in the previous Topic; Electrical Distribution systems for nursing homes and residential custodial care facilities , we talk about the electrical design methods for such buildings.
You can review the following previous topics for more information and good following:
- the Electrical Design Requirements for Health Care Facilities – Part One
- the Electrical Design Requirements for Health Care Facilities – Part Two
- the Electrical Distribution Systems for Hospitals - Part One
- the Electrical Distribution Systems for Hospitals - Part Two
Today, i will explain the Common Power System Architectures for Health Care Facilities as follows.
Common Power System Architectures for Health Care Facilities:
the health care facilities have (4) common Power System Architectures as follows:
- Radial – Generator.
- Dual Source and Radial Secondary – Generators.
- Secondary Selective – Generators.
- Dual Source and Secondary Selective – Generators.
1- Radial – Generator
This is the simplest system to operate and has the lowest first cost. It is also very easy for maintenance people to understand. System can have outages for faults and maintenance. If utility source A is lost, the entire system is lost for 10 seconds until generators can be brought on-line. This system is normally used on smaller healthcare facilities.
Radial – Generator Power System Architecture |
Where there will be significant emergency power requirements, several transfer switches may be used to increase reliability. The transfer switches used for the equipment system can be adjusted to transfer sequentially, thus minimizing generator inrush requirements.
Advantages:
- Low first cost.
- Simple operation and understanding by personnel.
- Easily expanded.
- Radial ground fault.
Disadvantages:
- Low Reliability.
- Maintenance causes outages.
2- Dual Source and Radial Secondary – Generators
A double-ended substation should be considered where transformation will exceed 750 kVA.
System has the ability to switch between two utility sources via auto throw-over scheme. Electrically operated medium voltage breakers are required for this transfer system. If both utility sources are lost, generators back up essential electrical loads via transfer switches. System design is reliable and used for medium to large size hospitals.
Dual Source and Radial Secondary – Generators Power System Architecture |
Further, reliability can be obtained by placing the transfer switches as close to the ultimate load as possible.
For example, fig (1) shows two schemes for distributing power through vertical risers.
Fig (1) |
Advantages:
- Protection against loss of primary source.
- Possible paralleling of sources.
- Choice between Sources A or B.
- Reliable.
Disadvantages:
- Additional cost of equipment.
3- Secondary Selective – Generators
The secondary selective system allows the transfer of load from one transformer to the other with the use of electrically operated main and tie-breakers via auto throw-over scheme. This is important if one transformer fails or needs maintenance. If both utility sources are lost, generators backup essential electrical loads via transfer switches. Transformer sizing is critical if all secondary loads are to be serviced from one transformer. This is usually accomplished by either loading the transformers to 50%, or by using the transformer forced air (fan) rating with temperature controllers.
|
This system is common in large cities where the utility companies use transformers, located in vaults, to service hospitals.
Advantages:
- Normal operation as radial system with stand-by generators.
- Isolation of cable or transformer for faults or normal maintenance.
- Feed other side with use of transfer scheme and electrically operated breakers.
- Main and tie breakers can be interchanged for maintenance to keep outages to a minimum.
- Additional cost.
- Transformer load monitoring.
- May require complex ground fault system if neutrals are tied together and sources have multiple grounding points.
4- Dual Source and Secondary Selective – Generators
This system combines the advantages of both primary sources and secondary selective systems used with backup generators. It not only provides the more reliable system, but also one of the most costly system.
Dual Source and Secondary Selective – Generators Power System Architecture |
3 pole transfer switches are used for 4 wire loads. This causes circulating current on the neutral busses. This power system is popular for large hospital complexes.
Advantages:
- High Reliability.
- Combined advantages of both sources and generators.
- Higher initial cost.
- May require complex ground fault system if neutrals are tied together and sources have multiple grounding points.
in the next Topic, I will explain the Major Types of Electrical Loads. so, please keep following.
Really useful for me
ReplyDelete