Danfoss VLT Brook Crompton Motor FCM 300, Design Manual

Page: 80 / 102

Illustration 4.1 Galvanic isolation
4.1.3 Extreme Running Conditions
Motor-generated overvoltage
The voltage in the intermediate circuit is increased when
the motor acts as a generator. This occurs in two cases:
•
The load drives the motor (at constant output
frequency from the frequency converter), i.e. the
load generates energy.
•
During deceleration ("ramp-down") if the moment
of inertia is high, the load is low and the ramp-
down time is too short for the energy to be
dissipated as a loss in the VLT frequency
converter, the motor and the installation.
The control unit attempts to correct the ramp if possible.
The inverter turns off to protect the transistors and the
intermediate circuit capacitors when a certain voltage level
is reached.
Mains drop-out
During a mains drop-out, FCM 300 Series continues until
the intermediate circuit voltage drops below the minimum
stop level, which is typically 15% below FCM 300 Series's
lowest rated supply voltage.
The time before the inverter stops depends on the mains
voltage before the drop-out and on the motor load.
Static overload
When FCM 300 Series is overloaded (the current limit in
parameter 221 has been reached), the controls will reduce
the output frequency in an attempt to reduce the load.
If the overload is excessive, a current may occur that
makes the FC motor cut out after approx. 1.5 s.
4.1.4 Acoustic Noise
Below are the typical values measured at a distance of 1 m
from the unit at full load:
2 pole 4 pole
FCM 305 54 dB(A)
FCM 311 58 dB(A)
FCM 315 59 dB(A)
FCM 322 58 dB(A)
FCM 330 61 dB(A)
FCM 340 62 dB(A) 63 dB(A)
FCM 355 64 dB(A) 60 dB(A)
FCM 375 61 dB(A)
Table 4.1
4.1.5 Balance
The FCM 300 is balanced to class R according to ISO8821
(reduced balance). For critical applications especially at
high speed (>4000 RPM) special balance (class S) might be
required.
4.1.6 Thermal Protection and Derating
The FCM 300 Series motor is thermally protected in case
limits are exceeded. At high temperatures the switching
frequency will be gradually reduced down to 2 kHz and
eventually the motor will trip.
NOTICE
Combination of high switching frequency and
missing fan cooling might damage the unit.
All about FCM 300
VLT
®
DriveMotor FCM Series
78 MG03BA02 - VLT
®
is a registered Danfoss trademark
4 4