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It's HOT, and an article about keeping things cool is appropriate...
An electric motor’s insulation system separates electrical components from each other, preventing short circuits and, thus, winding burnout and failure. Insulation’s major enemy is heat, so it’s important to be sure to keep the motor within temperature limits. There is a rule of thumb that says a 10-degree Celsius (18-degree Fahrenheit) rise reduces the insulation’s useful life by half, while a 10° C (18° F) decrease doubles the insulation’s life. This implies that if you can keep a motor cool enough, the winding will last forever. However, that thinking ignores factors such as moisture, vibration, chemicals and abrasives in the air that also attack insulation systems.
The real issue is at what temperature the motor windings are designed to operate for a long and predictable insulation life — 20,000 hours or more. The National Electrical Manufacturers Association (NEMA) sets temperature standards based on thermal classes, the most common being A, B, F and H. The table below tin this article provides a summary.
Class B or Class F insulation systems are usually used in today’s industrial-duty NEMA “T frame” motors. Many manufacturers also design their motors to operate cooler than their thermal class might allow. For example, a motor might have Class F insulation but a Class B temperature rise. This gives an extra thermal margin. Class H insulation systems are seldom found in general-purpose motors but rather in special designs for very heavy-duty use, high ambient temperature or high altitudes.
Class A insulation, while not used on today’s industrial-duty motors, was standard on industrial “U frame” motors built in the 1960s and earlier. Because Class A insulation has such a low temperature rating, older motors were required to have far lower maximum temperatures. This accounts for the perception among many long-time motor users that modern motors “run hot.” In fact, they do when compared with older motors, but modern insulation systems are so much better that the reliability and durability of new motors are equal to or better than older-design motors. Plus, better insulation systems allow motor manufacturers to put more horsepower in a smaller package.
Insulation Classes and Their Thermal Ratings
Maximum Winding Temp.
*Most common classes for industrial-duty motors
Table shows highest allowable stator winding temperatures for long insulation life. Temperatures are total, starting with a maximum ambient of 40° C (104° F).
Determining Correct Operation
Though many people believe they can judge a motor’s operating characteristics by feeling its surface, this isn’t a very effective method. Design ratings for temperature apply to the hottest spot within the motor’s windings, not how much of that heat is transferred to the motor’s surface. Unless you have intimate knowledge of a specific motor model’s design — including benchmark lab readings of heat runs that show “normal” surface temperatures for that specific model in exact locations on the frame — a motor’s “skin temperature” provides little, if any, evidence of what’s going on inside. This is true even if temperature measurement methods far more sophisticated than the human touch are used. In addition, for safety reasons, it’s unwise to touch operating motors anyway.
Specifying motors with inherent overload protectors, thermostats or resistive temperature devices, or installing similar protection in motor controls, can help ensure that a motor is taken off-line before winding damage occurs. Motor protection of one sort or another is advisable in almost any application. A common and reliable field test for motor heating involves checking the motor’s amperage draw with a clamp-style ammeter. Use this to confirm that actual amps are less than or equal to the nameplate rating. A precise test for winding temperature is the resistance method. This involves careful measurements with sensitive equipment, calculations and several hours of time. Procedures to conduct such tests can be found in technical manuals. Or, contact your motor manufacturer.
Sometimes a motor overheats because of a manufacturing or design defect. But far more often, overheating can be traced to misapplication. Overloading is the leading cause. This could take the form of using an undersized motor, a situation that may become more common as concern for energy efficiency puts the emphasis on eliminating oversized motors. Use an 80 percent loading as your guide. Most electric motors reach their peak efficiency at that load, and a comfortable overload margin remains.
Other common causes of overloading include a load seizing up or misalignment of power transmission linkages. Plus, unanticipated changes in environment, aging of equipment, misuse and other factors can subject the motor to stresses for which it was not intended.
Environmental conditions that can result in motor overheating include high ambients (especially look at the near vicinity of the motor for any heat-generating device) and high altitudes (above 3,300 feet or 1,005.84 meters, where the thin air has less cooling potential). You might have to derate a motor under these conditions, probably choosing the next size up. Another environmental concern is dirt and fibers, which can clog ventilation openings, coat heat-dissipating surfaces and cause a variety of mechanical problems.
Power supply problems are another overheating cause. Low voltage will result in the motor drawing higher current to deliver the same horsepower, and the higher current means higher winding temperatures. A 10 percent drop in voltage could cause nearly that much rise in temperature. Excessive or sustained high voltage will saturate a motor’s core and lead to overheating, as well. In three-phase motors, phase imbalances can result in high currents and excessive heat, the extreme being the complete loss of voltage in one phase (called single phasing), which, if correct protection is not in place, will result in motor burnout.
Often overlooked as a cause of overheating is the number of start/stop cycles. It’s not uncommon for a motor at starting to draw five times or more the current it does while running. This accelerates heating dramatically. Though various provisions are made relative to loading and off-time, NEMA essentially limits a three-phase continuous-duty motor to two starts in succession before allowing sufficient time for the motor to stabilize to its maximum continuous operating temperature rating. This is highly dependent on application, so it’s best to check with your motor manufacturer if you’re facing a high-cycle application.
