Friday, January 1, 2010

Hospital LV electrical installation

The low voltage (LV) electrical installation for a hospital is designed based on the size and complexities of the hospital to be constructed. A small hospital would only require simpler design similar to other types of electrical works in buildings.

However for large hospitals, or hospitals with sophisticated equipment to be installed, the electrical installation will become more complex because of the wide variety of functions that is provided in the hospital. This ranges from industrial requirements, specialized medical departments, nurses’ hostels, staff accommodation areas, operating theaters and laboratories.

Specials requirements of a hospital electrical design
A hospital deals with life and death of patients. Therefore there are special requirements that must be met by the electrical installation. The most important of these is probably the reliability of the electrical system that is being designed. Many patients rely on life saving equipment and procedures just to stay alive. Therefore, power supply failures longer than certain duration cannot be accepted. Some of the equipment cannot even tolerate a power interruption any more than a few seconds.

All these means that a hospital electrical installation needs to be designed with not just a reliable electrical system, but also with a highly dependable backup electric supply sources. The fact that the power supply to some equipment cannot even be interrupted for any longer than just a few seconds means that an Interruptible Power Supply (UPS) system is an absolute necessity.

Hospital’s electrical installation write-up below
The following is a write-up on the low voltage (LV) electrical installation for a 500-bed government hospital. I modified it from part of an early draft that I did for a turnkey proposal a few years ago. I did not include the high voltage part of the installation here because the treatment on a HV system will best be handled on its own in a separate post.

You may notice that I have managed to give more explanations in certain sections, while the others are very short. I will get back into these short sections when I can steal a little bit more time from my work to finish them.

After reading this post, if you can spare the time, check out the following link. It is a link on how to convert your car into an electric car at minimal cost. It is a way we in the electrical industry can contribute in the global effort to save this planet . In any case, it can save some significant dollars from our daily transport costs. Check it out. It’s a good reading.

A. Distribution system

Usually the major load centers of a large hospital would consist of the Hospital Complex, the Mechanical Plant, and the accommodation areas which are the Nurses’ Hostels and the Staff Quarters.

1. Accommodation area substation
The nurses’ hostels and the staff quarters are usually mentioned separately because the each unit of the staff quarters would be provided with a separate individual meter installed by the electric supply authority. The occupants will need to pay for the electricity bill themselves.

While the electricity cost of all the nurses hostels would be part of the bulk electricity bill charged by the supply company to the hospital. The nurses’ do not have to pay for the bill themselves. This is usually the arrangement made by government hospitals. Private hospitals may have different arrangements. However, the separately billed electric meters of the staff quarters are a standard practice at all hospitals as far as I know.

This separately billed meters for the staff quarters may seem a trivial issue, but from the design of the electrical distribution, in many cases this has made the design of the distribution system at the accommodation area more complicated.

I may dedicate a post in future just to discuss this topic, but for now I will not go further because that can distract us from the overall distribution system of the hospital electrical installation.

2. Mechanical plant substation
The mechanical plant is actually not just for the mechanical systems. It is generally a separate building that houses the central plants for almost all major mechanical and electrical services at the hospital complex. The maximum load current drawn by these plants are usually very large, therefore there require large switchgears, equipment and rooms needed to house them.

The mechanical plants for large hospitals are also massive in terms of physical sizes (for example, the chilled water system for the air-conditioning, the cooling towers, fire protection pumps and water tanks, etc). The machines and equipment at each of these plants can also be relatively noisy even during normal operation.

All these and the need for proper design to allow for easy maintenance require that a separate and dedicated plant building be allocated. A dedicated electrical substation is usually provided to handle all the loads inside the mechanical plant building.

3. Hospital complex substation
Many equipment inside the hospital complex require very large current and also very low impedance.

As the mechanical plant building is usually a distance away from the main hospital complex, a significant voltage drop is difficult to avoid if the supply center is located there. The low voltage cables needed to overcome this will be unnecessarily large and difficult to maneuver along the cable route. Not to mention the cost of these unnecessarily large low voltage cables and their support system.

Apart from that, some equipment such as the X-ray machines require very low impedance for proper operation.

These factors means that the substation (i.e. Hospital Substation) needed to supply the electrical loads inside the main hospital complex must be located close the local load center, which is inside the main hospital building itself. Feeder cables are looped to the Hospital Substation from the Mechanical Plant Substation at high voltage (usually at 11 kV).

How is the distribution system designed to make it reliable?
As the reliability of the electrical supply in a hospital can make a difference between life and death of some patients, an elaborate design effort is usually given to achieve this objective.

Foremost of all, the supply authority is usually requested to provide two incoming feeders to the hospital site. The purpose is so that if one incoming fails, the supply for the full load can be fed through the other feeder. Needless to say, these are high voltage feeders (usually 11 kV). Under normal operation, both feeders are usually in operation with each feeder supplying half of the load generally.

