Electric Motor Efficiency Monitoring via Stator Resistance
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Solution Overview
Problem
Existing motor efficiency monitoring systems require additional sensors and invasive methods to measure rotor speed and shaft torque, which are costly and disruptive, making it difficult to accurately determine motor efficiency in-service without interrupting industrial processes.
Innovation Solution
A system that uses a processor to determine motor efficiency online by measuring stator winding resistance, input voltage, and input current, without the need for rotor speed measurement, using existing sensors and pre-installed transformers in motor control centers, and calculates output power based on input power and stator resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If speed and torque transducers are used to directly measure motor rotor speed and shaft torque, then measurement precision of motor output power is improved, but device complexity and installation cost increase significantly
Solution Approach 1:
The patent extracts the measurement function from the motor output shaft side and relocates it to the input power side. By measuring input power, voltage, and current at the motor terminals and using equivalent circuit modeling, the system determines output power without requiring transducers on the rotor or shaft, thus eliminating complex installations while maintaining measurement precision
Solution Approach 2:
The patent introduces an equivalent circuit model as an intermediary between input measurements and output power determination. The model uses measured input parameters (voltage, current, power) along with motor nameplate data to calculate output power indirectly, serving as a mediator that eliminates the need for direct mechanical measurements
2Measurement precision
If motors are removed from service for efficiency testing, then measurement precision of motor efficiency is improved, but productivity and operational continuity deteriorate
Solution Approach 1:
The patent performs preliminary measurements of motor parameters (input power, voltage, current) while the motor is still in service. By collecting and processing this data through equivalent circuit modeling, the system determines efficiency online without requiring motor removal, thus maintaining productivity while achieving accurate measurements
Solution Approach 2:
The system enables motors to self-monitor their own efficiency by using measurements taken at their input terminals. The equivalent circuit model processes the motor's own electrical parameters to determine its efficiency, eliminating the need for external testing facilities or motor removal
3Measurement precision
If additional sensors and transducers are installed for efficiency monitoring, then measurement precision is improved, but ease of operation and installation simplicity worsen
Solution Approach 1:
The patent makes the existing input power measurement infrastructure multi-functional. The same voltage and current sensors used for basic power monitoring are also utilized for efficiency determination through equivalent circuit modeling, eliminating the need for additional dedicated sensors and simplifying installation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables non-intrusive, accurate determination of motor efficiency while the motor is in-service, reducing costs and minimizing downtime, as it does not require additional sensors or speed transducers, and can be implemented using existing infrastructure.
Implementation Method 1
determine a stator resistance of the electric motor in operation based on the voltage
Data Source
AI summary
A system and method for determining electric motor efficiency includes a monitoring system having a processor programmed to determine efficiency of an electric motor under load while the electric motor is online. The determination of motor efficiency is independent of a rotor speed measurement. Further, the efficiency is based on a determination of stator winding resistance, an input voltage, and an input current. The determination of the stator winding resistance occurs while the electric motor under load is online.