1. Core Functions of Transformers

Transformers are essential for voltage conversion in AC power systems, enabling efficient energy transmission and distribution. Using electromagnetic induction, they step up voltages (e.g., from 10kV to 220kV) for long-distance transmission to minimize energy loss, then step down voltages (e.g., to 380V/220V) for safe end-user applications. They provide electrical isolation between circuits, stabilize system impedance, and ensure grid reliability.

2. Transformer Classifications

• By Phase: Single-phase vs. three-phase

• By Windings: Autotransformer, dual-winding, triple-winding

• By Cooling: Oil-immersed self-cooled (ONAN), forced-air cooled (AF), oil-forced air-cooled (OFAF), water-cooled (WF)

• By Insulation: Oil-immersed vs. epoxy resin (dry-type)

• By Application: Power transformers dominate 10kV systems, while specialized types include furnace, welding, rectifier, and instrument transformers.

3. Operational Principles

A transformer comprises a laminated iron core with primary and secondary windings. When AC voltage (U1U1​) energizes the primary winding, it induces a magnetic flux (ϕϕ) in the core, generating an electromotive force in the secondary winding via Faraday’s law. Load current (I2I2​) in the secondary alters the primary current (I1I1​) to maintain constant flux, enabling energy transfer without direct electrical contact.

4. Key Components of Oil-Immersed Transformers

• HV Bushings & LV Bushings: High/low-voltage terminal insulation and external circuit connections.

• Tap-Changer: Adjusts winding taps for voltage stabilization (on-load/off-load types).

• Buchholz Relay: Detects internal faults via gas accumulation (alarms for minor faults, trips for severe issues).

• Pressure Relief Device: Prevents tank deformation during internal explosions.

• Conservator Tank: Maintains oil levels, delays oxidation, and monitors oil condition via sight glass.

• Breather: Uses silica gel (blue when dry, pink when saturated) to absorb moisture from insulating oil.

5. Routine Inspection Checklist

• Monitor load current, voltage, oil level/temperature, and leakage.

• Inspect bushings for cracks/discharges and terminals for overheating.

• Verify uniform cooling operation, intact anti-explosion membranes, and open gas relay valves.

• Check breather silica gel color, grounding integrity, and structural stability (foundation, poles).