A power system for a marine ship includes a plurality of protection zones, wherein at least two protection zones are coupled to each other via at least one bus-tie converter. Each of the protection zones includes a plurality of direct current (DC) buses and a plurality of power converters. The bus-tie converter includes at least two converter legs coupled by at least one inductor. Each converter leg includes a first branch connected with a snubber circuit by an intermediate switching device. The first branch includes two outer switching devices and at least one inner switching device connected between the two outer switching devices. The snubber circuit includes a combination of a diode, a resistor and a capacitor. A controller controls the operation of the plurality of power converters and the at least one bus-tie converter.

A T-breaker is an all-in-one solution for dc microgrid fault protection, power flow control, and power quality improvement. A T-breaker features a modular multilevel “T” structure with integrated energy storage devices. The two horizontal arms of the T-breaker realize fault current breaking, load voltage compensation, and power flow control; and the vertical arm of the T-breaker realizes shunt compensation. The configuration provides excellent voltage scalability and relaxes the requirements on the switching signal synchronization during fault transients. The local energy storage in sub-modules eases the fault energy dissipation requirement placed on the traditionally-adopted surge arrestors. The modular multilevel structure also offers immense control flexibility for all types of targeted functions of the provided T-breaker.

While transient current magnitudes at different locations within a DC distribution system themselves are not a reliable indicator of fault location, it is recognized herein that accumulating energy or pseudo energy values provides a reliable basis for tripping the protection element at a fault location. Thus, in one aspect of the teachings herein, pseudo energy values are accumulated independently during a fault condition, for each of one or more protected branch circuits and the protection element for each such branch circuit is tripped responsive to the accumulated pseudo energy values reaching a defined pseudo energy threshold. The pseudo energy thresholds are defined so that the protection element in the branch circuit where the fault is located will trip first.

A DC-power system including a main DC bus, a power generating unit arranged to feed the main DC bus, an isolator switch arranged between the main DC bus and the power generating unit for isolating the power generating unit from the main DC bus in case of a main DC bus fault, a drive unit arranged to be fed by the main DC bus, wherein the drive unit includes a drive unit bus system, converter units connected to the drive unit bus system, and fuses arranged between the drive unit bus system and the converter units for protecting the converter units in case of a drive unit fault.

A source-network coordination type direct-current (DC) circuit breaker based on pre-charged capacitors for an MMC based DC grid is provided. The MMC based DC grid is provided with four converter stations, each having two converters, which are in loop connection through a double-loop DC overhead line. Two ends of each DC line connecting the converters are separately equipped with DC circuit breakers for isolating a fault of the DC line. An MMC active voltage adjusting control strategy is matched with pre-charged capacitor voltage in the self-adaptive mode to provide a beneficial breaking condition for a quick mechanical switch branch, so that the fault line is effectively cut off.

An electric power system includes a direct voltage rail (101), battery elements (102-104) connected with supply-converters (105-107) to the direct voltage rail, and load-converters (111-113) for converting direct voltage of the direct voltage rail into voltages suitable for loads of the electric power system, where the supply-converters and the load-converters are connected with over-current protectors (108-110, 114-116) to the direct voltage rail. The electric power system further includes a capacitor system (117) connected to the direct voltage rail and capable of supplying fault current for switching an over-current protector into a non-conductive state in response to a fault causing a voltage drop at an electrical node connected to the direct voltage rail via the over-current protector. The capacitor system may include one or more high-capacitance electric double layer capacitors. The fault current available from the capacitor system enables a selective protection.

A power supply device includes: a first system; a second system; an inter-system switch configured to be able to connect and disconnect between the first system and the second system; a determining unit configured to keep the inter-system switch in an ON state in a normal time, and turn off the inter-system switch and determine which system a ground fault has occurred in, if detecting a ground fault of the first system or the second system; and a suppression circuit configured to suppress an electric discharge of the second power supply and supply electric power for ground fault detection to the second system, and the determining unit determines whether any ground fault has occurred in the second system or not, based on the electric power which is supplied from the suppression circuit to the second system.

In the conventional elimination of a short-circuited point by using fuses, due to the fuse characteristics, it is not possible to ensure cooperation at the respective melting times of fuses in a short-circuit state. To solve such a problem, provided are a converter which limits a current passing through a distribution line in a short-circuit state and has a constant power drooping characteristic of passing a current greater than or equal to a rated current through the distribution line for a fixed time, and relays which have an operating characteristic of detecting a current greater than or equal to the rated current and hierarchically opening switches within the fixed time.

Technologies for detecting a fault location in a DC electrical distribution system include a bus protection unit that monitors a DC electrical bus. The bus protection unit includes at least one sensor to produce sensor data indicative of one or more characteristics of the DC electrical bus monitored by the bus protection unit. The bus protection unit monitors the sensor data, determines whether a fault has occurred based on the sensor data, and determines whether the fault occurred within a bus zone defined by the DC electrical bus in response to determining that the fault has occurred. Further, the bus detection unit trips isolation devices within the bus zone in response to a determination that the fault occurred within the bus zone or a communication from another bus protection unit indicating the fault has occurred within the bus zone. The bus protection unit transmits a bus fault indication signal to another bus protection unit in response to a determination that the fault has occurred.

The present invention relates to a system for distributing electrical energy, comprising an electricity grid configured to supply electrical energy to end users, characterized in that the grid is operated on a direct voltage.