Friday, December 18, 2009

Electrical rooms design

During the design of electrical installation for buildings, the spaces required as electrical rooms need to be provided for very early in the planning and design stage. Failure to do so would cause difficulties when the designers start producing their detail designs.

Types of buildings electrical supply needs

Two (or sometimes three) sources of electricity are normally required in high-rise buildings:

1) The normal mains supply from the electric supply authority or the local electricity supply company in some countries.

2) The standby or emergency supply for the standby electric generators. In most situations this supply is not an option, but a mandatory requirement for buildings that exceed a certain size.

3) The uninterruptible power supply, or commonly called UPS. This is only needed in certain types of office buildings and in some hospital buildings.

The choice of the supply voltage levels from the supply authority

The normal mains supply taken from the authority may be taken at HV (high voltage, normally 11 kV in this country), or LV (low voltage, 415 Volt, three-phase four-wire).

Whether it is LV or HV depends on the size of the maximum electrical demand to be expected of the planned building when it is in full operation.

It also depends on the effects of voltage drops and the level of voltages that are currently available from the supply authority.

Supply authority’s HV switch-room

When the incoming supply is HV, the authority usually only require a HV switch room to be built and handed over to them. This is where they house their high voltage switchgears and other equipment.

The location of this room must allow for easy access by the authority’s maintenance people and it should not present inconvenience to the occupants of the buildings or disrupts the building’s normal functions and operations.

Electrical distribution cables from the authority’s distribution network in the area will tapped and looped to the HV switchgear panels in this room. A series of panels are usually installed by them here.

Then from one of the HV panels, a supply feeder cable will be laid and connected to the consumer HV room and the HV energy meter.

Supply authority’s 11kV/.41vV transformer room

Often during the negotiations for the application of the supply, the authority may require that a transformer room is also provided and handed over to them together with the HV room.

Usually this happens when there is no suitable site available for their substation in the vicinity. This usually happens when the planned building site is at a congested area of towns like the city center.

Consumer HV room

As mentioned, the HV feeder cables that will carry the electric current to the planned building will need to connect to the consumer’s HV switchboard in the consumer HV room.

Part of the cost born by the authority in order to give supply to the new building are usually charged to the consumer (in what is usually called a “contribution fee”) and need to be paid before the authority commence their installation work.

Therefore, the nearer the consumer HV room is to the authority HV room, the shorter the HV cables that need to be laid and the lower the cost of the cables that need to be shared by both parties.

So in many cases, the consumer HV room needs to be nearer to the authority’s HV room.

Transformer room

Other than the HV room, the consumer also needs a transformer room, the LV room and the standby generator room.

When a large UPS supply is used, then a UPS room may also be needed.

The consumer transformer room and the LV room need to be as close to each other as possible in order to minimize the voltage drop.

For every meter of extra distance between these two rooms, a significant cost needs to be spent to overcome the voltage drop to an acceptable level.

Incoming supply at Low Voltage

If the supply taken from the authority is LV, then the supply authority will require a HV room and an transformer room to be provided.

The two rooms must be situated adjacent to each other although sometimes they accept that the HV switchgear and the transformers share the same room to save space.

The consumer is also required to provide a main switch room adjacent to the transformer room. The standby generator room also needs to be near the main switch room.

The locations of the electrical rooms

The location of the electrical rooms is also a major factor in the design of all types of electrical installations.

There are a few major requirements that must be taken into account when deciding on the locations for these rooms.

1) They should be located inside the buildings, as near as possible to the load centers.

2) The rooms should be as near as possible to each other.

3) They need to be accessible by maintenance vehicles and maintenance people for purposes of installation, operation and maintenance works.

4) They should be accessible by heavy vehicles during installation and when replacement of heavy equipment is necessary.

5) They should be adequately ventilated.

6) They should be adequately secured from possible disasters like flood, or even vandalism.

The above electrical rooms are in the category of substation rooms.

These rooms can actually be located at a separate building adjacent (or hidden behind) the main buildings.

However, there are still number more rooms that are needed by the electrical installation.

Other electrical rooms

1) Electrical service ducts or electrical risers. These service dusts are used to house the vertical submain cables that carry supplies to the upper floors of the buildings and to the plants and machines at the roof top such as the chiller plants, cooling towers or the lift motor rooms.

The vertical rising mains that supply the lateral distributions on individual floors are also located in these vertical ducts.

2) Individual floor electrical rooms. Each individual floors of significant size will usually need at least one dedicated electrical room to house the electrical distribution equipment for that floor.

However, sometimes the vertical service ducts may be able to fulfill these functions in which case a separate electrical room may not be necessary.

The architect may need to make these service ducts (sometimes also called “riser rooms”) bigger to give them enough space for proper operation.

The electrical rooms at each floor house the DB (distribution boards) that serves the final circuit wiring. Therefore, they should be as close as possible to the load center of the area that it serves.

Very tall buildings

If the planned building is very high (let’s say a 40 storey office building), or in cases where heavy loads are located at higher levels of the building, it may be necessary to provide substations at the higher levels of the building.

For the 40-storey office building, an 11/.415 kV substation may be necessary at one of the upper floor. It may be located at twentieth floor, for example.

All the substation room spaces as explained earlier will then need to be provided.

The floors of this substation will need to be designed by the structural to handle the loads of all the substation equipment.

Coordination with other design consultants and engineers

The above requirements need to be planned for at the early stages of the design and coordinated with the architects and structural engineers.

In many projects, the room spaces and their locations as requested by the electrical engineers are subject to “negotiations” with the architects and structural engineers, not merely technical coordination.

Copyright Electrical rooms design

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