Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1991-05-02
1993-08-03
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361 58, 361 9, H02H 104, H02H 906
Patent
active
052334988
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arrangement for forced triggering a spark gap at a voltage below self-ignition voltage, the spark gap being divided into at least two sub spark gaps arranged in series, whereby voltage division components for dividing voltage between the or sub spark gaps are arranged in parallel with said series connected sub spark gaps.
Forced triggering is needed, for example, in spark gaps used in a series capacitor battery in a high-voltage transmission line. In these arrangements the spark gap protects a metal oxide varistor (MOV) connected in parallel with the battery against damages caused by possible overvoltages. The spark gap thereby functions as a kind of extremely rapid protective device which by-passes the capacitor battery and the varistor before the bypass circuit breaker itself starts to operate. The spark gap can be forced-triggered in response to a protective relay measuring the energy of the varistor. Arrangements of this type are disclosed, e.g., in SE Patent Application 8205236 and FI Patent Application 822379.
FI Patent Application 822379 discloses a device for forced triggering in which an auxiliary electrode is disposed in the spark gap, whereby the spark gap is ionized by means of a separate ignition transformer. It is thereby necessary to synchronize the auxiliary spark with the spark gap voltage because forced triggering cannot be carried out successfully if the instantaneous value of the spark gap voltage is too low. The use of this kind of auxiliary electrode increases scattering in self-ignition voltage level; on the other hand, there is a risk of the auxiliary electrode being damaged during the operation of the spark gap. If the auxiliary electrode is disposed in one of the auxiliary spark gaps arranged in parallel with the main spark gaps, forced triggering will not take place until relatively near the self-ignition voltage of the whole spark gap.
The method of SE Patent Application 8205236 similarly utilizes a separate pulse transformer which applies a high-voltage pulse for igniting the spark gap. In the device of the SE Patent Application, one of the auxiliary spark gaps arranged in parallel with the main spark gaps is ignited by means of a high-voltage pulse, whereby the auxiliary spark gaps are ignited, finally triggering the main spark gaps. In this device, too, the ignition pulse has to be synchronized with the spark gap voltage to enable forced triggering. This synchronization as well as the acquisition and supply of energy to the pulse transformer for the high-voltage pulse require suitable means. Such means make the device for forced triggering more complicated in structure, increase the cost as well as the liability of the device to damage, thus deteriorating the overall reliability of the device.
The object of the present invention is to provide a device for forced triggering which is very simple in structure and thus highly reliable in operation. This is achieved by means of an arrangement according to the invention, which is characterized in that an element controlled to adopt a high-impedance or low-impedance state is arranged in series with the voltage division components, whereby the element, when adopting the high-impedance state, changes the voltage division between the spark gaps so that the sub spark gap arranged in parallel therewith is ignited. So the operation of the arrangement of the invention is not based on the ignition of one of the auxiliary or sub spark gaps by means of a high-voltage pulse; instead, the arrangement of the invention affects the voltage division between the sub spark gaps so that a substantially greater proportion of the supplied energy than at normal state is caused to act across one of the spark gaps, causing it to be ignited The ignition of one of the sub spark gaps, in turn, results in the ignition o the spark gaps as their voltage increases substantially after the ignition of one spark gap.
The element, preferably controlled to adopt a low-impedance or high-impedance state, comprises a transformer having a prima
REFERENCES:
patent: 3611044 (1971-05-01), Osterhout
patent: 4523249 (1985-06-01), Arimoto
Friedhofer Michael A.
Nokia Capacitors Ltd.
Pellinen A. D.
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