Enhanced Sleep Mode - Danfoss VLT 2800 Series Operating Instructions Manual

Enhanced Sleep Mode

The enhanced sleep mode has been developed to
work under all conditions and to overcome problems
when using pumps with flat pump curves or when suc-
tion pressure varies. Enhanced sleep mode provides
excellent control for shutting down the pump at low
flow, thus saving energy.
If operating with constant pressure control in the SYS-
TEM, for instance a drop in the suction pressure will
lead to an increase in frequency to maintain pressure.
Consequently there is a situation, where the frequency
will vary independent of the flow. This can lead to in-
appropriate activation of sleep mode or wake-up of the
frequency converter.
Flat pump curves leads to a situation where there will
be little or no change in frequency in response to flow
variation. Consequently, the frequency converter
might not reach the sleep frequency when setting it at
a low value.
Enhanced sleep mode is based on power/frequency
monitoring and works in closed loop only. Stop due to
the enhanced sleep mode function is initiated under
the following conditions:
• Power consumption is below the no/low flow
power curve and stays there for a certain time
(parameter 462 Enhanced sleep mode timer)
or
• The pressure feedback is above the refer-
ence when running at minimum speed and
stays there for a certain time (parameter 462
Enhanced sleep mode timer).
If the feedback pressure falls below the wakeup pres-
sure (Parameter 464 Wakeup pressure), the frequency
converter restarts the motor.
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 detec-
tion feature.
®
MG.27.A2.02 - VLT is a registered Danfoss trademark
®
VLT 2800 Series
How Does It Work?
Dry run detection is based on power/frequency moni-
toring and works in both closed and open loop.
Stop (trip) due to dry run is initiated under following
conditions:
Closed loop:
• The frequency converter is running at maxi-
mum frequency (parameter 202 Output fre-
quency high limit, f
• Feedback is below minimum reference (pa-
rameter 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
(parameter 470 Dry run time out) the frequen-
cy converter will trip.
The frequency converter can be set up for either man-
ual or automatic restart after stop (parameters 405
Reset function and 406 Automatic restart time).
• Enhanced Sleep Mode and Dry Run Detec-
tion can be enabled and disabled independ-
ently. 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 utilized to detect a no or low flow situa-
tion.
It is only necessary to enter two sets of values for pow-
er and frequency (min and max) at no or low flow. The
frequency converter then automatically calculates all
data in-between those two sets of values and gener-
ates the no/low flow power curve.
If the power consumption falls below the power curve,
the frequency converter enters Sleep-mode or trips
due to dry run, depending on the configuration.
) and
MAX
) and
MIN
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