OVERVOLTAGE PROTECTION DEVICE
United States Patent 3566197
An overvoltage protection device consists of a number of parallel connected columns containing nonlinear resistance stacks between upper and lower spark gap stacks. The spark gap stacks provide arc extension by magnetic effect. Cross-impedances are arranged between the columns for transferring ignition pulses. The spark gaps, nonlinear resistors and connecting members for the cross-impedances are so dimensioned and arranged that the impedance increase of a column after ignition in comparison with the impedance increase of one or more subsequent ignited columns is so great that the current through the first column is less than a value corresponding to its lowest current carrying voltage. The cross-impedances may be connected between the bottom of an upper spark gap stack and the top of a lower spark gap stack.
US Patent References:
Excess voltage discharge device
Zoller - June 1961 - 2989664
/3094648.html
Nilsson - June 1963 - 3094648
High voltage switching apparatus
Luehring et al. - August 1965 - 3198986
Excess voltage discharge device
Zoller - June 1961 - 2989664
/3094648.html
Nilsson - June 1963 - 3094648
High voltage switching apparatus
Luehring et al. - August 1965 - 3198986
Inventors:
Erland, Nilsson (Ludvika, SE)
Asle Schei (Ludvika, SE)
Asle Schei (Ludvika, SE)
Application Number:
04/771210
Publication Date:
02/23/1971
Filing Date:
10/28/1968
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
361/111, 361/134
International Classes:
H01T4/16; H02H7/085; H02H9/06; H01T4/00; H02H3/22
Field of Search:
317/31,61,73,74,68,69,70 315/36
Primary Examiner:
James, Trammell D.
Attorney, Agent or Firm:
Jennings Bailey Jr.,
Claims:
1. Overvoltage protection device comprised of a plurality of parallel-connected columns containing nonlinear resistors and spark gaps promoting arc extension by magnetic effect, and cross-impedances arranged between the columns for transferring ignition pulses between the columns in which the spark gaps, nonlinear resistors and connecting members for the cross-impedances are so dimensioned and arranged within the different columns that the impedance increase of a column after ignition in comparison with the impedance increase of one or more subsequently ignited columns is so great that the current through the first mentioned column is less than a value corresponding to the lowest current carrying voltage of
2. Overvoltage protection device according to claim 1, in which the ignition delay between the columns is determined by the cross-impedances
3. Overvoltage protection device according to claim 2, having shunt
4. Overvoltage protection device according to claim 1, in which in at least one of the columns the spark gaps are so dimensioned that their arc
5. Overvoltage protection device according to claim 1, in which in at least one of the columns the spark gaps are so dimensioned that the rate of increase speed of their arc voltage is higher than in the other columns.
6. Overvoltage protection device according to claim 1, in which the cross-impedance is connected geometrically and also electrically when not in operation, to the same point on the spark gap in each stack.
2. Overvoltage protection device according to claim 1, in which the ignition delay between the columns is determined by the cross-impedances
3. Overvoltage protection device according to claim 2, having shunt
4. Overvoltage protection device according to claim 1, in which in at least one of the columns the spark gaps are so dimensioned that their arc
5. Overvoltage protection device according to claim 1, in which in at least one of the columns the spark gaps are so dimensioned that the rate of increase speed of their arc voltage is higher than in the other columns.
6. Overvoltage protection device according to claim 1, in which the cross-impedance is connected geometrically and also electrically when not in operation, to the same point on the spark gap in each stack.
Description:
The invention relates to an over-voltage protection device for alternating current and high power.
2. The Prior Art
For overvoltage protection devices for alternating current and high power several parallel columns can be used containing spark gaps and nonlinear overvoltage resistors in order to be able to absorb the energy during a discharge interval. Since all the columns cannot be made exactly the same, at least one of them will spark over before the rest and, if no special precautions are taken, the column or columns sparking over first would be forced to take care of the entire discharge, whereas other columns would not take part at all. Thus a good deal of the effect intended with parallel-connection is lost. The problem has been solved by connecting cross-impedances between the various columns so that the alternation in voltage distribution within a certain rod which occurs during the discharge interval through one cross-impedance influences another column so that this ignites and all the columns therefore take part in the discharging.
With alternating current the protection device is normally extinguished when the voltage passes through zero the first time after the ignition and no extra steps need be taken to extinguish the overvoltage protection device.
With direct current the situation is quite different. If an overvoltage occurs in a direct current network so that an overvoltage protection device sparks over, the overvoltage will not necessarily drop as quickly as with alternating current since there is no zero-passage for the voltage. There is thus a considerable risk that the overvoltage protection device will burn for such a long time that it is destroyed due to overheating.
