It Mains; Efficiency - Danfoss VLT AutomationDrive FC 302 Design Manual

Electrical Installation Con...
Using RCDs
Where residual current devices (RCDs), also known as
ground leakage circuit breakers, are used, comply with the
following:
•
Use RCDs of type B only as they can detect AC
and DC currents.
•
Use RCDs with a delay to prevent faults due to
transient ground currents.
•
Dimension RCDs according to the system configu-
ration and environmental considerations.
The leakage current includes several frequencies
originating from both the mains frequency and the
switching frequency. Whether the switching frequency is
detected depends on the type of RCD used.
RCD with low f
Leakage current
RCD with high f
50 Hz 150 Hz
Mains 3rd harmonics
Illustration 10.14 Main Contributions to Leakage Current
The amount of leakage current detected by the RCD
depends on the cut-off frequency of the RCD.
Leakage current [mA]
Illustration 10.15 Influence of the RCD Cut-off Frequency on
Leakage Current
MG38C202
Design Guide
cut-
cut-
f Frequency
sw
Cable
100 Hz
2 kHz
100 kHz
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10.10 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).
Danfoss does not recommend using an output contactor
for 525–690 V drives connected to an IT mains network.

10.11 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 , whether the motor supplies 100% of the
M,N
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 Illustration 10.16. The factor in this graph
must be multiplied by the specific efficiency factor listed in
the specification tables in chapter 7.1 Electrical Data, 380–
500 V and chapter 7.2 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% 50%
% Speed
100% load 75% load
Illustration 10.16 Typical Efficiency Curves
100% 150% 200%
50% load 25% load
159
10 10