Maintenance and Troubleshooting
INSTRUCTOR INTRODUCTION;
Why do we perform preventative maintenance on motors? Without a proper maintenance schedule when something goes wrong with a motor you could be looking at, expensive repairs, buying a new motor, taking equipment out of service resulting in down time for a production line. A proper maintenance schedule is not going to guarantee that you’re not going to have any motor troubles, but what it is going to do is limit the troubles and down time that you would get without a proper maintenance schedule. We are about to look at a short video and from this video you will see why preventative maintenance is so important and what happens when you don’t have a proper maintenance schedule in place or perform proper and regular maintenance checks.
INSTRUCTOR TO SHOW THE FIRST VIDEO;
Why do we perform preventative maintenance on motors? Without a proper maintenance schedule when something goes wrong with a motor you could be looking at, expensive repairs, buying a new motor, taking equipment out of service resulting in down time for a production line. A proper maintenance schedule is not going to guarantee that you’re not going to have any motor troubles, but what it is going to do is limit the troubles and down time that you would get without a proper maintenance schedule. We are about to look at a short video and from this video you will see why preventative maintenance is so important and what happens when you don’t have a proper maintenance schedule in place or perform proper and regular maintenance checks.
INSTRUCTOR TO SHOW THE FIRST VIDEO;
INSTUCTOR INTRODUCTION;
MAINTENANCE AND TROUBLESHOOTING:
The very first thing that you should do before starting any type of maintenance on a motor is a visual inspection, a lot of times the trouble can be found just by looking, because if the problem is that bad then it should be very obvious by observation. Listed below are just some of the visual checks that you can perform before disconnecting the motor and taking it apart.
Visual and Mechanical Inspection:
An important aspect of large machine maintenance is the visual and mechanical inspection;
1. Inspect the machine’s physical and mechanical condition.
2. Check for signs of oil or water leakage.
3. Check for abnormal sounds or smells.
4. Check the surroundings for any environmental issues that may affect performance or service life.
5. Check for appropriate lubrication and lubrication systems.
6. Verify the bearing oil level.
7. Look for dirty oil or old oil ( should be replaced or tested)
8. Check for poor alignment
9. Make sure that there are no rough bearings due to corrosion or careless handling. This can be accomplished by either running the motor or by turning the motor over by hand and listening for any abnormal noise
If the visual inspection does not reveal any noticeable problems then the next thing that you can do are comprehensive electrical tests. Electrical tests performed on large motors can yield significant information as to the health of the machine. The collection of valid test data and the trending of that data are vital if overall machinery health is to be determined. Some of the more common electrical tests and procedures include;
1. Resistance measurements taken through bolted connections with a low resistance ohmmeter.
2. Phase to phase stator resistance tests.
3. Insulation – resistance tests on insulated bearings.
4. Testing and inspection of surge protection devices.
5. Testing and inspection of motor starters.
6. Resistance tests on resistance temperature detector (RTD) circuits.
7. Vibration testing of motor after it has started running.
8. Insulation power factor or dissipation – factor tests.
9. Surge comparison tests.
10. Power factor tip up tests.
11. Verification of machine space heater operation, if applicable
An Electric Research Institute (ERPI) study of electric motor failures indicated that 53% of electric motor failures are related to mechanical components and 47% to electrical faults. Mechanical defects have traditionally been detected using vibration analysis and infrared thermographs, while electrical defects have been detected with resistance tests, insulation tests, high potential tests, surge comparison tests and partial discharge testing.
Bearing failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Motor repair shops can attribute much of their business to bearing failures. And motor users see bearing failure as the fundamental cause of virtually every electric motor repair expense. Studies conducted by the Electrical Apparatus Service Association also demonstrated that bearing failures are by far the most common cause of motor failures.
