Grounding Ring for Electric Submersible Motor Bearing Current
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Solution Overview
Problem
Voltage spikes and electrical harmonics generated by Variable Frequency Drives (VFDs) can cause voltage potentials between rotating and static components in downhole motors, leading to electrical arcs that break down the hydraulic oil film in plain journal bearings, resulting in catastrophic motor failure.
Innovation Solution
A grounding ring is installed on the lower end of the motor to provide a preferred current flow path to ground, reducing the current conducted through the bearings and minimizing voltage potential differences between the rotor and stator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a VFD is used to control motor speed and frequency, then productivity and operational control are improved, but voltage spikes and electrical harmonics are generated that can cause bearing current and motor failure
Solution Approach 1:
A grounding ring is introduced as an intermediary component between the motor shaft and the motor housing. This grounding ring provides a dedicated path for bearing current to flow to ground, acting as a mediator that intercepts harmful electrical currents before they can damage the bearings, while allowing the VFD to continue operating normally for speed control
2Reliability
If the hydraulic oil film in plain journal bearings acts as an insulator, then bearing protection is improved, but voltage potential builds up that creates electric arcs breaking down the oil film
Solution Approach 1:
The grounding ring connects the motor shaft to ground, establishing an equipotential connection that eliminates voltage potential differences between the rotating shaft and the stationary motor housing. By making the shaft ground-potential, electric arcs cannot form, and the hydraulic oil film remains intact without breakdown
Solution Approach 2:
The grounding ring serves as an intermediary conductive path that provides a controlled route for electrical currents. Instead of allowing uncontrolled arcing through the hydraulic oil film, the grounding ring intercepts bearing current and directs it safely to ground, preventing oil film breakdown while maintaining bearing protection
3Reliability
If bearing current flows through the motor bearings, then voltage potential is discharged, but damaging pitting and scoring of bearing materials occurs leading to motor failure
Solution Approach 1:
The grounding ring acts as a mediator that intercepts bearing current before it can flow through the bearing materials. By providing an alternative path to ground, the grounding ring protects the bearing races and rolling elements from the electrochemical damage that would otherwise occur, while still allowing voltage potential to be discharged safely
4Reliability
If a grounding ring is installed to provide a preferred current flow path, then bearing current is reduced, but device complexity increases
Solution Approach 1:
The grounding ring is a simple, inexpensive component that can be easily installed and replaced. Rather than using complex active electronics or sophisticated protection systems, the patent employs a basic conductive ring that provides effective bearing current protection through a passive, fail-safe design
Solution Approach 2:
The grounding ring provides a simple intermediary connection between the shaft and housing that effectively redirects bearing current without requiring complex control systems. This single component solution avoids the need for multiple sensors, controllers, and active elements, maintaining system simplicity while achieving reliable bearing protection
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 grounding ring effectively suppresses electrical interference, reduces noise, and provides reliable shaft grounding, protecting the bearings from destructive shaft voltages and currents, thereby increasing downhole motor reliability and preventing premature failure.
Implementation Method 1
The grounding ring may be configured to positively ground a rotor system. This may reduce conventional current that conducted between the rotor system and stator through the motor bearings.
Implementation Method 2
These bearings utilize a thin film of hydraulic oil to support the loads of the rotating system. This thin film may act as an insulator since hydraulic oil system of downhole motors is purposefully made to have very high dielectric properties.
Implementation Method 3
This potential grows to a point where it is large enough to produce an electric arc breaking down the thin film of the hydraulic oil in the plain journal bearings
Data Source
AI summary
Embodiments disclosed herein describe methods for an improved electrical connector system.