Chapter_06 Power Cable

Electric Submersible Pumps Mohamed Dewidar 2013

Chapter 6

1

Electric Submersible Power Cable

Table of Content

Section Content Page

1 General concept 3

2 Cable construction 3

2.1 Conductor

2.2 Insulation

2.3 Barrier

2.4 Jacket

2.5 Armor

3 Motor connection options 8

3.1 Potheads

4 General considerations in cable type and

size selection 10

5 Conductors 10

5.1 Definition

5.2 General properties

5.3 Types

5.4 Mil

5.5 Circular mil

5.6 AWG

5.7 Conductivity

5.8 International Annealed Copper Standard

(IACS)

5.9 Resistivity

5.10 Temperature Coefficient

5.11 Number of wire in stranded conductors

6 Voltage drop in ESP cable 19

6.1 Correction of voltage drop for temperature

6.2 Maximum carrying capacity of the cable

7 Method of selecting cable wire size and

type 23

8 ESP cable pulling rates and decompression 24

8.1 Introduction

8.2 Decompression theory

8.3 Material hoop strength

9 Cable test 28

9.1 Types of tests

9.2 Resistance vs. length in ESP cables

9.3 Resistance vs. current

9.4 Resistance vs. wire size

9.5 Resistance vs. shielding

9.6 Industry methods

9.7 Recommended practice

9.8 Megohm correction

9.9 DC Hi-Pot voltage


Chapter 6

2

9.10 DC Hi-Pot leakage current

9.11 Time before test

10 Cable Nomenclature 40

11 Cable families and designation examples 41

Cable selection example 48


Chapter 6

3

Electric Submersible Power Cable

6.1. General Concept

Power is supplied to the electric motor by electric cable.

As mentioned in the previous chapter that the downhole

electric motor is a three phase, accordingly the power cable

has three conductors one for each phase.

The configuration of the electric cables is either flat or

round. Each one of them has different sizes and each size has

different types for different operating conditions.

Round Flat

As an option both Round and Flat include injection tube for

injecting chemicals down hole.

Round and flat cables includes injection tube

6.2. Cable Construction

The cable construction is mainly consists of:

Three copper conductors

Insulation

Barrier

Jacket

Armor

Injection tube (option)

Conductors

Insulation

Barrier

Injection tube

Jacket

Armor


Chapter 6

4

6.2.1. Conductor

The conductors are made of alloy-coated copper. The

alloy coating provides corrosion protection for the copper and

prevents degradation of the adhesive bond between the

conductor and the insulation.

6.2.1.1. Conductor configurations

Conductor is configured in three types,

SOLID

Smallest diameter / lowest cost

Lower interfacial electrical stress

Stranded

Greater diameter / higher cost

Greater flexibility

Greater damage resistance

Compacted

Up to 10% decrease in diameter versus round stranded

conductor

Conductor types

6.2.1.2. Factors to be considered in conductor Selection

Size

Resistance

Flexibility

Cost

6.2.2. Insulation

The purpose of the cable insulation is to provide

protection to the current carrying conductors from attack from

well fluids which will result in a short down-hole circuit. In

addition the insulation can be applied in thicknesses to meet

kv rating required (phase to phase)

6.2.2.1. Insulation types

Polypropylene (Thermoplastic)

(used in cables for lower temperature applications)

Advantages

Excellent resistance to well fluids


Chapter 6

5

Excellent electrical properties

Low cost

Disadvantages

Upper temperature range, softens at 205°F (96°C)

Subject to crazing in certain environments

<205°F/96°C >205°F/96°C

EPDM (Ethylene Propylene Diene Methylene) RUBBER (Thremoset)

(used in cables for higher temperature applications)

Advantages

Excellent high-temperature stability has been used at up to 550°F (288°C) in geothermal wells.

Excellent electrical properties, although higher power

losses than polypropylene.

Disadvantages

Limited well fluid resistance, oil swells EPDM compounds.

Susceptible to mechanical damage at elevated temperatures.

6.2.2.2. Thermoplastic vs. Thermoset

Thermoplastic Thermoset

• Definite melt point

• Limited by temperature

• Ease of processing

• Simple formulations

• Thermal failure is often dramatic

• No melting point

• Often higher temperature rating

• More difficult to process

• Complex formulations

• Thermal failure is generally gradual

6.2.3. Barrier (tape and braid)

Tapes are added over insulation. A synthetic braid is

woven over the tape. Tape is used as protection against oil

and chemical attack. Braid is used to provide additional

reinforcement and hoop strength (to prevent any swelling and

gas decompression of EPDM insulation) i.e, ensuring superior

performance in wells with hostile environments or wells with

high gas/oil ratios.

6.2.3.1. Barrier Selection

Factors to be considered:

Temperature

Chemical environment

Gas


Chapter 6

6

Handling

Barrier

6.2.3.2. Barrier Types

Polyvinyl dine Fluoride Extrusion - 300°F (150°C)

TEDLAR™ tape - 300°F (150°C)

TEFLON™ FEP Extrusion - 350°F (175°C)

PROPRIETARY High Temperature tape - 400°F (205°C)

Lead - 550°F (288°C)

6.2.3.3. Tape vs. Extruded Barrier

Tape advantages

Superior hoop strength

Higher temperature

Extruded Barrier advantage

Faster to process

6.2.4. Jacket

The jacket is there mainly to provide mechanical protection to internal components of the cable.

The jacket also physically binds all three conductor strands together.

It also allows armor to be applied to the cable without

damaging the conductors.

Control temperature resistance.

6.2.4.1. Factor to be considered

Temperature

Chemical environment

Gas

Handling conditions

Jacket

6.2.4.2. Jacket types

185°F (85°C), HIGH DENSITY POLYETHYLENE (HDPE)

275°F (135°C), NITRILE*

>350°F (176°C), EPDM * Some manufacturer produce another types of Nitriles worked

at 250 °F and 350 °F.


Chapter 6

7

6.2.4.2.1. Nitrile Rubber Jacket

Excellent resistance to oil

Good physical properties

Poor electric properties

Poor resistance to water

Hardens at temperature above 275 OF (135 OC)

Slow decompression rate

6.2.4.2.2. EPDM Rubber Jacket (>350 F)

Excellent high temperature stability

Poor resistance to oil

+ Oil =

Nitrile (NBR) EPDMPhysical properties Good Poor to fair

Oil resistance Good Poor to fair

Water resistance Poor to fair Good

Damage resistance Good Poor

H2S resistance Fair Good

Amine resistance Fair Good

Heat resistance Fair Good

Service temperature up to*275°F/135°C

Greater than350°F/176°C

HSN is available up to 350 oF

6.2.5. Armor

Cable armor made from steel strips featuring a

galvanized coating on all sides is the standard. The use of

one of many armor options can improve resistance to corrosion

and mechanical damage.

Armor

6.2.5.1. Armor Types

Standard galvanized armor(GSA, 0.020"/0.51mm and 0.025"/ 0.64 mm thick)

Heavy galvanize steel (0.034"/0.86mm thick)

+ Water =

Swelled

Swelled


Chapter 6

8

Stainless steel

Monel

6.2.5.2. Armor configurations

Standard crown profile interlocked

Flat profile interlock

Flat profile

Standard crown profile interlocked

Flat profile interlocked

Flat profile

6.2.5.3. Factors to be considered in armor selection

Damage resistance

Decompression containment

Corrosion resistance

Casing and tubing coupling sizes

The following table summarizes the cable construction

Conductors Solid Compacted Stranded

Insulation PPE EPDM

Barriers Tedlar tape

FEB extrusion

High temp. tape Lead

Jacket HDPE Nitrile EPDM

Armor Galvanized HG Double armor SS Monel

6.3. Motor Connection Options

Motor lead extension cable (MLE) (sometimes called Flat

Cable Extension (FCE)) has special configuration designs

provide the optimum combination of installation clearance and

downhole performance due to the following reasons:

1. Size of ESP (always bigger than the tubing coupling) 2. Size of casing 3. Adapt different motor amperes


Chapter 6

9

4. Down-hole temperatures

Example:

KEOTB - 250 OF (121 OC)of Reda

KELB - 450 OF (232 OC)of Reda

4KLHT – 450 OF (232 OC) of Centrilift

K = Polyimide (Kapton™ ) primary insulation

E = EPDM secondary insulation

O = Nitrile jacket

TB = Tape (probably Tedlar™) & braid

4 = # 4 AWG

L = Lead

HT = High Temperature

6.3.1. Potheads

Types:

Tape-In Pothead - Tape wrapped around individual connector leads inside motor.

Advantages:

o Most Reliable o Highest breakdown strength in industry

Disadvantages

o Longer installation time on rig floor

Tape-in design

Plug-In Pothead - mating block mounted in motor.

Advantages:

o Easy of installation

Disadvantages


Chapter 6

10

o Lower breakdown strength o Not as reliable as Tape-In

Direct Connect Pothead - Power cable attached directly to the Pothead. (Plug-In Type)

6.4. General consideration in cable type and size

selection

The best cable type for each selection is based on the

environment for each application where the cable will be

utilized and exposed.

It is important to review all of the data and study these factors specifically for each well condition to ensure the

cable selected is compatible with the well environment.

