Build circuit breaker maintenance into the shutdown scope
Maintenance of your electrical system during a shutdown, turnaround or outage is crucial for much of your electrical equipment, especially your circuit breakers. This is the only time to do fault finding and determine their operating characteristics. It is important for both a reliable and safe system to properly plan and schedule these outages so that they become an important part of your shutdown scope.
Over the past five to 10 years, and since the introduction to CSA Z462 Workplace Electrical Safety Standard (2015, 3rd Edition), industry as a whole has done a great job in recognizing the dangers of Arc Flash, the need for an arc flash/power system study, and then training their personnel on the proper use of PPE in regards to the calorie ratings coming from the study.
Unfortunately, most of these studies are not accurate due to the fact that maintenance and inspections of the electrical system are not done on regular basis. Any Arc Flash study that is completed is based on the assumption that the breakers and any other electrical equipment are working as designed or “as new.” This makes maintenance and inspections of your electrical systems one of the most important things that you can do on your next shutdown.
Breakers, and for that matter, most electrical equipment, will never show you signs that they are not operable unless you do the proper checks.
A circuit breaker without proper maintenance or inspections will sit idle for months and sometimes even years. This will cause the circuit breaker’s mechanical parts to seize up and the lack of exercise or lubrication will render the device inoperable. This device is called upon to isolate the fault current that flows during a system disturbance protecting the downstream equipment and personnel. When these types of devices do not operate as intended, major destruction of equipment and major impact to personnel safety is imminent.
In a 2008 survey, NETA (InterNational Electrical Testing Association) polled their North American membership to derive statistics from field level experts regarding their findings during maintenance testing of protective devices. Numerous types of facilities, various manufacturers and all types and vintages of equipment were polled. A national survey of field performance on approximately 340,000 protective devices was reviewed, and the results of those findings were astonishing. The results illustrate that proper personnel protective equipment (PPE) and PPE assessment cannot be performed without accurate and reliable data, including properly functioning protective devices. Based on the results of the survey, approximately 23 per cent of the circuit breakers tested had an issue affecting the protective device operation. With percentages in these ranges, approximately one in five of the devices in the field will not operate as indicated on the arc flash studies. The actual overall impact to personnel in the field is not known, but it can be reasonably assumed that incident energies will significantly increase in the defective equipment. Of the units with issues affecting performance, 42.8 per cent were mechanical issues, and 26.7 per cent had issues related to electrical diagnostic testing. Lubrication issues caused the main mechanical failures at 51.4 per cent. This has been a long-standing problem within industry and is often dealt with during preventive maintenance operations.
Any RCM or maintenance specialist will tell you that operating characteristics and environment are critical in determining fault-finding intervals. With a potash environment including a highly corrosive atmosphere and fine dust that enters almost every crack and crevice. These results can reasonably be expected to be worse.
The dilemma this creates with arc flash incident energy exposures, and the overall impact of the performance to the facility, will help the owners and users of the electrical equipment understand the importance of proper maintenance to ensure a safe, reliable power system. It is very important to start with all breakers to get baseline tests. In other words, you need to know where you are to know where you are going. Also, since there is a high likelihood that some breakers may not operate as designed, it is important to use a qualified electrical maintenance and testing company to not only ensure all work is completed properly but safely. The first thing that needs to be done will be to ensure that the breakers be put into an electrically safe condition. Technicians and field engineers will then inspect and test the various apparatus. Maintenance includes cleaning, lubricating and exercising the devices. Test currents are applied with highly specialized equipment to simulate fault conditions and measure the tripping speeds of the system. Test voltages are applied to stress the insulation systems and ensure the equipment is adequate for continued service. A comprehensive maintenance test report is assembled including all test sheets, deficiencies found and recommendations. Each test sheet contains nameplate information, as found and as left settings and test results along with detailed comments on the inspections.
During much of this testing, there is a very good chance that some breakers will fail. Whether this is because of poor insulation resistance due to moisture, dust or dirt, poor trip times of breakers (breaker trip times do not match the manufacturers times), or the breaker just does not open or close at all, it is important to both safety and reliability to deal with the problems as they arise.
Potash and its dust get into everything and in turn assist in speeding up corrosion. Although cleaning and lubricating will fix a majority of the problems in the short term, there comes a time in any piece of equipment’s life that it needs to be rebuilt or replaced. With the costs associated with new “retrofit” breakers, lead times and mere continuity of equipment, it makes sense to add a new digital trip unit if needed, or if there are signs of mechanical wear or corrosion, to refurbish.
One of the more critical pieces of equipment at a potash mine, or for that matter, any plant or facility, is circuit breakers. Arc Flash studies can provide a false sense of security. Workers will look at the study results and think the PPE they are wearing is adequate, but that may not be the case. Unfortunately, most controls for electrical hazards fail with no warning that functionality has been compromised. A hidden failure can go undetected until an injury or major catastrophe occurs.
Just because you don’t physically see any issues, it does not mean that there aren’t any. Proper maintenance is essential.
This article is published in the Fall 2015 issue of REM.