The measurement of partial discharges is non-destructive Test on electrical apparatus or equipment. The measured quantities are valuable data to determine the quality of an insulation. In high-voltage Test technique, special importance is therefore attached to measurement of partial discharges.
The reading of partial discharge intensity is in Pico-coulombs (pC) or, alternatively, radio interference voltage (RIV) in micro volts (µV).
The partial discharge/RIV measuring system consists of,
Partial discharges in or on the Test object cause charge transfers in the high-voltage circuit, giving rise to voltage pulse variations on the measuring impedance (Quadripole). These are evaluated by the partial discharge meter. The filter with adjustable centre frequency allows to select parts of the high-voltage spectre for measurement purposes.
Partial Discharge Meter (Type:DTM)
The measured partial discharge intensity either in pC or in mV in accordance with IEC 60270 or VDE 0434 and VDE 0876. According to IEC 60270, the measured quantity shall be multiplied by a correction factor, which considers the circuit characteristics of the complete Test arrangement. With built-in correction circuit it is possible to incorporate the correction factor into the display. The actual partial discharge intensity can then be read directly without the usual calculations. At switch position "CORR", the correction factor is displayed directly. An analogue output terminal is provided for the display of the partial discharge pulses on an oscilloscope.
An internal calibration voltage allows to verify proper performance of the instruments in position "CAL".
for PD meter (DTM), a selective filter for variable center frequency and a broadband filter can be supplied.
Variable center frequencies 0.6 .....2.4MHz
Band width 9 kHz
Bandwidth 40 kHz to 220 kHz
The basic noise level of the instrument is less than 0.5 pC in the most sensitive measuring range. The measuring accuracy and linearity correspond to VDE 0876 and IEC 60270
2 pC to 50,000 pC (IEC 270)
1 µV to 25,000 pV (VDE, CISPR, NEMA)
The measuring impedance (Quadripole) filters the HF voltage portions from the Test circuit. It can be continuously loaded with 4 A. Built-in surge diverters protect the instrument against over voltages.
DIMENSIONS AND WEIGHT
206mm wide x 177mm high x 245mm deep
(1/2-19" plug in unit) units
Weight : approx 5Kgs.
Housing, in case the instruments is not intended for rack-mounting.
Fig. 1 : Connection of partial discharge meter DTM between Test object and ground (Test circuit according to IEC Publ. 270 and VDE 0434.
CK = Coupling Capacitor
AKV = Measuring Impedance
Fig. 2. Connection of partial discharge meter DTM between coupling capacitor and ground (Test circuit according to NEMA Publ. 107)