400 hp hammermill motor common failure once a year
400 hp hammermill motor common failure once a year
(OP)
I have a 400 hp motor on a hammermill that has failed every year for the past seven years.
The motor is equipped with a telamecanique altistart 48 soft start and is 3 phase 480 volt. This hammermill is used to grind corn for a feed mill.
When the motors are taken to a motor shop, it always reveals that it appears to be an overload. After studying how the hammermill is operated, it is never overloaded nor exceeds its nominal nameplate current. The softstart, I believe, has been programmed correctly.
We have tried several different brands of motors and all have had the same result. The insulation is deterioted and goes to ground.
I have had several people to look at this application and I still have no answers.
Any help would be greatly appreciated.
The motor is equipped with a telamecanique altistart 48 soft start and is 3 phase 480 volt. This hammermill is used to grind corn for a feed mill.
When the motors are taken to a motor shop, it always reveals that it appears to be an overload. After studying how the hammermill is operated, it is never overloaded nor exceeds its nominal nameplate current. The softstart, I believe, has been programmed correctly.
We have tried several different brands of motors and all have had the same result. The insulation is deterioted and goes to ground.
I have had several people to look at this application and I still have no answers.
Any help would be greatly appreciated.





RE: 400 hp hammermill motor common failure once a year
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 400 hp hammermill motor common failure once a year
RE: 400 hp hammermill motor common failure once a year
Keith Cress
kcress - http://www.flaminsystems.com
RE: 400 hp hammermill motor common failure once a year
How close are the phase voltages while it's running?
Keith Cress
kcress - http://www.flaminsystems.com
RE: 400 hp hammermill motor common failure once a year
For a ODP motor, the problem is more difficult to deal with. The dust will get inside the motor, clogging the stator core cooling vents and the stator-rotor air gap. This will dramatically reduce the motor's ability to cool itself and lead to winding failures that have a uniform dark appearance similar to an overload. Unfortunately, it may be difficult or impossible to adequately blow the dust out of the motor interior. This will be especially true if the motor interior is contaminated with grease or oil that will cause the dust to coagulate into a solid mass.
If you have a ODP motor and are unable to swap to a TEFC motor due to space limitations or budget, you should consider removing the ODP motor every six months for cleaning. The cost to clean a motor is only a fraction of the cost to rewind one and the time required for cleaning is also much shorter than rewinding. It sounds like you should have several of these motors laying around by now so you may be able to swap, or rotate, motors every six months with minimum downtime.
RE: 400 hp hammermill motor common failure once a year
If it is bypassed, do you have an OL relay in the circuit so that the motor is still being protected once the bypass contactor closes? I've seen that one time and time again. The problem is, the diagrams that Telemecanique puts into their manuals do NOT show a thermal OL relay in the circuit! They simply add this statement as a footnote:
"External differential thermal protection will need to be added."
So people who don't fully read all instruction details (translate to mean MOST MEN) fail to notice and don't put in an OL relay at all. Then once the bypass contactor pulls in, the motor is running completely unprotected and nobody realizes it!
Worst possible scenario: are you using the dreaded "inside the delta" connection of the soft starter to save money on the soft start size? If so, that is a quick way to damage motors! If you have one shorted SCR or one welded contactor, you have power flowing through one winding at all times, with nothing but the fuses or breaker to protect it from damage. Usually, the current flow is enough to cause something to clear, but that is not guaranteed.
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RE: 400 hp hammermill motor common failure once a year
A conventional overload relay would not detect over temperature, only over current!
RE: 400 hp hammermill motor common failure once a year
RE: 400 hp hammermill motor common failure once a year
RE: 400 hp hammermill motor common failure once a year
RE: 400 hp hammermill motor common failure once a year
UPDATE: I did a vibration analysis on the machine, and the result was the base was flexing and that the anchor system was not Sufficient. After reanchoring and grouting the machine, also found that the rotor inside the machine was out of tolerance by an eight of an inch causing an imbalance. Replaced rotor, vibration has disappeared. Thank you all for your responses.
RE: 400 hp hammermill motor common failure once a year
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 400 hp hammermill motor common failure once a year
Or are these just additional facts to fill in the case study ?
=====================================
(2B)+(2B)' ?
RE: 400 hp hammermill motor common failure once a year
After repairs were made, vibration was .185 in/sec.
RE: 400 hp hammermill motor common failure once a year
Had a similar problem with a pellet mill in a feed mill,
found the operators would plug up the pellet mill, instead of
cleaning it out they would "plug the motor" to try and free it up,
was also through a Benshaw soft start, number of starts per hour
for a 400 hp motor is very low, one or two per hour recommended, a
softstart may help that, but if your exeeding this number of starts/hour
by a large amount, the heat build up in the motor is significant.
RE: 400 hp hammermill motor common failure once a year
RE: 400 hp hammermill motor common failure once a year
you are likely seeing the cause of overheating. First thing would be to check which class of O/L your set up for. Bearings will dump thier grease at elevated temps, leading to shortened cycles. Exceeding belt tensions on overhung loads are a potential from maintenance. Do you monitor the frequency of starts? Are you regulating the mill's rotor current, possibly via a feed system?