Electrical Risk Assessments: Evaluating Your Power Distribution System
EP Editorial Staff | March 23, 2012
You can’t run safely and reliably without them. Here are some tips for ensuring these assessments pay off for your operations.
At some point, most engineers with responsibility for the maintenance of their facilities’ electrical distribution systems will find themselves struggling to prioritize their maintenance and upgrade budgets. The challenge is to spend the least amount of money while maximizing system reliability, minimizing equipment downtime and ensuring the highest degree of personnel safety.
These ongoing tasks are difficult enough for a plant engineer with an electrical power distribution system under his/her charge that’s been programmed for routine maintenance. The challenges, though, can be greatly compounded for anyone who has inherited a system that’s been neglected, was originally intended for a different purpose or has poor documentation. Further, the tendency in today’s market for corporations to acquire or take over the functional operations of other companies and their facilities can multiply the need for management to determine the exact conditions, existing configurations and interconnections and operational state of existing electrical power distribution systems.
Unfortunately, an assessment of specific electrical equipment—or an entire electrical system—can also be triggered by an unexpected shutdown, unexplained equipment damage, electrical shock injury, an arc flash burn or an inoperative emergency power system (i.e., one that does not perform its desired or intended function.)
This article addresses the vital concerns of any facility that relies on continuous electrical power: the “health” of the electrical power distribution system. Like any other engineered system, electrical power distribution systems cannot be designed and constructed to operate 100% of the time indefinitely. Whether for a relatively new power system or for an older network that has been in service for decades, an assessment of its condition can be a valuable starting point for improving the reliability of your electrical distribution system.
An Electrical Risk Assessment can offer a solid solution to the “how to allocate the limited budget for maximum effect” dilemma. It can also provide expert guidance on any initiative to return a degraded electrical system to the required level of reliability and safety. Even for a well-maintained system, the well-performed assessment can provide an independent, objective evaluation of a facility’s vulnerability to a particular event or dysfunction. Either way—should it lead to a major system overhaul or mere tweaking of a well-functioning program—an Electrical Risk Assessment can fill the bill.
A systematic process is used to evaluate the condition of the electrical system as well as the vulnerability of a facility or process to the adverse effects of an unexpected electrical event. The risk assessment combines the qualitative assessment of the electrical system from four perspectives:
- Personnel safety
- Critical-function impact
- Likelihood of occurrence
- Facility vulnerability
The assessment should be performed by a registered Professional Engineer, who has in-depth experience in the design, operation, maintenance, safety and reliability of AC and DC power systems and equipment. This individual also needs to be deeply familiar with applicable codes and standards and with the optimal design practices of each type of facility—i.e., healthcare facility, water-treatment operations, manufacturing plant, data center, office building, research center, critical operation center, correctional facility, airport, military installation, etc.
Safety and security of the facility must be maintained during the onsite activities necessary for completion of the Electrical Risk Assessment. The plant engineer needs to verify that the engineering team performing the assessment has a demonstrated record of safe work practices and intends to comply with the safe work practices outlined in NFPA 70E and other applicable standards.
One measure of the company’s safety effectiveness is the Medical Incident Rate (MIR). The average MIR for service organizations in the United States is about 6.0 incidents per 200,000 hours of work performed. However, industry-leading service organizations can have an MIR below 1.0.
The plant engineer should also recognize and assume a share of the safety responsibility and establish the expectation that safety will not be compromised during any portion of the work. In addition, he/she should ensure that the assessment team is made aware of all safety issues specific to the type of facility, whether electrical, biological, environmental or other potential hazards. Finally, the plant engineer should assign a person familiar with the facility to escort the assessment engineer, provide access to all areas required and locate and identify all specific electrical equipment.
Fig. 1. Electrical diagrams, especially single-line diagrams like this, are a key aspect in helping define the scope of an Electrical Risk Assessment (as well as for successful computer modeling).
Scope of work
The successful Electrical Risk Assessment provides a documented scope of work to clarify which equipment and systems will be evaluated, and what that evaluation will include. Some key aspects in defining the scope include determining the availability and accuracy of the following documentation:
- Electrical drawings, especially single-line diagrams (Fig. 1)
- Maintenance records for key equipment
- Power system studies (short-circuit analysis, protective-coordination analysis, arc flash hazard analysis)
- Power monitoring data, including trend charts of voltage, current, power and power factor, at key points in the electrical system
- Facility safety practices and policies
- Facility emergency response procedures related to the electrical system, such as the electric utility emergency contact information, electrical service company information and electrical system training records
In addition, the work scope needs to clarify whether the onsite assessment will include internal inspection of electrical equipment and where it can be shut down or otherwise safely accessed. While internal access adds tremendously to the value and completeness of the assessment, the additional cost and potential risk may outweigh those benefits or require that they be performed during a scheduled shutdown when other maintenance tasks are completed.
The reason for studies
Computer-based engineering studies provide a wealth of information with regard to the health and vulnerability of a power distribution system. For this reason, the Electrical Risk Assessment will recommend that power system studies be performed if none exist, or updated if the current studies are over five years old. This latter requirement is straight from NFPA 70E—which requires that arc flash hazard analyses be updated every five years or whenever major modifications to the distribution system or loads occur.
The risk assessment may recommend at least three studies, as noted previously: short circuit, time/current coordination and arc flash. All three are necessary to satisfy Occupational Safety and Health Administration (OSHA) requirements to establish a safe electrical work environment for employees. Each study focuses on a different aspect of power distribution system reliability and safety, but all three can be performed from the same computer model of the distribution system.
This computer model relies on the accurate depiction of components of the power distribution system, and the configuration(s) in which the components are connected. “Accurate depiction” requires an accurate, up-to-date and detailed single-line diagram (Fig. 2).
