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    Home > Product > Power Systems > Power Transformer
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Power Transformer

A power transformer is a static device that transfers electrical energy between circuits without any moving parts, relying instead on electromagnetic induction. It operates on the principle of electromagnetic induction to efficiently adjust voltage levels for power transmission or distribution. The transformer includes two or more wire coils linked by a common magnetic core.

Typically, a power transformer has two coils—referred to as the primary and secondary windings—wound around a central laminated iron core. This core, constructed from stacked steel laminations, concentrates and directs the magnetic flux generated by the current flowing through the windings. The complete magnetic and electrical assembly is enclosed within a steel tank filled with insulating oil, which provides both electrical insulation and cooling for large power transformers during operation. In addition, larger utility transformers may include auxiliary components such as bushings, cooling ducts, tap changers, and protection circuits, enabling voltage adjustments and enhancing operational flexibility during power transmission.

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Types of Power Transformer

1. Classification by Application:

  • Step-up transformer – Used to increase low voltage to high voltage for long-distance transmission.
  • Step-down transformer – Used to decrease high voltage to low voltage to meet grid requirements.
  • Distribution transformer – Used in distribution networks to meet the needs of industrial and agricultural production.
  • Interconnecting (or coupling) transformer – Used to connect two substations or networks.
  • Auxiliary (or station service) transformer – Used specifically for industrial and mining enterprises or in-plant power supply.

2. Classification by Number of Phases:

  • Single-phase transformer – Used for single-phase loads and as part of a three-phase transformer bank.
  • Three-phase transformer – Used for step-up or step-down voltage applications in three-phase systems.

3. Classification by Winding Configuration:

  • Autotransformer – Used for interconnecting extra-high-voltage (EHV), large-capacity power systems.
  • Two-winding transformer – Used to connect two different voltage levels.
  • Three-winding transformer – Used to connect three different voltage levels, typically applied in regional substations of a power system.

4. Classification by Winding Material:

  • Copper-wound transformer
  • Aluminum-wound transformer

5. Classification by Voltage Regulation Method:

  • Off-circuit (or off-load) tap changer transformer – Tap changing is performed only when the transformer is de-energized.
  • On-load (or on-circuit) tap changer transformer – Tap changing is performed while the transformer is energized.

6. Classification by Core Form:

  • Core-type transformer
  • Shell-type transformer

7. Classification by Cooling Method:

Oil-immersed transformers:

  • Oil-immersed self-cooled (ONAN)
  • Oil-immersed air-blast / forced-air cooled (ONAF)
  • Oil-immersed water-cooled (OFWF or ONWF)
  • Forced oil circulation (OF or OD depending on flow direction)

Dry-type transformers:

Rely on natural air convection for cooling; used in locations where oil is not permissible.

Gas-filled (or gas-insulated) transformers:

Use a special chemical gas, such as SF₆ (sulfur hexafluoride), instead of transformer oil for insulation and heat dissipation.

Power Transformer Applications

Power transformers are essential for voltage conversion across various applications, including:

  • Substations – Step-up transformers raise voltage for long-distance transmission; step-down transformers reduce voltage for local distribution.
  • Copper Mines – Special isolated transformers with enclosed coils prevent arcing in hazardous, explosion-prone underground environments.
  • Power Plants – Station service transformers adjust generator output to match transmission voltage levels.
  • Residential Distribution – Pole-mounted or pad-mounted transformers reduce distribution voltage to safe levels for home use.
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