Service
Tap changer (OLTC) repair
Repair and maintenance of on-load (OLTC) and de-energized (DETC) tap changers: contacts, mechanism, oil and acceptance testing.
The tap changer is the most mechanically-stressed part of a transformer, and a frequent source of faults. TEVKO repairs and maintains on-load (OLTC) and de-energized (DETC) tap changers — contacts, diverter, mechanism and oil — and validates the work with turns ratio and winding resistance testing.
The tap changer adjusts the transformer's ratio to regulate voltage, and because it physically switches under load (OLTC) it accumulates more mechanical wear than any other component. Worn or carbonized contacts, a sluggish or mis-timed diverter, degraded changer oil and mechanism wear are common faults — and a failing tap changer can take the whole transformer out of service.
Repair covers the full assembly: inspection and replacement of fixed and moving contacts, service of the diverter switch and selector, mechanism adjustment and timing, and replacement or filtering of the changer oil (which degrades faster than the main-tank oil because of the switching arcs). De-energized tap changers (DETC) are inspected and serviced as well, since contacts left in one position for years can oxidize and develop high resistance.
TEVKO repairs tap changers of any manufacturer and validates the work with the electrical protocol — turns ratio at every position and winding resistance — under IEEE C57 and IEC 60076, with Omicron and Megger instrumentation. The acceptance test confirms the changer makes contact correctly at all positions before the transformer returns to service, documented in a protocol.
Scope of tap-changer repair
OLTC repair
Contacts, diverter, selector, mechanism timing and changer oil of on-load tap changers.
When it applies: Contact wear, mis-timing or faults found in diagnostics.
DETC service
Inspection and service of de-energized tap changers to clear oxidized, high-resistance contacts.
When it applies: Changers left in one position for years, abnormal winding resistance.
How we execute the repair
Diagnosis
Turns ratio and winding resistance to localize the changer fault before opening.
Repair
Contacts, diverter and mechanism serviced; changer oil replaced or filtered.
Adjustment
Mechanism timing and position alignment set to specification.
Acceptance testing
Turns ratio at all positions and winding resistance, documented before return to service.
Frequently asked questions — tap changer (oltc) repair
Why do tap changers fail so often?
Because the on-load tap changer (OLTC) physically switches under load, it accumulates more mechanical wear than any other transformer component. Worn contacts, a mis-timed diverter, degraded oil and mechanism wear are common — and can take the whole transformer out of service.
What does an OLTC repair include?
Inspection and replacement of fixed and moving contacts, service of the diverter and selector, mechanism adjustment and timing, and replacement or filtering of the changer oil. De-energized tap changers (DETC) are inspected and serviced as well.
Why does the tap-changer oil degrade faster?
Because the switching arcs in an on-load tap changer carbonize and contaminate its oil faster than the main-tank oil. That is why the changer compartment oil is serviced or replaced as part of the repair.
How is a tap-changer repair validated?
With the turns ratio test at every tap position and winding resistance, under IEEE C57 and IEC 60076. The test confirms the changer makes correct contact at all positions before the transformer is re-energized.
Tap changer (OLTC) repair in images
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