The Rogowski Coil is a transducer used for measurement of the high frequency current pulses generated by partial discharge activity in the stator insulation structure.
The design and termination of the Rogowski Coil are such that it acts as a current transformer at high frequencies but has very low sensitivity to power frequency current.
The high frequency current pulses are significantly attenuated whilst travelling through the stator winding and associated cable system.
It is therefore desirable that the Rogowski Coil be located as near as possible to the source of the discharges, i.e. as near as possible to the H.V. terminal of the phase winding.
The low-level signals, which are output from the Rogowski Coil, are routed to a high-gain amplifier which has an appropriate frequency characteristic to accept the discharge pulse spectrum but to reject the power frequency and the harmonics associated with the machine operation.
The discharge signal pattern is captured on a digital recorder, together with the power frequency phase voltage waveform. Subsequent computer assisted analysis is carried out using software specially designed for this purpose. A permanent record is stored to assist future trending analysis.
The charge content of a discharge pulse is a measure of the energy content of the discharge and the measured pulses are calibrated in terms of charge content by a comparison technique.
A train of low-voltage pulses of known charge content is injected into an H.V. terminal of the machine selected for calibration, whilst the machine is shut down, and the response of the Rogowski Coil is recorded.