Maintenance and repairs

Maintenance of on-load tap-changers

More than 150 service fitters in 15 service centers worldwide carry out more than 4,000 maintenance processes a year Alongside all the variants we have ever produced, we also maintain on-load tap-changers from Siemens and Trafo Union, tap changers produced under license and numerous external makes. Our technicians have the equipment they need for this and also take measurements on the transformer. We can of course combine maintenance with repair work on a transformer.

Maintenance of on-load tap-changers, yes – but when?

Maintenance criteria for on-load tap-changers are the number of operations or the maintenance interval, whichever is reached first. These criteria vary according to type and application. You will find the maintenance criteria on a label on the inside of the door of the housing in the case of tap-changers that are equipped with a TAPMOTION® ED motor drive. Information for older on-load tap-changers can be found in the respective user manuals. We would be glad to help if you have any other questions. Just tell us the serial number of the tap-changer. You can find this easily on the type plate attached to the door of the motor drive. Also let us know the current number of switching operations. This can be read off from the operation counter on the motor drive.

Tips for servicing

Above all preparation

A service should be prepared well. This saves both time and money. Simply use our checklist. It contains all the information you need. Our colleagues often travel to you by plane or with our mobile service station in Germany and its neighbouring countries. This is a workshop on wheels with which we can offer you a complete on-load tap-changer service. All you have to do is open the transformer station and disconnect the transformers. The rest you can leave to us.

Sometimes is not possible to carry out a service on the spot. That is why we recommend our perfectly equipped service workshop in Regensburg for larger repairs. If required we can even manufacture single parts for old on-load tap-changers here. It goes without saying that the parts are thoroughly tested before they are dispatched. We have a permanent stock of over 15,000 parts in Regensburg. In emergencies these are sent by express delivery to places all over the world.

Scope of services

  • Dismounting and mounting of the on-load tap-changer insert
  • Cleaning and inspection of the mechanical parts
  • Visual inspection of insulation distances of the on-load tap-changer insert and the oil compartment
  • Parts replacement
  • Replacement of the switching oil (unused oil with a breakdown voltage of > 50 kV/2.5 mm, in compliance with IEC 60156)
  • Determination of the contact wear
  • Measurement of the transition resistors
  • Inspection of the motor drive, drive shaft and protective relays
  • Functional test


Why OLTC Maintenance

  • OLTC switching principle conventional OLTC types (switching operation in Oil)
  • What happens inside the OLTC while switching operation?
    à Switching Arc / Arcing in Oil (Contact wear, Carbonization of the switching oil, Oil pullotion,…)
    à High Speed Switching Operation - Mechanical Stress (Springs, Braided contact leads, Screw connections, Energy accumulator,…)
  • OLTC Maintenance Criteria
    à Time of operation or Number of switching operations - whichever occurs first


Scope of work / qualified premium service (PSP Certified)

  • Dismounting and mounting of the on-load tap-changer insert
  • Cleaning and inspection of the all parts
  • visual, electrical and mechanical tests & measurements
  • checking of insulating material (insulation distances of the on-load tap-changer insert and the oil compartment)
  • Parts replacement
    à worn out parts
    à screws and locking pieces
    à gaskets and sealing rings
  • Determination of the contact wear
  • Measurement of the transition resistors
  • Inspection of the motor drive, drive shaft and protective relays
  • assembly, testing and commissioning
  • Replacement of the switching oil (unused oil with a breakdown voltage of > 50 kV/2.5 mm, in compliance with IEC 60156)
  • maintenance approval report