Andy Smith and Jason Hill provide insight into the importance of breakers, their safety standards, maintenance, and how to avoid downtime with predictive diagnostics.
By Andy Smith and Jason Hill, MCCB Product Integrati on Engineers, Eaton
Why does breaker health matter?
Simply put, both MCCBs and LVPCBs are use in nearly every application around the world to provide an essential function: personnel and equipment protection. To this end, the proper operation of circuit breakers is critical. These breakers operate reliably in countless settings, however, an effective ongoing maintenance program is critical to supporting reliable operations and controlling costs.
In a hospital, for example, the cost of an unexpected outage ranges from USD $800,000 to USD $1 million each day. In agriculture, a failed irrigation pump, or system protected by a breaker, could result in the loss of entire crops. Breaker health is crucial to keeping things moving around the world.
How do you find the needle in the proverbial haystack, the device that should be replaced? To explore this question, one can look to the assessment done by a single paper mill. The paper mill with 876 MCCBs in operation, took a closer look at its devices as part of a robust preventative maintenance plan. Of those 876 devices, five (or 0.57%) needed to be replaced.
The questions to ask become:
• How do you know with confidence which circuit breakers need to be serviced?
• How do you avoid investing the time and resources to inspect all 876 circuit breakers to identify the equipment that needs to be replaced or serviced?
• How can you determine the current condition of MCCBs and LVPCBs?
For MCCBs, most components are sealed in the frame and maintenance has historically been limited to the mechanical mounting, electrical wiring, and manual operation of the mechanism. Low-voltage insulated case breakers, and LVPCBs have more options for maintenance due to their unique construction. The traditional challenge has been determining when circuit breakers, and especially MCCBs, need to be removed from service, as shown in the typical ‘bathtub’ failure curve. This distribution shows how a majority of breaker failures occur either immediately upon commissioning or far down the road when there has been enough electric and physical events to compromise the integrity of the breaker.
Environmental factors such as excessive temperature, moisture, dust, chemical vapor, and vibration can also have a major effect on the health of the breaker. Further, if the circuit breaker has been in service for a long period, it is difficult to know with confidence that the device is capable of performing its intended functions. When a circuit breaker interrupts a high-level fault current at or near the device interrupting rating, determining if the circuit breaker would be able to continue to protect the system traditionally proved difficult. The internal damage that occurs during repeated fault current interruption could impact the breaker’s ability to interrupt a future fault.
By understanding environmental conditions and electrical power system issues, operations and maintenance (O&M) personnel can know when to replace the circuit breaker. A variety of innovations have made it simpler to determine the cumulative effect of these issues. Early on, infrared (IR) technology was applied to get a better picture of breaker performance. While this method provided valuable insights, it required waiting for scheduled maintenance and IR scans. These scans cannot provide a true 24/7 picture of the breaker’s performance during all operations. There is also a chance that these scans may not pickup a loose terminal connection because the load current may not be high enough to cause a heat rise that can be detected at the time of the scan.
Recent innovations are yielding a new generation of circuit breakers that are more intelligent, connected, and contain more internal sensors to enable predictive maintenance. Self-diagnosing trip units can measure a variety of parameters in real time and can provide a better indication of when a breaker needs to be replaced before a problem occurs, averting downtime. Importantly, maintenance personnel are now able to proactively target circuit breakers that require service or replacement, rather than inspect all the circuit breakers in a facility or system; this yields dramatic reductions in maintenance costs.
What safety standards apply?
As either UL 489 or 1066-approved devices, MCCB’s and LVPCBs are subject to thousands of endurance test operations under challenging electrical conditions including high fault currents, overload conditions, and dielectic withstand. They must also meet stringent design requirements for corrosion protection, insulating materials, current carrying parts, and spacing.
The Institute of Electrical and Electronics Engineers (IEEE®) standard 1458, provides the “Recommended Practice for the Selection, Field Testing, and Life Expectancy of Molded Case Circuit Breakers for Industrial Applications.” The 2005 version of this standard established specific methods to determine the remaining life of an MCCB and if it should be removed from service.
The National Electrical Manufacturers Association (NEMA®) published its AB-4 Standard, which provides the guidelines for inspecting and preventative maintenance of circuit breakers. This standard provides information on inspection and testing procedures for circuit breakers in service.
In other words, diagnosing the health of a circuit breaker involves intense investigation to determine when breakers need to be replaced. Contact wear, a critical parameter, is only one factor that needs evaluation. There are some circuit breaker manufacturers who offer a contact erosion alarm. If contacts were the only, or the major cause of breaker replacement, then this method would be a great fit. A much larger range of parameters must be monitored, however, to have a holistic picture of the performance of the device.
What are the maintenance basics and new innovations in predictive diagnostics?
Built to support global, long-term reliability, each of these breakers are rigorously tested in manufacturers’ factories to ensure quality and consistency. Outside of the factory, NEMA AB-4 and IEEE 1458 test standards offer excellent instructions to field test MCCBs even if it is factory sealed.
