Baldor has introduced the MST Soft Starter with six SCR three-phase voltage control that offers advanced protection for the motor, the soft starter and the load. Available from 7.5 to 1,000 HP at 208 to 575 VAC, it is suitable for a variety of applications, including pumps, compressors, fans, conveyors, mixers and stirrers. It features programmable torque control, providing a more linear acceleration during start that reduces wear and tear, and during stop it virtually eliminates pump water hammer.
Replacing components is costly and time consuming, but by scheduling machine downtime to properly maintain each piece of the system, a user can increase the effective long-term life of machinery. Bearings, seals and gears are wear components. This means they will fail — it’s just a matter of when.
Inspecting and observing components should always be included in the preventative maintenance guidelines for a conveyor system. Monitoring lubrication, temperature, noise, vibration, wear and alignment will help uncover potential problems prior to failure.
Routine vibration measurements of the entire equipment train should be taken at regular intervals so that problems can be found well in advance of a component failure. The foundation and equipment base should be checked regularly for movement or looseness.
The majority of motor failures can be divided into two categories: bearings and windings.
More motors fail due to bearing problems than for any other reason. The leading cause of bearing failures relate to a variety of issues surrounding lubrication. Antifriction bearings should be re-lubricated on a regular basis. The lubrication schedule depends greatly on the motor’s operating environment and service conditions. While failures may occur due to lack of lubrication, bearings may also fail due to grease contaminated by water or other materials.
The second most common cause of motor failures is stator-winding failures. To insure long motor life, it is important the motor operate within the temperature class of its insulation system and be kept clean and free of particle build up on the frame surface, air inlet and fans.
There are several simple tests that can be performed to detect and prevent premature failure of a motor winding. First, motor current can be measured to determine if a motor is overloaded. Measurement of voltage imbalance is the second test. Voltage imbalance between phases may increase motor temperature and cause the motor to exceed rated temperature. The third test uses non-contact infrared pyrometers to help identify potential motor temperature problems by identifying abnormal hot spots, bearing problems, air flow and cooling problems. You can also perform an insulation resistance test. Motor insulation systems may deteriorate because of contamination, mechanical movement, cracking, attack by solvents, mechanical impact, or many other factors.
Technology today also offers the mine engineer sophisticated tools that evaluate the health of a running motor. There are tools available that evaluate the current signature and vibration of a motor concurrently to provide a comprehensive evaluation of motor health. This type of analysis can be performed as a routine survey throughout the mine, or these monitors can be installed on specific critical machines for continuous monitoring. These tools allow the easy transmission of motor data back to motor engineers who can perform a detailed analysis of the data collected from anywhere in the world.
The gearbox is a key component of the conveyor drive and one of the most expensive. Proper lubrication is critical to maintain long-term performance. The oil has two main purposes: it keeps the components from wearing and also keeps them cool.
An oil-sampling program is an effective way to monitor the health of a gearbox. Periodic oil analysis indicates if water is getting into the oil, if the oil is breaking down, or if there is gear or bearing wear. Sampling also can be used to establish oil-change intervals based on the actual condition of the lubricant. When inspecting the gearbox, check for leaks at the shaft seals.
Temperature monitoring is another useful tool. After establishing a baseline, subsequent readings can be used as comparisons, and the data can be trended. A rise in temperature or localized hot spots can indicate problems with the gears or bearings.
A person’s ears are also a useful preventative-maintenance tool. Abnormal sounds are often the first indicator that something is wrong with the gearbox. Vibration readings can be a good indicator of gearbox health, and this analysis can help detect coupling misalignment, improper foundation support (soft foot), and gear or bearing damage. Take a baseline reading with the gearbox installed and connected to the conveyor. Like temperature measurement, trends can help tell what is happening inside the gearbox.
Conveyor Pulley Bearings
Routine maintenance and proper lubrication will ensure a bearing’s maximum life span. The bearings on a conveyor pulley normally run at low speeds and should be filled 100-per-cent full of grease before they leave the factory. This helps prevent water from getting into the bearings during shipping and storage. This fill also helps keep contaminates out during operation.
Effective lubrication is critical to prevent premature bearing failure. If the bearing is not re-lubricated properly then its life is essentially only as good as the service life of the grease. Therefore, re-lubricating the bearing at predetermined intervals is recommended. Most instruction manuals list re-lubrication intervals based upon speed and hours of operation. However, these are typically general recommendations and don’t reflect how temperature and environment may impact the bearing. The manufacturer will be able to supply more detailed recommendations.
