OLTC diagnosis

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OLTC diagnosis

Electrical field tests:

  • Exciting current; exciting current tests have the ability to detect a myriad of transformer tap changer problems (DETC and OLTC), including: misalignment, coking and wear of contacts, loose moveable contacts, improper wiring from the tap winding to the OLTC, reversed connections to the preventative autotransformer (PA) of an OLTC, open- or short-circuited turns or high resistance connections in the OLTC PA, series autotransformer or series transformer, and more.
  • DC winding resistance; a DC winding resistance test is used to detect any problem which impacts the integrity of the current carrying path between terminals of a winding, including the tap changer.  It is particularly adept in identifying partial open-circuited conditions.
  • Dynamic winding resistance; a dynamic winding resistance test is the measure of the DC current and resistance (as a function of time) as the OLTC changes tap position.  It is particularly effective at identifying problems with the diverter switch, diverter switch contacts and transition resistors of a resistive style OLTC.  Generally, the test assesses the integrity of any component which makes, carries or breaks current during an OLTC operation.
  • Sweep frequency response analysis (SFRA); the mechanical integrity of the tap windings and their leads are assessed in the mid- to upper-frequency ranges of an FRA test on a transformer

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