The present disclosure relates to methods and devices for calculating winding currents at a delta side for a transformer. The transformer has two or more windings, with a first winding being a delta connected winding. The method includes obtaining line currents measured with measurement equipment associated with lines connected with the windings. The method further includes calculating zero sequence currents for at least a second winding, from the line currents of a corresponding line. The method further includes calculating zero sequence currents for the first winding, based on the zero sequence currents for at least the second winding, a phase displacement between the windings, and a turns ratio associated with the windings. The winding currents is calculated from the zero sequence currents of the first winding, and the line currents of a corresponding line.

A protection circuit is disclosed. The protection circuit includes a direct current (DC) blocking component electrically connected between a neutral of the transformer and a ground, and an overvoltage protection device electrically connected in parallel with the DC blocking component. The overvoltage protection device is constructed to repeatably and reliably provide overvoltage protection in response to a voltage at the transformer neutral above a threshold. The DC blocking component has an impedance below a predetermined value, thereby effectively grounding the neutral of the transformer. The DC blocking component is persistently maintained in connection to the transformer neutral.

A differential protection method for generating a fault signal. Current measurement values are acquired at different measuring points of a component. Differential current values and stabilizing values are formed using the current measurement values, and the fault signal is generated when a tripping range test indicates that a measured value pair formed from one of the differential current values and a respective associated stabilizing value lies in a predetermined tripping range. Differential current values are estimated from successive differential current values and associated stabilizing values and associated estimated stabilizing values are formed. A value of an expected future trend of the differential current values and of the stabilizing current values is estimated. A tripping range test finds the position of a measured value pair formed from an estimated differential current value and the respective associated estimated stabilizing value. An electrical protective device has a corresponding evaluation unit.

A differential protection method for generating a fault signal. Current measurement values are acquired at different measuring points of a component. Differential current values and stabilizing values are formed using the current measurement values, and the fault signal is generated when a tripping range test indicates that a measured value pair formed from one of the differential current values and a respective associated stabilizing value lies in a predetermined tripping range. Differential current values are estimated from successive differential current values and associated stabilizing values and associated estimated stabilizing values are formed. A value of an expected future trend of the differential current values and of the stabilizing current values is estimated. A tripping range test finds the position of a measured value pair formed from an estimated differential current value and the respective associated estimated stabilizing value. An electrical protective device has a corresponding evaluation unit.

A differential protection method allows monitoring a three-phase transformer. Current measured values are recorded for each phase on all sides of the transformer, a phase-related formation of difference values is carried out using the current measured values from a reference side and amplitude-adjusted and phase-angle-adjusted current measured values from all other sides. An internal error is detected if a difference value exceeds a threshold value. In order to form the amplitude-adjusted and phase-angle-adjusted current measured values, the current measured values recorded for all phases are initially subjected to an amplitude adjustment and then to a phase angle adjustment. In order to allow the phase angle shift to be freely adjusted, a defined matrix equation with a defined matrix coefficient is used for the phase angle adjustment of the current measured values from the particular other side of the transformer. There is also described a differential protection device.

A differential protection method allows monitoring a three-phase transformer. Current measured values are recorded for each phase on all sides of the transformer, a phase-related formation of difference values is carried out using the current measured values from a reference side and amplitude-adjusted and phase-angle-adjusted current measured values from all other sides. An internal error is detected if a difference value exceeds a threshold value. In order to form the amplitude-adjusted and phase-angle-adjusted current measured values, the current measured values recorded for all phases are initially subjected to an amplitude adjustment and then to a phase angle adjustment. In order to allow the phase angle shift to be freely adjusted, a defined matrix equation with a defined matrix coefficient is used for the phase angle adjustment of the current measured values from the particular other side of the transformer. There is also described a differential protection device.

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 contactpair (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).

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 contactpair (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).

An electrical transformer includes a first winding, called primary, at least one second winding, called secondary, switches, and a current detection system, wherein it comprises at least one metal screen having a connection point linked to a neutral potential of the primary winding or intended to be linked to an electrical ground and placed between the primary winding and the at least one secondary winding, the screen being made of an electrically conductive material having a melting point higher than that of the materials constituting the windings; in that the primary winding comprises an input intended to be linked to an external energy source, the switches are placed at the input of the primary winding so as to be able to isolate the primary winding from the external energy source and in that the current detection system is configured to detect a current at the input of the primary winding or a current at the connection point and to close or open the switches based on the detection of the current, the detection system being differential or thermal.

A protection circuit is disclosed. The protection circuit includes a direct current (DC) blocking component electrically connected between a neutral of the transformer and a ground, and an overvoltage protection device electrically connected in parallel with the DC blocking component. The overvoltage protection device is constructed to repeatably and reliably provide overvoltage protection in response to a voltage at the transformer neutral above a threshold. The DC blocking component has an impedance below a predetermined value, thereby effectively grounding the neutral of the transformer. The DC blocking component is persistently maintained in connection to the transformer neutral.