Some clients go as far as requiring that each of the high voltage feeders must not come from the same supply source in the authority’s local distribution network. This is to further reduce the downtime of incoming supply which some local distribution networks can fulfill and some not able to do so due to the limitations of their existing local distribution network.

Busbar couplers increase the electric supply reliability
In order to provide further flexibility, and therefore reliability, the arrangement of the busbars can be designed with a little bit more sophistication. For example, by providing separate busbars at suitable sections of a distribution center (e. the main switchboards, the downstream sub-switchboards, the standby diesel generator panels, the distribution board busbars, etc), the various sections of the busbars can be coupled with a switching system to direct the electric supply via alternative routes to critical areas and machines.

Reliability increased by the choice of distribution cables
The choice of the types of cables used in the distribution can also be used to increase reliability. The mineral insulated (MICC) cables give an added advantage of being a comparatively low impedance cable for a given size compared with other types of cables. This is a particularly important requirement for a supply to x-ray machines.

Use metal-clad busducts where possible
The metal enclosed busducts can also give significant further improvements because of its flexibility in allowing additional tappings at any point along the supply route without reducing the reliability of the supply feeder. Other types of cables would require an elaborate work and workmanship to provide the additional tappings, which can further reduce the reliability in the long run. It has been an established fact that many of faults on low voltage distribution feeders develop from these tapping locations.

A hospital’s backup power supply sources.
The strategies shown above on how to provide flexibility to the electrical distribution system will not deliver the reliability of the electric supply that it intends to if the causes of power failures come from the source of the supply, which is the authority’s local distribution network.

A hospital cannot take this chance. That is why a system of standby power supply sources are always designed for in the electrical installation of a hospital especially the large ones.

The standby power is used to allow the hospital to keep running its essential services during the mains fail. Normally fifty percent of the general lighting at the main hospital complex would be connected to the essential supply circuit so the light level is reduced to fifty percent. However this lighting level is still sufficient to allow the hospital to operate normally on a temporary basis.

Which socket outlets are connected to the hospital’s essential supply?
How many and which socket outlets (and other power points) are connected to the essential circuit are usually decided on a project to project basis. Normally during the design stages, the end users of the hospital being designed, which are usually the future staff for each department, would be called in for sessions of technical interaction with the hospital designers, architect and engineers.

In these sessions, the need of the users would be captured and incorporated into the design. These types of sessions can take thousands of hours for large hospitals. They are also highly technical and stressing sessions with parties from all sides clashing (I mean that in the construction management terms) with one another in trying to bring all the conflicting objectives to a compromise so that the designers can give a practical solution in the form of a design that can be built within the cost allocated.

Mechanical and electrical services for a hospital construction can easily come to 30 percent of the total construction cost. This does not yet include the cost of medical equipment and the IT system.

Sorry for the digression.

Similar to the power socket outlets, the air conditioning loads connected to the essential circuit are also usually decided on project to project basis with the aid of the information gathered during the interaction sessions described above.

Usually the central air conditioning system for a large hospital is provided with a smaller chiller (some people like to call it “baby chiller”). This chiller unit is chosen from a smaller capacity and it des not run during daytime operation. It will supply the load of the air conditioning system during very low load such as after midnight. Some machines may need to be air-conditioned 24 hors a day so the spaces housing these machines are supplied by the baby chiller during the low load periods. Therefore, this baby chiller may also be required to be connected to the essential supply circuit.

THE backup supply sources
These backup sources are almost always in the form of standby diesel automatic generators. These generators are usually located away from the main hospital building due to the level of noise produced during their operation. That is one of the reasons for a separate building to house the mechanical and electrical plants. So the “standby gensets” (another common words used to call this equipment) are housed inside the Mechanical Plant.

Uninterruptible Power Supply (UPS) System
As mentioned above, some equipment in the hospital cannot tolerate power supply failures at all when they are in use. So they are connected to the UPS system. The UPS system is in turn connected to the essential supply circuit, which is backed up by the standby generators.

One important point need to be noted with regards to the standby electrical generators. These generators are installed to fulfill two requirements. One is the operation requirements of the hospital which need some services to keep operating in the even of mains power failure. The other reason is the requirements of the Fire Department that some the fire system is fully operational in the event a fire case occurs during the absence of the mains supply which include also some lighting for evacuation purposes.

The Fire Department requirements on the standby electric generators
The Fire Department usually requires that the standby generators be up and supplying load within a few seconds (within 15 seconds the last time I checked, if I remember it correctly. This number may vary slightly from country to country.) from the moment of mains failure. However in practice, some generators in some installations are up to this performance. It can take longer.

Even with 15 second blackout, some works in the hospital may be disrupted long enough to cause danger to patients. The prime examples are the procedures in the operation theatres (OT) and the patients who are continuously dependent on some live-saving machines.

The UPS batteries
Therefore the UPS system is installed to fill this 15-second gap. The batteries in the UPS system will be supplying power only for this 15-second period plus a few seconds more added inside the UPS system settings to make sure the electrical supply (the mains supply or the standby generator’s supply) is stable before the UPS storage batteries are switched out of the supply circuit (and back into the charging circuit).

