Large Induction Motor Experience
Large Induction Motor Experience
(OP)
I'm looking for any experience feedback or comments on the use of induction motors in the range of 10,000 hp - 25,000 hp, at any speed. I'm not concerned about starting methods, etc, since we can design the system to adequately take care of starting. I'm more concerned about machine issues such as reliability, failure modes that might be more pronounced in this size range, operating issues, etc. Any personal experience feedback in this regard, or pointers to studies or surveys would be greatly appreciated. I have reference lists from several suppliers, but am interested in the user's perspective.
Thanks
Thanks





RE: Large Induction Motor Experience
I've some experience in caring for motors in your size range. I find no particular accelerated incidence of failure related to size.
You may want to consider on-line diagnostic equipment such as offered by Iris or others.
Obviously, protection of your investment is a consideration, and I'd recommend good protective relaying with advanced capabilities, i.e., GE UR or SR series, or Schweitzer. I'm familiar with those.
You will also want to include a very comprehensive regimen of inspection and testing during periodic maintenance. Since these things aren't portable, in situ preventive maintenance is an issue.
Actually, the only real problems I've had are related to starting issues: utility voltage sags due to offsite switching issues, incomplete cycle on synchronous motors due to operational issues, etc.
old field guy
RE: Large Induction Motor Experience
I do know that motors of this size do not like to be started very often. The physical movement of the coils and the stresses on the rotor take their toll.
RE: Large Induction Motor Experience
RE: Large Induction Motor Experience
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
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RE: Large Induction Motor Experience
You really need to prepare a good specification document because there are some areas that manufacturers can take shortcuts.
What is your application? Is this a compressor train that runs 10 years without shutting down, or an extruder that starts and stops many times per week? What is your reliability target for this machine; how long can you be down for repair until major production losses occur?
Incorporate any commonalities into this machine that may exist in a future spare machine such as shaft height, terminal box location, etc. Search surplusrecord.com to see what's available now to get an idea.
Consider installation and removal of the motor at its installed location for repairs. If possible, leave room or provisions for heavy lift equipment (cranes, etc.) to be sited near the motor for repair/replacement.
If you don't have access to API-541 (American Petroleum Institute guideline for large induction motors), I would recommend getting it as a reference and potentially a specification basis.
If this machine is very critical to operations, I would recommend heat run and winding immersion tests; both witnessed. Expect the stator to fail the immersion test at least once and incorporate this (rewinding or building a new stator) into the delivery schedule with your internal procurment/project department.
These motors are pretty low maintenance, but good online monitoring is important. Some important things to monitor are internal air temperature, winding temperature, bearing temperature, vibration, current signature analysis, and partial discharge (especially above 10kV).
Protection is also important, but this also depends on what operational constraints you have. In some processes, the motor is sacrificial, most others it is not.
If there is a lot of fines in the area (powder, dust, dirt, etc.) then consider getting a TEWAC or TEAAC enclosure. We have had very good results with these enclosures with reliability significantly better than WP-II style enclosures within our large motor population.
I'm not a motor expert, but we do have a fair number of very large machines in my area. Let me know if there is anything specific you would like to ask. Most of the information above is based on the assumption this will be a newly manufactured motor.
RE: Large Induction Motor Experience
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Large Induction Motor Experience
We have had sucess indentifying motor issues with CSA. We use a tester from a company called PdMA.
RE: Large Induction Motor Experience
Good post indeed deserving a star.
What is a "winding immersion test" ?
RE: Large Induction Motor Experience
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Large Induction Motor Experience
RE: Large Induction Motor Experience
I can understand OEMs' taking objection to this rather stringent test. The IEEE/IEC standards I use (for rewinds) don't call for such a test.
Unless it is a submersible motor (which is invariably LV and low HP), I don't see the point of such a test.
Do you happen to have a reference standard for this test ?
RE: Large Induction Motor Experience
While the test can be a little intimidating for the supplier, it can also be a little intimidating for the buyer. I personally would be nervious about putting a "brand new" critical motor into my plant which had already been operated flooded. My preference would be to test take some sample coils and clamp steel plates to the slot sections to simulate the actual motor. Then put those sample coils in the tank at the same time as the actual stator. Then do sumbersion test on the coils. If they fail, the stator has to be rewound (condition of the contract).
It may not be quite as thorough as testing the whole motor since you don't have any connections which may be a weak point in the insulation. But at least you don't have any concern about lingering damage or contaminants which may exist from the test.
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RE: Large Induction Motor Experience
20.18 MACHINE WITH SEALED WINDINGS—CONFORMANCE TESTS
An alternating-current squirrel-cage machine with sealed windings shall be capable of passing the following tests:
20.18.1 Test for Stator Which Can Be Submerged
After the stator winding is completed, join all leads together leaving enough length to avoid creepage to terminals and perform the following tests in the sequence indicated:
a. The sealed stator shall be tested while all insulated parts are submerged in a tank of water containing a wetting agent. The wetting agent shall be non-ionic and shall be added in a proportion sufficient to reduce the surface tension of water to a value of 31 dyn/cm (3.1 microN/m) or less at 25°C.
b. Using 500 volts direct-current, take a 10-minute insulation resistance measurement. The insulation resistance value shall not be less than the minimum recommended in IEEE Std 43.
(Insulation resistance in megohms ? machine rated kilovolts plus 1.)
c. Subject the winding to a 60-hertz high-potential test of 1.15 times the rated line-to-line rms voltage for 1 minute. Water must be at ground potential during this test.
d. Using 500 volts direct-current, take a 1 minute insulation resistance measurement. The insulation
resistance value shall be not less than the minimum recommended in IEEE Std 43. (Insulation
resistance in megohms ? machine rated kilovolts plus 1.)
e. Remove winding from water, rinse if necessary, dry, and apply other tests as may be required.
20.18.2 Test for Stator Which Cannot Be Submerged
When the wound stator, because of its size or for some other reason, cannot be submerged, the tests
shall be performed as follows:
a. Spray windings thoroughly for one-half hour with water containing a wetting agent. The wetting
agent shall be non-ionic and shall be added in a proportion sufficient to reduce the surface tension
of water to a value of 31 dyn/cm (3.1µN/m) or less at 25°C.
b. Using 500 volts direct-current, take a 10-minute insulation resistance measurement. The
insulation resistance value shall not be less than the minimum recommended in IEEE Std 43.
(Insulation resistance in megohms > machine rated kilovolts plus 1.)
c. Subject the winding to a 60-hertz high-potential test of 1.15 times the rated line-to-line rms voltage
for 1 minute.
d. Using 500 volts direct-current, take a 1-minute insulation resistance measurement. The insulation
resistance value shall be not less than the minimum recommended in IEEE Std 43. (Insulation
resistance in megohms ? machine rated kilovolts plus 1.)
e. Rinse winding if necessary, dry, and apply other tests as may be required.
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RE: Large Induction Motor Experience
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RE: Large Induction Motor Experience
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RE: Large Induction Motor Experience
You also need to specify XY proximity probes, and you need to carfully consider the coupling type, including prestretch if using a discpack style. The flimsy frame also means that it is important to do a good job of designing the foundation and sole plates, and installing the motor. A twisted motor frame will deform the stater assemble, screw up air gaps, resulting in a motor that runs rough.
Oil seals on the bearing housing are also important, but most big motors use a Renk bearing assembly and oil leakage into the motor housing is not much of a problem. Motor cooling however can be, I was involved with a 10,000 Hp air cooled motor that had a tendancy to suck in rain water, resulting in a explosion as it shorted phase to phase while being started during a rain storm.
My two cents for what it is worth....
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RE: Large Induction Motor Experience