Pre commissioning Tests for Oil Filled Power Transformer

Power Transformer is the most important equipment in any electrical power system.

As we know all Oil Filled Power Transformer gone through the Factory Acceptance test (FAT) but still we need to do some pre commissioning tests before energies or give power supply to the Oil Filled Power Transformer.

Pre commissioning Tests for Oil Filled Power Transformer

This article showing a list of pre commissioning test for Oil Filled Power Transformer.

Overall Check of The Oil Filled Power Transformer

  • Check the erection of Power Transformer is carried out as per the approved drawings.
  • The Power Transformer is cleaned, and all insulators are free from dust/dirt etc.
  • Check the Earthing has been properly done and connected to the Earthing grid with Main Tank, Marshalling box, Cable boxes (if equipped), Radiator & Fan Motor of the Power Transformer.
  • Check the High Voltage / Low Voltage Neutral grounding properly connected to two earth pits.
  • Check Oil Level in

Main Tank



Plain Oil Level gauge

High Voltage Bushings

Low Voltage Bushings

  • Check Oil Temperature Indicator (OTI) and Winding Temperature Indicator (WTI) pockets are filled with oil.
  • Check for fire protection system & emulsifier operation (if equipped).
  • Check bushing test tap caps are fully tightened
  • Check the horn gaps (if equipped) are adjusted as specified in the manufacturer’s drawing.
  • Check Silica get in the Main & OLTC breather is active and blue in colour.
  • Oil is filled in the oil cup of breather up to level marked
  • Lock of Buchholz relay, oil surge relay and MOG released, keep in service position.
  • Unused secondary cores of Bushing CT have been shorted if equipped.
  • Check CT saturation point is formed correctly and earthed at one end only as per scheme.
  • Terminal of control cables in marshalling Box completed as per drawings, terminals are tightened properly, and unused holes of gland plates are sealed properly.
  • Cable tags, ferrules are provided for all cores
  • Cable are properly dresses and clamped
  • Check OLTC operation in Local/Remote/ Auto Mode and direction of rotation.
  • For off load tap changer, the tap switch is locked properly in desired tap position
  • Check the operation of space heaters in marshalling box in Auto/ Manual mode
  • Check the operation of space heater in RTCC in auto / manual mode.

Transformer Oil Filtration

    • Break Down Voltage on transformer oil
    • Dissolved Gas Analysis

Insulation Resistance Measurement

  • High Voltage to Earth
  • Low Voltage to Earth
  • High Voltage to Low Voltage

Turns Ratio Test for all Tap position

  • Applied HV Volts
    • 1U1V
    • 1V1W
    • 1W1U
  • Measured LV Volts
    • 2U2V
    • 2V2W
    • 2W2U
  • Ratio Calculated
    • 1U1V/2U2V
    • 1V1W/2V2W
    • 1W1U/2W2U
  • Actual Ratio

Magnetic Current Test for all Tap position

    • Applied HV Volts
      • 1U1V
      • 1V1W
      • 1W1U
  • Measured HV Current in mA
    • 1U
    • 1V
    • 1W

Magnetic Balance Test

  • 1U1N = 1V1N + 1W1N
  • 1V1N=1U1N+1W1N
  • 1W1N=1U1N+1V1N

Vector Group Test

Winding Resistance Test for all Tap Position

  • High Voltage Side
    • Primary Winding Resistance
      1. 1U1V
      2. 1V1W
      3. 1W1U
  • Low Voltage Side
    • Secondary Winding Resistance
      1. 2U2V
      2. 2V2W
      3. 2W2U

Functional Checks

Oil Temperature Indicator – Alarm

Oil Temperature Indicator – Trip

Winding Temperature Indicator – Alarm

Winding Temperature Indicator – Trip

Buchholz- Alarm

Buchholz- Trip

On Load Tap Changer Buchholz- Alarm

On Load Tap Changer Buchholz- Trip

Low Oil Level- Alarm

Pressure Relief Valve – Trip

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