DESC:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to power system protection and control, and more particularly, to a power circuit assembly for tracking single phase failure in a three phase electrical network.

BACKGROUND

[002] Single phasing is a condition in three phase electrical network wherein the supply to at least one of a phases connected to a load, is cut off in case of a fault as the electrical network becomes imbalanced due to an overload or an under load condition in at least one of the phases. Single phasing is caused by tracking single phase fault in at least one of the phases by the use of single-phase protection devices such as fuses and circuit breakers. This protects the electrical loads by using protection devices such as protection relays or backup contactors, that monitors continuous current flowing in the three phase system, and further interrupts the supply of power to all three phases simultaneously when a fault occurs and thus isolate the electrical loads.

[003] In case of switchgear testing set up, at least one of a test unit (any switchgear that may include but not limited to contactor, MCCB, MCB, Fuse, Relay, Starter, ACB and the like) is/are connected to the three phases R-Y-B and subsequently the test unit is connected to the electrical loads. Thus, tracking of single phase failure in the test unit is essential, as it may cause detrimental effect to electrical loads connected in the circuit.

[004] Conventionally, system to detect single phase failure in test unit includes voltage sense system as illustrated in figure 1, wherein K1,K2,K3 contactors are added across the R, Y, B phases respectively and the secondary of the coil of contactor K1, K2, K3 are star pointed and connected to the star point of load. When circuit gets completed because of supply flowing through the circuit, the fault detecting contactors K1, K2, K3 will get operated with test unit. If any single phase fault occurs, these contactors sense the single phase fault and thus terminate the operation of test unit.

[005] However, such conventional system is not effective in case of variable voltage test, as the coil voltage of K1, K2 and K3 contactor are fixed. Also in case of AC3 duty tests, the Y pole of three phase power system is not controlled by a hybrid circuit and thus the Y Pole is continuously alive. Therefore in case of single phase failure, voltage is continuously available across Y Pole and therefore single phasing across Y pole is not determined using the conventional method. If any single phasing failures occur, then the test unit still remains operational continuously. Due to this, detection of fault will involve manual intervention wherein operator personnel have to observe each and every circuit manually after some interval. Thus, the end user fails to track the actual of operations and type of failure that is occurring in the electrical system.

[006] In view of the drawbacks of conventional system for tracking failure of single phasing in test units, there exists a need to provide an improved system for tracking failure in test unit that would provide accurate data of performance and test failure and also to provide safety of electrical load connected in the circuit.

SUMMARY OF THE INVENTION

[007] 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.

[008] The main object of the present invention is to provide an improved system to overcome at least one of the disadvantages/drawbacks of the known art as indicated above.

[009] Another object of the present invention is to improved system for tracking phase failure in a test unit during testing of a circuit breaker, so as to provide accurate data of performance and test failure.

[0010] Yet another object of the present invention is to provide an improved current based system for tracking failure of single phasing in test unit in a three phase electrical system so as to overcome the drawbacks of the voltage based conventional system and to provide safety of electrical load and circuit.

[0011] Accordingly, in one implementation, the present invention provides an improved system for tracking of single phasing in at least one test unit connected in a three-phase electrical system during testing of at least one circuit breaker, said system comprising:
at least three current transformer in said three-phase electrical system, adapted to receive input alternating current (AC) from said test unit and generate an AC output corresponding to said input AC received, wherein said current transformer adjusted to receive variable test voltage;
at least three electronic circuit assembly coupled to said current transformer, said electronic circuit assembly adapted to receive said AC output as an input current, rectify said input current and thereby produce output direct current (DC);
at least three semi-conductor device operable coupled to said electronic circuit assembly, wherein actuation of said semi-conductor device corresponds to said output DC from said electronic circuit assembly;
an assembly at least three protection relay devices and a main protection relay device, said protection relay devices operable by means of said semi- conductor device, wherein, during single phasing in at least one phase in said three-phase electrical system said main protection relay device switches off due to zero input current at said current transformer, and thereby terminates testing of said circuit breaker.

[0012] In one implementation, the present invention provides a method for tracking single phasing in at least one test unit connected in a three-phase electrical system during testing of at least one circuit breaker, said method comprising:
receiving, by means of at least one current transformer, an input AC of at least one parameter from said test unit at plurality of primary winding of said current transformer, and thereby generating output AC at plurality of secondary winding of said current transformer;
transmitting, by said secondary winding of said current transformer, said output AC to an input port of at least one electronic circuit assembly for obtaining DC corresponding to said AC;
actuating, by said DC, at least one semi-conductor device for controlling operation of at least one protection relay device;
actuating, by means of said protection relay device, at least one programmable logic controller (PLC) to perform testing of said circuit breaker;
wherein, during single phasing in at least one phase in said three-phase electrical system, said protection relay device stops operating due to zero input current at said current transformer, terminating said PLC and thereby stopping said testing of said circuit breaker.

[0013] 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:

[0014] Figure 1 illustrates the conventional setup or voltage sense system, in accordance with subject matter of the present invention.

