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When to use medium-voltage cables

Medium voltage cables, such as these from TANO Cable, are often used in mobile substations or for power distribution.

Three ranges of voltages are available for cables today. Low-voltage designs—often those used in industrial settings—are rated to 2kV or lower. Medium voltage designs range from 2kV to 35kV and high-voltage cables are those rated above 35kV.

Medium-voltage cables are commonly used in mobile substation equipment, for distribution of power in industrial settings and in mining to supply power to drills, shovels, haulers, etc., These cables often come in standard voltages, including 5,000; 8,000; 15,000; 25,000; and 35,000 V.

A common application for medium-voltage cables is in maintenance and repairs, Utilities personnel use mobile workstations to provide scheduled downtime maintenance for substations or to conduct repairs due to damage caused by a storm, for example.

In addition, industrial facilities might have an in-house team or contractors that install and repair these types of cables for distribution of power, as some facilities have responsibility for some of the power that is coming into them.

Perhaps the biggest difference between low- and medium-voltage cables is their construction. Most medium-voltage designs offer extra protection to prevent the build-up of potential charges anywhere along the cable.

A typical, single-conductor, low-voltage design is usually constructed of the following:
• An aluminum or copper conductor
• Insulation and
• Jacketing

Medium-voltage designs are usually constructed as follows:
• An aluminum or copper conductor
• A conductor shield—which is usually made of some type of semiconductor material,
• Insulation
• Insulation shield, which again can be a semiconductor or a metallic braid or tape, and
• Jacketing

The conductor and insulation shields help reduce the effects of imperfections on the cable or the effects of the cable coming in contact with a ground potential, where voltage can accumulate. Electricity will always find the lowest point of resistance, so the semiconductor, copper tape or metal braid is there to spread out the charge more evenly.

This safety mechanism prevents possible discharges that can damage the cable, equipment or worse yet, cause injury.

Copper and aluminum are the two main conductor materials. Copper is used mostly in medium voltage designs, while the lighter weight aluminum is used more often in high voltage cables.

A variety of materials are used in medium voltage jacketing. Cross-linked polyethylene or XLPE is one of the most recommended, but ethylene propylene rubber or EPR, chlorinated polyethylene or CPE, and Neoprenes are also used. The most important factor cable manufactures must consider when selecting a cable and its jacket material is whether the wall thickness is suitable, especially according to UL and CSA standards. The end-user should consider how the jacket will hold up to its environment, such as sunlight, heat, cold, etc.

Finally, different design requirements exist if medium voltage cables are going to be direct buried. For example, if there is a fault the copper tape or copper braid insulation shield must carry a current. As a result, the cable must have a specified area or mass for the shield to be able to carry a fault if something goes wrong.

Hope this article sharing is helpful to you.
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