Schweitzer Engineering Laboratories, Inc.

Jianchun Qin

Marcos A Donolo

Subhash C Patel

Vinod K Yedidi

Angelo D'Aversa

Jay Hartshorn

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

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

Disclosed herein are systems and methods for converting data samples representing alternating electric currents. The data samples may be obtained by sampling a first alternating electric current having a first frequency at a sampling frequency, sampling a second alternating electric current having a second frequency at the sampling frequency, and converting the data samples using a conversion algorithm to compensate for any discrepancy caused by the difference between the first frequency and the second frequency. The corrected data samples may be utilized to determine various characteristics of the alternating electric current, such as voltage magnitude, voltage phase angle, current magnitude, current phase angle, and other related attributes. In one application, the systems and methods disclosed herein may be utilized in connection with an intelligent electronic device used to couple a first electrical system, such as a power generator, to a second electrical system, such as a utility intertie.

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