Optical decoupling in measurements of corona currents

The paper deals with the measurements of the corona parameters in a linear eight-electrode pin-to-plane array generator. The pins were made of tungsten, arranged in one row of eight, and were biased negative. The ground plane was flat, made of aluminum, and incorporated brass current-sensing electrodes, insulated from the anode. The anode was grounded, and each of the sensing electrodes was connected to an operational amplifier based current-to-voltage converter with sensitivity of R=1V·μA^-1. The output of each of the converters was connected to a scanner and a microcontroller, which was supported by a personal computer, that provided graphical user interface, data storage, and the RS232C link needed to communicate with the microcontroller. Corona current was measured simultaneously on the eight corona pins; at the same time the value of the voltage applied to the generator and the total current supplied to the array were measured. The measurement of the total current was performed by a transmitter module, floating at a voltage of up to 30 kV, decoupled from the rest of the system by an optical fiber link. The data acquisition apparatus could be configured to operate with four, eight, or sixteen input channels, trading the number of inputs for the sampling rate and frequency response in three steps: 4 channels, 16000 samples.s^-1 , 8 kHz; 8 channels, 8000 samples.s^-1, 4 kHz; 16 channels, 4000 samples.s^-1, 2 kHz bandwidth