Safe Torque Off; Safe Torque Off Operation - Danfoss VLT AutomationDrive FC 300 Design Manual

Product Introduction
the method used for controlling the intermediate circuit
voltage level.
NOTICE
OVC cannot be activated when running a PM motor
(when1-10 Motor Construction is set to [1] PM non salient
SPM).
Mains drop-out
During a mains drop-out, the frequency converter keeps
running until the intermediate circuit voltage drops below
the minimum stop level. Minimum stop level typically is
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 mode
An overload occurs when the torque limit in 4-16 Torque
Limit Motor Mode/4-17 Torque Limit Generator Mode is
reached.
When the frequency converter is overloaded, the controls
reduce the output frequency to reduce the load. If the
overload is excessive, a current may occur that makes the
frequency converter cut out after approximately 5-10 s.
Operation within the torque limit is limited in time (0-60 s)
in 14-25 Trip Delay at Torque Limit.
3.11.1 Motor Thermal Protection
To protect the application from serious damages, VLT
AutomationDrive offers several dedicated features.
Torque limit
The motor is protected from being overloaded
independent of the speed. Torque limit is controlled in
4-16 Torque Limit Motor Mode and 4-17 Torque Limit
Generator Mode. The time before the torque limit warning
trips is controlled in 14-25 Trip Delay at Torque Limit.
Current limit
The current limit is controlled in 4-18 Current Limit, and the
time before the current limit warning trips is controlled in
14-24 Trip Delay at Current Limit
Minimum speed limit
4-11 Motor Speed Low Limit [RPM] or 4-12 Motor Speed Low
Limit [Hz] limit the operating speed range to between 30
and 50/60 Hz. 4-13 Motor Speed High Limit [RPM] or
4-19 Max Output Frequency limit the max output speed the
frequency converter 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. Illustration 3.39 provides the
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VLT AutomationDrive FC 300 Design Guide 90-1200 kW
following example, where the X-axis shows the ratio
between I
time in seconds before the ETR cut of and trips the
frequency converter. 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 is 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 16-18 Motor Thermal in
the FC 300.
t [s]
2000
1000
600
500
400
300
200
100
60
50
40
30
20
10
Illustration 3.39 ETR Example
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3.12 Safe Torque Off

3.12.1 Safe Torque Off Operation

The FC 302 is available with Safe Torque Off (STO)
functionality via control terminal 37. STO disables the
control voltage of the power semiconductors of the
frequency converter output stage, which in turn prevents it
from generating the voltage required to rotate the motor.
When the Safe Torque Off (T37) is activated, the frequency
converter issues an alarm, trips the unit, and coasts the
motor to a stop. Manual restart is required. The Safe
Torque Off function can be used for stopping the
frequency converter in emergency stop situations. In the
normal operating mode when Safe Torque Off is not
required, use the frequency converter's regular stop
function instead. When automatic restart is used, the
requirements according to ISO 12100-2 paragraph 5.3.2.5
must be fulfilled.
MG34S202 - Rev. 2013-08-19
and I nominal. The Y- axis shows the
motor motor
1.0 1.2 1.4 1.6 1.8 2.0
3
f OUT = 1 x f M,N (par. 1-23)
f OUT = 2 x f M,N
f OUT = 0. 2 x f M,N
I
M
I (par. 1-24)
MN
53
3