Monitoring leakage currents from high-voltage devices

Apparatus for monitoring leakage currents from an insulator for a high voltage conductor to ground comprising:

• a transformer comprising a primary wire and a secondary winding,
• the secondary winding having a secondary resistance,
• the primary wire constructed and arranged to carry a leakage current from the insulator to the ground;
• an amplifier having an input connected to the secondary winding, constructed and arranged to produce an output signal proportional to the leakage current;
• and
• wherein the amplifier has a temperature-dependent input impedance adapted to produce a voltage rise substantially canceling the voltage drop due to the resistance for a range of temperatures.

Apparatus for monitoring leakage currents between a high voltage insulator and ground, comprising:

• a transformer having a primary wire and a secondary winding,
• the secondary winding having a secondary resistance,
• the primary wire adapted to carry a leakage current from the high voltage insulator to the ground;
• and
• an amplifier having input terminals connected across the secondary winding,
• the amplifier constructed and arranged to produce a voltage rise across the secondary winding substantially canceling a voltage drop across the resistance of the secondary winding and to output signal characteristic of the leakage current in the primary wire.

A method of monitoring a leakage current from an insulator for a high voltage conductor, comprising:

• directing the leakage current into a grounding wire;
• inducing a secondary current in a secondary winding having a resistance inductively coupled to the grounding wire;
• applying a voltage across the secondary winding to substantially cancel a voltage drop in the winding across the resistance;
• and
• processing the secondary current to provide an output signal characteristic of the leakage current.