Application Notes; Medium And High Voltage Cables; Measurement Set-Up; Calibration - Megger Power Diagnostix ICMflex User Manual

Partial discharge and loss factor measurement system
6

Application notes

The application notes for medium and high voltage cables, rotating machines, and single stator bars de-
scribe the specific measurement set-up, calibration, step by step procedure for performing the measurement,
software usage, and evaluation criteria according to the relevant standards.
6.1

Medium and high voltage cables

6.1.1 Measurement set-up

A general description of the measurement set-up is given with section 3. In the following example, the focus
lies on the medium and HV voltage cable application. The order of connecting the various links is shown in
Figure 55. Most important is the interconnection between the main grounding of the high voltage supply and
the cable ground shield (1–3). The final link from the grounded baseplate of the ICMflex to the ground shield
must be as short as possible (3). The high voltage output cable of the ICMflex has to be connected to the
inner conductor or termination (6).

6.1.2 Calibration

Performing high voltage tests including partial discharge measurements and PD fault location on cables re-
quires calibration of both the apparent charge and the cable length. When the safety procedure as mentioned
in section 1.3 is accomplished and when the set-up is built-up as described above, the calibration can be
performed. General procedures are described in the Power Diagnostix's user manual for calibration impulse
generators. However, the detailed calibration procedure for cable fault location is explained below.
Since a test specimen has a capacitance against the ground shield, for medium and high voltage cables
varying from 200 pF/m to 425 pF/m, the cable capacitance will cause strong attenuation of the injected pulse.
The difference between the injected and measured Qp level is the k factor, the overall attenuation factor of the
complete test circuit. The k factor has to be compensated by the calibration.
(4)
Figure 55: MV cable measurement set-up
pdix.com
(5)
(6)
(3)
(2)
(1)
ICMflex
(6)
(5)
(3)
(2)
User guide for ICMflex
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