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High Voltage Systems


High Voltage, according to the CEC, is anything above 750V.
Most residential electricians do not deal with high voltage on a regular basis, it is mostly the commercial and industrial electricians that are required to install these systems.
There are many details to consider, and there must be an experienced electrician that takes supervision of a high voltage installation.

Having said that, the following information is provided for you to wet your feet regarding terminology and processes. The chances of working on these systems during your apprenticeship are low, but in any case, the information is here for you to view at any time.

High Voltage Classes
The most common high voltage classes are:
single conductor (unshielded, shielded, concentric neutral)
multi-conductor (unshielded, shielded, concentric neutral)

High Voltage Advantages
The advantages of high voltage systems are:

-Higher Voltage (kVA) lower current (amps) - lower power consumption.
-Smaller conductors
-Less room used for installation

The higher the voltage, the lower the current draw. Meaning, this is an economic advantage for the consumer. Having a lower draw of current allows a smaller conductor to be used, which is also cheaper for installation costs. Even comparing a low voltage system with equipment, and size of cables respectively - it still gains an advantage of cable size.

High Voltage Cable Construction
High voltage cables are commonly described for the voltage rating of the cable, or the insulating material. It is very important that these high voltage cables are able to withstand severe stress factors. Although it is the prime function of an electrical engineer to select the proper cables, it is the electrician's job to properly terminate for safe operation.

Common Insulations
The insulation around a high voltage wire is one of the most important factors for stress and heat resistance the wire can have. Here are some of the most common types of insulation you'll see in your career. As research and development improves in the future, and products become available - this list will change.
EPR - ethylene propylene rubber.
PE - polyethylene. [pol-ee-eth-uh-leen]
PIAS - paper insulated, aluminum sheath.
PILC - paper insulated, lead covered.
PVC - polyvinylchloride.
RINJ - rubber insulated, neoprene jacket.
XLPE - cross link polyethylene.

Common Voltages
High voltage equipment and cable are usually marked with kilovolt ratings. An example is 2.5kV, or 15kV. Just move the decimal place three spaces to the left.
750V =.75 kV
2400V = 2.4kV
4160V = 4.16kV
7200V = 7.2kV
8000V = 8kV
13,800V = 13.8kV

High Voltage Handling, Installation, and Storage.

Protect from physical damage. If you are careless with the handling of the high voltage wire, and damage it during the handling, it will be useless to install. The wire integrity must be kept sound throughout transport to termination.

Forcing a high voltage cable/cables through conduit and machinery will only damage the wire. Looking at the installation, and planning ahead for easier ways to get the job done, will save you time in the long run. Work smart, not hard.
-Proper bending radii (Table 15)
-Proper parts and material for moisture control
-Proper lubricant and pullers
-Proper conductor spacing as required by code.
-watch out for high temperatures like torches

This factor can sometimes be overlooked, and it'll end up costing thousands of dollars if ignored. For instance, water damage. Are your cables being stored in an area that have puddles of water? Are the ends of the cable taped up and tightly secured from water damage? Make sure that the manufacturers specifications are adhered to when considering storage.

High Voltage Cable Stress
Cable defects or damage will cause current leakage and insulation breakdown.
A short term stress voltage, only lasting microseconds, are called impulse voltages.
For this reason there is a separate rating used for stress measurement of the insulation. It is called basic impulse insulation level, or, BIL. As the BIL rating is increased, the cost of the insulation also increases. It's more expensive to get the insulation that will really protect the conductor from HV stress.
Skin Effect
Skin effect is the term given when the electric current distributes itself towards the "skin" of the conductor (outer edge). This is only present in AC systems because of the eddy currents. By concentrating the amount of current travelling in the "skin" of the conductor, the effective cross sectional area of the cable is decreased, thus its effective resistance is increased.