In Electric Submersible Pump (ESP) installations, when the power supply is removed, it is possible for the fluid column to drain back to the reservoir. This may occur in installations where there is no check valve installed or the check valves are leaking. As the fluid drains back down the tubing, the submersible pump is forced to rotate in the reverse direction; commonly referred to as “backspin.” Starting the motor under this condition can be very stressful to its shaft, potentially causing failure.
The SUBCOE Reverse Rotation & Ground Fault system monitors the rotating frequency and direction of the downhole motor, and intelligently determines when conditions are safe to start the ESP. In case where a well is naturally flowing (fluid moving up the tubing without the ESP running), the RRGFS–RRGFR system will permit starting as the downhole motor direction is known to be forward and it is safe to start.
While the ESP is running, the SUBCOE RRGFS–RRGFR system will also monitor the Leg Ground by measuring each phase of the downhole motor with respect to ground. When insulation in a single motor winding degrades, a ground fault may occur. This type of fault can be detected at the surface and displayed as Leg Ground through the RRGFR. When an insulation breakdown occurs on two or more phases of the motor, a serious failure has occurred and the motor/cable should be repaired or replaced. Ground fault monitoring is therefore a useful maintenance tool for determining the health of ESP electrical insulation.
The SUBCOE RRGFS–RRFGR system is designed to work with Variable Frequency Drives (VFDs) and/or switchboard motor controllers through RS485 Modbus or digital inputs to monitor and control the following:
- Reverse rotation of the downhole motor
- Ground Fault (voltage imbalance in downhole cable)
- Fundamental phase voltage and operating frequency of the downhole motor.
Integrated Backspin Protection System (IBPS)
The IBPS is a CSA Special Inspected, stand alone, enclosure system that connects to the monitored motor leads, a power supply and the power system control device to directly monitor any system voltage (up to 4750V) and measure the line voltage and to recognize the presence of backspin in the pump system.