DESC:FIELD OF INVENTION
The present invention relates to a power source changeover contactor. More particularly, the present invention relates to an automatic source changeover contactor with current limiter, which can make / break full load current without contact heating / welding. Advantageously, the present invention eliminates arc formation during change over.
BACKGROUND ART
In modern days the demand for electrical energy for domestic use is ever increasing. In developing countries always there is mismatch between the supply and demand for the electrical energy and hence the usage of power from alternate source is inevitable. In multi storey buildings, apartments, group housing complexes and the like, the power from main supply is used as a main source and power from alternate source is used as a standby power source or second source.
In order to connect the load seamlessly between the available power sources, namely the main supply and the standby supply, automatic source changeover with current limiter (ACCL) is used as the change over device. When the power is available from the mains supply, the ACCL connects the load to the mains supply. On mains supply failure, the ACCL connects the load to the standby power source, for example the power from diesel generator (DG).
The ACCL is used for efficient distribution of individually rationed generator power and stationary in the individual user place. During the alternate supply operation, load drawn is monitored and if the load exceeds the allotted limit, it disrupts the alternate supply and rechecks in intervals. On reducing the load and keeping it within the limit, load is continued to be connected with the alternate supply.
As shown in Figure 6, accompanying this specification, the conventional single phase ACCLs are fitted with miniature T-type relays. The T-type relays are single butt contact type and normally have an air gap between contacts in the range from 0.5mm to 0.7mm. In T-type relays, contacts present on either side of the moving carrier. In the conventional T-type relays the Normally closed (NC) contacts present in the alternate supply sides are rated for 20A and the Normally open (NO) contacts present in the mains sides are rated for 30A. In case of overload, contact welding, severe arcing and heating takes place due to less contact pressure in the conventional T-type relays. Even during normal load conditions if the contactor changes over from mains supply to the alternate supply or vice versa there is chance of severe arcing and welding. Hence, the conventional single phase ACCLs is capable of switching AC-31B utilization category, the detail of which is shown in Table-1 below.
Table- 1: Illustrates utilization category of the conventional single phase ACCLs for different types of loads / applications

Nature of current Utilization category
Typical applications
Frequent operations Infrequent operations

