Method and a device for overvoltage protection, and an electric system with such a device
View Patent ↗A method and device for protecting an electric system against overvoltage occurrences, the electric system being adapted to be subjected to voltages. The device includes a plurality of surge arresters and a detector configured to detect overvoltage occurrences in the electric system. The surge arresters are connected in series, the plurality of surge arresters including a first surge arrester which is connectable to ground and a second surge arrester which is connectable to the electric system which is to be protected. The device includes a switch connected in parallel with at least one surge arrester of the plurality of surge arresters, and the switch is adapted to be open when no overvoltage occurrence is detected and adapted to close upon overvoltage occurrence detection and short-circuit the surge arrester with which it is connected in parallel. An electric system includes at least one such device.
1. A device for protecting an electric system against overvoltage occurrences, the electric system being adapted to be subjected to voltages, which device comprises a plurality of surge arresters and comprises a detector configured to detect overvoltage occurrences in the electric system, the surge arresters of said plurality of surge arresters being connected in series, and said plurality of surge arresters comprises a first surge arrester which is connectable to ground and a second surge arrester which is connectable to the electric system which is to be protected, the device comprises a switch connected in parallel with the first surge arrester, and the switch is adapted to be open when no overvoltage occurrence is detected and adapted to close upon overvoltage occurrence detection and short-circuit the first surge arrester, wherein the first surge arrester, has a lower knee-point voltage in relation to the other surge arresters of said plurality of surge arresters and a lower knee-point voltage in relation to the second surge arrester, where the knee-point value of the first surge arrester is a normalized voltage value of 0.8 p.u. and the knee-point value of the second surge arrester is a normalized voltage value of 1.0 p.u.
2. The device according to claim 1 , wherein the detector comprises a measuring device configured to measure the voltages applied to the electric system.
3. The device according to claim 1 , wherein the device comprises a control for controlling the switch, the control being connected to the detector, and the control is adapted to control the switch to close upon detection of overvoltage occurrence.
4. An electric system adapted to be subjected to voltages, comprising at least one device for protecting the electric system against overvoltage occurrences, wherein said at least one device comprises the device according to claim 1 .
5. The electric system according to claim 4 , wherein the electric system comprises a line-commutated converter to which the device is connected, and the device is adapted to protect the line-commutated converter against overvoltage occurrences.
6. The electric system according to claim 4 , wherein the electric system comprises a VSC-converter to which the device is connected, and the device is adapted to protect the VSC-converter against overvoltage occurrences.
7. The electric system according to claim 4 , wherein the electric system comprises a power transmission line to which the device is connected, and the device is adapted to protect the power transmission line against overvoltage occurrences.
8. The device according to claim 2 , wherein the device comprises a control for controlling the switch, the control being connected to the detector, and the control is adapted to control the switch to close upon detection of overvoltage occurrence.
9. An electric system adapted to be subjected to voltages, comprising at least one device for protecting the electric system against overvoltage occurrences, wherein said at least one device comprises the device according to claim 2 .
10. The electric system adapted to be subjected to voltages, comprising at least one device for protecting the electric system against overvoltage occurrences, wherein said at least one device comprises the device according to claim 3 .
11. The electric system according to claim 5 , wherein the electric system comprises a VSC-converter to which the device is connected, and the device is adapted to protect the VSC-converter against overvoltage occurrences.
12. The electric system according to claim 5 , wherein the electric system comprises a power transmission line to which the device is connected, and the device is adapted to protect the power transmission line against overvoltage occurrences.
13. The electric system according to claim 6 , wherein the electric system comprises a power transmission line to which the device is connected, and the device is adapted to protect the power transmission line against overvoltage occurrences.
14. A method for protecting an electric system against overvoltage occurrences, the electric system being adapted to be subjected to voltages, the method comprising the steps of:
connecting a plurality of surge arresters in series;
connecting a first surge arrester of said plurality of surge arresters to ground;
connecting a second surge arrester of said plurality of surge arresters to the electric system;
detecting overvoltage occurrences in the electric system; and
when overvoltage occurrence is detected, short-circuiting the first surge arrester by means of a switch which is connected in parallel therewith, wherein the first surge arrester, has a lower knee-point voltage in relation to the other surge arresters of said plurality of surge arresters, has a lower knee-point voltage in relation to the second surge arrester, with the knee-point value of the first surge arrester being a normalized voltage value of 0.8 p.u. and the knee-point value of the second surge arrester being a normalized voltage value of 1.0 p.u.
15. The method according to claim 14 , further comprising the steps of keeping the switch open when no overvoltage occurrence is detected, and closing the switch upon overvoltage occurrence detection to effect said short-circuiting of the surge arrester.
16. The method according to claim 14 , further comprising the step of short-circuiting the first surge arrester, upon overvoltage occurrence detection, by means of the switching means which is connected in parallel therewith.
17. The method according to claim 14 , wherein the step of detecting overvoltage occurrences comprises measuring the voltages applied to the electric system.
18. The method according to claim 15 , further comprising the step of short-circuiting the first surge arrester, upon overvoltage occurrence detection, by means of the switching means which is connected in parallel therewith.
19. The method according to claim 15 , wherein the step of detecting overvoltage occurrences comprises measuring the voltages applied to the electric system.
20. The method according to claim 16 , wherein the step of detecting overvoltage occurrences comprises measuring the voltages applied to the electric system.