Efficiency; Acoustic Noise; Peak Voltage On Motor - Danfoss VLT AQUA Drive FC 202 Design Manual

General Specifications and ...
CAUTION
Connection to PC is carried out via a standard host/
device USB cable.
The USB connection is galvanically isolated from the
supply voltage (PELV) and other high-voltage terminals.
The USB connection is not galvanically isolated from
protection ground. Use only an isolated laptop/PC as
connection to the USB connector on the frequency
converter or an isolated USB cable/converter.

8.2 Efficiency

Efficiency of the Frequency Converter (η
The load on the frequency converter has little effect on its
efficiency. In general, the efficiency is the same at the
rated motor frequency f
100% of the rated shaft torque or only 75%, in case of
partial loads.
The efficiency of the frequency converter does not change
even if other U/f characteristics are chosen. However, the
8 8
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 mains voltage is 480 V, or if the
motor cable is longer than 30 m.
Frequency Converter Efficiency Calculation
Calculate the efficiency of the frequency converter at
different speeds and loads based on Illustration 8.2. The
factor in this graph must be multiplied with the specific
efficiency factor listed in the specification tables in
chapter 8.1.1 Mains Supply 3x380-480 V AC and
chapter 8.1.2 Mains Supply 3x525-690 V AC.
1.01
1.0
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0%
100% load
Illustration 8.2 Typical Efficiency Curves
Example: Assume a 160 kW, 380–480 V AC frequency
converter at 25% load at 50% speed. Illustration 8.2 shows
0.97 - rated efficiency for a 160 kW frequency converter is
0.98. The actual efficiency is then: 0.97x 0.98=0.95.
Efficiency of the Motor (η
The efficiency of a motor connected to the frequency
converter depends on magnetizing level. In general, the
efficiency is as good as with mains operation. The
efficiency of the motor depends on the type of motor.
184
Design Guide
)
VLT
, whether the motor supplies
M,N
50% 100% 150%
% Speed
75% load 50% load
MOTOR)
Danfoss A/S © Rev. 06/2014 All rights reserved.
In the range of 75–100% of the rated torque, the efficiency
of the motor is practically constant, both when the
frequency converter controls it and when it runs directly
on mains.
In small motors, the influence from the U/f characteristic
on efficiency is marginal. However, in motors from 11 kW
and up, the advantages are significant.
In general, the switching frequency does not affect the
efficiency of small motors. Motors from 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
frequency converter (η
the motor (η
MOTOR
η x η
=η
SYSTEM VLT

8.3 Acoustic Noise

The acoustic noise from the frequency converter comes
from three sources:
1. DC intermediate circuit coils.
2. Integral fan.
3. RFI filter choke.
The typical values measured at a distance of 1 m from the
unit:
Enclosure
N110
N132
N160
N200
N250
N315
E1/E2 *
E1/E2 **
F1/F2/F3/F4
F8/F9/F10/F11/F12/F13
* 315 kW, 380–480 VAC. 450 kW and 500 kW, 525–690 V
AC only.
** Remaining E1+E2 power sizes.
200%
Table 8.16 Acoustic Noise Levels
25% load

8.4 Peak Voltage on Motor

When a transistor in the inverter bridge switches, the
voltage across the motor increases by a dU/dt ratio
depending on:
•
the motor cable (type, cross-section, length
screened or unscreened)
•
inductance
The natural induction causes an overshoot U
motor voltage before it stabilises itself at a level
)
SYSTEM
) is multiplied by the efficiency of
VLT
):
MOTOR
Full fan speed [dBA]
71
71
72
74
75
73
74
83
80
84.5
PEAK
in the
MG20Z202