3 phase AC motor derating calculation
3 phase AC motor derating calculation
(OP)
Hi,
I am trying to figure out when I am varying the voltage and cycle of a three phase AC motor, what kind of derating would I need to do. I know if I am switching from 60Hz to 50Hz, the HP(final)=HP(initial)*50/60. Is there anyway to calculate change of RPM and other parameters? How do I derate my motor HP if my voltage changed.
Thanks
I am trying to figure out when I am varying the voltage and cycle of a three phase AC motor, what kind of derating would I need to do. I know if I am switching from 60Hz to 50Hz, the HP(final)=HP(initial)*50/60. Is there anyway to calculate change of RPM and other parameters? How do I derate my motor HP if my voltage changed.
Thanks





RE: 3 phase AC motor derating calculation
Otherwise, check here first and come back with any specific questions: FAQ237-1224: Motors: Changing between a 50 and 60Hz supply.
RE: 3 phase AC motor derating calculation
But see the excellent FAQ FAQ237-1224: Motors: Changing between a 50 and 60Hz supply.: Motors: Changing between a 50 and 60Hz supply
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3 phase AC motor derating calculation
RE: 3 phase AC motor derating calculation
"If the load remains the same and the voltage is lowered the motor will draw more current to continue meeting the load's hp requirement. Remember the motor will still be running at the same speed since the frequency wasn't changed." Would I run into any heating problem?
RE: 3 phase AC motor derating calculation
But it depends on several things.
For instance:
Does the motor run continuously or for more than, say, 20 minutes at a time.
Is the motor running at its rated output?
Is the load constant?
If that motor is running at its rated hp and you shave off 10% of its voltage the current will now be over name plate and its early demise is assured.
If the motor's constant load is 10% less than its rated hp it may be fine as the current won't be exceeding name plate.
Or if it's only cyclically loaded and is idling most the time it will cool between the otherwise short over-currenting events.
Not an easy call from here.
Main thing is if you have a motor going into that situation, you leave space for several boost transformers and then measure the motor current while the motor is working. If it's below name plate it's OK if it's over name plate put in the transformers.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 3 phase AC motor derating calculation
RE: 3 phase AC motor derating calculation
RE: 3 phase AC motor derating calculation
RE: 3 phase AC motor derating calculation
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3 phase AC motor derating calculation
P=>hp
That motor, like a faithful dog, is going to want to turn at its rated speed and deliver the needed hp. The hp comes from the power it draws. If the voltage drops the only way for it to still get the power is for the current to rise. You are right this is not linear but for the first 10% of abuse it's fairly linear.
Keith Cress
kcress - http://www.flaminsystems.com
RE: 3 phase AC motor derating calculation
Cowern has a knack for keeping his explanations simple and easy to read, understand and implement.
You probably know this but others may be interested.
http:/
Bill
--------------------
"Why not the best?"
Jimmy Carter