Alternating current AC-31A AC-31B Non-inductive or slightly inductive loads
AC-33A AC-33B Motor loads or mixed loads including motors, resistive loads and up to 30% incandescent lamp loads
AC-35A AC-35B Electric discharge lamp loads
AC-36A AC-36B Incandescent lamp loads
The possible major reason for the contact welding which happens while breaking overload condition may be due to presence of lesser air gap between contacts. This is the precise reason why the conventional single phase ACCLs is unable to carry full load (inductive load) on the alternate source side as that of mains supply side.
The conventional single phase ACCLs uses relay coils which are getting energised even during the time when the loads are connected to mains supply. This results in unnecessary power consumption as well as the heating of the electronic circuits.
4444/CHE/2013 discloses a trip-free switching mechanism for actuating double contact arrangement of a circuit breaker, comprising: an actuator assembly is composed of a hook member, a trip bar member and a movable contact holder pivotally attached to a plate member, where the movable contact holder formed of an extended arm with a linear slot. The actuator assembly and the carrier assembly in the circuit breaker facilitates maximum isolation gap between the stationary contacts and the movable contact.
Accordingly there is a need for a cost effective single phase ACCLs which is free from the problems noted in the prior art.
OBJECTS OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.
The primary object of the present invention is directed to provide an energy efficient automatic source changeover contactor with current limiter, which can make / break full load current without contact heating / welding during change over from main power source to standby power source and vice versa.
It is another object of the present invention to provide a compact automatic source changeover contactor with current limiter which eliminates arc formation during change over from main power source to standby power source and vice versa.
It is another object of the present invention to provide a cost effective automatic source changeover contactor with current limiter, which eliminates electronic circuits in the main power source side.
It is another object of the present invention to provide an automatic source changeover contactor with current limiter that consumes minimum power during the main power source operation.
SUMMARY OF INVENTION
Thus according to the basic aspect of the present invention there is provided an automatic source changeover contactor type with current limiter, comprises of a printed circuit board (PCB); a base assembly; a magnet assembly; a coil bobbin; an armature assembly; and a cross bar fitted with one or more moveable contacts,
wherein the base assembly comprises plurality of stationary contacts fitted with contact rivets of pre determined diameter and height,
wherein the stationary contacts are electrically connected to a first circuit that connects the load to the mains lines and a second circuit that connects the load to the standby power source,
wherein the cross bar is fitted with one or more moveable contacts that connects the load either to the first circuit or to the second circuit, and
characterised in that the stationary contact and the moveable contacts are Double Butt contact type and provides pre determined air gap between them during making contact.
It is another aspect of the present invention, wherein the pre determined air gap per contact is in the range 2.30 to 2.70mm preferably 2.50mm.
It is another aspect of the present invention, wherein the coil bobbin is not energised during mains condition in order to minimise the heat generation and power consumption.
It is another aspect of the present invention, wherein the stationary contacts of mains side and standby power source side are physically separated with suitable side walls of sufficient width and height in order to suppress the arc produced during the making and breaking of contacts and to eliminate phase to phase short.
It is another aspect of the present invention, wherein the PCB is isolated from the power supply circuit for enhanced protection of electronic circuit.
It is another aspect of the present invention, wherein the standby power source include Diesel generator (DG).
It is another aspect of the present invention, wherein the device is capable of switching AC-32A & AC-22A utilization category.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Illustrates the perspective view of the automatic source changeover contactor type with current limiter according to the present invention.
Figure 2: Illustrates the exploded view of the automatic source changeover contactor type with current limiter according to the present invention
Figure 3: Illustrates the top view of the automatic source changeover contactor type with current limiter according to the present invention shown connected between main power source and standby power source.
Figure 4: Illustrates the base of the automatic source changeover contactor type with current limiter according to the present invention
Figure 5: Illustrates the base mounted with the contacts used in the automatic source changeover contactor type with current limiter according to the present invention
Figure 6: Illustrates the single butt contacts used in the automatic source changeover contactor type with current limiter according to the prior art.
Figure 7: Illustrates the double butt contacts used in the automatic source changeover contactor type with current limiter according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
The present invention is thus directed to an automatic source changeover contactor with current limiter, which can make / break full load current without contact heating / welding.
The automatic source changeover contactor type with current limiter (ACCL) according to the present invention is a two pole changeover contactor with double butt contacts construction. The ACCL comprises a means to connect to a first circuit in order to connect the load to the mains (Electricity Board) lines such that when mains supply is ON, ACCL will give the mains supply without any interruption to load directly. The ACCL further comprises means to connect to a second circuit in order to connect a pre determined loads to the standby power source, for example Diesel Generator Power.
Figure 2 Illustrates an embodiment of the automatic source changeover contactor type with current limiter (ACCL) according to the present invention. The ACCL includes a Printed circuit board (PCB) (1), a base assembly (2), a magnet assembly (3), a coil bobbin (4), an armature assembly (5) and a cross bar (6) fitted with one or more moveable contacts (MC). These parts are housed within a detachably mountable enclosure comprising a bottom cover (10) and a top cover (7). The bottom cover (10) and top cover (7) are made of insulating materials like thermosetting plastic material such as Nylon 6 and are disposed to protect and insulate the contacts as well as to provide some measure of protection against personnel touching the contacts.
The base assembly (2) shown in Figure 5 comprises plurality of stationary contacts (SC) which are detachably mounted on the base part (2a) with pre determined spacing between them. As shown in Figure 6 and 7 the stationary contacts (SC) are fitted with contact rivets (8) of pre determined diameter and height. While the stationary contacts (SC) of mains side are electrically connected to the first circuit, the stationary contacts (SC) of alternate source side are electrically connected to the second circuit.
The stationary contacts of stationary (SC) of mains side and alternate side are physically separated with suitable side walls of sufficient width and height in order to suppress the arc produced during the making and breaking of contacts. The cross bar (6) fitted with plurality of moveable contacts (MC) is slidably mounted in the base part (2a) .The moveable contacts (MC) are also fitted with contact rivets (8) of pre determined diameter and height as shown in Figure 6 and 7. The coil bobbin (4) fitted with the magnet assembly (3) is assembled with the base part (2a) .The armature assembly (5) is detachably mounted to the end of the cross bar (6) that is away from the coil bobbin (4). On energising the coil bobbin (4), the magnet assembly (3) attracts the armature assembly (5) connected with the cross bar (6) in a manner the moveable contacts (MC) mounted on it breaks the contacts from the stationary contacts (SC) of the first circuit and makes contact with the stationary contacts (SC) of the second circuit. The cross bar (6) is spring loaded, and on de energising the coil bobbin (4) the cross bar (6) is pushed in opposite direction until that the moveable contacts (MC) mounted on it breaks the contacts from the stationary contacts (SC) of the second circuit and makes contact with the stationary contacts (SC) of the first circuit. A closer cover (9) made of non metallic material such as PVC is installed between the base assembly(2) fitted with contacts and the PCB (1) for insulation purpose.
During normal course of working, when mains power is available, the ACCL connects the load to the mains (Electricity Board) lines by the first circuit through the stationary contacts (SC) and the moveable contacts (MC).
When mains power is unavailable and the alternate Power is available, the same is fed to the coil bobbin (4) of the ACCL. The energising of the coil bobbin (4) magnetizes the magnet assembly (3) which produces a magnetic field that attracts the armature assembly (5) connected with the cross bar (6). This results in the breaking of the contacts from the first circuit and making of contacts with the second circuit since force developed by the electromagnet holds the armature assembly (5) and magnet assembly (3), thus the moving contacts (MC) and stationary contacts (SC) are in closed condition. In this fashion the ACCL will automatically change over the load to alternate power after a pre determined time delay for example 5 seconds, which is governed by the PCB (1). During alternate power operation, load drawn is monitored by the PCB (1) and if the load exceeds the allotted limit, it disrupts the supply and disconnects the load from the alternate source. On reducing the connected load and keeping it within the limit, the ACCL connects load to alternate supply continuously.
If the load is connected to the alternate power and mains resume and the alternate source is switched OFF, there will be no power supply to the coil bobbin (4). Consequently, no magnetic force is generated by the magnet assembly (3) and the armature assembly (5) connected with the cross bar (6) is no more attracted. Now the cross bar (6) is pushed in opposite direction by the spring force such that the moveable contacts (MC) establish contact with the stationary contacts (SC) of the first circuit. By this arrangement the ACCL will reconnect the load to the mains through the first circuit.
According to one of the inventive feature, the ACCL according to the present invention uses Double Butt contacts in place of Single Butt contact known in the art. This enables the construction of ACCL with enhanced air gap (AG) between the stationary contact (SC) and the moveable contacts (MC). In a preferred embodiment the air gap (AG) between the stationary contact (SC) and the moveable contacts (MC) is in the range 2.3 mm to 2.7 mm, preferably 2.5mm. This enhanced air gap (AG) eliminates the formation of arc to the greater extent during breaking (opening) of contacts in overload condition. By virtue of the Double Butt contact construction the contacts at the mains side and alternative source side are physically separated and there is no chance of phase to phase short. The Double Butt contact type construction enable the full rating of the both NO & NC contacts up to 30 ampere, where as the T-type relays with single butt contact known in the art has a limitation of 20 ampere for the Normally closed (NC) contacts.
Unlike the ACCL known in the art, the ACCL according to the present invention provides reduction in overall size due to elimination of electronic circuits in the mains side. This contributes significant reduction in manufacturing cost of the equipment.
For better protection of electronic circuit, the PCB used in the ACCL according to the present invention is isolated from the power circuit unlike the electronic & power circuit is combined in a single PCB in the known ACCL, which results in enhanced reliability of the equipment.
During mains condition, coil bobbin (4) (relay coils) are not energised and electronic circuit is used only for indicating LEDs. This reduces the power consumption as well minimises the heating there by reducing the power consumption under normal conditions to less than 0.2VA.
The ACCL construction according to the present invention enables its usage in switching of mixed resistive and inductive loads, including moderate overloads in different utilization category shown in Table 2.
Table- 2: Illustrates utilization category of the automatic source changeover contactor type for different types of loads / applications

