Claims:1. A high power hybrid solid state contactor assembly for providing making and breaking of branch circuits without any production of arc in switchgear arrangements, said assembly comprising:
at least one high power rated electromechanical contactor;
at least one solid state device, said solid state device being located upon a heat sink assembly; and
a control circuit;
Wherein said contactor is operatively electrically connected to say solid state device so as to provide making and breaking of the branch circuit without formation of any arc.
2. The assembly as claimed in claim 1, wherein the said electrical connection between the contactor and the solid state device comprising line and load terminals of the contactor being connected in parallel with the anode and cathode terminals of the solid state device.
3. The assembly as claimed in claim 1, wherein the heat sink assembly is adapted to provide adequate cooling to the solid state device to make it suitable for a maximum breaking capacity of about 3.5kA, 415V, 50Hz.
4. The assembly as claimed in claim 1, wherein the heat sink assembly comprises vertical fins for natural cooling.
5. The assembly as claimed in claim 1, wherein the heat sink assembly further comprising an insulator means.
6. The assembly as claimed in claim 1, wherein the control circuit comprising microcontroller such that it produces two analogue output.
7. The assembly as claimed in claim 1 further comprising a three phase bridge rectifier adapted to convert AC to DC.
8. The assembly as claimed in claim 1 further comprising a fly-back converter adapted to convert high voltage DC to intended low voltage DC.
9. The assembly as claimed in claim 1 further comprising a buck converter for providing a regulated low voltage DC supply to the microcontroller.
10. The assembly as claimed in claim 1 further comprising an optocoupler adapted to receive DC control signal from the control station for feeding the control signal to the ADC of microcontroller.
11. The assembly as claimed in claim 1, wherein the solid state device comprising at least one silicon controller rectifier (SCR) anti-parallel to the contactor.
12. The assembly as claimed in claim 11, wherein the SCR is turned ON by the minimum turn on voltage developed due to opening of the electromechanical contactor.
13. The assembly as claimed in claim 11, wherein the SCR is turned OFF due to self-commutation.
, Description:TECHNICAL FIELD

The present invention described herein, in general, relates to contactor assembly for used in switchgear arrangements. More particularly, the invention relates to a high power hybrid solid state contactor assembly for providing making and breaking of branch circuits without any production of arc in switchgear arrangements. The assembly can be used for both two poles and three poles version as per IEC 60947-4-2/3 and IEC 60947-1 international standards.

BACKGROUND

Reference is made to US4356525 which discloses a method and circuit for minimizing DC current offset generated by the voltage integrating property of an inductive load First, second and third hybrid contactors connect first, second and third output lines of an AC power source to first, second and third input lines of an inductive load. Each hybrid contactor includes a pair of relay contacts in parallel with a semiconductor switching unit having two anti-parallel-connected silicon-controlled –rectifiers. A latching circuit and several delay circuits are used to turn-on and off the hybrid contactors; the timing of the turn-on points is controlled relative to a zero-crossing of a voltage from the AC power source such that minimal DC offset current occurs.

Reference is made to US12/976,432 which discloses hybrid switch circuit includes a hybrid switch that couples an input conductor connected to an AC power supply to an output conductor connected to a load. The hybrid switch includes a power semiconductor in parallel with the contacts of an electromagnetic relay. A control circuit turns on the hybrid switch by turning on the power semiconductor at a zero voltage crossing of the AC voltage to provide a conductive path and then closing the relay to provide a conductive by pass path that bypasses the power semiconductor. The control circuit turns off the hybrid switch by opening the relay and subsequently turning off the power semiconductor at a zero crossing of the load current. The control circuit operates in response to at least one switch control signal that indicates whether an operating fault condition exists.

Reference is made to US12/325,466 which discloses a hybrid Power relay for making and breaking an electrical circuit which includes electromagnetically operated contacts for making and breaking the circuit, a solid state switch connected across the contacts, a control circuit responsive to a control signal for actuating the solid state switch and the contacts such that the solid state switch closes before the contacts to make the circuit and the contacts open before the solid state switch to break the circuit, and a protective circuit for monitoring the temperature of the solid state switch and opening the switch in the event of a rise in temperature produced by the abnormal current flow in the switch due to failure of the contacts to make and maintain the circuit.

Reference is further made to US2005/0270716 which provides a hybrid relay generating low electric noise used for controlling the on/off of an electrical equipment. A hybrid relay inserted to a line supplying power to a load has lines L1 and L2 branched in parallel. A first mechanical relay is inserted to the first line L1, and a semiconductor relay and a second mechanical relay are inserted serially to the second line L2. When turned on, the second mechanical relay is closed, the semiconductor relay is closed, and then the first mechanical relay is closed, and finally the semiconductor relay is opened. When turned off, the opposite operation is carried out. The semiconductor relay will not always be closed, and the generation of electric noises by the mechanical relay can be prevented.