Finally, pay special attention when applying adjustable-speed inverter drives, especially if you are introducing an inverter in a system of older motors. Some additional heating to the motor windings will inevitably occur because of the inverter’s “synthesized” AC waveform. A greater cooling concern involves operating for an extended time at low motor speed, which reduces the flow of cooling air. Modern inverter-duty motors have higher insulation ratings to help alleviate this concern, and the robust insulation systems used in most of today’s general-purpose industrial motors are also adequate for many applications. In extreme cases, though, a secondary cooling source may be required.
Industrial Motor Service is an authorized re-seller for LEESON Electric Corporation, a manufacturer of motors, gearmotors and drives. To learn more, visit www.IndustrialMotorService.com or call 864-226-2893.
FIVE IMPORTANT TIPS FOR YOUR PREVENTATIVE MAINTENANCE CHECKLIST!
It is important to ensure electric motors perform well because they have a massive impact on a business' productivity and profit. Although operating these motors may seem straightforward and simple, their condition should not be overlooked. This is why it is essential to perform preventive maintenance (PM) checks on electric motors as a part of managing facility assets.
By preparing a checklist for PM program, facilities can make sure that every motor is properly examined and monitored. This also provides managers with an opportunity to detect potential issues and address these ahead of time. By doing so, costly repairs or unplanned expenses can be prevented in case there is a need to replace motors completely.
These five components are essential for a PM program and must be implemented regularly by a business owner.
1. Perform visual inspections on the motor
There are so many things to discover by just conducting a visual check on an electric motor. Take a good look at its physical condition and be sure to record any pieces of information. If the motor has been operating in a rugged environment, it is possible to find signs of corrosion or dirt buildup on its individual components. These all present a potential internal problem since any debris can limit the performance of the equipment.
Make it a point to observe the motor windings and look for a burned odor from overheating. The contacts and relay should also be free from dirt and rust, which are detrimental to the life of the motors. Situate the equipment in an environment without exposure to dirt, moisture, toxic elements, and harsh conditions.
2. Maintenance checks on the commutator and brush
Do not wait until the electric motors stop working or experience inconsistencies in performance. As a part of the PM schedule, users should take a closer look at the brush and commutators. Make sure there are no signs of wear and tear. An excessive wear in the brush can lead to commutation problems with the motor. This is why the brush will need to be changed to regain the integrity of the equipment's function.
In the same way, the commutator needs to be kept in check. Its natural condition is smooth and polished. It should also have no dents, scratches, or grooves since any rough spot suggests brush sparking. Make a thorough inspection of the motor mount, stator, rotor, and the belts. Replace any worn components, which no longer serve their purpose.
3. Conduct a motor winding test
After the different machine components have been inspected, the next thing to do is test the motor windings. This will give the user a better idea on existing anomalies or failures in the motor windings. Moreover, if burn marks and odors, as well as cracks in the windings have been discovered, motor winding tests are mandatory.
To prepare for the test, be sure to disassemble the motor. This will help determine any abnormalities that the motor has been undergoing. In case the windings have experienced overheating, then there is a high chance that a serious damage is present. Rewinding the motor is a crucial part of this test, along with the testing of the wind insulation that reveals information on the resistance level.
4. Check the bearings
Inspect the bearings if there is any vibration or noise. These are signs of potential problems including dirt buildup, poor lubrication, or wear and tear. The bearing housing may also end up too hot to the touch. This could signal issues such as an insufficient amount of grease or overheating of the motor.
Depending on the bearing type, a specific PM task might be necessary. Other factors include the motor application and the environment where the equipment is situated. There are some motors with a low horsepower that no longer need lubrication as these have sealed bearings. Managers have to be aware of the type of bearing and the kind of repair it requires.
5. Keep records
Each time PM schedules occur, users should document the tests performed, and the results gathered for the purpose of establishing trends. Record all repairs or replacements made on every motor component. This creates a better understanding of each piece of equipment, which includes issues addressed or parts replaced. This will be handy for future inspections.
Industrial Motor Service can assist you with this important aspect of Plant Operations and Facilities Management. Call on us to assist or to execute your Preventative Maintenance Program to avoid costly shutdowns or repairs!
A person who has had the pleasure of seeing the inner workings of a pool pump (on their own workbench or looking over the shoulder of a technician) may have noticed it looks simpler than expected. Considering the pump is this piece of machinery that can pump 80 gallons or more a minute, leaves one to expect a few SECRETS hidden away inside the casing. But in practice the pool pump can be broken down into two categories of parts; the drivetrain and the outer structure. Or, the parts that push and pull the water and the ones that keep it from leaking.
This is an informal guide to identifying pool pump parts, so a "Do-it-yourselfer" can either fix it themselves or at least understand the terminology when talking to a tech. Let’s break down the parts of a pump and see how they contribute to the overall functionality.
Inside a Pool Pump Housing
All of the pump’s inner workings – the impeller, diffuser, seals, and motor – fit in or onto this outer casing. The standard housing material is currently the high impact plastic composite called Noryl. This resilient, lightweight material is rustproof and holds up extremely well under duress from heat, rain and water pressure.
