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2012 Paris Session
http : //www.cigre.org
Study Committee D1,
Preferential subject 3: Diagnostic tools
Improvement of defect detection by measurement of the UHF signal
transmission inside single phase and three phase encapsulated GIS
DAVID GAUTSCHI1, ALAIN GIRODET2
1ALSTOM Grid AG, Oberentfelden
Switzerland
[email protected]
2ALSTOM Grid, Lyon
France
[email protected]
The measurement of partial discharge activity in gas-insulated substations is used during type
testing, routine testing in the factory and on site for commissioning tests. In addition it is
increasingly used for condition monitoring purposes. The UHF method is a modern way of
measuring partial discharges. Special UHF sensors for partial discharge detection typically
work in the frequency range between 100 MHz and 2 GHz.
In this frequency range the GIS acts as a waveguide. Part of the signal is propagating along
the inner conductor and a part in the free space between the conductor and the enclosure.
Every difference in the diameter of the conductors or the enclosure for example in
disconnectors, circuit breakers etc or in the material (for example cones) result in a change of
impedance for the signal. A part of the high frequency signal is reflected, the rest is
transmitted towards the next component.
The knowledge of the signal transmitting behavior inside the substation is of basic interest for
the following reasons:

For the manufacturer to know the best locations to install the UHF sensors.

For the customer to know how many sensors and where they have to be installed to meet
the sensitivity requirements of the monitoring equipment.

For the manufacturer and the customer to specify the needed sensitivity of the UHF PD
sensors.

For standardization bodies on how to improve or develop related standards.
Measurements of the attenuation inside GIS components have been published in different
publications like [1]. Most of the published data was taken in special arrangements and do not
take into account a collection of different components.
In a measurement campaign the attenuation of different type of GIS components (single phase
and three phase encapsulated types) have been measured. The measurements were taken on a
full bay with disconnectors, earthing switches and circuit breakers or on multiple bays or
complete substations. It was clearly seen that the transmission of UHF signals do depend on
the position of operation of the switching device (closed or open position) and on the position
of the device inside the substation or bay. It could be demonstrated that the influence of the
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different design does influence the attenuation behavior in a way that resonances and
extinction of signals occur. It is therefore not possible to reduce the frequency dependent
attenuation to a single value like proposed in different papers like [1].
The paper shows the differences between different GIS designs. The data will be valuable for
the ongoing work on the Cigré D1.25 working group which is at the moment preparing an
update of the well known sensitivity check according [2].
[1] Kijun Park et al, “Measurement of ultra-high frequency (UHF) partial discharge sensor sensitivity and
partial-discharge (PD) signal losses in the 800 kV gas-insulated substation (GIS)“, XIIIth International
Symposium on High Voltage Engineering, Netherlands, 2003
[2] CIGRE Task Force 15/33.03.05, “Partial discharge detection system for GIS: sensitivity verification for the
UHF method and the acoustic method”, ÉLECTRA No. 183, pp. 74-87, 1999
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