Designing an effective electrical system involves creating plans and specifications that ensure the system operates efficiently and cost-effectively for its owner. This article will cover the 10 key considerations that should be integrated into an electrical system design.
These considerations include simplicity, flexibility, compatibility, code compliance and safety, protection / coordination / selectivity, reliability, maintenance, and energy conservation and efficiency. These principles apply to all types of facilities, industries, and both new construction and renovation or retrofit projects.
1. Simplicity
In general, the more complex an electrical system becomes, the higher the likelihood of component or subsystem failures, or even total system failures. Complex systems are harder to operate and even more challenging to restore during emergencies, especially if operators lack proper training and regular practice.
Such systems also demand extensive training for personnel. Additionally, they often require a vast network of backup systems to ensure reliability, which can lead to significant costs for purchase, installation, and maintenance. However, these costs are usually justified due to the high expense associated with downtime.
On the other hand, simpler electrical systems are easier and less costly to operate and maintain, both during normal operations and in emergencies. They are less prone to shutdowns, and operators are more likely to manage emergencies effectively without errors.
2. Flexibility
As facility construction costs continue to rise, manufacturing and process firms must ensure their facilities can expand for new operations with minimal impact on cost and production.
In the late 1980s, industries recognized that expansion in existing facilities was inevitable. New technologies, techniques, and processes have transformed the industrial environment, making it essential for manufacturers to invest in these advancements to remain competitive. Innovations like robotics have made production more energy and control-intensive.
Manufacturing companies typically cannot afford to close plants or offices for new installations to expand the electrical system. Therefore, the electrical system must be flexible and easily expandable to service a more energy and control-intensive environment. For instance, spare capacity should be included in power distribution and instrumentation during the design phase.
Flexibility also involves adapting to changes in plant space usage. For example, if a company decides to scale down production of one product and use the available space to manufacture a new product, the electrical system must be flexible enough to accommodate the new load requirements with minimal adjustments.
3. Compatibility
When designing an electrical system, the adage "a chain is only as strong as its weakest link” holds true. Electrical system designers should consider the system as an integrated whole rather than just a collection of individual components.
In practice, this means ensuring that all components are compatible and work together to optimize performance, efficiency, maintenance, reliability, service life, and other operational aspects. Additionally, designers must ensure that their plans and specifications align with those of professionals in other disciplines, such as mechanical and civil/structural engineers, to achieve a cohesive and well-functioning system.
4. Compliance and Safety
Electrical system designs must comply with all energy, personnel safety and other applicable codes. The most important code for electrical system design is the Electrical Code. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. Electrical Codes will be enforced by governmental bodies and insurance inspectors, who will carry the additional responsibility of its interpretation.
5. Protection, Coordination and Selectivity
The power distribution system should be designed to safeguard electrical equipment by specifying devices like circuit breakers and fuses. This allows for the selective isolation of electrical issues and failures, enabling timely and safe corrective actions.
6. Reliability
When designing an electrical system, reliability can be considered in two main aspects: the reliability of the power supplied by the local electric utility and the reliability of the system’s components.
A failure in the primary power source can halt all production, leading to costly downtime, delays in fulfilling orders, and potential damage to machinery, capital, and goods in production. While it may be too expensive to provide an emergency backup for the entire plant, protecting critical loads is essential. The design team should identify these critical loads during the design process and specify an emergency backup system to power, control, and condition these loads until normal power is restored. This backup system might include generators or uninterruptible power systems (UPS).
Additionally, if critical equipment fails and shuts down one segment of the production process, it can cause the entire process to stop, as most manufacturing relies on a production-line system. Therefore, designers should either specify duplicate backup equipment to ensure continuous power distribution or choose the highest-quality equipment from reputable manufacturers. A mixed approach may be best, with critical loads protected by a duplicate system and the entire system equipped with high grade products.
8. Maintenance
Electrical system maintenance is performed largely by Electrical personnel who are involved with the system on a continuous basis. It is likewise important to involve civil and mechanical engineering disciplines in the design process. Maintenance and operating personnel should be consulted prior to beginning the actual design work. Their input, based on their experience, is invaluable.
To adapt the system toward effective and safe maintenance, the design team should consult with plant personnel with regards to:
- Proper spacing between components to allow maintenance personnel ready access for routine maintenance
- Equipment that comes with diagnostic features or accessories which allows operators to easily and quickly identify problems
- Equipment that has spare parts which can be obtained easily and through more than one supplier in a short period of time
- Equipment that can be maintained in both an energized and non-energized environment:
- Equipment manufactured by companies that have technical service and support staff who are always available;
- Equipment that can operate in a wide range of environments:
- Modular equipment that is factory-assembled (such equipment generally requires less labor to install);
- Equipment that can be used in several voltage or current ratings.
Taking these and other applicable steps to ensure that the electrical system can be safely and easily maintained will result in greater personnel safety, minimized downtime, lower life-cycle costs and ultimately greater owner satisfaction.
9. Cost
The design team is accountable to the owner of the electrical system. A significant consideration is how much investment will be spent to purchase the system, install, operate and maintain it.
Traditionally, designers have sought to provide standard system performance at the lowest initial cost, with minimum regard to equipment operating and maintenance costs. Today, energy and labor prices as well as the need for more reliable, high-performance equipment are steadily increasing. This has placed new emphasis on electrical equipment's life-cycle cost. This is the total cost of ownership of equipment over its service life, including the costs of purchase, installation, operation and maintenance.
Technological advancement has generated a diversity of equipment and products that provide a wide range of characteristics related to efficiency, performance and maintenance. As would be expected, those products which offer higher performance and lower operating and maintenance costs carry a premium on the initial cost. However, such products typically pose a lower life-cycle cost and can even present positive "cash flow" from the value of cost avoidance.
10. Energy Efficiency
Energy conservation and efficiency increases industrial competitiveness and profitability. Energy conservation in electrical system design stems from specifying a more simple, flexible system and properly sizing the system for current and anticipated loads. Energy conservation provides savings on the initial costs associated with purchasing and installing the equipment, in addition to the costs of operation and maintenance.
Energy efficiency in electrical system design stems from specifying equipment that experiences fewer losses and offers a higher work output-to-electrical input ratio. It also stems from the optimization of the process via implementation of control strategies. Energy-efficient equipment typically costs more than conventional equipment, but often the savings in reduced operating costs pay for the premium on the initial outlay to produce a satisfying payback. After payback, the owner realizes "positive cash flow" via cost avoidance over the alternative relatively inefficient system.
All things considered, energy-efficient equipment usually presents a lower life-cycle cost than conventional equipment. As previously stated, based purely on initial purchase price, conventional equipment is a more sensible choice and therefore is often chosen. More conscientious judgment leads to recommendation of energy-efficient equipment, as it presents a lower total cost of ownership to the owner. Additionally, energy-efficient equipment typically offers greater reliability, performance and service life.
This is not to say that energy-efficient equipment is proper for every application. The designer should consistently choose the best product for the application that will best suit the owner's priorities and requirements.
Note that some energy-efficient equipment can impact electrical system design. For example, high-efficiency electric motors have lower reactcinces and higher I/R ratings which contribute to a larger starting circuit current. This will affect the power system design.
Reference:
The Electrical Systems Design & Specification Handbook for Industrial Facilities
Steven J. Marrano, D.E., C.E.M & Craig Dilouie
Fairmont Press (1998)