Patent ID: 7106078

Claim:
A method for measuring resistance of at least one winding of a transformer utilizing a test current with a maximum test current less than either a core saturation current of a transformer whose at least one winding is having its resistance measured or a current limit of a source of electrical energy used for measuring of the resistance comprising: selecting at least one transformer winding for measurement of winding resistance of the at least one winding; connecting the at least one winding to the source of electrical energy; increasing driving power from the source of electrical energy applied to the at least one winding until current in the at least one winding provided from the source of electrical energy reaches a predetermined level which is below a core saturation current level of the transformer whose at least one winding is having its resistance measured or a current limit of the power source of electrical energy; controlling the power from the source of electrical energy applied to the at least one winding to maintain the predetermined current flowing through the at least one winding over a time period sufficient to cause a L di/dt contribution to a voltage drop across the at least one winding to decrease below a threshold level; and calculating the resistance of the at least one winding from a measured current flowing through the at least one winding and a voltage drop across the at least one winding which are measured after the time period.