Claims:WE CLAIM:

1. A test system (1) to detect current transformer orientation, said test system (1) is operably coupled to at least one current transformer (7) to receive a plurality of test signals, and is operably coupled to a regulated DC power supply (8), said test system (1) comprising:
a signal conditioning unit (2) configured to amplify the test signal received from the current transformer (7);
wherein said signal conditioning unit (2) is operably coupled to the current transformer (7) to receive the test signal, and is operably coupled an analog to digital converter (3);
said analog to digital converter (3) converts the analog test signal received from the current transformer (7) into a digital test signal;
wherein said analog to digital converter (3) is operably coupled to a processor (4);
said processor (4) is operably coupled to a DC current switching device (6), said DC current switching device (6) is configured to:
loop DC current path through at least one current transformer (7) coupled to the test system (1); and
switch the current path between open and close at pre-defined interval of time for at least one cycle of AC signal along with said processor (4);
wherein the signal conditioning unit (2), the analog to digital converter (3), the processor (4), the status indicators (5) and the DC current switching device (6) are operably coupled to the regulated DC power supply (8) through a switch (9) to ON / OFF said power supply (8);
said processor (4) is configured to:
process the digital test signal received from the analog to digital converter (3); and
determine the CT orientation by calculating difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open;
wherein if the difference between said two digital test signals is a positive value, the CT orientation is correct; and
wherein if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

2. The test system (1) as claimed in claim 1, wherein the DC current switching device (6) is operably configured by the processor (4) to open and close the current path at the pre-defined interval of time for at least one cycle of AC signal.

3. The test system (1) as claimed in claim 2, wherein said pre-defined interval of time is about the order of a millisecond.

4. The test system (1) as claimed in claim 1, wherein the status indicator (5) will remain ON continuously when orientation of the current transformer (7) is correct.

5. The test system (1) as claimed in claim 1, wherein the status indicator (5) will blink with about 250ms of ON time and about 250ms of OFF time when orientation of the current transformer (7) is incorrect.

6. The test system (1) as claimed in claim 1, wherein the processor (4) is operably coupled to a plurality of status indicators (5).

7. A method to detect current transformer orientation in a test device (1), said method comprising the steps of:
looping a DC current path (S1), by a DC current switching device (6), through at least one current transformer (7);
sending (S2), by the current transformer (7), test signal to a signal conditioning unit (2);
amplifying (S3), by a signal conditioning unit (2), the test signal received from the current transformer (7);
converting (S4), by an analog to digital converter (3), the analog test signal, received from the signal conditioning unit (2), into a digital test signal;
applying (S5), by a DC power supply (8) controlled by a switch (9), regulated DC power supply to the test device (1);
switching (S6), by the DC current switching device (6), the current path to open and close at pre-defined interval of time for at least one cycle of AC signal;
processing (S7), by a processor (4), the digital test signal received from the analog to digital converter (3); and
determining (S8), by a processor (4), difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open;
wherein if the difference between said two digital test signals is a positive value, the CT orientation is correct; and
wherein if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

8. The method as claimed in claim 7, wherein the DC current switching device (6) is operably configured by the processor (4) to open and close the current path at the pre-defined interval of time for at least one cycle of AC signal.

9. The method as claimed in claim 8, wherein said pre-defined interval of time is about the order of a millisecond.

10. The method as claimed in claim 7, wherein the status indicator (5) will remain ON continuously when orientation of the current transformer (7) is correct.

11. The method as claimed in claim 7, wherein the status indicator (5) will blink with about 250ms of ON time and about 250ms of OFF time when orientation of the current transformer (7) is incorrect.

12. The method as claimed in claim 7, wherein the processor (4) is operably coupled to a plurality of status indicators (5).

Dated this 31st day of March 2018

Abhishek Sen
Of S. MAJUMDAR & CO.
(Applicant’s Agent)
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to current transformers and more particularly, pertains to a test system and a method to detect current transformer orientation.

BACKGROUND OF INVENTION

[002] A current transformer (CT) is a type of transformer that is used to measure alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary. The current transformer provides a secondary current that is accurately proportional to the current flowing in its primary. The current transformer presents a negligible load to the primary circuit. The current transformers are the current-sensing units of the power system and are used at generating stations, electrical substations, and in industrial and commercial electric power distribution.

[003] The current transformers are used for protection, measurement and control, in high-voltage electrical substations and the electrical grid. These are installed inside switchgear or in apparatus bushings, but very often free-standing outdoor current transformers are used. The primary of the winding can be evenly distributed around the magnetic core, which gives better performance for overloads and transients. Since the major insulation of a live-tank current transformer is not exposed to the heat of the primary conductors, insulation life and thermal stability is improved.