The most critical data values for selecting cable are

temperature considerations and the fluid composition.

The proper cable size is governed by the amperage, voltage drop, and space available between the tubing collar and

casing.

There are many factors which can negatively affect the

performance of cable downhole. Amongst these factors to be

considered are:

Temperature

Pressure changes

Gas oil ratio (GOR)

CO2

H2S

Oil attack

6.5. Conductors

6.5.1. Definition

Conductor is a body so constructed from conducting

material that it may used as a carrier of electric current.

6.5.2. General properties of conductors

Electric current in general possess four fundamental

electric properties, consisting of, resistance, inductance,

capacitance, and leakage conductance. That portion of a

current which is represented by its conductors will also

possess these four properties, but only two of them are

related to the properties of the conductor consider by it

self. Capacitance and leakage conductance depend in part upon

the external dimensions of the conductors and their distance

from one another and from other conducting bodies and in part

upon dielectric properties of the material employed for

insulating purpose.

Inductance is a formation of the magnetic field established by

the current in a conductor but this field is a whole is

divisible into two parts; one being wholly extended to the


Chapter 6

11

conductor and the other being wholly within the conductor,

only the latter portion can be regarded as corresponding to

magnetic properties of the conductor material.

Resistance is strictly a property of the conductor it self.

Both resistance and internal conductance of conductors change

in effective values when the current changes with great

rapidly as in case of high frequency alternating current, this

termed as “skin effect”.

6.5.3. Types of conductor

In general, conductor consists of solid wire or

multiplicity of wires stranded together, made of conducting

material and use either bare or insulated. Usually conductor

is made of copper or aluminum, but application requiring high

strength such as transmission lines, bronze, steel, and varies

composite construction are made.

Pure copper, rolled, forged, or drawn and then annealed are

always used in power cables (density of 8.89 g/cm3 at 20

OC or

8.90 g/cm3 at 0

OC).

6.5.4. Mil

Mil is a term universally used to measure wire diameter

and is a unit of length equal to one-thousandth of an inch.

6.5.5. Circular Mil

Is a term universally used to define cross sectional

area, being a unit of area of a circle 1 mil in diameter. Such

circle, however, has an area of 0.7854 (or π/4) mil2. Thus a

wire 10 mils in diameter has cross sectional area of 100 cmils

or 78.54 mils2. Hence, a cmil equals 0.7854 mil

2.

6.5.6. American Wire Gauge

This gauge has the property, in common with a number of

other gauges that is sizes represent approximately the

successive steps in the process of wire drawing. Also, like

many other gauges, its numbers are retrogressive, a large

number denoting a smaller wire, corresponding to the

operations of drawing. These gauge numbers are not arbitrarily

chosen, as in many gauges, but follow the mathematical law

upon which the gauge is found.

Basic of the AWG is a simple mathematical law. The gauge is

formed by the specification of two diameters and the law that

a given number of intermediate diameters by geometric

progression. Thus, the diameter of No.0000 (4/0 AWG) is

defined as 0.4600 in and of No. 36 AWG is 0.0050 in. There 38

sizes between these two; hence the ratio of any diameter to

the diameter of the next greater number is given by this

expression

1229322.1920050.0

4600.0 3939


Chapter 6

12

The square of this ratio = 1.2610. The sixth power of the

ratio, that is, the ratio of any diameter to the diameter of

the sixth greater number = 2.0050. The fact that this ratio is

so nearly 2 is the basis of numerous useful relations or short

cuts in wire computation.

In general AWG diameter conventional formula for bare copper

wire is:

Wire diameter in millimeter = (92^((36-AWG)/39))/39)*0.127

Wire diameter in mils = (92^((36-AWG)/39))*5

There are a number of approximate rules applicable to the AWG

which are useful to remember

o An increase of three gauge number (for example No. 10 to 7) doubles the area and weight and consequently halves the dc

resistance.

o An increase of six gauge numbers (for example No. 10 to 4) doubles the diameter.

o An increase of ten gauge numbers (for example No. 10 to 1/0) multiplies the area and weight by 10 and divides the

resistance by 10.

o A No. 10 wire has a diameter of about 0.10 in, an area of about 10,000 mils, and (standard annealed copper at 20

OC) a

resistance of approximately 1.0 Ω/1000 ft.

o The weight of No. 2 copper wire is very close to 200 lb/ 1000 ft.

AWG tables for some sized of bare Copper Wire

AWG Dia.(mils) Dia.(mm) D.C.

ohms/kft lbs/kft Amps

Max.

Amps

0000 459.99 11.684 0.0501 640.48 282.12 423.18

000 409.63 10.405 0.0631 507.93 223.73 335.6

00 364.79 9.2657 0.0795 402.8 177.43 266.14

0 324.85 8.2513 0.1003 319.44 140.71 211.06

1 289.29 7.348 0.1264 253.33 111.59 167.38

2 257.62 6.5436 0.1593 200.9 88.492 132.74

3 229.42 5.8272 0.2009 159.32 70.177 105.27

4 204.3 5.1893 0.2533 126.35 55.653 83.48

5 181.94 4.6212 0.3195 100.2 44.135 66.203

6 162.02 4.1153 0.4028 79.46 35.001 52.501

7 144.28 3.6648 0.508 63.014 27.757 41.635

8 128.49 3.2636 0.6405 49.973 22.012 33.018

9 114.42 2.9063 0.8077 39.63 17.456 26.185

10 101.9 2.5881 1.018 31.428 13.844 20.765

AWG: American Wire Gauge size varying from #000m0 to #40 `

Dia. (mils): Wire diameter in mils (1 mil = 0.001 inches)


Chapter 6

13

Dia. (mm): Wire diameter in millimeters. This was included to help when

dealing with metric system.

D.C. ohms/kft: Wire electrical resistance against direct current in ohms

per 1,000 feet

lbs/kft: Wire section weight in pounds per 1,000 feet

Amps: Wire conservative current rating in amperes

Max. Amps: Wire maximum allowable current rating in amperes. Do NOT

exceed this rating.

AWG wire size (solid)

Area CM* Resistance Ω/kft @ 20

0C

Diameter inch

0000(4/0) 211600 0.049 0.46

000(3/0) 167810 0.0618 0.40965

00(2/0) 133080 0.0779 0.3648

0(1/0) 105530 0.0983 0.32485

1 83694 0.124 0.2893

2 66373 0.1563 0.25763

3 52634 0.197 0.22942

4 41742 0.2485 0.20431

5 33102 0.3133 0.18194

6 26250 0.3951 0.16202

AWG = American Wire Gauge

Dia Mils = Diameter in Mils (1 Mil = 0.001 inch)

The following cables are the most usable one in oil business:

AWG # 1

o Solid

Conductor size 1 AWG

Area 42.408 mm^2 (square-mm)

Area 83693 CM (circular mil)

Diameter 289.3 mil (1)

Diameter 7.348 mm (1)

DC-resistance 0.000407 Ohm/m

Tensile strength 1272.23 kgf (2)

Weight 377.004 kg/km (Cu)

Weight 114.501 kg/km (Al)

Construction: solid

Note:

1. Diameter of stranded conductor is an approximation.

2. Tensile strength of crimped terminal is about 60 % of

conductor.

o Stranded Conductor size 1 AWG


Area 83693 CM circular mil)






Chapter 6

14



Construction: stranded

Note:



conductor.

AWG # 2

o Stranded

Conductor size: 2 AWG

Area: 33.631 mm^2 (square-mm)

Area: 66371 CM (circular mil)

Diameter: 297.6 mil (1)

Diameter: 7.558 mm (1)

DC-resistance: 0.000523 Ohm/m

Tensile strength: 1008.93 kgf (2)

Weight: 298.978 kg/km (Cu)

Weight: 90.803 kg/km (Al)


Note:

1. diameter of stranded conductor is an approximation.


conductor.

o Solid Conductor size: 2 AWG









Construction: solid

Note:

1. Diameter of stranded conductor is an approximation. 2. Tensile strength of crimped terminal is about 60 % of

conductor.

AWG # 4

o Solid Conductor size: 4 AWG







Chapter 6

15




Construction: solid

Note:



conductor.

o Stranded

Conductor size 4 AWG


Area 41741 CM (circular mil)








Note:


2. Tensile strength of crimped terminal is about 60 %

of conductor.

6.5.7. Percent Conductivity

Conductivity is an important property of a material

used in electric circuits, which is a measure of its ability

to conduct electricity, the definition of conductivity ( ) is

= meter per volt in gradient Potential

meter sq. per amperein density Current

= J/E = conductivity Ω

-1/m

J = current density A/m2

E = Electric field density v/m

= A/m2 v/m = A/m2 x m/v = Ω-1/m = Siemens/m (S/m)

The units of conductivity are thus the reciprocal of ohm.meter

or siemens/meter. Typical values of conductivity for good

conductors are 1000 to 6000 s/m. The reciprocal of

conductivity is called resistivity.

Percent conductivity is very common to rate the conductivity

of a conductor in terms of its percentage ratio to the

conductivity of chemically pure metal of the same kind as the

conductor is primarily constituted or in ratio to the

conductivity of the international copper standard. Both forms

of the conductivity ratio are useful for various purposes.

