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US 2010/0060227 A1Published application
Motor protection using accurate slip calculations
AssigneeSchweitzer Engineering Laboratories, Inc.
InventorsStanley E. Zocholl, Subhash C. Patel
Life of this patent
Estimating the term…
Abstract
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.
Claims36
A method for providing thermal protection and monitoring to a three-phase electric motor during startup of the motor, comprising:
- sampling an electrical signal to the motor;
- calculating positive-sequence voltage values from the sampled electrical signal during a startup period;
- calculating positive-sequence current values from the sampled electrical signal during the startup period;
- calculating resistance values from the calculated positive-sequence voltage values and the calculated positive-sequence current values during the startup period;
- determining an initial resistance value equal to a minimum of the resistance values calculated during a predetermined initiation period;
- calculating slip values from the initial resistance value;
- calculating rotor resistance values from the slip values;
- and,
- calculating rotor temperature from the rotor resistance values and current values sampled from the power signal to the motor.
6 more elements
A system for monitoring a rotor temperature of a rotor of a three-phase electric motor during a startup period, comprising;
- a three-phase electric motor comprising a rotor, a stator, and an electric power input for providing electric power to the electric motor;
- a current transformer in communication with the electric power input for providing a current signal;
- a potential transformer in communication with the electric power input for providing a voltage signal;
- a first sampler in communication with the current transformer for sampling the current signal to provide current samples;
- a second sampler in communication with the potential transformer for sampling the voltage signal and to provide voltage samples;
- a positive-sequence current calculator in communication with the first sampler for calculating positive-sequence current values from the current samples;
- a positive-sequence voltage calculator in communication with the second sampler for calculating positive-sequence voltage values from the voltage samples;
- a resistance calculator in communication with the positive-sequence current calculator and the positive-sequence voltage calculator for calculating resistance values from the positive-sequence current values and the positive-sequence voltage values;
- an initial resistance calculator in communication with the resistance calculator for determining an initial resistance value equal to a minimum of the resistance values during a predetermined initiation period;
- a slip calculator in communication with the initial resistance calculator and the resistance calculator for determining slip values from the initial resistance value and the resistance values;
- a rotor resistance calculator in communication with the slip calculator for calculating slip-dependent rotor resistance values from the slip values;
- and
- a rotor temperature calculator in communication with the rotor resistance calculator and the first sampler, for calculating rotor temperature values from the current values and the slip-dependent rotor resistance values.
10 more elements
An apparatus for monitoring a rotor temperature of a rotor of a three-phase electric motor during a startup period, comprising;
- a first sampler in communication with an electric power input to the electric motor for sampling a current signal to provide current samples;
- a second sampler in communication with the electric power input for sampling a voltage signal and to provide voltage samples;
- a positive-sequence current calculator in communication with the first sampler for calculating positive-sequence current values from the current samples;
- a positive-sequence voltage calculator in communication with the second sampler for calculating positive-sequence voltage values from the voltage samples;
- a resistance calculator in communication with the positive-sequence current calculator and the positive-sequence voltage calculator for calculating resistance values from the positive-sequence current values and the positive-sequence voltage values;
- an initial resistance calculator in communication with the resistance calculator for determining an initial resistance value equal to a minimum of the resistance values during a predetermined initiation period;
- a slip calculator in communication with the resistance calculator and the initial resistance calculator for determining slip values from the resistance values and the initial resistance value;
- a rotor resistance calculator in communication with the slip calculator for calculating slip-dependent rotor resistance values from the slip values;
- and
- a rotor temperature calculator in communication with the rotor resistance calculator and the first sampler, for calculating rotor temperature values from the current values and the slip-dependent rotor resistance values.
7 more elements
Dependencies are inferred from the claim text.