Reference is further made to US5578980 which discloses a hybrid switch comprises an electromagnetic contactor for conducting a current flow after the current making operation, a semiconductor switch device connected in parallel with a main contact of the electromagnetic contactor, for conducting operations of making and breaking a current; and a semiconductor unit body including a case having a square shape in section for housing the semiconductor switch device, and conductor plates which are respectively connected to terminals of the semiconductor switch device and drawn out from sides of the case, end portions of the conductor plates being bent to form main circuit terminals, the semiconductor unit body being mounted on a top portion of the electromagnetic contactor, and the main circuit terminals of the conductor plates drawn out from the semiconductor unit body being fastened to main circuit terminals of the electromagnetic contactor by using terminal screws respectively.

Reference is also made to US 7079363 which discloses a hybrid DC electromagnetic contactor. In a hybrid DC electromagnetic contactor, by including a power unit for supplying a certain power voltage; a main contact point of a breaking switch for providing a supply path of the power voltage by being switched in accordance with a voltage apply to an operational coil; a switch for providing a supply path of the power voltage according to a gate signal; a snubber circuit for charging voltage at the both ends of the switch in turning off of the switch and being applied – discharged an electric current when the charged voltage is not less than a certain voltage; and a discharge current removing unit for removing the discharge current by providing a discharge current path to a load block in turning off of the switch, it is possible to minimize a size of leakage current when the main contact point and the semiconductor switch are turned off, and accordingly it can be practically used.

Reference is also made to CN203894384 which relates to zero-current hybrid breaking technology testing apparatus, which comprises a current source, a follow current circuit, a fast mechanical switch, a zero-current converting circuit and a voltage source. When a test is conducted, the current source is inputted at first to generate high pulse current, then the follow current circuit stabilizes follow current, and the fast mechanical switch is controlled to be turned off; when contacts of the fast mechanical switch reach a required opening distance, the zero-current converting circuit is inputted to enable the fast mechanical switch to get into a conversion breaking process; and when current of the fast mechanical switch crosses zero, the voltage source is inputted after a period of time delay to generate high-frequency recovery voltage. The zero-current hybrid breaking technology testing apparatus can meet requirements of a high-current breaking test by adopting small capacitors and inductors, is easy to control, realizes accurate cooperation between the current source and the voltage source, can reduce requirements for a test circuit, and reduces the test cost.

Reference is also drawn to Indian patent applications 2547/MUM/2014 and 2605/MUM/2012. Both these applications disclose a single pole hybrid contactor up to less than 100A rate current, which is suitable for switching a resistive and slightly inductive load.

However, with the existing electromechanical contactors it has been observed that while making and breaking the branch circuit arcing is produced which leads to heavy erosion of the contactors and hence poor electrical life of few thousands.

The problem associated with conventional contactor is frequent maintenance due to arcing, parallel arrangement of contactor to share the high current, higher response time, unreliable operation, higher test lead time and hence higher operational and running cost. Thus, there exists a need for hybrid contactor assembly for addressing all the issues of a conventional contactor and will provide uninterrupted millions of operation to satisfy the demand.

SUMMARY OF THE INVENTION

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.

An object of the present invention is to overcome the various problems of a conventional electromechanical air break contactor.

Another object of the present invention is to provide a high power hybrid solid state contactor assembly for providing making and breaking of branch circuits without any production of arc in switchgear arrangements.

Accordingly to one aspect, the present invention provides a high power hybrid solid state contactor assembly for providing making and breaking of branch circuits without any production of arc in switchgear arrangements, said assembly comprising:
at least one high power rated electromechanical contactor;
at least one solid state device, said solid state device being located upon a heat sink assembly; and
a control circuit;
wherein said contactor is operatively electrically connected to said solid state device so as to provide making and breaking of the branch circuit without formation of any arc

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:

Figure 1 illustrates a block representation of the hybrid contactor of the present invention.
Figure 2 illustrates a block representation of the control circuit for the hybrid contactor assembly of the present invention.
Figure 3 illustrates detailed control and gate drive circuit of the hybrid contactor assembly of the present invention.
Figure 4 shows the assembly of the high power hybrid contactor of the present invention.
Figure 5 shows the heat sink assembly of the hybrid contactor of the present invention.
Figure 6 shows the making circuit test set up with the hybrid contactor of the present invention.
Figure 7 illustrates the hybrid contactor voltage and current waveform for arc less operation in the present invention.
Figure 8 shows the condition of hybrid contactor before make-break test.
Figure 9 shows the condition of hybrid contactor after make-break test.
Figure 10 shows the condition of conventional air break contactor after make-break test.
Figure 11 shows the condition of insulation of hybrid contactor after make-break test.

