Common faults and protection technology analysis of oil immersed transformer: from partial discharge to short circuit accidents

1.Why oil immersed transformer faults cannot be ignored

Once an internal fault occurs in an oil immersed transformer, it often results in huge losses, long repair cycles, and even causes power grid accidents.
Therefore, understanding the fault mechanism and configuring the protection system reasonably is a key issue in power engineering.

2.Analysis of common types of internal faults

2.1 Partial discharge

Initial manifestation of insulation defects
Strong concealment
Sustainable for months or even years

It is the most easily overlooked but dangerous form of malfunction.

2.2 Overheating of windings

Common reasons include:

• Long term overload
• poor contact
• Blocked heat dissipation

2.3 Interturn short circuit

mechanical stress
thermal aging
Insulation breakdown

2.4 Severe internal short circuit

Extremely destructive
May cause deformation or even explosion of the fuel tank

3.The core role of insulating oil in fault diagnosis

3.1 Gas Analysis (DGA)

By analyzing the dissolved gases in the oil, it can be determined that:

• Fault Type
• Fault development stage

3.2 Oil deterioration

Increase in moisture content
Decrease in dielectric strength
Acid value increases

4.Main protection device system for oil immersed transformer

Protection Device	Function
Gas Relay (Buchholz Relay)	Early internal fault detection
Differential Protection	Primary protection
Temperature Controller	Overheating protection
Pressure Relief Valve	Explosion prevention
Oil Level Indicator	Operational monitoring

5.Engineering case analysis

Case: Ignoring gas relay alarm

Alarm has occurred but has not been processed
Continuous development of internal discharge
Final inter turn short circuit
The direct economic losses have expanded several times

6.Typical Misconceptions in Operations and Maintenance

Only focus on tripping and do not attach importance to alarms
Ignore regular oil sample testing
Operating without capacity reduction in high temperature environment
The protective device is not regularly calibrated

7.New trend: Intelligent oil immersed transformer

Online DGA
Digital temperature monitoring
Intelligent casing
Remote state assessment

Oil immersed transformers are not “prone to failure”, but require proper understanding and maintenance.
A scientific protection system and professional operation and maintenance strategy are the key to ensuring its long-term stable operation.