Du/Dt On Motor; Switching On The Input; Acoustic Noise - Danfoss VLT 2800 Manual

The inverter turns off after 5-10 s and the frequency
converter displays a fault code, although this depends
on impedance and motor frequency.
Earth fault
The IGBT module cuts out within 100 s in case of an
earth fault on one of the motor terminals U, V, W (96,
97, 98), although depending on impedance and motor
frequency.
Output connection
Motor terminals U, V, W (96, 97, 98) for the motor can
be connected/disconnected as often as required.
There is no way that the frequency converter can be
destroyed by connecting/disconnecting the motor ter-
minals. However, fault messages may appear.
Motor-generated overvoltage
The voltage in the intermediate circuit is increased
when the motor acts as a generator. To protect the
frequency converter the IGBT module is disconnected
when a specific voltage level is reached.
Motor-generated overvoltage can occur in two instan-
ces:
1. The load drives the motor, i.e. the load gen-
erates energy.
2. During deceleration (ramp-down) if the mo-
ment of inertia is high, the load is low and the
ramp-down time too short for the energy to
be dissipated as a loss in the frequency con-
verter, the motor and the unit. The control unit
attempts to correct the ramp if possible.
The fault can be removed by connecting a brake re-
sistor, if the frequency converter has an integrated
brake module. If the frequency converter does not
have an integrated brake module an AC brake can be
used, see parameter 400 Brake function.
See the section entitled Brake resistors.
Static overloading
When the frequency converter is overloaded (current
limit in parameter 221 Current limit I
control reduces the output frequency in an attempt to
reduce the load. If the overloading is extreme, there
might be an output current that causes the frequency
converter to trip after approx. 1.5 sec. See parameter
409 Trip delay overcurrent, I
An extreme overload will cause the switching frequen-
cy to be derated to 3000 Hz.
MG.27.E2.02 - VLT is a registered Danfoss trademark
is reached), the
LIM
.
LIM

dU/dt on motor

When a transistor in the inverter is opened, the voltage
across the motor terminals will rise by a voltage/time
ratio (dU/dt) determined by:
- the motor cable (type, cross-section, induc-
tion, capacity, length and screened/arm-
oured/unscreened/unarmoured)
- the mains voltage
Self-induction in the motor cable leads to an overswing
U of the output voltage each time a transistor in
PEAK
the inverter is opened. After U
will stabilise at a level determined by the voltage in the
intermediate circuit. U and dU/dt influence the life-
PEAK
time of the motor, especially motors without phase
insulation paper in the coils. If the motor cable is short
(a few metres), the overshoot U
dU/dt is high. If the motor cable is long (>20 m),
U is increased, while dU/dt decreases. When us-
PEAK
ing small motors without phase insulation paper, it is
recommended that an LC-filter is connected after the
frequency converter.

Switching on the input

The waiting time between switching the mains voltage
on terminals 91, 92 and 93 must be min. 30 sec. Start
up time appr. 2.3 sec.

Acoustic noise

The acoustic noise from the frequency converter
comes from two sources:
1. DC intermediate circuit coils.
2. Integral fan.
Below are the typical values measured at a distance
of 1 m from the unit at full load:
VLT 2803-2815 1 x 220 V: 52 dB(A).
VLT 2822 1 x 220 V PD2:54 dB(A).
VLT 2840 1 x 220 V PD2: 55 dB (A).
VLT 2840 3 x 200 V PT2: 54 dB (A).
VLT 2803-2822 3 x 220 V: 52 dB(A).
VLT 2805-2840 3 x 400 V: 52 dB(A).
VLT 2855-2875 3 x 400 V: 54 dB(A).
VLT 2880-2882 3 x 400 V: 55 dB(A).
Derating for ambient temperature
The ambient temperature (T
temperature allowed. The average (T
ured over 24 hours, must be at least 5 °C lower. If the
frequency converter operates at temperatures above
the output voltage
PEAK
is low, while the
PEAK
) is the maximum
AMB,MAX
) meas-
AMB,AVG
135