Abstract :
The paper describes null methods of measuring the ratio and phase displacement of two alternating voltages. The methods are particularly applicable to high voltages and are discussed in connection with the testing of power transformers and potential transformers. An important feature is the use of a capacitance potential divider in place of the resistance typeof potential divider which has hitherto been used. Capacitance potential dividers possess considerable advantages over those of the resistance type from the point of view of simplicity and low cost of equipment and ease of operation, while the accuracy can be made as high as is desired. The maximum voltage at which the use of resistance potential dividers is practicable is of the order of 30 kV, whereas there is practically no limit to the voltage at which capacitance potential dividers can be used. The theory of a method of measuring the ratio and phase displacement of transformers is given and the operation of the method is illustrated by a test on a 66 000-volt potential transformer. Suggestions are made for the developing of an apparatus for routine industrial testing and it is pointed out that a robust construction and adequate safety to the operator could be secured while retaining ample accuracy for commercial purposes. The use of a tapping on the secondary winding of a high-voltage testing transformer for the purpose of operating a wattmeter or voltmeter is considered, anda method of determining the ratio and phase displacement of the full and fractional voltages is given. The testing of high-voltage potential dividers is also briefly considered.
