Schweitzer Engineering Laboratories, Inc.

Subhash C Patel

Marcos A Donolo

Vinod K Yedidi

Angelo D'Aversa

Jay Hartshorn

Veselin Skendzic

Jianchun Qin

Stanley E Zocholl

George Edmund Alexander

Chandrasekaran Swaminathan

Anushka M Dissanayake

Pallavi Kulkarni

Hang Li

Signal transducers in electrical communication with shorted leads of current transformers are used to provide monitoring and protection functions to an electric power delivery system. Differential protection is performed by comparing a predetermined threshold against a voltage signal from series-connected leads of signal transducers in electrical communication with shorted leads of current transformers. The signal transducers may be Rogowski coils. Signal transducers in communication with shorted leads may be used to improve safety and increase performance of the current transformers by decreasing susceptibility to saturation.

Differential protection using instrument transformer signal transducers

A method includes receiving electrical measurements of an input signal of a power system. The method includes determining an estimated frequency of the power system using a rate of change of phase of the power system and using zero crossings of the power system. Selection between using the rate of change of phase of the power system and using zero crossings of the power system is based on a comparison between an estimated phase angle and a measured phase angle of the power system.

Frequency measurement for load shedding and accurate magnitude calculation

An intelligent electronic device (IED) according to the present disclosure can estimate a full load rotor resistance value as a function of motor positive-sequence resistance. The IED may estimate the full load rotor resistance value by measuring zero-crossings of voltage after a motor disconnect. The IED may also acquire motor current and voltage measurements and calculate motor slip using the acquired motor current and voltage measurements and the estimated full load rotor resistance value.

Induction motor slip calculation

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

Monitoring thermal conditions of an electric motor using current signals from power supplied to the motor is disclosed herein. The current signals may be used to calculate composite current values which may be used to calculate slip. The slip may be used to provide thermal monitoring and protection to the electric motor. Slip may be calculated using only values from the stator of the electric motor for providing thermal monitoring and protection to electric motors where rotor measurements are not available.

Electric motor thermal protection using stator current measurements

An accurate slip calculation for providing monitoring and protection to an electric motor. The slip calculation is made using a minimum value of stator resistance as the initial stator resistance, where the minimum value of stator resistance is the minimum value of stator resistance calculated during an initiation period of the motor. The initiation period may be a predetermined time period or a predetermined number of cycles during the motor startup. The initiation period may start after a predetermined settling time or after a predetermined condition is met.

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West Chester, PA, United States of America

Subhash C Patel