Line Reactor Size

Status
Not open for further replies.
ptonsparky said:
Customer with a PwrFlex4 feeding a 3 HP pump. 480v.
They had a 5 HP unit that was giving them a great deal of grief so we changed it to the 3 HP unit they had as a spare..
The existing line reactor is sized for a 5 HP motor. Is it advisable to change to the 3?
Click to expand...
I wouldn't.
 
Besoeker3 said:
Just the current would be less. We'd still make them 20uH
Click to expand...
Just wondering why you'd use 20uH reactor! My computations doesn't match what you are saying.
Besides, AB's manual say it's 5mH for 3HP and 3mH for 5HP. Can we have clarifications from you?
 
ptonsparky said:
The LRs we have are rated in current, not mH. I would guess if I look back the data sheets would tell me. The newer models list both.
Click to expand...
This is a snapshot of the Allen Bradley manual that I was talking about. Please see that it shows the inductance of the recommended line reactors for each size of VFD. Better still, you can calculate the required line reactor inductance using the formula:
XL = %Z x voltage/(1.732 X amps); L = XL/(2 x pi x freq).
In this case: Capacity = 3HP; Amps = 4.8 A; frequency = 60Hz; Voltage = 480V and %Z = 3%
Substituting: XL = (0.03 x 480)/(1,732 x 4.8) = 1.7 ohms and L = (1.7 ohms)/(2 x 3.1416 x 60) = 4.6 mH ~ 5 mH.

line reactors, 480V - AB.jpg
 
ptonsparky said:
Customer with a PwrFlex4 feeding a 3 HP pump. 480v.
They had a 5 HP unit that was giving them a great deal of grief so we changed it to the 3 HP unit they had as a spare..
The existing line reactor is sized for a 5 HP motor. Is it advisable to change to the 3?
Click to expand...
The line reactor is there to add some impedance to the line. For most small VFDs it is not really needed anyway.
 
Status
Not open for further replies.
Top