When it is time to re-lubricate the bearings, it is important to use with the proper type of lubricant. Not all lubricants, whether grease or oil, are compatible. Contamination, including dirt, dust, moisture, etc., will wreak havoc on a bearing once it has penetrated the seal cavity. It is best to lubricate just before shutdown, especially in moist or humid environments.
Noise and audible vibrations are other easy characteristics to identify. When bearings begin to show audible signs of noise and vibration there is something wrong and a scheduled inspection is due. Vibration is a key characteristic growing in popularity to identify bearing trends and predict failure. Accelerometers can be used to measure vibration on the equipment. Bearing frequencies that correlate with vibration measurements might identify inconsistencies on the raceways or rollers; signs of on setting fatigue failure. Routine measurements should be recorded for future comparisons.
The pulley needs to be monitored for rim or lagging wear. Typically a pulley is not designed with additional material added for wear. So if the pulley in use on a conveyor is not lagged, and the user is experiencing rim wear, lagging should be applied. However, lagging wear also needs to be monitored because uneven wear can cause problems with belt tracking.
On the drive pulley you can monitor the wear by looking at the depth of the grooves. The grooves are there to allow water and other material that gets between the pulley and the belt to move to the edge of the pulley and out from under the belt. When the grooves are almost gone, or you start to have problems with the belt slipping, it is time to replace the lagging. On non-drive pulleys, the lagging should be replaced before it has worn down to the rim.
The pulley may also be monitored for noise and vibration, which can detect cracks in the rim or end disc.
Metallic, grid or gear couplings are most commonly used on large conveyor drives. They require grease lubrication, which should be monitored and changed normally every six to 12 months. Particles found in the grease would indicate the coupling is wearing, typically caused by misalignment. Vibration monitoring of the gearbox can also help determine if there is a problem with misalignment.
Instead of focusing on one or two components of a conveyor system, creating a maintenance program that encompasses the entire system will lead to longer effective life of machinery. Inspecting, observing and caring for the system as a whole will help prevent unplanned downtime and increase productivity.
David Keech is a mining industry engineer with Baldor Electric, a member of the ABB Group. For more information, visit www.blador.com.
While other manufacturers have left the DC motor market, ABB and Baldor continue to invest in DC product development and U.S. manufacturing. A complete offering of Baldor round body DC motors has the same shaft height and mounting dimensions as competitors motors, making the Baldor product an easy drop-in replacement. Baldor also offers a full range of laminated frame DC motors, including explosion proof designs.
When these high efficiency and premium efficient motors entered the marketplace, organizations such as NEMA (National Electrical Manufacturers Association) and CEE (Consortium for Energy Efficiency) worked with manufacturers to develop standard levels of efficiency. These standards were later adopted by the U.S.’s Department of Energy (DOE) as the benchmark for the Energy Policy Act of 1992 (EPAct), which went into effect October 1997. This law mandated that general-purpose TEFC (totally enclosed fan cooled) and ODP (open drip proof) motors, one to 200 horsepower (HP), were required to meet the energy efficient table as defined by NEMA MG 1, Table 12-11.
Both the U.S. and Canada require motors to be tested for efficiency in a certified lab using specific test procedures, such as IEEE 112 Method B or CSA 390. Most NEMA members have their test labs certified. Although the IEC test method IEC 60034-2-1 has been harmonized with the IEEE and CSA methods, the E.U. does not require a certified test lab.
The most recent energy law, which broadened the scope of EPAct in the United States, was the Energy Independence and Security Act of 2007 (EISA). This new law went into effect on Dec. 19, 2010. The Canadian version of this law, enacted by Natural Resources Canada (NRCan), went into effect on April 12, 2012. These new laws brought the original one-to-200 HP, 2-4-6 pole motors from the energy efficient levels of table 12-11 up to the premium efficient levels of Table 12-12. A second group of motors was also added under this new legislation, which includes U-frame motors, close-coupled pump motors, footless motors, and eight-pole motors, to name a few.
Understanding the laws and which motors are required to meet them is most of the battle. When one has developed a familiarity with these laws and what they mean, including the motor efficiency tables, it’s a matter of checking this information against the motor manufacturer’s nameplate to identify a motor’s efficiency. It is important to note that if a motor was purchased and installed prior to the implementation of the energy law, the motor only had to meet the requirements of any law in place during the time of installation. If an old motor were to fail, it can be repaired — but one must count the cost and decide if it would be more beneficial to invest the money toward a new, efficient motor. Additionally, if one has a motor in stock that was built prior the energy bill, the motor is also good to use as long as it was in the country prior to the energy bill implementation.
