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Motor Drive Analyzer
Motor Drive DC-Bus
17
Motor Drive DC-Bus
The Motor Drive DC-Bus functions check the intermediate
circuit of the motor drive.
XW
Warning
To prevent possible electrical shock, fire, or
personal injury, be aware that the voltage
that is present on the dc bus outputs
remains on these outputs after the motor
drive is turned off. The amount of time
depends on the internal impedance.
Voltage DC Level
The Voltage DC Level checks the value and stability of the
internal DC-bus of the drive and influence of braking or
power feedback (if supported by the drive).
The readings show the dc level, as well as, the peak and
peak-peak value. Use Voltage AC Ripple for a closer look at
the ac component.
The dc bus voltage should be about 1.414 times the rms
line voltage, except when controlled rectifiers (IGBT) are
used in the input section. A dc voltage that is too low can
trip the drive. Low voltage can be caused by low input mains
voltage or distorted input voltage by flat topping.
Tips:
•
Use the
RECORD
function to check the dc voltage
stability over time and detect slow fluctuations. The test
tool continuously records the digital readings of the
measurements and displays these as a graph.
•
The TrendPlot graph rolls from right to left like a paper
chart recorder. Observe that the recorded time from
start appears at the bottom of the screen. The present
reading appears on top of the screen.
•
See
Using the Record Functions
chapter in the
ScopeMeter
®
Test Tool 190 Series II User Manual
for
more information.
Voltage AC Ripple
The Voltage AC Ripple function detects rapid fluctuations
and ac components on the dc-bus.
Tips:
•
A slight ripple can be visible and is load dependent. If
the peaks of ripple have a different repetitive level, one
of the rectifiers could be malfunctioning.
•
Ripple voltages >40 V can be caused by malfunctioning
capacitors or the drive rating is too small for the
connected motor and load.