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
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
MAX
) and
•
Feedback is below minimum reference (
parameter
204 Minimum reference
, Ref,
MIN
) and
•
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
(
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.
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.
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.
Programming
Design Guide
102
Danfoss A/S © Rev. May/2014 All rights reserved.
MG27E402
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