Circuit Breaker Maintenance
Almost every building with an electrical system uses a circuit breaker to protect it. Industrial facilities are no different. Just like residential applications, industrial circuit breakers protect the electrical systems from short circuits, undercurrents and other potentially dangerous or costly damages. If a circuit breaker fails, it could have deadly consequences for personnel. It could catch fire or cause harmful arc flashes. However, many of these problems are identifiable beforehand, with the help of proper maintenance.
Completing maintenance tasks is vital for any facility, but due to the idle nature of a circuit breaker, many businesses don’t think about them as much as they should. Considering the damaging effects of a broken circuit breaker, facilities must take a close look at their maintenance procedures and programs.
Why Circuit Breaker Maintenance Is Important
A circuit breaker is a crucial component of the safety and success of a facility. If it goes down, a company can lose significant amounts of capital in the time it takes to repair it. The circuit breaker is what makes the electrical functioning of an industrial facility possible. Without it, most businesses wouldn’t be able to maintain their building’s electrical system at all. Industrial electrical systems handle high loads and many connections, so circuit breakers are particularly crucial for these types of systems.
At its core, a circuit breaker prevents electrical surges and fires by cutting off the power if levels become too high. Remember that a circuit is present throughout the building and needs to be a continuous path to deliver electricity. When that circuit is broken, power can no longer reach appliances, light fixtures or machinery. The breaker can “trip” via electromagnets, vacuum bottles and more, some of which require more maintenance work than others.
Without a fully functioning circuit breaker, a facility is at a significant risk for safety issues. This situation poses both a danger to workers and the risk of non-compliance with regulatory agencies. Different types of breakers have different requirements too. While they share similarities, the differences are notable between the different types of breakers, including insulated-case (ICCB), molded-case (MCCB), low-voltage power (LVPCB), medium-voltage air-magnetic (MVACB) and medium-voltage vacuum (MVVCB) breakers. Each of them work in subtly different ways, so checking the manufacturer specifications helps in determining the correct procedures. Many maintenance tasks need to be done by a trained and certified professional, and OEM-certified repair specialists are ideal.
Frequency of Circuit Breaker Maintenance
Though a circuit breaker may not show any apparent need for maintenance on the outside, it is a critical part of its performance and longevity. Maintenance of a circuit breaker is more complicated than replacing a filter or changing oil like other industrial machines. Often, a certified professional needs to perform the job due to the hazards associated with electricity. Once completed, circuit breaker maintenance provides needed safety improvements and keeps the electrical system moving efficiently. Performing maintenance regularly helps facilities stay on top of their equipment and alerts them to any problems in a timely manner.
MCCBs are the simplest breakers to maintain, as they are designed to run with very little maintenance. They should still be exercised at least once per year, with routine trip testing every three to five, depending on their operation.
LVPCBs should have inspection and maintenance performed every one to three years. Operation patterns may influence how frequently these tasks should be done. Some conditions that require more frequent maintenance include:
- A dusty, dirty or corrosive atmosphere
- High moisture levels or ambient temperature
- Aging equipment
- Frequent switching or fault operations
- Current that is interrupted or near its rated capacity
According to the United States Bureau of Reclamation, medium-voltage circuit breakers should see maintenance annually or after every 2,000 operations, whichever occurs first.
High-voltage circuit breakers should be inspected every six to 12 months.
What Maintenance Includes
Like any machine, a circuit breaker must be cleaned and maintained. Again, maintenance can vary from manufacturer to manufacturer, but some near-universal tests and procedures can be done to inspect and uphold the condition of most circuit breakers. In all instances, the circuit breaker should be disconnected from power before inspection or repair. Below is our circuit breaker maintenance checklist.
1. Visual & Mechanical Inspection
A straightforward visual inspection is an excellent way to identify physical problems like inadequate lubrication, overheating or loose connections. Some components to inspect include:
- the housing and general condition
- grounding and anchorage
- arc chutes
- all contacts
- correct operation of any protective devices or auxiliary features, such as ground-fault trip devices, zone interlocking or tip and pickup indicators
- bolts, which should have appropriate torque levels
Before even touching the circuit box, a visual inspection can reveal problems like water, rust, evident physical damage or pests that could make operation hazardous. If none of these are present, a technician can open the circuit breaker and look for any loose components or discoloration. Discoloration on connections is a sign of overheating. Other signs of burning, arcing or heat need to be addressed.
In addition to merely looking at the circuit breaker parts and functions, they should be exercised, just like a muscle, every so often. Moving the handle a few times to ensure linkages are free, opening the door several times repeatedly and tripping the breaker with a push-to-trip button are things you can do to ensure the mechanical system is working correctly. If the breaker is stiff or sticks, it could lead to a delay that adds a significant amount of risk to the possibility of an arc flash that could exceed the ratings for most personal protective equipment.
