Claims:1. A test device for testing an earth leakage module in an electrical switching device, said test device comprising:
at least one test switch communicably connected to a controller unit, wherein said test switch actuated to trigger said controller unit to perform test operation;
at least one oscillator unit actuated by at least one input from said controller unit, wherein oscillator unit generate at least one sinusoidal output wave corresponding to said input;
at least one test winding adapted to receive sinusoidal current through at least one test resistor, and thereby generate at least one magnetic flux into at least one differential transformer;
wherein, output at said differential transformer transmit to said controller unit to compare with at least one preset threshold value, wherein if said comparison exceeds said threshold value, said controller unit generates at least one trip command.
2. The test device as claimed in claim 1, wherein said test switch actuated to trigger said controller unit to receive at least one input corresponding to the switch position selected by a user.
3. The test device as claimed in claim 1, comprises at least one multiplexer unit adapted to control voltage of said sinusoidal output wave generated by oscillator unit.
4. The test device as claimed in claim 3, wherein said multiplexer unit receives control signal from said controller unit.
5. The test device as claimed in claim 1-4, comprises an operational amplifier adapted to receive said sinusoidal output wave from said oscillator unit and thereby generate at least one amplified sinusoidal output wave.
6. The test device as claimed in claim 5, wherein said sinusoidal current is generated from said amplified sinusoidal output through said test resistor.

7. The test device as claimed in claim 1, wherein said preset threshold value corresponds to at least one leakage current value preset by said user.
8. The test device as claimed in claim 7, wherein said leakage current value is adjusted by changing feedback resistor controlled by said controller unit using said multiplexer unit.
9. A method for testing an earth leakage module in an electrical switching device, the method comprising:
triggering, by at least one test switch, at least one controller unit for receiving at least one input corresponding to said test switch position selected by a user;
actuating, by said controller unit, at least one oscillator unit for generating at least one sinusoidal output wave corresponding to input from said controller unit;
simulating, by said sinusoidal output wave and test resistor, at least one sinusoidal current into at least one test winding;
generating, by said sinusoidal current into said test winding, at least one magnetic flux induced into at least one differential amplifier to generate an output;
transmitting, said output from said differential amplifier to said controller unit for comparison with a preset threshold value;
wherein if said comparison exceeds said preset threshold value;
generating, by said controller unit, at least one trip command for breaking contacts in said electrical switching device.
, Description:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to a mechanism for testing the functionality of electrical switching devices, and more particularly relates to a test devices for the earth leakage detection module of the electrical switching device.

BACKGROUND

[002] The Earth leakage device is a safety device used in electrical installations with high earth impedance to prevent shock and to protect the people and appliances arranged in an electrical circuit from residual currents. Many times, earth leakage devices are used in conjunction with an electrical switching device, such as a switchgear, circuit breaker, molded case circuit breaker (MCCB), residual current circuit breaker and the like, for sensing leakage current faults and actuating a tripping mechanism in the circuit breaker that opens the breaker contacts upon the detection of the leakage fault.

[003] The Earth leakage device includes a differential transformer from which the line and neutral are passed. In normal condition when no leakage current is present, the current will flow through the line and return to the neutral, thus the net magnetic flux induced in the differential transformer is zero. So no output is present .When the leakage current is present, some current will not return to the neutral so magnetic flux gets induced into the transformer and if the output in the secondary is greater than the threshold value preset by the user then a trip command is initiated which trips the breaker.

[004] Normally, in these earth leakage devices there includes a test feature for testing the functionality of the device. It usually includes a test resistor and a test button whereby the operation of the test button will close off the test circuit module and thereby a simulated residual current is produced from one conductor to another conductor past the differential transformer which produces resultant magnetic flux into the transformer thus tripping the circuit breaker.

[005] However, following are the problems occurring in the test circuit module stated above:
• As directly operated from AC supply, it is exposed to the noise that exist on the line conductor of the AC supply which can possibly infer with the test.
• Due to the large fluctuations in the AC supply, the device is tested for higher leakage current which in actual case may not necessarily trigger in smaller residual currents.
• As operated directly from mains supply using a resistor, power dissipation is high.
• Instead of a mechanical switch, electronic switch is used to pass the test leakage current, the power rating and the size of the electronic switch increases.
• In case of selective leakage current devices, the test feature is carried on one setting irrespective the user selective knob.

