The present disclosure relates to field of overload protection devices for motors. More particularly, the present disclosure relates to a system for tripping of motors, particularly employed in lifting operations.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Motors used in lifting operations drive mechanical equipment such as elevators, lifts, escalators, dumbwaiters, hoists, and cranes. Typically, a Motor Protection Circuit Breaker (MPCB) is employed for tripping the motor circuit under abnormal conditions such as short circuit, under voltage, earth faults, and overloads. However, for lifting equipment like hoists, an increase in load (i.e. weight being lifted) leads to a very small increase in the current being drawn, which cannot be easily detected by the MPCB.
Therefore, hoists are rated at their maximum load, i.e., the maximum weight of a load that can be handled and a worker is always instructed to use a hoist within its normal rating.
However, a worker is not always familiar with the weight of a load being handled by the hoist and may occasionally handle a load over the normal rating of the hoist, causing the load sheave, load chain and a reduction gear train to be overloaded. This may result in a dangerous break down of the hoist, thereby halting the operation being performed by it. To prevent this, the hoist is always equipped with an overload protection device.

One of the overload protection devices conventionally used is a load cell. The load cell is employed in the hoist circuitry and is used to monitor the force being exerted on vital points along the hoist rope/chain by the load. Most importantly, the load cell is used to make sure no part of the hoist is carrying more load than it can handle. If an overload condition is detected, the load cell generates a trip signal to trip a circuit breaker.
Although load cells have fast response times compared to thermal tripping of the MPCB, they are bulky in size and require special mounting arrangements and expensive electronics. Further, the load cell cannot be configured as per the user's requirement. The response time of a load cell is generally of the order of 3-5 milliseconds, but this does not take into consideration the mass of the body attached to the load cell. Depending on what is attached to the load cell, the response time could be much slower than expected.
There is, therefore, felt a need for developing a cost-effective system for tripping of motors employed in lifting operations. There is also a need for a system that is sensitive to current variations and accurately detects overload conditions, thereby providing increased safety and avoiding unwanted mechanical and electrical failures.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to provide a system for tripping an electric motor.

Another object of the present disclosure is to provide a system for tripping an electric motor that accurately detects an increase in current drawn by the motor due to overloading.
Still another object of the present disclosure is to provide a system for tripping an electric motor that provides high current sensitivity.
Yet another object of the present disclosure is to provide a system for tripping an electric motor that ensures safe operation.
Still another object of the present disclosure is to provide a system for tripping an electric motor that facilitates programming of the tripping instance and time as per the user's requirement.
Yet another object of the present disclosure is to provide a system for tripping an electric motor that eliminates any chance of electrical or mechanical failure.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a system for tripping an electric motor for a hoist. The system comprises a current sensor and a digital relay. The current sensor is configured to sense the current drawn by the motor. The sensed current is directly proportional to the weight being handled by the motor. The digital relay is configured to receive the sensed current, and is further configured to generate a tripping signal to switch off the power to the motor when the sensed current exceeds a set threshold current value.

In an embodiment, the digital relay includes a signal conditioning unit, a memory, and a comparator. The signal conditioning unit is configured to receive the sensed current, and is further configured to generate sensed current values corresponding to the sensed current. In an embodiment, the signal conditioning unit includes a filter and an Analog to Digital Converter (ADC). The filter is configured to receive the sensed load current, and is further configured to filter out unwanted frequencies from the sensed current to generate a filtered sensed current. The Analog to Digital Converter is configured to receive the filtered sensed current, and is further configured to generate the sensed current values corresponding to the filtered sensed current.
In an embodiment, the memory is configured to store the set threshold current value. The threshold current value corresponds to a safe weight on the motor employed for lifting operation. In an embodiment, the threshold current value is defined by an operator.
In an embodiment, the comparator configured to receive the sensed current values and the threshold current value, and is further configured to compare the sensed current values with the threshold current value. The comparator is configured to generate a tripping signal when the sensed current values exceed the threshold current value, wherein the tripping signal is configured to trip a switch to switch off the power to the motor. In an embodiment, the signal conditioning unit and the comparator are implemented using one or more microprocessors.
In an embodiment, the switch is selected from the group consisting of a Vacuum Circuit Breaker (VCB), an Air Circuit Breaker (ACB), a Miniature Circuit Breaker (MCB), a Molded Case Circuit Breaker (MCCB), and a Motor Protection Circuit Breaker (MPCB).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A system for tripping an electric motor of the present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a line diagram of a system for tripping an electric motor, in accordance with an embodiment of the present disclosure;
Figure 2 illustrates a block diagram of a system for tripping an electric motor, in accordance with an embodiment of the present disclosure; and
Figure 3 illustrates a block diagram of a signal conditioning unit of the system of Figure 2.
LIST OF REFERENCE NUMERALS
100-System
102-Switch
104-Motor
202 - Current sensor
204 - Digital relay
206 - Signal conditioning unit
208 - Comparator
210-Memory

302-Filter
304 - Analog to Digital Converter (ADC)
DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details, are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," "including," and "having," are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or

illustrated. It is also to be understood that additional or alternative steps may be employed.
When an element is referred to as being "mounted on," "engaged to," "connected to," or "coupled to" another element, it may be directly on, engaged, connected or coupled to the other element. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
Terms such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used in the present disclosure to describe relationships between different elements as depicted from the figures.
A system for tripping an electric motor for a hoist (hereinafter referred as "system 100"), of the present disclosure, is now being described with reference to Figure 1 through Figure 3.
Referring to Figure 1 and Figure 2, the system 100 comprises a current sensor 202 and a digital relay 204. The current sensor 202 is configured to sense the current drawn by the motor 104. The current drawn by the motor 104 is directly proportional to the weight by handled by the motor 104. In an embodiment, the current sensor 202 is a current transformer. The digital relay 204 is configured to receive the sensed current, and is further configured to generate a tripping signal to switch off the power to the motor 104 when the sensed current exceeds a set threshold current value.