[004] In an industry where three phase supply is used and there is need to measure, monitor and protect the electrical devices / system working on three phase supply, CT orientation of all the phases plays very important role. CT orientation should be in line with each other for each device / system so as to derive electrical parameters for measurement, monitoring and protection purpose. But if the CT orientation of any one of the phase is reversed then it will result in wrong computation of electrical parameters thereby resulting in failure of device / system.

[005] For some existing technology in this field, reference is made to CN Utility Model 204882789 U, wherein a CT polarity test device is disclosed. The CT polarity test device includes resistance (R1), resistance (R2), resistance (RS), diode (D), relay (CJ), switch (AN1), switch (AN2), switch (AN3), single -pole double -throw (K2), switch (K1), DC power supply (EC1), DC power supply (EC2), emitting diode (LED1), emitting diode (LED2). It discloses satisfying relay protection job site's actual need completely, having characteristics such as test sensitivity, convenient operation, portable, reliable practicality, can improve site work efficiency greatly, and it is directly perceived, concrete to test light indication, electronic components power consumption is few, and is with low costs, and the power consumption is low, can be used to long -time test.

[006] This prior art document discloses a CT polarity test device based on discrete component. The device uses two DC power supplies, one to pass primary current through the CT and the other to show the polarity status. This test device requires manual intervention twice, one to press the switch (AN1) to pass DC current though CT and the other to press the switch (K1) to get the status using LED. This device takes significant time (tenths of seconds) to test CT polarity. While this device improves site work efficiency, but on-site, rework at final product is not recommended. For this device, it is recommended to test the polarity at sub assembly at production level only, i.e., before final assembly of the product.

[007] Significantly, Polarity of current transformers is extremely important. Just like a battery, a current transformer also has a polarity. The polarity determines the direction of the secondary current in relation to the primary current. Wrong connection of the current transformers can cause false operation of the protection relays. Therefore, it is vital to ensure that the current transformers are connected with the correct polarity.

[008] Reference is made to Figure 1 that illustrates an existing setup to test the polarity of current transformers. A DC source is connected with the positive terminal to P1 and the negative terminal to P2. An analog voltmeter is connected to the secondary terminal of the CT. The positive terminal of the meter is connected to terminal S1 of the CT while the negative is connected to terminal S2. A contact is momentarily made through the switch. The contact is made for a second and broken. This is important as continuous contact can short-circuit the battery. The momentary make-break contact causes a deflection in the analog multimeter in the positive direction, if the polarity is correct. If the deflection is negative, it indicates that the polarity of the current transformer is reversed. The terminals S1 and S2 need to be reversed and the test can be carried out.

[009] This existing method of testing CT involves an analog instrument to detect polarity. It requires an analog multimeter for each CT. Thus, testing of more than one CT at a time will add cost to the setup and make the monitoring more tedious process. The testing time required for this method is comparatively larger and also requires regular charging of the battery.

[0010] The drawbacks associated with the existing technology are that CT orientation is detected based on power factor after final assembly and they also require an alternating current source. The use of alternating current source makes the entire set up more complex and requiring more processing time. Moreover, if CT orientation is incorrect then it is time consuming to correct the CT orientation in the final assembled product.

[0011] Accordingly, there is a need to allow the production process to verify / detect CT orientation before final assembly without the use of alternating current source that results in complex test setup. There is also the need to eliminate the rework after final assembly to sub assembly level. Therefore, there is a need for a test system and a method to detect current transformer orientation that employs a direct current source.

[0012] The above-described need to eliminate the rework after final assembly to sub assembly level and the need to allow the production process to verify / detect CT orientation before final assembly is merely intended to provide an overview of some of the shortcomings of conventional systems / mechanism / techniques, and is not intended to be exhaustive. Other problems/ shortcomings with conventional systems/ mechanism /techniques and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.

SUMMARY OF THE INVENTION

[0013] 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.

[0014] An object of the present invention is to provide a test system and a method to detect current transformer orientation.

[0015] Another object of the present invention is to allow the production process to verify / detect CT orientation before final assembly without the use of alternating current source that requires complex test setup.

[0016] Yet another object of the present invention is to replace the existing process of detecting the CT orientation at final assembly, to sub assembly level.

