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Annual service of Substations

For the proper and safe operation of a HV/MV substation, the following preventive maintenance tasks shall take place, either on the first time on commissioning or on an annual service base: 

  • Optical / thermal checks
  • Mechanical / electrical checks
  • Secondary protection checks by network fault simulation methods through voltage and current injection
  • Primary Injection checks for:
    • Current transformers
    • Voltage Transformers
    • Power transformers
    • Switches

Diagnostics measurements of power transformers

The power transformer (T/F) is the core of a substation. High purchase costs and long delivery times lead to capital and income losses. The diagnostics mentioned below should be carried out depending on various circumstances as described

Before the 1st electrification

  • Confirmation of operation status
  • Confirmation of proper transport and installation
  • Guarantee
  • Development of the proper state for future measurements


  • Confirmation of operation status
  • Detection of problems in an early stage
  • Targeted maintenance / Decision on corrective actions 

After a fault

  • Decisions on energizing / repair / replacement
  • Tracing and localizing  the cause of the fault

Diagnostic checks of Transformers

  1. Dissipation Factor (tanδ)
  2. Transformer ratio for each TAP position
  3. Excitation current
  4. Winding Resistance for each TAP position
  5. Short Circuit Impedance Test

All of the above mentioned measurements are performed according to the international standards IEC 60076, IEEE 62-1995, IEEEC57-12-90-1999 etc.

Additional Transformers’ checks

  • Oil level check (for oil type Transformer)
  • Oil leakage check (for oil type Transformer)
  • Core status check (for oil type Transformer)
  • Replacement of silica gel (for oil type Transformer)
  • Degassing of T/F body and bushings (for oil type Transformer)
  • Oil sampling for test and chemical analysis (for oil type Transformer)
  • Resin check and magnetic core (for dry type Transformer)
  • Cleaning the internal of the Transformer windings (for dry type Transformer)
  • Endoscopic check of the Transformer windings (for dry type Transformer)
  • Check and Cleaning of the MV & LV cables in the Transformer area
  • Check and maintenance of Transformer  Bushings
  • Temperature check of Transformer
  • Ventilation Check  of Transformer
  • Oil tank check  for leakage (for oil type Transformer)
  • Mounting Check of Transformer
  • Outside cleaning of Transformer
  • Transformer’s Isolations Check
  • Check of Transformer’s protection systems and operational testing
  • Measurement of the earthing of the neutral point and of metallic parts
  • Tightening checks
  • Isolation measurement of the MV cables