DGFLOW DGB MV 30, Operator And Maintenance Manual

Page: 12 / 40

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.