Backspin Detection in Electrical Submersible Pumps
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Solution Overview
Problem
Current methods for detecting backspin in electrical submersible pump motors are inadequate, as they rely on monitoring residual magnetism voltage, which is not reliable for determining when a motor has stopped backspinning, potentially leading to motor shaft breakage due to sudden power surges when restarting.
Innovation Solution
A system and method that utilize sensors to measure motor impedance and fluid properties, with a controller comparing these measurements to thresholds to detect backspin and prevent power restoration until the motor has ceased spinning, employing a variable speed drive and power cable to monitor current and impedance, ensuring safe restart conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current method of monitoring voltage generated by residual magnetism is used to detect backspin, then the detection system is simple, but the detection reliability is insufficient leading to potential motor shaft breakage
Solution Approach 1:
The patent replaces the electrical measurement method (monitoring residual magnetism voltage) with a mechanical measurement method (using vibration sensors to detect motor housing vibrations). This substitution provides more reliable backspin detection because mechanical vibrations are directly caused by the backspin motion itself, whereas voltage measurements are indirect and can be unreliable. The vibration sensor directly measures the physical phenomenon of backspin, improving detection reliability while maintaining reasonable system complexity.
2Productivity
If power is restored immediately after shutdown, then productivity is maintained, but motor shaft breakage occurs due to sudden torque surge during backspin
Solution Approach 1:
The patent implements a feedback control system where the vibration sensor continuously monitors motor housing vibrations and provides real-time feedback to the controller. The controller processes this feedback signal and compares it against threshold values to determine backspin conditions. Based on this feedback, the controller automatically controls power delivery to the motor, preventing power restoration during backspin and only allowing restart when vibrations indicate safe conditions. This closed-loop feedback ensures both safety and productivity by making restart decisions based on actual motor conditions.
Solution Approach 2:
The patent performs preliminary detection of backspin conditions before allowing power restoration. The vibration sensor continuously monitors for backspin vibrations during the shutdown period, and the controller evaluates these vibrations in advance before permitting restart. This preliminary action ensures that the motor is in a safe state before power is restored, preventing sudden torque surges that could cause shaft breakage while still enabling quick restart when conditions are appropriate.
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
Effectively detects backspin and prevents motor shaft damage by ensuring the motor is not restarted until it has stopped spinning, thereby extending motor lifespan and maintaining production efficiency.
Implementation Method 1
The current method of detecting a backspinning motor is to monitor the voltage generated by the residual magnetism of the motor. This voltage is proportional to the motor shaft speed and disappears when the motor stops.
Data Source
AI summary
A system for determining whether a motor in an electrical submersible pump is backspinning is described herein. The system comprises a sensor mounted in a well bore proximate to a ground surface, the sensor outputting a backspin signal; a communication link connected to the sensor, the communications link communicating the backspin signal; and a controller receiving the backspin signal from the communications link and processing the backspin signal to determine whether the motor is backspinning. Computer readable instructions associated with the system perform the steps of: monitoring the signal to determine whether the signal is above a threshold, the threshold for determining whether the signal is a noise signal or a backspin signal, and outputting the backspin signal; impeding operable AC power to the motor, responsive to the backspin signal; monitoring the backspin signal to determine whether the backspin signal is below the threshold; and returning AC power to the motor responsive to the determination that the backspin signal is below the threshold.