Rockwell Automation Allen-Bradley PowerFlex 7000, Руководство пользователя

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Rockwell Automation Publication 7000L-UM301F-EN-P - March 2020 271
Component Definition and Maintenance Chapter 5
When the MOV is clipping the voltage transient, the energy of the transient is
being absorbed by the MOV. The varistor has a limited energy absorbing
capability and generally there is not enough time for the heat generated to be
conducted out of the device. The MOV is sized based on the steady-state voltage
rating, the energy in the transient, and the repetition rate of the transients. A
critical element in the MOV selection and protection offered is the impedance in
the line supplying the transient. This impedance will be mainly that provided by
the Isolation Transformer or the AC Line Reactor on the input of the drive. That
is why an impedance level is specified for these input devices.
MOV Fuse
In series with each of the Phase MOVs is a medium voltage fuse. As seen in
Figure 225 , these fuses may be located on the assembly or remote from the
assembly (on the Line Terminal Module). Check the part number on your
module and the information in this documentation to determine which assembly
you should have in your case.
The fuses provide overload protection for the conductors feeding the suppression
network (and overcurrent protection if a short circuit occurs on the downstream
side of the fuse). These conductors will normally have a much smaller current
carrying capacity than the drive input conductors and thus will not be protected
by the drive input fuses. The fuses also serve to isolate a failed MOV. Varistors
initially fail in a short-circuited condition. The high follow-through current will
open the fuse and remove the MOV from the circuit.
The fuses used are E-rated current limiting fuses with a high interrupting rating.
Because they are current limiting, they will limit both the magintude and
duration of fault currents. They are small dimension, ferrule-type fuses with a
fiberglass body, and mount in standard fuse clips.
IMPORTANT
The fuses sent with the Transient Suppression Network have been selected
based on their characteristics (including internal resistance). This is necessary
for optimum MOV performance and protection. Do not substitute other fuses
without contacting the factory first.
TIP
Voltage sensing occurs after the MOV fuse, and as a result open fuses will be
detected in drive control as a Master or Slave Undervoltage or Unbalance.