200Kva Three Phase Distribution Transformer

The main components of a 200 KVA, 11kV/433V, 3 Phase, 50 Hz, Aluminium Wound, Oil cooled Distribution Transformer can be categorized into core functional parts and external fittings for operation and safety.

 

Core Components

These components are essential for the transformer's basic function of voltage transformation.

• Core (Iron Core): Made of high-quality, cold-rolled silicon steel laminations to provide a low-reluctance magnetic path and minimize energy losses. The laminations are stacked to reduce eddy current losses.
• Windings (Coils): Consist of high-quality aluminium conductor wires, wound around the core limbs.
• High-Voltage (HV) Winding: The 11 kV primary winding, typically connected in a Delta configuration.
• Low-Voltage (LV) Winding: The 433 V secondary winding, typically connected in a Star configuration to provide a neutral point for single-phase loads.
• Transformer Oil (Insulating Oil): A highly refined mineral oil that serves two critical functions: electrical insulation and heat dissipation (cooling). It immerses the core and coil assembly within the tank.
• Main Tank: The robust steel enclosure that contains the core-winding assembly and the transformer oil. It is designed to withstand internal pressure and protect the components from the external environment.

 

External Fittings and Accessories

These parts are vital for the monitoring, protection, and maintenance of the transformer.

• Oil Conservator (Conservator Tank): A small auxiliary tank mounted above the main tank. It accommodates the expansion and contraction of the transformer oil due to temperature variations, ensuring the main tank remains completely filled with oil.
• Breather Unit (Breathing Apparatus): Connected to the conservator tank, it contains silica gel to absorb moisture from the air entering the transformer during oil contraction, thus preventing moisture from contaminating the oil and degrading insulation.
• Bushings: Insulated terminals (typically porcelain or polymer) that bring out the high-voltage and low-voltage winding connections through the tank cover or sides. These isolate the live conductors from the earthed tank.
• Radiators (Cooling Tubes): External cooling fins or tubes connected to the main tank. The transformer oil circulates through these to dissipate heat into the atmosphere (ONAN cooling - Oil Natural Air Natural).
• Tap Changer (Off-load): A mechanism, usually accessible externally, used to adjust the turns ratio of the transformer in steps to fine-tune the output voltage to the required level. For this size, it's typically an off-load type, meaning the transformer must be de-energized before adjustment.
• Explosion Vent / Pressure Release Device: A safety device designed to release excessive pressure built up inside the tank during a severe internal fault, preventing a catastrophic explosion.
• Oil Level Indicator: A gauge mounted on the conservator tank to monitor the level of the transformer oil.
• Temperature Indicators: Thermometers (Oil Temperature Indicator OTI and sometimes Winding Temperature Indicator WTI) to monitor the operating temperature of the oil and windings.
• Rating Plate: An aluminium plate fixed to the tank, detailing all the key specifications and technical data of the transformer (e.g., kVA rating, voltages, winding material, standards, serial number, etc.).
• Grounding/Earthing Terminals: Points provided for safely earthing the transformer tank.
• Lifting Hooks: Provided on the tank and conservator for ease of transportation and installation.
• Lightning Arrestors: External surge protection devices, often installed near the HV bushings, to protect the transformer from high voltage surges caused by lightning strikes.

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