DGFLOW DGB MVF 30 - Page 12

12
CONTROL OF DRY RUNNING APPLICATIONS WITHOUT FLOW SENSOR, with
one or more pumps, submersible or surface
In the presence of the flow sensor, dry running is automatically detected from the inverter,
which gives a DRY RUNNING alarm.
In the absence of flow sensor, to detect dry running it is necessary to properly set the
parameters listed below.
Table setting of parameters to determine the dry running of pumps
Parameter
Symbol
Description u.m.
1
surface
pump
1
subs.
pump
More surface
pumps
More subs.
pumps
2.5 MIN DRY PRES PD
Minimum operating
pressure
%
> than
positive
delivery
head *
> than
positive
delivery
head *
> than
positive
delivery
head *
> than
positive
delivery
head *
2.6 DRY RUN TIME TD
Dry operating time
before error of water lack
s 15 8 15 8
2.7 MIN POWERF1 x
Pump 1 minimum COSPHI
-
Recommended
(self-learning) **
Necessary
(self-learning) ***
2.8 MIN POWERF2 x
Pump 2 minimum COSPHI
- - -
Necessary
(self-learning) ***
2.9 MIN POWERF3 x
Pump 3 minimum COSPHI
- - -
Necessary
(self-learning) ***
2.10 MIN POWERF4 x
Pump 4 minimum COSPHI
- - -
Necessary
(self-learning) ***
2.11 POWERF TIME x
Dry operating time
before error of dry run
s 5 3 5 3
2.12
DRY RUN
RESTART
TR
Time
interval before
restarting after error of
water lack
min 10 30 10 30
* The positive delivery head (geodetic Hg) is the hydrostatic pressure resulting from the maximum water level in
the system.
The parameter PD (% of the set pressure) should NEVER be less than the positive delivery head, otherwise the
control of dry running through PD is always verified by the positive delivery head itself.
EXAMPLE:
10-floors building (height of each floor = 3.5 m)  the hydrostatic pressure resulting from the maximum height of
the system is equal to:
10 floors x 3.5 m = 35 m = 3.5 bar (positive delivery head)
If PSET = 7 bar, then PD must be HIGHER than 50% (7 bar x 50% = 3.5 bar).
By setting PD = 60% (correct), the pressure corresponding alarm is 7 x 60% = 4.2 bar; if the operating pressure falls
below 4.2 bar, DGBOX stops for DRY RUNNING.
By setting PD = 40% (mistake), the pressure corresponding alarm is 7 x 40% = 2.8 bar, but this pressure is ALWAYS
GUARANTEED BY the positive delivery head (hydrostatic pressure of 3.5 bar), and therefore DGBOX should NOT
detect any dry running.
** Parameter PD, when properly set, it is sufficient to detect a state of dry running with one pump; for security, we
should also use the power factor COSPHI, which detects if the motor is running without any load, and stops the
pump immediately.
*** Parameter PD is NOT sufficient to detect a state of dry running with multiple pumps; It is therefore NECESSARY
also use the power factor COSPHI (for every single pump), which detects if the motor is running without any load,
and stops the pump immediately.