Power cable of Higher voltages

A power cable is a cable that is an assembly of one or more electrical conductors usually held together by an integral sheath.This component is used to transmit electricity. Power cables can be installed as permanent wiring within buildings, buried underground, overhead or exposed.Power cables bundled in thermoplastic sheaths and intended to be laid in buildings are called NM-B (Non-Metallic Sheathed Building Cables). Flexible power cables for portable equipment, mobile tools and machinery.

Higher voltages 

For circuits with a voltage between conductors of 2,000 volts or more, the insulation of the conductors shall surround the conductive shield.This balances the electrical stress on the cable insulation.This technique was patented by Martin Hochstadter in 1916; the shield is sometimes called the Hochstadter shield.In addition to semiconductor (“semiconductor”) insulating shields, there will also be conductor shields. Conductor shields can be semi-conductive or non-conductive. However, only one cable company produces shields for non-conductive conductors.A conductor shield serves a similar purpose to an insulation shield: it is a void filler and voltage stress equalizer.

To drain stray voltages, a metal shield will be placed over the "semiconductor".This shield is designed to "secure" the cable by pulling the voltage on the outside of the insulation down to zero (or at least below OSHA's 50 volt limit).This metal shield can consist of thin copper tape, concentric drain wires, flat tape, lead sheath, or other designs.The metal shield of the cable is grounded at the end of the cable and possibly along the length if the voltage rise during a fault would be dangerous. Multi-point grounding is the most commonly used grounding method for cable shielding.Some special applications require shield disconnection to limit circulating current during normal circuit operation.Circuits with shield disconnection can be earthed at one or more points. Special engineering situations may require cross-connect.

Liquid or gas filled cables are still used today in power distribution and transmission systems.Cables of 10kV and above can be insulated with oil paper and laid in hard steel pipes, semi-hard aluminum pipes or lead sheaths.For higher voltages, the oil may be kept under pressure to prevent the formation of voids, which can cause partial discharges within the cable insulation.

Liquid-filled cables are known for their extremely long service life with virtually no power outages.Unfortunately, oil spills into soil and water bodies are a serious problem and maintaining the required set of pumping stations is a boon to most utilities' O+M budgets. Despite the expected short service life, tubular cables are usually converted to solid insulation circuits at the end of their service life.Modern high voltage cables use polyethylene or other polymers, including XLPE for insulation.They require special connection and termination techniques, see High Voltage Cables.

Flexibility of cables (stranding class)

All cables are somewhat flexible so they can be transported to the installation site on reels, drums or hand coils.Flexibility is an important factor in determining the proper level of stranding for a cable because it directly affects the minimum bend radius. Power cables are usually type A, B or C twisted.These categories allow the cable to be trained to the final installation position where it would not normally interfere with the cable.Types A, B, and C are more durable, especially when pulling cables, and are usually less expensive.Utilities typically order Class B stranded wire for primary and secondary voltage applications. Sometimes solid conductor medium voltage cables can be used when flexibility is not a concern but low cost and waterproofing are priorities.

Applications that require repeated movement of the cable, such as portable equipment, use more flexible cables called "corded" or "flexible" (strand grades G-M). A flexible cord consists of finely stranded conductors, strands or bundles.They feature an overall jacket with just the right amount of padding to enhance its flexibility, trainability and durability.Heavy-duty flexible power cords, such as the ones that power mine face cutters, are engineered to last their life is measured in weeks. Very flexible power cables are used in automated machinery, robots and machine tools.Extension Cords for more instructions on flexible power cords.Other types of flexible cables include twisted pair, extendable, coaxial, shielded, and communication cables.X-ray cables are a special type of flexible high voltage cables.