The energy efficiency laws in the U.S. and Canada are for both motors sold in commerce and motors embedded in machinery. If a company is importing a machine using covered electrical motors, those motors must be compliant with the laws. Identifying and understanding the information on motor nameplates can be a bit tricky, especially given the fact all motor nameplates do not always look the same. Two of the main things to look for are the NEMA nominal efficiency and the Certified Compliant (CC) mark for the U.S. and an NRCan mark for Canada. As other countries adopt Minimum Efficiency Performance Standards (MEPS), specific approvals and markings may be required.
The NEMA nominal efficiency is the nominal efficiency as defined by the NEMA tables for a particular motor enclosure, size and speed. This efficiency is expressed in a percentage. For instance, if a motor’s efficiency is labeled as 91-per-cent efficient, then that means the motor will convert 91 per cent of the electrical energy into mechanical energy, resulting in nine per cent of losses due to heat and other factors. For each NEMA nominal efficiency in the tables there is a NEMA guaranteed minimum efficiency based on a 10-per-cent variance in losses as shown in table 12-10. The CC mark is the number provided to each motor manufacturer after their motor line has been approved by the DOE. If this number is not present on the motor, it could be because that particular motor is exempt from law, was built prior to the law, or has not been properly submitted to the DOE for approval. Another distinguishable feature to look for on motor nameplates is the NEMA Premium logo. Although this logo is a registered trademark of NEMA, motor manufacturers can receive the license from NEMA to use this logo on their nameplates and marketing materials. One of the requirements of NEMA Premium usage is for the manufacturer to annually submit their line of motors for efficiency testing to a certified third-party lab facility.
If questions or concerns arise related to identifying the proper motor for an application, especially in regards to efficiency, one should contact their local motor sales representative. Any reputable manufacturer should be more than happy to back up their motor line with whatever data is necessary to demonstrate their performance. As the old saying goes, if something sounds too good to be true, it probably is.
David Steen is a product manager for small/medium AC motors with Baldor, member of the ABB Group. For more information, visit www.baldor.com.
This article considers only reciprocating engine generators, those using diesel, natural gas or liquefied propane for a piston-type prime mover turning a connected alternator. In general, these generators are 10 kWe and larger.
Required Duty and Electrical Output
The first consideration to correctly specify a generator is to understand how it will be used. There are three duty types. Standby duty is when a generator is to be used in the event and for the duration of a power outage. Prime duty is when the generator supplies power in place of utility power. Continuous duty requires the generator to provide power up to its rated maximum for an unlimited amount of time. Each rating has a different effect on performance and equipment selection.
The next step is to configure the required output frequency (hertz), voltage and amperage.
In regards to frequency, some applications in Canada and the United States are 50 Hz; however, most are 60 Hz. Engine generators are constant speed machines operating at 1,800 rpm (sometimes 3,600 rpm) for 60 Hz and 1,500 rpm for 50 Hz.
Different voltage outputs can be made by alternator selection and connection. Typical low voltages are 120-600V single and three-phase and medium voltages 2,400-13,800V three-phase. There are other frequency and voltage combinations that can be generated but most of these would be for special applications and are not as common.
The total amperage output and load starting characteristics required of the generator is a huge consideration. This determines in large part the physical size of the generator and the cost. Determining the required engine horsepower and correct alternator combination is the process of sizing.
Sizing takes into account the number of loads and load steps required to be run and for how long. It is always best to have the most comprehensive load list prepared and analyzed to correctly size the generator. This load list should include all of the various electrical appurtenances (loads) organized in the order they would be started (load steps). Knowing start sequences for the loads is important. For instance, a generator for a pump house with multiple pump motors (total load) would have to be sized differently to start all the motors at once as opposed to individually (same total load, different load steps). Engine generator manufacturers have sizing software that can correctly size a unit based on this list. Certain loads require special consideration, such as UPSs, variable frequency drives and large motors. The better the load list, the more accurate the sizing.
• Fuel Selection.
The decision about what fuel to use comes down to the application and what is available at the job site.