The present invention relates to an overvoltage protection device which is particularly suitable for use in direct current networks but which can also be used in alternating current networks.
The accompanying drawing shows a schematic diagram for an overvoltage protection device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention the overvoltage protection device consists of a number of parallel-connected columns 1, 2, 3, 4, and so on between the network and earth. The drawing shows the use of four columns, but both larger and smaller numbers are possible and the number depends, amongst other things, on the value of the overcurrents arising and also on the type of the separate elements. A rod is built up of a centrally arranged nonlinear overvoltage resistance stack 5 consisting of a required number of resistance blocks and upper and lower spark gap stacks 6 and 7, respectively. Between two preferably adjacent columns is a cross-impedance 8 which is suitably resistive and which may be nonlinear like the overvoltage resistor. In the embodiment shown in the drawing a cross-impedance is connected between the overvoltage resistance stack at the upper end in one column and the lower end of the overvoltage resistance stack in the other column. When the overvoltage protection device is not in operation these two points are electrically equal but geometrically different. It is, however, possible and in certain cases suitable to connect the cross-impedance in a different manner, for example between two geometrically equal points.
The mutual control between the discharge process in two adjacent rods is not only determined by the impedance element 8 but also by the impedance of the spark gap stack itself and the control can be further influenced with the help of shunt impedances 9 and 10 inserted parallel to the rods and also connected to the cross-impedance 8. The shunt impedances preferably consist of capacitive elements, but other impedance elements are also feasible.
As mentioned previously, it is not necessary for all the parallel rods to be alike. On the contrary, it may even be suitable to make them different so that at least one of them ignites earlier when an overvoltage occurs. If the column 1 in the drawing is so dimensioned that it ignites first, the voltage drop over the upper and lower spark gap stack in this column will fall to a low value before the extension of the arc due to the magnetic field has started to make itself noticeable. Most of the voltage drop in the column 1 then lies in the beginning across the resistance stack 5 and this voltage drop is transferred to the lower spark gap stack of the column 2 with a time delay determined by the cross-impedance 8 and the impedance of the spark gap itself, the shunt impedance 9 and 10. This increased voltage ignites the lower spark gap 7 stack of the rod 2 and then also the upper spark gap 6 so that the whole column 2 sparks over and in turn ignites the column 3 in the same way as the column 1 ignited the column 2.
After a certain time the arc is extended in the spark gap stacks in the column 1 and the impedance of this column increases so much that it gives a voltage drop across the column which corresponds to the voltage drop over the other rods. The current in the column 1 is thus forced down to such a low value that the arc through the column is extinguished and the current through the column is interrupted. At the moment of extinction the voltages over the upper and lower spark gap stacks in the column 1 are practically equal, but the voltage over the lower spark gap stack in the column 2 is very small since the arc extension has not had time to become apparent. This means that the voltage across the nonlinear resistance stack in the column 2 increases the voltage over the upper spark gap stack 6 in the column 1 so that, after a certain time, this reignites and the entire column 1 reignites and takes part in the discharge. A similar process takes place in each of the other rods and in this way the discharge voltage can be maintained at the desired level and a high extinction voltage is ensured, since the arc in the spark gap is extinguished as soon as it has been blown out to its full length due to the influence of the magnetic field and no appreciable heating of the gap takes place. Thus a repeated ignition and extinction of the arc in all the rods is obtained so that the current is constantly moved from one column to the other. This means that the discharge current can pass the overvoltage protection device without its extinguishing capacity being reduced.
By suitably dimensioning the cross-impedances 8 and possibly also the shunt impedances, the column 3 can be brought to spark over before the column 1 is extinguished. In this way it can be arranged that two rods burn simultaneously if this is suitable in order to obtain a sufficiently powerful discharge.
The energy absorption capacity of the protection device is substantially determined by the number of parallel-connected legs and can in principle be made any size.
2. The Prior Art
For overvoltage protection devices for alternating current and high power several parallel columns can be used containing spark gaps and nonlinear overvoltage resistors in order to be able to absorb the energy during a discharge interval. Since all the columns cannot be made exactly the same, at least one of them will spark over before the rest and, if no special precautions are taken, the column or columns sparking over first would be forced to take care of the entire discharge, whereas other columns would not take part at all. Thus a good deal of the effect intended with parallel-connection is lost. The problem has been solved by connecting cross-impedances between the various columns so that the alternation in voltage distribution within a certain rod which occurs during the discharge interval through one cross-impedance influences another column so that this ignites and all the columns therefore take part in the discharging.