In actual industrial environments bearing failure is caused by less –than- ideal lubrication. Because of contaminated lubrication, bearings fail well before they serve their theoretical life. There are many reasons for less-than-ideal lubrication, lubricants can leak out; chemical attacks or thermal conditions can decompose or break down lubricants; lubricants can be contaminated with non-lubricants such as water, dust, or rust from the bearings themselves. These lubrication problems can be eliminated. Motor bearings can last virtually forever by simply providing an ideal contamination free, well lubricated bearing environment. Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip seal or using sealed (lubricated for life) bearings. Such bearing protection techniques are often sufficient to allow bearings to last as long as the equipment itself.
Maintenance professionals may fine the following suggestions on how to forestall motor bearing failures, but some new techniques and technologies are available.
Lubricate Bearings at Correct Intervals;
Despite years of warning from bearing manufactures, over lubrication continues to plague many motor bearings. Too much grease can cause overheating of bearings. The lubrication instructions supplies by the motor manufacture will specify the quantity and frequency of lubrication. Generally, two pole motors should be greased twice a year, four pole and slowed motors only once a year.
Use the Best Available Grease;
The most commonly used bearing grease is polyurea-based, a low cost, low performance, highly compatible lubricant. However it does not handle water well, a serious drawback for many industrial applications. It reacts readily with water and loses its ability to lubricate bearings. Industrial motor bearings should be lubricated with synthetic-based aluminum complex grease. A high quality grease pays for its additional costs in reduced motor downtime and repair costs.
Keep Out Moisture;
Unless the motor is being hosed down or it operates in a humid environment, reasonably shielded motor bearings may not become contaminated with moisture while the motor is running. However, when the motor is shut down, moisture and condensation can collect on the surface of 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 resulting in premature failure of the bearing because of surface degradation.
Keep Out Dirt;
One successful approach to keeping 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 the suppliers, combine a tortuous labyrinth pate with impingement and centrifugal forces to trap and remove air-borne dirt and liquid; virtually no contamination can reach the bearing. Because the bearing isolator is a non-contact device, it will generally be the longest-lasting component of the motor. Bearing isolators constructed of bronze or other non-sparking materials also prevent hazardous sparks that could otherwise occur when the bearings rolling elements fail.
Other Suggestions;
Improved 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, high tech winding insulation, superior fan design, high performance paint (such as epoxy) and a strong rigid cast iron frame. Specifying permanent bearing protection for new motors, or retrofitting isolators onto existing equipment, usually requires initiative on the part of the user’s 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 right amount of clean uncontaminated, high quality lubricant allows bearings in most industrial motors to outlast all other motor components.
Listed below is a basic troubleshooting guide that you can follow to troubleshoot a motor and controls.
The very first thing that you should do before starting any type of maintenance on a motor is a visual inspection, a lot of times the trouble can be found just by looking, because if the problem is that bad then it should be very obvious by observation. Listed below are just some of the visual checks that you can perform before disconnecting the motor and taking it apart.
Visual and Mechanical Inspection:
An important aspect of large machine maintenance is the visual and mechanical inspection;
1. Inspect the machine’s physical and mechanical condition.
2. Check for signs of oil or water leakage.
3. Check for abnormal sounds or smells.
4. Check the surroundings for any environmental issues that may affect performance or service life.
5. Check for appropriate lubrication and lubrication systems.
6. Verify the bearing oil level.
7. Look for dirty oil or old oil ( should be replaced or tested)
8. Check for poor alignment
9. Make sure that there are no rough bearings due to corrosion or careless handling. This can be accomplished by either running the motor or by turning the motor over by hand and listening for any abnormal noise
If the visual inspection does not reveal any noticeable problems then the next thing that you can do are comprehensive electrical tests. Electrical tests performed on large motors can yield significant information as to the health of the machine. The collection of valid test data and the trending of that data are vital if overall machinery health is to be determined. Some of the more common electrical tests and procedures include;
