Danfoss VLT 2800 Design Manual page 104

Programming
4.6.1 Dry Run Detection
For most pumps, especially submersible bore-hole pumps,
it must be assured that the pump is stopped in case of dry
run. This is assured by the Dry-run detection feature.
How does it work?
Dry-run detection is based on power/frequency monitoring
4 4
and works in both closed and open loop.
Stop (trip) due to dry run is initiated under following
conditions:
Closed loop:
•
The adjustable frequency drive is running at
maximum frequency (parameter 202 Output
frequency high limit, f
•
Feedback is below minimum reference (parameter
204 Minimum reference, Ref,
•
Power consumption is below the no/low flow
power curve for a certain time (parameter 470 Dry
run time out)
Open loop:
•
Whenever the power consumption is below the
no/low flow power curve for a certain time
Illustration 4.19 Relation between Power Consumption and Flow
4.6.2 Benefits
•
Dry run protection. Shuts down at no or low flow
and protects the motor and pump from
overheating.
•
Improved energy savings with enhanced sleep
mode.
•
Minimised risk of bacterial growth in drinking
water because of insufficient motor cooling.
•
Easy commissioning.
102
Design Guide
) and
MAX
) and
MIN
Danfoss A/S © Rev. May/2014 All rights reserved.
(parameter 470 Dry run time out) the adjustable
frequency drive trips.
The adjustable frequency drive can be set up for either
manual or automatic restart after stop (parameters 405
Reset function and 406 Automatic restart time).
•
Enhanced sleep mode and dry-run detection can
be enabled and disabled independently. This is
done in parameter 462 Enhanced sleep mode timer
and parameter 470 Dry run time out.
Centrifugal pumps with radial impellers show a clear one-
to-one relation between power consumption and flow,
which is utilised to detect a no or low flow situation.
It is only necessary to enter 2 sets of values for power and
frequency (minimum and maximum) at no or low flow. The
adjustable frequency drive then automatically calculates all
data in-between those 2 sets of values and generates the
no/low flow power curve.
If the power consumption drops below the power curve,
the adjustable frequency drive enters sleep mode or trips
due to dry-run, depending on the configuration.
Only centrifugal pumps with radial impeller show a clear
one-to-one relationship between flow and power.
Consequently, proper functionality of the enhanced sleep
mode and dry-run detection is only given for this type of
pump.
MG27E402