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 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.

Disclosed are systems and methods to determine an overexcitation condition on electric power delivery system equipment that includes a magnetizing core. Overexcitation conditions are determined even during sub-synchronous resonance, ferro-resonance, and other complex events. Power system voltage is integrated and normalized to determine a flux on the magnetizing core. The flux is compared with a protection model to determine the overexcitation condition on the magnetizing core. Once an overexcitation condition is detected, a protective action may be taken to remove power from the effected power delivery system equipment.

A differential protection method for generating a fault signal includes measuring current measurements at least at two different measuring points of a multiphase transformer for each phase. The current measurements for each phase are used to form differential current values and stabilization values. The fault signal is generated if it is determined during a trigger region check that a measurement pair of at least one of the phases, being formed by using one of the differential current values and the associated stabilization value in each case, is in a predefined trigger region. In order to be able to selectively and reliably distinguish an external fault from an internal fault, the transformer has a grounded star point and a zero system current flowing through the star point is used to form the stabilization values. A corresponding differential protection device is provided for performing the differential protection method.

Examples of the disclosure include a system for modifying a trip level of a circuit, the system comprising a protection device configured to activate responsive to a differential current exceeding the trip level, a first current transformer coupled to an input of the circuit, a second current transformer coupled to the output of the circuit, at least one measurement circuit coupled to the first current transformer and to the second current transformer, the at least one measurement circuit being configured to obtain a first current measurement from the first current transformer, obtain a second current measurement from the second current transformer, determine a bias current based on the first current measurement and the second current measurement, and modify the trip level of the protection device based on the bias current.

Disclosed are systems and methods to determine an overexcitation condition on electric power delivery system equipment that includes a magnetizing core. Overexcitation conditions are determined even during sub-synchronous resonance, ferro-resonance, and other complex events. Power system voltage is integrated and normalized to determine a flux on the magnetizing core. The flux is compared with a protection model to determine the overexcitation condition on the magnetizing core. Once an overexcitation condition is detected, a protective action may be taken to remove power from the effected power delivery system equipment.

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.

The present invention is concerned with pre-magnetizing a Modular Multilevel power Converters connected transformer in order to moderate inrush currents upon connecting the transformer to an electric grid. The invention takes advantage of the high amount of stored energy in MMC converters as compared to other converter types. This stored energy is used to pre-magnetize the converter-connected transformer, therefore no additional or dedicated pre-magnetizing hardware is required in addition to the charging hardware provided to charge the converter capacitors. As the transformer pre-magnetizing takes place subsequent to the converter charging, the converter charging circuit is not used to, and therefore does not need to be designed to, directly magnetize the transformer.

A method of current differential protection performed in a control device is disclosed, wherein the control device has a first operate-restrain characteristic with a differential characteristic pick-up setting I.sub.D. The method includes: determining currents of all terminals of a protected object; determining a differential current based on the determined currents; determining direct current, DC, components in the respective determined currents; detecting a fault; and adjusting, for a detected external fault, the operate-restrain characteristics by setting an adjusted differential characteristic pick-up setting I.sub.D.sub._.sub.adj to be equal to the sum of the differential characteristic pick-up setting I.sub.D and the determined DC components, providing an adapted operate-restrain characteristics. Corresponding control device, computer program and computer program product are also disclosed.

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.