[0017] According to a first aspect of the present invention, there is provided a test system to detect current transformer orientation. The test system is operably coupled to at least one current transformer to receive a plurality of test signals, and operably coupled to a regulated DC power supply, said test system comprising: a signal conditioning unit configured to amplify the test signal received from the current transformer; wherein said signal conditioning unit is operably coupled to the current transformer to receive the test signal, and is operably coupled an analog to digital converter; said analog to digital converter converts the analog test signal received from the current transformer into a digital test signal; wherein said analog to digital converter is operably coupled to a processor; said processor is operably coupled to a DC current switching device, said DC current switching device is configured to: loop DC current path through at least one current transformer coupled to the test system; and switch the current path between open and close at pre-defined interval of time for at least one cycle of AC signal along with said processor; wherein the signal conditioning unit, the analog to digital converter, the processor, the status indicators and the DC current switching device are operably coupled to the regulated DC power supply through a switch to ON / OFF said power supply; said processor is configured to: process the digital test signal received from the analog to digital converter; and determine the CT orientation by calculating difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open; wherein if the difference between said two digital test signals is a positive value, the CT orientation is correct; and wherein if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

[0018] In a possible implementation of the test system according to the first aspect, the DC current switching device is operably configured by the processor to open and close the current path at the pre-defined interval of time for at least one cycle of AC signal.

[0019] In another possible implementation of the test system according to the first aspect, the pre-defined interval of time is about the order of a millisecond.

[0020] In yet another possible implementation of the test system according to the first aspect, the status indicator will remain ON continuously when orientation of the current transformer is correct.

[0021] In yet another possible implementation of the test system according to the first aspect, the status indicator will blink with about 250ms of ON time and about 250ms of OFF time when orientation of the current transformer is incorrect.

[0022] In yet another possible implementation of the test system according to the first aspect, the processor is operably coupled to a plurality of status indicators.

[0023] According to a second aspect of the present invention, there is provided a method to detect current transformer orientation. This method comprises the steps of looping a DC current path, by a DC current switching device, through at least one current transformer; sending, by the current transformer, test signal to a signal conditioning unit; amplifying, by a signal conditioning unit, the test signal received from the current transformer; converting, by an analog to digital converter, the analog test signal, received from the signal conditioning unit, into a digital test signal; applying, by a DC power supply controlled by a switch, regulated DC power supply to the test device; switching, by the DC current switching device, the current path to open and close at pre-defined interval of time for at least one cycle of AC signal; processing, by a processor, the digital test signal received from the analog to digital converter; and determining, by a processor, difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open; wherein if the difference between said two digital test signals is a positive value, the CT orientation is correct; and wherein if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

[0024] In a possible implementation of the method according to the second aspect, the DC current switching device is operably configured by the processor to open and close the current path at the pre-defined interval of time for at least one cycle of AC signal.

[0025] In another possible implementation of the method according to the second aspect, the pre-defined interval of time is about the order of a millisecond.

[0026] In yet another possible implementation of the method according to the second aspect, the status indicator will remain ON continuously when orientation of the current transformer is correct.

[0027] In yet another possible implementation of the method according to the second aspect, the status indicator will blink with about 250ms of ON time and about 250ms of OFF time when orientation of the current transformer is incorrect.

[0028] In yet another possible implementation of the method according to the second aspect, the processor is operably coupled to a plurality of status indicators.

[0029] 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

[0030] 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:

[0031] Figure 1 illustrates an existing test setup as prior art of the present invention.

[0032] Figure 2 illustrates the block diagram of the test setup according to a first embodiment of the present invention.

[0033] Figure 3 illustrates the flow chart for testing CT orientation according to a second embodiment of the present invention.

[0034] 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

[0035] 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.

[0036] 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.

[0037] 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.

[0038] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0039] 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.

[0040] 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.

[0041] 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 component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0042] The present invention lies in providing a test system and a method to detect current transformer orientation.

[0043] In particular, the present invention describes the construction and working a test system and a method that would allow the production process to verify / detect CT orientation before final assembly without the use of alternating current source that complicates the test setup by employing an 18V DC / 500mA power supply. The CT orientation detection time is minimized to about 20msec. This test system is capable of replacing the existing process of detecting the CT orientation at final assembly, to sub assembly level.

[0044] In the prior art, CT orientation detection is based on power factor after final assembly and by employ an alternating current source. The use of alternating current source makes the entire set up more complex and requiring more processing time. Significantly, if CT orientation is incorrect then it is time consuming to correct the CT orientation in the final assembled product.

[0045] Figure 2 illustrates the test system (1) to detect current transformer orientation. This system comprises a signal conditioning unit (2), an analog to digital converter (3), a processor (4), status indicator (5) and a DC current switching device (6). The CT (7) to be tested is connected to the signal conditioning unit (2). A DC power supply (8) with switch (9) to turn said power supply ON/OFF is connected to the test system (1).

