Transformer Testing

Transformer Testing

Transformer testing is crucial for mitigating the risk of operating failure. Due to its static nature the power transformer can be regarded as a very reliable unit. Nevertheless there is a possibility of failure because of internal faults as well as being subjected to stresses from external sources which could cause the internal fault condition.

We provide the the following transformer testing (not limited to):

  • Turns Ratio Testing
  • Pressure Tests (AC)
  • Voltage Withstand Testing
  • Vecta Group
  • Bucholz Relay Testing
  • Dissolved Gas Analysis (DGA)
  • Tap Changer Resistance
  • Voltage Output
  • Phase Rotation

Faults which are internal in origin are:

  • Failure of insulation of windings, laminations or core bolts; from damage in erection; inadequate quality or brittleness through ageing or overloading.
  • Failure of the winding insulation resulting in inter-turn or earth faults. The possibility of a fault between phases is very small. Failure of the lamination or core-bolt insulation leading to increased eddy current causing heating of the core.
  • Oil deterioration which could be caused by poor-quality oil; penetration of moisture; decomposition because of overheating or the formation of sludge by oxidation as a result of bad electrical joints.
  • Loss of oil by leakage.
  • Inability to withstand fault stresses. This may be due to poor design or where repeated heavy currents set up severe mechanical stresses which cause packing and wedges to be loosened and finally shaken out.
  • Tap changer faults.
  • Cooling system faults.

External conditions which could cause faults to develop are:

  • Heavy through faults. The high current would produce severe mechanical stress in the transformer windings and insulation.
  • Overloads. This would result in overheating and also produce mechanical stress in the windings and insulation. Although these would be much less than under fault conditions, they would be of much longer duration.
  • Switching surges. These surges, which may be several times the rated system voltage, have a very steep from and therefore a high equivalent frequency. This causes stress in the end of the winding and a risk of a partial winding flash-over even though the insulation is usually reinforced in this area.
  • Lighning. This is only a risk where the transformer is connected to an overhead line and is usually protected by arrestors or spark gaps.
  • Pink Condition. This whereby the cooling fins on a transformer radiator fail due to rusting through due to lack of regular paint treatments.

For more information about how C&P can help with your Transformer Testing, please call 01792 897002 or email

For further information about C&P’s High Voltage and other Integrated Electrical Services, please click on one of the links below: