Danfoss FC 300 Design Manual page 50

3 Introduction to AutomationDrive FC 300
Mains Drop-out
During a mains drop-out, the frequency converter keeps running until the intermediate circuit voltage drops below the minimum stop level, which is
typically 15% below the frequency converter's lowest rated supply voltage. The mains voltage before the drop-out and the motor load determines how
long it takes for the inverter to coast.
plus
Static Overload in VVC
When the frequency converter is overloaded (the torque limit in par. 4-16
the controls reduces the output frequency to reduce the load.
3
If the overload is excessive, a current may occur that makes the frequency converter cut out after approx. 5-10 s.
Operation within the torque limit is limited in time (0-60 s) in par. 14-25
3.11.1 Motor Thermal Protection
To protect the application from serious damages VLT AutomationDrive offers several dedicated features
Torque Limit: The Torque limit feature the motor is protected for being overloaded independent of the speed. Torque limit is controlled in
Torque Limit Motor Mode
par. 4-16
par. 14-25 Trip Delay at Torque Limit
Current Limit: The current limit is controlled in par. 4-18
Trip Delay at Current Limit
par. 14-24
Min Speed Limit: (par. 4-11
between 30 and 50/60Hz. Max Speed Limit: (par. 4-13
the drive can provide
ETR (Electronic Thermal relay): The frequency converter ETR function measures actual current, speed and time to calculate motor temperature and
protect the motor from being overheated (Warning or trip). An external thermistor input is also available. ETR is an electronic feature that simulates a
bimetal relay based on internal measurements. The characteristic is shown in the following figure:
Illustration 3.7: Figure ETR: The X-axis shows the ratio between I
ETR cut of and trips the drive. The curves show the characteristic nominal speed, at twice the nominal speed and at 0,2 x the nominal speed.
At lower speed the ETR cuts of at lower heat due to less cooling of the motor. In that way the motor are protected from being over heated
even at low speed. The ETR feature is calculating the motor temperature based on actual current and speed. The calculated temperature
is visible as a read out parameter in par. 16-18
50
mode
Torque Limit Generator Mode
and or par. 4-17
.
Current Limit
.
Motor Speed Low Limit [RPM]
or par. 4-12
Motor Speed High Limit [RPM]
Motor Thermal
MG.33.BC.02 - VLT
Torque Limit Motor Mode
/par. 4-17
Trip Delay at Torque Limit
.
and the time before the torque limit warning shall trip is controlled in
and the time before the current limit warning shall trip is controlled in
Motor Speed Low Limit [Hz]
) limit the operating speed range to for instance
Max Output Frequency
or par. 4-19
and I nominal. The Y- axis shows the time in seconds before the
motor motor
in the AutomationDrive FC 300.
® is a registered Danfoss trademark
FC 300 Design Guide
Torque Limit Generator Mode
is reached),
) limit the max output speed