Claims:1. A current sensor assembly for sensing current flowing through molded case circuit breaker (MCCB) pole placed in a distribution system, comprising:
at least one primary winding for the flow of primary current, wherein said primary winding comprises an incoming terminal, an outgoing terminal, at least one primary conductor means connector to said incoming terminal on one end and said outgoing terminal on other end;
at least one secondary windings enclosed in an enclosure within a central position of said sensor, wherein said secondary windings comprises at least two windings having a current transformer winding and a Rogowski coil winding, inside said enclosure;
wherein, when primary current flows through said primary windings, causes generation of heat, enabling said current transformer winding and said Rogowski coil winding for powering a trip unit of said MCCB through sensor output leads and used for control and protection of a circuit by giving trip command to said MCCB.

2. The sensor assembly as claimed in claim 1, wherein said primary conductor means forms two turns and pass through said central portion of said sensor, wherein said two turns are insulated from each other with help of an in-turn insulation.

3. The sensor assembly as claimed in claim 2, wherein said central portion is encapsulated by encapsulation resin of high thermal conductivity and high temperature withstand properties that facilitates better conduction of heat from local hot spots to the entire central portion.
4. The sensor assembly as claimed in claim 3, wherein said encapsulation facilitates primary conductors to be embedded within said encapsulation resin, for providing structural support to said primary conductors.
, Description:TECHNICAL FIELD OF THE INVENTION

[001] The present subject matter described herein, in general, relates to current sensors for trip unit of molded case circuit breakers (MCCB), and more particularly relates to a current sensors having improved heat transfer arrangement and improved insulation system for better thermal, structural and electrical performance of the system.

BACKGROUND OF THE PRESENT INVENTION

[002] The electrical systems in residential, commercial and industrial applications usually include a panel board for receiving electrical power from a utility source. The power is then routed through overcurrent protection devices to designated branch circuits supplying one or more loads. These overcurrent devices are typically circuit breakers which are capable to interrupt the electrical current in case of fault. Interruption of the circuit reduces the risk of injury or the potential of property damage from a resulting fire.

[003] Circuit breakers are a preferred type of circuit interrupter because a resetting mechanism allows their reuse. Typically, circuit breakers interrupt an electric circuit due to a trip condition such as a current overload or ground fault. The current overload condition results when a current exceeds the continuous rating of the circuit breaker for a time interval determined by the trip current. The ground fault trip condition is created by an imbalance of currents flowing between a line conductor and a neutral conductor such as a grounded conductor, conductive object causing a current path to ground, or an arcing fault to ground.

[004] A sensor is a device used for sensing the current flowing through the MCCB pole placed in a distribution system. The sensor assembly consist of Primary winding and secondary winding. The primary winding for a MCCB sensor can be single turn or multi-turn depending on the magnitude of primary current. The primary winding is generally an integral part of main current path of the circuit breaker. Thus the current flowing through the circuit breaker is tapped with the help of sensor and is used for measurement and control of the circuit breaker.

[005] With present trend of compact circuit breakers, every component calls for optimization. One of the major challenges for the design of sensor remains the compact while meeting thermal and insulation requirements. The primary conductor is placed very close to the windings of current transformers and Rogowski coils with a very small layer of insulation. When the primary current flows through the primary conductor high amount of heat is generated. While the primary current is flowing, the current transformer and Rogowski coils also being used for powering up trip unit, protection and control function of the trip unit. So the heat is being produced simultaneously on current transformer as well as the Rogowski coils. The net heat within the enclosure due to primary and secondary current is very high. This may lead to faster deterioration of insulation and therefore insulation failure of the sensor.

[006] During short circuit there is repulsive force between the primary conductors (in case of multi-turn secondary winding) due to this force the primary conductor which is placed very close to the secondary conductor due to force and heat, breaks the insulation between primary and secondary winding thus primary winding conductor gets shorted with the secondary winding.

[007] The conventional sensors (current transformer /Rogowski) with a conductor passing through its centre recess sometimes enclosed in the enclosure or sometimes open. For higher insulation requirements, the sensor is potted completely which leads to higher space requirement.

[008] Reference is made to JP2015184179A which discloses current measurement system, current measuring device and current measuring method teaches the sensor used for measurement of current through cables which in turn is used for measurement and control of circuit breaker. The sensor disclosed in the invention does not have encapsulation for better cooling and higher electrical performance.

