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Introduction

Strength

Electrical Power

Electrical
Communication

Depth Measurement

Temperature Rating

Special Cable
Problems

Cable Service

Reversing a Line

Attenuation VS
Frequency

Electrical Fault
Location

Derivation  of Fault
Detection Formula

Wire Stress

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ELECTRICAL COMMUNICATION

A variety of signals are transmitted from down  hole instruments to the surface by means of the cable conductors and armor.  These signals vary in frequency for DC to 100 KHZ.  At 100KHZ the attenuation of a 7J46RP cable is in the range of 1.2  db/kft.   For a 25  Kft cable, the total attenuation is of the order of 30  db.  Attenuation vs. frequency is measured for all Camesa 7 conductor cables manufactured and is available on request.

  1. Capacitance and Resistance. The cable is basically  a R C network for most of the frequencies used on the cable.  Therefore, to improve signal transmission, it is desirable to reduce capacity and resistance.  Unfortunately as the conductor diameter is increased to reduce electrical resistance, the electrical capacitance of the conductor (with respect to armor) increases.

For the center conductor, #7, of a 7J46RP cable, the D/d ratio of 2.4 results in a nominal characteristic impedance in the range of 38 to 50 ohms for the frequencies normally used.  The attenuation of this conductor, #7, using the armor as a return circuit is shown on the attached graph.

  1. Dielectric Materials. Signal attenuation in different dielectric materials varies due to the differences in dielectric constants.

  1. Poly Propylene 2.3

  2. Tefzel 2.6

    3.

  3. FEP Teflon 2.1

    4.

  4. PFA Teflon 2.1

The dielectric losses for all of these materials  is so low over the frequencies involved that it can be ignored.

  1. Temperature Effects. For all practical purposes the dielectric constant of all the plastic materials is unchanged up to the maximum operating temperature.  On the other hand the resistance of the copper conductors goes up rapidly and therefore so does the attenuation of the cable. At 526 degrees F. the resistance of copper is double its value at 68 degree F. Therefore that portion of a cable at 526 degree F. will have double the attenuation of that portion of the same cable at 68 degree F.

  2. Shielding. Different service companies use different combinations of the 7 conductors and armor to send a variety of signals up the hole and power down the hole. To minimize cross talk between conductors, a semi conductive electrostatic shielding material is applied around and between all conductors. The string fillers between conductors and the tape binding the seven conductors together are also conductive to provide a good ground to the armor.

When terminating or testing a cable electrically it is very important to clean all of this shielding material off of the conductors.

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