There are a few different types of tests that can tell someone about the condition of a circuit breaker.
In an MCCB, a millivolt drop test displays abnormalities like loose connections or eroded or contaminated contacts. It uses low DC voltage at 50A-100A.
An overload tripping test checks the trip system by applying 300 percent of the breaker-rated continuous current to the poles. Tripping times, which can be affected by other environmental conditions, are less valuable than the circuit breaker’s ability to automatically open.
A medium-voltage oil circuit breaker also needs to be tested for the dielectric strength of the oil. If this is below 22kV, then the oil must be filtered or replaced.
A ground-fault trip test measures the effectiveness of a circuit breaker’s ability to provide ground-fault protection on equipment with adjustable pickup and delay values. A breaker with a ground-fault delay feature determines the time that elapses before it initiates a trip during a ground fault. Testing the ground-fault delay can ensure that the timing is adequate and within safe limits.
3. Insulation Resistance
An insulation resistance (IR) test is a simple test that checks the integrity of the insulation material. Its goal is to resist the flow of current and keep it contained to the conductor. Insulation wears down during its lifetime, and sound insulation can maintain high resistance levels.
An IR test is temperature-sensitive, and readings vary significantly in different temperatures. Based on the class of the equipment, a technician applies voltage to the insulation and takes readings at 30 seconds and one minute. If a winding is present, like a motor or transformer, the technician also performs another 10-minute reading. With these numbers, they can calculate the Dielectric Absorption Ratio. This number is found by dividing the one-minute reading by the 30-second reading. Another figure that may be needed is the polarization index. This reading is available with the help of the 10-minute reading, if taken. To find the polarization index, divide the 10-minute reading by the one-minute reading. Finally, these numbers can help determine the condition of the insulation across several grades, ranging from dangerous to excellent.
Dielectric Absorption Ratios above 1.6 are excellent, and those between 1.0 and 1.25 are questionable. For the polarization index, values above four are excellent, while those below one are dangerous. These values are somewhat tentative, as factors like temperature, humidity and moisture can heavily influence them. IR readings over time are good indicators of how insulation may be degrading. Take measurements of those miscellaneous factors as well, so you know the conditions in which each was taken.
4. Contact Resistance
When checking for contact resistance, you measure how much the electrical connections, like terminations, joints and busbar sections, contribute to the total resistance in a system. This data can tell you about the health of a system’s contacts. If contacts are damaged, they can cause arcing or fire and be serious detriments to an electrical system as a whole.
Ductor testing is another term for the contact resistance test, performed with an Ohmmeter, which may use micro- or milli-ohms. To test contact resistance, one would use the Ohmmeter to inject a fixed current through the contacts. Three phases within the current path are measured and compared. The change in voltage drop can help to calculate the resistance value using Ohm’s law. If the highest reading exceeds the lowest one by more than 150 percent, it is an indication of a problem in the circuit breaker. The technician should compare this number to the one provided by the manufacturer.
This type of test is similar to the IR test but is more common on medium- and high-voltage breakers. It involves putting high DC voltage through an insulation system, which stresses it to bring moisture, dirt and weak insulation to light. The overpotential test is also used in vacuum breakers, but a specific test set must be used, or it will wreck the vacuum bottle. Check the manufacturer specifications to see what type of high-potential voltage is needed. If an arc occurs inside the vacuum bottle during the test, X-Ray radiation may occur, so the tester should take appropriate precautions and maintain distance.
Timing a circuit breaker ensures that it performs at manufacturer specifications. The process varies based on the type of breaker.
Low-voltage circuit breakers use either primary or secondary injection test sets. Primary injection, typically the preferred method, trips the breaker by pushing current through the whole current path. Secondary injection applies the current to the current input terminals on the breaker’s overcurrent device. Both are measured with the correct characteristic curve for that combination of breaker and overcurrent.
Medium- and high-voltage circuit breakers have similar tests, but with different equipment, such as a travel analyzer. In this setup, a transducer connects the breaker linkage to the analyzer. The transducer sends a signal to the analyzer as soon as the trip coil on the breaker is activated. With the breaker opened, the analyzer records the movement of the contacts. The resulting travel trace allows a tester to measure several factors, including the opening speed of the contacts, the total distance of contact travel, any binding on the linkage that may affect travel or opening speed and contact bounce at the end of the opening stroke. All three phases need to be monitored to look for contact synchronization.
Earlier, we mentioned that circuit breakers should be exercised regularly to check for normal functioning and to avoid rust or dirt accumulation. Aside from regular operation, proper cleaning can help prevent these problems as well by keeping rust, dirt, grime and other foreign materials at bay. If these substances have time to accumulate inside a breaker, they can cause disruptions in the power supply, potentially leading to blown fuses, interrupted currents or fires. Cleaning out a breaker should only be completed by a trained, experienced professional with the right tools for the job, such as a grounding mat, anti-static wristbands and non-abrasive cleaning materials that won’t remove plating or insulation.
