Principle Of Operation - Megger Power Diagnostix ICMflex User Manual

ICMflex
Partial discharge and loss factor measurement system
2

Principle of operation

The ICMflex is a unique measurement system that covers PD detection, PD fault location on cables, and tan
delta measurements (standard ICMflex, only). It has been designed to simplify the application and to combine
different measurement tasks with one instrument. This new principle minimises testing and operation time, in-
creases operator's safety, and guarantees highest sensitivity and precision. Main users of these systems are:
Service groups testing motors, generators, and accessories of the same
z
Service groups testing high voltage cables, termination, and joints
z
Maintenance and repair shops
z
High voltage laboratories
z
Research and development departments
z
The system is mainly used for on-site testing but can be used in laboratories and workshops as well. It op-
erates with any fixed or portable high voltage power supply, such as transformers, hi-pots, resonant test
systems, motor generator sets, and VLF systems (cos/square and sine waves). Power Diagnostix offers
complete systems as well as modular components.
A complete acquisition system is shown here in Figure 1. It con-
sists of a reference capacitor C
C , a decoupling circuit for PD measurement, and the acquisi-
sx
tion box with battery module. If PD measurement is not want-
ed, the decoupling circuit will not be built in. For systems above
30 kV the main box is surrounded by an aluminium electrode to
smoothen the electrical field. The communication from a com-
puter to the instrument can be established via Bluetooth or via
fibre optic serial bus. All measurement values are displayed by
the ICMflex remote control software on the computer.
Two voltages can be measured with this system. U
the capacitive divider between the external capacitance of the
test object C and the internal shunt capacitor C
x
voltage U is provided by the capacitive divider C
n
form of both voltages is displayed in a special graph in parallel
with the absolute values of U
tion of both signals gives further results like the tan delta value,
the power factor, and the capacitance C
test. Due to the high sampling rate of 100 kS with a 16-bit A/D
conversion, sufficient precision and accuracy can be guaran-
teed.
The high frequency PD signal is used for PD pattern acquisition as well as for PD fault location on cables, if
needed. The PD scope comes with an 8-bit resolution vs. phase and amplitude. The pulse counting goes up
to 65536 (16 bits) per phase-amplitude position. The sensitivity of PD measurements depends strongly on the
quality of the power supply. Power Diagnostix offers various modular filter units to block noise generated by
the source (see section 3.5). Furthermore, the instrument comes with a built-in gating input to trigger on HF
pulses from the input side. External noise signals do not interfere with the measurements as all signals are
directly taken on high voltage potential and, therefore, critical ground loops to the instrument are not existent.
10 User guide for ICMflex
, two shunt capacitors C
n
is taken from
x
. The reference
sx
/C . The wave-
n sn
, U , and U . The correla-
peak rms peak/sqrt2
of the sample under
x
and
sn
Figure 1: Design of the ICMflex
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