Rockwell Automation 7000L PowerFlex 7000 Medium Voltage AC Drive C Frame - Marine - Manual (Page 21)

Overview of Drive 1-7
7000 “C” Frame - Marine 7000L-UM302B-EN-P – June 2013
The PowerFlex 7000L with “Direct-to-Drive” technology is typically
smaller and lighter than drive technologies that use Isolation
Transformers. Isolation Transformers represent 30 to 50% of a drive
system size and 50 to 70% of the system‟s weight. This means that
there is no interwiring between drive and transformer (for external
transformer configurations). This makes the PowerFlex 7000L the
simplest to install.
Motor Compatibility
The PowerFlex 7000L achieves near sinusoidal current and voltage
waveforms to the motor, resulting in no significant additional heating
or insulation stress. Temperature rise in the motor connected to the
VFD is typically 3 °C (5.5 °F) higher compared to across the line
operation. Dv/dt in the voltage waveform is less than 10 volts /
microsecond. The peak voltage that the motor insulation will see is
the rated motor RMS voltage divided by 0.707. Reflected wave and
dv/dt issues often associated with VSI (voltage source inverter)
drives are a non-issue with the PowerFlex 7000L. Typical motor
waveforms are shown in Figure 1.5. These motor friendly waveforms
are achieved by utilizing a selective harmonic elimination (SHE)
pattern in the inverter to eliminate major order harmonics, in
conjunction with a small output capacitor (integral to the drive) to
eliminate harmonics at higher speeds.
Standard motors are compatible without derating, even on retrofit
applications.
Motor cable distance is virtually unlimited. This technology has been
tested, controlling motors up to 15 km (9.3 miles) away from the drive.
300.00
200.00
100.00
0.00
-100.00
-200.00
-300.00
10.00K
7.50K
5.00K
2.50K
0.00K
-2.50K
-5.00K
-7.50K
-10.00K
100.00 110.00 120.00 130.00
TIME (ms)
140.00 150.00
Arms
Vrms
Figure 1.4 – Motor waveforms @ full load, full speed
Motor current
Motor voltage