Rockwell Automation 1336T Wiring and Grounding Guide, (PWM) AC Drives - Manual (Page 44)

44 Rockwell Automation Publication DRIVES-IN001M-EN-P - March 2014
Chapter 2 Power Distribution
• Use the formula below to verify that the impedance of the selected reactor
is more than 0.5% (0.25% for drives with internal inductors) of the
smallest drive in the group. If the impedance is too small, select a reactor
with a larger inductance and same amperage, or regroup the drives into
smaller groups and start over.
EXAMPLE There are five drives. Each drive is rated 1 Hp, 480V, 2.7 A. These drives do not
have internal inductors.
Total current is 5 x 2.7 A = 13.5 A
125% x Total current is 125% x 13.5 A = 16.9 A
From 1321 Power Conditioning Products Technical Data, publication 1321-
TD001 , we selected the catalog number 1321-3R12-C reactor. This reactor has
a maximum continuous current rating of 18 A and an inductance of 4.2 mH
(0.0042 henries).
1.54% is more than the 0.5% impedance recommended. The catalog number
1321-3R12-C reactor can be used for the five 2.7 A drives in this example.
Z
drive
=
Z
reactor
= L * 2 * 3.14 * f
V
line-line
3 * I
input-rating
L is the inductance of the reactor in henries and f is the AC line frequency.
Z
drive
=
V
line-line
3 * I
input-rating
480V
3 * 2.7
= = 102.6 Ohms
Z
reactor
= L * (2 * 3.14) * f = 0.0042 * 6.28 * 60 = 1.58 Ohms
Z
reactor
Z
drive
1.58
102.6
= 0.0154 = 1.54% =