What Is the Tap Selector in an OLTC?
Quick answer — The tap selector is the part of the OLTC that makes the connection to each winding tapping, while the diverter (or vacuum) switch handles the actual current interruption and transition. The selector moves the connection to the desired tap, and the diverter bridges the transition so the current is never interrupted. The selector contacts do not interrupt current but must carry it and be well-insulated. It is a key wear and maintenance point.
Contents
What does the tap selector do in an on-load tap-changer?
Its role
The selector connects the tap-changer to the selected winding tapping; the diverter switch then makes the transition to the new tap under load.
How it works
The selector is moved to the required tap (usually off- or on-load but without interrupting the load), and the diverter (oil or vacuum) carries out the current-transfer transition with a resistor or reactor.
Maintenance
The selector contacts must be checked for wear, and the diverter and its oil (including DGA for acetylene) serviced; it is a leading wear point of the OLTC.
References & standards
- IEC 60214 (tap-changers)
- IEC 60076-1
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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