VLT® 7000 Booster
■ Peak voltage on motor
When a transistor in the inverter is opened,
the voltage across the motor increases by a
dV/dt ratio that depends on:
- the motor cable (type, cross-section, length
screened/armoured or unscreened/unarmoured)
- inductance
The natural induction causes an overshot U
PEAK
in the
motor voltage before it stabilises itself at a level which
depends on the voltage in the intermediate circuit. The
rise time and the peak voltage U
PEAK
affect the service
life of the motor. If the peak voltage is too high, motors
without phase coil insulation are the ones that will
primarily be affected. If the motor cable is short (a few
meters),therisetimeandpeakvoltagearelower.
If the motor cable is long (100 m), the rise time
and peak voltage will increase.
If very small motors are used without phase coil
insulation, it is recommended to fit a LC filter after
the frequency converter. Typical values for the rise
time and peak voltage U
PEAK
measured on the
motor terminals between two phases:
VLT 7002-7011 400 V
Cable Mains Rise Peak
length voltage time voltage
50 metres 380 V 0.3 µsec. 850 V
50 metres 460 V 0.4 µsec. 950 V
150 metres 380 V 1.2 µsec. 1000 V
150 metres 460 V 1.3 µsec. 1300 V
VLT 7016-7072 400 V
Cable Mains Rise Peak
length voltage time voltage
50 metres 380 V 0.1 µsec. 900 V
150 meters 380 V 0.2 µsec. 1000 V
■ Switching on the input
Switching on the input depends on the mains
voltage in question.
The table states the waiting time between cut-ins.
Mains voltage 380 V 415 V 460 V
Waiting time 48 s 65 s 89 s
MG.70.A1.02 - VLT is a registered Danfoss trademark
120
To Next Page
Loading...
General