushings having longer creepage distance or take anti-pollution measures like adding silicone rubber skirts.
4. Internal or atmospheric overvoltage in the system. Conduct tests and inspections on bushings and transformers, only putting them into operation when fully qualified.
5. Foreign objects short-circuiting part of the porcelain skirt on the bushing surface. Remove using an insulated rod while energized.
6. Cease operation during rainy, snowy weather, or when covered in ice.

3. Oil Leakage

This is an issue present in almost every transformer, occurring at sealing points and even through pinholes in iron plates. While oil leakage generally doesn't cause immediate transformer shutdown, if not addressed promptly, it can seriously endanger the safe operation of the transformer. Due to the numerous and varied sealing locations on transformers, oil leakage symptoms can be diverse. The main causes and measures are:

1. Aging and cracking of sealing gaskets, usually due to poor quality or overdue replacement. Replace timely during maintenance.
2. Insufficient tightening of sealing points, which can accelerate gasket aging in oil-free areas and allow air to enter the transformer body. Tighten immediately upon discovery.
3. Poor manufacturing quality of valves leading to incomplete closure. Drain oil and replace valves.
4. Pinholes or poor welding quality. Can be welded while oil-filled, but fire prevention measures must be taken. For pinholes in iron plates, covering the surface with a welded iron plate of certain area can also address the issue.
5. Oil pump leakage. Some parts may not leak during operation due to negative pressure but will leak once stopped, often introducing air into the transformer, triggering gas relay signals or even tripping. This is difficult to detect and requires stopping and checking each pump individually for identification and treatment.
6. Gasket deformation due to excessive force, unreasonable sealing structure, poor manufacturing and installation processes can also lead to oil leakage. Treatment should be specific to the particular cause.

~The End~