ICMseries Accessories: Calibrators
Partial discharge measurement is a useful tool to analyze the insulation of high voltage components. However, partial discharges can usually not be measured directly, just the apparent charge of such signals are captured by the measuring instrument. Therefore a calibration of the whole measuring system is required in principle. Hereby short-duration current pulses of known charge magnitude are injected into the system, and by this a scale factor can be calculated for later PD measurements.
Power Diagnostix produces a wide range of calibration charge injectors suitable for use in calibrating partial discharge measurements. The appropriate choice of a calibration instrument depends on the range of typical charge values of the PDs being measured. Calibrators can also be used for time domain reflectometry in cables to determine cable length and location of joints.
Simple to Use
The calibrator is switched on with the pushbutton On/Off. Both amplitude (Range) and polarity (Pos/Neg) of the single charge pulse per cycle are displayed and can be adjusted by pressing of the two buttons. Each calibrator is also available supplying two pulses per cycle, as well as with double impulse output with adjustable interval. The instrument automatically synchronizes to line frequency by a photo diode. In case of insufficient pick-up of power frequency light, the calibrator automatically selects the internal quartz oscillator (50Hz and 60Hz versions available).
The Power Diagnostix line of calibration impulse generators is unique in that the charge pulse is generated by injecting a variable voltagestep (correlated to an internal reference) via a fixed capacitor. This injection capacitor is relatively small, as the step voltage amounts up to 120 V for full range output. Therefore, the Power Diagnostix calibrators offer excellent impulse properties. Further, calculation of the correction factor is usually not necessary (CI<<CS).