Exploring a methodology in costing LV electrical cable losses.
Introduction
This article looks at the long-term cost implications and ROI of sizing cable for the domestic, commercial and industrial sectors. The authors also answer the much contested question of whether power factor correction equipment is indeed a better solution than increasing cable sizing.
The outcome of this sophisticated process will be a simple rule of thumb for a few specific cases and a “cookbook recipe” detailing how to arrive at such a result under different conditions. 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 renewable energy sources the electrical network could function optimally, provided losses are reduced through various interventions assisting in optimizing consumption and improving performance (with some of these interventions being power factor correction and replacing incandescent globes with LED lighting as practical examples).
Standards
Standards define minimum criteria and do not always consider best practice. Although cable sized according to the (IEC or SABS) standard, should ensure a level of safety, it does not necessarily address efficiency. Cables heat up during operation and if the maximum permissible 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.
The original article was written in Europe with currency 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 standards, i.e. SANS60364 (Electrical Installations for Buildings) specifically 60364-7-712 and SANS62305 (Lightning protection).
An individual consumer
A standardized load profile for homes exists within the IEC range of standards, namely H0 [4]. This, however, is only to be used for the connection of the entire property, for instance from the distribution network to the meter. Behind the meter, the power is distributed to the final circuits in a very uneven manner in terms of both time and space. Consider, for example, the socket in the laundry room. If that is intended solely for the washing machine, the load of this circuit can be estimated fairly accurately. During a two-hour wash cycle, there is approximately half an hour in which the machine consumes a current that represents a substantial load for the installation cable (Figure 2).
The rest of this article considers Residential, commercial and industrial case studies.
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