Schweitzer Engineering Laboratories, Inc.

Demetrios A Tziouvaras

Jeffrey B Roberts

Gabriel Benmouyal

Daqing Hou

Hector J Altuve-Ferrer

Ralph W Folkers

The present disclosure provides systems and methods for calculating the flux in a core of an unloaded power transformer using current measurements taken from a capacitance-coupled voltage transformer (CCVT) attached to the same phase line as the power transformer. According to various embodiments, the current sensors may both be positioned at zero-voltage points in the CCVT, eliminating the need for high-voltage insulated current sensors. An intelligent electronic device (IED) may determine the magnetic flux within the core of the power transformer using the measured and/or derived currents through capacitive assemblies of the CCVT. The IED may calculate the residual flux in the power transformer when it is de-energized. The IED may use the calculated residual flux to facilitate an optimized re-energization of the power transformer, thereby reducing inrush currents during re-energization.

Systems and methods for determining residual flux in a power transformer

A system and method for accomplishing power swing blocking and unstable power swing tripping schemes during disturbances of electrical networks is disclosed. The disclosed system and method eliminates the requirement of stability studies. The no-setting scheme utilizes the swing center voltage of the electrical network to carry out its functions.

Systems and methods for protection of electrical networks

The fault identification system includes a first logic circuit which is responsive to conventional protective elements which recognize the presence of low resistance single line-to-ground faults for the A, B and C phases on a power transmission line. The first logic circuit includes a portion thereof for recognizing and providing an output indication of single line-to-ground faults, faults involving two phases and three-phase faults, in response to the occurrence of different combinations of outputs from the protective elements. A calculation circuit, when enabled, is used to determine the angular difference between the total zero sequence current and the total negative sequence current for high resistance faults when the protective elements themselves cannot identify fault conditions. The angular difference is in one of three pre-selected angular sectors. An angular difference in the first sector indicates an A phase-to-ground fault or a BC phase-to-phase to ground fault; an angular difference in the second sector indicates a B phase-to-ground fault or a C phase-to-phase to ground fault; and a signal in the third sector indicates a C phase-to-ground fault or an AB phase-to-phase to ground fault. A processor is used to determine which of the two possible for each angle determination is the actual fault type. An output indication of the actual fault type is then provided.

Fault type selection system for identifying faults in an electric power system

In a power line current differential protection system, all three phase current values (I , I and I ) are obtained from both the local end and the remote end of a power transmission line. The magnitude of the ratio of the remote current values to the local current values are calculated. Also, the angle difference between the local and the remote current values for each phase are calculated. Comparison elements then compare the ratio and angle values against preselected values which establish a restrain region in the current ratio plane. Current values which result in the ratio being within the region do not result in a tripping signal for the circuit breaker on the power transmission line, while current values which result in a ratio outside of the region result in a tripping of the circuit breaker. Similar circuitry is used for negative sequence current quantities, with the negative sequence preselected values being set substantially lower to produce a more sensitive response to possible faults in the line.

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Vacaville, CA, United States of America

Demetrios A Tziouvaras