[0015] Figure 2 illustrates the improved power circuit assembly for tracking Single phase failure, in accordance with subject matter of the present invention.

[0016] Figure 3 illustrates the electronic circuit assembly for tracking single phase failure, in accordance with subject matter of the present invention.

[0017] Figure 4 illustrates a series circuit for detecting single phasing, in accordance with subject matter of the present invention.

[0018] Figure 5 illustrates a PLC ladder diagram for single phasing, in accordance with subject matter of the present invention.

[0019] Figure 6 illustrates a flow chart for working of the improved system, in accordance with subject matter of the present invention.

[0020] 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

[0021] 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.

[0022] 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.

[0023] 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.

[0024] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Referring now to figure 1, the conventional setup using voltage sense system for tracking failure of single phasing in test unit is illustrated. The present invention may provide an improvement over the conventional voltage sense system for tracking single phasing in the test unit.

[0029] Referring now to figure 2, the power circuit assembly includes a main circuit comprising of a molded case circuit breaker (MCCB) (1) connected to a backup contactor (2), at least two of a test unit (3) such as test unit 1 and test unit 2 and an electrical load.

[0030] In one implementation, the power circuit assembly further comprises at least one Programmable logic controller (PLC) configured to perform said testing of the circuit breaker by means of output received from a protection relay device.

[0031] In one implementation, as shown in figure 2, there is provided an improved current based system in the power circuit assembly. The improved current based system comprises of three current transformers (5) A1, A2,A3connected to each of the three phases R-Y-B respectively, wherein each of the current transformers (5) are further connected to an electronic circuit assembly (6) that includes full-wave rectifier and a semi-conductor device that may include but not limited to a bipolar transistor. The output of the semi-conductor device adapted to actuate switching operation of an assembly of protection relay device (7) and main relay device (11) are connected in series with each other.

[0032] Referring now to figure 3, the electronic circuit assembly (6) for tracking single phase failure in test unit is illustrated. In one implementation, the electronic circuit assembly (6) includes four diodes D1, D2, D3 and D4 and a capacitor filter assembled in a full wave rectifier circuit assembly (8) and the output of the full wave rectifier circuit assembly (8) is subsequently fed to a bipolar transistor (10) to control the operation of relay.

[0033] Referring now to figure 4, a series circuit arrangement of protection relay (7) and a main protection relay (11) for detecting single phasing is illustrated.

[0034] Referring now to figure 5, a PLC (13) ladder circuit assembly for single phasing with preset value of a counter is illustrated.

[0035] Referring now to figure 6 a flow chart of working of the improved system for tracking single phase failure in a test unit during testing of circuit breaker is illustrated.

[0036] In one implementation, the improved system for tracking failure of single phasing in test unit wherein each of the three current transformer (5) as connected in three phases R-Y-B respectively can monitor current by detecting the present current in a primary winding and thereby providing a proportional lower value in the secondary winding. This output is use for relay operation through a transistor. The output current from the secondary winding is fed to the electronic circuit assembly that includes an arrangement of diodes in a full wave rectifier with a capacitor filter and at least one transistor so as to control the flow of larger electric current. The output of transistor is used to operate the working of the protection relay device connected in the circuit.

[0037] In one implementation, in case of a phase fault in at least one of the phases in three phase electrical network, a programmable logic controller (PLC)may be terminated due to termination of the main protection relay (11). This may prevent the operation of test unit before any major damage occurs in the electrical load connected in the circuit.

[0038] In one implementation, in case of testing of the circuit breaker, molded case circuit breaker (MCCB) (1) is in closed position, the backup contactor (2) also remains in the closed position and thus the test unit (3) also remains closed, thereby completing the electrical circuit for current to flow through the circuit. Three current transformers (5) A1, A2, and A3 are added across the R, Y, B phases respectively. Current transformers (5) detect the present current in the primary winding (15) and provide the proportional lower value in the secondary winding (16). This output is use for relay (7) operation through bipolar transistor (10).

[0039] In one implementation, as shown in figure 3,the secondary winding (16) of current transformers (5) are connected to four-diode full-wave bridge rectifies (8) circuit. Current transformer (5) is designed to produce an alternating current in its secondary winding (16) which is proportional to the current being measured in its primary winding (15). The four-diode bridge rectifies (8) the alternating current (AC) of load's current into direct current (DC) for the transistor (10) to control. The capacitor is connected in parallel to a diode bridge. The diode bridge converts rippled output into smooth DC. By using this smooth DC output the NPN bipolar transistors (10) get operated. Transistor (10) operates only when the supply is given to the base terminal. For an NPN, transistor base terminal has a positive polarity. The bipolar transistors (10) are extremely useful devices, allowing a small electric current to control the flow of a much larger electric current. The transistor (10) operation is used for closing of relay (7) which is used for single phase detection.

