Protective Device Coordination Studies

What is a protective device coordination study?

Electrical systems commonly use fuses and circuit breakers to protect electrical equipment such as conductors, transformers, motors, and other components. If a failure occurs within this equipment, usually a short circuit results. It would be desirable that this short circuit would affect only that portion of the system where the failure occurs. In a properly coordinated system the protective devices are selected and adjusted to minimize the impact of equipment failures within a system. A coordination study analyzes the characteristic curves of the fuses and breakers and compares them against one another on log-log plots similar to that shown in the following figure. Any areas of miscoordination will be apparent by overlapping of curves from the various devices.

Most electrical power distribution systems are not planned with protective device coordination in mind. A distribution system can be designed for minimum losses and minimum upfront investment and yet fail miserably in the proper coordination of the protective devices. As a result, equipment failures within the system can easily result in the shutdown of the entire plant or office building. There have been many instances where the failure of a single motor or branch circuit within a building has resulted in the shutdown of most of the facility.

As a side benefit of a coordination study the interrupting ratings of all protective equipment, conductors, and switches are checked for adequacy. Inadequate equipment ratings can result in either extensive damage to the equipment during faults and system operation and may introduce hazards to plant operating personnel.

A protective device study analyzes the impacts of short circuits and equipment failures within a facility and determines the effects on the facility operation. It is study that must be combined with arc flash hazard analyses required by present electrical safety codes and enforcement agencies. Informed decisions can then be made as to the changes necessary for the system.

Do I need such a study?

If you can answer yes to any of these questions or if any of these questions describe your situation, you should consider such a study.

• I am in need of an arc flash hazard analysis for my electrical power system.
• Recent electrical equipment failures within my facility caused extensive and costly downtime to my business operation.
• I am currently beginning or in the preliminary design stages for a building or facility which will house my employees and the facility will exceed $1 million.
• I have or am I planning to install emergency generators, uninterruptible power supplies (UPS), or static transfer switches in my electrical system.
• If an electrical failure occurred in my facility, would the downtime cost exceed $3,000/hour?
• I have critical equipment or inventory that could be damaged if a long term power outage occurred within the plant.
• I need an experienced consultant to oversee or guide the work of my plant engineers who are peforming similary studies.

It is a reality that, with time, failures will occur within an electrical distribution system. The failures themselves can result from a number of causes; operator error, aging of equipment, weather induced failures. Regardless of the cause, the effect is the same. Various parts of a system will be left without power. In some instances where electrical systems have been designed by untrained individuals, injury can be the result of equipment failure. The injury results when electrical equipment virtually explodes because the equipment was designed with inadequate capacity to handle the magnitude of short circuit current within the system or when equipment malfunctions. Such an event may be classified as a arc flash event.

Where insulation failures have resulted in short circuits (faults), it would be desirable that the electrical protective devices operate to minimize both the damaged caused by the fault and the impact of the fault on the rest of the system. The analysis procedure that looks at the fault possibilities and their impact on the electrical system is known within the industry as a protective device coordination study. This procedure looks at probable and possible values of fault currents within the system and analyzes the impact of those faults upon the operation of circuit protective devices such as fuses and circuit breakers. As a side benefit the analysis usually compares maximum possible fault current levels against the withstand ratings of equipment within the system. Equipment that have inadequate withstand ratings can be a hazard to personnel. Such equipment will thus be identified and corrective action can be taken.

Most of the time, protective device coordination studies are implemented after a design is complete and the system has been constructed. Unfortunately, this is the worst time to perform such a study. Why, because correction is costly. In fact to quote I.E.E.E. Std 242:

"System protection is one of the most essential features of an electrical system and must be considered concurrently with all other essential features. There is too often a tendency to consider system protection after all other design features have been determined and the basic system design established. Such an approach can result in an unsatisfactory system that cannot be adequately protected, except by a disproportionately high expenditure. System protection is so basic to the safety of personnel and the reliability of electrical supply, and can have such a profound influence on the economics of system design, that examining the system protection needs only after all other design features have been determined is a completely unrealistic approach."

Quadrelec Engineering Corporation has developed considerable expertise in the area of such studies and can assist you during the design development phases of your system.  Our involvement can help you develop a power system that meets your expectations for protective device coordination. State of the art computational software is utilized in support of these studies that assist in the rapid development of the system one-line diagram.

What does a study cost?

The cost of a protective device study vary greatly depending on the complexity of the system, the amount of field data that must be collected, and the goals of the client. Even the smallest study however will normally exceed $3,000. Studies for larger facilities with hundreds of panelboards, such as major hospitals or industrial plants, can run $50,000 to $80,000. We can provide studies that can be customized to your needs and economic goals. Please contact us for a price estimate.

Why should I use Quadrelec Engineering for this study?

We feel that the reasons are numerous. With over 49 years of practicing experience and 30 years of experience training engineers in the proper design, analysis, and construction of electrical power systems Quadrelec Engineering has broad based knowledge in all areas of electrical systems. As members of the Institute of Electrical and Electronics Engineers (I.E.E.E.) since 1976, Quadrelec Engineering maintains a knowledge base that ensures the most technically sound analysis possible. This provides you with a capable firm that understands the impact of all recommendations we make as a result of such a study.

Most firms providing such services provide as a final product a report that are indadequate, inaccurate, and that leaves all of the data interpretation to the client. Unfortunately most clients are not well versed in the proper interpretation of such complex data and how the findings affect their operation. We strive to provide more in depth analysis of the data providing you the client with design options and problem solutions in plain English so that you can make the proper decisions.

Since 1989, Quadrelec Engineering instructors have been providing classroom instruction to electrical engineers within the U.S. Army Corps of Engineers, U.S. Air Force, FAA, and the private sector in the correct procedures used for these studies. Student responses have been exceptionally favorable. Most students have stated that they have learned more at these courses than other comparable courses within the industry.

The software we use to analyze your power system, EasyPower® , is recognized as the leader within the industry. As a result of the study, you receive complete one-line diagrams of your system that provide fault currents and load currents presented directly on a system one-line diagram. This therefore eliminates wading through piles of computer printout to find fault current levels when you later desire to make system expansions or changes. EasyPower was the first within the industry to provide this capability. One-line diagrams can be provided in electronic CAD format files in either AutoCAD or Microstation formats to conform to your own facility drafting standards.