FIELD OF THE INVENTION
The invention relates to a system for protection of submersible pumps from dry running.
More particularly, it relates to a current based protection system involving an undercurrent
relay provided in the starter circuit for the submersible pump to avoid dry running of pumps
used in dewatering application and a method of implementation of such controlled operation
of pumps. Importantly, the undercurrent is set at a value just over the no-load current
rating of the pump/motor such that as soon as the submersible pump runs without water,
the resultant low motor current is sensed by the relay permanently connected in the starter,
generating a signal that is used for warning/tripping and thus protecting the stator winding
and also the mechanical seal between the stator chamber and the impeller chamber from
damage/failure due to dry running and resultant over heating. Advantageously, the under
current relay based control system of the drive unit of the submersible pump takes care of
all the conditions of dry running i.e. dry sump and clogged mesh around impeller in a
simple, cost effective, reliable and fail-safe manner over the conventional system and thus
having wide scale industrial or household applications for dewatering of sumps/pits or
similar other operation.
BACKGROUND ART
It is well known in the art that oil cooled dewatering submersible pump is widely used for
lifting water from under ground sump/reservoir operating on a continuous cycle. The
construction of such submersible pump comprises a rotor at the center, which is housed in a
stator that is filled with oil to cool the stator winding while in continuous operation. The
discharge of the pump i.e. the water at room temperature, passes through the casing
surrounding the stator, which carries away the heat from oil that cools the stator winding.
There is also a mechanical seal provided in these pump that isolates the stator chamber
from the impeller chamber. The seal is cooled by water at one end and by oil at the other
end. If for any reason, the discharge becomes zero so that the heat transfer does not take
place so that heat is accumulated in the stator coil as well as seal and the cooling oil
causing rise in temperature of stator winding and mechanical seal. As a consequence, the
stator winding as well as the mechanical seal get heated up and fail. For longer life and
reliable performance of submersible pumps for dewatering application, an appropriate
protection is thus essential which can sense the condition of dry running and protect the
submersible pump and the components from dry running and resultant failure/damage.
Conventionally, Liquid Level Controller (LLC) and probes at different level of water column is
provided to detect the water level and accordingly control the running of pump. When the
sump become dry i.e. all water collected in sump has been lifted and discharged outside the
pit/well, the probe activates the LLC and this in turn gives a corresponding signal which is
used for warning or tripping.
It has been experienced in the conventional LLC based control of dry run protection, when
the pumps are put in emergency situation and the installation is temporary in nature, it
becomes difficult to install the probe in a fail-safe manner. Very often the leakage water
spilling on the probes activate them leading to false sensing of low level. Also when the
pump is shifted to another location the probes need to be reinstalled at the new location
which is time consuming as well as cumbersome.
It has also been experienced in the conventional LLC based control of dry run protection,
that if the wire mesh surrounding the submersible pump gets clogged by some foreign
materials, the probe fails to detect the dry condition/fall in water level, and as a result the
stator winding or seal fails due to lack of adequate cooling as the pump runs dry in absence
of timely detection.
There has thus been a continuing need in the art to developing a system of protection for
submersible pumps from dry running such that the system operates in a reliable and fail
safe manner. It is possible by studying the nature of variation of current with discharge, to
provide an indication as to find out a means of protection against dry running which shows a
drastic fall in discharge leading to fall in current taken by the submersible pump motor.
Irrespective of the reason of dry running except a locked rotor or other electrical faults
which are taken care of by other conventional electrical protection, there is always a very
low current which is of the value near no load current at the time of no discharge. Use of
under current relay of proper rating commensurate with motor/pump rating, sensing no-
load stator current as a signal for controlling pump on/off operation such that dry running is
completely avoided, even if there is reason for non detection of depletion of water level in
sump leading to dry run. This necessity has led to the present invention as described below.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to developing a protection system to
avoid dry running of submersible pump by detection of no load motor/stator current for

