Electricity: electrical systems and devices – Safety and protection of systems and devices – Transformer protection
Patent
1997-05-19
1999-08-31
Gaffin, Jeffrey
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transformer protection
361 38, 361115, H02H 700
Patent
active
059461713
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of the prevention against explosion and fire of electrical transformers cooled by a combustible fluid.
Electrical transformers exhibit losses both in the windings and in the core, for which reason the heat produced needs to be dissipated. High-power transformers are thus generally cooled using oil. The oils used are dielectric and can ignite above a temperature of the order of 140.degree.. Since transformers are very expensive components, particular attention must be paid to protecting them.
Fires in power transformers insulated by dielectric oil generally occur because of an internal electrical insulation break, causing an often very violent deflagration. This results in extensive rupture of the enclosure of the transformer and combustion of the oil which spreads the fire to other on-site equipment which may also contain large quantities of combustible products.
Explosions can be caused by overloads, voltage surges, progressive deterioration of the insulation, an insufficient oil level, the appearance of moisture or mould or the failure of an insulating component.
Safety valves, which trigger in the event of an overpressure within the enclosure of the transformer, are known in the prior art. However, these valves are not suited to the consequences of an internal insulation fault in the transformer.
Fire protection systems for electrical transformers are also known which are actuated by temperature detectors. However, these systems are implemented with a significant time lag, when the oil of the transformer is already burning. A compromise is then made to limit the combustion to the equipment in question, and to prevent the fire from spreading to the neighbouring plant.
The object of the present invention is therefore to provide a method which protects both against overpressure inside the transformer, due to deflagration when the internal electrical insulation breaks, and against the fire which results from such insulation breaks.
A further object of the invention is a device for prevention against explosion and fire, which allows immediate detection of the electrical insulation break.
According to the invention, the method of prevention against explosion and fire in an electrical transformer equipped with an enclosure filled with a combustible coolant, comprises the following steps: pressure-sensor means, and into the bottom of the enclosure in order to stir the coolant and flush the oxygen located in proximity.
According to the invention, the device for prevention against explosion and fire in an electrical transformer equipped with an enclosure filled with a combustible coolant comprises a means for sensing the pressure in the said enclosure and a means for partially draining the coolant contained in the enclosure.
An insulation fault firstly generates a strong electric arc which causes actuation of the electrical protection systems which trigger the supply cell of the transformer (circuit breaker) . The electric arc also causes resultant dissipation of energy, which generates an increase in the internal pressure of the transformer, sufficient to cause its enclosure to rupture.
The device for prevention against explosion and fire is preferably equipped with a means for detecting the triggering of the supply cell of the transformer, and with a control unit which receives the signals emitted by the sensor means of the transformer and can emit control signals.
The device for prevention against explosion and fire preferably comprises a means for cooling the hot parts of the fluid, by injecting inert gas into the bottom of the enclosure, which is controlled by a control signal from the control unit. The reason for this is that some parts of the coolant undergo heating which can cause them to ignite. Injecting an inert gas at the lower part of the enclosure causes stirring of the coolant, which equilibrates the temperature and makes it possible to flush the oxygen present in proximity to the fluid.
The invention will be understood more clearly on studying the detaile
REFERENCES:
patent: 5534853 (1996-07-01), Pioch
Patent Abstracts of Japan JP5182838 published Jul. 23, 1993 for "Abnormality Monitoring Device of Oil-Immersed Electric Equipment", 1 sheet.
Dialog Web search results for English-language abstract for EPO 0238475 downloaded and printed Nov. 25, 1998, 1 sheet.
Dialog Web search results for English-language abstract for EPO 2624882A downloaded and printed Oct. 13, 1998, 1 sheet.
Gaffin Jeffrey
Jackson Stephen
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