Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 179)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 179
Diagnostics and Protection Chapter 3
Removing Battery
To remove the battery, simply use a screwdriver to press down on the metal tab
going across the battery. Prying the battery out of its holder can result in
permanent damage to the main control board.
Reflected Wave Reflected waves are a phenomenon associated with long cables and fast changes
in voltage levels. They were first identified on power transmission lines that are
hundreds of miles long. When the power is switched on at one end, the step in
voltage travels the length of the transmission line and is reflected back to the
switch. The voltage at the far end often surges to twice the initial value of the
voltage. Because the voltages involved are quite high, for example 230,000V or
more, a surge of 460,000V can result in a damaging arcing fault.
Adjustable speed drives, using IGBT switches that turn on and off within a few
nanoseconds, experience the same phenomenon at the AC motor terminals. This
can cause motor failures within months or even weeks of commissioning the
motor with a drive.
A PWM AC drive provides variable voltage and variable frequency to a motor
from a DC bus voltage. It creates the sinusoidally varying voltage to the motor by
continually changing the duty cycle of the IGBT switches in a pulse-width-
modulated fashion. Because the motor is largely an inductive load, the current
that flows is an integration of the voltage with a lagging phase angle.
Figure 18
shows what the drives line-to-line output voltage looks like. The peaks of the
output voltage are equal to the value of the DC bus in the drive. Only the widths
and polarities change.