Data analytics and predictive diagnostics of MCCBs and LVPCBs can be used to make more informed decisions about actual equipment conditions. These intelligent circuit breakers can display an intuitive summary of the
breaker’s current health that can be easily leveraged by a customer or maintenance person. The parameters that are monitored by Eaton’s Power Xpert Release (PXR) trip units, for example, include short-circuits, overloads, operations, temperature, and run-time, and many more. This combination of parameters can provide the overall condition of the breaker that can be used for predictive maintenance increasing system reliability.
Specific insights include:
• Operation data provides insight on when the breaker mechanism was last exercised, and if the mechanism was bound or jammed.
• Total number of operations can provide indication of the endurance and contact wear on the circuit breaker.
• Number of interruptions, and the magnitude of the energy interrupted, are vital parameters to the contact wear indication and the arc chute condition.
• Overload interruptions have less of an effect than short-circuits, but they are included in the calculation and weigh in on the health.
• Short-circuits can be damaging to the contacts, integrity and dielectric strength of the circuit breaker. The magnitude of a short-circuit event is compared to the rating of the circuit breaker and weighed as another factor in the health of the circuit breaker.
• Run-time is also considered and demonstrates how long the breaker has been in use with current flowing through it.
• The environmental temperature is one of the most important measurements; this is the highest temperature recorded and the date and time of that temperature is saved in the analysis.
The health parameter aggregates these data points in an algorithm that allows a user the ability to quickly, accurately, and immediately understand the breaker’s overall health. The analysis of the data will drive improved operating efficiency by minimizing downtime and supplying information that will determine if the breaker needs to be replaced.
What is the importance of embedded intelligence for circuit breaker and electrical system health?
The fundamental function of circuit breakers is evolving to, not only provide personnel and equipment protection, but to also support system visibility and predictive diagnostics. With internal metering capability, these new electronic trip units not only use breaker health diagnostics for predictive maintenance but can generate information to react to energy usage trends and maximize the efficiency of the system for lower operating costs and less downtime. Furthermore, they also provide the ability to communicate this information to a user’s BMS, SCADA, network, or the cloud. With this real time data for: voltage, current, power, ambient temperature, run time, and other metrics pointing to mechanical wear on the breaker, users have usable analytics about the circuit breaker and a greater understanding of what is happening in the system.
Through increased intelligence and understanding at the circuit breaker level, the following system level impacts can be realized.
• Maintenance model can be established: less need to check every breaker; having the visibility to easily shift critical loads so that maintenance does not impact critical functions.
• Fewer maintenance resources: breaker health diagnostics and real-time system data enable maintenance personnel to perform maintenance only when required freeing up resources and operating costs.
• Electricity consumption: full system visibility enables users to see and target inefficiencies (previously undetected).
• Regulatory compliance: expediting and simplifying compliance with real-time data.
• Outage restoration: quickly identify the fault through more intuitive systems that process the data, promoting rapid power restoration and the ability to repair the condition that caused the fault initially.
• New equipment installation: expanding on an electrical system typically requires a full power system study; today, the capacity and capability of the system is readily available.
Is there anything else you’d like to add about breakers?
Yes. At the end of the day, the reliable, safe performance of processes, facilities, and circuits is critical. In a data center application, for example, even if less than one percent of a critical load is lost, the enormous costs of downtime is well documented and are now in the range of USD $9,000 per minute or USD $540,000 each hour. Cooling pump outages at either a nuclear power or natural gas facility present not only lost revenue but also signficant dangers to safety as well.
Equipment reliability, safety, and maintenance-related expenses are top priorities and new technologies are providing ways to boost predictive maintenance methods efficiently. With data-driven insights, organizations can increase equipment uptime and reduce the effort and costs involved in determining which equipment needs to be serviced or replaced while also boosting system reliability.
While there may be some manufacturers making decisions based solely on an operation count, or field inspection of an IR snapshot, diagnostics that operate 24/7 with prudent maintenance practices yield the highest uptime performance. Even if the impact is on a small number of installed devices, there is a significant ROI to avoid downtime and moving beyond simply scheduled maintenance to a more dynamic and potentially effective model.
Decades of circuit breaker design, testing, and field analysis knowledge is being applied to the development of intelligent algorithms. These algorithms are programmed to provide simple, powerful, and previously unavailable diagnostic indicators about the breaker. By leveraging these ‘smart’, communicating circuit breakers at all levels of the power distribution system, there are enormous system benefits that can be realized. The data collected from the circuit breaker can be communicated to HMI displays, PLCs, BMS, SCADA, or other network systems.
About the Authors
Mr. Jason Hill is a Product Integration Engineer for Eaton’s Circuit Protection Division. He has a BS Electronics Engineering Technology from DeVry University. He has been involved in technical support, engineering, sales and product marketing roles during his career at Eaton.