GrigPC: Constant Pressure system
Elettrotecnica Grig S.r.l. presents a new series of control
panels with frequency inverters.
The cost of electrical supply for submersible pumps, as well
as for vertical pumps and other types of pumps is steadily
increasing.
It is foreseeable that the increase of the cost of energy will be
higher then the average increase of the cost of life in the next
decade.
Frequency inverters dose the supply to the pumps according
to actual needs and cut down the absorbtion of energy.
Saves in energy can be dramatic in pumps and fans. The
couple of resitance to motion of pumps and fans is a square
function of the working speed.
The power they need, on the
contrary, is a cube function of the working speed.
This means that a small reduction in speed results in
substantial savings in energy.
In fact, the savings in energy costs in most cases balance
the cost of a frequency inverter in just 1-2 years. On top of
that, you have a constant pressure system and avoid all the
troubles such as the water-hammer.
Today,in order to reduce the delivery pumps are sometimes
operated with choking valves which do not reduce the power
used by the motor. They just choke its output and simply
waste the surplus energy.
Some pumps are equipped with a re-cycle device, which
sends back the exceeding water. This results in a double
waste of energy as the water is pumped one way and back
for no reason.
Energy wastings are proportional to the delivery reduction or
to the recycled water.
Besides, employing a valve implies:
- wearing out of the valve and need for maintenance
- wearing out of the pumps which are constantly being used
at full load of work
- wasting energy even when the valve is completely open,
as it absorbs about 10% of the pump delivery, anyway.
Using a frequency inverter has several benefits, such as:
- energy savings: it is proportional to the actual needs of water
and the time the pump is operated;
- no need for choking valves and savings in installation/
maintenance costs;
- longer life of impellers as they are operated at a lower average
speed;
- lower wearing out of the whole pumping system;
- lower noise thanks to a lower average speed;
- less vibrations which can damage the pipelines, thanks to
elimination of water-hammer;
- lower entry current thanks to a smooth cranking; the supply
net is not overloaded as would be with other starters;
- possibility of updating an old pump in a constant pressure
system. It is enough to connect the old pump to a GrigPC
panel.
GrigPC panels:the advanced controller for constant pressure systems
The controller mounted in GrigPC inverters has many built-in
advanced features and does not need external expansions.
Among those features are:
- digital control of the curve of speed in relation to pressure;
- input for pressure probe (0-10V) or (0..20, 4..20mA) with
+24V in the cable terminals for supplying the probe itself;
- automatic stand-by for exceeding pressure and automatic
start-up in case of pressure drop;
- emergency mode: the customer can set the speed of the
motor in case the probe fails;
- start/stop of up to 3 auxiliary pumps with automatic
adjustment of the inverter;
- change-over of auxiliary pumps (optional) to balance the
pumps wearing-out;
- adjustable electronic thermal protection for the motor;
- under/overload protection;
- digital display showing the working hours and energy
consumptions
All the parameters can be set easily from the front panel
This catalogue does not include all the models of Grig PC
panels. Panels up to 400kW and multi inverter panels are
avaliable on request.
Automatic mode
The main purpose of GrigPC panels is to keep constantly
the pressure of water at a certain point (Pn).
The inverter compares the signal from the pressure sensor
with the value set by the user. The inverter sets the speed
of the pump in order to match the pressure to the set point.
If the pump runs at a given speed, the inverter starts/stops
the auxiliaries pumps in sequence. The delay between one
pump and the next can be set by the user as well as the
max/min speed of the main pump. The panel will work out
the most efficient time of switching from auxiliary pumps to
the main pump.
Emergency mode
If the pressure sensor fails the inverter will switch to the
emergency mode.
In the emergency mode the main pump works at a fixed
speed.
Auxiliary pumps will start/stop according to the signals of
mechanical pressure switches.
If the inverter fails the auxiliary pumps will still work.
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