Thermal Protection And Derating; Derating For Ambient Temperature; Derating For Air Pressure; Derating For Running At Low Speed - Danfoss VLT FCM Series Manual

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.

Derating for ambient temperature

The ambient temperature (T
temperature allowed. The average (T
over 24 hours must be at least 5ºC lower.
If FCM 300 Series is operated at temperatures
above 40 ºC, a derating of the continuous
output current is necessary.

Derating for air pressure

Below 1000 m altitude no derating is necessary.
Above 1000 m the ambient temperature (T
max. output current (I
VLT,MAX
accordance with the following diagram:
1. Derating of output current versus altitude
at T = max. 40°C
AMB
2. Derating of max. T
AMB
100% output current.

Derating for running at low speed

When a centrifugal pump or a fan is controlled
by a FC motor, it is not necessary to reduce the
output at low speed because the load characterstic
of the centrifugal pumps/fans, automatically
ensures the necessary reduction.
FC motors running constant load torque applications
continuously at low speed must be derated (see
diagram) or an independent fan must be used
(cooling option 2, not yet available).
Nominal torque (100%) can be yielded up to 15 min
and at a duty cycle up to 25% at low speed.

Derating for high switching frequency

The FCM 300 Series motor can use two different
PWM schemes, SFAVM and 60° AVM. Factory setting
is SFAVM. The PWM scheme can be changed in
MG.03.H3.02 - VLT is a registered Danfoss trademark
) is the maximum
AMB,MAX
) measured
AMB,AVG
) or
AMB
) must be derated in
versus altitude at
®
VLT FCM Series
NB!:
Combination of high switching frequency and
missing fan cooling might damage the unit.
parameter 446. Below 25 Hz motor speed the FCM
300 Series motor automatically change to SFAVM.
Factory setting of the switching frequency is
4000 Hz. It can be changed between 2 and
14 kHz in parameter 411.
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