The components described in studies include major power-distribution equipment, such as switchgear, switchboards, motorcontrol centers and panelboards, as well as overcurrent protective devices like fuses and power circuit breakers. It is also necessary to know ratings of all the equipment and the available settings of any adjustable overcurrent protective devices. Since an electrical power distribution system can often be configured in multiple ways by opening and closing power switches and circuit breakers, multiple computer scenarios may be required.
As indicated at the beginning of this article, the purpose of an Electrical Risk Assessment is to assist the facility engineer in optimum allocation of electrical-system dollars (Fig. 3). As such, the outcome is less about absolute reliability than about relative risk (meaning that results are not intended to predict when a particular deficiency will result in downtime or hazard, but rather which deficiencies should receive higher priority than others in the allocation and distribution of limited resources). For this reason, it is essential that the assessment be conducted by 1) an experienced power engineer 2) who is equipped with a sound methodology for ranking deficiencies.
It is also important for the facility engineer to be engaged in the ranking process—especially in communicating priorities for management to consider. For example, the facility engineer often helps to determine which loads or parts of the operational processes or electrical system are more critical than others. In addition, the facility engineer should provide guidance in the part of the Electrical Risk Assessment that estimates corrective action costs. (Some facilities prefer to fix lower-priority issues with internal resources, at their internal labor cost, as opposed to hiring contractors for this purpose.)
Fig. 3. An Electrical Risk Assessment should generate an effective ranking of deficiencies, which should aid decisions regarding the optimal allocation of electrical-system dollars. (Click to enlarge)
For most plants, the key considerations for ranking deficiencies fall into one of four categories, as mentioned earlier. Every deficiency identified during the assessment receives a score in each of four categories, typically between 1 (lowest priority, or “green”) and 5 (highest priority, or “red”). The overall risk assessment score is the product of the four ratings. Consequently, the maximum “score” can be 5x5x5x5, or a product of 625, and the minimum score can be 1x1x1x1, or a product of 1.
However, the overall score may not represent the highest priority for some facilities! Rather than sort the deficiency list by the highest score, some operations may focus on other areas such as Personnel Safety. By this logic, any Personnel Safety score of “4” or higher will receive corrective-action funds, regardless of the overall score.Each category is briefly described below.
All facilities should place personnel safety above any other consideration. As such, the Electrical Risk Assessment ranks deficiencies with regard to their hazard to people. A glowing-hot or a readily exposed electrical conductor, for example, is a “5.” In fact, a deficiency of this type will be reported at once, with the expectation that the facility engineer is prepared to take immediate corrective action. This may include barricading the affected area and shutting down the circuit while repair parts and materials are obtained.
“Critical function” is simply defined as the most important mission of the facility. In healthcare facilities, the critical function is anything that has a direct patient impact. For a data center, the critical function is server uptime. For a production facility, it’s the most critical manufacturing process, and so on. For this category, the risk assessment engineer considers the likelihood that an event from a particular deficiency would adversely impact the most important function(s) of the facility.
Likelihood of occurrence…
Clearly, the glowing-hot conductor illustration is considered very likely to result in an occurrence. Other deficiencies, however, often require an experienced electrical engineer to provide an appropriate or necessary ranking.
A variety of factors are taken into account in determining the likelihood of an electrical occurrence. These involve multiple considerations, including 1) how well the power equipment was originally installed; 2) the level of regular preventive maintenance after the initial installation; and 3) the actual age of the equipment relative to the expected-use life.
During the site evaluation, special emphasis is given to the integrity of the existing bonding and grounding systems. This aspect of the power distribution system is often overlooked yet is vital to personnel safety and proper equipment operation. Environmental issues are also considered, especially temperature, moisture and dust and other airborne contaminants.
Probability also factors the degree to which the power equipment is subjected to operational stress, like overloading, excessive temperatures, under- and over-voltage conditions, surges and transients, highly fluctuating loads, excessive switching and harmonic distortion.
While it is important to maintain a low probability of an occurrence, what is the facility’s susceptibility to adverse effects should one occur? This aspect of the Electrical Risk Assessment is identified as vulnerability. It basically evaluates the preparedness of the facility to deal with unscheduled events.
As with probability, vulnerability weighs many factors: Does the facility have accurate electrical drawings, especially a single-line diagram, to facilitate troubleshooting? Is the power equipment properly labeled, with designations that facilitate load and circuit identification? Is there a power-monitoring system, and is it well-configured with alarms and diagnostic tools? Is the staff well trained and equipped (i.e., spare parts) to deal with power-system disturbances?
The success of a facility engineer depends on the cost-effective reliability of the electrical distribution system. Some plant engineers are fortunate enough to have presided over key decisions associated with the electrical system—from concept and design, to installation and commissioning, to operation and maintenance. With few exceptions, however, most facility engineers have assumed responsibility for a distribution system with an unknown and poorly documented history or one that is dated.
For these engineers, the Electrical Risk Assessment provides a valuable tool to help reset the reliability bar and—more importantly—offers essential intelligence on the best use of limited electrical-system funds. It is vital to choose an assessment partner with:
1. An in-depth power engineering experience and expertise
2. A safety-first-and-always attitude and track record
3. A systematic methodology and process
With this type of partner, the facility engineer can be assured of having sound engineering judgment to support justification of necessary power-system repairs and improvements. MT
Frank Waterer is with Schneider Electric’s Power Systems Engineering Division. He has over 23 years experience with Square D in various engineering and R&D roles. Waterer’s activities in the area of engineering standards include having served as chairman of the PES/IEEE Committee responsible for the design, development and installation of all IEEE Standards relating to all surge-protective devices.