A Current-Comparator-Based Wattmeter for High Voltage Power Measurements at Very Low Power Factors

A current-comparator technique for obtaining a wattmeter for accurate high voltage power measurements at very low power factors is described. The quadrature component of the load cturrent is automatically balanced in the current comparator against a quadrature current obtained from a slave supply, thereby reducing the stringent high accuracy requirement of the wattmeter when used for measuring power at very low power factors. The current-comparator-based wattmeter has an estimated accuracy with respect to its readings of better than 3 percent at 0.001 power Factor, 1 percent at 0.005 power factor, and 0.5 percent at 0.01 power factor and higher. It features an internal high-voltage active-divider and displays to indicate source voltage, current, power factor, and reactance of the load, in addition to the power.