[006] Moreover, due to the large fluctuations in the line voltage, the testing is carried out at much more larger current. So the earth leakage device tripped during the operation of the testing phase does not necessarily trigger safely in case of significantly smaller residual current. So there is a need for test device for earth leakage module which can be more precisely tested then previously possible.

[007] Reference is made to US20130120091A1, provides a test circuit which becomes independent of the line voltage with minor additional costs. Test current is dependent on the line voltage and limited by the Zener diode. However, the invention disclosed in ‘091A1 has drawbacks as it is effected by line fluctuations as it is directly tapped from the line voltage, more power is dissipated since the current is generated directly from mains and there is no control on the test current as it is line voltage dependent.

[008] Reference is made to US20110222194A1, provides a test circuit to test the GFCI by implementing a low voltage power supply from which a test stimulus signal is generated instead directly from the AC supply. Since the DC current is passed and it’s constant since it is generated from voltage regulator. Therefore it is not affected by line voltage as DC current is generated from voltage regulator. Moreover, less power is dissipated since the current is generated from the voltage regulator. However, the invention disclosed in ‘194A1 has the drawbacks as the module is tested only for one current settings irrespective of the current set by the user.

[009] Thus, there exists a dire need to address the hitherto problems of the prior art for testing the functionality of the leakage devices.

SUMMARY OF THE INVENTION

[0010] 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.

[0011] An object of the present invention is to provide a test device for testing the functionality of a leakage device more precisely than was previously possible and that overcomes the drawbacks of the prior art mentioned above.

[0012] Another object of the present invention is to provide a test device which is not effected due to the fluctuations in the AC supply voltage and is not exposed to the noise present on the line conductor of AC supply voltage.

[0013] Yet another object of the present invention is to provide a test device that enables the user to test the earth leakage devices at the current preset by the user.

[0014] Still another object of the present invention is to provide a test device wherein power dissipation is reduced to a great extent as the test current is not taken directly from the mains.

[0015] Accordingly to one aspect, the present invention provides a test device for testing an earth leakage module in an electrical switching device, said test device comprising:

at least one test switch communicably connected to a controller unit, wherein said test switch actuated to trigger said controller unit to perform test operation;
at least one oscillator unit actuated by at least one input from said controller unit, wherein oscillator unit generate at least one sinusoidal output wave corresponding to said input;
at least one test winding adapted to receive sinusoidal current through at least one test resistor, and thereby generate at least one magnetic flux into at least one differential transformer;
wherein, output at said differential transformer transmit to said controller unit to compare with at least one preset threshold value;
wherein if said comparison exceeds said threshold value, said controller unit generates at least one trip command.

[0016] In second aspect, the present invention provides a method for testing an earth leakage module in an electrical switching device, the method comprising:
• triggering, by at least one test switch, at least one controller unit for receiving at least one input corresponding to said test switch position selected by a user;
• actuating, by said controller unit, at least one oscillator unit for generating at least one sinusoidal output wave corresponding to input from said controller unit;
• simulating, by said sinusoidal output wave and test resistor, at least one sinusoidal current into at least one test winding;
• generating, by said sinusoidal current into said test winding, at least one magnetic flux induced into at least one differential amplifier to generate an output;
• transmitting, said output from said differential amplifier to said controller unit for comparison with a preset threshold value;
wherein if said comparison exceeds said preset threshold value;
• generating, by said controller unit, at least one trip command for breaking contacts in said electrical switching device.

[0017] 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

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 an arrangement of the test device for testing earth leakage module used in an electrical switching device, in accordance with an embodiment of the present invention.

[0019] 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

[0020] 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.

[0021] 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.

[0022] 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.

[0023] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] It is also to be understood that the term “module” is used in the specification to indicate an apparatus, unit, component and the like. The term “means” when used in the specification is taken to specify the mode by which desired result is achieved.

