Digital Measurement of Active and Reactive Power

Accurate measurement of active and reactive power is becoming increasingly important as problems of process-energy balance become more complicated and cost savings receive more critical attention. In large electrical systems, very special attention must be given to these measurements to maintain losses at a minimum. In the modern panoramic control unit with its attendant off-limit alarms, digital display of these power values is highly desirable. However, because of the nonlinearity of one of the three variables (the product of which defines the power value), direct digital measurements present difficulties. Conventional solid-state digital voltmeter equipment allows the construction of voltage and resistance parameters in a straightforward manner. The third parameter, the sine or cosine of the electrical angle, is a nonlinear function and, therefore, requires more elaborate measuring equipment.