Do you postpone changing your car tires until they blow out, or do you change them well before the tread is gone — before the “wear out” period? Most of us are smart enough to replace them before a catastrophic failure occurs. But do you do the same thing with your electrical system components? 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 when they are 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 to 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 Fig. 1, 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 perform 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’re 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. The Table shows us the expected life of various types of well-maintained electrical equipment.
Let’s consider a quick example. The Table indicates that a transformer’s useful life is 25 to 30 years. After that time period, the end-of-life period begins — with 80% of transformers failing between the 40th and 50th year of life, as shown in Fig. 2.
It’s important to note that the Table describes rather ideal situations. In reality, there are a number of factors that cause life expectancies to vary, such as cleanliness, loading levels, ambient temperature, maintenance practices, lightning frequency, harmonics/power quality, 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 every 10°C rise in average temperature. Thus, switchgear run fully loaded at its rated insulation temperature of 105°C has a life expectancy of about 10 years. If the temperature drops to 85°C, that same piece of equipment may last for 36 years. On the other hand, if temperature is increased to 125°C, it may only last two years. In summary, running switchgear at 80% load increases its typical life from about 10 to 40 years. (Source: “Expected Life of Electrical Equipment,” Siemens Tech Topics No. 15, W10-0002). High temperatures and full-loading shortens the “bathtub” and quickly pushes equipment into its wear-out period.
Returning to the tire analogy, consider the risk of a blowout on a car with four 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 expensive 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 regular maintenance as part of your regular work procedures. Keep equipment clean, schedule annual preventive maintenance, and verify the equipment is in safe working condition. If you follow the simple process in Five Steps to a Safer Electrical Room, you’ll be headed down the right path to finding small problems before they become big ones.
Post, P.E., P.Eng., is president of Interstates Engineering, Sioux Center, Iowa. He can be reached at [email protected].