Schweitzer Engineering Laboratories, Inc.

Marcos A Donolo

Jay Hartshorn

Edmund O Schweitzer, Iii

Armando Guzman-Casillas

Subhash C Patel

Vinod K Yedidi

Angelo D'Aversa

Anushka M Dissanayake

Veselin Skendzic

Jianchun Qin

Pallavi Kulkarni

David E Whitehead

Normann Fischer

Scott M Manson

Mangapathirao Venkata Mynam

Chandrasekaran Swaminathan

Yusuf Zafer Korkmaz

Andrea Di Tomasso

Hang Li

A system for high-impedance differential protection for power systems using a variety of signals from the power system. A fault may be detected using filtered phase current or filtered phase voltage magnitudes from current transformers (CTs) connected in parallel by phase. A fault may be detected using filtered phase voltages and raw phase voltages from the CTs. A fault may be detected using raw phase currents and raw phase voltages from the CTs. A fault may be detected using filtered phase currents and raw phase currents. A fault may be detected using raw phase currents and raw neutral currents. The embodiments herein maintain dependability and security of a differential element even when low-class CTs are used. The embodiments herein may allow users to optimize pickup settings even when low-class CTs are used.

High-impedance differential protection using a diversity of signals

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

Systems and methods may be used to measure a frequency of a power delivery system and/or of a supply signal transmitted to a load. A system may record an input waveform, determine a frequency of the input waveform at a present time based at least in part on the input waveform and a derivative of the input waveform, and control an operation of a power delivery system based at least in part on the determined frequency.

Frequency sensing systems and methods

A system to reconfigure a motor from induction mode to synchronous mode at a zero crossing of the field voltage during startup using only stator current signals is described herein. The zero crossing may be detected by asymmetry induced in the stator currents by a current asymmetry inducing module of the motor. The current asymmetry inducing module may include a resistor and diode in series and in parallel with a discharge resistor of the field windings. Asymmetry is induced in the current obtained from the stator, and used to determine a zero crossing of the field voltage. Upon the rotor reaching a startup frequency and the detected zero-crossing of the field voltage, the motor may be reconfigured from induction mode to synchronous mode.

Synchronous motor startup configuration to synchronous mode at a field zero-crossing

Residual voltage measurements taken after removal of electric power to an electric motor are used to improve the functioning of an electric motor monitoring system. For example, an intelligent electronic device (IED) may acquire residual voltage measurements of a motor after disconnected electric power to the motor. The IED may determine a thermal condition of the motor based at least in part on the residual voltage measurement. The IED may prevent starting of the motor based at least in part on the thermal condition.

Motor monitoring and protection using residual voltage

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.

Electric power system differential protection with DC compensation

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

In-phase transfer of an electric power source to a load bus from a first feeder to a second feeder is disclosed herein. Voltage phase difference, voltage frequency difference, and voltage rate-of-change of frequency difference, between the second feeder and the load bus are used along with a breaker delay time to determine whether the breaker will close while the phase of the second feeder and the load bus are within an acceptable range. One or more breaker close time checks may be performed, including a breaker close time consistency check and a breaker close time uncertainty check.

In-phase motor bus transfer

Monitoring conditions of an electric motor using stator current and voltage signals from power supplied to the motor is disclosed herein. The stator voltage and current signals may be used to calculate instantaneous power values which may be used to calculate slip. The slip may be used to monitor for a locked rotor condition during startup of the motor. The slip value may be used to provide thermal protection to the electric motor.

Electric motor protection using stator current and voltage measurements

Monitoring a health status of a current interruption device, such as a circuit breaker, is disclosed herein. For example, a device for monitoring a current interruption device may include a processor and a memory. The processor may execute instructions stored in the memory to cause the processor to monitor one or more current measurements of current from an electrical conductor that delivers electrical energy to a load. The processor may provide a signal indicating a health status of the current interruption device based at least in part on the one or more current measurements.

Circuit breaker health monitoring

Systems and methods are disclosed herein for monitoring and detecting a loss of synchronism in an electric motor, such as a synchronous motor. A monitoring system may compare a measured or provided electric power system frequency with a measured rotational frequency of the rotor of the electric motor. The rotational frequency of the rotor may be obtained from a shaft-mounted device. The monitoring system may determine a slip condition and/or a loss of synchronism of the electric motor.

Systems and methods for motor slip calculation using shaft-mounted sensors

The present disclosure provides systems and methods for utilizing two or more magnetometers for current measurements. The systems and methods may include two or more multi-axis magnetometer sensors to monitor a high-voltage three-phase alternating current (AC) transmission line carrying a current, I. The magnetometers may be positioned at varying distances from the transmission line. The systems and methods may isolate or otherwise account for external magnetic fields, such as the earth's magnetic field, to generate accurate current measurements in a conductor.

Systems and methods for magnetometer-based current measurement

Disclosed herein is a shaft-mounted monitor for monitoring conditions of a rotating shaft using a calculated rotational component of the rotating shaft. The monitor may include a sensor such as an accelerometer, thermal sensor, strain gauge, or the like. In various embodiments, a variety of parameters relating to the rotating shaft may be monitored, such as a temperature, rotational speed, angular position, torque, power, frequency, or the like. The monitor may include a wireless transmitter to transmit the monitored condition of the rotating shaft to an intelligent electronic device or a monitoring system.

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Pullman, WA, United States of America

Marcos A Donolo