Low Voltage Effects on Ac Motors

Low potential Effects on AC drives A drop in potentiality provide solving in a proportionate increase in current. If the current exceeds the nameplate rating and is non corrected, this stern result in deadening to the force from over heat uping Nameplate Rating An electric aim will retain a nameplate rating for both potential and amperage. When a load is on a force back, the force back must draw a fixed cliff of power. The required power is about equal to volts times amps. Should the voltage f each below the nameplate rating, the amperage will increase. This chiffonier result in increased heat that will shorten the gos life history, according to drivesanddrives. om. Torque The travel is subject to some(prenominal) kinds of torque. The starting or start-up torque is the amount present when the travel is unmoving and power is applied. The pull-up torque is the minimum amount necessary for the drive during the starting term. Effects of Low Voltage on Torque A pr uned amount of voltage will reduce the amount of torque. This can result in difficulty for start loads. A reduction of voltage to 80 percentage would result in a torque mensurate of scarce 64 percent. In light loads, a reduction in voltage may actually be preferable because it will result in increased efficiency.Even a small voltage unbalance will result in large current unbalance during the go alongning of push back by a factor of 6 times. Negative phase chronological succession components will lead to heating of motor Negative phase sequence currents leads to reduction in motor output torque. Motor is forced to run at higher slip leading to increased rotor redness and reduced efficiency. Electricity boards should look in to this phenomenon severely where irrigation pump sets drop off the voltage imbalance, even 1% loss of efficiency for the country standardised India would mean a great loss. HP irrigation pump sets with a meter of 6 Lakh approximate, the loss of powe r would be 22MW and annual wastage of Rs. 47. 5 millions (At 3 Rs/unit, 4 Hrs of Pump working and 6 months season Keys to maximize the service life of industrial motors Why do motors fail? Certain components of motors degrade with time and operating stress. Electrical separation weakens over time with exposure to voltage unbalance, over and under-voltage, voltage disturbances, and temperature. pertain between moving surfaces causes wear.Wear is affected by dirt, wet, and corrosive fumes and is greatly accelerated when lubricant is misapplied, becomes overheated or grime, or is not replaced at regular intervals. When any components are degraded beyond the point of sparing repair, the motors economic life is ended. For the smallest and least expensive motors, the motor is put out of service when a component such as a mission fails. Depending upon type and replacement apostrophize, larger motorsup to 20 or 50 horsepower (hp)may be refurbished and get wise objectives, but are usually scrapped after a winding burnout.Still larger and more expensive motors may be refurbished and rewound to extend life indefinitely. An economic analysis should always be completed prior to a motors bankruptcy to ensure that the appropriate repair/replace conclusiveness is made. Extend Motor Life with Improved port Care gallery failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Bearing and motor manufacturers are aware of the situation. Motor repair shops can attribute much of their business to aim failures.And motor users see accusation failure as the fundamental cause of near every electric motor repair expense. Studies conducted by the Electrical utensil Service Association also demonstrate that target failures are by far the most(prenominal) common cause of motor failures. Knowing that irradiation strengths are the Achilles heel of industrial electric motors is not a bleak idea in maintenance department s, but what is new is recognizing that something can be done to baffle most motor bearing failures. Factors Affecting Bearing Life Electric motors actually present a relatively halcyon duty for cheat bearings.The motor rotor is lightweight, yet because of its large shaft diameter, the bearings are large. For example, the bearings supporting the 140 lb. Rotor for a typical 40 hp. 1800 rpm industrial motor are so large that they m some other an L-10 minimum design fatigue life of 3000 days, or 10 percent of the bearings are statistically expected to fail from fatigue after 3000 years of operation. Plant operating experience, however, strongly contradicts such optimistic estimates of motor bearing life. In actual industrial surroundingss, bearing failure is rarely caused by fatigue it is caused by less-than- example lubrication.Because of contaminated lubrication, bearings fail well before they behave their theoretical fatigue life. There are galore(postnominal) reasons for le ss than-ideal bearing lubrication. Lubricants can leak out chemical attacks or thermal conditions can decompose or break down lubricants lubricants can become contaminated with non-lubricants such as pissing, dust, or rust from the bearings themselves. These lubrication problems can be eliminated. Motor bearings can go away virtually forever by simply providing an ideal contamination-free, well-lubricated bearing env ironment.Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip legal tender or using soaked (lubricated-for-life) bearings. Indeed, for many light-duty applications, such bearing protection techniques are often sufficient to allot bearings to last as long as the equipment itself. However, these bearing protection methods have not significantly reduced the rate of bearing failure in severe-duty industrial motors. Bearings in industrial applications continue to fail because of inadequate lubrication cause d by lubricant loss, contamination, and dissolution and break-down.Lip revenue stamps invariably wear out well before the bearing fails, and sealed bearings inherently foreshorten the life of a bearing to the service life of the contained grease (usually only about 3,000 to 5,000 hours for most industrial services). Maintenance professionals may find the following suggestions on how to forestall motor hearing failure obvious, but some new techniques and technologies are purchasable. Lubricate Bearing at Correct Intervals Despite years of warnings from bearing manufacturers, over lubrication continues to plague many motor bearings. Too much grease can cause heat up of the bearings.The lubrication instructions supplied by the motor manufacturer will specify the criterion and frequency of lubrication. Generally, two-pole motors should be greased twice a year, four-pole and slower motors only once a year. Use the Best Available Grease The most commonly used bearing grease is polyur ea-based, a low-cost, low-performance, highly congruous lubricant. However, it does not handle water well, a serious drawback for many industrial applications. It reacts quickly with water and loses its ability to lubricate bearings. Industrial motor bearings should be lubricated with a synthetic-based aluminum complex grease.A high-quality grease pays for its additional cost in reduced motor downtime and repair costs. Keep come forward wet Unless the motor is being hosed down or it operates in a wet environment, reasonably shielded motor bearings may not become seriously contaminated with moisture while the motor is running. However, when the rotor is shut down, moisture and condensation can collect on the surface of the bearing components. Eventually, this water breaks through the oil and grease barrier, contacts the metal parts of the bearing, and produces tiny particles of iron oxide.These rust particles make an excellent grinding compound when mixed with the grease. resulti ng in premature failure of the bearing because of surface degradation. Preventing water contamination is a major challenge to bearing housing design. Close shaft-to-endbell clearances cannot stop the social movement of humid air. Contact seals will quit contacting, resulting in large gaps that ply movement of air and water vapor across the bearing. Vapor-blocking bearing isolators, such as the one illustrated, are among the more successful devices presently available to prevent water vapor from entering a stationary bearing.When the motor shaft is rotating, the isolator opens, eliminating the possibility of friction and wear. However, when the shaft is stationary, the isolator closes, preventing movement of air or water across its face. With no wear from rotating friction, the seal may last indefinitely, and surely as long as the fatigue-failure life of the bearing. Keep Out Dirt Lip seals, contact seals, and stalk grease replacement answer minimize the amount of dirt and other air-borne abrasives that can contaminate bearing lubricant. These solutions, however, have some drawbacks.Lip seals have a short service life, and frequent grease displacement is expensive and messy. One successful approach to safekeeping air-borne dirt and liquids out of an operating bearing is to install a labyrinth-type non-contact seal over the bearing housing. These bearing isolators, readily available from suppliers, combine a tortuous labyrinth path with impingement and centrifugal forces to trap and unpack air-borne dirt and liquid virtually no contamination can acquire the bearing. Because the bearing isolator is a non-contact device, it will generally be the longest-lasting component of the motor.Although not intended as such, a bearing isolator could serve as an collar sleeve bearing if the primary bearing fails, possibly preventing damage to the motors stator and rotor. In emergency situations, the bearing isolator can allow continued operation for a short time and st ill prevent the need to rewind the motor when the bearing is replaced. Bearing isolators constructed of bronze or other non-sparking materials also can prevent hazardous sparks that could otherwise occur when the bearings rolling elements fail. Other SuggestionsImproved bearing protection and lubrication will reduce downtime and the maintenance costs of electric motors, but other important motor design features contribute to long service life, including over-sized high quality bearings, sophisticated winding insulation, superior fan design, high-performance paint (such as epoxy) and a strong, rigid cast iron frame. These features, usually standard or readily available, are found in most industrial-grade severe-duty electric motors. High-performance bearing protection systems. however, are not universally accepted as inseparable for long motor life.Specifying permanent bearing protection for new motors, or retrofitting isolators onto existing equipment, usually requires initiative on the part of the users maintenance or engineering staff. Permanent, absolute bearing protection has a greater effect on motor life than any other decisions made in specifying, equipping, and caring for electric motors. Keeping bearings lubricated with the accountability amount of clean, uncontaminated, high-quality lubricant allows bearings in most industrial motors to outlast all other motor components.