Another risk that could occur with breakers that have been left untouched has to do with lubrication. When they come from the manufacturer, circuit breakers have appropriate lubrication to keep things moving, but this can wear away over the years. The formation of rust or added friction in the operation of the system can reduce torque in certain connections. As rust gathers, it can slow down the entire system past manufacturer limits. Keeping the system well-lubricated improves its safety.
One way to keep a breaker in optimal condition is through restoration. When restoring a circuit breaker, a technician will completely take it apart and reassemble it, paint or powder-coat it, replate it and retest it. This overhaul of a system can increase its longevity.
8. Re-Testing, Certification and Test Reports
A facility should retest its circuit breakers often. Each time they are tested, you gain more information about their status. Any performance improvements that maintenance brings or degradation in quality throughout the years show up in these tests. Another component of quality that may be desirable is certification. Circuit breaker certification provides third-party evidence that your breakers are up to par and can protect the building and its occupants from various electrical hazards. Depending on the type of circuit breaker you’re working with, it could help to seek certification that shows adherence to specific standards like those of the American National Standards Institute and the National Electrical Manufacturers Association.
Other local standards may also be applicable. A KEMA Type Test Certificate is another form that shows that a switch is interoperable and compatible with components from different vendors on the power grid. Some companies provide a report of performance or an inspection report, which might not show results and only state that they performed the test.
In addition to certifications, test reports are a great way to obtain more detailed information about the performance and status of a circuit breaker. They provide documentation for anyone who may need to see it and can help you review the condition of a breaker over time. If IR testing reveals a drop in insulation after several years, test reports provide convenient ways to review that movement and make adjustments.
How to Develop a Maintenance Program
Now that we’ve established the importance of maintaining your circuit breaker, let’s take a look at how a facility can implement that on a regular basis. By following a consistent maintenance program, facilities can stay on top of any deteriorating components and help collect proper documentation and records of circuit breaker performance. Collecting data is a significant element of a maintenance program, as it provides information about the breaker’s condition, brings needed repairs to light and can help with further analysis.
Some of the typical maintenance tasks require repeated action periodically. The time that passes between these occurrences can vary depending on factors like specific hardware and frequency or type of use. Manuals and manufacturers are good places to start to find more information on how often to perform these tasks like visual inspections, as well as insulation resistance, contact resistance and other types of testing. If a facility has an extensive network of electrical systems and circuit breakers, this list may be quite long. One option would be to use a Computerized Maintenance Management System (CMMS), which digitizes the various aspects of maintenance and helps makes them more navigable.
An active maintenance program focuses on several components, the first of which is to make a plan. This plan should be comprehensive and include a database of all equipment. Electric Energy Online provides the following list of information that a database should contain:
- Equipment type
- Year of manufacture
- Serial number
- Technology (SF6, oil, air blast, etc.)
- Electrical characteristics (amperage, voltage, breaking capacity, etc.)
- Date of installation
- Miscellaneous information
Also, it should identify the types of tasks, inspections and readings that need to be taken at various intervals. Here is some of the data it may be wise to collect:
- Inspection results (updated with each one)
- Repairs performed
- Temperature readings
- Timing readings
- Insulation resistance test results
- Contact resistance test results
- Oil quality inspection results
- Moisture readings
- Incident reports and interventions
- Tools needed
With this expansive database, facility managers can more effectively monitor the status of the circuit breakers in their network. It offers an actionable list of tasks to be performed regularly and includes consistent collections of data. By gathering data like this, engineers can come up with a verdict about the performance of the circuit breakers and direct further maintenance or intervention procedures. They may also be able to catch any dangerous conditions that require immediate repair.
Developing a maintenance program is an excellent way to complement the tasks performed. By paying attention to circuit breaker maintenance before there is a problem, a facility can reduce the downtime that occurs when a circuit breaker fails. Remember the value of a plan like this as you move forward with a facility’s circuit breaker maintenance program.
Circuit Breaker Maintenance for a Safer Facility
Regular maintenance is one of the best ways to keep a circuit breaker in good condition. It also helps to improve the safety of everyone inside the building while protecting the investment of a facility’s entire electrical system. Without maintenance, an overheating circuit breaker could lead to fires or arc flashes, injuring personnel, destroying property or worse. A breaker may show signs of wear before an incident occurs, so have a robust maintenance program to prevent them from ever occurring.
If you find that your circuit breaker needs repair, Global Electronic Services is there with skilled and certified staff and fast turnaround times. For more information on our process, reach out to a representative today, or request a quote for a repair job.