Danfoss VLT CDS302 Operating Instructions Manual page 114

Parameter Descriptions
6.14.4 25-5* Alternation Settings
Parameters for defining the conditions for alternation of
the variable speed compressor (lead), if selected as part of
the control strategy.
25-50 Lead Compressor Alternation
Option:
6 6
[0] Off
*
[1] At Staging
[2] At
Command
[3] At Staging
or at
Command
25-51 Alternation Event
Option:
[0] External
*
[1] Alternation
Time Interval
25-52 Alternation Time Interval
Range:
24 h [1 – 999
*
h]
114
Operating Instructions VLT
Function:
Lead compressor alternation equalizes the
use of compressors by periodically changing
the compressor that is speed controlled. This
ensures that compressors are equally used
over time. Alternation equalizes the usage of
compressors by always choosing the
compressor with the lowest number of used
hours to stage on next.
No alternation of lead compressor function
will take place. It is not possible to set this
parameter to options other that [0] Off if
25-02 Motor Start is set other than [0] Direct
on Line.
NOTE
It is not possible to select other than [0]
Off if 25-05 Fixed Lead Compressor is set
to [1] Yes.
Alternation of the lead compressor function
will take place when staging another
compressor.
Alternation of the lead compressor function
will take place at an external command
signal or a pre-programmed event. See
25-51 Alternation Event for available options.
Alternation of the variable speed (lead)
compressor will take place at staging or the
"At Command" signal. (See above.)
Function:
This parameter is only active if the options
[2] At Command or [3] At Staging or
Command have been selected in 25-50 Lead
Compressor Alternation. If an Alternation
Event is selected, the alternation of lead
compressor takes place every time the event
occurs.
Takes place when a signal is applied to one
of the digital inputs on the terminal strip
and this input has been assigned to [121]
Lead Compressor Alternation in parameter
group 5-1* Digital Inputs.
Takes place every time 25-52 Alternation Time
Interval expires.
Function:
If [1] Alternation Time Interval option in
25-51 Alternation Event is selected, the
®
MG34M302 - VLT is a registered Danfoss trademark/Commercial Compressor
®
CDS302 and CDS303
25-52 Alternation Time Interval
Range: Function:
alternation of the variable speed compressor
takes place every time the Alternation Time
Interval expires (can be checked out in
25-53 Alternation Timer Value).
25-53 Alternation Time Value
Option: Function:
0 N/A Readout parameter for the Alternation Time Interval
value set in 25-52 Alternation Time Interval.
25-55 Alternation if Capacity < 50%
Option: Function:
[0] Disabled
[1] Enabled If Alternation If Capacity <50% is enabled, the
*
compressor alternation can only occur if the
capacity is equal to or below 50%. The capacity
calculation is the ratio of running compressors
(including the variable speed compressor) to the
total number of available compressors (including
variable speed compressor, but not those
interlocked).
N Running
Capacity =
N Total
For the Basic Cascade Controller all compressors
are equal size.
Disabled [0]: The lead compressor alternation will
take place at any compressor capacity.
Enabled [1]: The lead compressor function will be
alternated only if the numbers of compressors
running are providing less than 50% of total
compressor capacity.
Only valid if 25-50 Lead Compressor Alternation is
different from [0] Off.
25-56 Staging Mode at Alternation
Option: Function:
This parameter is only active if the option selected
in 25-50 Lead Compressor Alternation is different from
[0] Off.
Two types of staging and destaging of compressors
are possible. Slow transfer makes staging and
destaging smooth. Quick Transfer makes staging and
destaging as fast as possible; the variable speed
compressor is just cut out (coasted).
[0] Slow At alternation, the variable speed compressor is
*
ramped up to maximum speed and then ramped
down to a stand still.
[1] Quick At alternation, the variable speed compressor is
ramped up to maximum speed and then coasted to
stand still.
Illustration 6.37 is an example of the Slow transfer staging.
The variable speed compressor (top graph) and one fixed
speed compressor (bottom graph) are running before the
staging command. When the [0] Slow transfer command is
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