Recommendations for architecture optimization
From Electrical Installation Guide
These recommendations are intended to guide the designer towards architecture upgrades which allow him to improve assessment criteria.
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, busway), allowing the volume of operations on site to be limited,
- Limit the variety of equipment implemented for example, when possible harmonize transformers power,
- Avoid mixing equipment from different manufacturers.
The optimization of the environmental impact of an installation will involve reducing:
- Power losses at loaded and also no-load conditions during all the period of operation of the installation,
- Overall, the mass of materials used to build 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 D28 gives an example of the contribution per equipment category to the weight and energy dissipation for a 3500 kVA of installed power spread over an area of 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.
- Energy consumption is 9,1 GWh per year.
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.
- Second is reactive energy. This lead to additional load on upstream electrical network. and additional energy invoicing. This can be optimized with power factor correction solutions.
- Third is wiring system which represent 75% of the installation losses. Cable losses can be reduced by appropriate organisation and design of site and use of busway wherever appropriate.
- MV/LV transformers are fourth with approx. 20% of the losses (1% of the site energy consumption).
- MV and LV switchboards come last with approximately 5% of the losses (0,25% of the site energy consumption).
Generally speaking, LV cables and busway as well as the MV/LV transformers are the main contributors to losses and weight of equipment used.
Environmental optimization of the installation by the architecture design will therefore involve:
- reducing the length of LV circuits in the installation, as proposed by the barycentre method in IEC60364-8-1 §6.3, and as described in LV distribution - centralized or distributed layout
- clustering LV circuits wherever possible to take advantage of the diversity ks (see Estimation of actual maximum kVA demand)
|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 diversity 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:
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.
Fig. D29: Environmental optimization : Objectives and Resources.
|Solution 1: 1 transformer per workshop, 2 x 1600 kVA, 1 x 630 kVA|
|Solution 2: 1 transformer per line of process, 4 x 1000 kVA|
Fig. D30: Example of barycentres positioning according to load clustering
As an example Figure D30 shows the impact of clustering circuits on different ways and the impact on the barycentres of the clustered loads. This example concerns a mineral water bottling plant for which:
- the installed power is around 4 MVA.
- In solution No.1, the circuits are clustered by workshop.
- In solution No.2, the circuits are clustered by process functions (production lines).
In this example 2 different solutions can be used at the MV/LV level:
- solution 1, a MV/LV transformer is moved close to workshop 3 to optimize its place according to the barycentre of the loads (its more economic to transmit the power in MV when possible)
- solution 2, all MV/LV transformers are in the same substation, and with the same size, allowing also a partial operation of the plant (1/2 of the plant).
In addition, in the 2 solutions the optimization can also be carried out by the following points:
- the setting up of LV power factor correction to limit losses in the transformers and LV circuits if this compensation is distributed,
- the use of low losses transformers,
- the use of aluminum busway when possible, since natural resources of this metal are greater.
Preventive maintenance volume
Recommendations for reducing the volume of preventive maintenance:
- Use the same recommendations as for reducing the work site time,
- Focus maintenance work on critical circuits,
- Standardize the choice of equipment,
- Use equipment designed for severe atmospheres (requires less maintenance).
Electrical power availability
Recommendations for improving the electrical power availability:
- Reduce the number of feeders per switchboard, in order to limit the effects of a possible failure of a switchboard,
- Distributing circuits according to availability requirements,
- Using equipment that is in line with requirements (see Service Index ),
- Follow the selection guides proposed for steps 1 & 2 (see Fig. D3 in The whole process).
Recommendations to increase the level of availability:
- Change from a radial single feeder configuration to a parallel transformers configuration,
- Change from a parallel transformers configuration to a double-ended configuration,
- Add to a double-ended configuration a UPS unit and a Static Transfer Switch
- Increase the level of maintenance (reducing the MTTR, increasing the MTBF)