Provided is a determination method of differential protection suitable for an electricity transmission line with multi-terminal T-connection. The determination method includes: sampling and calculating all phase currents, and calculating a maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current, a differential current I.sub.cd in the each phase current, a resistive current I.sub.res in the each phase current and a vector sum Δİ.sub.Σ of fault component currents except Δİ.sub.max in the phase current amplitudes of the each phase current; and comparing the maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current and a threshold setting value I.sub.max0, determining a value of a resistive coefficient K corresponding to the phase current amplitudes of the each phase current according to a comparison result, and performing differential determination on the differential current I.sub.cd and the resistive current I.sub.res in phase current amplitudes of the each phase current according to a differential determination formula: if the differential current I.sub.cd of the target phase satisfies the above differential determination formula, it is determined that a fault occurs in an area of the target phase.

Provided is a determination method of differential protection suitable for an electricity transmission line with multi-terminal T-connection. The determination method includes: sampling and calculating all phase currents, and calculating a maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current, a differential current I.sub.cd in the each phase current, a resistive current I.sub.res in the each phase current and a vector sum Δİ.sub.Σ of fault component currents except Δİ.sub.max in the phase current amplitudes of the each phase current; and comparing the maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current and a threshold setting value I.sub.max0, determining a value of a resistive coefficient K corresponding to the phase current amplitudes of the each phase current according to a comparison result, and performing differential determination on the differential current I.sub.cd and the resistive current I.sub.res in phase current amplitudes of the each phase current according to a differential determination formula: if the differential current I.sub.cd of the target phase satisfies the above differential determination formula, it is determined that a fault occurs in an area of the target phase.

An intelligent electronic device (IED) may obtain a residual flux of each phase of a transformer. The IED may determine a maximum difference (DIF) signal based on the residual flux and the prospective flux associated with potential close POWs of the corresponding phase. The TED may select a closing POW that results in a minimum DIF signal. The TED may send a signal to close a ganged switching device of the transformer at a time based on the selected closing POW.

A transformer system including a transformer including a set of wye windings, a three-phase current transformer, a neutral-current transformer, and a controller. The three-phase current transformer outputs a first signal indicative of a three-phase current conducting through the set of wye windings and the three-phase current transformer. The neutral-current transformer couples the current flowing from the ground to the neutral node of the transformer, and outputs a second signal indicative of a neutral current conducting from the ground node to the neutral node of the transformer. The controller receives the first signal and the second signal, determines whether an external ground fault condition or an internal ground fault condition is present based on the three-phase current and the neutral current, and determines whether a wiring error is present for the three-phase current transformer or the neutral-current transformer based on the three-phase current and the neutral current.

Provided is a determination method of differential protection suitable for an electricity transmission line with multi-terminal T-connection. The determination method includes: sampling and calculating all phase currents, and calculating a maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current, a differential current I.sub.cd in the each phase current, a resistive current I.sub.res in the each phase current and a vector sum Δİ.sub.Σ of fault component currents except Δİ.sub.max in the phase current amplitudes of the each phase current; and comparing the maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current and a threshold setting value I.sub.max0, determining a value of a resistive coefficient K corresponding to the phase current amplitudes of the each phase current according to a comparison result, and performing differential determination on the differential current I.sub.cd and the resistive current I.sub.res in phase current amplitudes of the each phase current according to a differential determination formula: if the differential current I.sub.cd of the target phase satisfies the above differential determination formula, it is determined that a fault occurs in an area of the target phase.

Provided is a determination method of differential protection suitable for an electricity transmission line with multi-terminal T-connection. The determination method includes: sampling and calculating all phase currents, and calculating a maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current, a differential current I.sub.cd in the each phase current, a resistive current I.sub.res in the each phase current and a vector sum Δİ.sub.Σ of fault component currents except Δİ.sub.max in the phase current amplitudes of the each phase current; and comparing the maximum fault component current Δİ.sub.max in phase current amplitudes of each phase current and a threshold setting value I.sub.max0, determining a value of a resistive coefficient K corresponding to the phase current amplitudes of the each phase current according to a comparison result, and performing differential determination on the differential current I.sub.cd and the resistive current I.sub.res in phase current amplitudes of the each phase current according to a differential determination formula: if the differential current I.sub.cd of the target phase satisfies the above differential determination formula, it is determined that a fault occurs in an area of the target phase.

A current transformer connector (10; 102) for connecting a current transformer of an electrical network to a protection relay via a current transformer data acquisition board (12; 104), is provided. The current transformer connector (10; 102) comprises first and second pairs (14, 20) of first and second current contacts (16, 18, 22, 24), each current contact pair (14, 20) being connectable in use to the current transformer so as to permit current flow from the electrical network through the current contact pairs (14, 20) to the protection relay. Each current contact pair (14, 20) is arranged to be in a short circuit configuration. The first current contact (16, 22) in each current contact pair (14, 20) is arranged to be independently moveable relative to the corresponding second current contact (18, 24) so that during initial insertion of the current transformer data acquisition board (12; 104) into the current transformer connector (10; 102) in use the first current contact (16) of the first current contact pair (14) is configured to separate from the second current contact (18) of the first current contact pair (14) to permit breaking of the short circuit configuration of the first current contact pair (14) and making of an electrical connection between the first current contact pair (14) and the current transformer data acquisition board (12; 104), while the second current contact pair (20) remains in the short circuit configuration. The first current contact (16, 22) in each current contact pair (14, 20) is further arranged to be independently moveable relative to the corresponding second current contact (18, 24) so that during further insertion of the current transformer data acquisition board (12; 104) into the current transformer connector (10; 102) in use the first current contact (22) of the second current contact pair (20) is configured to separate from the second current contact (24) of the second current contact pair (20) to permit breaking of the short circuit configuration of the second current contact pair (20).

Detection of, and protection against faults within a restricted earth fault (REF) zone of a transformer or a generator is disclosed herein. Security of the REF protection element uses comparison of a negative-sequence reference quantity. The REF condition is only detected when there is sufficient ground involvement and a fault in the reverse detection has not been detected. Dependability of the REF protection element in low-impedance grounded systems is improved by ensuring that the element operates when a zero-sequence reference quantity and a neutral operate quantity are orthogonal to each other. The REF protection element further determines an open CT condition and blocks detection of an REF fault upon determination of the open CT condition. A tripping subsystem may issue a trip command based upon detection of the REF condition.

Detection of, and protection against faults within a restricted earth fault (REF) zone of a transformer or a generator is disclosed herein. Security of the REF protection element uses comparison of a negative-sequence reference quantity. The REF condition is only detected when there is sufficient ground involvement and a fault in the reverse detection has not been detected. Dependability of the REF protection element in low-impedance grounded systems is improved by ensuring that the element operates when a zero-sequence reference quantity and a neutral operate quantity are orthogonal to each other. The REF protection element further determines an open CT condition and blocks detection of an REF fault upon determination of the open CT condition. A tripping subsystem may issue a trip command based upon detection of the REF condition.

A system and method for determining when an electronic interrupting device will open in response to detecting overcurrent, where the interrupting device protects a transformer in a power distribution network. The method includes obtaining a time/current through fault protection curve that is defined by a plurality of time/current points for the transformer that identifies when the transformer may experience thermal or mechanical damage in response to a certain current flow over a certain time in the transformer windings, selecting a time multiplier, and determining an operating curve for the interrupting device by multiplying the multiplier and a time portion of each of the plurality of time/current points on the through fault protection curve, where the operating curve identifies when the interrupting device will open in response to a certain current flow over a certain time.