System Planning
An industrial plant is only as good as its electric distribution system. For this reason, careful system planning for an industrial power system is very important. This wiki outlines the procedures of system planning and presents a guide which will make the details of Electric Power Distribution Design for Industrial Plant more understandable.
A standard electric distribution system is not adaptable to all industrial plants because no two plants have identical requirements. Methods must be used to analyze the specific requirements of the industrial plant qualitatively and quantitatively, and design the system which will most adequately meet the electrical requirements of the particular plant, with consideration given to both present and future operating conditions.
Basic Design Consideration
Any approach to the problems must include several basic considerations which will affect the overall design. These are
- Safety
- Safety takes two forms; safety to personnel and safety to property. The safety of personnel involves no compromise; only the safest system can be considered.
- Safety to property may involve some compromise where safety to personnel is not jeopardized.
- Reliability
- The continuity of service required is dependent on the type of manufacturing or process operation of the plant. Some plants can easily tolerate momentary outages while others require a very high degree of service continuity. In view of this, the system should designed to isolate faults with a minimum disturbance to the system and should have features to give the maximum dependability consistent with the plant requirements.
- First Cost
- While the first cost is important, it is often minimized if the system is reliable and its operation is satisfactory. It should not be the determining factor in the design of the plant since distribution cost represents only 2 to 10 percent of the plant investment.
- Simplicity of Operation
- Simplicity of operation is a big factor in the safe and reliable operation of a plant. Avoid complicated and dangerous switching operations under emergency conditions.
- Voltage Regulation
- For some plant power systems, voltage spread may be the determining factor of the distribution design. Poor regulation is detrimental to the life and operation of electrical equipment.
- Maintenance
- A well-designed distribution system with properly chosen equipment will reduce emergency maintenance. In planning the system, the accessibility and availability for inspection and repairs should be given careful consideration.
- Plant Expansion
- Plant loads generally increase. Consideration of the plant voltages, ratings of equipment, pace for additional equipment and capacity for increased load must be given serious study.
Planning Guide for Distribution Design
With the above factors in mind, the following procedure is given to guide the Electrical Engineer in the design of an electric distribution system for any industrial plant.
- Obtain a general layout and mark it with the major loads at various locations and determine the approximate total plant load in kilowatts, and kilovolt-amperes.
- Estimate the lighting, air-conditioning, and other loads from known data and the system load preliminary information.
- Determine the total connected load and calculate the maximum demand by using demand and diversity factors.
- Investigate unusual loads, such as the starting of large motors, operation of arc furnaces or welders, and operating conditions such as boiler auxiliary motors, loads that must be kept in operation under all conditions, and loads that have a special duty cycle.
- Investigate the various types of distribution systems and select the system or systems best suited to the requirement of the plant. Make a preliminary single line diagram of the power system.
- If power is to be purchased from the utility, obtain such information concerning the supply system or systems as
- voltage available and voltage spread,
- type of systems available,
- method of system neutral grounding, and
- other data such as
- relaying,
- metering and
- the physical requirements of the equipment.
- interrupting rating and momentary ratings of power circuit breakers should be obtained as well as the present and future short-circuit capabilities of the utility system at the point of service to the plant.
Investigate the utility’s power contract to determine if off-peak power at lower rates is available, and any other requirements, such as power factor and demand clauses, that can influence power cost.
- If considering a generating station for an industrial plant, such items should be determined as: generat- ing kva required including standby loads, generating voltage, and such features as relaying, metering, voltage regulating equipment, synchronizing equip- ment and grounding equipment. If parallel operation is contemplated, be sure to review this with the utility and obtain its requirements.
- A cost analysis ‘may be required of the different voltage levels and various arrangements of equip- ment to justify and properly determine the voltage and equipment selected. The study should be made on the basis of installed cost including all the com- ponents in that section of the system.
- Check the calculations of short-circuit requirements to be sure that all breakers are of the correct rating. Review the selectivity of various protective devices to assure selectivity during load or fault disturbances.
- Calculate the voltage spread and voltage drop at various critical points.
- Determine the requirements of the various components of the electric distribution system with special attention given to special operating and equipment conditions.
- Review all applicable national and local Codes for requirements and restrictions.
- Check that the maximum safety features are incorporated in all parts of the system.
- Write specifications on the equipment and include a single line diagram as a part of the specifications.
- Obtain typical dimensions of equipment and make drawings of the entire system.
- Determine if the existing equipment is adequate to meet additional load requirements. Check such ratings as voltage, interrupting capacity, and current-carrying capacity.
- Determine the best method of connecting the new part of the power system with the existing system so as to have a minimum outage at minimum cost.
Naturally the sbove procedure will not automatically design the electric power system in itself; it must be used with good, sound, basic engineering judgment.
General Layout
A general layout of the plant should be available the Engineer can begin his study. This layout usually the location and the size of the proposed building in the initial particular project. The extent of the available layout gives the Engineer an idea of the possible expansion of the plant in the future, and must be considered by the Engineer in planning the electric distribution system.
