--- title: "Parts of a power transformer" subject: "Power Plant Equipment" chapter: 4 key: "semester_7/power_plant_equipment:power-transformer-parts" source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/power-transformer-parts site: BCT Engineering --- # Parts of a power transformer Power Plant Equipment · Chapter 4: Substation Equipments - Asked in: 2072 Chaitra, 6 marks; 2079 Baisakh, 4 marks (asked 2 times) - Video: [Different parts of a Transformer and its function #transformer](https://www.youtube.com/watch?v=TTbgWeeY2ds) — Let's Grow Up - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/power-transformer-parts - Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-4 ## Question Explain the function of various parts of a power transformer with a neat sketch. ## Short answer Core provides low-reluctance flux path; windings induce voltage; oil insulates and cools; conservator handles oil expansion; breather with silica gel dries incoming air; Buchholz relay detects gas from faults; radiators/fans dissipate heat; bushings insulate leads; tap changer adjusts turns ratio; OTI/WTI monitor temperature. ## Answer A **power transformer** transfers power between two voltage levels by mutual induction. Besides the core and windings it has many accessories for cooling, protection and voltage control. ```text HV bushing LV bushing conservator | | | | +---------+--breather | | | | | oil | (silica gel) vent _|__|________|__|_____+----+----+ ===> | oil-filled tank | Buchholz relay | +--------------------+ | | | core + HV/LV wndgs | |=== radiators | +--------------------+ | | tap changer OTI WTI | +---------------------------+ drain valve earthing ``` #### Parts and functions | Part | Function | |---|---| | Core (CRGO laminations) | Low-reluctance path for flux; laminated to cut eddy loss | | HV and LV windings (copper) | Carry current; induce voltage in ratio of turns | | Tank | Holds core, windings and oil; mechanical protection | | Transformer oil | Insulation and cooling medium | | Conservator | Takes up oil expansion and contraction; keeps main tank full | | Breather (silica gel) | Dries the air entering the conservator | | Buchholz relay | Gas-operated relay between tank and conservator; alarms/trips for internal faults | | Explosion vent / pressure relief valve | Releases sudden high pressure during severe internal faults | | Radiators, fans, pumps | Remove heat (ONAN, ONAF, OFAF cooling) | | Bushings | Bring winding leads out through the tank with insulation | | Tap changer (on-load/off-load) | Changes turns ratio to control voltage | | Oil and winding temperature indicators (OTI, WTI) | Show temperature; give alarm and trip, start fans | | Oil level indicator | Shows oil level in conservator | | Drain and filter valves | Draining, sampling and filtering oil | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does the Buchholz relay do? A. Gas-operated relay between tank and conservator that alarms or trips on internal faults B. Dries the air entering the conservator C. Changes the turns ratio on load D. Shows the oil level Answer: A. Internal faults produce gas that collects in the relay, giving an alarm or trip. (Key point: Buchholz relay) 2. Why is the core made of CRGO laminations? A. To carry the load current B. To give a low-reluctance flux path while cutting eddy-current loss C. To insulate the HV winding from earth D. To cool the oil Answer: B. Laminations are insulated from each other to reduce eddy loss, and CRGO steel offers low reluctance. (Key point: Core construction) 3. What is the purpose of the tap changer? A. Release pressure in a severe fault B. Remove heat from the oil C. Change the turns ratio to control voltage D. Bring leads out through the tank Answer: C. Changing the number of turns in service adjusts the output voltage. (Key point: Tap changer) 4. Which part releases sudden high pressure during a severe internal fault? A. Breather B. Radiator C. Oil temperature indicator D. Explosion vent / pressure relief valve Answer: D. It vents the gas pressure so that the tank does not burst. 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