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All About FCD
300
IEC 68-2-34: Random vibration broad-band
- general requirements.
IEC 68-2-35: Random vibration broad-band
- high reproducibility.
IEC 68-2-36: Random vibration broad-band
- medium reproducibility.
■
Air humidity
The variable frequency drive has been designed to
meet the IEC 68-2-3 standard, EN 50178 item 9.4.2.2/
DIN 40040 class E at 104 °F (40 °C). Cyclic damp heat
IEC 68-2-30. 100% humidity with temperature cycling.
■
UL Standard
This device is UL-approved.
■
Efficiency
To reduce energy consumption it is very important
to optimize the efficiency of a system. The
efficiency of each single element in the system
should be as high as possible.
Efficiency of variable frequency drives (
η
INV
)
The load on the variable frequency drive has little
effect on its efficiency. In general, the efficiency is the
same at the rated motor frequency f
M,N
, regardless of
whether the motor supplies 100% rated shaft torque
or only 75%, e.g. in case of part loads.
This also means that the efficiency of the variable
frequency drive does not change even if other
U/f characteristics are chosen. However, the U/f
characteristics influence the efficiency of the motor.
The efficiency declines a little when the switching
frequency is set to a value above 4.5 kHz (parameter
411
Switching frequency
). The rate of efficiency will also
be slightly reduced at a high AC line voltage (480 V).
Efficiency of the motor (
η
MOTOR
)
The efficiency of a motor connected to the variable
frequency drive depends on the sine shape of
the current. In general, the efficiency is just as
good as in AC line operation. The efficiency of the
motor depends on the motor type.
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 variable frequency drive
and when it runs directly on AC line.
In general, the switching frequency does not affect
the efficiency of small motors.
Efficiency of the system (
η
SYSTEM
)
To calculate the system efficiency, the efficiency of the
variable frequency drives (
η
INV
) should be multiplied
by the efficiency of the motor (
η
MOTOR
):
η
SYSTEM
=
η
INV
x
η
MOTOR
.
Based on the graph above, it is possible to calculate
the system efficiency at different loads.
■
Electrical supply interference/harmonics
A variable frequency drive takes up a non-sinusoidal
current from AC lines, which increases the input current
I
RMS
. A non-sinusoidal current can be transformed by
means of a Fourier analysis and split up into sinusoidal
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
Frequency [Hz]
50
250
350
0,9
0,4
0,3
The harmonic currents do not affect power
consumption directly, but they 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
MG.90.F2.22 - VLT is a registered Danfoss trademark
183
