bengineer08 (Customer) asked a question.
Hello,
We're having some issues with a relatively new large sanding machine. The main motor is 15kW, it's driving multiple pulleys and belts. We keep getting amperage overload trips on startup (measuring sometimes upward 80A, adjustable motor starter only adjustable up to 63A, think the motor name plate says 50-something A). We disconnected everything from the motor, and the motor seems to run fine on it's own. We checked all the bearings belts, etc.. and nothing seemed worn or damaged. The belts were somewhat tough to move by hand, but they could actually be started moving by hand. If we can get it started running, it'll seem to run fine after that. The manufacturer has been in and out, but seems to have given up.
We're thinking that either the motor and drives are undersized to account for the start up load, or that we might benefit from a soft starter.
Now to the question:
If we replace the Wye-Delta contactors with a soft start, will it be likely that we'll still see the 80A demand on start up and still trip the overload?
I'd be willing to just buy one and try if it were a couple hundred bucks, but the size I'm looking at is a grand or two...
Incidentally, does anyone know if a large soft starter can be returned if it's been used (assuming it's in good working order) and doesn't work for the scenario?
If it trips on contactor,most likely will trip on softstart as well....80A at start up for 50A motor is perfect,should be much higher...try replacing OL may be...also check the wiring if its happening from the begining...timer set points.
In my past life, I worked with somewhat big Centrifuges.. 60hp and 100 hp units.. The Spinning member weights up to 1,500 Lbs.. On Y-Delta Start.. Usually takes 8 Minutes to get to speed.. That is 8 Minutes in Y Start Mode..
Generally the Y-Start had a different Overload Device for that, and then a 'Main Overload' that went into the Circuit on the Delta Run..
My Favorite was my little 60 Hp unit ( Westfalia SA-80 ).. In playing around with it for Production Changes.. We put a 100 HP VFD on it, and programmed it to Start at 'Amperage Limited Start'.. It would get to speed in 2 Minutes.. That was impressive!.. Generally the Thought was it was too much Torque on the Bearings and belts, So I cut it back to a 5 Minute start ramp..
My take on all of this, is it's not amp draw, it's winding heat that you have to worry about. My C fuges were limited to 2 Starts per day as per the Motor MFG.. As it takes a while for the Hot Spots Deep in the Windings to settle down..
I think the same thing applies here.. Put a separate Start Overload to protect the motor from 'Gross Overload' During starting, Like Locked Rotor Start from Bearing Failure or the like, then have your Normal Overload for the Running Overload of operation Overloads.. And limit the number of Starts you do per day
Cap
15KW motor is about 20 HP. What voltage are you using? What class of overloads? 10, 20, 30? When does it trip? Wye or Delta stage? (as stated above) Have the contactors been examined for wear and proper operation?
Excessive belt tension can be an issue.
It's 230V. It'll trip on Startup, during wye stage. If we can get it to delta, it seems to run fine. contactors all appear fine, and are relatively new, the machine hasn't been run too often because of this.
Belts have been checked, went through the machine looking for bad bearings or misalignment etc... but all appears good.
We'll probably try the larger size overload, one to handle 80A. But then my concern is for the contactors themselves. It seems they would need to be upsized too? I finally dug up the data sheet, and it appears they're only rated for 32A / 12.5kW.
It just feels like this whole set up is just a little bit undersized.
How long is the motor in this overload situation of 80 amps?
Again class 10,20 or 30 overloads. They make a difference. Think 10, 20 or 30 second delays.
Are you sure the motor is starting in wye?
Replacing the overload block may help but will allow the smoke to come out if you set it at over the Nameplate FLA of the motor.
Undersized motor & equipment is a very good thought.