The measurement of partial discharges is a non-destructive text on electrical power apparatus. The measured quantities are available data to determine the quality of an insulation. In high voltage Test techniques, special importance is therefore attached to measurement of partial discharges.
The reading of partial discharge intensity is in pico-coulombs (pC) or, alternatively, Radio Interface Voltage (RIV) in micro volts (µV). The Voltage AC voltage display is also available to measure peak, peak and RMS using suitable Voltage Divider.
The partial discharge/RIV measuring system consist of :
Partial discharges in the Tes tobject cause charge transfers in the high-voltage circuit, giving rise to voltage pulse variations on the measuring impedance(Quadripole). These pulses are evaluated by the partial discharge meter. The filter with adjustable centre frequency allows to select parts of the high-voltage spectrum for measurement purpose.
Partial discharge meter (DTM D)
The measured partial discharge intensity is displayed either in pC or in mV in accordance with IEC60270/IS6209 or NEMA 107. According to IEC 60270, the measured quantity shall be multiplied by a correction factor, which takes care of 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. The PD pulses are tapped from the analogue output terminal and displayed of the built-in Digital Storage Oscilloscope.
AC Test voltage Display
The power frequency Test voltage is displayed as Peak, Peak /2 or RMS values in conjunction with suitable voltage divider.
Software for PD Analysis
The built-in Digital Storage Oscilloscope is used to capture/transfer the Analog PD pulses measured by the basic PD Meter (clause 3.1)
The Digital PD data is transferred to a computer through GPIB and can be manipulated using Microsoft Windows compatiable software loaded in the Laptop.
The Digital PD data is transferred to a computer through GPIB and can be manipulated using Microsoft Windows compatible software loaded in the Laptop.
With use of this built-in software the following features can be obtained :
Filter Inserts :
A selective narrow band filter with variable center frequency and a broadband filter can be supplied.
Narrow Band Filter :
Variable center frequencies from 600 kHz to 2400 kHz, Bandwidth 9kHz
Broad-band Filter :
Frequency range 40 kHz to 220 kHz, Bandwidth 180kHz. The basic noise level of the instrument is less than 0.6 pC in the most sensitive measuring range. The measuring accuracy and linearity correspond to IEC 60270 and IS 6209
Measuring ranges :
2.5 pC to 50,000 pC (IEC 60270) / 1mV to 25,000 mV (VDE, CISPR)
Measuring Impedance :
The measuring impedance (Quadripole) filters out the power frequency currents from the high-voltage Test circuit and allows only HFPD pulses. It can be continuously loaded with 4A. Built-in surge arresters protect the instrument against over voltages.
Laptop PC with suitable GPIB card.
Co-axial cables to connect Quadripoles to meter.
Fig. 1 :
Connection of partial discharge meter DTM between Test object and ground (Testcircuit according to IEC60270 and IS6209).
Fig. 2 :
Connection of partial discharge meter DTM between coupling capacitor and ground (Test Circuit according to NEMA Publ. 107)