This ratio can also express in two different terms, one where

the conductor cross sections are equal and therefore termed

the volume-conductivity ratio and the other where the

conductor masses are equal and therefore termed the volume-


Chapter 6

16

conductivity ratio.

6.5.8. International Annealed Copper Standard (IACS)

IACS is the international accepted value of the

resistivity of annealed copper of 100% conductivity. This

standard is expressed in terms of mass resistivity as 015328

Ω.g/m2 or the resistance of a uniform round wire 1 m long and

weight of 1 g at standard temperature of 20 OC.

Equivalent expressions of the annealed copper standard, in

various units of mass resistivity or volume resistivity are as

follows:

0.15328 Ω.g/m2

875.2 Ω.lb/mi2

1.7241 µΩ.in @ 20 OC

1.725x10-8 Ω.mt @ 20 OC

10.371 Ω.Cmil/ft

0.017241 Ω.mm2/m

6.5.9. Electric resistivity of conductor

It is a measure of resistance of a circuit of a unit

quantity of a given material, it may expressed in terms of

either mass or volume

Mass resistivity = =

2

Rm Ω/m

Resistance = R = m

2 Ω

Volume resistivity = =

RA Ω.m

Resistance = R = A

R = Resistance, m = Mass, = Length, and A = Area

Accordingly,

Voltage drop in conductor = IR = A

I volts

Voltage drop per meter “potential gradient” = A

I volts

Conductivity = meter per volt in gradient Potential

meter sq. per amperein density Current =

= A/m2 x m

2/(A.Ω.m) = Ω

-1m-1 (Siemens/m)

6.5.10. Temperature coefficient of conductor resistance

The resistance of all pure metals increases with

increase temperature, where as the resistance of carbon,

electrolytes and insulating materials degreases with increase

temperature. For a moderate range of temperature such 100 OC,

the change of resistance is usually proportional to the change

of temperature, if Rt1 is the resistance at temperature t1, and

αt1 is the coefficient at that temperature, the resistance at


Chapter 6

17

some other temperature t2 is expressed by the formula

Rt2 = Rt1[1+αt1(t2-t1)]

Upon assuming the general linear relationship between

resistance and temperature, the new coefficient at any

temperature t within the linear range is expressed

)()/1(

1

12 ttt

t

The coefficient of resistance is the ratio of the increase of

resistance per OC rise to resistance at 0

OC. Alternative the

temperature coefficient of resistance can be defined as “the

increase in resistance of 1 Ω at 0 OC for 1 OC rise of

temperature”.

The variation of resistance of copper for the range over which

copper conductors are usually operated is represented by the

following graph,

If this graph extended backwards, the point of intersection

with the horizontal axis is found to be -234.5 OC.

Hence, for standard annealed conductor having a resistance of

1 Ω @ 0 OC, the variation of resistance over 234.5

OC

(resistance of annealed copper is 0 Ω @ -234.5 OC) is 1 Ω,

0t = 5.234

1 = 0.004264 Ω/

OC

In general, coefficient of conductor resistance at t OC is:

t =

t5.234

1 = 0.004264 Ω/

OC

Example:

Coefficient at t =15 OC is

15t = 155.234

1

= 0.004008 Ω/

OC



Chapter 6

18

20t = 205.234

1

= 0.003929 Ω/

OC


25t = 255.234

1

= 0.0038535 Ω/

OC

From above graph,

115.2345.234

5.2341

11

0

1

ttt

R

R

115.2345.234

212

0

2 5.234

t

tt

R

R

R1 = R0(1+ t1)

R2 = R0(1+ t2)

1

1

2

1

2

1

t

t

R

R

5.234

5.234

2

1

2

1

t

t

R

R and, 5.2345.234 1

1

22 t

R

Rt

Over moderate range of temperature, the change of resistance is

usually proportional to the change of temperature. Resistivity

is always expressed at standard temperature, usually 20 OC (68

OF).

The coefficient of copper less than standard conductivity

(100%) is proportional to the actual conductivity, expressed

as decimal percentage. Thus if n is the percentage conductivity (95% = 0.95), the temperature coefficient will be

α’t = nαt, where αt (0.00393) is the coefficient of the

annealed copper standard at 100% conductivity.

)201

1()]00393.0(*/1[

1

tn

Example:

Coefficient of annealed copper conductor of 95% conductivity

at 20 OC is

00373.0()]00393.0(*95.0/1[

1

)202020

Coefficient of annealed copper conductor of 95% conductivity

at 25 OC is

00367.0()]00393.0(*95.0/1[

1

)202525

6.5.11. Number of wires in stranded conductors

Each successive layer in a concentrically stranded

conductor contains six more wires than the proceeding one. The

total number of wires in conductor for 1-wire core


Chapter 6

19

construction (1,7,9,….etc) is

N = 3n(n+1)+1

Where n is number of layers over core, which is not counted as

layer.

if n = 1 then N = 7

If n = 2 then N = 19

6.6. Voltage drop in the ESP cables

The voltage drop per 1000 ft (kft) length of cable is

published as a chart for each manufacture at certain

temperature. For cables operating at conductor temperatures,

the value obtained from voltage drop chart must be multiplied

by correction factor (issued by manufacturer) Although the

actual conductor temperatures varies along the length of the

cable, an acceptable industry practice is to assume that the

conductor temperature is equivalent to the maximum well

temperature.

The voltage drop formula used for a given length of cable ia

as follows:

sin

60cos732.1

fXRxlIdropVoltage Lac

Where:

I = current in ampere,

l = length of cable in 1000 ft

Rac = ac resistance at specified conductor temperature in

Ω/kft.

Cos φ = Power factor

XL = Inductive reactance

f = Frequency c/s

Layer 1 Layer 2

Core

Layer 1 Core


Chapter 6

20

p.f cos φ sin φ

--- ----- -----

80% 0.80 0.600

85% 0.85 0.527

90% 0.90 0.436

95% 0.95 0.312

For the inductive reactance XL (Ω/kft) each manufacturer issued

values of each of their cables. For example the following

values are for Philips cables (Ω/kft @ 60 hz)

AWG # Round Flat

----- ----- -----

1 0.033 0.042

2 0.034 0.044

4 0.036 0.047

6 0.039 0.050

In case if the frequency is other than 60, the above mentioned

values should multiply by (f/60).

For example, cable size AWG #2, motor amps is 100 A, cable

length is 8000 ft, the PF = 0.85 and conductor resistance at

77 OF is 0.1708 Ω so, The voltage drop =

527.0

60

50034.085.01708.01100732.1..DV 27.73 volts

Each manufacturer issues the voltage drop curves for their

cables conductor at certain temperature, the following curves

represent an example (Reda),

Voltage Drop for Reda Cables @ 77 OF

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

Motor Amps

Vo

lta

ge

Dro

p v

olt

s/k

ft

AWG #6 AWG #4 AWG #2 AWG #1

For example, if the motor amperage (name plate) is 100 amp so,

The voltage drop of conductor size AWG# 1 is 17.75 volts.




Chapter 6

21


Definitions

Maximum Well Temperature: It is defined as the ambient

temperature surrounding the cable during steady state

operation. This temperature depends on the initial bottom

hole temperature, the heat rise from the operating

submersible equipment, and the heat generated by the power

losses in the cable.

Conductor temperature: It is defined as the temperature on the surface of the current carrying conductor during steady

state operation.

Maximum conductor temperature: It is the highest temperature at which the cable can continuously operate without causing

significant degradation of cable dielectric material.

6.6.1. Correction of voltage drop for temperature:

The issued voltage drop curves (by manufacturers) are at

certain temperature (20 OC [68

OF] or 25

OC [77

OF), so the

voltage drop must be corrected to the conductor temperature.

The following steps are used for the corrections:

Calculate the conductor temperature using the motor amperage and the maximum well temperature,

TIaT wellC 2* OF

Where:

TC = Conductor temperature

I = Motor amperage

a = Factor for each cable size (issued by manufacturer)

Twell = Maximum well temperature

Adjust the voltage drop at maximum well temperature from the following equation using the voltage drop have got from the

manufacturer chart at motor amperage, cable size, and

conductor temperature calculated in the previous step

))77(00214.01( TVV Caadj

Where:

Vadj = Adjusted voltage drop

Va = Voltage drop from the curve

Example:

I = 50 A, Twell = 200 OF, cable is AWG# 4 Reda hot type

a = 0.00117 (from Reda issued table)

Tc = 0.00117 x (50)2 + 200 = 229

OF

Vadj = 22 x (1+0.00214(229-77)) = 29 volt/1000’

Note:

Most of the cable manufacturers issue tables of

temperature correction factor which can be used directly


Chapter 6

22

instead of using the previous equation. For example, the

following table is issued by Centrilift for their cable:

Conductor V.D. Temp. factor @ 77 OF

Temp. OF Corr. factor Temp.

