Medium-voltage cable components are examined in this Knowledge DropSM video featuring John Crawford, Engineer and Environmental Compliance Specialist for Anixter.
Medium-Voltage Cable Dissection
Medium-Voltage Cable Dissection Video Transcript
Hello. I’m John Crawford, an engineer and environmental compliance specialist with Anixter.
Today, we are going to review a dissection of some medium-voltage cable. Our sample is a 5-inch length of 500 kc mil, 15 kV bare-copper single-conductor cable. From the end view, it can be seen that this cable is made up of several layers:
- A copper conductor
- An extruded strand shield
- An extruded insulation shield
- A copper tape shield
- The jacket
In this example, the first layer is a 37-strand compressed concentric copper conductor. This large conductor allows for a higher current to flow.
Next, we have the thin black inner layer, which is the semiconductor strand shield that is compatible with insulation and serves a very important function. The semiconductor nature of this material allows it to equalize the charge across the smooth surface of the relatively bumpy conductor. This is important to reduce distress placed on the insulation and significantly increases the life expectancy of the insulation.
The next layer is the white layer, which is the insulation. This particular insulation is ethylene propylene rubber, which is abbreviated as EPR. This is a protective layer, which allows medium-voltage cable to be laid and installed without the flow of electricity grounding to any adjacent structures. The insulation is the barrier that contains the electrons and is sort of like the wall of a pipe.
The next layer is the outer thin black layer of the seminconducting insulation shield. This is also used to create a smooth surface for even charge dispersion. Like the strand shield, it is an important part of a system of components used to increase the service life of the installation.
The next layer is the copper tape shield, which helps to protect the user from shock hazards and increases cable reliability by draining off energy that might otherwise cause partial discharge in cables. The shield also carries fault current in the event of a fault.
The outermost layer of the cable is the jacket. The primary function of the jacket is to protect the shield, insulation and conductor core from external physical forces and chemical deterioration.
Thank you for watching. For more information on medium-voltage cables, contact your local Anixter representative.