Rotating Machines; Test Set-Up; Calibration - Megger Power Diagnostix ICMflex User Manual

ICMflex
Partial discharge and loss factor measurement system
6.2

Rotating machines

6.2.1 Test set-up

A general description of the measurement set-up is given in section 3. In this case, the focus is set on the
rotating machines application. Of main importance is the interconnection between the main grounding of the
high voltage power supply, i.e., a transformer or resonance test set, and the main grounding of the machine
frame. The final link from the grounded baseplate of the ICMflex to the ground shield must be as short as
possible. The high voltage output cable of the ICMflex has to be connected to the phase terminals of the
motor or generator housing. An installation scheme showing the connections is given with Figure 69.
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Figure 69: Rotating machines measurement set-up

6.2.2 Calibration

Performing high voltage tests, including partial discharge measurements on rotating machines' insulation
systems according to IEC 60270, requires a calibration of the apparent charge. When the complete 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' user manual
for calibration impulse generators. However, the detailed calibration procedure for generators and motors is
explained below.
A calibrator is connected to the phase terminal connected to the ICMflex as shown in Figure 70. The selection
of the relevant charge level to be injected into the measurement circuit is mainly depending on the machine's
ratings. The main parameter influencing the required charge is the stator windings capacitance. In general,
the capacitance is depending on the nominal voltage, number of poles, and the core length. It's important to
have a reasonable signal to noise ratio in order to ensure sufficient sensitivity. Select a value that is approx-
imately 5 to 10 times higher than the present background noise. Typical values used for on-site testing are
varying from 1 nC to 5 nC, even 10 nC in case of hydro or turbo generators.
54 User guide for ICMflex
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