Nature of current Utilization category
Typical applications
Frequent operations Infrequent operations

Alternating current AC-32A AC-32B Switching of mixed resistive and inductive
loads, including moderate overloads
AC-22A AC-22B Switching of mixed resistive and inductive
loads, including moderate overloads

Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.
,CLAIMS:WE CLAIM:
1. An automatic source changeover contactor type with current limiter, comprises of:
a Printed circuit board (PCB) (1) ;
a base assembly (2) ;
a magnet assembly(3) ;
a coil bobbin (4) ;
an armature assembly (5); and
a cross bar (6) fitted with one or more moveable contacts (MC),
wherein the base assembly (2) comprises plurality of stationary contacts (SC) fitted with contact rivets (8) of pre determined diameter and height,
wherein the stationary contacts (SC) are electrically connected to a first circuit that connects the load to the mains (Electricity Board) lines and a second circuit that connects the load to the standby power source,
wherein the cross bar (6) is fitted with one or more moveable contacts (MC) that connects the load either to the first circuit or to the second circuit, and
characterised in that the stationary contacts (SC) and the moveable contacts (MC) are Double Butt contact type and provides pre determined air gap (AG) between them during making contact.

2. The automatic source changeover contactor type with current limiter as claimed in claim 1, wherein the pre determined air gap (AG) per contact is in the range 2.30 to 2.70mm preferably 2.50mm.

3. The automatic source changeover contactor type with current limiter as claimed in claim 1, wherein the coil bobbin (4) is not energised during mains condition in order to minimise the heat generation and power consumption.

4. The automatic source changeover contactor type with current limiter as claimed in claim 1, wherein the stationary contacts (SC) of mains side and standby power source side are physically separated with suitable side walls of sufficient width and height in order to suppress the arc produced during the making and breaking of contacts and to eliminate phase to phase short.

5. The automatic source changeover contactor type with current limiter as claimed in claim 1, wherein the PCB (1) is isolated from the power supply circuit for enhanced protection of electronic circuit.

6. The automatic source changeover contactor type as claimed in claim 1, wherein the standby power source include Diesel generator (DG).

7. The automatic source changeover contactor type as claimed in claim 1, wherein the device is capable of switching AC-32A & AC-22A utilization category.