Rockwell Automation 1391 USER MNL/DIGITAL AC SERVO DR - Manual (Page 93)

Chapter 10
Transformers and Shunt Regulators
10-5
Frequent overvoltage trips and blown fuse on high inertia systems during
regenerative states (deceleration) may be an indication that an external
shunt resistor having increased power dissipation capacity is required.
Based on the data supplied, Allen-Bradley will specify a shunt resistor with
the proper resistance value for the drive being used.
Shunt Regulator Installation External Shunt Resistors
The 1391-DES is designed to allow the use of an external shunt resistor on
the 22.5 and 45A units. To use an external shunt resistor with the 22.5A
units, the user must reconfigure the drive at terminal block TB5.
The following steps provide the information needed to properly convert
22.5A drives for use with an external shunt resistor and fuse. Refer to the
resistor and fuse mounting dimensions provided in Appendix A and the
Interconnect Diagram in Appendix B, as required. A minimum wire size of
12 AWG (2.5 mm
2 ) must be used when connecting an external resistor.
ATTENTION: To guard against an electrical shock hazard,
ensure that all power to the drive has been removed prior to
performing the following procedure and the bus voltage at
terminal 9 (+) and 7 (–) of TB5 measures 0.00 volts.
!
1. Remove and discard the jumper present between terminals 8 and 10 of
TB5. This disconnects the internal shunt resistor and fuse from the
shunt regulator circuit.
ATTENTION: When using an external shunt resistor assembly
with the 22.5A 1391-DES, ensure that the internal resistor
assembly has been disconnected per the above instructions.
Personal injury and/or equipment damage could result from an
overheated resistor if the internal resistor is not disconnected.
!
2. Connect one end of the new external shunt fuse to terminal 9 of TB5.
Connect the other end of the fuse to one end of the shunt resistor.
Important: The external shunt resistor must have a fuse in series with
the shunt resistor. Refer to the paragraph entitled “Shunt Fusing” for
more information.
3. Connect the remaining end of the shunt resistor to terminal 8 of TB5.
4. Using Table 10.B, set the Duty Cycle Selector Switch to the
appropriate setting for the resistor being used.
5. Install the appropriate shunt fuse in its holder.