OF Corr. factor

50 0.95 221 1.31

59 0.96 230 1.33

68 0.98 239 1.35

77 1.00 248 1.37

86 1.02 257 1.39

95 1.04 266 1.40

104 1.06 275 1.42

113 1.08 284 1.44

122 1.10 293 1.46

131 1.12 302 1.48

140 1.13 311 1.50

149 1.15 320 1.52

158 1.17 329 1.54

167 1.19 338 1.56

176 1.21 347 1.58

185 1.23 356 1.60

194 1.25 365 1.62

203 1.27 574 1.64

212 1.29 383 1.65

6.6.2. Maximum carrying capacity of the cable (Imax)

The maximum carrying capacity of a cable can be

calculated using the following equation:

a

BHTTI

C

maxmax

Where:

maxTC = Maximum conductor temperature OF

BHT = Bottom hole temperature OF

a = Current temperature factor (an example here is below Reda

current temperature factor table for their cables)

Current temperature factor (a) table for Reda cables

Cable Type Conductor Size (AWG)

6 4 2 1 1/0 2/0

Redablack Flat (EEF) 0.0275 0.0167 0.0086 0.0064 0.005 0.0039

Redablack Round (EER) 0.0199 0.0115 0.0058 0.0043 0.0032 0.0025

Redalead Flat (ELB) 0.0281 0.0169 0.0086 0.0064 0.005 0.0039

Redalead Round (ELBE) 0.0202 0.0116 0.0058 0.0042 0.0031 0.0025

Redablack Round (ETBE-300) 0.0199 0.0115 0.0058 0.0043 0.0032 0.0025

Redablack Flat (ETBE-300F) 0.0275 0.0167 0.0086 0.0064 0.005 0.0039


Redahot Round (ETBO) 0.02 0.0117 0.0062 0.0046 0.0034 0.0027

Motorlead (KELB) 0.0281 0.0169 0.0086 0.0064 0.005 0.0039

Low Temperature Motorlead (KEOTB) 0.0275 0.0169 0.009 0.0068 0.0053 0.0042

Redalene Flat (POTB) 0.0281 0.0176 0.0097 0.007 0.0048 0.0038


Chapter 6

23

Redalene Round (PPEO) 0.0199 0.0112 0.0062 0.0045 0.0031 0.0025

Current temperature factor (a) table for Centrilift cables

Cable type Max. OF AWG 6 AWG 4 AWG 2 AWG 1

CPNF 205 0.0261 0.0155 0.0091 0.0065

CPNR 205 0.0222 0.0132 0.0077 0.0056

CENF 260 0.0289 0.0171 0.01 0.0072

CENR 260 0.0195 0.0115 0.0068 0.0049

CEBNR 280 0.0195 0.0092 0.0054 0.0039

CEBER 300 0.0195 0.0092 0.0054 0.0039

CEBER-HT 400 0.0156 0.0092 0.0054 0.0039

CEEF 400 0.0272 0.0161 0.0095 0.0068

CEER 400 0.0156 0.0092 0.0054 0.0039

CELF 450 0.0272 0.0161 0.0095 0.0068

Example:

The maximum current carrying capacity for Reda black

round 400 OF (ETBE) size AWG #2 at bottom hole temperature 200

OF is:

a

BHTTI

C

maxmax =

0058.0

200400 = 185.7 amps

for size AWG #4 Imax is:

=0115.0

200400 = 131.9 amps

6.7. Method of selecting Cable wire size and type

1. From the voltage drop (VD) chart, select a cable gauge that results in a three phase voltage less than 30 volts per 1000

ft at motor name plate amps. For example at the motor

amperage 100 the VD of size AWG 4 is 42.29 volts and size

AWG 2 is 28.59 volts, accordingly, size AWG 2 is selected as

is VD is <30 volts/kft. This VD’s are at 77 OF.

Note:

VD = 1.732 x R x I in case if the p.f is 1.00 i.e. cosφ =1

VD = 1.732 x 0.176 x 100 = 30.48 v/kft for AWG 2.

At VD = 28.59 v/kft the p.f is 0.86 (φ=30.7O) and inductance

reactance is 0.027 ohm/kft at 50 hz and 77 OF.


Chapter 6

24

2. Adjust VD for the selected cable to the down hole well

temperature, suppose that the average DHT is 200 OF, then,

))77(00214.01( TVV Caadj

Vadj = 28.59 x (1+0.00214(200-77)) = 36.1 volt/1000’

Vadj > 30 volts/kft, accordingly, the bigger size should be

selected (lower AWG), so size AWG 1 is selected, VD of AWG 1

is 17.75 volts/kft,

))77(00214.01( TVV Caadj

Vadj = 17.75 x (1+0.00214(200-77)) = 22.4 volt/1000’

3. Adjust conductor temperature based on the well DHT as

follows,

TIaT wellC 2* OF

=0.0058 x 1002 + 200 = 258

OF

AWG 1, Reda Hot 275 OF (maximum cable temperature) is a good

choice.

6.8. ESP cable pulling rates and decompression

6.8.1. Introduction

When discussing cable handling techniques one area of

concern is the effect of pulling rates on the internal

components of the cable. Unfortunately, this is not simple

issue and there are not definitive means for determining

optimum pulling rates. The intent of this part, however, is to

discuss the factors involved in decompression of the cable,

whether it is due to pulling of the downhole equipment or

simply drawdown of the fluid.

6.8.2. Decompression theory

When a cable is initially installed in the oil well it

is exposed to an external pressure created by gas pressure and


Chapter 6

25

the static head of the fluid. The cable components, however,

undergo a pressure equalization process whereby the insulation

and jacket compress and gases and fluids migrate into the

material. The rate at which this migration occurs, however, is

highly variable.

Two general factors control the permeation rate,

1. The diffusion between molecular chains.

2. The stability the permeant (the migrating fluid or gas) in

the polymer (the insulation and jacket).

The diffusion is dependent on pressure and concentration

factors; for liquids this referred to as the concentration

gradient and for gas as the partial pressure (total pressure

multiplied by gas concentration). Other parameters affecting

the above two factors include the temperature at which the

cable is operating (high temperature increase the permeation

rate), jacket and insulation thickness, intermolecular chain

forces, degree of cross-linking, molecular size, and chemical

similarity between the permeant and the polymer.

Once the internal components of the cable have reached the

same pressure as the well through the diffusion and physical

compression, the cable has reached equilibrium. Once the

fluids are drawdown, however, or the equipment is pulled, a

pressure differential is created with the high pressure

existing in the cable insulation and jacket material

themselves. The material will physically expand to relieve

some of this pressure, much as they compressed under an

external pressure. The problem arises, though, due to gas

which “dissolved” in the polymer. Give sufficient time this

gas will migrate back out the material without imparting any

permanent damage to the cable. In some instances, however, the

polymer are not given sufficient time to outgas thereby

causing the pressure differential to exceed the strength of

the material causing a “blowout” which appears as a bubble or

cavity in the insulation or jacket.

6.8.3. Material hoop strength

6.8.3.1. Insulation

A fundamental property when dealing with decompression

is the hoop strength of the cable material. Hoop strength of

tubing reflects the amount of internal pressure that the tube

can contain without yielding the tube material. Likewise, the

hoop strength of an insulation would approximate the pressure

differential that could be maintained across the insulation

without yielding the insulation material. The equation of hoop

strength is as follows:

D

tP H2


Chapter 6

26

Where

P = Internal pressure psi

H = Yield or tensile strength (hoop strength) of material psi t = Thickness of material inch

D = Diameter over insulation inches

Hoop Strength = t

PDH

2

Or

P = Internal pressure Mpa

S = Yield or tensile strength (hoop strength)of material Mpa

t = Thickness of material mt

D = Diameter over insulation mt

Example 1

P (internal pressure) = 6.6 Mpa

D (outside diameter) = 6.6 mt

t (thickness) = 18.5 mm

Hoop strength = 3.11770185.02

6.66.6

H Mpa = 170.75 psi

281.30185.02

89974.6

6.6281.36.6

H = 170.75 psi

Example 2

Assume we are looking at a polypropylene insulated, 3

kv rated, AWG #4 conductor as a Redalene type cable. The

tensile strength of polypropylene is approximately 3500 psi,

the insulation thickness on a 3kv rated cable is 0.075”, and

the diameter over the insulation is 0.354”, therefore,

354.0

75.035002 P = 1483 psi

Unfortunately, the above tensile strength is at room

temperature and since polypropylene is a relatively low

temperature thermoplastic and softens at higher temperature,

Internal

Pressure t

D


Chapter 6

27

the hoop strength is considerably reduced at normal operating

temperature. Here are below tables of the calculated hoop

strengths for polypropylene insulated conductors for different

conductor sizes and voltage ratings, at two different

temperatures.

Hoop strength of polypropylene at 115 OF conductor temperature

kV AWG #4 psi AWG #2 psi

3 112 90

4 124 101

Hoop strength of polypropylene at 160 OF conductor temperature


3 28 22

4 31 25

EPDM insulation, on the other hand, by its nature as a

thermoset or cross linked compound has much better temperature

stability than polypropylene so that it retains a fairly

constant tensile strength in the 212-300 OF temperature range

for which the following data was calculated.

Hoop strength of EPDM at 212-300 OF conductor temperature


3 390 312

4 431 351

The above shows first that EPDM insulations may provide

greater decompression resistance than polypropylene, but

second that neither provides sufficient decompression strength

on stand alone basis to prevent cable blowout.

