The demand factor varies considerably for different types of loads. services, and structures. The National Electrical Code
® . Article 220. provides the requirements for determining demand factors. Demand factors for some military structures are given in table 3-2.
Example: A machine shop has a total connected load of 50.3 kilowatts. The demand factor for this type of structure is taken at 0.70. The maximum demand is 50.3 × 0.70 = 35.21 kilowatts.
Generators are not permitted to be closer than 25 feet to a load; however, in setting up the generator, try to place the equipment near points of large demand to reduce the size of wire required: to hold the line losses to a minimum. and to afford adequate voltage control at the remote ends of the lines.
Moving the generator may be accomplished by lifting or pulling. The generator set comes equipped with a lifting sling usually stored in the skid on the side of the unit opposite the operator's control panel.
You should study a plot or chart of the area on which the individual buildingsand facilities have been plotted. The site you select should be large enough to meet present and anticipated needs. Then select a location where there will be sufficient space on all sides for servicing and operation of the unit. It should be level. dry, and well drained. If this type of site is not available, place the generator set on planks, logs, or other material for a suitable base foundation.
Table 3-2. - Demand Factor
|Aircraft maintenance facilities||.7|
|Laundry, ice plants, and bakeries||1.0|
Although advanced base portable generators are designed to be operated outdoors, prolonged exposure to wind. rain. and other adverse conditions will definitely shorten their lives. If the generators are to remain on the site for any extended period of time, they should be mounted on solid-concrete foundations and installed under some type of shelter.
Presently, there are no predrawn plans for shelters for a small advanced base generating station. The shelter will be an on-the-spot affair, the construction of which is determined by the equipment and material on hand plus your ingenuity and common sense.
Before a Builder can get started on the shelter, you will have to inform him of such things as the number of generators to be, sheltered; the dimensions of the generators; the method of running the generator load cables from the generator to the distribution system outside the building; and the arrangement of the exhaust system, radiator discharge, and cooling air. Installation specifications are available in the manufacturer's instruction manual that accompanies each unit. Be sure to use them. Appropriate consultation with the Builder regarding these speci- fications may help minimize various installation and piping problems and costs.
The following hints and suggestions also will be helpful:
1. Ventilation is an important factor to consider when you are installing the units inside a building. Every internal combustion engine is a HEAT engine. Although heat does the work, excess amounts of heat must be removed if the engine is to function properly. Heat can be removed by setting the engine radiator grille near an opening in the wall and providing another opening directly opposite the unit. In this manner, cool air can be drawn in and the hot air directed outdoors. These openings can be shielded with adjustable louvers to prevent the entrance of rain, sand, or snow. In addition, when the engine is operating in extremely cold weather. the temperature in the room can be controlled by simply closing a portion of the discharge opening. Additional doors or windows should be provided in the shelter if the plants are installed in localities where the summer temperatures exceed 80°F at any time.
2. Working space is another consideration. Be sure to provide sufficient space around each unit for repairs or disassembly and for easy access to the generator control panels.Continue Reading