Electricity + Control February 2018

CABLES + ACCESSORIES

Calculate Costing LV Cable Losses

Carel Ballack, Copper Development Association Africa (CDAA)

This article looks at the long-term cost implications and ROI of sizing cable for the do- mestic, commercial and industrial sectors. The much contested question of whether power factor correction equipment is indeed a better solution than increasing cable sizing, is answered.

Take Note!

How to approach calcu- lations on cable sizing savings. Comparesavingsbetween commercial-and-industri- al electrical networks. Increase end-user sav- ings and efficiency by be- ing informed on different aspects of cable sizing.

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T he outcome of this sophisticated process will be a simple rule of thumb for a few spe- cific cases and a ‘cookbook recipe’ detailing how to arrive at such a result under different con- ditions. This is completed with a list of basic rules. The ultimate goal is a minimum life cycle cost, which will also lead to safety and reliability levels that are higher than the minimum requirements. A number of factors have contributed to the global trend to operate more environmentally friendly. This focus-shift to manage operations more efficiently has resulted in renewables being pushed to the forefront of innovation both from a generation as well as storage point of view. By combining energy efficiency and renewa- ble energy sources the electrical network could function optimally, provided losses are reduced through various interventions assisting in optimis- ing consumption and improving performance (with some of these interventions being power factor correction and replacing incandescent globes with LED lighting as practical examples). Standards The original article was written in Europe with cur- rency indicators being in Euros. In South Africa, the South African Bureau of Standards is slowly moving over to IEC standards. This can be seen when we consider the various local standards that have been converted from IEC to SANS stand- ards, i.e. SANS 60364 [1] (Electrical Installations for Buildings) specifically SANS 60364-7-712 [1a], SANS 62305 [2] (lightning protection). Standards define minimum criteria and do not always best practice. Although cable sized accord- ing to the standard, should ensure a level of safety, it does not necessarily address efficiency. Cable

heat up during operation and if the maximum per- missible operating temperature is actually reached, the cable is already way beyond its energetic and economic optimum. Choosing a larger cable cross section than what the standard prescribes saves energy and money and provides genuine safety. More cable actually costs less In reality, cables and wires are rarely operated at a constant load. And if they are, this load is hardly ever equal to the maximum permissible load. To a certain extent, cable sizing will be determined by the user’s load profile, i.e. household vs office block vs commercial and industrial user’s all have different load profiles. Through this article or appli- cation note, we would like to show how to calcu- late the basis that it is worth considering a thicker cable cross-section than required by the present standards even with less heavy-load consumption patterns. The question arises as to how to calcu- late the optimum size of the cable cross-section with the aim of minimising life cycle costs. The approaches by the IEC standards, to-date; to designing cable and wiring installations for minimum life cycle costs simply assume the load profiles are accurately known. This is also what standard IEC 60364-8-1 [1a] (energy efficiency of low voltage in- stallations) states in clause 6.2 – ‘Determination of load profile’. This clause reads as follows: ‘The main load demands within the installation shall be determined.The loads in kVA, together with their durations of operation and/or an estimation of the annual load consumption (in kWh) should be identified and listed’. Clause 6.7.2 further states that: ‘Increasing the cross-section of conductors will re- duce the power losses. This decision shall be made by balancing the energy savings achieved over a cer-

A number of factors have contributed to the global trend to operate more environmentally friendly.

Electricity + Control

FEBRUARY 2018

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