Compensation for voltage variations causing wattmeter errors - using braking magnet affecting wattmeter disc according to supply voltage

摘要

The compensation method is applicable to electric supply wattmeter for errors caused by variations in the supply voltage using a compensating braking magnet associated with the wattmeter disc. A rotating disc (2) is mounted on a vertical shaft (4) beneath a magnetic circuit (1) through which a field is produced by a voltage coil, and above a further circuit (3) activated by a current coil. A magnetic bearing (5) supports the shaft (4). A compensating braking magnet (8) is arranged at the periphery of the disc and the operation of this is such that the Thompson force on the shaft is offset by a braking force dependent on the supply voltage to produce the compensation required.