We have expert and experienced engineers for servicing and repair of NGEF OLTC.

What is NGEF OLTC complete details?

   The on-load tap changer is used to change the tapping connection of the transformer winding to change the voltage ratio while the transformer is still in service without interrupting the load .OLTC comprises two major components, the tap selector and the NGEF diverter switch. The tap selector selects the tapping and its electrical contact-ngef transformer oltc-on-load-tap-changers are designed to carry the rated current of the transformer but not to make or break this current. The diverter switch, however, needs to be designed to carry, make and break the load current in circuits previously selected by the tap selector switch. During the operation of diverter switch the transition resistors bridge the tap in use and the tap next to be used, thereby limiting the circulating current due to the inter-tap voltage.

   The OLTC motor drive mechanism is used to control the OLTC to increase the tap operation or decrease tap,it consists of motor, reduction gear box,planetary gear box and motor drive panel.

Why OLTC servicing is required?

   During operation arcing at diverter switch contacts results in carbonisation of oil in the diverter switch tank and wear and tear of the mechanical parts of the diverter switch.To ensure normal operation of OLTC diverter switch should be regularly inspected ,overhauled and repaired.The carbonised oil should be replaced with new oil after filtration & checking BDV value.


  • Maintenance of On load & Off load tap changers(NGEF ,TRAFOTECH ,AEG and MR GERMANY make OLTC’s).
  • Overhauling of In-Tank & Flange mounted OLTCs.
  • Diverter switch repair and overhauling.
  • Selector switch repair and overhauling .
  • Motor drive panel overhauling and rewiring.
  • Conversion from Off circuit tap changer to On load tap changer.
  • Supply of all critical spares for OLTC.
  • Fault diagnosis & solutions.