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Learn about power transformers — construction, working, testing, protection, and maintenance for efficient voltage transformation in power systems.
An Oil Surge Relay, or OSR, is a type of mechanical relay. It operates in response to a sudden oil surge. Need for Separate Diverter Tank Every modern power transformer includes an On-Load Tap Changer (OLTC). During tap-changing operations, some arcing always occurs at the diverter switch contacts. It is desirable to change tap positions … Read more
The Nitrogen Injection Fire Protection System (NIFPS) prevents and extinguishes fires in oil-filled transformers. Thereby, it safeguards critical power infrastructure. We also commonly call it the Nitrogen Injection Fire Prevention & Extinguishing System (NIFPES). This system operates on a “drain and stir” principle, effectively mitigating fire hazards through a coordinated sequence of actions. Working Principle … Read more
A power transformer has high cost, large size, and complex design. So, identifying defects at the final stage of manufacturing can lead to significant delays, expenses, and operational challenges. Therefore, standards always recommend performing different tests and inspections during various stages of manufacturing. That means the standards always prefer to perform stage inspections of a … Read more
The clearance requirements for HV and LV terminals in the air are as follows:For 66 kV side, the phase-to-phase and phase-to-earth clearance should be 700 mm, and 660 mm respectively.For 12 kV side, the phase-to-phase and phase-to-earth clearance should be 280 mm, and 140 mm respectively. The following points should be noted for designing winding … Read more
The transformer differential protection belongs to the unit protection scheme. A unit protection confines itself within a defined zone. A differential protection scheme compares the vector sum of currents entering and leaving the protected equipment. In other words, it uses Kirchhoff’s current law. Under healthy and external fault conditions, the currents entering and exiting the … Read more
Restricted Earth Fault (REF) protection is a special type of protection. This protection scheme is mainly applied to power transformers. This scheme is designed to detect only the internal earth faults of the transformer. It provides highly sensitive and selective protection for internal earth faults. Restricted earth fault protection is a unit protection scheme. REF … Read more
There is a disadvantage in a low-impedance restricted earth fault scheme. Suppose, due to any fault, any of the line CTs comes under saturation. A spill current starts flowing through the earth fault relay. As a result, the relay may initiate mal-tripping to the transformer circuit breakers. Although the fault is not related to the … Read more
A simple overcurrent (O/C) and earth fault (E/F) protection is essential for a power transformer. The O/C protection operates whenever the phase current exceeds a preset value. E/F protection responds to residual or zero-sequence current. Overcurrent and earth fault protection of power transformers uses simple IDMT or DMT relays. It cannot distinguish between internal and … Read more
Type Tests for the transformer Routine Tests on the Transformer Stage Inspection Tests On Core: On Coil On Tank Acceptance Tests
Type Tests on New Transformer Oil or Insulating Oil