I have an ongoing problem that happens rarely enough to pinpoint, but enough to be irritating. I have a 3 phase, 440 volt, 17 amp, 7.5 Kw motor installed as a suction blower on a paper sheeting machine. When the machine is running production, the motor runs well within it's current limit of 17 amps. When the machine is started and stopped, the motor starts up and runs fine. The problem is when the machine is powered down for an extended period of time (days) and them restarted. This is when it blows 2 fuses. The fuses we were using were Bussman-LPS-RK-25, dual element time delay fuses, we now use Amp Trap AJT-25, dual element time delay fuses. Each has the same end result. The motor is fed from a MCC bucket and the only other thing tied into these main fuses is the control transformer inside the bucket, which has primary fusing at 1.5 amps. These fuses are not blowing. I have megged the motor and the wires, resistance checked the transformer and starter and have found nothing wrong. Let me mention that this same thing happens on the exact same motor of an identical machine. If anyone has any insight to this issue, any and all help would be appreciated. Thanks.
blowing fuses at start up
- Thread starter spongebob
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: blowing fuses at start up
The code would permit the use of 30 amp time delay fuses on that motor. (Table 430.52) There may be additional "inrush" load or a longer start up time when the motor has not been used for a few days. This extra start up load could exceed the rating of the 25 amp fuses. This may be a lubrication, temperature or mechanical issue.
Don
The code would permit the use of 30 amp time delay fuses on that motor. (Table 430.52) There may be additional "inrush" load or a longer start up time when the motor has not been used for a few days. This extra start up load could exceed the rating of the 25 amp fuses. This may be a lubrication, temperature or mechanical issue.
Don
- Location
- Bremerton, Washington
Re: blowing fuses at start up
Do you have a clamp on electronic amp meter? If so try it to record the max inrush current. If the motor is not coming up to speed within a few cycles it will draw above FLA and blow the fuses. If you get the time current curve for the fuses you can see how long it will hold a particular current.
"Its always an electrical problem" is not true. The motor is resonding to some load on start up, I agree with Don, its a mechnical issue.
Start it after shut down with the clamp on meter and see how long the current is above FLA.
Do you have a clamp on electronic amp meter? If so try it to record the max inrush current. If the motor is not coming up to speed within a few cycles it will draw above FLA and blow the fuses. If you get the time current curve for the fuses you can see how long it will hold a particular current.
"Its always an electrical problem" is not true. The motor is resonding to some load on start up, I agree with Don, its a mechnical issue.
Start it after shut down with the clamp on meter and see how long the current is above FLA.
G
Guest
Guest
Re: blowing fuses at start up
In my experience in the electric motor field i agree that mechanical problems are very possibly the problem. If this is a blower that picks up and ejects material from the sheeting pocess it is very possible that this material is damp fibre. When the machine is runnining normally this stuff is probably ejected just fine. Shut down with wet material attached to the blades of the blower it hardens and is an additive load to the wheel when it restarts. Just A guess anyways good luck.
In my experience in the electric motor field i agree that mechanical problems are very possibly the problem. If this is a blower that picks up and ejects material from the sheeting pocess it is very possible that this material is damp fibre. When the machine is runnining normally this stuff is probably ejected just fine. Shut down with wet material attached to the blades of the blower it hardens and is an additive load to the wheel when it restarts. Just A guess anyways good luck.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: blowing fuses at start up
spongebob
Don hit it right on the head as I have had this very problem with a fiber condenser. What we found was we changed to a new grease that had a higher viscosity at lower temps and when the motor was allowed to cool off it would blow the fuses. We had to go back to the lighter grease.
spongebob
Don hit it right on the head as I have had this very problem with a fiber condenser. What we found was we changed to a new grease that had a higher viscosity at lower temps and when the motor was allowed to cool off it would blow the fuses. We had to go back to the lighter grease.
- Location
- Massachusetts
Re: blowing fuses at start up
While I worked at an amusement park we would literally control the speed of the roller coaster cars by the viscosity of the oil used in the wheel bearings.
In the early spring with cool temps and rusty track we would run 10 weight or else we would occasionally get a car "stuck" on the roll backs at the top of a hill.
Sorry for going off topic, but I agree with Don and Wayne I would look into the lubricants being used in the motor and fan bearings.
While I worked at an amusement park we would literally control the speed of the roller coaster cars by the viscosity of the oil used in the wheel bearings.
In the early spring with cool temps and rusty track we would run 10 weight or else we would occasionally get a car "stuck" on the roll backs at the top of a hill.
Sorry for going off topic, but I agree with Don and Wayne I would look into the lubricants being used in the motor and fan bearings.
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