Cable Sizing Calculation

Posted: November 16, 2011 in Electrical Engineering

After designing or obtaining the lighting and the electrical equipment loads, cables has to be selected.

There are 3 main factors that effecting our calculation in selecting the right cable for each of our electrical equipment..

1) Temperature correction factor

2) Group de-rating factor

3) K factor

**These 3 factors are obtained from the cable vendor that we intended to use.

Then, we had other requirement to be meet which could be considered the next important factors after the main 3 factors..

1) 5% Allowable Voltage Drop

2) Cable Length of the respected cables.

3) Let through energy for Cable > Let through energy for Circuit Breaker/Fuse

4) Cable site rating > FLC + Safety margin

**Cable site rating = Max. current can flow in the cable

**FLC = Full Load Current

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Just sharing the information regarding the Steel Armoured Cable, I was ask about what is SWA cable.. and I was blurr at the time.hehe.. So, better to read briefly about what is the cables is all about (the functions and how it is structured).

Steel Wire Armoured (SWA) Cable

High Voltage XLPE (Cross Linked Poly-Ethylene) Power Cable – Showing Details of conductor, insulation, bedding, armour & sheath

Steel Wire Armoured Cable, commonly abbreviated as SWA, is a hard-wearing cable designed for the supply of mains electricity. It is one of a number of armoured electrical cables – which include 11kV Cable and 33kV Cable – and is found in underground systems, power networks and cable ducting.

The typical construction of an SWA Cable can be broken down as follows:

Conductor: consists of plain stranded copper (cables are classified to indicate the degree of flexibility. Class 2 refers to rigid stranded copper conductors as stipulated by British Standard BS EN 60228:2005)

Insulation: Cross-linked polyethylene (XLPE) is used in a number of power cables because it has good water resistance and excellent electrical properties. Insulation in cables ensures that conductors and other metal substances do not come into contact with each other.

Bedding: Polyvinyl chloride (PVC) bedding is used to provide a protective boundary between inner and outer layers of the cable.

Armour: Steel wire armour provides mechanical protection, which means the cable can withstand higher stresses, be buried directly and used in external or underground projects. The armouring is normally connected to earth and can also be used as the circuit protective conductor (“earth wire”) for the equipment supplied by cable.

Sheath: a black PVC sheath holds all components of the cable together and provides additional protection from external stresses.

SWA Cable can be referred to more generally as Mains Cable, Armoured Cable, Power Cable and Booklet Armoured Cable. The name Power Cable, however, applies to a wide range of cables including 6381Y, NYCY, NYY-J and 6491X Cable.

Aluminium Wire Armoured Cable

Steel Wire Armour is only used on multicore versions of the cable. A multicore cable, as the name suggests, is one where there are a number of different cores. When SWA Cable has only one core, aluminium wire armour (AWA) is used instead of steel wire. This is because the aluminium is non-magnetic. A magnetic field is produced by the current in a single core cable. This would induce an electric current in the steel wire, which could cause overheating.

Use of armour for earthing

The use of the armour as the means of providing earthing to the equipment supplied by the cable (a function technically known as the circuit protective conductor or CPC) is a matter of debate within the electrical installation industry. It is sometimes the case that an additional core within the cable is specified as the CPC (for instance, instead of using a two core cable for line and neutral and the armouring as the CPC, a three core cable is used) or an external earth wire is run alongside the cable to serve as the CPC. Primary concerns are the relative conductivity of the armouring compared to the cores (which reduces as the cable size increases) and reliability issues. Recent articles by authoritative sources have analysed the practice in detail and concluded that, for the majority of situations, the armouring is adequate to serve as the CPC under UK wiring regulations.

According to Petronas Technical Standards (PTS), the allowable voltage drop percentage from the main power supply to the end load is capped at 5%. In our design, we need to make sure this condition is met.

In formulating the best allowable voltage drop at each feeder and loads, we also need to consider the power supply that comes from the battery terminal when power obstruction occurs. The percentage of allowable voltage drop from the battery to the end load also needs to be 5%.

Below is the simple single line example I had made for the project I’m assigned too. This helps to deepen my understanding and help me to have a quick overview of the allowable voltage drop percentage in the system.

Initially you could assume the allowable voltage drop at each feeder and loads by putting a rough figure. Then, from your cable sizing calculation you can then alter them accordingly to obtain the best result. Usually, your concern is to use the smallest cable possible in every design.

Smaller cable = Less cost = More profit! 😉

Illumination Calculation

Posted: September 30, 2011 in Electrical Engineering

One of the first task given to me is to do the Illumination Study. This study is to calculate and determine the number of lamps needed and the power required by the designated areas.

As the client for my project is PETRONAS, I need to refer to Petronas Technical Standard (PTS) in order to design the lighting according to their standard. In PTS, it explained what PETRONAS are expecting from the study.

Different areas at the platform will be having a different average lux required.

To carry out the task, I have been using CHALMLITE v4.05. This is an open source software, you can download it free from the website. We could calculate lux easily rather by using this software and save a lot of time rather than doing a manually calculation. The average lux are differ depending on the type of lamps that being used. There are lots of option such as fluorescent, floodlight and well-glass.

After obtaining the desired average lux, we also need to make sure the ratio of our lighting. In my case, PETRONAS need to ratio to be 0.25

I’ll find sometime to put the actual report in the web in my next post. 😉

First Job

Posted: September 9, 2011 in Electrical Engineering

To be frank, I already started working about 7 months ago when I wrote this post. Well, before I started forgetting my feeling and excitement getting my first job as an Engineer, I wanted to at least shared with you.hehe.. 😉

I graduated overseas. I tried very hard to secure a job in overseas, but being an International graduate with an ordinary performance in academic, making it hard for me to be short listed.

I did manage to be called for 1 inetrview and 1 phone interview, but the the result was not as expected. I am sure all of you will went through a stage where your email mailbox full of email with the sentences “We are sorry to inform you..”,”We will keep your CV/resume for the next opening in the company..”. These are some of the regular sentences used if your application are being denied. I know.. I know.. it can be quite depressing.

At last, I decided to try my luck in my home country, Malaysia. Yeah, being a local with a overseas university’s certificates does gives you advantages. I managed to went into 2 interviews session and I choose to work in Kuala Lumpur as I wanted to explore the Oil and Gas Industry. My first position is as Project Engineer. I felt really happy and excited to start this journey. A new chapter of my life has begun and I am officially employed!haha.. 😉

Registering with BEM

Posted: September 8, 2011 in Electrical Engineering

First ever step when you graduate is to register yourself with the Board of Engineers Malaysia (BEM). You can go to their website at www.bem.org.my for further instruction.

It is important to register if you are planning to do Ir. after 5-6 years in your careers. You will need to keep a record of all the knowledge and task you had done to be presented. Plus, you actually need to register to practice your degree LEGALLY in Malaysia!

BEM will ONLY accepting records starting for the first date you officially registered with them. Therefore, do not waste your time and start register NOW!

I registered mine in the month of May 2011. Now it is already September and yet I have not receive any news yet. Some says BEM only had their board meeting twice a year. Hopefully my application will get approved soon.

Also, please be mind that for an Electrical Engineer that are majoring in POWER SYSTEM, make sure you only tick 1 BOX (which is ELECTRICAL) when applying for your major in BEM. DO NOT tick ELECTRONIC ever… there has been a complaint by some of my seniors that BEM accidently put them into Electronic and it would be pointless as Malaysia would only gives Ir. based on your major in the university.