Rockwell Automation 1336E IMPACT Adjustable Frequency AC Drive User Manual V 1-4.XX - Manual (Page 26)

2-8 Mounting and Wiring Your 1336 IMPACT Drive
Reducing Voltage Reflections
Voltage doubling at motor terminals, known as reflected wave
phenomenon or transmission line effect, can occur when using drives
with long motor cables.
The 1336 IMPACT drive is equipped with an internal voltage
reflection reduction mechanism. This mechanism provides a
minimum dwell time that is controlled so that voltage transients are
allowed to decay, thus reducing motor overvoltage. This limits the
voltage seen at the motor terminals to 2.2 per unit and greatly
increases the run length of the motor cable before a terminator is
required.
You should use inverter duty motors with phase-to-phase insulation
ratings of 1600 volts or higher to minimize effects of reflected wave
on motor insulation life.
Without the dwell time correction, the voltage reflection transients
surpass the insulation rating of the motor with less than 500 feet of
cable. With the introduction of a controlled dwell time, the voltage
transients are safely maintained below the insulation rating of the
motor. In Figure 2.1, the terminal voltage is plotted as a function of
cable distance for a 1336 IMPACT drive at a 4 kHz carrier frequency.
Figure 2.1
Terminal Voltage at a 4 kHz Carrier Frequency
Optional Cable Terminator
Applications with non-inverter duty motors or any motor with
exceptionally long leads may require an output inductor or cable
terminator. An inductor or Bulletin 1204 terminator helps limit
reflection to the motor, to levels that are less than the motor insulation
value.
1800
1700
1600
1500
1400
1300
1200
1100
25 100 800 700 600 500 400 300 200
1600 V
Corrected Code
No Correction
4 kHz Terminal Overvoltage
Cable Length (Feet)
Voltage (Vpk)