Natural gas delivered by utility offers an unlimited supply without truck delivery to the site. There are some regional variations in BTU content so be aware of the heat value of the gas. Natural gas can be subject to supply interruption and the possibility of interruption can disqualify the use of natural gas in certain applications.
Liquefied propane (LP) gas is often used in a locale where utility source gas is not available, or prohibited from use. LP must be stored onsite so truck delivery is required, but it transports and stores well. There can be issues vaporizing enough gas off the top of the storage tank to fuel the engine in cold weather. This requires the LP be sent to the engine as a liquid to be vaporized just before entering the combustion stream.
Diesel, the most popular choice for standby duty, is a good reliable fuel for engine generators. It does require on-site storage, how much to store depends on how many hours of operation at load are required before refuel is available. Diesel does not store indefinitely: two years is its approximate storage life before it starts to settle or separate. Diesel can be susceptible to gelling in very cold temperatures. Winter grades, or fuel heaters, are available for cold climates; in tropical areas, a microbicide may be needed.
• Environmental Considerations.
Job site temperatures and elevation must be considered for generator selection. There should be provision to address any harsh conditions, such as temperature extremes, dust or dirt, humidity, sea air or corrosive environments. Consider if the job site is in a high-wind area or subject to heavy snow loads. Seismic certifications are required in certain areas.
Generators can either be located indoors in a specially designed generator room or outdoors in their own enclosure. The enclosure design should provide protection from the elements and unauthorized entry. Consider noise from the unit and proximity to distribution switchboards and transfer switches. Ensure engine exhaust will disperse away from other building openings and vents.
Generator room applications require adequate space for service access and clearances required by electrical code. There must be adequate airflow for combustion and cooling. Vibration isolators should be installed between the generator base and floor.
Outdoor enclosures are typically made of sheet metal, steel or aluminum. They can be skintight or walk in with space to allow personnel entry. The structure of the enclosure can be designed to attenuate sound. Many provisions to address harsh environments are by enclosure design and options.
No other concern about engine generators is more stringently regulated than emissions. Both Canadian and U.S. environmental protection agencies set standards for allowable emissions from diesel and gaseous generators. Standards are imposed based on engine horsepower and application. There can be significant legal and monetary penalties for violating standards. Keep in mind there can also be regional or local standards that exceed federal standards. A professional should be consulted to make sure all regulations are known, the equipment being supplied is legal for the application and permitting processes are followed.
• Standards of Safety and Performance.
The International Organization for Standardization (ISO) has relevant standards for generators in regards to ratings and performance, as well as standards for the manufacturing process. Underwriters Laboratories (UL) and Underwriters Laboratories of Canada (CUL) set standards and makes a listing available for demonstrated product safety and integrity. The National Fire Protection Association (NFPA) sets fire prevention standards, establishes safety and performance standards for transfer switches and addresses the performance of emergency standby generators in critical applications. Some regions are subject to the provisions of the International Building Code (IBC) that require the generator to be designed and tested to operate after an earthquake and to withstand high wind loads. Additional sources of standards include the Canadian Electrical Code and US National Electrical Code, the Canadian Standards Association and CE mark. These are common for generator professionals to understand and your chosen manufacturer should be knowledgeable about how they apply.
Find a Professional
Good distributors and manufacturers welcome the opportunity to help you. Be prepared to discuss the duty type. Share your load list and particulars of your job site. Let them know fuel preference and how many hours you intend for the generator to run. Determine if the generator is intended for indoor or outdoor installation. Find out if there are noise restrictions and absolutely understand emissions regulations and permitting processes prior to purchasing any equipment. This should give you a good start on selecting the right generator.
Rob Hilkemeier is the Western regional sales manager for Baldor Generators. For more information, visit www.baldor.com.
Bearing monitoring is guided by three main senses: sight, sound and touch. Basic monitoring is conducted through elemental observations. However, many highly sensitive tools are available that amplify these observations so they are more noticeable, recordable, and include basic logic to assist with warning identification.
Monitoring bearings visually through classical methods include observing lubricant condition, corrosion, and deterioration. Mounted bearings that are lubricated properly will purge grease from their seals. The condition of the grease upon purging can indicate improper relubrication intervals and/or contamination. Dark, cakey or milky grease are visual signs that relubrication intervals and procedures may be improved.
Evidence of corrosion is a valuable monitoring tool as well. High levels of corrosion can degrade material strength and performance. Deterioration of the surface, seals, or obvious physical dimensional characteristics should also warrant further investigation. These observations are often signals of wear, heat and other abnormal performance prior to total bearing failure.
