A system includes a generator. Three AC feeders are connected for feeding AC output from the generator. A rectifier is electrically connected to the three AC feeders and to a load via a first DC feeder and a second DC feeder. A first resistor connects between a first one of the DC feeders and ground. A first voltage sensor is operatively connected to detect voltage across the first resistor. A second resistor connects between the second DC feeder and ground. A second voltage sensor is operatively connected to detect voltage across the second resistor. A controller is configured to monitor for changes in common mode voltage based on the input from the first sensor and from the second sensor, and to determine presence of a fault if change in the common mode voltage exceeds a predetermined threshold.

A system includes a generator. Three AC feeders are connected for feeding AC output from the generator. A rectifier is electrically connected to the three AC feeders and to a load via a first DC feeder and a second DC feeder. A first resistor connects between a first one of the DC feeders and ground. A first voltage sensor is operatively connected to detect voltage across the first resistor. A second resistor connects between the second DC feeder and ground. A second voltage sensor is operatively connected to detect voltage across the second resistor. A controller is configured to monitor for changes in common mode voltage based on the input from the first sensor and from the second sensor, and to determine presence of a fault if change in the common mode voltage exceeds a predetermined threshold.

A generator system includes a generator including terminals, a generator circuit breaker coupled to the terminals and that couples and decouples the generator from a power grid, multiple sensors, and a controller that operates the generator system. The controller determines whether an active power is less than a reverse active power threshold and whether one or more turbine valves are closed, and determines that a breaker failure has occurred based on the active power being less than the reverse active power threshold and the one or more turbine valves being closed. If the active power remains less than the reverse active power and the turbine valves remain closed after a threshold time period after the trip command, and if a reactive power is less than a reverse reactive power threshold, then a breaker failure has occurred. In response, the controller may transmit another trip command to the generator circuit breaker to initiate the breaker failure protection.

A method for operating a wind turbine generator connected to a power network to account for recurring voltage faults on the power network caused by automatic reclosure of at least one circuit breaker following a short-circuit. The method comprises: identifying a deviation of voltage level of the power network from a normal operational voltage level of the network; determining that the identified deviation fulfils criteria for automatic reclosure; and operating the wind turbine generator in a recurring fault mode if automatic reclosure criteria are fulfilled. When operating the wind turbine generator in recurring fault mode, the method comprises: monitoring the recovery of the voltage level from the deviation; categorising the recovery of the voltage as one of at least a strong recovery or a weak recovery; and implementing a ride-through protocol according to the category of recovery.

An arrangement for injection-based ground fault protection handling including a number of stator windings of an electric machine that are connected to a neutral point, a first transformer including at least one primary winding connected to at least one measurement point of the stator windings and at least one secondary winding for measuring an electrical quantity of the machine at the measurement point. There is also a second transformer having a primary winding connected between the neutral point and a ground potential and a secondary winding for connection to a signal generation and detection unit in order to inject a signal into the neutral point and receive a response. The impedance of the second transformer is in the range of the impedance of the machine.

An arrangement for injection-based ground fault protection handling including a number of stator windings of an electric machine that are connected to a neutral point, a first transformer including at least one primary winding connected to at least one measurement point of the stator windings and at least one secondary winding for measuring an electrical quantity of the machine at the measurement point. There is also a second transformer having a primary winding connected between the neutral point and a ground potential and a secondary winding for connection to a signal generation and detection unit in order to inject a signal into the neutral point and receive a response. The impedance of the second transformer is in the range of the impedance of the machine.

Detection and protection against electric power generator rotor turn-to-turn faults, rotor multi-point-to-ground faults, and rotor permanent magnet faults is provided herein. A fractional harmonic signal is used to determine the rotor fault condition. The fractional harmonic signal may be a fractional harmonic magnitude of the circulating current of one phase. The fractional harmonic may be a fractional harmonic magnitude of a neutral voltage. A tripping subsystem may issue a trip command based upon detection of a rotor turn-to-turn fault condition.

Detection of electric power generator stator ground fault conditions and protection of the generator due to such conditions is provided herein. In one embodiment, a generator protection element may calculate generator third harmonic voltage quantities using measurements from the generator terminals, and determine a stator ground fault condition using the calculated generator third harmonic voltage quantity. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

Detection of electric power generator stator ground fault conditions and protection of the generator due to such conditions is provided herein. In one embodiment, a generator protection element may calculate generator third harmonic voltage quantities using measurements from the generator terminals, and determine a stator ground fault condition using the calculated generator third harmonic voltage quantity. A tripping subsystem may issue a trip command based upon detection of a stator ground fault condition.

An electrical converter (203) having an active diode-clamped multilevel topology is shown. Each clamping diode is connected in antiparallel with a switch (S5A, S5B). The converter comprises polyphase supply phases (A, B, C) each of which are connected via a respective phase leg (401, 402, 403) to dc rails (301, 302) and a dc-link capacitor. The dc-link capacitor includes a plurality of series-connected capacitors (404, 405). A controller is configured to, in response to an event signal, for each phase leg, activate a combination of switches therein to form a pair of parallel conduction paths to a midpoint (406) between two capacitors in the dc-link capacitor, thereby connecting each phase to the same node.