Cooling fan overload
Cooling fan overload
(OP)
Currently commissioning a compressor skid, however having trouble with the motor running the cooling fan.
Basically the motor is rated for 15kw / 33.7amps OPERATING BETWEEN 380 - 415v however during the test the amp reading is 36amps. Have reduced the angle of the blades to reduce the effort and its now down to 14.3kw but still pulling 36amps. I was told by the lead electrical test to change the ABB overload to a higher rating, but I feel this only masks the problem as the problem seems to lie within the motor set up.
Any ideas or experience of similar, I am wandering if it could be a waiting issue.
Many Thanks,
B
Basically the motor is rated for 15kw / 33.7amps OPERATING BETWEEN 380 - 415v however during the test the amp reading is 36amps. Have reduced the angle of the blades to reduce the effort and its now down to 14.3kw but still pulling 36amps. I was told by the lead electrical test to change the ABB overload to a higher rating, but I feel this only masks the problem as the problem seems to lie within the motor set up.
Any ideas or experience of similar, I am wandering if it could be a waiting issue.
Many Thanks,
B





RE: Cooling fan overload
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Cooling fan overload
*RE above, last line. It is meant to say wiring issue, not waiting issue
RE: Cooling fan overload
RE: Cooling fan overload
eg: It is possible for 1 4% line to line voltage unbalance to cause an additional 15% current on the worst phase. This may cause overheating in the rotor as well as in the stator.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Cooling fan overload
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Cooling fan overload
RE: Cooling fan overload
On a centrifugal fan, load = flow. Over load then generally means one of two things: mechanical issues such as bearing friction, or more air flow than the fan motor was designed for. You were attempting to deal with that by adjusting the blade pitch, but maybe it wasn't enough, because someone went way overboard on the system design. One thing I see happen too often is that someone wants more flow, sees an inlet guide vane or outlet damper, and simply removes it or adjusts it beyond the fan's design capacity. There ain't no free lunch as they say, so the dumb animal that is the fan and motor is trying its hardest to satisfy the new system flow requirements, but is overloading the motor in the attempt.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Cooling fan overload
In line with what jraef has said the pitch of the blades had been designed to operate in low humidity / High temperature situations (26deg c to 46deg c stick it in the desert......) so changing the blades to suit a new set of calculations based on North Sea ambient conditions (-4 to +17) led us to reduce the blade pitch from 29 degrees to 23 degrees, reducing the load from 36amps to 29.8amps, below the 33.7amp the motor is designed for and still provides sufficient cfm of air to cool the main motor.
Thanks all, appreciate your comments
RE: Cooling fan overload
Thanks for coming back with the solution, as we love that around here.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Cooling fan overload
Must be summer North Sea conditions.
RE: Cooling fan overload
We had previously faced same problem some time ago. I would suggest that you read the name plate of cooling fan motor very carefully and ensure that whatever connections they say (Star or detla), you are connecting them in same way.
Also, I would suggest that to rule out if fault is inside motor, Remove the cooling fan from motor shaft (makes motor carry no load) and perform no load test by allowing motor to run on no - load. The no - load current should be between 30 - 40 % of the rated current for an induction motor. Then with the help of Clamp on Meter, measure current on all three phase leads. Are all three currents balanced? Also measure voltage on all three phase leads, they should also be equal. Also, check voltages at the motor terminal end when motor is running, because if cable if of not sufficient cross sectional area, then voltages shall be reduced at motor end and it will draw more current. Also, if one phase misses out of three phases, then current also increase (but it is not what seems in your case).
I totally agree with Jraef, don't increase the settings of Overload relay or you will burn the wnding.
My advice is to share the name plate data of motor, and remove all the load from motor shaft (remove fan), when you have only motor with you, switch it on, allowing motor to run without load, hear the sound of motor, check vibrations & temperature, monitor current on all three phases and voltages of all three phases both at MCC end and motor terminal end.
Share these data and we will soon resolve your problem. THanks,
RE: Cooling fan overload
Keith Cress
kcress - http://www.flaminsystems.com
RE: Cooling fan overload
" if cable if of not sufficient cross sectional area, then voltages shall be reduced at motor end and it will draw more current. "
Huh? The voltage will be there but motor will be starved for enough current and things start to get interesting.
Chuck
RE: Cooling fan overload
RE: Cooling fan overload
Scotty, So torque is proportional to Sq(v) and when torque decreases, slip is increased and motor draws more current?
Chuck
RE: Cooling fan overload
When torque decreases, slip is decreased and motor draws less current!
Walt
RE: Cooling fan overload
RE: Cooling fan overload
Will the slip increase in that case? Maybe, maybe not. If you decrease the voltage, and thus the torque CAPABILITY of the motor enough, the mass of its own rotor will at some point be enough of a load to make the slip increase. But if you simply place an unloaded motor on a bench and begin to give it less and less voltage than it was designed for, it will appear to be operating normally for quite a while before you will see the slip decrease significantly.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington