Rotary Electric Machine Isolation for Parasitic Current Measurement
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Solution Overview
Problem
Multi-phase AC machines experience parasitic currents due to common-mode voltage excitations, which can lead to arcing and resistive losses, necessitating a method to characterize and mitigate these induced voltages and currents.
Innovation Solution
An apparatus for electrically isolating a rotary electric machine is designed, featuring an enclosure with isolated bearings, slip rings, and a rotational sensor, along with a fixture mechanically grounded through isolator pads to minimize parasitic currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the bearings are directly attached to the end plates, then the structural complexity is reduced, but parasitic currents are induced causing arcing and resistive losses
Solution Approach 1:
The patent introduces an intermediate bearing hub component between the end plate and the bearing. This hub acts as a mediator that provides both mechanical support and electrical isolation, preventing parasitic current paths while maintaining structural integrity. The bearing hub is electrically isolated from the end plate, breaking the harmful current path without adding excessive complexity to the overall structure.
2Reliability
If the fixture is mechanically grounded to the enclosure, then grounding is achieved, but parasitic currents are induced through the enclosure
Solution Approach 1:
The patent introduces isolator pads as intermediary components between the fixture brackets and the enclosure. These pads provide mechanical coupling for grounding while simultaneously blocking electrical current paths. The isolator pads allow the fixture to be grounded through the enclosure structure without creating direct electrical pathways that would induce parasitic currents in the stator windings.
3Device complexity
If the static portion of the rotational sensor is directly affixed to the end plate, then the device complexity is reduced, but parasitic currents are induced
Solution Approach 1:
The patent introduces an isolator pad as an intermediary component between the static portion of the rotational sensor and the end plate. This isolator pad provides mechanical support for the sensor while simultaneously providing electrical isolation to prevent parasitic current paths from forming through the sensor mounting structure.
4Device complexity
If the slip rings are directly supported by the end plates, then the structural complexity is reduced, but parasitic currents are induced
Solution Approach 1:
The patent introduces isolator pads as intermediary components between the slip rings and the end plates. These isolator pads provide mechanical support for the slip rings while simultaneously providing electrical isolation to prevent parasitic current paths from forming through the slip ring support structure.
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
The apparatus effectively isolates the rotary electric machine, reducing parasitic currents and their associated effects, while allowing for the characterization of induced voltages and currents, thereby enhancing machine design and operation.
Implementation Method 1
the bearings being isolated from the end plates
Implementation Method 2
the enclosure is mechanically grounded to the fixture through a fixture bracket that is isolated from the enclosure by an isolator pad
Implementation Method 3
first and second slip rings maintaining dynamic galvanic contact with the rotor at respective opposite ends
Implementation Method 4
O-ring seals between each respective isolator pad and the respective bearing hub and between the respective isolator pad and the respective one of the first and second end plates
Data Source
AI summary
An enclosure for a rotary electric machine may include a housing supporting a stator of the electric machine and first and second end plates attached to the housing and rotatably supporting a rotor at opposite ends with respective first and second bearings isolated from the end plates.