US3733520A

US3733520A - Means for limiting the residual level during superimposed over-voltage conditions in a surge diverter

Info

Publication number: US3733520A
Application number: US00248601A
Authority: US
Inventors: A Schei
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1971-05-03
Filing date: 1972-04-28
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15
Also published as: CA986574A; DE2218962A1; CH543823A; SE352206B

Abstract

In a surge diverter, in order to limit the residual level during superimposed over-voltage conditions, a plurality of spark gap stacks with associated non-linear resistors are provided with a shunt spark gap shunting at least one spark gap stack with the associated non-linear resistor. A shunt impedance is provided shunting at least one spark gap stack which is shunted by the shunt spark gap. The surge diverter includes a sufficient number of shunt gaps to prevent the total voltage over the diverter upon super-imposed over-voltage conditions from exceeding the protection level of the diverter.

Description

ilnited States Patent 1191 Schei 1 May 15, 1973 [54] MEANS FOR LIMITING THE [56] References Cited RESIDUAL LEVEL DURING UNITED STATES PATENTS SUPERIMPOSED OVER-VOLTAGE 3,489,949 1/1970 Carpenter ..3I7/69 X CONDITIONS IN A SURGE DIVERTER 3,673,459 6/1972 Carpenter ..3l5/36 3,348,100 10/1967 Kres e l ..3l7/70 [75] Invent Asle sch", Ludvlka, Sweden 3,414,759 12/1968 Conn ell et a1. ....317 70 x Assignee: Aumanna Svenska Elektriska 3,413,524 11/1968 Tram ..3]7/69 tlebolaget Vasteras Sweden Primary ExaminerC. L. Albritton [22] Filed: Apr. 28, 1972 Attorney-Jennings Bailey, Jr. [21] App]. No.: 248,601 ABSTRACT In a surge diverter, in order to limit the residual level [30] Foreign Application Priority Data during superimposed over-voltage conditions, a plurality of spark gap stacks with associated non-linear May 3, 1971 Sweden ..5673/71 resistors are provided with a Shunt spark p shunting at least one spark gap stack with the associated non- CL 317/70, linear resistor. A shunt impedance is provided shunt- 338/2] ing at least one spark gap stack which is shunted by [51] Int. Cl. ..H02h l/00 the shunt spark gap. The surge diverter includes a suf- [58] Field of Search ..338/2l, 13, 20; ficient number of shunt gaps to prevent the total voltage over the diverter upon super-imposed over-voltage conditions from exceeding the protection level of the diverter.

4 Claims, 7 Drawing Figures I MEANS FOR LIMITING THE RESIDUAL LEVEL DURING SUPERIMPOSED OVER-VOLTAGE CONDITIONS IN A SURGE DIVERTER BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a means for limiting the residual level during super-imposed over-voltage conditions in a surge diverter.

2. The Prior Art A surge diverter in an electric power line may under certain conditions during the extinguishing interval of the diverter be subjected to superimposed overvoltages or over-voltages superimposed on the operating voltage. Such conditions are most likely to appear in equipment for high voltage direct current and may occur when different diverters in the equipment ignite at different moments. An example of this is when a diverter for a converter-rectifier sparks-over while a phase-earth diverter discharges a connection overvoltage from the AC side. The phase-earth diverter is then connected to the DC line over the diverter of the converter-rectifier, thus causing a current increase in the phase-earth diverter. At the moment when the diverter over the converter-rectifier is ignited, the phaseearth diverter may very well operate with arcs extended by a magnetic field and under such conditions normal diverters do not give sufficient protection.

SUMMARY OF THE INVENTION The present invention relates to a means for surge diverters, preferably in equipment for high voltage direct current, to limit the residual level during superimposed over-voltage conditions.

