Capacitance & Tan Delta Analysis

Measurement of winding capacitance can indicate problems such as thermal deterioration or saturation of the insulation by moisture within the bulk of insulation. Capacitance tip-up test is the indirect partial discharge test and is closely related to tan delta tip-up.

Dissipation factor or Tan delta provides an indication of the dielectric losses within the insulation. Certain deterioration such as thermal deterioration and moisture absorption will increase these losses. Power factor tip-up is also an indirect way of determining partial discharge occurring.

Tan d and Capacitance will be measured both below and above discharge inception voltage. Capacitance and tan delta measurements will be performed using a Tan delta measurement instrument.  Maximum test voltage will be VL  /Ö 3  r.m.s (VL  – Machine Line Voltage ).

Test will be performed on each phase individually by shorting other phases to ground. Test will be performed on slot region and end winding region separately.

The results will be analyzed in order to assess the winding insulation with regard to:

  • Extent of De-lamination (if any)
  • Condition of the corona protection shield
  • Aging of Insulation
  • Contamination