High voltage DC breaker apparatus
View Patent ↗A high voltage DC breaker apparatus configured to interrupt a fault current occurring in a high voltage DC conductor comprises a mechanical interrupter, at least one semiconductor device connected in series with the interrupter, an arrester connected in parallel with the semiconductor device and an LC-circuit connected in parallel with the series connection of the semiconductor device and the interrupter. A control unit is configured to, upon detection of a fault current, control switching of the semiconductor device at a frequency adapted to the values of an inductance and a capacitance of the LC-circuit for charging the capacitance by the fault current while making the current through the interrupter oscillating with an increasing amplitude and the interrupter to open for having the mechanical contacts thereof separated when current zero-crossing is reached for obtaining interruption of the fault current through the interrupter.
1. A DC breaker apparatus capable of interrupting a fault current occurring in a high voltage DC conductor, said apparatus comprising
at least one mechanical interrupter configured to be connected in series with said DC conductor, and
an arrangement configured to obtain zero-crossing of the current through said interrupter upon occurrence of a fault current in said conductor,
a control unit configured to control said arrangement and mechanical interrupter,
wherein said arrangement comprises
at least one semiconductor device of turn-off type connected in series with said mechanical interrupter,
an arrester connected in parallel with said semiconductor device for defining a maximum voltage across said device, and
an LC-circuit in the form of a series connection of an inductance and a capacitance connected in parallel with the series connection of said at least one semiconductor device and the mechanical interrupter,
and wherein
said control unit is configured to, upon detection of a fault current:
control switching of at least one of said at least one semiconductor devices at a frequency adapted to the values of said inductance and capacitance, in order to charge said capacitance by the fault current while making the current through the mechanical interrupter oscillate with an increasing amplitude, and
control the tripping of the mechanical interrupter so that the mechanical contacts thereof will be separated when a current zero-crossing is reached, so that interruption of the fault current through the mechanical interrupter is obtained, the DC breaker apparatus further comprising
at least one measuring device configured to measure at least one parameter relating to the operation of said arrangement upon occurrence of a said fault and send the result of a measurement to said control unit, and wherein the control unit is configured to adapt said switching in response to such measurement result.
2. The apparatus of claim 1 , wherein
said arrangement comprises a rectifying diode connected in anti-parallel with said semiconductor device.
3. The apparatus of claim 2 , wherein
said arrangement comprises a series connection of two semiconductor devices of opposite conducting directions and a series connection of two rectifying diodes of opposite conducting directions, wherein the semiconductor devices and rectifying diodes are connected such that each semiconductor device is connected in anti-parallel with a rectifying diode.
4. An apparatus according to claim 3 , wherein
the control unit is configured to carry out said switching of the semiconductor device at a frequency being 90% -110% of the eigenfrequency of said LC-circuit.
5. An apparatus according to claim 2 , wherein
the control unit is configured to carry out said switching of the semiconductor device at a frequency being 90% -110% of the eigenfrequency of said LC-circuit.
6. The apparatus of claim 1 , wherein
said arrangement comprises two semiconductor devices of opposite current direction connected in anti-parallel, said anti-parallel connection of semiconductor devices being connected in parallel with said arrester.
7. An apparatus according to claim 6 , wherein
the control unit is configured to carry out said switching of the semiconductor device at a frequency being 90% -110% of the eigenfrequency of said LC-circuit.
8. An apparatus according to claim 1 , wherein
the control unit is configured to carry out said switching of the semiconductor device at a frequency being 90% -110% of the eigenfrequency of said LC-circuit.
9. An apparatus according to claim 8 , wherein
said measuring device is configured to measure the current through said semiconductor device.
10. An apparatus according to claim 9 , wherein said measuring device is configured to measure the voltage across said capacitance.
11. An apparatus according to claim 1 , wherein said control unit is configured to delay initiation of separation of the mechanical contacts of the interrupter by a determined period of time with respect to the start of the switching of said semiconductor device for possibly refraining from opening the interrupter should said control unit receive -information about a disappearance of said fault within this period of time.
12. An apparatus according to claim 1 , further comprising a further arrester connected in parallel with said LC-circuit.
13. An apparatus according to claim 1 , wherein
the control unit is configured to carry out said switching of the semiconductor device with a frequency of 100 Hz -10 kHz or 500 Hz -5 kHz.
14. An apparatus according to claim 1 , wherein
said inductance has a value of 0.1 mH -10 mH.
15. An apparatus according to claim 1 , wherein said capacitance has a value of 10 nF -100 μF or 0.5 -5 μF.
16. An apparatus according to claim 1 , wherein
the protective level of said arrester connected in parallel with said semiconductor device is less than 50% or less than 10% of the voltage level intended for said high voltage DC conductor with respect to ground.
17. An apparatus according to claim 1 , further comprising a fault-current detector configured to detect occurrence of a fault current in a conductor in which the apparatus is connected.
18. An AC/DC converter station comprising an apparatus according to claim 1 , wherein the DC breaker apparatus is connected to said high voltage DC conductor of the AC/DC converter station.
19. A DC grid comprising an apparatus according to claim 1 , wherein the apparatus is configured to protect equipment of the DC grid.
20. A method of controlling a DC breaker apparatus for interrupting a fault current occurring in a high voltage DC conductor, the DC breaker apparatus including a mechanical interrupter and an arrangement configured to obtain zero-crossing of the current through said interrupter upon occurrence of a fault current in said DC conductor, the arrangement including at least one semiconductor device of turn-off type and an LC circuit in the form of a series connection of an inductance and a capacitance, wherein the method comprises:
initiating the switching of a said semiconductor device of turn-off type at a first frequency adapted to the values of said inductance and capacitance;
initiating the opening of the mechanical interrupter;
receiving measurements of at least one parameter relating to the magnitude of the current through the mechanical interrupter;
checking whether the ratio of an oscillating part of said current to a DC part of said current is larger than one but smaller than a predetermined value; and if not,
adjusting the frequency of the switching of the semiconductor device.