1. Resistance measurements taken through bolted connections with a low resistance ohmmeter.
2. Phase to phase stator resistance tests.
3. Insulation – resistance tests on insulated bearings.
4. Testing and inspection of surge protection devices.
5. Testing and inspection of motor starters.
6. Resistance tests on resistance temperature detector (RTD) circuits.
7. Vibration testing of motor after it has started running.
8. Insulation power factor or dissipation – factor tests.
9. Surge comparison tests.
10. Power factor tip up tests.
11. Verification of machine space heater operation, if applicable
An Electric Research Institute (ERPI) study of electric motor failures indicated that 53% of electric motor failures are related to mechanical components and 47% to electrical faults. Mechanical defects have traditionally been detected using vibration analysis and infrared thermographs, while electrical defects have been detected with resistance tests, insulation tests, high potential tests, surge comparison tests and partial discharge testing.
Bearing failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Motor repair shops can attribute much of their business to bearing failures. And motor users see bearing failure as the fundamental cause of virtually every electric motor repair expense. Studies conducted by the Electrical Apparatus Service Association also demonstrated that bearing failures are by far the most common cause of motor failures.
In actual industrial environments bearing failure is caused by less –than- ideal lubrication. Because of contaminated lubrication, bearings fail well before they serve their theoretical life. There are many reasons for less-than-ideal lubrication, lubricants can leak out; chemical attacks or thermal conditions can decompose or break down lubricants; lubricants can be contaminated with non-lubricants such as water, dust, or rust from the bearings themselves. These lubrication problems can be eliminated. Motor bearings can last virtually forever by simply providing an ideal contamination free, well lubricated bearing environment. Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip seal or using sealed (lubricated for life) bearings. Such bearing protection techniques are often sufficient to allow bearings to last as long as the equipment itself.
Maintenance professionals may fine the following suggestions on how to forestall motor bearing failures, but some new techniques and technologies are available.
Lubricate Bearings at Correct Intervals;
Despite years of warning from bearing manufactures, over lubrication continues to plague many motor bearings. Too much grease can cause overheating of bearings. The lubrication instructions supplies by the motor manufacture will specify the quantity and frequency of lubrication. Generally, two pole motors should be greased twice a year, four pole and slowed motors only once a year.
Use the Best Available Grease;
The most commonly used bearing grease is polyurea-based, a low cost, low performance, highly compatible lubricant. However it does not handle water well, a serious drawback for many industrial applications. It reacts readily with water and loses its ability to lubricate bearings. Industrial motor bearings should be lubricated with synthetic-based aluminum complex grease. A high quality grease pays for its additional costs in reduced motor downtime and repair costs.
Keep Out Moisture;
Unless the motor is being hosed down or it operates in a humid environment, reasonably shielded motor bearings may not become contaminated with moisture while the motor is running. However, when the motor is shut down, moisture and condensation can collect on the surface of 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 resulting in premature failure of the bearing because of surface degradation.
Keep Out Dirt;
One successful approach to keeping 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 the suppliers, combine a tortuous labyrinth pate with impingement and centrifugal forces to trap and remove air-borne dirt and liquid; virtually no contamination can reach the bearing. Because the bearing isolator is a non-contact device, it will generally be the longest-lasting component of the motor. Bearing isolators constructed of bronze or other non-sparking materials also prevent hazardous sparks that could otherwise occur when the bearings rolling elements fail.
Other Suggestions;
Improved 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, high tech winding insulation, superior fan design, high performance paint (such as epoxy) and a strong rigid cast iron frame. Specifying permanent bearing protection for new motors, or retrofitting isolators onto existing equipment, usually requires initiative on the part of the user’s 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 right amount of clean uncontaminated, high quality lubricant allows bearings in most industrial motors to outlast all other motor components.
Listed below is a basic troubleshooting guide that you can follow to troubleshoot a motor and controls.
| maintenance_and_troubleshooting_guide.docx |
STUDENTS NOW WE WILL WATCH A VIDEO ON MAINTENANCE AND TROUBLESHOOTING;
