7.9 IT Mains
Mains supply isolated from ground
If the drive is supplied from an isolated mains source (IT
mains, floating delta, or grounded delta) or TT/TN-S mains
with grounded leg, the RFI switch is recommended to be
turned off via
parameter 14-50 RFI Filter
on the drive and
parameter 14-50 RFI Filter
on the filter. For more detail, see
IEC 364-3. In the off position, the filter capacitors between
the chassis and the DC link are cut off to avoid damage to
the DC link and to reduce the ground capacity currents,
according to IEC 61800-3.
If optimum EMC performance is needed, or parallel motors
are connected, or the motor cable length is above 25 m
(82 ft), Danfoss recommends setting
parameter 14-50 RFI
Filter
to [ON]. Refer also to the
Application Note, VLT on IT
Mains
. It is important to use isolation monitors that are
rated for use together with power electronics (IEC
61557-8).
7.10 Efficiency
Efficiency of the drive (η
VLT
)
The load on the drive has little effect on its efficiency. In
general, the efficiency is the same at the rated motor
frequency f
M,N
, whether the motor supplies 100% of the
rated shaft torque or only 75%, in case of part loads.
The efficiency of the drive does not change even if other
U/f characteristics are selected. However, the U/f character-
istics 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 (98 ft).
Drive efficiency calculation
Calculate the efficiency of the drive at different speeds and
loads based on
. The factor in this graph
must be multiplied by the specific efficiency factor listed in
the specification tables in
.
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 7.15 Typical Efficiency Curves
Example: Assume a 160 kW, 380–480/500 V AC drive at
25% load at 50% speed.
shows 0.97 - rated
efficiency for a 160 kW drive is 0.98. The actual efficiency is
then: 0.97x 0.98=0.95.
Efficiency of the motor (η
MOTOR
)
The efficiency of a motor connected to the drive 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.
In the range of 75–100% of the rated torque, the efficiency
of the motor is practically constant, both when the drive
controls it and when it runs directly on the mains.
In small motors, the influence from the U/f characteristic
on efficiency is marginal. However, in motors from 11 kW
(15 hp) and up, the advantages are significant.
Typically the switching frequency does not affect the
efficiency of small motors. Motors from 11 kW (15 hp) 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
SYSTEM
)
To calculate system efficiency, the efficiency of the drive
(η
VLT
) is multiplied by the efficiency of the motor (
η
MOTOR
):
η
SYSTEM
=
η
VLT
x
η
MOTOR
7.11 Acoustic Noise
The acoustic noise from the drive comes from 3 sources:
•
DC intermediate circuit coils.
•
Internal fans.
•
RFI filter choke.
lists the typical acoustic noise values measured
at a distance of 1 m (9 ft) from the unit.
Enclosure size
dBA at full fan speed
J8
73
J9
75
Table 7.11 Acoustic Noise
Test results performed according to ISO 3744 for audible
noise magnitude in a controlled environment. Noise tone
has been quantified for engineering data record of
hardware performance per ISO 1996-2 Annex D.
Electrical Installation Con...
Design Guide
MG06K102
Danfoss A/S © 03/2019 All rights reserved.
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