Multiple AC Drives on a Single Line Reactor

Summary

Multiple AC Drives on a Single Line Reactor

Question

Can multiple AC drives be installed on a single line reactor?

Environment

Pulse Width Modulated (PWM) AC Drives

Answer

Reference Wiring and Grounding Guidelines for Pulse Width Modulated (PWM) AC Drives Installation Instructions, publication DRIVES-IN001.

Use a separate line reactor for each drive that shares a common power line. Individual line reactors provide filtering between each drive to provide optimum surge protection for each drive. However, if it is necessary to group more than one drive on a single AC line reactor, use this process to verify that the AC line reactor provides a minimum amount of impedance:

• In general, up to five drives can be grouped on one reactor.
• Add the input currents of the drives in the group.
• Multiply that sum by 125%.
• Refer to 1321 Power Conditioning Products Technical Data, publication 1321-TD001 to select a reactor with a maximum continuous current rating greater than the multiplied current
• 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, the reactor will not provide proper protection to the smallest drive. Select a reactor with a larger inductance and same amperage, or regroup the drives into smaller groups and start over.

The impedance of the drive and the impedance of the reactor can be calculated as follows, where L is the inductance of the reactor in Henries and f is the AC line frequency in Hz:

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).

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Source: Rockwell Automation’s Technote database.