Tag Archives: VFD

Step 8 – Downhole and Surface Accessory Equipment

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This article “Downhole and Surface Accessory Equipment” is the step 8 of the nine-step procedure to design an ESP with an efficient and cost-effective performance. The required downhole and surface accessory equipment are discussed and recommended practices are highlighted.

Downhole Accessory Equipment:

  • Motor Lead Extension (MLE):

API RP 11S4 defines the Motor Lead Extension as a “special power cable extending from the pothead on the motor to above the end of the pump where it connects with the power cable. A low-profile cable (flat configuration) is usually needed in this area due to limited clearance between the pump housing and the well casing”. It is recommended to select a length at least 6 ft. (1.8 m) longer than the upper end of the pump. The length of MLE has to be select in a way to avoid a splice over a tubing collar. Doing so could allow the cable to catch on the wellbore casing and damage the equipment.

  • Banding Cable Protectors:

Cable protectors are used to protect the Motor Lead Cables from damage during installation, operation and pulling. The figures below show an example of cable protectors.

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Variable Frequency Drive Basics

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In this article, Variable Frequency Drive (also, named: Variable Speed Drive) basics are presented in a simple and easy way with explanation graphs. To understand how the Frequency Speed Controller operates, it is necessary to understand how the VSD supplies variable voltage and frequency for speed control.

The below block diagram illustration depicts a typical three-phase AC variable speed drive system. It has three main components: an Operator Control, a Drive Controller, and an AC Motor.

An Operator Control device provides a means to start and stop the motor and adjust the operating speed. The Drive Controller consists of a variety of components that work together to convert an AC input into a frequency and voltage output necessary to change the speed of an AC motor.

Main sections of a Variable Frequency Drive:

The converter section:

This section converts the incoming 3-phase AC voltage to DC voltage. The converter is essentially a 3-phase, full wave rectifier with Silicon Control Rectifiers, a specialized type of control diode, in the bridge.

The following video explains what SCR is and how it works:

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