What Is the OLTC Oil and How Is It Maintained?
Quick answer — The OLTC has its own (often separate) oil in the diverter compartment. It is tested for the same condition (BDV, moisture, DGA) but the focus is on acetylene, which indicates contact arcing from a diverter/contact fault. The oil is changed on a schedule and when the acetylene rises. The tap-changer oil is a key maintenance point because an OLTC fault is a leading cause of transformer trips.
What is the on-load tap-changer oil?
Why separate oil
The diverter switches are in their own oil compartment so the arcing products are kept from the main oil, and the OLTC oil is tested and changed separately.
What to test
BDV, moisture and DGA, with the acetylene level indicating contact arcing. A rise in acetylene means the contacts/diverter need attention.
Maintenance
Change the oil and filter it per the schedule, check the contacts, and trip on the DGA rise to avoid a fault.
References & standards
- IEC 60214 (tap-changers)
- IEC 60599
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
Related components
Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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