A power detector (100, 200, 300, 400) comprising a first (110) and a second (115) bipolar junction/FET transistor. The first transistor (110) is arranged as a common base/gate transistor with its base/gate being biased by a bias voltage (V.sub.b1) and the second transistor (115) is arranged as a common emitter/source transistor with its emitter/source being grounded. The power detector also comprises a diode or current source connected to ground from the emitter/source of the first transistor (110), in which power detector an input port (105) is connected to the emitter of the first transistor (110) and to the base/gate of the second transistor (115), and an output port (125) is connected to the collectors/drains of the first (110) and second transistor (115), said collectors/drains also being connected to a DC supplier (V.sub.c) via a first resistor (130).

An apparatus and method for accurately detecting and monitoring leakage currents on porcelain and glass insulator disc strings is disclosed. The sensor apparatus includes a sensor unit configured to attach to a cap of an insulator disc string. The sensor unit includes a sensor disc configured to surround the cap and a housing connected to the sensor disc. The sensor disc includes a conducting lower disc set, a conducting upper disc set, an insulating disc set sandwiched between the upper and lower conducting disc sets, and a conducting mesh connected to a bottom of the lower disc set. The housing including electronics configured to measure and communicate leakage currents on an insulator disc. Leakage currents on a surface of the insulator disc are intercepted by the sensor disc and transferred to the housing for processing and communication by the electronics.