In-situ calibration of three different types of transformer loss measuring systems using a current-comparator-based load loss standard

The application of a current-comparator-based load-loss standard with adjustable loss tangent (or power factor) to the in-situ calibration of three different types of transformer loss measuring systems is described. The standard, driven by the test voltage through a low-loss high-voltage gas-dielectric reference capacitor, simulates an inductive load that can provide load currents up to 1000 A. It features three current ranges of 10 A, 100 A, and 1000 A and a direct-reading loss tangent (tan δ) adjustment in the range from 0 to 0.1 with five-digit resolution and an accuracy of better than 20 p.p.m. Adjustment of the loss tangent (or power factor) is achieved by comparing the load current, using the current comparator, with in-phase and quadrature reference currents derived from the test voltage