Protect your electrical system: Make the move to condition monitoring
Increasing inspection frequency has a huge impact on the bottom line.
Machinery and Equipment Maintenance
Electrical systems play a critical role in a manufacturer’s ability to be competitive and profitable. They have to be properly maintained. Unplanned outages cost millions of dollars and have a direct negative impact on the performance of plant engineers, operators and managers. Although often poorly understood by stakeholders, electrical system reliability is directly tied to productivity and operating costs. Quantifying the statistical probability of an electrical system failure opens the door to prioritizing critical system components and minimizing maintenance costs.
It’s not surprising then that how we look at the maintenance of electrical power systems and equipment is evolving. This is being driven by several influences – cost, technology and an enhanced human resource base. Efforts are directed to exploring new approaches to monitoring, diagnosis, life assessment and condition evaluation of critical plant infrastructure.
Power interruptions and electrical equipment failures are one of the major symptoms of ageing electrical distribution components. Consequently, many manufacturers are migrating from traditional time-based maintenance to condition-based reliability maintenance.
One of the monitoring technologies is electrical maintenance surveillance. Surveillance and inspection systems determine the condition of individual assets and include – but are not limited to – infrared thermography, airborne ultrasound, motor current analysis, partial discharge testing, corona cameras and visual inspections.
Arc flash danger
Making the transition from reactive maintenance to a totally proactive structure is not an overnight project. It takes time, effort and planning, with commitment from all levels of an organization. The key is to have a reliable means to evaluate the condition of equipment components and the system as a whole.
These aspects of electrical systems maintenance have been specifically addressed in MainTrain maintenance conferences, convened by the Plant Engineering and Maintenance Association of Canada (PEMAC).
Here are highlights from presentations by Rudy Wodrich and Doug Marshall (see Meet the presenters, page 26):
Wodrich says the challenge of an electrical maintenance surveillance system is the inspection and equipment used yield their most valuable results when inspecting equipment operating under full load conditions. But this is also the time when equipment is most dangerous to maintenance technicians. The surveillance equipment normally requires direct access, or direct line of sight, to the energized components inside the electrical system. This means panels have to be open, which is an extremely dangerous condition. In many cases the posted arc fault currents are too high, and access is prohibited.
Every year, thousands of electrical workers in the US and Canada are injured or even killed while performing their duties. Ontario’s Ministry of Labour reports over a 10-year period 28 workers were killed and 255 seriously burned from arc flash incidents. According to the Bureau of Labor Statistics in the US, there are more than 300 fatalities each year from electrocution with an arc flash component, making this the fourth leading cause of occupational fatality. These numbers are nearly half of what they were 20 years ago, which is a marked improvement, for several reasons. First, personnel have a better understanding of risks due to training. Second, arc flash labelling requirements on equipment provide information to front-line personnel regarding the kind of personal protective equipment (PPE) they should use. Finally, there have been significant improvements in the types and quality of PPE.
Unfortunately, the average number of annual arc flash occurrences has not fallen at the same rate over that period. In fact, there are still 4,000 non-disabling electrical contact injuries each year and 3,600 disabling electrical contact injuries, and non-age-related or random failures account for nearly 90% of equipment failures.
The value of condition-based maintenance (CBM) is avoiding costs related to material and labour to perform repairs, as well as downtime and lost productivity. Material lead-time may be substantial, depending on what has failed and the severity of the failure. A 2 MVA liquid-filled pad-mount transformer, for instance, could easily have 12 to 16 weeks lead-time. If that transformer was the linkage to a renewable power generation asset, such as a solar inverter or wind turbine, the downtime in lost energy harvest would be between $40,000 and $55,000, which is more than the cost of the transformer itself.
Several technologies are used to measure the condition of electrical equipment. They include ultrasonic testing, motor current analysis and power quality spot monitoring.
Harmonics pose the greatest risk of potential premature equipment failure. Non-linear loads that draw current for only a portion of the voltage waveform cause harmonic current. This includes variable-speed drives, DC rectifiers, UPS systems and lighting ballasts. In addition, harmonic currents can be magnified by poorly designed power factor corrections through a phenomenon called resonance. The issue with harmonic currents is a significantly higher heating in current-carrying components of the distribution network, proportional to the square of their harmonic order.
