Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Patent
1992-06-22
1994-06-28
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
361 15, 361 16, H02H 716
Patent
active
053252594
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an overvoltage protective device for series capacitor equipment, comprising a main spark gap with a first and a second main electrode for connection in parallel with a series capacitor and adapted to be ignited at a predetermined level of the voltage across the series capacitor.
BACKGROUND OF THE INVENTION
Series capacitors are used in electric power lines, primarily for increasing the transmission capacity of a power line. Such series capacitor equipment comprises a capacitor bank, which is connected into the power line and traversed by the current of the power line. The voltage across a series capacitor becomes proportional to the current in the power line, and at an overcurrent in the power line, caused, for example, by a short circuit in the power network, an overvoltage occurs across the series capacitor. To protect the capacitor against overvoltages, it is previously known to connect the capacitor in parallel with a spark gap, which is triggered in a suitable way at an overvoltage across the capacitor. In this way the line current is shunted past the capacitor, which is thus protected. To limit the discharge current of the capacitor through the spark gap, it has so far been necessary to arrange an impedance element, usually an inductor, in series with the spark gap. However, use of the inductor means a not significant complication of the protective equipment, rendering the equipment more expensive.
Furthermore, it has proved to be difficult or impossible to produce spark gaps of the kind referred to above which, without demands for maintenance, provide a reliable function also at lower voltage levels. For this reason, the use of series capacitors has been limited at lower system voltages. However, there is a need to be able to use series capacitors also at lower mains voltages, for example in distribution networks for elecric power.
SUMMARY OF THE INVENTION
The present invention aims to provide an overvoltage protective device for series capacitor equipment, which functions reliably also at low mains voltages and which has a simple and economically favorable design.
What characterizes an overvoltage protective device according to the invention will be clear from the appended claims.
In an overvoltage protective device according to the present invention, the first igniting auxiliary spark gap, which determines the level of protection of the device, is only subjected to limited current and for a very brief period of time. This makes the stresses on this spark gap low, which results in a reliable mode of operation of the overvoltage protective device for a long period of time, and this without the need of maintenance. According to a preferred embodiment of the invention, this first igniting spark gap is designed as a so-called surface flashover path, thus obtaining a relatively long arc with a high arc voltage drop very rapidly and at a low flashover voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following the present invention will be described in greater detail with reference to the accompanying FIGS. 1-6 in which:
FIG. 1 shows a circuit diagram of one embodiment of the present.
FIG. 2 shows an example of the mechanical configuration of the overvoltage protective device according to FIG. 1;
FIG. 3 shows in more detail how the auxiliary spark gaps are arranged adjacent to the main spark gap in the device according to FIGS. 1 and 2;
FIG. 4 shows how the first igniting auxiliary spark gap according to a preferred embodiment may be designed as a surface flashover path;
FIG. 5 illustrates how the voltage across and the current through the overvoltage protective device vary during an operation of the protective device;
FIG. 6 shows an alternative embodiment in which a voltage transformer is used for igniting the first igniting auxiliary spark gap.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an embodiment of an overvoltage protective device according to the invention. The figure shows the protective device for one phase of a power lin
REFERENCES:
patent: 4625254 (1986-11-01), Fahlen
patent: 4652963 (1987-03-01), Fahlen
patent: 4860156 (1989-08-01), Stenstrom et al.
Asea Brown Boveri AB
Jackson S.
Pellinen A. D.
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