Efficiency; Acoustic Noise - Danfoss VLT AutomationDrive FC 300 Design Manual

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4.4 Efficiency

Efficiency of the Adjustable Frequency Drive (η
The load on the adjustable frequency drive has little effect
on its efficiency. In general, the efficiency is the same at
the rated motor frequency f
supplies 100% of the rated shaft torque or only 75%, in
4 4
case of partial loads.
The efficiency of the adjustable 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 slightly when the switching
frequency is set to a value of above 5 kHz. The efficiency is
slightly reduced when the AC line voltage is 480 V, or if
the motor cable is longer than 100 ft [30 m].
Adjustable Frequency Drive Efficiency Calculation
Calculate the efficiency of the adjustable frequency drive at
different speeds and loads based on Figure 4.2. The factor
in this graph must be multiplied with the specific
efficiency factor listed in the specification tables in
chapter 4.1 Electrical Data, 380–500 V and
chapter 4.2 Electrical Data, 525–690 V.
1.01
1.0
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0%
100% load
Figure 4.2 Typical Efficiency Curves
Example: Assume a 160 kW, 380–480 V AC adjustable
frequency drive at 25% load at 50% speed. Figure 4.2
shows 0.97 - rated efficiency for a 160 kW adjustable
frequency drive is 0.98. The actual efficiency is then: 0.97x
0.98=0.95.
84
Design Guide
, whether the motor
M,N
50% 100% 150%
% Speed
75% load 50% load
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
Efficiency of the Motor (η
The efficiency of a motor connected to the adjustable
)
frequency drive depends on magnetizing level. In general,
DRIVE
the efficiency is as good as with line power operation. 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 the
adjustable frequency drive controls it and when it runs
directly on line power.
In small motors, the influence from the U/f characteristic
on efficiency is marginal. However, in motors from 15 hp
[11 kW] and up, the advantages are significant.
In general, the switching frequency does not affect the
efficiency of small motors. Motors from 15 hp [11 kW] and
up have their efficiency improved (1–2%) because the
shape of the motor current sine wave is almost perfect at
high switching frequency.
Efficiency of the System (η
To calculate system efficiency, the efficiency of the
adjustable frequency drive (η
efficiency of the motor (η
η
=η
SYSTEM DRIVE

4.5 Acoustic Noise

The acoustic noise from the adjustable frequency drive
comes from three sources:
1. DC intermediate circuit coils
2. Integral fan
3. RFI filter choke
Table 4.15 lists the typical acoustic noise values measured
200%
at a distance of 1 m from the unit.
25% load
Frame size
E1/E2-Frames
E1/E2-Frames
F-Frames
Table 4.15 Acoustic Noise
1) 250 kW, 380–500 V and 355/400 kW, 525–690 V only.
2)
All other E-frame units.
MOTOR)
)
SYSTEM
) is multiplied by the
DRIVE
):
MOTOR
x η
MOTOR
dBA at full fan speed
N90k
N110
N132
N160
N200
N250
1)
2)
71
71
72
74
75
73
74
83
80
MG34S222