According to the invention, in a surge diverter, in order to limit the residual level during super-imposed over-voltage conditions, a plurality of spark gap stacks with associated non-linear resistors are provided with a shunt spark gap shunting at least one spark gap stack with the associated nonlinear resistor. A shunt impedance is provided shunting at least one spark gap stack which is shunted by the shunt spark gap. The surge diverter includes a sufficient number of shunt gaps to prevent the total voltage over the diverter upon superimposed over-voltage conditions from exceeding the protection level of the diverter.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIGS. 1, 2 and 3 show three different embodiments of the invention and FIG. 4 shows the total discharge current through the surge diverter as a function of the time;

FIGS. 5 and 6 show the voltage over the non-linear valve-resistors and the voltage over the spark gap in a phase-earth diverter, for example;

FIG. 7 shows the total voltage over the diverter as a function of the time. The four latter figures show the conditions during super-imposed over-voltage conditrons.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A surge diverter according to FIGS. 1, 2, and 3 comprises a number of spark gap stacks 1 alternating with non-linear valve-resistors 2. Parallel therewith is a control chain with control impedances 3. The figures only show part of a diverter.

In order for the diverter to be able to protect even under the conditions mentioned during super-imposed over-voltages, it is now proposed that a number of gapplus-block units are shunted with an extra spark gap, shunt gap,4. FIG. 1 shows two gap stacks and a resistor being shunted, whereas FIG. 2 shows the case in which the shunt gap bridges a gap stack and a resistor. In FIG. 3 the valve-resistor 2 is a part of the control chain. Other combinations are of course also possible. In view of the ability of the diverter to limit the ensuing current it is advisable to use gaps with magnetic blowing for the shunt gaps as well. In the examples shown in FIGS. 1 and 3 it is preferable to shunt one of the spark gap stacks l shunted by the spark gap 4, with a shunt impedanceS. The spark-over voltage of the shunt gap 4 is chosen so high that it does not fire during normal over-voltages but only when such superimposed overvoltages occur as might jeopardize the protective capacity of the diverter. The number of shunts necessary for a certain diverter may vary from time to time and can be determined so that the diverter can ensure the necessary protection level.

FIG. 4 shows the current as a function of the time in a phase-earth diverter,for example. At the time t 0 the phase-earth diverter sparks-over and the current increases to its maximum value, after which it decreases in the normal manner. At the time 2,, however, a converter-rectifier diverter sparks-over so that the DC line is connected to earth over the two diverters in series, the current increasing almost instantaneously to a high value and then decreasing.

FIG. 5 shows the corresponding sequence for the voltage U,, over the resistance block in the first sparked-over phase-earth diverter. At the time t, a voltage peak appears. In the same way, FIG. 6 shows the voltage over the gap stacks. From a low value immediately after the gaps have sparked-over the gap voltage increases as the arcs are extended because of the magnetic blowing. However, here also a strong voltage peak occurs at the time t when the second diverter sparks-over.

FIG. 7 shows the voltage U,, over the phase-earth diverter, this voltage being U,, U

In the last three figures the protection level U of the diverter is indicated by a broken line and from FIG. 7 it is clear that the total voltage over the diverter exceeds its protection level, so that the diverter is not capable of protecting the equipment.

If according to the invention some of the spark gaps and valve-resistor blocks are shunted with extra gaps, this means that part of the voltage peak occuring at the time t in FIGS. 5 and 6 can be removed. The number of shunt gaps is chosen so that the voltage peak at t shown in FIG. 7 is kept under the line U,,.

I claim:

1. In a surge diverter, means to limit the residual level during superimposed over-voltage conditions, said means comprising a plurality of spark gap stacks (1) with associated serially connected non-linear resistors, and a shunt spark gap shunting at least one spark gap stack (1) with the associated non-linear resistor (2).

2. In a device according to claim 1, said shunt spark gap shunting two spark gap stacks (1) having a nonlinear resistor (2) connected therebetween.

3,733,520 3 4 3. In a device according to claim 1, having a shunt vent total voltage (U over the diverter upon superimpedance (5) shunting at least one Spark gap Smck imposed over-voltage conditions from exceeding the (1) which is shunted by the shunt spark gap.

4. In a device according to claim 1, the surge diverter includes a sufficient number of shunt gaps (4) to pre- 5 protection level (U,,) of the diverter.

Claims

2. In a device according to claim 1, said shunt spark gap shunting two spark gap stacks (1) having a non-linear resistor (2) connected therebetween.

3. In a device according to claim 1, having a shunt impedance (5) shunting at least one spark gap stack (1) which is shunted by the shunt spark gap.

4. In a device according to claim 1, the surge diverter includes a sufficient number of shunt gaps (4) to prevent total voltage (Ua) over the diverter upon super-imposed over-voltage conditions from exceeding the prOtection level (Un) of the diverter.