That was the case when the standby generator is up and running within 15 seconds. What if it takes longer (never mind the fire regulations regarding this)? What if the generator actually fails to start? In can happen, and it does happen, as the case when the starting batteries fail to supply sufficient voltage after a few years because of negligence by the maintenance team.

I purposely drag this point longer just to emphasize it, just to stress on the critical function served by the UPS in the backup electric supply system of a hospital.

More points on the distribution system (which I will elaborate further soon)

1. A substation’s low voltage section consists of the Main Switchboard (MSB), the Essential Main Switchboard (EMSB) and a bus coupler. The EMSB board supplies the required essential lighting, power and critical equipment in the Hospital Complex. Part of it also will serve the mechanical load such as air condition, compressed air, vacuum system, and boiler and fire protection system.

2. Local UPS will be provided to support the emergency power requirements of critical loads.

3. The normal, essential and emergency supplies will have separate main switchboard, sub-switchboard and distribution board to supply the respective lighting, power and mechanical services.

4. All switchboards and distribution boards will be provided with suitable types of protection. The sheet metal materials of the board enclosures will be of electro-galvanized type.

5. The design will provide at least 20% spare capacities in all switchboard and distribution boards for future needs, while the main switchboards will be provided with a spare capacity of 30 percent. The main switchboard of the hospital complex will be installed with an automatic power factor board and capacitor bank to keep power factor of the installation at not less than 0.85 lagging in any load condition.

6. A power monitoring system will be installed at the incomers. They will monitor the incomers for all the important electrical parameters including harmonic and also load shedding of non-essential loads. It will also be able to communicate with remote stations by any microprocessor.

7. One bulk electricity meter is provided for the hospital complex including the staff accommodation buildings. Separate meters will be provided for the retail spaces, the cafeteria, canteen, kitchen area, staff quarters and any other spaces for hospital functions that are planned for privatization by the hospital management.

However, as the detailed design develops, a separate bulk meter taking a supply at low voltage from the authority may be provided for the staff quarters, nurses’ hostels and housemen mess.

The reason being the limit set by the authority that any new site with load demand bigger than 5 MVA are required to surrender an empty 100 feet by 100 feet substation space for a future 33/11 kV substation.

At present, the estimated maximum demand for the whole complex including the accommodation area is 5.5 MVA, which has exceeded the % MVA limit.

As the detailed design is developed deeper, in tandem with the gradually more information available on the end-user requirements from the Client-Contractor interaction sessions, the expected maximum demand may be trimmed to below 5 MVA.

If it cannot be trimmed down to below 5 MVA, the application of supply that will be submitted to the electric supply authority will request two bulk meters: one HV bulk meter for 4.8 MVA that will supply both the Hospital Substation and the Mechanical Plant Substation.

The other will be an LV bulk meter for 700 kVA at the Accommodation area Substation which will provide supply to all the accommodation buildings.

Many times the authority approved this arrangement. However, there have also been cases where these types of arrangement were rejected.

B. Cabling and wiring

1. Normal, essential and emergency circuits should be installed in separate trunking and conduits. They need all be properly labeled.

2. All cabling and wiring should be in G.I. conduit. All trunking / tray / ladders shall be of unpainted electro-galvanized sheet metal and marked with proper a color coding system.

C. Electrical socket outlets

Minimum two 13A switched socket outlets should be provided for each bed in the normal wards whereby one of them is connected to essential supply.

Isolators should be provided to suffice the requirement of all equipment.

D. Fans

1. In buildings or rooms where air-conditioning is not provided such as at certain selected wards and at the residential buildings, fans should be installed as required.

2. The sweep fans provided should be complete with speed controls, located at the entry door.

E. Lighting installation

1. A hospital is a very complex, task-intensive institution. The selection of lighting services and control gears should be on the basis of functional aspects, energy efficient, good color rendition and low maintenance.

2. The lighting for various areas should be designed in the compliance with IES, DHSS and current Work Ministry’s code of practice to achieve the average illumination levels as described in attached schedule (will be uploaded later).

3. Labor room, Procedure room, Autopsy room and Treatment room should have the ceiling mounted examination light 0f 30000 lux.

Electrical HV switchgear installation pictures for hospitals
Below you may find some pictures (Well, only one for now.) on electrical installation in hospitals. I may upload more of them in future when I come back to finish on the short sections remaining in this post. So stay tuned.

P/S: You can also see quite a number of electrical installation pictures that I have uploaded at this post: Temporary electrical installations

Picture 1 - Hospital HV switchgear installation in progress

Picture 2 - HV switchgear installation - Rear view

Copyright - Hospital LV electrical installation

1 comment:

Bud Furn said...

Really i am impressed from this post....the person who created this post is a genius and knows how to keep the readers connected..

Turnkey Office Interiors Chennai