Recommendations for architecture optimization

MV & LV architecture selection guide

 Recommendations for architecture optimization

These recommendations are intended to guide the designer towards architecture upgrades which allow him to improve assessment criteria.

On-site work

To be compatible with the “special” or “critical” work-site time, it is recommended to limit uncertainties by applying the following recommendations:

• Use of proven solutions and equipment that has been validated and tested by manufacturers (“functional” switchboard or “manufacturer” switchboard according to the application criticality),
• Prefer the implementation of equipment for which there is a reliable distribution network and for which it is possible to have local support (supplier well established),
• Prefer the use of factory-built equipment (MV/LV substation, busbar trunking), allowing the volume of operations on site to be limited,
• Limit the variety of equipment implemented (e.g. the power of transformers),
• Avoid mixing equipment from different manufacturers.

Environmental impact

The optimization of the environmental assessment of an installation will involve reducing:

• Power losses at full load and no load during installation operation,
• Overall, the mass of materials used to produce the installation.

Taken separately and when looking at only one piece of equipment, these 2 objectives may seem contradictory. However, when applied to whole installation, it is possible to design the architecture to contribute to both objectives. The optimal installation will therefore not be the sum of the optimal equipment taken separately, but the result of an optimization of the overall installation.Figure D26 gives an example of the contribution per equipment category to the weight and energy dissipation for a 3500 kVA installation spread over 10000m².

• Installation is operating at 50% load on average, with 0,8 power factor
• Site is operating 6500 hours per years : 3 shifts + week ends with reduced activity at night and week ends and full stop 1 month per year for site maintenance and employees holidays.
• Power consumption is 9,1 GWh
• Reactive power is 6,8 GVARh. This reactive power will be invoiced in addition to power consumption according to local energy contract.
  

These data helps to understand and prioritize energy consumption and costs factors.

• Very first factor of power consumption is... energy usage. This can be optimized with appropriate metering and analysis of loads actual consumption.

Generally speaking, LV cables and trunking as well as the MV/LV transformers are the main contributors to operating losses and the weight of equipment used.

• Second is reactive energy. This lead to additional load on electrical network. and additional energy invoicing. This can be optimized with power factor correction solutions.
• Third is cables. Cable losses can be reduced by appropriate organisation and design of site and use of busbar truncking instead of cables wherever accurate.
• MV to LV transformers are fourth with approx. 1% of losses.
• MV and LV switchboards come last with approximately 0,25% of losses.

Generally speaking, LV cables and trunking as well as the MV/LV transformers are the main contributors to operating losses and the weight of equipment used.
Environmental optimization of the installation by the architecture will therefore involve:

• reducing the length of LV circuits in the installation,

clustering LV circuits wherever possible to take advantage of the factor of simultaneity ks (see chapter A: General rules of electrical installation design, Chapter – Power loading of an installation, “Estimation of actual maximum kVA demand”)

Objectives	Resources
Reducing the length of LV circuits	Placing MV/LV substations as close as possible to the barycenter of all of the LV loads to be supplied
Clustering LV circuits	When the simultaneity factor of a group of loads to be supplied is less than 0.7, the clustering of circuits allows us to limit the volume of conductors supplying power to these loads. In real terms this involves: setting up sub-distribution switchboards as close as possible to the barycenter of the groups of loads if they are localized, setting up busbar trunking systems as close as possible to the barycenter of the groups of loads if they are distributed. The search for an optimal solution may lead to consider several clustering scenarios. In all cases, reducing the distance between the barycenter of a group of loads and the equipment that supplies them power allows to reduce environmental impact.