Imaging devices, a non-contact method, also measure condition. They keep the user away from danger and don’t intrude upon, or affect, the target’s operation.
Corona cameras work in the UV spectrum and detect coronal ionization around a conductor or insulator.
Thermal imaging cameras provide extremely accurate quantitative results. Accurate temperature readings are impacted by various factors, such as the distance to the target, reflectivity of the surface, geometry, humidity of the air and transmission rate of an infrared viewing window. Modern IR cameras adjust for most of these factors and an experienced technician can secure very accurate results. NETA publishes guidelines for maximum temperatures in different types of electrical equipment compared to actual measurements.
Safety concerns for electricians and other maintenance personnel are front and centre. Appropriate controls eliminate hazards, reduce risk by design, and apply safeguards. The final type of electrical maintenance safety devices is online monitoring. It includes permanently installed versions of power quality and partial discharge (PD) monitoring. PQ monitoring, with permanently installed hardware and sensitive software, detects transients that often come down from the utility and have an impact on sensitive equipment. Without PQ monitoring in place, it’s often impossible to prove the utility was the cause of damage or production outage. PD monitoring is permanently installed monitoring of the ultrasound signature of equipment and is primarily used in HV utility substation applications.
Keep personnel safe
Wodrich emphasized the need for electrical maintenance safety device technologies to be part of a CBM program to ensure personnel are kept as safe as possible. The hierarchy of control concept encourages employing a “safety by design” approach as the next best protocol in instances where it’s not possible to perform the necessary work with the equipment de-energized. Permanently installed online monitoring technologies provide significant additional value to determine when it may be prudent to conduct in-depth inspection and proactive maintenance.
“They can be even more valuable when they tell us nothing is wrong and allow us to use our limited maintenance man-hours on more productive tasks than pure calendar-based maintenance activities,” Wodrich said.
In his presentation about evaluating the reliability of electrical distribution systems in a plant, Doug Marshall stated a study could be conducted. This reduces unplanned outages (production loss), as well as maintenance costs and spare parts inventory, while increasing equipment performance, extending equipment life, reducing safety risks and providing financial benefits.
There is a specific process to this. It’s called value stream mapping, which is a lean management method for analyzing the current and future state of a manufacturing process that details the series of events. It takes a product or service from beginning to the customer. For an electrical system that’s running a complex manufacturing process, it’s a way to identify the critical processes (motors/pumps, boilers, crushers, filters, process machinery) in the value chain and a means to prioritize where reliability improvements are to be made.
There are several RCA techniques that can be employed, depending on the complexity of the electrical distribution system. The best-suited are fault tree diagram and failure mode and effects analysis.
Marshall said that an electrical reliability study identifies improvements to reduce single points of failure, identifies aged components that require replacement, reduces loading in electrical equipment, reduces insulation stresses in electrical equipment, improves preventive maintenance planning, installs predictive maintenance technologies, and reduces MTTR with critical spares inventory and contingency planning.
He concluded his presentation by emphasizing it’s of paramount importance that reliability be one of the cornerstones of electrical distribution design at the outset, along with meeting code and safety requirements. However, once an optimal design is implemented, factors such as ageing components, changing operating conditions and maintenance procedures can affect the system’s reliability. So it’s recommended an electrical reliability analysis be conducted at regular intervals.
MEET THE PRESENTERS
Rudy Wodrich is the leader of product development at IRISS Inc. in Bradenton, Fla., a company that provides asset tracking for the electrical industry. He’s an electrical engineer whose career has revolved around designing electrical distribution systems for industrial, commercial and power generation applications. He holds an MBA from the University of Toronto and works on critical asset surveillance technologies.
Doug Marshall is a senior project engineer at Magna IV Engineering with locations in Western Canada and offices in the US, a company in the field of high voltage power, automation and controls, and that commissions electrical power systems for industry. Marshall has 35 years of experience in electronics and electrical power distribution. He currently conducts feasibility and power system studies and holds degrees from Concordia and McGill universities in Montreal.
Steve Gahbauer is an engineer, a Toronto-based business writer and a regular contributing editor. E-mail firstname.lastname@example.org.