Service and Tests of Transformer Online-Tap-Changer

The transformer On-line Tap Changer (OLTC) is a critical component of large power transformers and the only one containing moving parts. A OLTC typically have over 300 parts and servicing it requires a certified trained professional.


MVA is the only Israeli company certified to work on Huaming and MR compatible OLTC


 The role of an OLTC is to change the voltage ratio of the transformer while the transformer is energized (hence on-line). This is used mainly in regulating the voltage to varying loads. In special transformers the OLTC is sometime used to regulate oven temperature via voltage change.

Servicing an OLTC is performed after a manufacturer-specified number of operations or number of years in operation (the earlier of the two). Every OLTC is equiped with an operation counter and part of the scheduled yearly maintenance includes recording the number of operations.

Usually common OLTC devices require maintenance every five years or above 50,000 operations – the earlier of the two

Picture gallery from one of MVA OLTC maintenance

OLTC are roughly divided into two types, depending on the arc-suppression medium: oil immersed contacts and vacuum contacts. There are also dry transformer OLTC but they are very few of them in the country..

סוגי מחליף דרגות מקוון OLTC
OLTC Types

 

Tests and Checks on Transformers OLTC

  • Oil draining from the diverter switch compartment.
  • Removal of the diverter switch using a specialized crane and transfer to on-site service station.
  • Full check of the energy-charging/discharging system, transfer system, contact and engagement system and replacement of worn parts as necessary.
  • Visual inspection and thickness measurements of all contacts (in oil immersed) and replacement as necessary.
  • Static resistance test of contacts and transfer resistors.
  • Dynamic resistance check of the OLTC in operation.