Capacitance And Tan Delta On Rotating Machines

Apparatus insulation system has measurable electrical parameters such as Capacitance, Dielectric loss, and Power Factor, in addition to other less well-known characteristics. By detecting changes in these important electrical characteristics, failure hazards can be revealed, there by preventing loss of service by permitting orderly repaired or reconditioning of defective insulation. In this Power Factor / Tan d test, the measured quantities are dissipation factors (Tan d or PF), Tip up PF (D Tan d), capacitance and dielectric power loss.
Principle:
Insulation of High Voltage apparatus is selected in part for their low dielectric losses (i.e., low power factor). An insulation specimen having a low P.F as measured between its terminals can be represented equally by the parallel circuit of capacitance Cp and resistance Rp (Fig: 1(a)). Mathematical formulas have been derived to show the correlation between the parallel network, Cp & Rp. For a specimen with zero P.F (i.e., no dissipated losses), Rp is infinity.
The equivalent circuit, on which the Doble Type M circuit in the M2H test set is based showing the various parameters of currents with respect to the applied test voltage E
Watts = E * I t * Cos (q)