System Monitoring - Danfoss VLT 380-500 V Design Manual

Product Features
NOTICE
[7] PTC 1 & Relay W and [8] PTC 1 & Relay A/W in
parameter 5-19 Terminal 37 Safe Stop opens up for
automatic restart when the external safety device is de-
activated again.
The automatic restart is only allowed in the following
cases:
•
The unintended restart prevention is
implemented by other parts of the Safe Torque
Off installation.
•
A presence in the dangerous zone can be
physically excluded when Safe Torque Off is not
activated. In particular, paragraph 5.3.2.5 of ISO
12100-2 2003 must be observed.
®
See chapter 7.3.10 VLT PTC Thermistor Card MCB 112 and
®
the VLT PTC Thermistor Card MCB 112 Operating Guide for
more information about MCB 112.

5.4 System Monitoring

The frequency converter monitors many aspects of system
operation including:
•
Mains conditions.
•
Motor load and performance.
•
Frequency converter status.
An alarm or warning does not necessarily indicate a
problem with the frequency converter itself. It can be a
condition outside of the frequency converter that is being
monitored for performance limits. The frequency converter
has various preprogrammed fault, warning, and alarm
responses. Extra alarm and warning functions can be
selected to enhance or modify system performance.
This section describes common alarm and warning
functions. Understanding that these functions are available
can optimize a system design and possibly avoid
introducing redundant components or functionality.
5.4.1 Operation at Overtemperature
By default, the frequency converter issues an alarm and
trips at overtemperature. If Autoderate and Warning are
selected, the frequency converter warns of the condition
but continues to run and attempts to cool itself by first
reducing its carrier frequency. Then, if necessary, it reduces
the output frequency.
5.4.2 High and Low Reference Warning
In open-loop operation, the reference signal directly
determines the speed of the frequency converter. The
display shows a flashing reference high or low warning
when the programmed maximum or minimum is reached.
MG37N102
Design Guide
5.4.3 High and Low Feedback Warning
In closed-loop operation, the frequency converter monitors
selected high and low feedback values. The display shows
a flashing high or flashing low warning when appropriate.
The frequency converter can also monitor feedback signals
in open-loop operation. While the signals do not affect the
operation of the frequency converter in open loop, they
can be useful for system status indication locally or via
serial communication. The frequency converter handles 39
different units of measure.
5.4.4 Imbalance of Supply Voltage or
Phase Loss
Excessive ripple current in the DC bus indicates either a
mains imbalance of supply voltage or phase loss. When a
power phase to the frequency converter is lost, the default
is to issue an alarm and trip the unit to protect the DC bus
capacitors. Other options are to issue a warning and to
reduce output current to 30% of full current, or to issue a
warning and continue normal operation. Operating a unit
connected to an imbalanced line can be desirable until the
imbalance is corrected.
5.4.5 High-frequency Warning
Useful in staging on extra equipment such as pumps or
cooling fans, the frequency converter can warn when the
motor speed is high. A specific high-frequency setting can
be entered into the frequency converter. When the output
of the unit exceeds the set warning frequency, the unit
shows a high-frequency warning. A digital output from the
frequency converter can signal external devices to turn on.
5.4.6 Low-frequency Warning
Useful in staging off equipment, the frequency converter
can warn when the motor speed is low. A specific low-
frequency setting can be selected for warning and to turn
off external devices. The unit does not issue a low-
frequency warning when it is stopped nor after start-up
until after the operating frequency has been reached.
5.4.7 High Current Warning
This function is similar to high-frequency warning (see
chapter 5.4.5 High-frequency Warning), except a high current
setting is used to issue a warning and turn on external
equipment. The function is not active when stopped or at
start-up until the set operating current has been reached.
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