6.8.3.2. Tape and Braid

The incorporated of tape and braid over the

insulation provides two advantages to the cable when

considering decompression. First, the tap acts as a barrier to

migration of the well fluids and gases into the insulation,

preventing the absorption of agents which would latter have to

migrate out of the insulation upon decompression. Second, both

the tape and braid provide additional hoop strength to the

insulation. Rough calculations indicate that the additional

hoop strength provided by the poly-vinyl-fluoride (PVF) tape

and nylon braid is approximately 25 psi at 160 OF.

6.8.3.3. Lead jacket

The use of a lead jacket goes one step beyond the

protection provided by the tape and braid and provides a

totally impervious barrier to migration of well fluids or

gases, thereby totally insulating the insulation from the

chemical environment in the well. Therefore, the initial

pressure equalization is accomplished entirely through the

build up of compressive forces in the lead jacket and the


Chapter 6

28

insulation which are easily relieved during compression ; with

the lead jacket there are no trapped gases which must permeate

out of the insulation. Thus the lead jackets are the best

means of preventing decompression damage.

6.8.3.4. Armor

Not surprisingly, the primary cable component for

preventing decompression damage in non-leaded cables is the

armor. The jacket provides additional hoop strength, but

generally just transfers stresses from the insulation to the

armor. Provided below the hoop strengths for a single wrap of

0.025” galvanized steel armor (GSA) with an interlocked

profile; due to the temperature vs strength relationship for

steel, these values would essentially be constant across the

range of operating temperature.

Hoop strength of 0.025” GSA


3 1260 1074

4 1190 1064

Obviously these values will quickly decrease if armor

corrosion is problem. Various armor packages are available to

increase the degree of containment provided by the armor.

These include the use of 0.034” armor strip instead of the

standard 0.025” strip on round cables, the use of second wrap

of armor applied over the first, the use of flat profile armor

configuration, and finally the use of higher strength, more

corrosion resistant alloys such as 316 stainless steel.

6.8.3.5. Recommendation

The key, therefore, is to be aware of the role of the

different cable component and after choosing the appropriate

cable type, to monitor its decompression performance; this

information should be then fed back into the cable selection

criteria. This of course means being aware of the downhole

conditions when the cable is pulled, as well as the pulling

rates themselves.

In terms of cable choices, three key things should be

evaluated:

1. The insulation and jacket polymer type being used. 2. Is a barrier tape or lead jacket being used to prevent the

migration of gases into the insulation?

3. What type of armor is being used and is corrosion negating the containment role of the armor?

6.9. ESP Cable Test

A variety of test devices and procedures are used in an

effort to determine the quality of cable. Even when using the

same test device, different interpretations and widely

divergent values are used by various companies.


Chapter 6

29

Reuse of cable is a serious consideration in the economic

evaluation of a well. A cable may present up to one-third of

the equipment cost of an installation. Even more important is

the fact that premature cable failure may well result in

pulling the well before payout of the installation.

Where pulling costs are extremely expensive, many many

producers opt to avoid reuse of cable because of risk. Junking

a $30,000 cable that may be perfectly good, has been

determined to be economically prudent in these conditions.

There must be better way of evaluating ESP cable for use.

6.9.1. Types of tests

Various test are used to determine the performance of

cable. The most common are volt-ohmmeter (VOM), insulation

resistance (IR), and high potential dc test (dc hi-pot). As

with most things worth doing, more valuable information is

obtained from the more expensive and difficult tests.

6.9.1.1. VOM

Since volt-ohmmeter is common, inexpensive, safe, easy

to use, it is very popular. Although useful for some

application, the volt-ohmmeter is virtually useless for

evaluating cable insulation. The instrument usually relies on

a 9 volt battery to energize the cable.

This test is only used for an initial indication of cable

condition while it still in the well. About the best that can

be said about a VOM test is that if the reading indicates bad,

then the cable or some other component of the electric system

is bad. However, if it indicates good, little or nothing is

known about the quality of the cable.

6.9.1.2. IR

The megohmmeter is a portable, moderately expensive

test device that provides limited information about cable

quality. The instrument usually contains a 1000 volt supply to

energize the cable. Some machines are rated up to 5000 volts.

The higher voltage can help determine the basic performance

level of the cable. However, the meter readings are subjected

to so any variations that consistent results are seldom

achieved.

6.9.1.3. Hi-pot

The high potential dc tester is an expensive test machine

which, given the present state of the art, provides the most

information about cable quality. It typically can apply up to

35,000 volts to energize the cable. Some machines at research

facilities are rated up to 200,000 volts or more.

The higher voltage can be used to cause virtually any cable to

fail at weakest point. However, it is very difficult to find a

way to interpret the readings so that the quality of cable can

be determined without taking the cable to destruction.


Chapter 6

30

Experience, skill, and knowledge of local conditions taken in

conjunction with test results are major aids in analyzing the

suitability of cable for reuse.

6.9.2. Resistance vs. Length in ESP cables

Cable insulation is essentially a large resistor that I

spread over along distance. Using finite element analysis, the

insulation ca modeled as numerous resistors. Each resistor

represents a unit length. All the resistors between the

conductors and ground are then connected in parallel to obtain

the total insulation resistance as shown as the following

figure.

Based on the relationship for parallel resistors, the total

resistance will always be lower than the lowest resistor

anywhere on the cable. In addition, the value will lower

exponentially as the length increases.

RRRRR nt

1..........

1111

321

The reciprocal of the total resistance, Rt, is equal to the sum

of the reciprocals of all individual resistances along the

length of the cable.

End effects, associated with where the conductors are exposed

to air, constitute two additional resistors. These are also in

parallel with insulation resistance.

The concept of parallel resistances is important in gaining an

appropriate understanding of the total leakage current, the

insulation resistance, and leakage conductance. These have a

pronounced effect on the mega-ohmmeter and dc hipot leakage

current test leakage.

6.9.3. Resistance vs current in ESP cables

The insulation resistance R in megohms and the leakage

current I in microamps are related by Ohm’s low.

V = R * I

It is apparent that the test voltage V plays a role in the

relation ship. For cable insulation, the resistance varies

with the length. As the length increases, the megohm value

decreases. This is a non linear change. For a fixed test

voltage, the leakage current must increase exponentially as

the length increases.

During varies tests, we have observed that the leakage current

R1 R2 R3 Rn

Grounded shield

Energized conductor


Chapter 6

31

and megohm values vary over a wide range. For a particular

group of conditions, one value of leakage current and

insulation resistance might be appropriate, but no single

number satisfies all conditions. Some of the conditions

influencing both leakage current and insulation resistance

include length, temperature, material, moisture, and oil

gravity.

Cable length has to be incorporated in Ohm’s law relationship.

If the resistance is multiplied by length the appropriate

units are megohm-thousand feet (MΩ-kft). The reciprocal is

called conductance and has units of micromhos per thousand

feet (μmho-kft).

Alternatively, the conductance can be expresses in units of

microamps per volt per thousand feet (μA/kv/kft). Observe that

the leakage conductance is directly related to the reciprocal

of the insulation resistance.

Traditionally, the industry has strived to determine one

megohmmeter number that can be used to judge the quality of

any cable. Basic analysis reveals it is futile to try to

define performance of all cables by using single number read

from meter. Length, wire diameter, insulation type,

construction geometry, and voltage must be considered.

The example below illustrates the the effect of length and

voltage on the meter r99 eading. These based on a leakage

conductance of 0.2 μa/kv/kft.

Effect of length and voltage on insulation resistance

Length

Kft

Voltage

kv

Current

μa

Conductance

μA/kv

Resistance

megohm

1 1 0.2 0.2 5000

1 5 1 0.2 5000

1 15 3 0.2 5000

2 15 6 0.4 2500

5 1 1 1.0 1000

5 15 15 1.0 1000

10 15 30 2.0 500

I = V/R = 1/5000*103 = 0.2*10

-6 amps = 0.2 μa/kv/kft

I = V/R = 5/5000*103 = 1.0*10


I = V/R = 15/5000*103 = 3.0*10


I = V/R = 15*2/5000*103 = 6.0*10


I = V/R = 15/5000*103

= 3.0*10-6

amps = 1.0 μa/kv/kft

I = V/R = 1*5/5000*103 = 1.0*10


I = V/R = 15*10/5000*103 = 30.0*10

-6 amps = 30 μa/kv/kft

R = V/I = 1/0.2*10-6 = 5*10

6 ohm = 5000 MΩ

R = V/I = 5/0.2*10-6 = 5*10

6 ohm = 5000 MΩ

R = V/I = 15/3.0*10-6

= 5*106 ohm = 5000 MΩ

R = V/I = 15/6.0*10-6

= 2.5*106 ohm = 2500 MΩ

R = V/I = 1/1.0*10-6 = 1*10

6 ohm = 1000 MΩ

R = V/I = 15/30*10-6 = 0.5*10

6 ohm = 500 MΩ


Chapter 6

32

The measured megohm value is not a single number, but varies

with length. This corresponds to the parallel resistance model

previously discussed.

6.9.4. Resistance vs wire size

Insulation resistance is related to dimensions of by

resistivity (ρ).

A

LR

Characteristic material properties are included in the

resistivity. The length (L) and surface across sectional area

(A) define the volume occupied by the insulation. Previous

discussion identified the effect of length on the resistance.