[0046] According to a first embodiment of the present invention, a test system (1) to detect current transformer orientation is disclosed. The test system (1) is operably coupled to at least one current transformer (7) to receive a plurality of test signals, and is operably coupled to a regulated DC power supply (8). The test system (1) comprises a signal conditioning unit (2) configured to amplify the test signal received from the current transformer (7); wherein said signal conditioning unit (2) is operably coupled to the current transformer (7) to receive the test signal, and is operably coupled an analog to digital converter (3). The analog to digital converter (3) converts the analog test signal received from the current transformer (7) into a digital test signal; wherein said analog to digital converter (3) is operably coupled to a processor (4). The processor (4) is operably coupled to a DC current switching device (6), said DC current switching device (6) is configured to: loop DC current path through at least one current transformer (7) coupled to the test system (1); and switch the current path between open and close at pre-defined interval of time for at least one cycle of AC signal along with said processor (4). The signal conditioning unit (2), the analog to digital converter (3), the processor (4), the status indicators (5) and the DC current switching device (6) are all operably coupled to the regulated DC power supply (8) through a switch (9) to ON / OFF said power supply (8). The processor (4) is configured to: process the digital test signal received from the analog to digital converter (3); and determine the CT orientation by calculating difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open; wherein if the difference between said two digital test signals is a positive value, the CT orientation is correct; and wherein if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

[0047] The signal conditioning unit (2) amplifies the analog signal input from the current transformer (7). The analog to digital converter (3) converts this input analog signal to a digital signal. The processer (4) is preferably a microprocessor that processes this digital signal. A plurality of status indicators (5) of the user interface indicates the status of current transformer orientation. A plurality of polarity indication LED’s will glow continuously if the CT polarity is correct. These LED’s will start blinking if the polarity is incorrect.

[0048] The DC current switching device (6) of DC current path along with switching circuit / device to open or close the current path and the regulated DC power supply circuit to drive the test system (1). This test system (1) requires only one DC power supply (8) for its functionality. This test system detects the status of the current transformer (7) within tenths of milliseconds instead of tenths of seconds required by existing test devices. This significantly aids with the production process.

[0049] According to a second embodiment of the present invention, a method to detect current transformer orientation in a test device (1) is disclosed. Figure 3 illustrates flow-chart for the method to detect current transformer orientation. This method comprises the following steps:
Step 1: looping a DC current path, by a DC current switching device (6), through at least one current transformer.
Step 2: sending, by a current transformer (7), test signal to a signal conditioning unit (2).
Step 3: amplifying, by a signal conditioning unit (2), the test signal received from the current transformer (7).
Step 4: converting, by an analog to digital converter (3), the analog test signal received from the signal conditioning unit (2) into a digital test signal.
Step 5: applying, by a DC power supply (8) controlled by a switch (9), regulated DC power supply to the test device (1).
Step 6: switching, by the DC current switching device (6), the current path to open and close at pre-defined interval of time for at least one cycle of AC signal. This pre-defined interval of time is about the order of a millisecond.
Step 7: processing, by a processor (4), the digital test signal received from the analog to digital converter (3).
Step 8: determining, by the processor (4), difference between the digital test signal received when the DC current path is closed and the digital test signal received when the DC current path is open. Significantly, if the difference between said two digital test signals is a positive value, the CT orientation is correct and if the difference between said two digital test signals is a negative value, the CT orientation is incorrect.

[0050] For detecting the CT orientation, a DC current is looped through CT / CT’s (7) under test. As soon as power supply (8) is turned on logic running into the microprocessor (4) will operate the switching circuit / device (6) to open and close the current path at an interval of millisecond for period of one or two cycles of AC signal. CT (7) will provide output signal, that will be connected to signal conditioning unit (2) for amplification and then further it gets converted to digital test signals using analog to digital converter (3). Microprocessor (4) will find the difference between the digital test signal received when the DC current path is close and the digital test signal received when the DC current path is open. If the difference between the two digital test signals is positive, then CT orientation is correct else the orientation is incorrect.

[0051] Notably, separate status indicators (5) are provided for each CT (7) under test, by LED / LED’s or any other user interface. In the present disclosure, LED’s are used by way of an example for the status indicators (5). The LED with respect to a particular CT (7) will be continuously ON if orientation is correct else it will blink with 250ms ON and 250ms OFF time. Thus, the tester will able to identify the specific CT or a CT from the combined assembly of more than one CT. Then tester / operator can proceed perform the corrective measure before going for the final assembly of the complete product.

[0052] Some of the non-limiting advantages of the present invention are mentioned hereinbelow:
1. It can be used to replace the existing process of detecting the CT orientation at final assembly, to sub assembly level;
2. It does not require the complex setup of alternating current source of few amperes to detect CT orientation;
3. It requires only 18V DC / 500mA power supply for its complete functionality;
4. It requires a low cost test setup as it runs on DC source;
5. Its test set-up is less complex since it does not include alternating current source for looping the current through CT / CT’s under test; and
6. It has minimized the CT orientation detection time to 20msec.

[0053] Although a method and a test system to detect current transformer orientation have been described in language specific to structural features and/or methods as indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations to replace the existing process of detecting the CT orientation at final assembly, to sub assembly level.