7.Electric Cable
Select Suitable ESP Power Cable for given Application
Motor Lead Extension MLE
Series Casing & length
Electrical Requirements
Well fluid properties
ESP Main Cable
Electrical Requirements
Series Selection on Casing Diameter
The three-phase electric power is led from the surface to the electric motor through the three wires of the ESP cable. The individual wires of the cable can be considered as long, thin conductors, the electric resistance of which is directly proportional to their length and inversely proportional to their cross-section, as described by the equation:
The main power cable consists of three conductor wires extending from the top of the motor flat lead extension to the wellhead of Supported and held to the tubing by cable bands.
• Round and flat configurations are available in various materials and sizes
• Common voltage ratings for submersible pump cable are 3 KV and 5 KV
Cable Conductors
• Carry the electrical current
• Generally made from copper but, aluminum is occasionally used
• Must be protected from H2S
• Available as solid or compacted strands in AWG No. 1, 2, 4, and 6 Insulation
• Polypropylene ethylene (PPE) for conductor temperatures up to 205 °F (96 °C)
• Ethylene propylene diene monomer (EPDM) for conductor temperatures up to 400 °F (204 °C)
• Kapton is used to supplement motor lead cable insulation Jacket
• An elastomer material that covers the insulation
• Protects insulators
• Provides a form for armor
• Serves as a hydrocarbon barrier
• Manufactured from NBR or EPDM
• In hot and/or gassy applications or wells with H2S then a lead coated jacket is used Armor
• Protects the cable while running in hole
• Protects cable elastomers during out gassing caused by decompression
• Available in galvanized steel, stainless steel, and Monel
• The most common armor thickness is 25 mils in the round configuration and 20 mils in the flat configuration. There is a 34 mil, galvanized armor available for round cables.
The power cable is the single most expensive item in a submersible installation, and must be considered very carefully for the job it is expected to perform.
• Criteria to consider when selecting the power cable are:
o Length of cable needed.
o Cable size (conductor size).
o Bottom Hole Temperature.
o Corrosive or sour environments and chemicals in use.
o Power cost and losses.
o Future expected loads.
When calculating the length of power cable, you should start at the pump discharge setting depth.
Pump Discharge Depth = Pump intake - Pump Length
• This is the minimum cable length that is needed.
• If this is a new installation or the surface cable is not in place, you should add the distance from the wellhead to the vent box and the distance from the vent box to the motor controller.
• Finally include an extra 100’ of cable for splicing purposes.
selection of esp cable
Analyze all well and equipment data and select the type of cable to be used (cable configuration).
Using the Voltage Drop Chart (Figure 5.1 – page 80), select the smallest conductor size that limits the voltage drop to 30 volts or less per thousand feet of cable.
Using the Well Temperature vs. Current Charts for the type of cable selected, obtain the conductor temperature to confirm the correct cable type has been selected.
Use the Temperature CorrectionChart and obtain the correction factor for theconductor temperature obtained in Step 3.
Multiply the original voltage drop er 1000 feet (Step 2) by the correction factor obtained in Step 4.
VDCT = VD77 x CF
VDCT = voltage drop per 1000 feet at conductor temp
VD77 = voltage drop per 1000 feet at 77° F
CF = temperature correction factor
Calculate the total drop by multiplying the drop from Step 5 by the total length of cable divided by 1000.
Total Drop = (VDCT x Cable Length) / 1000 API recommends no more than 5% of the total or no more than
30 volts drop per 1000 ft of cable. The voltage drop in the power cable must be known in order to
calculate:
Surface Voltage
Power Costs
7. Calculate the required surface voltage by adding the total cable drop to the motor nameplate voltage.
Surface Volts = Total Drop + NPV
Starting the motor can be checked using the chart "Motor Voltage At Startup"
• First the ratio of cable voltage drop to surface voltage required is calculated by: Ratio = Total Drop / Surface Volts
• Entering the vertical axis at this ratio and moving horizontally until the curved line is intersected we find the % Nameplate Voltage at Startup.
• This needs to be above 50% toguarantee a motor start.
• This chart assumes a “hard start”.
The power cost can be broken into two categories, cable losses and motor usage
o Cable losses can be calculated by the following equation:
CableKW = I2 x 3 x (L / 1000) x (R / 1000)
o The KW required by the motor is calculated by:
MotorKW = (HP x 0.746) / ME
• The surface power consumption is calculated by adding the cable and the motor power consumptions
SurfaceKW = CableKW + MotorKW
Motor Lead Cable
Is a special low profile (flat) power cable extending from the pothead on the motor to above the end of the pump, where it is spliced to the main power cable
FCL = PL + IL + SL + 10
• A low profile cable is needed due to the limited clearance between the OD of the pump housing and the ID of well casing
• The motor lead/flat cable extension has a pothead on one end of it, for plugging or splicing into the motor
• The motor lead cable extends along the side of the seal and pump and generally is spliced to the regular cable a few feet above the top of the pump
• A motor lead cable should never be reused