The ara is calculated from circumference around the conductor

(Пd) and thickness (t) of the insulation.

A = Пd*t

Because cable insulation is essentially a tube around a wire,

an alternate from this relationship is used. It takes into

consideration the overall diameter (D), the wire diameter (d)

and the bulk resistivity constant (K) which is a constant for

each material.

d

DKR log

Typical resistance constants for high quality electrical

insulations have been determined by the power cable industry.

These are based on years of experience at high voltage levels.

For example, the bulk constant of ethylene propylene diene

monomers (EPDM) insulation for use at service level up to

138,000 volt ac is 20,000 megohm-thousand feet for new

insulation. The polyethylene value is 50,000 Mohm-kft.

Insulation that has been environmentally exposed will have

values that are significantly lower than these new resistance

constants. Because new insulation is such high quality, lower

values on used cable may still represent excellent insulation

for this application.

Stranded wire will be having more insulation in contact with

the wire than solid conductor. This greater surface causes a

proportional increase in the area. In addition, a large size

will have a greater area.

An increase in area causes a decrease in the resistance of the

insulation. Because of the very small dimensions involved in a

wire configuration, any increase in area can have a dramatic

effect.

The table below shows the impact of the wire configuration.

The EPDM constant for new cable is used to determine the

minimum insulation resistance and corresponding leakage

conductance for cables with nominal 75 and 90 mil insulation


Chapter 6

33

thickness. The minimum thickness (t) for nominal 75 mil

insulation is 68 mils. The overall diameter (D) is calculated.

D = d + 2t

As an example, the overall diameter for AWG #1 is 439 mils

(289+75+75).

Size effect on insulation resistance, EPDM (K=20,000 MΩ-kft)

Wire Size

AWG

Wire

Diameter

(d) mil

R MΩ-kft

for 75

mil wall

G

μa/kv/kf

t

R MΩ-kft

for 90

mil wall

G

μa/kv/kft

6 162 5290 0.19 6020 0.17

4 205 4430 0.19 5070 0.20

4S 232 4110 0.24 4710 0.21

2 258 3680 0.27 4240 0.24

2S 292 3390 0.30 3910 0.26

1 289 3350 0.30 3860 0.26

1S 328 3080 0.33 3560 0.28

It is apparent that the measured insulation resistance changes

significantly with a change in wire dimensions. The resistance

will also change depending on the insulation material. The

same table recalculated for polypropylene.

Size effect on insulation resistance, Poly (K=50,000 MΩ-kft)

Wire Size

AWG

Wire

Diameter

(d) mil

R MΩ-kft

for 75

mil wall

G

μa/kv/kf

t

R MΩ-kft

for 90

mil wall

G

μa/kv/kft

6 162 13240 0.076 15050 0.066

4 205 11080 0.090 12680 0.079

4S 232 10275 0.096 11775 0.084

2 258 9210 0.109 10600 0.094

2S 292 8470 0.118 9780 0.102

1 289 8370 0.120 9660 0.104

1S 328 7690 0.130 8900 0.112

When insulation resistance decreases, the leakage conductance

increases. The relationships demonstrate some of the reasons

why it is very difficult to have a single value of leakage

conductance or insulation resistance for every submersible

cable. These changes are for new cable. The effect is even

more pronounced for used cable.

Example:

In AWG #1, 75 mils nominal insulation, EPDM thickness is 75

mils, and wire diameter is 289 mils.

So, d = 75 mils, D = 289 + 2 * 75 = 439 mils = 0.239 inch

d

DKR log

289.0

439.0log*000,20 = 3,631 MΩ-kft

In AWG #4, stranded, 75 mils nominal insulation, EPDM

thickness is 75 mils, and wire diameter is 205 mils.


Chapter 6

34


d

DKR log

205.0

355.0log*000,20 = 4,769 MΩ-kft

In AWG #1 stranded, 75 mils nominal insulation, polyethylene

thickness is 75 mils, and wire diameter is 289 mils.


d

DKR log

289.0

439.0log*000,50 = 9,078 MΩ-kft

6.9.5. Resistance vs. shielding

During a test or use, a voltage gradient is set up

between the conductor and the ground plan as illustrated I the

following figure. This potential difference is distributed

across all the insulating materials in the electric field.

Therefore, the total measured resistance depends on the

insulating properties of all materials between energized

conductors and ground plane.

Voltage gradient between conductor and ground

If shielding is placed directly over the individual insulated

wire, the ground plane is moved closer conductor. This reduces

the resistance, so it increases the leakage conductance and

leakage current. For example, a lead covered cable provides a

very effective shield. Hence the leakage current values will

be greater for leaded cable than for other designs.

Most three phase cables have three conductors twisted a

triplex configuration. This spacing tends to fog the

dimensions between the conductor and ground plane. Hence, this

insulation resistance tends to be greater than most other

configurations.

Ground

Armor

Insulation

Conductor

energized

Jacket


Chapter 6

35

6.9.6. Industry methods

There are many diverse methods used in an effort to

determine if a particular cable is suitable for reuse in a

well. For example, many users merely require that the cable be

visually inspected and that it pass a five minutes hi-pot dc

withstand test at specified voltage level. Even this rather

straightforward evaluation method is complicated by the lack

of consensus on the appropriate voltage test level for various

types of cable.

For a used 75 mil, EPDM insulated cable, the dc voltage used

in the industry is usually 11,000 volts. At the other extreme,

some users reportedly test the same cable at level up to

25,000 volts. This extreme difference indicates a series lack

of understanding about the basic testing criteria of cable.

Furthermore, certain users attempt to establish a specified

maximum leakage current. Others specify a leakage conductance

which is leakage current per thousand volts per thousand feet.

Still others may require that the leakage current or

insulation resistance be balanced within a maximum ratio of 3

to 1.

6.9.7. Recommended practice

There are several organizations responsible for

recommended practices addressing this high performance cable.

An overview of the development of these guidelines has been

represented by Institute of Electric and Electronic Engineers

(IEEE).

IEEE has three documents that address the performance of new

cable; these provide conservative criteria for evaluation of

newly manufactured cable and acceptance of the shipped cables.

The guidelines are supported by broad experience outside the

submersible industry. They were developed and accepted by

submersible cable manufacturers and producers based ob

industry knowledge at the time of development.

IEEE test values

Thickness

Mils

Factory

kv

Acceptance

kv

Maintenance

kv

75 27 22 11

90 35 28 14

These provide a starting point for evaluating used cable.

Maintenance test are performed on cables that remain installed

but can be tested. Used submersible cable is usually tested

after removal from the well where considerably higher test

voltages can be applied. Therefore, the maintenance values are

often regarded by some evaluators as too low for used cable.

Despite the lack of hard data to support their

recommendations, an API task Group is pressing forward in an

attempt to provide guidance for reuse testing. At this time,


Chapter 6

36

the tentative draft guideline for testing used EPDM and

polypropylene (poly) cable is based solely on new cable

criteria. More work needs to be done.

6.9.8. Megohm correlation

There is considerable controversy about the minimum

required megohm reading on a used cable. The test method is

widely used, but how it works on this specialty cable is not

well under stood. Perhaps it will be useful to review what

this test actually measures. How test results are related to

cable length and other variables are then considered.

An insulation resistance (megohmmeter) test is usually

performed by 1000 volts dc to one conductor. The other two

conductors and the armor are grounded.

The following figure illustrates the relationship between

insulation resistance and cable length. Two assumptions are

used, first, resistance is uniformly distributed along the

length of the cable, second, the end effects are ignored.

Insulation resistance vs Length

0

200

400

600

800

1000

1200

1400

1600

1800

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Thousand feet

Me

go

hm

The curve is based on a 200 megohm resistance for an 8000 foot

cable. This a value some have used as a threshold for

acceptance used cable. However, we will develop more effective

relationship later.

The graph dramatically illustrates that as cable get shorter,

the insulation resistance (IR) reading increases very rapidly.

As a result, it is very difficult for those unaware of this

relationship to properly interpret megohm readings as a

function of length. The relationship is definitely not liner.

In addition, it should be observed that as the cable gets

shorter, it becomes more and more difficult to get meaningful

results. The meter has limited resolution for values greater


Chapter 6

37

than 5000 megohms.

Furthermore, for short length, the end effect resistance

begins to dominate more than the actual insulation resistance.

The end effect resistance is lowered by increasing humidity,

lack of cleanliness, and preparation of the ends.

One other observation from the simple parallel resistance

model is worthy of further comment. The megohmmeter will

always indicate a value lower than the lowest resistance along

the complete length of the cable. The lower value arises

because of the parallel nature of the resistors. This effect

depicts how the entire length of an otherwise perfectly good

cable can be condemned because a small section has been

damaged locally.

In other words, one can not determine the overall quality of a

cable from the megohm reading. The value may reflect the

insulation resistance and presumably the condition of all the

insulation along the cable or it may reflect just the

resistance of a local spot along the cable.

Because of these inherent test limitations, it is clear that

megom readings alone do not provide sufficient information to

be used as the sole criteria for evaluating the condition of a

cable.

6.9.9. DC Hi-pot voltage

The preferred method of evaluating cable at this time is

the high potential dc tester. Even this respected method

always many interpretations. As a result, there is no

consensus of appropriate voltage or current levels for

evaluating used cable.