Older pumps (early 80’s and back) were made of brass or bronze; these materials proved to be extremely durable, but costly to maintain. A plastic injection molded impeller is going to be much less expensive than a brass version that has to be smelted and forged. Also, the switch to plastic allowed major weight reduction as those metal pumps weigh upwards of 100 pounds. Metal pumps were really durable workhorses and can still be found on pools today.
The strainer lid is the pump’s main inspection point from which a tech or homeowner can determine a system’s health. If we find large air bubbles or no water at all in the strainer lid while the pump is running, that could be a sign of an air leak along the suction side. Because of its necessity as an inspection point, the lid is made of a clear or tinted Lexan glass. If you are unfamiliar with Lexan, it is the material used in bulletproof windows and other glass-like materials.
The strainer basket collects debris before it reaches the important parts of the drivetrain. This basket can save you a bundle just by preventing hard debris like pebbles from surging into the pump and chipping the impeller.
Gaskets & Seals
Pool Pump Gaskets
The gaskets and seals are what keep your equipment pad dry and your water moving. A bad set of gaskets can have your equipment area flood or a pump filled with air rather than water. There are four main gaskets and seals on a pool pump:
Lid Gasket – located on or under the strainer lid.
Diffuser Gasket – Found on the cone tip of the diffuser.
Housing Gasket – Largest of the gaskets and found in the seam between the main housing on the motor seal plate. This gasket is also called seal plate gasket.
Shaft Seal – The two sided seal that sits underneath the impeller on the shaft of the motor. This is the most important seal as it prevents water from surging into the motor and causing fatal damage.
The seal plate is a motor’s mounting flange that allows it to be secured to the pump housing. The seal plate is named so because it houses the shaft seal that encloses around the shaft to prevent water leaks into the motor. This is made of the same Noryl plastic as the housing, making it lightweight and super strong.
The Drive Train
The driving force behind the pump is its motor which creates the churning force necessary to prime the pump and circulate water. The standard is single speed induction motors, but they are slowly losing ground to dual speed and variable speed motors. Variable speed and dual speed have grown into popularity due to their energy efficiency and have also been bolstered by electric companies offering rebates for homeowners who choose to upgrade.
Most single speed motors run a dual voltage setup which allows them to run on either 230 or 115 voltage (user must adjust voltage before installing). Variable speed and most dual speed run strictly on 230 voltage; there are some exceptions in the dual speed category that run on 115.
The impeller is what makes all the magic happen; magic meaning, transforming the spinning shaft of the motor into the pulling force for pumping. An impeller is essentially two discs glued together to sandwiching fan blades (also called veins). The front disc has an opening with a porthole to focus the churning power of the impeller towards the suction pipe to the pool. The water is pulled through the impeller face and then expelled through the impeller’s slotted sides – it’s H2O’s version of a merry-go-round. The water is then rushed back to the pool.
We call this an impeller accessory and a very important one at that. A diffuser amplifies the pull of the impeller by creating a tightly enclosed vacuum lock to the front housing to maximize its power. The diffuser resembles a funnel or a cone that shrouds the impeller; its tip butts up to the front housing, sealed by the diffuser gasket. As the impeller spins, the diffuser shroud concentrates the turbulent energy of the impeller towards the suction pipe which makes the pump prime.
The impeller ring, aka the wear ring, is a plastic ring that fits to the tip of the impeller. The purpose of a wear ring is to act as an extension of the impeller tip to ensure a seal between the impeller and diffuser. The centrifugal force of the impeller forces the wear ring to affix to the diffuser to ensure an even tighter vacuum for priming and pumping. Wear rings are not found on every pump style but are usually seen on high pressure and high head style pumps, i.e. Hayward Super II or Pentair Challenger.
The impeller screw is meant to secure an impeller to internal threaded shaft motors. The impeller screw is quickly becoming obsolete as most manufacturers switched to external thread motor shafts. This change to external threads allows for the impeller to be screwed directly to the motor shaft without the need for extra securing. The thread type of the new impellers also means the impeller is being spun in the direction that keeps it tight to the motor to prevent any slippage.
If you’re still in need of more information, please do not hesitate in calling us at 864.226.2893 at Industrial Motor Service. We’re here to help!
Did you know that Industrial Motor Service is accredited by the Better Business Bureau? Did you know that Industrial Motor Service is also rated "A+" by the Better Business Bureau? Can you be confident in your decision to contact Industrial Motor Service for your Electric Motor Repair and Service? Absolutely!
Oh, we've been here since 1989, but this is our new Internet Home where you can learn more about us and the services we offer. We offer Industrial Motor repairs, parts, service and delivery amongst other things. And we are serious about Customer Service! We work quickly and efficiently to assure you the least downtime at affordable rates with free pick-up & delivery, a "No Charge for Overtime" Program and we offer a ONE-YEAR Parts and Labor Warranty(You won't need it though, our "Return Rate" is less than 1%)! Visit us online at www.industrialmotorservice.com or call us at 864.226.2893.
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