A power conversion system including: a self-excited power converter that converts power between an alternating-current (AC) power system and a direct-current (DC) line; an AC circuit breaker disposed between the AC power system and the self-excited power converter; an arrester connected between the DC line and a ground or between an AC line and the ground, the AC line connecting the AC circuit breaker and the self-excited power converter; and a control device. The control device causes the self-excited power converter to stop a switching operation when the control device detects a ground fault accident on the DC line, and opens the AC circuit breaker after the self-excited power converter stops the switching operation.

A power conversion system includes a first switch configured to be connected between a first phase of a polyphase alternating current (AC) power source and an electrical load and a first diode configured to be connected between the first phase of the polyphase AC power source and the electrical load, the diode configured to conduct a current from the AC power source to the electrical load. The power conversion system also includes a control unit configured to interface with the first switch to close, responsive to the occurrence of a short circuit fault, the first switch during a negative current portion of the AC cycle of the first phase of the polyphase AC power source and open, responsive to the occurrence of the short circuit fault, the first switch during a positive current portion of the AC cycle of the first phase of the polyphase AC power source.

In a method for coordinating a distribution grid of different levels of electromechanical switches and automatically electrically closable apparatuses in a DC circuit, the distribution grid is arranged between feed-in devices and loads and includes at least one busbar. Each of the apparatuses includes an electrical switch to open or close the DC circuit, a fault current detection device, a tripping unit, and a pre-charging apparatus.

An electrical network is equipped with feed-in devices, loads, a distribution grid arranged therebetween, at least one semiconductor switch, and at least one electromechanical switch for separating a feed-in device or a load in the event of a fault. The feed-in devices and loads are arranged in groups which are connected together by a busbar and paired semiconductor switches. Each feed-in device and load can be separated from the grid by an electromechanical switch in the event of a fault, and the individual groups of feed-in devices and loads can be separated from one another by the semiconductor switches in the event of a fault in order to prevent cross currents on the busbar.

An electrical network includes feed-in devices, loads, and a distribution grid, which is arranged therebetween and 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 detection device; 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. Multiple loads can be individually electrically separated via a respective electromechanical switch, and multiple loads can be electrically separated as a group via the at least one device.

An example method may include generating an alternating current (AC) output at a power source within a borehole in a subterranean formation. An electrical component may receive a direct current (DC) output from a converter circuit coupled to the power source and the electrical component. One or more measurements corresponding to the power source, the converter circuit, the electrical component, or a protection circuit coupled to the converter circuit may be received. Blocking devices within the protection circuit may be selectively caused to block current flow in the converter circuit based, at least in part, on the one or more received measurements.

Systems, methods, techniques and apparatuses of fault protection. One exemplary embodiment is a protection system including a solid-state switching device, a galvanic isolation switching device, and a controller. The solid-state switching device is coupled between a switch arrangement of a power converter and a direct current (DC) link capacitor of the power converter. The galvanic isolation switching device is coupled between the DC link capacitor and a DC network. The controller is structured to determine a fault is occurring within the DC network, open the solid-state switching device in response to determining the fault is occurring, receive a measurement corresponding to an electrical characteristic of a fault current flowing through the galvanic isolation switching device while the solid-state switching device is open, and determine a location of the fault based on the received measurement.

An AC/DC converter includes: an AC circuit breaker, configured as a hybrid circuit or semiconductor circuit breaker; a rectifier; a smoothing capacitor; a semiconductor switch connected in series with the smoothing capacitor; and a first isolation relay for galvanic isolation. One input of the AC circuit breaker forms an AC input of the converter. One output of the AC circuit breaker is connected with an input of the rectifier. The smoothing capacitor, and the first semiconductor switch, connect a first output of the rectifier with its second output. The first output of the rectifier is connected, with one input of the first isolation relay. The one output of the first isolation relay forms a first DC output of the AC/DC converter. The AC circuit breaker, the first semiconductor switch, and the first isolation relay are interconnected.

A control unit of an electrical system is described. The control unit causes some of the switches in a power converter of the electrical system to not be shut down and not conducting upon detection of a fault current caused by a line-to-line fault. Instead, the control unit causes at least one of the switches to be switched-on and conducting to allow the some of the fault current to flow through the at least one switch, before activating a protection device that creates an open circuit and breaks the fault.

A modular multilevel converter (MMC) includes multiple converter arms, each converter arm having: N submodules connected to each other in series, N being an integer equal to or greater than 2; and a circuit opening unit connected to the N submodules in series to open a circuit of the converter arm, wherein the N submodules has n submodules including full-bridge circuits and N−n submodules including half-bridge circuits, n being less than N.