Differential protection of electric power delivery system equipment using a compensated operating signal under spurious conditions is disclosed herein. Current transformers (CTs) may provide spurious current signals under certain operating conditions resulting in unintended operation of differential protection. The present disclosure uses a compensated operating signal during such conditions. The compensated operating signal is calculated using operate current and a difference between direct current content of currents obtained from the CTs. Switching between use of the operate current and the compensated operating signal is based on a comparison of the average direct current content of the CTs and a threshold.

Differential protection of electric power delivery system equipment using a compensated operating signal under spurious conditions is disclosed herein. Current transformers (CTs) may provide spurious current signals under certain operating conditions resulting in unintended operation of differential protection. The present disclosure uses a compensated operating signal during such conditions. The compensated operating signal is calculated using operate current and a difference between direct current content of currents obtained from the CTs. Switching between use of the operate current and the compensated operating signal is based on a comparison of the average direct current content of the CTs and a threshold.

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 monitors a line of an electrical energy supply network. Current signals are generated at the ends of the line using inductive current transformers, which current signals are proportional to a current flowing at the respective end. For each end, current measurement values are formed from the respective current signal using measuring devices, which current measurement values indicate a profile of the current flowing at the respective end. For each end, a respective charge value is determined from the current measurement values. The charge values of all the ends are summed to form a charge sum, and a fault signal that indicates an internal fault on the line is generated when the charge sum exceeds a charge threshold value. To perform line differential protection in the case of current transformer saturation, when transformer saturation of a current transformer is present, an estimated charge value is ascertained.

The present disclosure relates to a method for preventing a maloperation of differential protection of an optical fiber caused by saturation of a single Current Transformer (CT) of 3/2 connection. By applying a combination of the differential judgment and the sub-CT current judgment, reliable identification of internal and external faults is ensured, and the problem of misjudging of the internal fault as the external fault can be prevented as well.

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.

Methods and systems to prevent relay misoperation and enhance relay dependability during ultrasaturation is disclosed. An ultrasaturation detection system may identify an ultrasaturation condition by comparing a differential current to a first and second derivative of the differential current. When an ultrasaturation condition is determined to be present, the ultrasaturation detection system may provide parameters to a relay to prevent misoperation and enhance relay dependability.

The present invention discloses a method for identifying the fault by current differential protection and a device thereof. The method comprises: measuring the full component currents of the two terminals of a two-terminal line system and calculating the corresponding fault component current vectors; obtaining an operate value by calculating a first difference between an absolute value of the sum of the fault component current vectors and I.sub.set1; obtaining a restrain value by multiplying a second difference with a control factor, in which the second difference is calculated between the maximum of the absolute values of the fault component currents and I.sub.set2 or between the absolute value of the difference of said fault component currents and I.sub.set2; and identifying a fault as an external one or internal one by comparing the operate value with the restrain value. The solutions of the present invention achieve better reliability, sensitivity and faster speed than existing products.

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.

A differential protection method monitors a line of an electrical energy supply network. Current signals are generated at the ends of the line using inductive current transformers, which current signals are proportional to a current flowing at the respective end. For each end, current measurement values are formed from the respective current signal using measuring devices, which current measurement values indicate a profile of the current flowing at the respective end. For each end, a respective charge value is determined from the current measurement values. The charge values of all the ends are summed to form a charge sum, and a fault signal that indicates an internal fault on the line is generated when the charge sum exceeds a charge threshold value. To perform line differential protection in the case of current transformer saturation, when transformer saturation of a current transformer is present, an estimated charge value is ascertained.