Du/Dt Conditions; Special Conditions; Manual Derating - Danfoss VLT AutomationDrive FC 300 Design Manual

Selection

4.6 dU/dt Conditions

NOTICE
To avoid the premature ageing 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
4 4
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 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
screened or unscreened)
•
inductance
The natural induction causes an overshoot U
motor voltage before it stabilises itself at a level
depending on the voltage in the intermediate circuit. The
rise time and the peak voltage U
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 metres), the
rise time and peak voltage are lower. If the motor cable is
long (100 m), the rise time and peak voltage are higher.
Peak voltage on the motor terminals is caused by the
switching of the IGBTs. The frequency converter complies
with the demands of IEC 60034-25 regarding motors
designed to be controlled by 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 4.16 and Table 4.17 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 to be controlled by frequency converters, and
NEMA MG 1-1998 Part 31.4.4.2 for inverter fed motors. The
power sizes below do not comply with NEMA MG 1-1998
Part 30.2.2.8 for general purpose motors.
Power Cable
size length
[m]
90-250 kW/ 30
380-500 V
Table 4.16 dU/dt, D-frame, 380-500 V
76
®
VLT AutomationDrive FC 300 Design Guide 90-1200 kW
in the
PEAK
affect the service life
PEAK
Mains Rise Peak dU/dt
voltage time voltage
[V/µs]
[V] [V]
[µs]
400 0.26 1180 2109`
Power Cable
size length
[m]
315-800 30
kW/380-500
30
V
30
30
Table 4.17 dU/dt E-frame, 380-500 V
1)
With Danfoss dU/dt filter
Power Cable
size length
[m]
90-132 kW/ 150
525-690 V
160-315 150
kW/525-690
V
Table 4.18 dU/dt D-frame 525-690 V
1) With Danfoss dU/dt filter
Power Cable
size length
[m]
355-1200 30
kW/525-690
30
V
30
Table 4.19 dU/dt E- and F-frames 525-690 V
1)
With Danfoss dU/dt filter.

4.7 Special Conditions

This section provides detailed data regarding the operating
of the frequency converter in conditions that require
derating. In some conditions, derating must be done
manually. In other conditions, the frequency converter
performs a degree of automatic derating when necessary.
This is done to ensure proper performance at critical
stages where the alternative could be a trip.

4.7.1 Manual Derating

Manual derating must be considered for:
•
Air pressure – relevant for installation at altitudes
above 1 km
•
Motor speed – at continuous operation at low
RPM in constant torque applications
•
Ambient temperature – relevant for ambient
temperatures above 50 °C
MG34S202 - Rev. 2013-08-19
Mains Rise Peak dU/dt
voltage time voltage
[V/µs]
[V] [µs] [V]
500 0.71 1165 1389
1) 0.80 906 904
500
400 0.61 942 1233
0.82 760 743
400 1)
Mains Rise Peak dU/dt
voltage time voltage
[V/µs]
[V] [V]
[µs]
690 0.36 2135 2.197
1) 0.46 2210 1.744
690
Mains Rise Peak dU/dt
voltage time voltage [V/µs]
[V] [µs] [V]
690 0.57 1611 2261
575 0.25 2510
1.13 1629 1150
690 1)