[0040] In one implementation, in case single phasing occurs in test unit, at least one of phases of test unit gets opened. Because of single phasing, the main circuit will not get completed and there is no current in faulty pole. The current transformer (5) may not produce output current in secondary winding (16) due to zero input current in primary winding and therefore fault detecting relay (7) R1, R2, and R3 fails to operate their regular manner.

[0041] In one implementation, if at least one of relays (7) R1, R2, and R3 is not functional, the circuit will not get completed and thus a main relay R4 (11) will not operate. Hence as the main relay R4 (11) is not operating the PLC counter (13) fails it regular operation enabling the value of the counter to increase continuously. When the counter value becomes equal to set value of the counter, then the contacts of the counter (14) gets operated and before any major damage occurs in main circuit the PLC may stop the operation of the test unit (3) before any major damage occurs. The PLC stops operating due to switching off of the main protection relay device R4 (11), and the termination of the PLC further terminates testing of the circuit breaker.

[0042] In one implementation, the improved circuit assembly for detecting single phasing failure in test unit includes the following components:
Name Description Values Qty
R1,R2,R3,R4 24 VDC Relay NA 4
A1,A2,A3 Current Transformer NA 3
D1,D2,D3,D4 1N4007S NA 4
RL Load resistance 16GOhm 1
C Capacitor 47µf 63V 1
Transistor Bipolar Transistor (NPN) NA 1
R Current limiting Resistance 180MOhm 1
K1,K2,K3 Contactor NA 3

[0043] Some of the important features of the present invention, considered to be noteworthy are mentioned below:

1) The present invention overcomes the disadvantages/drawbacks of a voltage sensing system for detecting single phasing fault.
2) The present invention provides a circuit arrangement for detecting single phasing fault in test unit by using a current detect device (5), wherein the test voltage can be changed frequently.
3) The circuit assembly for detecting single phasing fault in test unit provides more precise result and safety to testing unit, electrical load, electrical circuit and its element.
4) The improved provides a better tracking failure of single phasing in test unit and thus provides safety to electrical load in the circuit.
,CLAIMS:1. An improved system for tracking of single phasing in at least one test unit in a three-phase electrical system during testing of at least one circuit breaker, said system comprising:
at least three current transformer in said three-phase electrical system, adapted to receive input alternating current (AC) from said test unit and generate an AC output corresponding to said input AC received, wherein said current transformer adjusted to receive variable test voltage;
at least three electronic circuit assembly coupled to said current transformer, said electronic circuit assembly adapted to receive said AC output as an input current, rectify said input current and thereby produce output direct current (DC);
at least three semi-conductor device operably coupled to said electronic circuit assembly, wherein actuation of said semi-conductor device corresponds to said output DC from said electronic circuit assembly;
an assembly at least three protection relay devices and a main protection relay device, said protection relay devices operable by means of said semi-conductor device, wherein, during single phasing in at least one phase in said three-phase electrical system, said main protection relay device switches off due to zero input current at said current transformer, and thereby terminates testing of said circuit breaker.

2. The improved system as claimed in claim 1, wherein said current transformer receive, by means of plurality of primary windings, said alternating current (AC) as input AC current of at least one value and generate said AC output, by means of plurality of secondary windings of at least one lower value corresponding to said input AC current.

3. The improved system as claimed in claim 2, wherein during single phasing in at least one phase in said three-phase electrical system, said current transformer stops operating and thereby produce zero current to said secondary windings.

4. The improved system as claimed in claim 1, wherein said electronic circuit assembly comprises:
at least one bridge rectifier circuit to convert said input AC into said output DC; and at least one capacitor filter to convert rippled output DC into smooth DC output.

5. The improved system as claimed in claim 1, wherein semi-conductor device is a bipolar transistor adapted to actuate switching operation of said protection relay devices during normal condition and single phasing condition.

6. The improved system as claimed in claim 1, further comprises at least one Programmable logic controller (PLC) configured to perform said testing of said circuit breaker by means of output received from said main protection relay device.

7. The improved system as claimed in claim 6, wherein during single phasing, said PLC stops operating due to switching off of said main protection relay device, thereby said PLC terminates said testing of said circuit breaker.

8. A method for tracking single phasing in at least one test unit connected in a three-phase electrical system during testing of at least one circuit breaker, said method comprising:
receiving, by means of at least one current transformer, an input AC of at least one parameter from said test unit at plurality of primary winding of said current transformer, and thereby generating output AC at plurality of secondary winding of said current transformer;
transmitting, by said secondary winding of said current transformer, said output AC to an input port of at least one electronic circuit assembly for obtaining DC corresponding to said AC;
actuating, by said DC, at least one semi-conductor device for controlling operation of at least one protection relay device;
actuating, by means of said protection relay device, at least one programmable logic controller (PLC) to perform testing of said circuit breaker during normal condition;
wherein, during single phasing in at least one phase in said three-phase electrical system, said protection relay device stops operating due to zero input current at said current transformer, terminating said PLC and thereby stopping said testing of said circuit breaker.