The invention relates to a grounding fault protection method for a high-voltage capacitor of a direct-current filter. The method comprises the following steps of acquiring a head end voltage u and an unbalanced current i.sub.T2 of a direct-current filter, and acquiring a discrete head end voltage and unbalanced current sequence; calculating a virtual capacitance C.sub.zd; determining a protection setting value C.sub.set according to the bridge arm capacitance of the high-voltage capacitor, and when the virtual capacitance C.sub.zd is larger than the protection setting value C.sub.set, protecting and judging to be an internal fault; otherwise, protecting and judging to be an external fault.

An electric grid includes feed-ins, loads, and a distribution grid, which is arranged therebetween. The distribution grid comprises at least one busbar and at least one device for opening or closing a DC circuit. The at least one device includes an electric switch for opening or closing the DC circuit, a fault current detector, a trigger unit, a precharging device, and a control unit for automatically closing the electric switch after the precharging process. The electric switch opens the DC circuit via the trigger unit if a fault current is detected by the fault current detector, and the precharging device restores the voltage on the busbar prior to closing the electric switch.

A circuit breaker device is for coupling a DC voltage branch to a positive and a negative conductor on a DC voltage bus. In an embodiment, the circuit breaker device includes a series circuit including a safety fuse and a unidirectional switch module. The switch module has a parallel circuit includes a controllable semiconductor switch element that is conductive in a first current direction and a diode that is conductive in the opposite current direction.

The present disclosure provides a control method for a current-limiting control circuit and an electrical system. The current-limiting control circuit includes a high voltage side connected with a direct-current (DC) bus, a low voltage side connected with a load, and a regulating unit connected with the high voltage side and the low voltage side, the regulating unit including at least one MOS transistor, and the control method includes: detecting current I.sub.0 of the current-limiting control circuit; determining whether the current I.sub.0 is greater than a preset current I; and determining that the current-limiting control circuit has a short circuit fault, and entering a current limiting control mode to limit a persistent growth of the current, in a case where the current I.sub.0 is greater than the preset current I.

A multi-voltage level direct current grid system and a control protection method, the direct current grid system comprising: at least two direct current buses; at least one direct current transformer, one end of which is connected to a first direct current bus while another end is connected to a second direct current bus or a lead-out wire, which may achieve direct current voltage conversion; and at least one lead-out wire current limiter, one end of the lead-out wire current limiter being connected to the second direct current bus while another end is connected to the lead-out wire; the lead-out wire current limiter comprises a first current-limiting unit, and the first current limiting unit comprises a group of direct current switches, as well as a first bypass switch and a first current-limiting resistor unit that are connected in parallel.

An energy storage system and a multi-stage short circuit protection system thereof are provided. The multi-stage short circuit protection system includes N stages of fuse units. Each battery pack is connected to a corresponding first-stage fuse unit, a direct-current side of a power conversion device is arranged with a third-stage fuse unit, and at least one second-stage fuse unit is arranged between multiple battery packs and the power conversion device. In a case that a short circuit fault occurs at a position on the direct-current side of the power conversion device, only a fuse unit at a stage preceding the position and a fuse unit at a stage following the position are broken, thereby avoiding a problem of a high maintenance cost in the conventional technology due to that all fuses are broken.

The present invention concerns a node of an HVDC grid composed of HVDC nodes and of a plurality of links interconnecting the HVDC nodes, each HVDC node being interconnected to at least one HVDC node of the HVDC grid by a link composed of conductive cables for high voltage direct current transportation and one optical fiber, at least one HVDC node being interconnected to at least two HVDC nodes, each HVDC node comprising, for each link connecting the HVDC node to the at least one other HVDC node, a link module comprising a fault sensing device, a breaker, and an optical transceiver for communicating through the optical fiber of the link.

A method is for locating a ground fault in a DC system to which a plurality of load zones can be connected. The method includes specifying a time window and, after the ground fault is detected, assigning the ground fault to a load zone which was connected to the DC system within the time window before the detection of the ground fault.

A method is for detecting a ground fault in a load zone that can be connected to a direct-current network. The load zone includes a first load zone line connectable to a first main line of the direct-current network via a circuit breaker, and a second load zone line connectable to a second main line of the direct-current network via an interrupter switch. In an embodiment of the method, at least one line voltage at a load zone line is continually measured. If a ground fault is not detected at any main line of the direct-current network before the load zone is connected, the interrupter switch is closed while the circuit breaker is open, and a ground fault in the load zone is inferred if at least one line voltage does not significantly change after the interrupter switch is closed.

A DC voltage switch includes a semiconductor-based electronically controllable switching device, a sensor provided upstream of the switching device for determining the DC voltage bus-side voltage level, a sensor provided downstream of the switching device for determining the DC voltage branch-side voltage level, a current sensor for determining current level and direction, a control device designed such that the direction and level of the current are determined, the flow of current is interrupted by the switching device when a first threshold value of the current level is exceeded, and when the first threshold value of the current level is exceeded in the reverse direction: the DC voltage bus-side voltage level is compared with the DC voltage branch-side voltage level, and the switching device is switched on upon a voltage difference being less than a voltage difference value.