Induction motor slip calculation
AssigneeSchweitzer Engineering Laboratories, Inc.
InventorsMarcos A. Donolo, Jay Hartshorn, Subhash C. Patel, Vinod K. Yedidi, Jianchun Qin
Life of this patent
Estimating the term…
Abstract
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.
Claims19
An intelligent electronic device (IED), comprising:
- a memory to store a full load rotor resistance value;
- a processor operatively coupled to the memory, wherein the processor is configured to:
- before disconnection, estimate the full load rotor resistance value as a function of motor-positive-sequence resistance, and calculate slip using the estimated full load rotor resistance for motor protection;
- after disconnection:
- acquire motor current and voltage measurements;
- measure zero-crossings of the voltage measurements;
- compute a time difference between the zero crossings;
- compute frequencies of the zero crossings;
- compute a slope of a frequency decay using the frequencies and a time of the zero crossings;
- compute a motor speed based on the slope;
- compute a slip frequency based on the motor speed;
- estimate the full load rotor resistance using the slip frequency;
- calculate motor slip using the acquired motor current and voltage measurements and the estimated full load rotor resistance value;
- and
- execute a motor protection process using the calculated motor slip.
A method for an IED, the method comprising:
- estimating a full load rotor resistance value as a function of motor-positive-sequence resistance;
- acquiring motor current and voltage measurements;
- measuring zero-crossings of the voltage measurements;
- computing a time difference between the zero-crossings;
- computing frequencies of the zero crossings;
- computing a slope of a frequency decay after the motor is disconnected using the frequencies and a time of the zero crossings;
- computing a motor speed based on the slope;
- computing a slip frequency based on the motor speed;
- estimating the full load rotor resistance value using the slip frequency;
- calculating motor slip using the acquired motor current and voltage measurements and the estimated full load rotor resistance value;
- and
- executing a motor protection process using the calculated motor slip.
An intelligent electronic device (IED), comprising:
- a memory to store a full load rotor resistance value;
- a processor operatively coupled to the memory, wherein the processor is configured to:
- upon disconnection:
- acquire motor current and voltage measurements;
- measure zero-crossings of the voltage measurements;
- compute a time difference between the zero crossings;
- computer frequencies of the zero crossings;
- compute a slope of a frequency decay using the frequencies and a time of the zero crossings;
- compute a motor speed based on the slope;
- compute a slip frequency based on the motor speed;
- estimate the full load rotor resistance using the slip;
- calculate motor slip using the acquired motor current and voltage measurements and the estimated full load rotor resistance value;
- and
- execute a motor protection process using the calculated motor slip.
Dependencies are inferred from the claim text.