Skip to the next section on common causes of electric motor failure. Are the techs CSA-certified? But if youre honest, how much of your time is spent firefighting instead of focusing on your to-do list? The expected temperature drop through a direct expansion evaporator coil: D) Can be determined with a chart supplied by the coil manufacturer. This is another biggie. Sounds simple. For this reason, it is important to check machine alignment more than just at the time of installationprecision alignment is a temporary condition that can change over time. Winding Shorted Turn-to-Turn Note:A one-percent voltage unbalance may result in a six- to ten-percent current unbalance. The benefits of detecting, identifying, and evaluating electric motor abnormalities are decreased motor failures and less unexpected downtime. Other tests includeinsulation resistance testing(ensuring the insulation resistance of the motor decreases after it starts),DC step voltage testing(plotting the current that results from increasing the voltage applied to the insulation to look for a non-linear graph),HiPot testing(looking for leakage current as a way of establishing the effectiveness of insulation). The sigma currents are created as a result of the signal frequency, voltage level, capacitance and inductance in conductors. c) are hard to detect Thermal deterioration of insulation in one phase of the stator winding can result from unequal voltage between phases. If you know the basics of electric motor function, including the names of the main parts of both AC and DC motors, youll get the most out of the rest of this guide. Indicate the relative amounts of potential and kinetic energy at each position. The rotor is sometimes called an armature. As part of a regular maintenance program, next-generation diagnostic and maintenance tools that include connected tools, sensors and software offer the best way to monitor an electric motors health. Youll notice there are no solutions or implementation sections. b) insulation faults Another common fault stems from mechanical rubs, which can be the result of looseness of the motor shaft and/or the motor bearings. to ask deciding whether to repair or replace your electric motor. Know the breakpoints at which youre willing to repair vs. replace. To help mitigate these failures, a variety of motor tests can be performed on electric motors. Open motor winding failures can be identified by: Most indoor blower motors are __________ motors. Motor design. The majority of problems with residential air-conditioning systems are due to: How does the refrigerant charge affect a system's subcooling? That way, action can be taken before its too late. Use a multimeter or an ohmmeter to test the voltage of the electric motor. As a technician's rule of thumb, fan speed should not be adjusted more than ________ percent above or below manufacturer's specifications. Once acid is identified in Impedance mismatches can occur as a result of improper installation, improper component selection or equipment degradation over time. De-energized testing runs a motor through its paces while its turned off. Which NEMA classification can withstand the highest temperature? Everyone is busy. Infrared sensors can seamlessly integrate with a software platform that gathers data from many other sensor types. Severe thermal deterioration of the insulation in all phases of the motor normally is caused by very high currents in the stator winding due to a locked rotor condition. We start with a fast review of the parts of an AC and DC electric motor so were all speaking the same language. Motor starting components can be made up of: Internal centrifugal switches, relays, starting, and running capacitors An open internal motor overload is distinguished by: a) measurable resistance between run and start b) infinite resistance between start and common c) infinite resistance between run and common d) all of these d) all of these Impact: Misalignment of mechanical drive components, Instrument to measure and diagnose: Fluke 830 Laser Shaft Alignment Tool. Identify causes you eliminated and why. Describe how energy changes as a ball is thrown in the air. There could also be thermal deterioration in all phases of the stator winding typically due to load demands exceeding the rating of the motor or by very high currents in the stator winding due to a locked rotor. However, if the motor is more than 10 years old and less than 1 HP, the motor is usually replaced. Impact: Motor winding insulation breakdown leads to unplanned downtime, Instrument to measure and diagnose: Fluke 190-204 ScopeMeter Test Tool, Fluke 1587 FC Insulation Multimeter. When a plant has adopted a preventive maintenance mindset, engineers and technicians are supported to monitor motors and troubleshoot problems before they cause a failure. , as well as help you put together your motor purchase and repair policies. Click to reveal It treats the underlying condition that created the situation in the first place. Bearing failure is an expensive problem both in terms of motor repair and downtime, so helping to prevent this by measuring shaft voltage