14-10 Mains Failure
Option:
Function:
link disappears before the motor is
ramped to 0, the motor is coasted.
Limitation:
See the introduction text in
[2]
Ctrl. ramp-
down, trip
The functionality is the same as in
option
[1] Ctrl. ramp-down
, except
in this option a reset is necessary
for starting up after power-up.
[3]
Coasting
Centrifuges can run for 1 hour
without supply. In those situations,
it is possible to select a coast
function at mains interruption,
together with a flying start, which
occurs when the mains is restored.
[4]
Kinetic back-
up
Kinetic back-up ensures that the
frequency converter keeps running
as long as there is energy in the
system due to the inertia from
motor and load. This is done by
converting the mechanical energy
to the DC-link and maintaining
control of the frequency converter
and motor. This can extend the
controlled operation, depending on
the inertia in the system. For fans, it
is typically several seconds; for
pumps up to 2 s; and for
compressors only for a fraction of a
second. Many industry applications
can extend controlled operation for
many seconds, which is often
enough time for the mains to
return.
130BC918.10
U
14-11*1.35
Ref
n [RPM]
t [S]
A B C D E
A
DC
U
DC
[V]
t [S]
A Normal operation
B Mains failure
C Kinetic back-up
D Mains return
E Normal operation: ramping
Illustration 4.40 Kinetic Back-up
The DC level during
[4] Kinetic back-
up
equals
parameter 14-11 Mains
Fault Voltage Level
x 1.35.
14-10 Mains Failure
Option:
Function:
If the mains does not return, U
DC
is
maintained as long as possible by
ramping the speed down towards 0
RPM. Finally, the frequency
converter coasts.
If the mains returns while in kinetic
back-up mode, U
DC
increases above
parameter 14-11 Mains Fault Voltage
Level
x 1.35. This is detected in 1 of
the following ways.
•
If U
DC
>
parameter 14-11 Mains
Fault Voltage Level
x 1.35 x
1.05.
•
If the speed is above the
reference. This is relevant
if the mains comes back
at a lower level than
before, for example
parameter 14-11 Mains
Fault Voltage Level
x 1.35 x
1.02. This does not fulfil
the criterion in point 1,
and the frequency
converter tries to reduce
U
DC
to
parameter 14-11 Mains
Fault Voltage Level
x 1.35
by increasing the speed.
This cannot be done as
the mains cannot be
lowered.
•
If running mechanically.
The same mechanism as
in point 2 applies, but the
inertia prevents the speed
from going above the
reference speed. This leads
to the motor running
mechanically until the
speed is above the
reference speed and the
situation in point 2 occurs.
Instead of waiting for that
criterion, point 3 is
introduced.
[5]
Kinetic back-
up, trip
The difference between kinetic
back-up with and without trip is
that the latter always ramps down
to 0 RPM and trips, regardless of
whether mains returns or not.
The function does not detect if
mains returns. This is the reason for
Parameter Descriptions
Programming Guide
MG06J202
Danfoss A/S © 03/2019 All rights reserved.
129
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