General Electric Company

Schweitzer Engineering Laboratories, Inc.

George Edmund Alexander

William James Premerlani

Stanley B Wilkinson

Emilie Thorbjorg Saulnier

Mark Gerard Adamiak

Birsen Yazici

Subhash C Patel

Detection of a locked rotor condition of an electric motor during startup herein uses a virtual speed switch. The methods and systems herein determine whether the motor is in a starting state, and the monitor the motor current to determine if it is greater than a predetermined threshold, and that the motor current decrease exceeds a predetermined threshold after a predetermined amount of time. If the decrease in motor current is not less than a predetermined threshold, then a speed switch bit is set, indicating that the rotor is turning. The methods and systems herein further determine whether a physical speed switch is faulty, and determine a locked rotor condition using the virtual speed switch signal, a physical speed switch signal, and whether the physical speed switch is faulty.

Electric motor protection using a virtual speed switch

A method of detecting faults on a power transmission line system includes simultaneously measuring phase current samples at each phase of each transmission terminal; calculating real and imaginary phaselets comprising partial sums of the phase current samples; for each phaselet, calculating a respective partial sum of squares of each phase current sample; calculating the sums of the real and imaginary phaselets over a variable size sliding sample window; calculating real and imaginary phasor components from the phaselets and a sum of the partial sums of the squares over the sample window; using the sums of the real and imaginary phaselets, the real and imaginary phasor components, and the sum of the partial sums of the squares to calculate a sum of squares of errors between the phase current samples and a fitted sine wave representative of the real and imaginary phasor components; using the sum of squares of errors to calculate a variance matrix defining an elliptical uncertainty region; determining whether a disturbance has occurred, and, if so, re-initializing the sample window; and determining whether a sum of current phasors from each terminal for a respective phase falls outside of the elliptical uncertainty region for the respective phase.

Digital current differential system

An improved reactance characteristic for an overall ground distance quadrilateral characteristic embodies a particular phase selector, possibly among a plurality of phase selectors and variables, that eliminates undesirable generation of a tripping signal other than only for a selected phase to ground fault. This phase selector is I,Z,, where Z,is the positive sequence replica impedance and I,is the fault component of the positive sequence current component, referenced to the proper phase. Preferably, the pre-fault load current is removed from this quantity. Additionally, an improved restricted phase directional function is implemented, further improving the overall performance of the quadrilateral characteristic relay.

Ground distance relay for AC power transmission line protection

A protective relay for detecting faults within a predetermined protected zone of a three phase alternating current electrical power distribution system, of the type which utilizes at least one restraint signal in conjunction with at least one operate signal to generate a net operate signal, generates an operate quantity which is related to a zero sequence component of current flowing in the power distribution system and a second operate quantity which is related to a negative sequence component of the current flowing in the power distribution system. The operate quantities are summed to form an operate signal. An adaptive restraint, which is proportional to a negative sequence component and a zero sequence component of a phase voltage of the power distribution system, is generated and utilized to provide increased sensitivity to higher resistance ground faults. A portion of a positive sequence component of the current flowing in the power distribution signal is utilized as a restraint signal to prevent the unit from operating on negative sequence currents present during normal load conditions. Adaptive restraint enables the directional overcurrent unit to operate correctly should a second fault occur on the transmission line during the period that one pole is open.

Negative and zero sequence directional overcurrent unit for AC power

A phase comparison type ground distance relay for a predetermined phase of three-phase AC transmission line includes a phase coincidence detector responsive to phase coincidence between an operating signal and a plurality of polarizing signals. Zero suppression networks are utilized for deriving second and third polarizing signals in order to improve discrimination between internal and external faults; thereby increasing the reliability of the relay operation and the security of the protection system. The second polarizing signal comprises that portion of a signal which exceeds a predetermined threshold value and which is related to the product of a signal proportional to the net current flowing in all three phases of the power system and the positive sequence replica impedence of the transmission line. The third polarizing signal comprises the sum of a signal related to the product of a negative sequence component of the current flowing in a predetermined phase of the AC power system and the positive sequence replica impedence of the transmission line; and that portion of a signal which exceeds a predetermined threshold value and which is related to the product of the net current flowing in all three phases of the system and the positive sequence replica impedence of the transmission line.

A phase relay utilizes improved polarizing and operating signals in order to provide discrimination between internal faults within a protected zone of an AC power transmission line and external faults than can appear as internal faults due to transients induced by capacitive voltage transformers or series capacitors. A zero sequence restraint signal is used to block operation of the phase relay on close-in single line to ground faults. A filter is used in a by-pass circuit to attenuate high frequency transients which might delay, and possibly prevent a trip output on an internal fault. A high set by-pass circuit, including zero suppression to preclude an output on an external fault, is employed to provide faster operating times on severe internal faults. Forward offset and/or zero suppression of the polarizing signal is used to reduce the characteristic timer setting and therefore increase the speed of the phase relay operation.

Growing community of inventors

Wallingford, PA, United States of America

George Edmund Alexander