Conductive Plate Coupling to Reduce Motor Shaft Voltage
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Solution Overview
Problem
The use of frequency converters in rotating electrical machines leads to common mode voltages, resulting in shaft voltages that cause bearing currents, which can wear down the bearings due to current flow to ground.
Innovation Solution
Introducing additional capacitance between the shaft and the machine frame, effectively connected in parallel with the bearing capacitance, to reduce shaft voltage by forming a capacitive coupling with an electrically conducting plate attached to the frame, thereby decreasing the voltage across the bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency converters are used to control rotating electrical machines, then voltage control precision and speed regulation are improved, but common mode voltages are generated that cause shaft voltages and bearing currents
Solution Approach 1:
An electrically conducting plate is introduced as an intermediary component between the shaft and the machine frame. This plate forms a capacitive coupling that acts as a mediator to divert common mode voltages away from the bearings, preventing bearing currents while maintaining the frequency converter's voltage control functionality
Solution Approach 2:
The electrically conducting plate is a simple, inexpensive component that can be easily installed and replaced if needed. It provides an effective solution to the bearing current problem without requiring complex or expensive modifications to the existing frequency converter or machine structure
2Object-generated harmful factors
If additional capacitance is added between the shaft and frame to reduce shaft voltage, then bearing currents are reduced, but device complexity increases
Solution Approach 1:
The electrically conducting plate is a simple, inexpensive component that can be easily installed and replaced if needed. It provides an effective solution to the bearing current problem without requiring complex or expensive modifications to the existing frequency converter or machine structure
Solution Approach 2:
The invention changes the electrical parameter (capacitance) of the system by adding the conducting plate, which modifies the voltage distribution across the capacitive coupling. This parameter change reduces shaft voltage and bearing currents without fundamentally altering the machine's mechanical structure or operation
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
This solution eliminates or reduces bearing currents, thereby increasing the service life of the rotating electrical machine by lowering the shaft voltage and distributing the common mode voltage more evenly across the capacitors.
Implementation Method 1
The additional capacitance is formed in an embodiment by attaching an electrically conducting plate with a hole for the shaft to the frame of the motor. With the electrically conducting plate, capacitance is formed between the plate and the shaft.
Data Source
AI summary
A rotating electrical machine and a method of manufacturing a rotating electrical machine. The machine including a machine frame, a rotor, a shaft attached to the rotor and bearings supporting the shaft and the rotor in the machine frame. The rotating electrical machine includes further an electrically conducting member having a hole, the electrically conducting member being attached to the frame such that the shaft extends through the hole.