A system for high-impedance differential protection for power systems using a variety of signals from the power system. A fault may be detected using filtered phase current or filtered phase voltage magnitudes from current transformers (CTs) connected in parallel by phase. A fault may be detected using filtered phase voltages and raw phase voltages from the CTs. A fault may be detected using raw phase currents and raw phase voltages from the CTs. A fault may be detected using filtered phase currents and raw phase currents. A fault may be detected using raw phase currents and raw neutral currents. The embodiments herein maintain dependability and security of a differential element even when low-class CTs are used. The embodiments herein may allow users to optimize pickup settings even when low-class CTs are used.

Provided is an apparatus and method for controlling a circuit breaker for a static synchronous compensator (STATCOM) such that the circuit breaker installed in a branch line for the STATCOM is operated according to the current control characteristics of the STATCOM, the apparatus including: a transformer protector for detecting the differential current between primary current and secondary current of a transformer connected in series to the circuit breaker in the branch line, and controlling the opening/closing of the circuit breaker; and a STATCOM controller for controlling an operation of the STATCOM, wherein the STATCOM controller outputs, to the transformer protector, an opening suspension signal for suspending the opening of the circuit breaker when overvoltage occurring in the STATCOM is detected, and the transformer protector suspends output of a circuit breaker opening signal to the circuit breaker according to the received opening suspension signal.

A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device.

A circuit breaker includes a circuit breaker main body unit having a main circuit unit forming a circuit line of each phase, a current transformer part having a coil disposed in the circuit line of each phase and a pair of terminals extending from both ends of the coil and selectively connected to an external power source unit, and a safety switching part configured to connect the pair of terminals such that the pair of terminals are not opened, when the power source unit and the pair of terminals are separated.

An exemplary electrical network in form of a ring system includes a plurality of infeed transformers which are arranged in parallel between a sourcing busbar/cable system and a ring load busbar/cable system. A junction point connects each infeed transformer to the ring load busbar/cable system. The network includes a plurality of current limiters, where each current limiter is positioned between two junction points. Upon a fault event of an infeed transformer, two current limiters on both sides of a respective junction point of the faulted infeed transformer are simultaneously tripped in order to reduce current in the ring load busbar/cable system.

A power harvesting system employs a saturable core transformer having first and second primary windings and a secondary winding. The first primary winding is a high impedance winding with a large number of turns and the second primary winding is a low impedance winding with a small number of turns. The first and second primary windings are connected to a load. A relay is operable in a first state to connect A/C power to the first primary winding and in a second state to connect A/C power to the second primary winding. When A/C power is connected to the first primary winding, a small current flows in the first primary winding which is insufficient to activate the load but sufficient to transfer power to the secondary winding. When A/C power is connected to the second primary winding, a larger current flows in the second primary winding sufficient to activate the load and to transfer power to the secondary winding.

Methods and systems for ensuring operation of one or more circuit breakers electrically connected on a phase of a multi-phase power line on a transformer electrically connected within a power grid at a substation are disclosed. The method includes detecting, at the transformer, a direct current component of a multi-phase power signal received at the transformer, the direct current component comprising a direct current received at a transformer neutral, the transformer neutral being electrically connected to a ground. The method further includes determining whether the direct current is above a predetermined threshold, the predetermined threshold being based on a determination that, above the predetermined threshold, at least one of the one or more circuit breakers is incapable of reliable operation. The method includes, in response to a determination that the direct current component is above the predetermined threshold, blocking the direct current between the transformer neutral and a ground.

The open-phase condition of a standby power transformer is detected by monitoring functions of the phase currents. The functions have parameters calculated based on reference currents, which constitute a fingerprint when all the phases are connected.

A power distribution monitoring system is provided that can include a number of features. The system can include a plurality of monitoring devices configured to attach to individual conductors on a power grid distribution network. In some embodiments, a monitoring device is disposed on each conductor of a three-phase network and utilizes a split-core transformer to harvest energy from the conductors. The monitoring devices can be configured to harvest energy from the AC power grid and saturate the magnetic core of the transformer in the event of a fault condition or when harvested power is not needed. Methods of installing and using the monitoring devices are also provided.

An exemplary transformer protection system including a protective housing having a transformer which is arranged in the protective housing, a transformer core, and at least one primary-side electrical winding and a secondary-side electrical winding which is magnetically coupled to the primary-side electrical winding. The protection system also includes at least one detection apparatus for a measurement variable from which the occurrence of an interference arc within the protective housing can be derived, and an evaluation unit for generating a fault signal from the measurement variable of the at least one detection apparatus in the case of an interference arc. Further, the protection system includes at least one rapid-earthing apparatus for at least one of the electrical windings which is intended to be activated by the fault signal, wherein the rapid-earthing apparatus is designed in such a way that effective electrical earthing immediately after activation of the fault signal is ensured.