Danfoss VLT Brook Crompton Motor FCM 300, Design Manual

Page: 83 / 102

1,02
1,01
1,00
0,99
0,98
0,97
0,96
0,95
0,94
0,93
0,92
0,91
0,90
0,89
0,88
0,87
0,86
0,85
0,84
0,83
0,82
0,81
0,80
30Hz 40Hz
50Hz 60Hz 70Hz
100% Load 75% Load 50% Load 25% Load
Output Frequency
175NA159.10
Rela
tiv
e E
fficienc
y
Illustration 4.6 Typical Efficiency Curves
FCM 300 efficiency calculation calculate the efficiency of
the FCM #300 at different loads based on
Illustration 4.6 .
The factor in this graph must be multiplied with the
specific efficiency factor listed in the specification tables.
Example: Assume an FCM 375 at 25% load at 30 Hz speed.
The graph is showing 0,845 – rated efficiency for an FCM
375 is 0.876.
The actual FCM 300 efficiency is then: 0.845x0.876=0.74 at
partial speed (30 Hz) and load (25%).
4.1.15 Mains Supply Interference/
Harmonics
An FC motor takes up a non-sinusoidal current from mains,
which increases the input current I
RMS
. A nonsinusoidal
current can be transformed by means of a Fourier analysis
and split up into sine wave currents with different
frequencies, i.e. different harmonic currents I
N
with 50 Hz
as the basic frequency:
Harmonic
currents I
1
I
5
I
7
I
11
Hz 50 Hz 250 Hz 350 Hz 550 Hz
In/I1 [%] 100% 44% 29% 8%
Table 4.3
The harmonics do not affect the power consumption
directly, but increase the heat losses in the installation
(transformer, cables). Consequently, in plants with a rather
high percentage of rectifier load, it is important to
maintain harmonic currents at a low level to avoid
overload of the transformer and high temperature in the
cables.
Some of the harmonic currents might disturb communi-
cation equipment connected to the same transformer or
cause resonance in connection with power-factor
correction batteries.
175HA034.10
Illustration 4.7
To ensure low, harmonic currents, FCM 300 has
intermediate circuit coils as standard. THD (current)
≤
54%
The voltage distortion on the mains supply depends on
the size of the harmonic currents multiplied by the mains
impedance for the frequency in question. The total voltage
distortion THD is calculated on the basis of the individual
voltage harmonics using the following formula:
THD =
U
1
U
22
+...+U
n2
(%)
All about FCM 300
VLT
®
DriveMotor FCM Series
MG03BA02 - VLT
®
is a registered Danfoss trademark 81
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