by D. Avital, V. Brandenbursky, A. Farber, V. Korzh - Israel Electric Company

The reliability of GIS (Gas-Insulated Switchgear) is very high but any failure that occurs can cause extensive damage result and the repair times are considerably long. The consequential losses to system security and economically can be high, especially if the nominal GIS voltage is 420 kV and above. In view of these circumstances, increasing attention is being given to diagnostic techniques for in-service maintenance undertaken to improve the reliability and availability of GIS. Recently considerable progress has been made in diagnostic techniques and they are now used successfully during the service life of the equipment [1-3]. These diagnostic techniques in general focus on the GIS insulation system and are based on partial discharge (PD) measurements in GIS. There are three main methods for in-service PD detection in GIS: the chemical method that rely on the detection of cracked gas caused by PD, the acoustic method designed to detect the acoustic emission excited by PD, and, the electrical method which is based on detection of electrical resonance at ultra high frequencies (UHF) up to 1.5 GHz caused by PD excitation in GIS chambers (UHF method).

These three dielectric diagnostic methods cannot be used for the detection of poor current carrying contacts in GIS. This problem does not always produce partial discharges and at early stages it does not cause gas cracking.

An interesting solution to use two techniques - the current unbalance alarm scheme and partial discharge monitoring was advised by A. Salinas from South California Edison Co. [4]. Unfortunately this way is complicated and very expensive. The investigations performed in Japan on standing alone SF6 breaker showed that joule heating of the contact accompanied by released power of 1600 Watt produce temperature difference on the enclosure up to 7 degrees centigrade that could be detected by infra-red thermo-camera [5]. According to CIGRE Joint Working Group 33/23.12 Report [6], 11% of all GIS failures are due to poor current carrying contacts in GIS. The Israel Electric Company (IEC) in seeking a solution to this problem have undertaken experimental work to examine the opportunity of in-service diagnostic of poor contact problem in GIS via direct local heating detection, using a Thermal Imaging System. The experiments were carried out on the part of the GIS with nominal SF6 pressure. The following aspects of the problem were examined:

• the range of power released in the defective contact that could give the practical temperature rise on the surface of enclosure;

• temperature distribution on the surface of enclosure;

• the influence of spacer type (with holes or without) on the heat transfer process;

• the influence of the length of SF6 tubes and there position (horizontal or vertical);

• the temperature difference between upper and lower parts of the tubes in horizontal position;

• practical use of the Thermal Imaging System for detecting poor contact problem in GIS..................

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Straight from the World Wide Web, here is what's going on in the world of infrared thermography.

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Here is a selection of recent new threads by IR Community members. Feel free to click the links, see how people have responded, and post your own response if you like.

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And of course if YOU have a question or want to start a discussion on a topic, we would love to hear from you. Just post a new thread on a message board.

Brainteaser of the Month 

Here is this month's brainteaser. Readers who email us the correct identification and explanation of the thermal pattern in the thermogram are entered into a drawing to win a prize from ITC.

Please put "Brainteaser" as the subject of the message.

Click here to email your guess

Do you have an interesting image that you think would challenge other thermographers? If so please email me your image (preferably in native .img, .jpg, .tif, .tgw, or .tmw format) with an accompanying visible photo and explanation. If your image is used, you receive a gift as well.

Last Month's Brainteaser

Well, you thermographers certainly know your BEESNEST (pun intended)!

Yeah, this is a thermogram of thousands of the tiny critters. Almost everyone got this one right.

Congratulations to our winner Gordon Clark and to our thermogram contributor Robert Lourdin from France. Gordon and Robert both receive low emissivity traveling coffee mugs.

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