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

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.

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.

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.

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

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.

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.

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.

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), other switchgears and the like.

The present invention relates to an innovative high power hybrid solid state contactor. Being solid state in nature, it makes and breaks the branch circuit without any arc. Due to this, the overall electrical life of the hybrid contactor is in millions. The hybrid contactor consists of a high power solid state device, whose anode to cathode terminal is connected in parallel with the individual line and load terminal of the electromechanical contactor. Unlike to a conventional contactor, control signal is provided from the control station by the test personnel. Figure – 1 and 2 shows the detailed power and control circuit of the hybrid contactor assembly suitable for three phase switching operation. The AC power is provided to power up the micro controller with the help of buck converter. The dc control signal is provided to trigger the micro controller through an optocoupler.

As explained above, the hybrid contactor consists of a high rated electromechanical contactor (1), whose line and load terminal is connected in parallel with the anode and cathode terminal of solid state device (2). The solid state device (2) rest upon the heat sink assembly(3) for adequate cooling so that it is suitable for a maximum breaking capacity of 3.5 kA, 415V, 50Hz. Figure – 4 shows the detail construction of the hybrid contactor for two pole switching. Heat sink assembly (3) as shown in figure - 5 consists of aluminum black painted and matt finish heat sink (4) with vertical fins for natural cooling, insulator(6) holding the rectangular shaped bus bar(5) for termination with the SCR and electromechanical contactor.

When control supply is fed to the hybrid contactor, the solid state switch initially turns ON, which carries making current. Next after certain delay depending upon the response time of the circuit, electromechanical contactor will switch ON to transfer the making current from SCR to its contacts. The drop across the line and load being in mV is not sufficient to turn ON the anti-parallel SCR of the solid state device as the current drawn by it is less than the hold on current. Due to this the solid state device turns OFF. Next when the control supply is cut off, no trigger signal available to the micro controller and hence the electromechanical contactor switches OFF and while opening, it develops high voltage across its contacts to turn ON the SCR. The rated current gets transfer to the SCR, being the lowest impedance path. Since no control supply is available, the SCR turns OFF at the nearest zero due to self-commutation. So while making and breaking the circuit, the hybrid contactor do not produce any arc.

Initially the 3 phase AC supply is fed to the 3 phase bridge rectifier (7) to convert AC to DC, the high voltage DC to its intended low voltage of 15 V DC by means of fly- back converter (9) and here EMI filter (8) is used to reduce the EMI noise in the line. The 15V DC supply can be used for gate drive signal for high power SCR’s and power supply to the microcontroller and its accessories. Here microcontroller and its accessories needs regulated low voltage DC supply by means of DC-DC buck converter (10).The LED (11) starts blinking showing the status of the control circuit. Next the DC control signal is fed through the branch circuit constituting (15)-(13)-(19)-(18). When the input voltage across the optocoupler (19) becomes more then the forward voltage drop, photodiode of (19) starts conducting and hence optically gets coupled with that of the opto-transistor to turn it ON. Output of optocoupler (19) conducts the branch circuit (20)-(14) || (21). The drop across (20) || (21) is fed as analogue input to pin 3 of microcontroller (22) to trigger it up. Pin 10 of the micro controller (22) is shorted through resistor (25) to pin 1(Vcc). This reset the programme after the intended cycle. The microcontroller (22) is programmed in such a way that it produce two analogue output from pin 2 and 8. The analogue output from pin 8 is first fed through resistance (24) to the input pin of MOSFET driver IC (26). The adjacent capacitor (28, 27) connected between the Vs and ground aids in rejecting effect due to EMI. The output voltage of (26) is fed to branch circuit (31)-(32) and capacitor (29).The voltage drop across (32) || (30) is fed between the gate and source. When it becomes more than Vgs, MOSFET (33) turns ON there by further driving the branch circuit consisting of (34)-(35)-(36). The potential available at (34) drives the branch circuit (38) – (37) and hence the pulse transformer (40, 41, 42) to trigger the gate of anti-parallel SCR pair, connected in the power circuit. Upon triggering, they conduct in both the positive and negative cycle to draw six times rated current. Next analogue out from pin 2 is fed to base of transistor (45) through resistance (44). When the base current of (45) becomes high, it turns ON and drives the photodiode of (46) through resistor (43). The photodiode upon conduction emits infrared light which optically gets coupled with that of the opto-traic of (46) to turn it ON. Output circuit of (46) along with branch circuit triggers the gate of the low power SCR (49) and (50), which conducts in both the positive and negative cycle. Conduction of (49) and (50) energizes the coil of high power electromechanical contactor. Resistor (54) and capacitor (55) are the snubber parameters, which control the dv/dt while switching OFF the antiparallel SCR. Upon energization of the coil, the electromechanical contactor picks up and its contacts close across anode and cathode of the power SCR. The resistance offered by the contacts is very less as compared to that of the dynamic forward resistance of the power SCR. Hence the making current gets transferred to the contacts of electromechanical contactor. At this instant, power SCR stops conducting at the nearest zero crossing. In order to switch OFF the hybrid contactor, initially the control signal is cut off. The coil of the electromechanical contactor being directly connected to the AC source will first drop down and while opening its contacts, develops high voltage across the anode and cathode terminal of the antiparallel SCR. This is sufficient to draw current more than it’s latching current value and hence power SCR conducts in both the positive and negative cycle. Thus the breaking current gets transferred to the power SCR from the EM contacts. Since there is no control supply available to the microcontroller, it do not produce any analogue output to trigger the low and high power SCR. Due to this reason the power SCR stops conducting at the nearest zero crossing due to self-commutation. So as compared to a conventional air break electromechanical contactor, the hybrid contactors do not produce any arc while making and breaking the circuit.

