Cable Conductors

The AC current is carried from the surface to the motor using either copper or aluminum cable conductors. For ESP applications, four sizes of conductors have been standardized: #1, #2, #4 and #6 AWG.

AWG stands for “American Wire Gauge”.

Power losses and operating temperature decrease by increasing the conductor size for a given current. Moreover, for a given conductor size increasing current will increase both the power losses and cable operating temperature.

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ESP cable

As shown in the figure below, the main cable consists of three conductor wires extending from the top of the motor flat lead extension to the wellhead banded to the production tubing. The ESP cable carries current (amperage) from the motor controller at the surface down to the motor.

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Updated list of API and ISO Standards for ESP

In this article, the last updated list of API & ISO standards for electrical submersible pump is presented. These standards can be considered as reference documents as well as a basis for training classes in the subject of electrical submersible pump.

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ESP motor

The electric submersible motor is simple in construction, rugged and reliable. In this article, the ESP motor compounds are detailed as well as their main functions.

Introduction to ESP motor:

  • ESP motor is installed below the motor seal and above the downhole sensor. In cases where a downhole sensor is not installed, the motor is installed at the very bottom of ESP string, generally attached to a motor guide.
  • ESP motor is an induction motor, two poles, three phases, squirrel cage type stator winding filled with specific motor oil, high dielectric strength (> 28 KV). The motor is rated for a specific horsepower, voltage, & current. Its role is to drive the downhole pump and seal section.
  • The ESP motor rotates at approximately 3500 RPM at 60 Hertz. The difference between actual and the synchronous speed (3,600 RPM) is called “motor slippage” and it is due to losses inside the motor. The actual RPM is usually noted on the motor nameplate (example:  3500 RPM / 60 Hz – 2917 RPM / 50 Hz).
  •  The ESP motor is constructed of rotors and bearings stacked on the shaft and loaded in a wound stator, the motor compounds will be detailed in the next section.
  • The motor contains synthetic dielectric mineral oil for lubrication, insulation, and for the homogeneous distribution of the heat generated inside the motor (cooling). Heat is then drawn off by the produced fluid past the housing OD on the way to the intake.

NB: ESP motor is close to the same design type as motors used on beam pumping units. Of course, it must be small in diameter in order to fit inside oil well casing sizes.

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Motor Seal

The Motor seal is installed below the intake and above the electric motor. It is also named: Equalizer, balance chamber, or Protector. Seal section types, functions, components, and applications are detailed in this article.

In addition to the main function of transferring the motor torque to the pump shaft, the seal section performs four primary functions (Equalization, Expansion, Isolation, & “Aabsorbsion):

  • Equalizes the pressure in the wellbore with the pressure inside the motor,
  • Provides area for motor oil expansion volume (induced by temperature changes in the motor),
  • Isolates the well fluid from the clean motor oil,
  • Absorbs the pump shaft thrust load (it houses the thrust bearing that carries the axial thrust developed by the pump, it can either be upthrust or downthrust, depending on the pumping conditions – obviously, for fixed impeller type only).


PS: The motor, pump and seal are often submerged below several thousand feet of fluid. The seal section allows the pressure in the motor and the annulus to equalize, so that there is very little pressure across the shaft seals or the pothead connection.

PS: When selecting the protector, we need to be certain that the protector shaft is capable of delivering the full torque required without exceeding its yield strength which could result in a broken shaft.

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