Howdy fellows electrical engineers, it’s Steven Mill! It’s been a while since I haven’t post something on this blog so here I am with a little article about 5 misconceptions existing around Power Cable.
Have you got an idea of what I’m about to list? Anyway, in any case I hope you’ll enjoy this material and make comments right after!
#1 Copper is always be better conductor than aluminium
It is true that copper conductor provides better conductivity and lower resistivity than aluminium conductor. However, if budget is your concern, aluminium conductor can be your alternative as aluminium conductor generally can offer cheaper price.
But, the larger the size or the higher the voltage of the aluminium conductor, the more uneconomical the aluminium conductor become as it needs larger size of the completed cable than copper conductor.
Nevertheless, the aluminium can be economical for super tension cable (132 kV and above) since an increased conductor offer less stress in the contiguous insulation. Hence, the insulation can be thinner and the price can become more economical. The very good example of this case is shown by Dutch utilities as they use a 1200 sq.mm solid aluminium conductor in their 110 kV XLPE cables.
Figure 1. Copper and Aluminium Conductor of a Cable
#2 Armour is used to protect the cable from impacts
Most people belief that the armour will provide protection from impacts. In fact, Steel Tape Armour (STA) provides a very limited protection against impact and Steel Wire Armour (SWA) is totally useless! Moreover it can aggravate the damage.
Armour in the cables is used to provide the tensile strength to the cable. Hence, the cables can be pulled using cable stocking. Cables installed on steep profile need to have enough tensile strength to support their own weight. Armour also provides protection against ground movement particularly for underground cable [1].
Figure 2. Armour of the cable | image: alibaba.com
#3 My cable has insulation, shield and armour. Hence I can install it in watery area
Armour and shield is not designed to protect the cable from water. If an armour contact with water, it can be corroded and destroy the armour. Shield is quite often used as grounding cable. If the shield contact with water, the shield may be corroded.
Furthermore, it can be broken and create unsafe condition due to the absence of the grounding. Whilst for cable insulation, the popular insulation material for marine and offshore application is ERP cable.
Finally, if your cable is not designed to be installed in watery area then provide protection for cable from water penetration.
#4 My cable current capacity remain same during its whole lifetime
Wrong! The cable current capacity is depend on several factors such as:
- Depth of laying
- Ground temperature
- Ground thermal resistivity
- Ambient temperature (cable in air)
- Multiple cable in various arrangement
- Bonding of the cable
- Other factors stated by the cable manufacturer
It even means that if you install new cables in existing cable tray with 3 cables already inside, the current rating of existing cable may be significantly reduced. Hence if you want to install new cable in new cable tray, it is better to consider whether in the future you will install more cables in the same cable tray or not. If yes, you need to step up your cable current capacity rating in order to cope with that possible future scenario.
Figure 3. Cables in cable tray
#5 I install a new power cable. I am sure my cable will last at least for more than 40 years
As a purchase, we expect that the cable we buy will have a long lifetime. Well, it is true that a power cable is designed to have 30-40 years lifetime. Whoever, not all manufacturers are created equal. A poor cable can cost you in the future or even in the short term. So that, it is paramount for purchaser to look for a reputable manufacturer who has proper technology, knowledge, and quality control procedures.
References
[1] I. C. Xerri, “Cable Components,” in Power Cables, Newcastle, Newcastle Univrsity, 2014, p. 48.
[2] “supreme cable,” [Online]. Available: http://www.sucaco.com/. [Accessed 24 April 2016].
Steven Mill.
So what do y’all think about these 5 misconceptions? Can you find another one?