Power System Design

Power System Design can be quite complex when all of the variables are considered.
However, it can begin simply.

A summation of the site loads is normally a good start and this is completed at LV level. Expansion is a consideration to plan for at this stage, and it would be normal to assess the absolute minimum and maximum of site loads possible, to produce the "span" inside which, our system will operate.

Normally, this summation would be transformed into what we call a Single Line Diagram (SLD).
MCS would produce a SLD for each aspect of a contract and this is the means by which the project size and therefore, costings can begin to evolve.

It is also a means by which equipment footprints can be assessed and, coupled with the actual available space, the purchaser can check if the equipment required can be accommodated within the site boundary or whether the purchaser needs to organise more square area for the project. 
 

Irrespective of physical size, the SLD would show Transformers, Switchboards, MCC's and any associated equipment such as Harmonic Filtration, Power Factor Correction, Uninterruptible Power Supplies, Neutral/Earth Panels and Standby Power Generator Connection Equipment.

MCS would discuss with our client, the geography of the project and break down our proposal further. This break down could suggest multiple incoming DNO supplies, multiple transformers, immediately suggesting a MV ring arrangement and could also suggest requirements for several Low Voltage Switchboards and several MCC's

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Factually, the SLD Design doesn't stop here. This is the time to discuss opportunities for Standby Power and whether this Standby Power is fixed or mobile. The points of connection should be discussed and so too should the operating philosophy. For example, if fixed equipment is decided upon then we could need auto changeover facilities on our switchboard in order that we could engage the Standby Power in the event our design detects a loss of main supply.

If mobile power is preferred then the current drawn at this point should be assessed and consideration should be made to the size and location of the connection Panel. 

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Additionally, there are opportunities at this stage, to discuss any site power cross connections. These can be beneficial when the MV ring is under maintenance and we need to get supplies from one side of the site to the other. We are now in the arena of unique key arrangements while supplies from one switchboard are transferred to another

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We have found in our experience, incomplete or unapproved SLD documentation can often lead to the purchase of incorrect equipment and the onset of commercial issues and programme delays

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Design - The next level

Hot or Cold

At this point MCS would assess the status of the client's current site power arrangement. For example, we would need to know how the site is supplied (overhead or by ground) and review any previous surveys with respect to resolving the site status, that is, whether it is a Hot or a Cold site with respect to earthing.

This could have significant impacts on the existing system as well as the upcoming new project scope.

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Fault Level

Fault Level is a further, major consideration and existing equipment should be checked with respect to their prevailing rating. 
Fault level is something that can be overlooked on the basis the current rating is capable of protecting the load. However, the inability to comprehensively protect under the most onerous circumstances can be very costly

Non Linear loads
Non-linear loadings are a further consideration on existing and prospective, new loads. Compliance with G5/4 is what we are aiming for.

To this end, MCS recommend a Pre-Installation Harmonic Study to be completed and this states the current baseline distortion and will indicate from the onset, to what degree we may require filtration (or, active filtration) to counter the effects of the new equipment 

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Tuned or De-Tuned 

Another necessity is the need to examine and review the degree of site inductive (or capacitive) load, known commonly as the site Power Factor. The mathematics in targeting a given power factor correction figure, are quite straightforward.
However, when we have a combination of linear and non linear loads we then need to consider the need for a combination of tuned and detuned power factor correction. This calculation is not straightforward but requires a high level review with an industry accepted software package.

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