[009] Reference is also made to CN1048335691B which discloses a common base and application of the base thermal magnetic and electronic MCCB teaches the construction of MCCB in which common base can be used for MCCB with both thermal magnetic and electronic trip unit. The sensor disclosed in the invention does not have encapsulation for better cooling and higher electrical performance.

[0010] Reference is also made to KR101227990B1 which discloses MCCB with current monitoring apparatus. This patent discloses the sensor arrangement for MCCB this sensor is used for measuring, control and monitoring of current through MCCB. The sensor disclosed in the invention does not have encapsulation for better cooling and higher electrical performance.

[0011] However, the in view of the prior art, the inventors of the present invention have a need to provide a better and more efficient system for heat transfer and better insulation is required. During short circuit there is repulsive force between the primary conductors (in case of multi-turn secondary winding), due to this force the primary conductor which is placed very close to the secondary conductor due to force and heat, breaks the insulation between primary and secondary winding thus primary winding conductor gets shorted with the secondary winding. Thus, there was a dire need for a system with better heat transfer and better insulation properties while retaining the compact shape.

SUMMARY OF THE INVENTION
[0012] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0013] An object of the present invention is to provide a system with better heat transfer and better insulation properties while retaining the compact shape.

[0014] Another object of the present invention is to achieve better heat transfer and better insulation properties by encapsulating the central portion of the sensor.

[0015] Accordingly to one aspect, the present invention provides a current sensor assembly for sensing current flowing through molded case circuit breaker (MCCB) pole placed in a distribution system, comprising:
at least one primary winding for the flow of primary current, wherein said primary winding comprises an incoming terminal, an outgoing terminal, at least one primary conductor means connector to said incoming terminal on one end and said outgoing terminal on other end;
at least one secondary windings enclosed in an enclosure within a central position of said sensor, wherein said secondary windings comprises at least two windings having a current transformer winding and a Rogowski coil winding, inside said enclosure;
wherein, when primary current flows through said primary windings, causes generation of heat, enabling said current transformer winding and said Rogowski coil winding for powering a trip unit of said MCCB through sensor output leads and used for control and protection of a circuit by giving trip command to said MCCB.

[0016] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0017] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0018] Figure 1 illustrates the isometric view of the sensor assembly, according to one embodiment of the present invention.

[0019] Figure 2 illustrates the exploded view of the sensor primary conductor assembly, according to one embodiment of the present invention.

[0020] Figure 3 illustrates the plan view of the sensor assembly, according to one embodiment of the present invention.

[0021] Figure 4 illustrates the cross-sectional view of the sensor assembly, according to one embodiment of the present invention.

[0022] Figure 5 illustrates the detailed view of the sensor showing the enclosure (encapsulation), according to one embodiment of the present invention.

[0023] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0024] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0025] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0026] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0027] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0028] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0029] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0030] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0031] In one implementation, the present invention discloses a current sensor that consists of a current transformer and Rogowski coil placed inside an enclosure. The output of the sensor is fed to the trip unit of circuit breaker. The power is harvested from primary conductor through the current transformer and the power is fed to the trip unit for powering up the trip unit for its operation. It is very important for the power system engineer to precisely measure current and power flowing through the distribution system for monitoring and control of system. The current input can be used for monitoring and protection from all type of system protection features viz. overload, overcurrent, unbalance, earth fault etc. The measurement of current flowing through the circuit is achieved by the Rogowski sensor placed inside the sensor. The measurement of power flowing through the circuit is achieved through combination of Rogowski sensor and voltage module placed on the primary conductor of sensor, the output is fed to the trip unit of the MCCB for measurement of power. Thus the trip unit is powered through the sensors and used for control and protection of circuit by giving trip command to the circuit breaker.

[0032] In one implementation, the sensor assembly of the present invention consist of Primary winding and secondary winding. The primary winding is the set of conductors through which main / primary current flows, In the present invention there are two secondary windings current transformer winding and Rogowski winding placed inside an enclosure. The primary winding for a MCCB sensor can be single turn or multi-turn depending on the magnitude of primary current. The primary winding is generally an integral part of main current path of the circuit breaker. Thus the current flowing through the circuit breaker is tapped with the help of sensor and is used for measurement and control of the circuit breaker. With present trend of compact circuit breakers, every component calls for optimization.

[0033] In one implementation, the present invention discloses a system with better heat transfer and better insulation properties while retaining the compact shape which is achieved by encapsulating the central portion of the sensor. The encapsulation material is selected in such a way that it has very high dielectric strength, high thermal conductivity, high temperature with stand properties and high mechanical strength.

[0034] In one implementation, figure 1 illustrates the general arrangement of sensor with key components marked.

