A new current-comparator-based high-voltage low-power-factor wattmeter

A current-comparator technique is applied to power measurements for obtaining a highly accurate high-voltage low-power-factor wattmeter. The instrument has two time-division-multiplier-type wattmeters. One wattmeter, in conjunction with a microcontroller, is used to provide automatic balancing of the quadrature component of the load current in a current comparator against a quadrature current from a current-comparator-based high-voltage quadrature reference source. The other wattmeter is used to measure the residual loss component of the load current. This new current-comparator-based high-voltage low-power-factor wattmeter has an order of magnitude improvement in accuracy and a lower measuring range in power factor than a previously developed instrument. It has an estimated uncertainty with respect to its readings of less than 0.25 percent at 0.01 power factor and higher, 0.5 percent at 0.001 power factor, and 5 percent at 0.0001 power factor.