and bearing current is an important diagnostic step. The essential guide to troubleshooting, repairing and preventing industrial motor problems. Note:Under-voltage and over-voltage (exceedingNEMAstandards) will result in the same type of insulation deterioration. C) Expansion of the heat exchanger as it heats up. It raises the clavicle. Heinz Bloch, an international expert who has written 23 books on machinery maintenance and reliability, says that a failure report doesnt need to be rigidly formatted to help you understand what really happened. Cloudflare Ray ID: 7a12d477b814c226 For this reason, it makes sense to begin your troubleshooting by checking for motor overload. A. Bonnett and C. Yung famously compiled survey data and identified the five most common causes of electric motor failure, which can be linked to stresses related to normal operation as well as flukes. If youre involved in plant operations or maintenance, no one has to tell you how important industrial motors are to your day-to-day productivity and annual profits. In fact, Cooper Bussmann says old age causes only 10% of electric motor failures. Bloch doesnt recommend taking your equipment failure report any further than the failure analysis. Create an archive reference of measurements to facilitate trend analysis and identify change of state conditions. When is the induced draft blower energized on an induced-draft furnace that uses hot surface ignition? When the liquid line is restricted, the supply of refrigerant to the metering device is reduced. Maintenance software and data gathering devices that integrate with third-party solution providers are ideal to accomplish this. c) 1/64th inch deflection per 1 inch span between drive shaft and driven shaft At the simplest level, all three phases of voltage should always have the same magnitude. Design is critical to the repair-replace decision. Reflections are generated when there is an impedance mismatch between the source and load. Nearly half (48 percent) of all motor failures are due to electrical issues, according to a survey by the Electric Power Research Institute (EPRI). It may also occur as a result of excessive starts or reversals. Often these mechanical faults are related: shaft imbalance, looseness, or misalignment left uncorrected will cause increased forces on the bearings which leads to rapid wear of the bearings. Possible solution: It is critical that the motor is kept as cool as possible, ensuring the operating environment is kept cool if possible will help prevent breakdowns. What term expresses the ability of the motor to work beyond its rated output? Which organizations specify standards for electric motors? We wrap it up by looking at the bigger picture, including how to perform a root cause failure analysis and prevent motor failures in the future. Its responsible for 51% of motor failures. Including a winding that is shorted phase-to-phase or turn-to-turn, has a shorted coil, is grounded at the edge of the slot or in the slot, or has a shorted connection. Non-rotating looseness happens between two normally stationary parts, such as a foot and a foundation, or a bearing housing and a machine. Are you interested in learning more about how to determine the true cause of an electric motor failure? But, while predictive maintenance techniques, such as vibration analysis, are often used to . Connected tools and sensors offer all key stakeholders with access to the data they need. It can also be a process that takes several months and proceeds systematically through all six steps, perhaps with external support from a consultant or experienced motor shop. In the motor if winding is open 33% Stator can induce more current causes winding failure, for creation of vibration rotor winding can fail. Heres how a motor failure report can help with motor management. Stator winding failures are generally attributed to groundwall or turn insulation failures. Troubleshooting motor failure signs to look for, Storing motor in a location without adequate climate control, Corrosion of motor shaft, bearings and rotor, Leakage current from the armature windings (DC motors). The first signs of this problem will be noise and overheating as the bearings begin to lose their original shape and metal fragments mix with the grease and increase bearing friction. Thankfully, computerized equipment and tools can detect issues at levels and in places that human senses arent able to. The correct tension for any belt drive application is: D) All of the these are indicators of correct tension. The open is usually caused by a blown fuse, an open contactor, a broken power line or bad connections. Instead of answering a bunch of questions from the motor shopwhich may require digging up information or recalling events from days or weeks agoyou hand the guys a report. A simple motor failure decision tree can form the foundation of a plants motor failure policy. These winding failures fall into four major categories related to what causes them: thermal stress, mechanical stress, electrical stress, and environmental stress. 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