Danfoss VLT AutomationDrive FC 301, Руководство по конструкции, Страница: 83 / 200

6.2.8 Efficiency
Efficiency of the frequency converter
The load on the frequency converter has little effect on its
efficiency.
This also means that the frequency converter efficiency
does not change when other U/f characteristics are chosen.
However, the U/f characteristics do influence the efficiency
of the motor.
The efficiency declines a little when the switching
frequency is set to a value above 5 kHz. The efficiency is
also slightly reduced when the motor cable is longer than
30 m.
Efficiency calculation
Calculate the efficiency of the frequency converter at
different loads based on
Illustration 6.35 . Multiply the factor
in this graph with the specific efficiency factor listed in
chapter 6.2 General Specifications .
1.0
0.99
0.98
0.97
0.96
0.95
0.93
0.92
0% 50% 100% 200%
0.94
Rela
tiv
e Efficienc
y
130BB252.11
1.01
150%
% Speed
100% load 75% load 50% load 25% load
Illustration 6.35 Typical Efficiency Curves
Example: Assume a 55 kW, 380-480 V AC frequency
converter with 25% load at 50% speed. The graph is
showing 0.97 rated efficiency for a 55 kW frequency
converter is 0.98. The actual efficiency is then: 0.97 x
0.98=0.95.
Motor efficiency
The efficiency of a motor connected to the frequency
converter depends on magnetising level. The efficiency of
the motor depends on the type of motor.
•
In the range of 75-100% of the rated torque, the
efficiency of the motor is practically constant,
both when it is controlled by the frequency
converter and when it runs directly on mains.
•
The influence from the U/f characteristic on small
motors is marginal. However, in motors from 11
kW and up, the efficiency advantage is significant.
•
The switching frequency does not affect the
efficiency of small motors. Motors from 11 kW
and up have their efficiency improved 1-2%. This
is because the sine shape of the motor current is
almost perfect at high switching frequency.
System efficiency
To calculate the system efficiency, the efficiency of the
frequency converter is multiplied by the efficiency of the
motor.
6.2.9 Acoustic Noise
Acoustic noise from the frequency converter comes from 3
sources
•
DC-link (intermediate circuit) coils
•
RFI filter choke
•
Internal fans
See Table 6.38 for acoustic noise ratings.
Enclosure type
50% fan speed
[dBA]
Full fan speed
[dBA]
A1 51 60
A2 51 60
A3 51 60
A4 51 60
A5 54 63
B1 61 67
B2 58 70
B4 52 62
C1 52 62
C2 55 65
C4 56 71
D3h 58 71
Table 6.38 Acoustic Noise Ratings
Values are measured 1 m from the unit.
Product Specifications
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
MG33BF02 - Rev. 2013-12-20 81
6 6