DC circuit breaker
Disclosed is a DC circuit breaker capable of interrupting fault currents flowing in both forward and backward directions. The DC circuit breaker includes: a mechanical switch installed on a DC transmission line and being opened to interrupt a current in the DC transmission line when a fault occurs at one side or remaining side thereof on the DC transmission line; a first bidirectional switching device connected in parallel with the mechanical switch and switching currents flowing in both forward and backward directions; an LC circuit connected in parallel with the mechanical switch and including a capacitor and a reactor connected in series to induce LC resonance; a first unidirectional switching device connected in parallel with the LC circuit and switching a current to induce LC resonance; and a second bidirectional switching device connected in series with the LC circuit and switching currents flowing in both forward and backward directions.
1. A DC circuit breaker comprising:
a mechanical switch installed on a DC transmission line and being opened to interrupt a current in the DC transmission line when a fault occurs at one side or a remaining side thereof on the DC transmission line;
a first bidirectional switching device, connected in parallel with the mechanical switch, for switching currents flowing in both forward and backward directions;
an LC circuit connected in parallel with the mechanical switch and including a capacitor and a reactor connected in series with each other to induce LC resonance;
a first unidirectional switching device, connected in parallel with the LC circuit, for switching a current, to induce LC resonance; and
a second bidirectional switching device, connected in series with the LC circuit, for switching currents flowing in the both forward and backward directions.
2. The DC circuit breaker according to claim 1 , wherein the first and second bidirectional switching devices respectively include a first power semiconductor switch and a second power semiconductor switch that are turn-on/turn-off controllable, are connected in parallel, and are arranged to be counter to each other and a pair of power semiconductor switches that are turn-on/turn-off controllable are connected in parallel, and are arranged to be counter to each other, and wherein the first unidirectional switching device includes a single power semiconductor switch that is turn-on/turn-off controllable.
3. The DC circuit breaker according to claim 2 , wherein when a fault occurs at the one side on the DC transmission line, in a state in which the mechanical switch is open and the second bidirectional switching device is in an OFF state, the first unidirectional switching device is turned on such that the capacitor is charged to a voltage Vc through LC resonance in the capacitor and the reactor, and subsequently the first unidirectional switching device is turned off and the first power semiconductor switch of the first bidirectional switching device and a third power semiconductor switch of the second bidirectional switching device are turned on such that a current is supplied through a closed circuit of the first power semiconductor switch and the third power semiconductor switch due to the voltage Vc charged in the capacitor, thereby preventing a current from being supplied to the mechanical switch.
4. The DC circuit breaker according to claim 3 , wherein when a fault occurs at the one side on the DC transmission line, opening the mechanical switch and changing the capacitor to the voltage −Vc through the first unidirectional switching device that is turned on are simultaneously performed, or sequentially performed in this order or in a reverse order.
5. The DC circuit breaker according to claim 3 , wherein as a current is supplied to the first power semiconductor switch, a transient recovery voltage generated in the mechanical switch is lowered by a reverse voltage applied between terminals of the mechanical switch.
6. The DC circuit breaker according to claim 2 , wherein when a fault occurs at the remaining side on the DC transmission line, the mechanical switch is opened and the second power semiconductor switch of the first bidirectional switching device and a fourth power semiconductor switch of the second bidirectional switching device are turned on such that a current is supplied through a closed circuit of the second power semiconductor switch and the fourth power semiconductor switch due to a voltage +Vc charged in the capacitor, thereby preventing a current from being supplied to the mechanical switch.
7. The DC circuit breaker according to claim 6 , wherein when a fault occurs at the remaining side on the DC transmission line, opening the mechanical switch and supplying the current through the closed circuit of the second power semiconductor switch and the fourth power semiconductor switch using the voltage +Vc stored in the capacitor are simultaneously performed or sequentially performed in this order or a reverse order.
8. The DC circuit breaker according to claim 6 , wherein as a current is supplied to the power semiconductor switch, a transient recovery voltage generated in the mechanical switch is lowered by a reverse voltage applied between terminals of the mechanical switch.
9. The DC circuit breaker according to claim 6 , further comprising a second unidirectional switching device connected in parallel with the first unidirectional switching device and switching a current flowing in a reverse direction with respect to the current switched by the first unidirectional switching device to induce LC resonance in the LC circuit.
10. The DC circuit breaker according to claim 9 , wherein after a fault current is interrupted in the mechanical switch, the second unidirectional switching device is turned on such that the capacitor is charged to a voltage −Vc through the LC resonance in the capacitor and the reactor.
11. The DC circuit breaker according to claim 1 , further comprising a resistor installed between a ground and a contact point between the LC circuit and the second bidirectional switching device.