controlling the operation of the pump motor and maintain adequate cooling of components
and thus avoiding failure of the stator winding and saving damage of the mechanical seal
between the stator chamber and the impeller chamber due to temperature rise beyond
permissible limits during continuous operation and a method of implementation of such
protection.
A further object of the present invention is directed to developing a protection system to
avoid dry running of submersible pump using an under current relay attached to the starter
such that the low no load current is detected by the relay set at a value just over no load
current as an alternative means to avoid dry running condition of pump.
A further object of the present invention is directed to developing a protection system to
avoid dry running of submersible pump using an under current relay attached to the starter
wherein the relay sense the low current near no load current under dry run condition so as
to generate a signal used for appropriate warning/tripping.
A still further object of the present invention is directed to developing a protection system
to avoid dry running of submersible pump using an under current relay which is
permanently connected in the starter and is easy to install.
A still further object of the present invention is directed to developing a protection system
to avoid dry running of submersible pump using a method which does away with the
difficulties associated with the conventional installation and using under current relay which
is permanently connected in the starter and is easy to install.
A still further object of the present invention is directed to developing a protection system
to avoid dry running of submersible pump using an under current relay attached to the
starter wherein the relay takes care of all the conditions of under loading including dry
running, in a simple, cost effective and reliable manner.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a protection system for
submersible pumps and the like comprising:

means for sensing the under loading conditions including under current;
means for generating a signal when the under loading conditions is sensed; and
means for activating a warning/trip means based on the under current signal thus sensed to
thereby protect the pump.
Another aspect of the present invention is directed to a protection system for submersible
pumps and the like wherein said means for sensing the under loading conditions comprises
means for sensing under current comprises an under current relay adapted to take care of
all conditions of under loading.
A further aspect of the present invention is directed to a protection system for submersible
pumps and the like wherein said under current relay is adapted to be set slightly above the
no load current and to sense the under current and generate said signal for
warning/tripping.
A still further aspect of the present invention is directed to a protection system for
submersible pumps and the like comprising an under current relay adapted to take care of
all conditions of under loading including dry-running.
A still further aspect of the present invention is directed to a protection system for
submersible pumps and the like wherein said under current relay is permanently connected
in the starter.
A still further aspect of the present invention is directed to a protection system for
submersible pumps and the like comprising:
a rotor at the center housed within a stator filled with oil;
a casing surrounding the stator adapted to allow passage of the discharge to carry out the
heat from the oil and cool the stator windings;
a mechanical seal isolating the stator chamber from the rotor chamber, said seal being
cooled by water at one end and by oil at the other end;
an under current relay connected in the starter adapted to sense a pre set no load current
in conditions of dry running and generate signal for warning/tripping of the pump.

The present invention and its objects and advantages are described in greater details with
reference to the following accompanying non limiting figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE in Annexure I
Figure 1: is the schematic illustration of the submersible pump with its construction feature.
Figure 2: is the schematic illustration of the submersible pump with conventional water level
based control system using a Liquid Level Controller and Probes dipped in water at different
levels.
Figure 3: is the schematic illustration of the control circuit diagram/block diagram showing
the different components in the control circuitry involving the under current relay and
means for signal generation , sensing and implementing protection against dry running.
Figure 4: is the schematic illustration of the control circuit diagram/block diagram showing
the comparative electrics of the conventional system using LLC and the invented system
using undercurrent relay.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
Reference is first invited to the accompanying Figure 1 that schematically illustrate the
arrangement of submersible pump and motor assembly showing the motor, pump, stator
chamber, impeller chamber, location of coolant oil, chamber surrounding the stator carrying
the water discharge from the pump, the mechanical seal isolating the stator chamber from
the impeller chamber.
It would be clearly apparent from the constructional features of the pump that the water
discharged by the pump when it runs is the main coolant fro the oil and in turn stator
winding and mechanical seal. This discharge is possible only when there is water in sump
and the mesh around the impeller is clear.
Reference is now invited to the accompanying Figure 2 that illustrates the control circuitry
involving the use of Liquid Level Controller and its probes. It is apparent that that when the
sump goes below the level of the middle probe the pump stops. But when there is clogging
of the mesh, water level doesn't go down and the LLC does not activate although this is a
case of dry running.
Reference is now invited to the accompanying Figure 3 of the under current relay based
dry running protection of submersible pump according to the present invention. It is clearly
apparent from the said circuit diagram that said under current relay is connected
permanently to the starter and is easy to install. The relay, which is connected to the
secondary side of CT, is having an operating current range of 0.1 Amp. to 5.0 Amp. The
current is set at a value preferably 40-45% of the full load current of the pump. As the
pump runs dry without any water, the current becomes very low i.e. near the no-load
current of the motor. The under current relay is able to sense this low current which is pre-
set at a value, that is slightly over the rated no load current i.e. about 30 amps for a 45HP
pump motor. The relay upon sensing the under current, generates a signal in the control
circuitry so that it is used for warning or tripping the supply power to the motor and thus
saving from failure of stator winding/ seal due to over heating due to lack of proper cooling
of stator and mechanical seal between the stator and the impeller chamber, due to dry
running of the pump.
Reference is now invited to the accompanying Figure 4 which gives a comparison between
both the schemes. It is apparent that with the elimination of probes the difficulties
associated with installation and malfunctioning of the LLC is completely done away with.
It is thus possible by way of the present invention to developing a protection system for
submersible pumps to avoid dry running and resultant over heating and failure of motor
windings or mechanical seal between the stator chamber and the impeller chamber. The
system and method of protection of submersible pump from failure due to dry running in
dewatering application on one hand utilizes an under current relay adapted to sensing the
low current/no-load motor current when the pump is running dry (i.e. without water) and on
the other hand generate reasonably at low response time a corresponding signal to activate
the control circuit to stop operation of the pump under such dry condition and thus
preventing failure of stator winding or the mechanical seal. Advantageously, the system