The IEEE recommended practice gas generally accepted voltage

values for factory test of newly manufactured and acceptance

test of newly delivered cable. These were given in the

previous table.

With the present improved quality of cable and the experience

of the industry, the values given for maintenance test are

often considered too low for cable removed from service. Many

service centers and users specify much higher dc voltage for

evaluating used cable.

One part of the argument is that higher voltage will find more

weak spots before installation of the cable in the well. The

counter point f argument is that excessive test voltage will

unnecessarily damage of insulation of otherwise perfectly good

cable. In addition, there is concern in some circles that

repeated testing of cable may cause deterioration of the

insulation. An underlying problem is the lack of experimental

data or information to validate either of these arguments.

6.9.10. DC Hi-pot leakage current

Another difficulty arises when trying to interpret the


Chapter 6

38

microamp current values observed during hi-pot test. The

microamp dc current is made of three components. There are

capacitance charging current, absorption current, and

conduction current.

The charging current energizes the capacitor formed by the

dielectric that exists between the conductors and ground. This

current component starts extremely high and decreases

exponentially. If the applied voltage remains stable, the

value drops to zero within a few seconds after the test

begins.

Absorption current results from the charge absorption in the

dielectric as a result of polarization of the insulation. This

current component starts high but decreases somewhat more

slowly. The current typically stabilized after 5 minutes,

although reasonably acceptable data is available after 2

minutes.

Conduction current is steady state leakage current value. This

is the current that flows over, under, around and through the

insulation.

A low value of steady state conduction current is commonly

accepted as indicating a good cable. However, a much more

through evaluation can be made by measuring the leakage

current at various voltages and plotting leakage current vs

applied voltages. If the resistance is “ideal”, it will not be

affected by voltage level and the relationship will be linear.

Increasing leakage current with voltage indicates that the

insulation has been weakened. As the cable ages, deteriorates,

or becomes wet, the leakage current increases dramatically for

the same applied voltage.

Leakage current values are primarily influenced by materials

and environmental conditions.

Some users are not concerned with the current level but simply

use a dc withstand test. The approach is to apply a dc voltage

level to the cable for five minutes. If the cable does not

fail, then it is accepted. This approach provides no true

information about comparative quality or stability for reuse

in the particular environment.

Other users try to look at the level of microamp leakage.

However, there are no consistent guidelines for evaluating

these current levels.

6.9.11. Time before test

The leakage current is influenced by many factors

including the physical condition of the cable, the ac strength

of the insulation, the physical and chemical condition of the

insulation material, and the amount of gas still absorbed in

the insulation system. External influences are leakage at the

ends because of improper termination, inadequate cleaning,

moisture in the air, wind velocity, and insulation

temperature. All these factors tend to increase the leakage


Chapter 6

39

current.

It is imperative that cable be stabilized at ambient

conditions before comparing results. This ensures the

temperature will be consistent, while gas and moisture will be

allowed to migrate from the insulation system.

We have evaluated cable tested within two hours after removal

from a well. When the same type cable was exposed to the same

test well conditions during simultaneous tests, but was

allowed to “set” for 5 days after removal, the test results

indicated much better quality.

The cables evaluated in this test had 75 mil EPDM insulation,

a barrier, 60 mil EPDM jacket, and galvanized steel armor.

Subsequent investigations were made using different materials

for barrier.

Representative migohmmeter results taken two hours after

removal from the well are as below.

Megohmmter values

Phase Mohms @

1000 v

Mohms @

5000 v

A-B 20,000 15,000

B-C 20,000 16,000

C-A 20,000 14,000

C-G 20,000 9,000

B-G 20,000 10,000

A-G 20,000 11,000

The magohmmeter values indicate the wet cable would be

expected to be good even though the 5000 v megohmmeter values

indicate some deterioration of the cable insulation system.

The cables were then subjected to a high potential as test at

two hours and five days after removal. The test was halted

when the insulation failed for the voltage exceeded the

termination rating.

Leakage Current and ac breakdown strength after delays

Material Two hours Five days

kV ma kV ma

Alpha 34 21 39 10

Alpha 34 20 42 16

Alpha 44 28 52 16

Beta 30 24 100 24

Gamma 32 23 48 19

Gamma 28 32 48 16

Although the magnitude of the results was different for the

various materials, the effect was identical. All the cables

failed at low levels when energized immediately after pulling.

When the cable was allowed to dry, the results were very

different. The five day results show values as good as any

used cable has been evaluated.


Chapter 6

40

6.10. Cable Nomenclature

Insulation

o Reda

PPE or P = Polypropylene /ethylene

E = EPDM (ethylene propylene dienemethylene)

K = Polyimide (Kapton™)

T = Semi-conductive tape(RedaSurface)

o Centrilift

P = Polypropylene

E = EPDM (ethylene propylene dienemethylene)

T = Thermolpastic

Barrier

o Reda

S = Extruded polyvinylidene fluoride

(PVDF or Solef™)

TB-300 = Tape & braid polyvinyl fluoride

(PVF or Tedlar™)

F = Extruded fluoropolymer (FEP)

TB-400 = Proprietary high temperature tape/braid

L = Lead

o Centrilift

L = Lead

Jacket

o Reda

PE = High density polyethylene (HDPE)

N = Nitrile (Oil resistant nitrile rubber compound)

E = EPDM (EPDM rubber compound)

o Centrilift

E = EPDM (EPDM rubber compound)

N = Nitrile (Oil resistant nitrile rubber compound)

T = Thermoplastic

Armor (General)

G = Galvanized steel

HG = Heavy galvanized steel

GG = Double galvanized (two layers)

SS = Stainless steel

M = Monel

= Standard interlocking profile

FP = Flat profile armor

Voltage rating and cable geometry (General)

3, 4, 5, 8 = Voltage rating (kV)

F = Flat cable configuration

R = Round cable configuration


Chapter 6

41

Cable Size (General)

#1 = AWG # 1 (American Wire Gauge # 1)




6.11. Cable families and designation examples

Reda

Redalene

Description

All cable designs in the Redalene family utilize

polypropylene insulation (designated P or PPE) and an oil-

resistant nitrile jacket (designated O).

Features

o Temperature

The maximum conductor temperature is 205°F [96°C].

o Conductor The conductors are made of alloy-coated copper. The alloy

coating provides corrosion protection for the copper and

improves long-term electrical properties of the

insulation.

o Insulation Polypropylene

o Barrier Tape and braid. Barrier prevents failure from chemical

attack and gas decompression, ensuring superior

performance in wells with hostile environments or wells

with high gas/oil ratios.

o Jacket Nitrile rubber compound with exceptional physical

properties and oil resistance is used.

o Armor Cable armor made from steel strips featuring a galvanized

coating on all sides is the standard. The use of one of

many armor options can improve resistance to corrosion and

mechanical damage.

POTBPOTBPPEOPPEO


Chapter 6

42

Redalene: 205°F (96°C)

Redahot

Description

All cable designs in the Redahot family utilize a

proprietary EPDM insulation (designated E) and an oil-

resistant nitrile jacket (designated O).

Features

o Temperature The maximum conductor temperature is 220° to 350°F [121°

to 177°C]. The temperature rating is based on the options

selected.

o Conductor

The conductors are made of alloy-coated copper. The alloy

coating provides corrosion protection for the copper and

prevents degradation of the adhesive bond between the

conductor and the EPDM (ethylene propylene diene

methylene) insulation.

o Insulation EPDM insulation compounds provide the optimum combination

of electrical, physical and chemical properties.

o Barrier Tape and braid. Barrier prevents failure from attack and

gas decompression, ensuring superior performance in wells

with hostile environments and wells with high gas/oil

ratios.

o Jacket Nitrile rubber compounds with exceptional physical

properties and oil resistance.

o Armor

Cable armor made from steel strips featuring a galvanized

coating on all sides is the standard. The use of one of

many armor options can improve resistance to corrosion and

mechanical damage.

ETBO

Redahot: 250-350°F (121-177°C)


Chapter 6

43

Redablack

Description

All cable designs in the Redablack family utilize a

patented EPDM insulation formulation (designated E) and a

patented EPDM jacket (designated E).

Features

o Temperature The conductor temperature range is 300°F to 400°F [149°F

to 204°FC]. The temperature rating is based on the

options selected.

o Conductor The conductors are made of alloy-coated copper. The

alloy coating provides corrosion protection for the

copper and prevents degradation of the adhesive bond

between the conductor and the EPDM (ethylene propylene

diene methylene) insulation.

o Insulation EPDM insulation compounds provide the optimum

combination of electrical, physical and chemical

properties.

o Barrier Tape and braid. Barrier prevents failures from chemical

attack and gas decompression, ensuring superior

performance in high-temperature wells with hostile

environments or wells with high gas/oil ratios.

o Jacket The patented EPDM rubber jacket compounds provide

exceptional physical properties and temperature

capabilities.

o Armor


galvanized coating on all sides is the standard. The use

of one of many armor options can improve resistance to

gas, corrosion and mechanical damage.

EEREERETBEFETBEF

REDABLACK: 300-400°F (149-204°C)

Redablead


Chapter 6

44

Description

All cable designs in the Redalead family utilize a

patented EPDM insulation formulation (designated E) and

an impervious lead barrier (designated L).

