Danfoss VLT 380-500 V, Руководство по конструкции

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between I
motor
and I
motor
nominal. The Y-AXIS- shows the
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.
1.2 1.0 1.4
30
10
20
100
60
40
50
1.8 1.6 2.0
2000
500
200
400
300
1000
600
t [s]
175ZA052.12
fOUT = 2 x f M,N
fOUT = 0.2 x f M,N
fOUT = 1 x f M,N(par. 1-23)
I
MN
(par. 1-24)
I
M
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
®
FC-Series Output
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
PEAK
in the
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
PEAK
affect the service life of the motor.
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
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
length (m
(ft))
Mains
voltage
(V)
Raise
time
(
µ
s)
Vpeak
(kV)
dU/dt
(kV/
µ
s)
None 150
(492)
400 0.818 1.06 3.249
Individual 1.692 1.22 0.579
Common 2.262 1.17 0.415
Table 10.4 dU/dt Specifications for 380–500 V Units
Filter Cable
length (m
(ft))
Mains
voltage
(V)
Raise
time
(
µ
s)
Vpeak
(kV)
dU/dt
(kV/
µ
s)
None 150
(492)
690 0.65 1.79 2.184
Individual 1.76 2.2 0.909
Common 2.02 2.1 0.831
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
INV
for the
frequency converter.
Motor Design Guide
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