Electric submersible pump control with the ACS880 drives

If the pump’s motor is started in a situation where oil is flowing back to the reservoir, the pump is forced to rotate in a reverse direction. This situation causes torque that can be very stressful for the motor shaft, potentially resulting in a failure. Backspin control detects the rotating rotor and delays restart, until it is safe to execute. Utilizing this method, a user can get rid of backspin timers, eliminate production delays and increase the well output.

In case the normal pumping mode is requested, a flying start (i.e. starting into the rotating motor) is also possible during the backspin procedure.

Energy optimization function of the drive software optimizes motor’s operation so that total energy consumption is minimized when the drive operates below nominal load. Total efficiency of the motor and drive combination can be improved up to 20% depending on load torque and speed. Energy optimization function is a handy way to reduce energy consumption while maintaining motor performance.

Motor voltage and frequency relationship can be modified via an automatic voltage/frequency curve setting of the drive’s software. Optimal voltage/frequency curve improves the ESP motor efficiency and increases motor lifetime by decreasing running temperature.

Customer comment: “10% reduction in motor current equates to a 5 degree reduction in motor temperature. As these motors are operating at upper limits of temperature tolerances, this is a significant change.”

Traditionally similar modification has been done manually when the step-up transformer tappings have been changed. By doing the change automatically without stopping the pump, the significant risk associated with restarting the pump is reduced.

While an ESP is pumping, it may occasionally ingest gas. Bigger quantities of gas will result in reduction or removal of fluid flowing over the motor casing which can cause overheating of the motor. The presence of gas can be detected from a pump underload condition, and the drive will automatically begin a recovery sequence to get rid of the gas and continue pumping. This helps extend motor lifetime without sacrificing productivity.

In ESP applications the starting can sometimes be challenging e.g. due to step-up transformer and solid material, like sand, that is stuck to impeller blades. ACS880 drive’s ESP control program includes various advanced features to overcome these challenges.

• Rocking start helps to remove solids stuck to impeller blades. The rocking start can be activated e.g. for every start or when the current needed to operate the pump has increased above the activation level.
• Torque thrust is an alternative for rocking start, without backward rotation of the pump. Clogging is prevented with a series of torque thrusts.
• Kick start and acceleration assistance are starting modes that deliver more starting torque than traditional IR compensation, resulting in a more reliable start. Kick start and acceleration assistance can be used both with induction and permanent magnet motors (IR compensation is only suitable with induction motors).
  

ACS880 ESP control program has a possibility to measure the actual flow rate by using pump specific pump curves. The user is also informed if pump operate in the nonproductive area i.e. down thrust or up thrust area.