Features

o Temperature range

The conductor temperature range is 400° to 450°F [203°

to 232°C].

o Conductor

The conductors are made of alloy-coated copper. The

alloy coating provides corrosion protection for the

copper and prevents degradation of the adhesive bond

between the conductor and the EPDM (ethylene propylene

diene methylene) insulation.

o Insulation

EPDM provide the optimum combination of electrical,

physical and chemical properties.

o Barrier

The fatigue and corrosion-resistant lead has an

impervious lead barrier that prevents failure from

chemical attack and gas decompression, ensuring

superior performance in high-temperature wells with

hostile environments or wells with high gas/oil ratios.

o Jacket

Additional barriers and various jacket types are

available to prevent mechanical damage and to maximize

cable run life

o Armor


galvanized coating on all sides is the standard. The

use of one of many armor options can improve resistance

to gas, corrosion and mechanical damag

ELBE ELB

Redalead: 400-450°F (203-232°C)


Chapter 6

45

Motorleads: 250-450°F(121-232°C)

Centrilift

Centriline CTT Cable (Centriline Thermoplastic

Thermoplastic)

Centriline CTT cable is designed for a maximum

operating temperature of 190°F (88°C) and can

be safely installed at temperatures as low as -

40°F (-40°C). This product is one of the most

cost effective cables in the Centriline cable

family.

The high dielectric electrical grade

thermoplastic insulation is formulated for

down-hole applications. Another layer of

electrical grade thermoplastic is applied over

the insulation as a jacket that adds physical

protection.

This cable can be used in shallow wells,

marginal oil wells and water well applications

where large quantities of CO2, and/or light

ends are not an issue. The CTT design is

available in a flat configuration for wells

with marginal clearance.

Galvanized steel armor provides an overall protection to

the cables. It is recommended that cable protectors be

used in highly deviated wells or wells with minimal

clearance.

CTT FLAT CABLE

1- Armor: Galvanized Steel

2- Jacket: Electrical Grade Thermoplastic

3- Insulation: High Dielectric Thermoplastic

4- Conductor: Soft Drawn Tin Coated Copper (SDTC)

Centriline CPN Cable (Centriline Polypropylene Nitrile)

Centriline CPN cable is designed for maximum operating

temperatures of 205°F (96°C) and can be safely

installed at temperatures as low as -30°F (-34°C). This


Chapter 6

46

product is one of the most cost effective cables in the

Centriline cable family.

CPN Flat Cable

1 - Armor: Galvanized Steel

2 - Jacket: Oil Resistant, Patented Flexible Nitrile

3 - Insulation: High Dielectric Polypropylene

4 - Conductor: Solid Tinned Copper

Features and Benefits

CPN Round Cable


2 - Jacket: Oil Resistant, Patented Flexible Nitrile

3 - Insulation: High Dielectric Polypropylene

4 - Conductor: Solid Tinned Copper


A specially formulated nitrile rubber jacket provides

added physical protection and reduces the possibility of

damage due to gas, heat or pressure

Centriline CEN Round Cable (Centriline EPDM Nitrile)

Centriline CEN Round cable is designed to operate over a

temperature range from -30°F (-34°C) to 280°F (138°C).

The insulation is a specially compounded, oil resistant

EPDM rubber with proven electrical properties. An oil

resistant nitrile jacket is used to protect the

insulation. This is the most cost effective construction

for wells operating below 280°F (138°C) with low to

moderate gassy conditions

Round constructions have a high temperature tape over the

insulation to allow the jacket to be removed without

damage to the insulation. Galvanized steel armor provides

an overall protection to the cables.

CEN Round Cable


2 - Jacket: High Modulus, Breathable Nitrile Rubber

3 - Tape: High Temperature Tape with Phase Identification

4 - Insulation: High Dielectric, Low Swell EPDM

5 - Conductor: Solid Bare Copper

Centriline CEE Cable (Centriline EPDM EPDM)

Centriline CEE cable is ideal for moderately gassy wells.

CEE cable features insulation compounded with oil

resistant EPDM rubber with proven electrical properties.

A patented, high module EPDM rubber jacket adds hoop

strength and allows breath-ability during decompression.

This cable is designed to operate over a broad range of


Chapter 6

47

temperatures from 60°F (-51°C) to 400°F (204°C). CEE

cables can be manufactured in special designs for

specific well conditions. CEE cable is available in a

round as well as a flat construction for wells with

marginal clearance.

CEE Flat Cable

1. Armor: Galvanized Steel 2. Tape/Braid: High Temperature Barrier Tape and

hydrolytically Stable B-400 Braid

3. Jacket: High Modulus, Breathable EPDM Rubber 4. Insulation: High Dielectric, Low Swell EPDM Rubber


o Flat construction is provided with a barrier tape and a

high temperature braid over EPDM jacket, adding hoop

strength to the product for decompression resistance.

o CEE cables can be provided with capillary cables to control safety valves or inject

chemicals.

CEE Round Cable


2 - Jacket: High Modulus, Breathable EPDM Rubber

3 - Tape: High Temperature Barrier Tape

4 - Insulation: High Dielectric, Low Swell EPDM Rubber


o Round constructions have a high

temperature tape over the insulation to

allow the jacket to be removed without

damage to the insulation. Additional tape

and braid can be added to provide hoop

strength.

o Galvanized steel armor provides overall

protection for the cable. Cables can be

provided with special armors and

configurations to meet different well

requirements

Centriline Duralead CPL (Centriline

Polypropylene Lead) Following extensive

testing at the Cable Development Center,

Centriline Duralead CPLF cable has been

rated to operate in a wide temperature

range* from -40ºF (-40°C) to 257°F (125°C). The

insulation is a specially compounded polypropylene with

proven electrical properties. A fatigue and corrosion

resistant lead sheath is used over the insulation, which

is imperious to chemical or gas penetration. The lead

sheath prevents decompression and is ideal for wells that

are gassy and have high levels of CO2 or H2S.

Using new technology, the galvanized steel armor is


Chapter 6

48

directly wrapped over the lead sheath. This armor has

been edge coated on all four sides, providing the best

corrosion protection. CPL is tested according to IEEE

1019 and API 11S6 and has 90 mil insulation tested to 5kV

standards. CPL has met rigorous repetitive bend testing

requirements. It is recommended that cable protectors be

used in highly deviated wells or wells with minimal

clearance. CPL cable is available with special armors as

required for different well conditions.

CPL FLAT CABLE

1- Armor: Galvanized steel

2- Lead Sheath: Lead sheath barrier, impervious to fluids

and gas

3- Insulation: High dielectric polypropylene

4- Conductor: Solid tinned copper

Example (cable selection)

In the example of chapter 2 (ESP motor), Motor is rated 120

hp, 60 HZ, 2270 v, 32.5 Amp

Pump Load is 104 hp

Motor operating current = (104/ 120) * 32.5 = 28.1 amp.

Choose a cable size with a volts drop < 30v/1000 ft

Choose #6 AWG cable

Voltage drop at 32.5 amps = 20 volts/1000 ft

Correct for Temp. [(160+100)/2]= 130 Deg F) = 20 * 1.12 = 22.4

volts/1000 ft

We have 5500 ft of cable allowing for 100 ft at surface


Chapter 6

49

Voltage drop = 5.6 * 22.4 = 126 volts

Surface Voltage required = 2270(motor) +126= 2396 v.

Calculate the conductor temperature using the motor amperage

and the maximum well temperature,

TIaT wellC 2* OF

Select Reda hot round cable (275 oF), then check the conductor

temperature,

I = 32.5 A, Twell = 160 OF, cable is AWG# 6 Reda hot type

a = 0.02 (from Reda issued table)

Tc = 0.02 x (32.5)2 + 160 = 181

OF

Cable Type Conductor Size (AWG)

6 4 2 1 1/0 2/0

Redablack Flat (EEF) 0.0275 0.0167 0.0086 0.0064 0.005 0.0039

Redablack Round (EER) 0.0199 0.0115 0.0058 0.0043 0.0032 0.0025

Redalead Flat (ELB) 0.0281 0.0169 0.0086 0.0064 0.005 0.0039

Redalead Round (ELBE) 0.0202 0.0116 0.0058 0.0042 0.0031 0.0025


Redablack Flat (ETBE-300F) 0.0275 0.0167 0.0086 0.0064 0.005 0.0039


Redahot Round (ETBO) 0.02 0.0117 0.0062 0.0046 0.0034 0.0027

Motorlead (KELB) 0.0281 0.0169 0.0086 0.0064 0.005 0.0039

Low Temperature Motorlead (KEOTB) 0.0275 0.0169 0.009 0.0068 0.0053 0.0042

Redalene Flat (POTB) 0.0281 0.0176 0.0097 0.007 0.0048 0.0038

Redalene Round (PPEO) 0.0199 0.0112 0.0062 0.0045 0.0031 0.0025

The maximum carrying capacity of a cable can be calculated

using the following equation:

a

BHTTI

C

maxmax


Chapter 6

50

Imax = [(275-160)/0.02]0.5 = 75.8 Amps

Chapter_06 Power Cable

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Transcript of Chapter_06 Power Cable