In an embodiment, the digital relay 204 comprises a signal conditioning unit 206, a memory 210, and a comparator 208. The signal conditioning unit 206 is configured to receive the sensed current, and is further configured to generate sensed current values corresponding to the sensed current. Referring to Figure 3, an embodiment of the signal conditioning unit 206 includes a filter 302 and an Analog to Digital Converter (ADC) 304. The filter 302 is configured to receive the sensed current, and is further configured to filter out unwanted frequencies from the sensed current to generate a filtered sensed current. The Analog to Digital Converter 304 is configured to generate the sensed current values corresponding to the sensed current.
In an embodiment, the memory 210 is configured to store the threshold current value. The threshold current value corresponds to a safe weight on the motor 104 employed for lifting operation. In an embodiment, the threshold current value is defined by an operator.
In an embodiment, the comparator 208 is configured to receive the sensed current values and the threshold current value, and is further configured to compare the sensed current values with the threshold current value. The comparator 208 is also configured to generate a tripping signal when the sensed current values exceed the threshold current value, wherein the tripping signal is configured to trip a switch 102 to switch off the power to the motor 104. The switch (102) is in electrical communication with the digital relay (204). In an embodiment, the signal conditioning unit 206 and the comparator 208 are implemented using one or more microprocessors.
In an embodiment, the switch 102 is selected from the group consisting of a Vacuum Circuit Breaker (VCB), an Air Circuit Breaker (ACB), a Miniature Circuit Breaker

(MCB), a Molded Case Circuit Breaker (MCCB), and a Motor Protection Circuit Breaker (MPCB).
In an embodiment, the response time of the digital relay 204 is programmable as per 5 the user requirements.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a 10 departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a system for tripping an electric motor 15 that:
• accurately detects an increase in current drawn by the motor due to overloading;
• provides high current sensitivity;
• ensures safe operation;
20 • facilitates programming of the tripping instance and time as per the user’s
requirement; and
• eliminates any chance of electrical or mechanical failure.
10

The embodiments herein and the various features and advantageous details thereof
are explained with reference to the non-limiting embodiments in the following
description. Descriptions of well-known components and processing techniques are
omitted so as to not unnecessarily obscure the embodiments herein. The examples
5 used herein are intended merely to facilitate an understanding of ways in which the
embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general
10 nature of the embodiments herein that others can, by applying current knowledge,
readily modify and/or adapt for various applications such specific embodiments
without departing from the generic concept, and, therefore, such adaptations and
modifications should and are intended to be comprehended within the meaning and
range of equivalents of the disclosed embodiments. It is to be understood that the
15 phraseology or terminology employed herein is for the purpose of description and not
of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
20 The use of the expression “at least” or “at least one” suggests the use of one or more
elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has
been included in this specification is solely for the purpose of providing a context for
25 the disclosure. It is not to be taken as an admission that any or all of these matters
form a part of the prior art base or were common general knowledge in the field
11

relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or
quantities are only approximations and it is envisaged that the values higher/lower
5 than the numerical values assigned to the parameters, dimensions or quantities fall
within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many
10 embodiments can be made and that many changes can be made in the preferred
embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted
15 merely as illustrative of the disclosure and not as a limitation.
12

WE CLAIM:

A system for tripping an electric motor (100) for a hoist, said system (100) comprising:
• a current sensor (202) configured to sense the current drawn by said motor (104), said current being directly proportional to the weight being handled by said motor; and
• a digital relay (204) configured to receive said sensed current, and further configured to generate a tripping signal to switch off power to said motor (104) when said sensed current exceeds a set threshold current value.
The system as claimed in claim 1, wherein said digital relay (204) includes:
• a signal conditioning unit (206) configured to receive said sensed current, and further configured to generate sensed current values corresponding to said sensed current;
• a memory (210) configured to store said threshold current value; and
• a comparator (208) configured to receive said sensed current values and said threshold current value, and further configured to compare said sensed current values with said threshold current value, said comparator (208) configured to generate said tripping signal when said sensed current values exceed said threshold current value, wherein said tripping signal is configured to trip a switch (102) to switch off the power to said motor (104),

wherein said signal conditioning unit (206) and said comparator (208) are implemented using one or more microprocessors.
The system as claimed in claim 2, wherein said switch (102) is in electrical communication with said digital relay (204).
The system as claimed in claim 2, wherein said signal conditioning unit (206) comprises:
• a filter (302) configured to receive said sensed current, and further configured to filter out unwanted frequencies from said sensed current to generate a filtered sensed current; and
• an Analog to Digital Converter (ADC) (304) configured to receive said filtered sensed current, and further configured to generate said sensed current values corresponding to said filtered sensed current.
The system as claimed in claim 1, wherein said threshold current value is defined by an operator.
The system as claimed in claim 1, wherein said threshold current value is corresponds to a safe weight on said motor (104) employed for lifting operation.

The system as claimed in claim 2, wherein said switch (102) is selected from the group consisting of a Vacuum Circuit Breaker (VCB), an Air Circuit Breaker (ACB), a Miniature Circuit Breaker (MCB), a Molded Case Circuit Breaker (MCCB), and a Motor Protection Circuit Breaker (MPCB).