Abstract: A method of testing transformers and other inductive devices comprises monitoring displacement of a conductor in a winding by injecting a high frequency alternating signal into the conductor while a supply-frequency alternating current is flowing in the conductor and subsequently observing the modulation of the high frequency signal resulting from displacement of the conductor. The high frequency signal has a frequency in the region of the resonance frequency of stray capacitances and inductances exhibited by the winding of which the conductor forms a part. Both the magnitude and the frequency response of the modulation of the high frequency signal may be monitored to determine parameters relating to the displacement of the conductor.

Abstract: In a method of testing electrical equipment having inherent stray impedances while the equipment is connected to a conductor a swept sinusoidal signal is injected and the response of the equipment to the signal analysed. In order to prevent current flow within the conductor affecting the results of the analysis a nulling signal is injected to nullify the current which would otherwise flow in the conductor as a result of the application of the swept-frequency signal. In a preferred embodiment the phase and amplitude of currents in the conductor and in the line through which nulling signals are injected are compared. The phase and amplitude of the nulling signal are adjusted in accordance with the result of these comparisons.