With alternating current the protection device is normally extinguished when the voltage passes through zero the first time after the ignition and no extra steps need be taken to extinguish the overvoltage protection device.
With direct current the situation is quite different. If an overvoltage occurs in a direct current network so that an overvoltage protection device sparks over, the overvoltage will not necessarily drop as quickly as with alternating current since there is no zero-passage for the voltage. There is thus a considerable risk that the overvoltage protection device will burn for such a long time that it is destroyed due to overheating.
The present invention relates to an overvoltage protection device which is particularly suitable for use in direct current networks but which can also be used in alternating current networks.
The accompanying drawing shows a schematic diagram for an overvoltage protection device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to the invention the overvoltage protection device consists of a number of parallel-connected columns 1, 2, 3, 4, and so on between the network and earth. The drawing shows the use of four columns, but both larger and smaller numbers are possible and the number depends, amongst other things, on the value of the overcurrents arising and also on the type of the separate elements. A rod is built up of a centrally arranged nonlinear overvoltage resistance stack 5 consisting of a required number of resistance blocks and upper and lower spark gap stacks 6 and 7, respectively. Between two preferably adjacent columns is a cross-impedance 8 which is suitably resistive and which may be nonlinear like the overvoltage resistor. In the embodiment shown in the drawing a cross-impedance is connected between the overvoltage resistance stack at the upper end in one column and the lower end of the overvoltage resistance stack in the other column. When the overvoltage protection device is not in operation these two points are electrically equal but geometrically different. It is, however, possible and in certain cases suitable to connect the cross-impedance in a different manner, for example between two geometrically equal points.
The mutual control between the discharge process in two adjacent rods is not only determined by the impedance element 8 but also by the impedance of the spark gap stack itself and the control can be further influenced with the help of shunt impedances 9 and 10 inserted parallel to the rods and also connected to the cross-impedance 8. The shunt impedances preferably consist of capacitive elements, but other impedance elements are also feasible.
As mentioned previously, it is not necessary for all the parallel rods to be alike. On the contrary, it may even be suitable to make them different so that at least one of them ignites earlier when an overvoltage occurs. If the column 1 in the drawing is so dimensioned that it ignites first, the voltage drop over the upper and lower spark gap stack in this column will fall to a low value before the extension of the arc due to the magnetic field has started to make itself noticeable. Most of the voltage drop in the column 1 then lies in the beginning across the resistance stack 5 and this voltage drop is transferred to the lower spark gap stack of the column 2 with a time delay determined by the cross-impedance 8 and the impedance of the spark gap itself, the shunt impedance 9 and 10. This increased voltage ignites the lower spark gap 7 stack of the rod 2 and then also the upper spark gap 6 so that the whole column 2 sparks over and in turn ignites the column 3 in the same way as the column 1 ignited the column 2.
After a certain time the arc is extended in the spark gap stacks in the column 1 and the impedance of this column increases so much that it gives a voltage drop across the column which corresponds to the voltage drop over the other rods. The current in the column 1 is thus forced down to such a low value that the arc through the column is extinguished and the current through the column is interrupted. At the moment of extinction the voltages over the upper and lower spark gap stacks in the column 1 are practically equal, but the voltage over the lower spark gap stack in the column 2 is very small since the arc extension has not had time to become apparent. This means that the voltage across the nonlinear resistance stack in the column 2 increases the voltage over the upper spark gap stack 6 in the column 1 so that, after a certain time, this reignites and the entire column 1 reignites and takes part in the discharge. A similar process takes place in each of the other rods and in this way the discharge voltage can be maintained at the desired level and a high extinction voltage is ensured, since the arc in the spark gap is extinguished as soon as it has been blown out to its full length due to the influence of the magnetic field and no appreciable heating of the gap takes place. Thus a repeated ignition and extinction of the arc in all the rods is obtained so that the current is constantly moved from one column to the other. This means that the discharge current can pass the overvoltage protection device without its extinguishing capacity being reduced.
By suitably dimensioning the cross-impedances 8 and possibly also the shunt impedances, the column 3 can be brought to spark over before the column 1 is extinguished. In this way it can be arranged that two rods burn simultaneously if this is suitable in order to obtain a sufficiently powerful discharge.
The energy absorption capacity of the protection device is substantially determined by the number of parallel-connected legs and can in principle be made any size.