according to the invention is adapted to take care of any operational limitations of the pump
due to clogging of the wire mesh/caging surrounding the submersible pump by foreign
materials while in operation for dewatering sump/pit, to thereby making conventional LLC
system inoperative and ineffective. The under current relay based protection system for
submersible pumps according to the present invention is thus having longer operating life in
a simple, cost effective, easy to install and reliable manner to meet the requirements of
industry and house hold applications.

WE CLAIM:
1. A protection system for submersible pumps and the like comprising:
means for sensing the under loading conditions including under current ;
means for generating a signal when the under loading conditions is sensed; and
means for activating a warning/trip means based on the under current signal thus sensed to
thereby protect the pump.
2. A protection system for submersible pumps and the like as claimed in claim 1 wherein
said means for sensing the under loading conditions comprises means for sensing under
current comprises an under current relay adapted to take care of all conditions of under
loading.
3. A protection system for submersible pumps and the like as claimed in claim 2 wherein
said under current relay is adapted to be set slightly above the no load current and to sense
the under current and generate said signal for warning/tripping.
4. A protection system for submersible pumps and the like as claimed in anyone of claims 1
to 3 comprising an under current relay adapted to take care of all conditions of under
loading including dry-running.
5. A protection system for submersible pumps and the like as claimed in anyone of claims 1
to 4 wherein said under current relay is permanently connected in the starter.
6. A protection system for submersible pumps and the like as claimed in anyone of claims 1
to 5 comprising:
a rotor at the center housed within a stator filled with oil;
a casing surrounding the stator adapted to allow passage of the discharge to carry out the
heat from the oil and cool the stator windings;
a mechanical seal isolating the stator chamber from the rotor chamber, said seal being
cooled by water at one end and by oil at the other end;
an under current relay connected in the starter adapted to sense a pre set no load current
in conditions of dry running and generate signal for warning/tripping of the pump.

7. A protection system for submersible pumps and the like substantially as hereindescribed.

The invention relates to a protection system for submersible pumps from dry running. More
particularly, the present invention relates to an undercurrent relay operated protection
system for the submersible pump adapted to avoid dry running of pumps in dewatering
application and a method of its implementation. The undercurrent relay is set at a value
selectively slightly over the no-load current. The relay upon sensing the under current
generates a signal that is used for warning/tripping and thus protecting the stator winding
and also the mechanical seal between the stator chamber and the impeller chamber from
over heating due to dry running and resultant failure. The present under current protection
system for submersible pumps takes care of all the conditions including dry running in a
simple, cost effective, reliable manner enhancing the operating life of submersible pumps
and thus having potential for wide scale industrial or household applications for
dewatering/other purpose.