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Introduction

Strength

Electrical Power

Electrical Communication

Temperature Rating

Special Cable Problems

Cable Service

Reversing a Line

Attenuation VS Freq
Graph

Electrical Fault
Location

Derivation of Fault
Detection Formula

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Cased Hole

Electrical Power

One of the main functions of the EM Cable is to transfer electrical power from surface panels to down-hole logging instruments. In order to determine which is the best cable for the job the following issues should be considered.

  1. Voltage Rating: The voltage rating of a new 1N32PP cable is 1500 volts D.C.   All new cables are tested at the factory at twice the rated maximum voltage rating for 5 minutes before they leave the factory. The specified maximum voltage is a conservative rating. The reason for this conservative rating is to take into account some of the stresses that the cable can be exposed to during normal operations. These stresses include splices, physical abuse the cable will normally experience in field use, and the effects of temperature and pressure.

The voltage ratings are not reduced by temperature within the temperature rating of the cable. Since the voltage ratings are conservative, the ratings can be applied to used Camesa cables, provided that splices are done carefully and physical abuse to the cable is not excessive.

  1. Power Handling:  The combination of cable maximum voltage rating and the conductor electrical resistance are the factors that limit the conductor current.

    Another factor, which needs to be considered, is the heat generated by high current applications. Passing several amps through the conductor for several hours, with a portion of the cable tightly wound on the drum, can cause a significant amount of heat to build up. With the cable tightly wound on the drum the conductor can not dissipate the heat and the cable on the drum acts as a big heating coil. Sustained high currents in such situations, can cause sufficient heating to melt the plastic insulation around the conductor.

  2. Insulation Leakage:  All plastic insulation used in logging cables are such an excellent dielectric that in un-spliced cable there should be no measurable leakage in any conductor.  To check cable insulation be sure:

  1. Cable is disconnected from collector (slip-rings)

  2. Cable is disconnected from the head or bridle cable

  3. The insulation at both ends has been cleaned and all conductive coating material is removed.

Under the above conditions there should be no measurable leakage once the conductor is fully charged.  This leakage will not vary with surface temperatures. The insulation resistance is so high, over 1.5 x 105 meg ohms/1000 ft., that even though it decreases slightly with temperature to the range of 104 x 103 meg ohms/1000 ft., it is of no significance. Most generally low insulation resistance is caused by rubber, neoprene, or similar type boots in contact with the connector pins.

  1. Insulation Defects: If any leakage can be observed after taking the above precautions it will due to:

  1. Manufacturing defects

  2. Mechanical damage to cable

  3. Splice in conductor

  4. Z-kinks

Methods of locating leaks will be discussed later under service, but experience clearly indicates that most electrical failures are associated with mechanical damage to the cable.  One form of mechanical damage can be caused by perforating, especially in an under-balanced well condition.  This can result in the formation of "Z" kinks in the conductors near the cable end.

  1. Conductor Resistance. The maximum electrical resistance of the cable conductors is listed in the catalog.  For the 1N32PP the maximum resistance is 3.1 ohms/Kft. at 68 degrees F.  A 1N32PP line typically has 2.8.ohm/Kft at 68 degrees F. 

    The conductor is made of copper and therefore the resistance of the conductor varies with temperature as

For T in degrees Centigrade

RT2 = RT1 (.9214 + .00393 T2)
(.9214 + .00393 T1)

For T in degrees Fahrenheit

RT2 = RT1 (.8515 + .00218 T2)
(.8515 + .00218 T1)
RT = Resistance at temperature
T =

Temperature at which RT was measured

More specifically for the 1M32PP cable with a typical resistance of 2.8 ohm/Kft. at 68 degrees F.

For T in degrees Centigrade

RT = (2.58 + .011 T) ohm/1000 ft.

For T in degrees Fahrenheit

RT = (2.38 + .00611 T) ohm/1000 ft.

At 274 degrees C (526° F) the resistance of copper is double its value at 20 degrees C (68° F).

This demonstrates the significant effect of temperature on conductor resistance.   Of course, as the resistance increases, the ability of the cable to transmit power and return signals decreases!

As a cable is lowered into the hole the total conductor resistance for the 1N32PP cable will be

For T in degrees Centigrade

RL = (2.58 + .011 Ts)L + [2.58 + .0055(TB - Ts) ] D ohms

For T in degrees Fahrenheit

RL = (2.38 + .00611 Ts )L + [2.38 + .00305( TB - Ts )] D ohms

where

RL = total conductor resistance - ohms

L = total length of cable on truck winch - units of 1000ft.

TS = surface temperature

D = depth of tool - units of 1000 ft

TB = bottom hole temperature


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Camesa, Inc · 1615 Spur 529 · P.O. Box 1048 · Rosenberg, Texas 77471
Phone: (281) 342-4494 · Fax: (281) 342-0531