Current transformer and electrical monitoring system

A calibration method for a current transformer comprising a core with a central opening, at least two conductors extending through the central opening, and a winding on the core, the calibration method comprising:

• transmitting currents through the at least two conductors;
• obtaining a measured differential current through the winding;
• and
• changing a spatial relative position of the at least two conductors and turns of winding with respect to the core to obtain a target reading.

An electric monitoring system, comprising:

• a current transformer comprising:
• a magnetic core having a closed central opening;
• at least two conductors of the system to be measured extending through the central opening and positioned symmetrically within the magnetic core;
• and
• at least one set of winding turns wound around the core in a balanced configuration with respect to the at least two conductors;
• and
• a processing module for receiving a measured differential current from the at least one set of winding turns and monitoring the measured differential current.

An insulation condition monitoring method for a rotating electric machine, the method comprising:

• calibrating a current transformer by transmitting currents with the same current amplitude and reversed direction through two conductors extending through a central opening of a magnetic core, receiving a measured differential current from a winding on the core, and changing a spatial relative position of the at least two conductors and turns of the of winding with respect to the core to obtain a target reading;
• measuring a first set of values for an instantaneous differential current using the calibrated current transformer and an instantaneous phase voltage during operation of the machine;
• calculating a second set of values for a phasor current and a phasor voltage based upon the first set of values of the instantaneous differential current and the instantaneous phase voltage, respectively;
• calculating an angular relationship between the phasor current and phasor voltage;
• and determining the insulation condition based on the angular relationship.