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Motor
between I
and I
nominal. The Y-AXIS- shows the
motor
motor
time in seconds before the ETR cuts off and trips the
frequency converter. The curves show the characteristic
nominal speed, at twice the nominal speed and at 0.2 x
the nominal speed.
At lower speeds the ETR cuts off at lower heat due to less
cooling of the motor. In that way, the motor is protected
from being overheated even at low speed. The ETR feature
is calculating the motor temperature based on actual
current and speed. The calculated temperature is visible as
a readout parameter in parameter 16-18 Motor Thermal in
the frequency converter.
t [s]
2000
1000
600
500
400
300
200
100
60
50
40
30
20
10
1.0
1.2
1.4
1.6
Illustration 10.11 ETR Example
10.7 dU/dt Conditions
NOTICE
To avoid the premature aging of motors that are not
designed to be used with frequency converters, such as
those motors without phase insulation paper or other
insulation reinforcement, Danfoss strongly recommends a
dU/dt filter or a sine-wave filter fitted on the output of
the frequency converter. For further information about
dU/dt and sine-wave filters see the VLT
Filters Design Guide.
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
shielded or unshielded).
•
Inductance.
The natural induction causes an overshoot U
motor voltage before it stabilizes itself at a level
depending on the voltage in the DC link. The rise time and
the peak voltage U
affect the service life of the motor.
PEAK
In particular, motors without phase coil insulation are
affected if the peak voltage is too high. Motor cable length
affects the rise time and peak voltage. For example, if the
MG37N102
Design Guide
f OUT = 1 x f M,N (par. 1-23)
f OUT = 2 x f M,N
f OUT = 0. 2 x f M,N
I
M
I
(par. 1-24)
1.8
2.0
MN
®
FC-Series Output
in the
PEAK
Danfoss A/S © 6/2016 All rights reserved.
motor cable is short (a few meters), the rise time and peak
voltage are lower. If the motor cable is 100 m (328 ft) or
longer, the rise time and peak voltage are higher.
Switching of the IGBTs causes peak voltage on the motor
terminals. The frequency converter complies with the
demands of IEC 60034-25 regarding motors designed for
use with frequency converters. The frequency converter
also complies with IEC 60034-17 regarding Norm motors
controlled by frequency converters.
High-power range
The power sizes in Table 10.4 and Table 10.5 at the
appropriate mains voltages comply with the requirements
of IEC 60034-17 regarding normal motors controlled by
frequency converters, IEC 60034-25 regarding motors
designed for use with frequency converters, and NEMA MG
1-1998 Part 31.4.4.2 for inverter fed motors. The power
sizes in Table 10.4 do not comply with NEMA MG 1-1998
Part 30.2.2.8 for general-purpose motors.
Filter
Cable
Mains
length (m
voltage
(ft))
(V)
None
150
400
(492)
Individual
Common
Table 10.4 dU/dt Specifications for 380–500 V Units
Filter
Cable
Mains
length (m
voltage
(ft))
(V)
None
150
690
(492)
Individual
Common
Table 10.5 dU/dt Specifications for 525–690 V Units
10.8 Parallel Connection of Motors
The frequency converter can control several parallel-
connected motors. When using parallel motor connection,
observe the following points:
•
Run applications with parallel motors in U/F
mode (volts per hertz).
•
VVC
+
mode can be used in some applications.
•
Total current consumption of motors must not
exceed the rated output current I
frequency converter.
Raise
Vpeak
dU/dt
time
(kV)
(kV/µs)
(µs)
0.818
1.06
3.249
1.692
1.22
0.579
2.262
1.17
0.415
Raise
Vpeak
dU/dt
time
(kV)
(kV/µs)
(µs)
0.65
1.79
2.184
1.76
2.2
0.909
2.02
2.1
0.831
for the
INV
113
10
10
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