Energy & Operating Cost Savings

Tires and MCCs: Replace Before They Blow

Fall 2017 Issue of Current Connections Newsletter

October 17, 2016

Do you postpone changing your car tires until they blow out? Or do you change tires well before the tread is gone ? before the ?wear out? period of your tires?

Do you do the same thing with your electrical system? Is your electric room aging and possibly nearing the end of its life expectancy? You want to get the most out of your equipment, but aging infrastructure is an imminent issue for many. The hard truth is that 80% of transformers fail between 40 and 50 years old. By year 10, 50% of circuit breakers no longer function per specification. This statistic jumps to 90% by year 20.

The general rule of thumb for electrical systems is a life expectancy of 20-30 years. After that you?re in the ?wear out period.? When planning long-term plant expenditures or electrical system retrofits, a good place to start is determining the age of your electrical system. Once you know this, you can begin to anticipate when your equipment is no longer operating per specification or is likely to fail completely.

Let?s take a closer look at when electrical equipment is likely to wear out. As you can see in the classic ?bathtub? curve in Figure 1 below, there is a much higher failure rate for equipment at both the beginning and the end of its life cycle. At the beginning of a component?s life, there is a higher ?infant mortality? rate. Failures are typically due to a manufacturing issue, a missing or incorrectly installed part, or a defective piece of equipment. As time progresses, failure rates decrease, and the equipment moves into its ?useful life period.? During this phase, there is a low ?constant? failure rate. While you may have to replace parts or do maintenance work, this is when fewer equipment failures are encountered. Over time, with wear on the equipment, the failure rate begins to steadily rise. When equipment becomes less dependable, you are entering the ?wear out period? for the component.

Determining the age of your equipment and system allows you to begin anticipating or planning for improvements or replacements rather than being caught off guard by an end of life failure during the ?wear out period.? See Table 1 for the expected life of various types of well-maintained electrical equipment.

Table 1

Let?s consider a quick example. Table 1 indicates that a transformer?s useful life is 25-30 years. After that period, the ?end of life? period begins, with 80% of transformers failing between the 40th and 50th year of life. This is illustrated in Figure 2 below.

Figure 2

Table 1 describes rather ideal situations. There are a number of factors that may cause life expectancies to vary: cleanliness, loading levels and ambient temperature, maintenance practices, lightning frequency, harmonics/power quality, as well as humidity and corrosion.

Loading levels and high ambient temperatures have a tremendous impact on life expectancy. There are a wide variety of insulating materials used in switchgear equipment, but a general rule of thumb is that the life of electrical insulation is reduced by half for each rise of 10o C in insulation average temperature. Thus, a switchgear run fully loaded and at its rated insulation temperature of 105oC has a life expectancy of about 10 years. If the temperature drops to 85oC: about 36 years; or, if increased to 125oC: about 2 years. In sum, running switchgear at 80% load increases typical life from about 10 to 40 years. High temperatures and full-loading shortens the ?bathtub? and quickly pushes equipment into its ?wear out period.?

Returning to our tire analogy, consider the risk of a blowout on a car with 4 bald tires versus just one. Or picture an entire fleet with bald tires. The odds of a blowout just dramatically increased. This also holds true for sites with multiple aging electrical components. Failures are likely as equipment ages, and ignoring the signs of aging equipment will likely cost you in unplanned downtime and costly repairs. Finding replacement parts will also become a challenge as parts for older equipment become obsolete.

To keep equipment running and maximize life expectancy, include maintenance as part of your regular processes. Keep equipment clean, schedule annual preventative maintenance, and verify the equipment is in safe working condition. Access our 5 Step DIY ideas and get started on the right road to finding small problems before they become big problems.

If you?d like more information or help assessing if your equipment is at the end of its expected life, Interstates is experienced and ready to kick the tires for you. We will provide a thorough analysis of your electrical system through our Electric Room Rx service. We will alert you to developing concerns and help you justify the investment to improve your infrastructure.

(1) Life expectancy info collected from ABB, CDA, CDM, IEEE Gold Book, and Siemens.

(2) By year 10, 50% of circuit breakers don't function properly per specs. By year 20, 90% don?t function properly.

(3) Abd El Aziz, M. M., Ibrahim, D.K., & Kamel, H. A. Estimation of the Lifetime of Electrical Components in Distribution Networks. The Online Journal on Electronics and Electrical Engineering. Retrieved from: http://infomesr.org/attachments/W10-0002.pdf

(4) Siemens. (2012). ?Expected life of electrical equipment.? TechTopics No. 15, from W10-0002. Retrieved from http://w3.usa.siemens.com/us/internet-dms/btlv/PowerDistributionComm/PowerDistribution/docs_MV/TechTopics/ANSI_MV_TechTopics15_EN.pdf

(5) Life expectancy info collected from ABB, CDA, CDM, IEEE Gold Book, and Siemens.

(6) By year 10, 50% of circuit breakers don't function properly per specs. By year 20, 90% don?t function properly.