Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Patent
1993-05-03
1995-03-07
Strecker, Gerard R.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
324520, 324536, 340647, G01R 3112, G01R 3108
Patent
active
053961803
DESCRIPTION:
BRIEF SUMMARY
This invention relates to diagnostic measurements in gas insulated electrical substations.
Gas insulated substations (GIS) are utilised in many electricity transmission networks and are advantageous because of their being compact in size. In a GIS the conductors and circuit devices, such as transformers and switchgear, are housed within pressure vessels containing an atmosphere of sulphur hexafluoride at elevated pressure. The pressure vessels are typically made of steel and, electrically, are held at earth. In a 3-phase network the conductors of the individual phases are separately encased in pressure vessels and are mechanically mounted therein via insulators. The pressure vessels typically comprise interconnected tubular members which may have side-wall inspection ports.
Fault conditions which arise in the GIS lead to lengthy disconnection periods due to the mechanical complexity of the GIS and there is therefore a requirement to provide diagnostic measurements during in service use of the GIS in order to predict the possibility of a fault condition and to enable corrective action at a planned and convenient time. These potential faults almost always show partial electrical discharge activity before breakdown occurs and this discharge activity can be sensed from the consequential ultra high frequency resonance modes established in the pressure vessels. Accordingly the UHF modes can be sensed by couplers built into the pressure vessels at the inspection ports as has been proposed in the article entitled "Diagnostic measurements at UHF in gas insulated substations" published in PROC IEE Vol 135 Pt.C No. 2, March 1988. However, this proposal requires the use of a spectrum analyser connected to the coupler output and human interpretation of the analyser result.
The present invention provides a diagnostic measurement system for gas insulated electrical substations, the system comprising means for automatically monitoring UHF couplers fitted to pressure vessels in the substation, the monitoring means comprising means for identifying individual partial discharge events, means for characterising identified events, means for communicating characterised events from a plurality of couplers to an analysing means, the analysing means comprising pre-stored data representative of known pre-fault conditions, and comparative means for comparing the pre-stored data with the communicated characterised events, and for issuing a warning signal in the event of identity.
The identifying and characterising means preferably form part of a microprocessor sub-system associated with a plurality of couplers. The sub-system preferably comprises means for compressing a plurality of characterised events into a single data word for communicating to the analysing means. The communicating means preferably comprises an optical fibre loop. The analysing means preferably comprises means for signalling the sub-system to communicate characterised events from a particular coupler without data compression.
An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
FIGS. 1 and 2 schematically illustrate a gas insulated electrical substation and a diagnostic measurement system coupled thereto;
FIGS. 3-5 illustrate components of the measurement system; and
FIGS. 6A-6G illustrates typical waveforms occurring at the components of FIGS. 3-5.
A gas insulated substation (GIS) 10 and a diagnostic measurement system 20 coupled thereto are shown schematically in FIGS. 1 and 2 wherein the UHF signals are taken from the GIS 10 using couplers 11 mounted on the inside of hatch covers formed on bus chambers 12. The couplers 11 have been designed to have a good high frequency performance, and are mechanically very robust and reliable. They may easily be fitted retrospectively to a GIS already in service.
The standard is to detect a 2 mm particle moving anywhere within the GIS, because this is below the size which might lead to breakdown. Because of the signal attenuation at these high fr
REFERENCES:
patent: 5107447 (1992-04-01), Ozawa et al.
patent: 5146170 (1992-09-01), Ishikawa et al.
"Conference Record of the 1988 IEEE International Symposium on Electrical Insulation"; Kranz and Krump; pp. 246-249.
"Diagnostic measurements at UHF in gas insulated substations"; Hampton and Meats; pp. 137-144.
Hampton Brian F.
Pearson John S.
Do Diep
Strecker Gerard R.
University of Strathclyde
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