[0028] The present invention can be implemented with an electrical switching system that may include but not limited to, circuit breakers or thermo-magnetic breaker, molded case circuit breaker (MCCB) residual circuit breaker (RCB), earth leakage circuit breaker (ELCB) and the like. In one implementation, the controller unit used in the present invention can be a microcontroller.

[0029] In one implementation, the present invention relates to a test device that can be used in an earth leakage module wherein a test winding is present on the differential transformer. When the test switch is pressed, the controller unit takes the input of the switch position selected by the user and initiates the oscillator which produce a sinewave signal whose output voltage can be controlled by a multiplexer unit and thereby simulating a current into the test winding using a resistor. As the current flows in the test winding the magnetic flux gets induced into the core and thereby crossing the threshold of the leakage current preset by the user, which thereby initiates a trip command to the circuit breaker.

[0030] Reference is made to figure 1 wherein an arrangement of various components involved in the test device for testing earth leakage module is illustrated.

[0031] In one implementation, as shown in the fig 1, the user selects the leakage current settings whose setting is fed to the controller unit using the port pin P1.4. When the user presses the test switch, the controller port pin P1.0 becomes low which initiates the controller to perform test operation. The controller will enable the port pin 1.1 high which turns the MOSFET M1 ON thereby making MOSFET M2 ON and the supply voltage is passed to the oscillator circuit. The Oscillator circuit produces a sinewave whose output may be given to an operational amplifier (Opamp). The controller will send the control signal to the multiplexer (MUX) which selects one of the switches thereby selecting the proper gain. Thus, an amplified sinewave can be generated at the output of the Opamp. From the output of Opamp through a test resistor, a sinusoidal current is injected in the test winding which causes a magnetic flux to get induced into the differential transformer. The output = generated at the secondary of the transformer which can be amplified by Opamp and given to controller port pin P1.2. The controller is configured to compare the input voltage with the threshold preset value and if it is greater than the threshold value, a trip command is initiated by the controller. The controller enables the port pin P1.3 high and the MOSFET M3 is turned ON. The solenoid can thereby be energized to trip the breaker by separating the breaker contacts.

[0032] In the implementation, the present invention tests the earth leakage module or earth leakage circuit breaker (ELCB) using the current preset by the user by changing the feedback resistor which is controlled by the microcontroller using MUX. As the Mux changes the feedback resistor, the voltage obtained at the output is adjusted such that the current setting knob preset by the user is passed and the ELCB is tested.

[0033] In one exemplary embodiment, the value of test Current is generated at 30mA. The values of the Secondary winding current is generated as 60uA (whereby the primary winding: 500 Secondary winding: 20). The value of test Resistance (R3) can be chosen as 700 ohms. The Voltage output is generated as 1.414V. The Power dissipation is 2.52uW.

[0034] Some of the noteworthy features of the present invention, considered to be noteworthy are mentioned below:
1. In the present invention, actual current is passed which eliminates the need for a test current.
2. Since in the present invention it consist of oscillator which is inbuilt which generates a pure sinewave, it is not affected by any line fluctuation on the line voltage.
3. The present invention tests the ELCB using the current preset by the user by changing the feedback resistor which is controlled by the microcontroller using MUX.
4. The power dissipation in the present invention is very low as very less current has to be passed to the secondary winding which takes advantage of the current transformer principle.
5. As the Mux changes the feedback resistor, the voltage obtained at the output is adjusted such that the current setting knob preset by the user is passed and the ELCB is tested.

[0035] Some of the advantages of the present invention, are as follows:
• The earth leakage module or ELCB can be more precisely tested than was previously possible.
• No effect on the test circuit due to the fluctuations in the AC supply voltage.
• Test circuit is not exposed to the noise present on the line conductor of AC supply.
• Power dissipation is reduced to a great extent as the test current is not taken directly from the mains.
• Allows the user to test the earth leakage device at the current preset by the user with the help of the multiplexer where the gain is changed with the help of feedback resistor.

[0036] Although a test device and method for testing earth leakage module have 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 test device and method for testing earth leakage module