Several monitoring tools commonly available to leverage visual observations include site gauges for oil lubricated bearings, and thermal imaging guns. Bearings that are lubricated by oil rather than grease are often fitted with site gauges, which will give an indication of the presence of oil and the quantity of oil available to the bearing. These gauges are practical and inexpensive.
Traditionally, audible monitoring is one of the most common methods of monitoring machinery because odd noises are obvious indicators of improper operation, even to the untrained user. It is conducted quickly through an operator’s daily routines. After all, if a bearing within the machine doesn’t sound well it usually isn’t well.
The main problems with bystander audible observations is that (1) it usually identifies the later stages of bearing failure, when planning downtime for bearing replacement is impractical and (2) when audible feedback of a single bearing is masked by the overall noise of its environment. That’s when instruments such as stethoscopes (with amplification) and decibel level meters are advantageous. Both tools are available with a wide range of features that include quantified readings and recording features so bearing performance can be trended. These tools are also more useful at identifying improper operation at a less threatening stage of failure.
Bearings should run quiet and smooth; anything different will likely reflect a flaw or a problem with the bearing itself. Noises such as grinding or banging should be investigated quickly. These noises may indicate complete bearing failure and continued use may lead to catastrophic failure and/or damage to neighboring equipment. Bearing noises such as light clicking and squealing may indicate looseness, faults or skidding and should be inspected for cause and remedy.
Audible evaluation is not as sensitive as other monitoring techniques. It is primarily a method of identifying a failure more so than identifying poor performance. Additionally, audible monitoring in the early stages of failure is more noticeable at higher operating speeds than lower speeds.
Physical (Touch) Monitoring
Monitoring bearings by touch, and then trending the observations against historical performance is by far the most useful and accurate means for assessing bearing condition and predicting bearing failure. The touch method can be used to monitor temperature, vibration, and lubrication.
Operating temperature is the most practical and beneficial monitoring method for bearings because expensive tools are not required and is appropriate to all types of applications; slow to high speeds, light to heavy loads. For example, the average threshold of pain for humans is approximately 130°F. If it is difficult to maintain hand-to-bearing contact for several seconds then the temperature is likely above 130°F. Furthermore, water droplets placed on a bearing housing that quickly boil will indicate that the bearing temperature will have easily exceeded 212°F.
There are also many useful tools available to measure and monitor bearing temperatures. The most common include thermocouples and resistance temperature detectors (RTDs), both of which can be permanently mounted to locations on the bearing housing for continuous real-time monitoring. Temperature switches are also available that can be utilized for warning and/or shutdown at dangerous operating temperatures. Many bearing manufacturers offer various permanently mounted sensors pre-installed in bearing housings in areas that will most accurately reflect the true bearing temperature, rather than the housing skin temperature.
Portable thermal imaging tools are also a quick and efficient means to monitor bearing performance. These tools use infrared thermography to visually identify variations in temperature over a broad area. However, the most common portable temperature measurement tool is the infrared thermometer. Although it does not measure temperatures over a broad area, they are inexpensive and easy to use.
Monitoring and trending bearing temperature is important because as a bearing fails, the temperature will continually increase. Trending temperature over time will help identify a failing bearing in the early stages of failure.
Vibration analysis is the most information-rich method available for bearing analysis, and touch can help identify smooth versus rough operation. As safety permits, feel the housing during operation. Rough operation, jostling, or grinding may indicate a bearing problem.
You may also consider vibration measurement instruments to not only identify stages of bearing failure, but also identify overall machine performance and problems. Sensors mounted to the bearing may include permanently mounted or portable magnetic base accelerometers, displacement probes, or velocity pickups. Sensor selection is dependent upon the bearing speed, sensitivity requirements and the application. Although vibration feedback is highly beneficial, proper training is important due to the complexity in data collection and interpretation.
Simple tests can also be conducted on purged grease to detect hard particle contaminants. Upon relubrication, rub some of the freshly purged grease between fingertips. Gritty grease may indicate a need to lubricate more often or wear from a failing bearing.
Many traditional and advanced options are available to monitor and evaluate bearing performance. Leveraging instrumentation to support traditional observations is a valuable practice in support of a predictive maintenance program.
Galen Burdeshaw is Baldor’s customer order engineering manager for DODGE bearings and power transmission components. For more information, visit www.baldor.com.