Safe Stop - Danfoss VLT AutomationDrive FC 300 Design Manual

Introduction
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.
Static Overload in VVC
3 3
When the frequency converter is overloaded (the torque
limit in 4-16 Torque Limit Motor Mode/4-17 Torque Limit
Generator Mode is reached), the controls reduces the
output frequency to reduce the load.
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 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 Torque limit feature the motor is protected for being
overloaded independent of the speed. Torque limit is
controlled in 4-16 Torque Limit Motor Mode and or
4-17 Torque Limit Generator Mode and the time before the
torque limit warning shall trip 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 shall trip is
controlled in 14-24 Trip Delay at Current Limit.
Min Speed Limit
(4-11 Motor Speed Low Limit [RPM] or 4-12 Motor Speed Low
Limit [Hz]) limit the operating speed range to for instance
between 30 and 50/60Hz. Max Speed Limit: (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. The characteristic is shown in
Illustration 3.39:
52
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®
VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
plus
mode
MG33BE02 - VLT
t [s]
2000
1000
600
500
400
300
200
100
60
50
40
30
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10
1.0 1.2
Illustration 3.39 ETR: The X-axis shows the ratio between I
and I nominal. The Y- axis shows the time in seconds before
motor
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 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
16-18 Motor Thermal in the FC 51 Micro Drive Programming Guide.

3.12 Safe Stop

The FC 302, and also the FC 301 in A1 enclosure, can
perform the safety function Safe Torque Off (STO, as
defined by EN IEC 61800-5-2
defined in EN 60204-1
Danfoss has named this functionality Safe Stop. Before
integrating and using Safe Stop in an installation, a
thorough risk analysis on the installation must be carried
out in order to determine whether the Safe Stop
functionality and safety levels are appropriate and
sufficient. It is designed and approved suitable for the
requirements of :
- Category 3 in EN ISO 13849-1
- Performance Level "d" in EN ISO 13849-1:2008
- SIL 2 Capability in IEC 61508 and EN 61800-5-2
- SILCL 2 in EN 62061
1) Refer to EN IEC 61800-5-2 for details of Safe torque off
(STO) function.
2) Refer to EN IEC 60204-1 for details of stop category 0
and 1.
Activation and Termination of Safe Stop
The Safe Stop (STO) function is activated by removing the
voltage at Terminal 37 of the Safe Inverter. By connecting
the Safe Inverter to external safety devices providing a safe
delay, an installation for a safe Stop Category 1 can be
obtained. The Safe Stop function of FC 302 can be used for
®
is a registered Danfoss trademark
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
I (par. 1-24)
1.6 1.8 2.0
1.4
MN
1 ) and Stop Category 0 (as
2
).
M
motor