I have a project coming up at my plant in which we are installing a new boiler. One of my primary concerns is the boiler forced draft fan. The project is still in the preliminary phases, but I am told that the forced draft fan motor will be anywhere from 200hp to 500hp depending on the boiler chosen.
I have 2400v and 480v switch gear available to serve this load.
What is the rule of thumb for the maximum motor hp served at 480v?
Is there an IEEE or other recommended practice for this question?
Depends on the size of the transformer supplying each voltage level.
480V is ususally limited to 3kVA due to the commonly available maximum secondary protection by switchgear. THat size may soon to change if we want to limit the available arc-flash duty for service on the swgr. 2400V is becoming an obsolete voltage, from the industrial standpoint, so equipment associated with it, including motors will not be as readily available in teh future, or even now. It still remains a relaiviely popular utility distribution level.
Our Corporate Standards used to limit the motors to be served @ 480V to 200HP, but now there is a qualifier to open it up the 200-500HP range to individual cosnideration if those motors are driven by a SSRV or ASD. (This is pretty much in line with the Petrochemical Industry Standards/Practice.) These larger motors often feed directly from the switchgear by a dedicated breaker, rather than form the MCC.
The secondary consideration is the overall cost. The distance of the motor form the starter can substanially sway that.