Introduction and Basic Fundamentals

With the increasing sophistication of modern power systems, it is easy to overlook the fact that the basic function of a power distribution system has been the same for over 100 years: the safe, reliable distribution of power from a source to the connected loads. Although this basic function has not changed, the complexity of the loads themselves, along with today’s reliability and efficiency requirements, makes its realization more complex.

This guide discusses the main considerations that must be taken into account to obtain an optimal system design. Because the characteristics of each load, process, or other issue, are unique, each design is unique to match the requirements imposed.

This guide is intended to present the fundamentals of power system design for commercial and industrial power systems. It is not designed as a substitute for educational background and experience in this area, nor is it designed to replace the multitude of detailed literature available about this subject. It does, however, bring into one volume much material or standards which has previously been available only by referencing several different sources with different formats and terminologies.

This guide is also intended to present the state of the art about power system design for commercial and industrial facilities, in a consistent format along with traditionally available material.

For the new college graduate from a four-year electrical engineering curriculum working in the field of commercial and industrial power systems, this guide can serve as a starting point for learning the different aspects of the profession. For the licensed design professional, this guide presents several guidelines in a handy and convenient reference.

This guide is not intended to substitute for the services of a licensed design professional, but can aid when working with such professionals on commercial and industrial power system design.

In both industrial and commercial environments, electric power is used for a wide number of applications. The following is a brief list of the most common uses for electric power, taken in part from Standard Handbook for Electrical Engineers New York: McGraw-Hill, 2001, pp. 21-1 – 21-99.*, which provides an expanded treatment of this subject:

Illumination: Whether for providing light for an office environment or a manufacturing shop floor, illumination is one of the most important applications of electric power.

Environmental systems: Electric heating, ventilation, and air conditioning are a large application for electric power, and an area in which electric power receives direct competition from other energy sources such as natural gas.

Industrial processes: Industrial processes account for a large percentage of the global use of electric power. Typical process applications listed below, are not all-inclusive, but do cover the majority of process applications:

• Pumping

• Motors

• Chemical processes

• Semiconductor preparation processes

• Furnaces

• Smelting

• Rolling mills

• Pulp-and-paper preparation processes

• Welding

• Refrigeration

• Drying

• Well drilling

• Materials handling

• Water treatment processes

Computers and Data Centers: With the advent of large computer networks, there is a need to reliably power these.

Health Care: Reliable power has always been a requirement of the health care industry but added to this is the need for power quality due to the nature of the equipment used.

Safety Systems: Systems such as fire alarm and smoke detection systems, sprinkler systems and fire pumps are vital to any commercial or industrial facility.

Communication Systems: Systems such as telephone and intrusion detection and monitoring are critically important.

The following basic considerations are fundamental to any power system design:

• Basic safety: The power system must be able to perform all of its basic functions, and withstand basic abnormal conditions, without damage to the system or to personnel.

• Basic functionality: The power system must be able to distribute power from the source to the connected loads in a reliable manner under normal conditions.

• Reasonable cost: The power system cost to obtain basic safety and functionality should be reasonable.

• Code compliance: All applicable codes must be complied with.

Above and beyond the basics are a multitude of considerations, some of which apply to each system design:

• Enhanced safety: The ability to withstand extremely abnormal conditions with a minimum of risk to personnel.

• Enhanced reliability: The ability to maintain service continuity during abnormal system conditions.

• Enhanced maintainability: The system can be maintained with minimum interruption to service and with minimum personnel protective equipment.

• Enhanced flexibility: The ability to add future loads to the system, and with loads of a different nature than currently exist on the system.

• Enhanced space economy: The power system footprint is optimized for the available space.

• Enhanced simplicity: The power system is easy to understand and operate for a qualified person.

• Reduced cost: The power system costs; both first cost and operating cost, are low.

• Enhanced power quality: The power system currents and voltages are sinusoidal, without large harmonics present. System voltage magnitudes do not change appreciably.

• Enhanced transparency: The power system data at all levels is simply acquired and interpreted, and the power system is simply interfaced with other building systems. Enhanced control of the system is also possible.

While it is the goal of every power system design to meet the above basic considerations, no system design can yield all the enhanced characteristics listed. The relationship between the considerations listed is shown in Power System Design Consideration Heuristics.

Some of the enhanced characteristics mentioned are mutually exclusive, and to obtain a combination of several enhanced characteristics requires a significant increase in cost. The design engineer, therefore, must consider the balance between the performance requirements of the system and the cost, while not compromising the basic safety elements, functionality, and code compliance.