ETR (Electronic Thermal Relay)
At lower speeds, the ETR cuts off at lower levels due to
reduced cooling of the motor. In that way, the motor is
protected from being overheated even at low speed. The
ETR feature calculates the motor temperature based on the
actual current and speed. The calculated temperature is
visible as a readout parameter in
16-18 Motor Thermal
in
the FC 300.
1.2
1.0
1.4
30
10
20
100
60
40
50
1.8
1.6
2.0
2000
500
200
400
300
1000
600
t [s]
175ZA052.11
fOUT = 0.2 x f M,N
fOUT = 2 x f M,N
fOUT = 1 x f M,N
IMN
IM
Figure 3.39 ETR Example
3.12 Safe Stop
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.
3.12.2 Safe Torque Off Operation (FC
302 only)
The Safe Torque Off function of FC 302 can be used for
asynchronous, synchronous, and permanent magnet
motors. It may happen that 2faults occur in the frequency
converter's power semiconductor. When using synchronous
or permanent magnet motors, this may cause a residual
rotation. The rotation can be calculated to Angle=360/
(Number of Poles). The application using synchronous or
permanent magnet motors must take this into consid-
eration and ensure that this is not a critical safety issue.
This situation is not relevant for asynchronous motors.
3.12.3 Liability Conditions
Liability conditions
The user is responsible for ensuring that personnel know
how to install and operate the Safe Torque Off function by:
•
Reading and understanding the safety regulations
concerning health and safety/accident prevention
•
Understanding the generic and safety guidelines
given in this description and the extended
description in the
Operating Instructions VLT
®
Frequency Converters – Safe Torque Off
.
•
Having a good knowledge of the generic and
safety standards for the specific application
The user is defined as integrator, operator, service, and
maintenance staff.
3.12.4 Additional Information
For more information regarding Safe Torque Off, including
installation and commissioning, refer to the Operating
Instructions VLT
®
Frequency Converters – Safe Torque Off.
Product Introduction
Design Guide
62
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
MG34S222
3
3
Содержание VLT AutomationDrive FC 300
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