[0035] In one implementation, figure 2 illustrates the exploded view of the sensor primary conductor assembly.

[0036] In one implementation, figure 3 illustrates the plan view of the sensor assembly.

[0037] In one implementation, figure 4 illustrates the cross-sectional view of the sensor assembly.

[0038] In one implementation, figure 5 illustrates the detailed view of the sensor showing encapsulation, the central portion of the sensor is encapsulated with the help of resin.

[0039] In one implementation, the sensor assembly consist of Primary winding and secondary winding. The primary winding is the set of conductors through which main / primary current flows. The primary winding of the present invention consists of incoming terminal (1), the flexible conductor (3) having two or more turns, where on end of the flexible conductor is connected to the incoming terminal (1) and the other end of the flexible conductor is connected to the outgoing terminal (2). As shown in figure 2, the two turns of flexible conductor (3) when passed through the central portion/limb are insulated from each other with the help of an inter-turn insulation (4). The secondary windings (7) & (8) will be enclosed in an enclosure (9), this entire assembly is termed as sensor sub-assembly (5). There are two secondary windings current transformer (7) and Rogowski (8) placed inside the enclosure (9). The output of the sensor is fed to the trip unit via the sensor output leads (6).

[0040] In one implementation, the current flowing through the circuit breaker is tapped with the help of sensor and will be used for measurement and control of the circuit breaker. The present invention discloses a system with better heat transfer and better insulation properties while retaining the compact shape which can be achieved by encapsulation (10) of the central portion of the sensor. The encapsulation (10) resin is selected in such a way that it has very high dielectric strength, high thermal conductivity, high temperature withstand properties and high mechanical strength.

[0041] In one implementation, during normal operation, the primary current flows through the primary conductor (1), (2) & (3), resulting into generation of heat. While the primary current will be flowing, the current transformer windings (7) and Rogowski coil windings (8), also being used for powering up trip unit, protection and control function of the trip unit. So the heat will be produced simultaneously on secondary side i.e. current transformer as well as the Rogowski coils. The net heat within the enclosure (9) is due to primary and secondary current specially within the central limb area, i.e., the central portion of the sensor, as shown in figure-5. This area being encapsulated (10) by the resin of high thermal conductivity and high temperature withstand properties that facilitates better conduction of heat from local hot spots to the entire central limb thereby reducing overall temperature.

[0042] In one implementation, during fault condition, due to very high current there is repulsive force between the primary conductors comprising multi-turn secondary winding specially on flexible conductor (3), due to this repulsive force between the primary conductor (3) which can be placed very close to the secondary conductor (7) & (8) under influence of force and heat (generated due to high current flowing through a narrow conductor), this area of the central portion is now being encapsulated (10) by the resin of high dielectric strength, high thermal conductivity, high temperature withstand properties and high mechanical strength properties. So the primary conductors (3) will be embedded within the encapsulation portion (10), and hence cannot move while increasing the dielectric strength between the primary (3) and secondary (7) & (8) by occupying space between them. So the chances of primary winding getting shorted with secondary winding are eliminated completely.

[0043] Some of the noteworthy features of the present invention, are as follows:
• Current sensors assembly for MCCB, consists of Primary winding and secondary winding. The primary winding is the set of conductors through which main / primary current flows. The secondary windings consists of current transformer (7) and Rogowski (8) placed inside an enclosure (9). The output of the sensor is fed to the trip unit via the sensor output leads.
• In the present invention, the encapsulation (10) facilitates better electrical insulation between the primary (3) and secondary (7) & (8) of the current transformer.
• The encapsulation (10) resin is selected in such a way that it has very high dielectric strength, high thermal conductivity, high temperature withstand properties and high mechanical strength.
• The encapsulation (10) facilitates better conduction of heat from local hot spots to the entire central portion thereby reducing overall temperature.
• In the present invention, the encapsulation(10) facilitates primary conductors to be embedded within the encapsulation (10) which in turn results into structural support to the primary conductors

[0044] Some of the non-limiting advantages of the present invention, are as follows:
• The present invention provides a simple and compact arrangement of sensor assembly.
• The present invention provides better thermal and insulation performance of the system.
• In the present invention, since the primary conductors are embedded within the encapsulation, hence during the short circuit, the chances of primary winding getting shortened with secondary winding is eliminated completely.

[0045] Although the sensor assembly for molded case circuit breakers has been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the sensor assembly for molded case circuit breakers which facilitates better conduction of heat and better electrical insulation.