The hybrid contactor is used in the making and breaking of electrical circuit as shown in figure – 1 and 2. The sequence of operation between the solid state switches and electromechanical contacts well explained through the time diagram in background section. The detailed prototype sample of the same in two pole version is shown in figure – 6. It consists of making circuit master contactor (57), hybrid contactor (61) and test contactor (59). Both the master (57) and test (59) contactor are air break electromechanical contactor. All the three contactors are connected in series with respect to each other as shown in figure – 1

The above set up is put under electrical life test with an inductive load set at 2.1kA, 415V, 50 Hz, power factor 0.35. It successfully cleared 3000 number of operations without any arc produced during making and breaking of the inductive load. Fig.7 shows the arc less operation of the hybrid contactor while making and breaking the high current load (6In). As shown in the figure, while breaking the load hybrid contactor do not produce any arc between the contacts and given to the perfect isolation to the load from the source. Due to high inductive energy a transient recovery voltage appears in the “R” and “B” pole voltage wave form. Snubber circuit which is connected in parallel to the SCR pair limits the dv/dt of the TRV. To further evaluate the arc less operation of the hybrid back up contactor surface morphology study being conducted upon the serrated contact. Figure 8 and 9 shows the micro structure image of the contact before and after the test at 2.1kA. As can be observed from the above figure there is hardly any difference in the contact surface texture of the hybrid contactor. However the contact which has been subjected to the electrical life test shows positive crack and breaking of the serration layer. This is due to heavy mechanical impact upon the contact surface. Few dark patches appearing upon the contact surface is due to formation of debris from the external polluted environment and oxide layer of contact. This was easily cleaned using a cloth.

Above results next compared with the microstructure of the contact button, which has been subjected to arcing during making and breaking of the electrical circuit. Fig.10 shows the detail microstructure of the eroded contact surface after making and breaking test of an air break electromechanical contactor at similar kind of load. It has been observed from the micro structure study that in case of a conventional electromechanical back up contactor, which produces arcing during making and breaking the circuit, there is formation of pit upon the surface of its contact. In addition to the above observation formation of crater, observed upon the contact surface at the outer boundary. This is due to melting and subsequent vaporizations and settling back after cooling of the molten mass during arcing between the contacts.

Further validation of the successful arc less operation of the hybrid backup contactor was done at various level of load current up to even 3.2kA, 415V, 50 HZ at 0.35 power factor. Unlike to conventional contactor, since there is no arc developed while making and breaking the circuit, therefore there is no burning of the adjacent insulation holding the current carrying parts. Fig.11 shows the clean condition of the insulation after 3000 number of electrical operations.

The scope of this invention is not limited to a particular assembly but on the contrary, the intention is to cover all the modifications, equivalents and alternatives to the invention disclosed here within.

[001] Some of the advantages of the present invention, are as follows:
• Millions of arc less operation of the hybrid contactor
• Higher operation per hour
• Highly reliable
• Higher operating current range
• Lower test lead time
• Lower operating and running cost
• Low response time