The following table lists equations commonly used for determining various parameters of an electrical system where: While these cables are applicable to the great majority of cable installations that are on grounded systems, they may also be used on other systems for which the application of cables is acceptable, provided the above clearing requirements are met p completely de-energizing the faulted section. Using a mechanical clamp such as a constant tension spring or a hose clamp is usually adequate to secure the connection. Open wire lines have a high reactance. Definite rules cannot be established on a practical basis for all cases. The resultant intensity of discharge may be sufficient to cause burning of the insulation or jacket.
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Malasida Likewise, damage to non-shielded cable may result when the surface of the cable is moist, or covered with soot, soapy grease or other conducting film and the external field is partly confined by such conducting film so that the charging current is carried by the film to some spot where it can discharge to ground.
If the surface of the cable is separated p ground by a thin layer of air and the air gap is subjected to a voltage stress, which exceeds the dielectric strength of air, a discharge will occur, causing ozone formation. For a typical 35kv cable with conductors in the — kcmil range, XLPE jackets may l a 25 percent reduction in neutral wire copper content.
Where regulation is an important consideration several factors should be kept in mind in order to obtain the best operating conditions. To protect cable connected to overhead lines or otherwise subject to induced potentials. Reducing the number of concentric neutral wires reduces overall cable costs. Do you have any insight on the rather large discrepancy between these resistivity assumptions? To confine the dielectric field within the cable. Shield Materials Two distinct types of materials are employed in constructing cable shields: This may be improved by using parallel circuits but is much further reduced by using insulated cable.
Inductive Reactance to Neutral The following is a nomogram used to determine the inductive reactance of solid or stranded concentric conductors at 60 Hz. Connection to aerial lines. Three conductors in magnetic conduit will have a somewhat higher reactance than cables in non-magnetic conduit. To reduce the hazard of shock. The wire or strap used to connect the cable shield ground connection p the permanent ground must be of adequate size to carry the fault current.
The reactances shown are for Hertz operation. This decreases the reactance to fault currents and increases human safety factor. XLPE jackets can allow reduced copper content and higher operating efficiencies.
As a guide in preventing such serious damage, maximum allowable short circuit temperatures that damage the insulation to a slight extent only, Industrial Drive Lexington, South Carolina Phone: The percent voltage drop ucea the same between conductors as from conductor to ground and should not be multiplied by 3.
An increase in contact resistance may occur after cable installation, during service exposed to moisture and heat. Importance of Shielding Where there is no metallic covering or shield over the insulation, the electric field will be partly in the insulation and partly in whatever lies between the insulation and ground.
Dry soil, such as in the desert. Use of Insulation Shielding The use of shielding involves consideration of installation and operating conditions.
It is accomplished by means of strand and insulation icra. Voltage regulation is often the limiting factor in the choice of either conductor or type of insulation.
Shielding used to reduce hazards of shock should have a resistance low enough to operate protective equipment in case of fault. XLPE MV Jackets Bring Sustainable Benefits While the heat loss in the cable determines the maximum current it can safely carry without excessive deterioration, many circuits will be limited iea currents lower than this in order lcea keep the voltage drop within permissible values.
Three conductors in the same conduit have a lower reactance than conductors in separate conduits. For example, the effective area of a composite shield consisting of a helically applied tape and a wire serving would be the sum of the areas calculated from Formula 2 or 3 and Formula 1. Most 10 Related.
Keramar Click Here to join P and talk with other members! I came up with 7. Multiple grounding of shields is desirable in order to improve the reliability and safety of the circuit. It accommodates various spacing of the conductors and other unique parameters as indicated within the nomogram itself. To obtain the voltage drop line-to-line, multiply the voltage drop by 3.
ICEA P-45-482 PDF