FIELD OF INVENTION
The present invention relates to a device for automatic changeover of electric power supply between the available power sources including current limiting on both the power/sources.
BACKGROUND OF THE INVENTION
Prior art discloses many devices available for automatic changeover from one supply source to another including current limiting on the secondary supply source. However, the known devices are bulky in size and fail to provide a current limiting feature on the primary supply side, which in-turn causes severe damages to the electronic circuitry of the device particularly when the excess current flows through the circuitry which may lead to accident. Further, the existing devices generally are enabled to provide a fixed rated current on secondary supply and are not equipped with an inbuilt synchronized ON/OFF features for the secondary supply. Such devices also have very less electrical life.
CN2766439 (Y) describes an automatic changeover device for a power supply, which comprises an automatic control part which comprises a signal detection circuit, an A/D changeover circuit, a power supply board, a CPU, a power module and a fire coupling, wherein the power supply parameters of the main power supply including that of the standby power supply are detected by the signal detection circuit, and the detected signals is outputted to the A/D changeover circuit.
CN2728082 (Y) discloses an automatic changeover switch, for power supply, comprising an electrical conductor means which is composed of a two-path power supply inlet wire that is respectively connected to the main power supply and an emergency power supply; and a one-path outlet wire that is connected to a load.
Publication No. US20050141154 discloses a power management system. In particular the invention relates to power averaging and power load management in recreational vehicles.
There are several microcontroller based source changeover cum current limiter available that provide control of power distribution from secondary source of supply. These ACCLs are generally used at multi storeyed buildings, high rise apartments, group housing complexes and townships. On receiving a Generator power, the ACCL connects the supply to each flat/office/shop in a sequence and starts monitoring its load circuits. Whenever the load current exceeds a predetermined limit for a specific duration, the ACCL disrupts the power supply as an warning and thereafter automatically restores the supply depending on load status. When the Main Supply is on, the ACCL allows the full load to be connected to the mains supply. In the event of mains supply failure, the back-up Generator is switched on. Since the generators are normally not installed to cater for the full load, only essential loads are allowed while running the generator. If overload occurs ACCL switches off the Generator supply to the premises. Only when the load is reduced to a specified limit within a pre decided period, the
ACCL automatically restores supply for the essential loads; otherwise it goes to a sleep mode.
The purpose of present invention is to provide an automatic changeover cum current limiter with additional benefits and to overcome the drawbacks of existing devices. The device in invention automatically changes the Load supply from primary supply source to secondary supply source and vice versa according to the availability of supply sources and predefined priorities. Moreover it provides current limiting feature on both supply sources.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a device for automatic changeover of electric power supply between the primary and a secondary including current limiting on both the power sources.
Another object of the present invention is to propose a device for automatic changeover of electric power supply between the primary and a secondary including current limiting on both the power/sources, which is enabled to limit the current amplitude on both supply sources by adapting a single sensing means.
A still another object of the present invention is to propose a device for automatic changeover of electric power supply between the primary and a secondary including current limiting on both the power/sources, which is enabled
to disconnect the circuit in case the current supply exceeds a predefined limit including a periodic review of the load status, and restore or otherwise the supply based on the review-result.
Yet another object of the present invention is to propose a device for automatic changeover of electric power supply between the primary and a secondary including current limiting on both the power/sources, which is provided with a multiple current rating adjustment enabling an user to adjust the current rating on the secondary supply source in case the installed load increases or decreases.
A further object of the present invention is to propose a device for automatic changeover of electric power supply between the primary and a secondary including current limiting on both the power/sources, which is reliable, modular, consistent, accurate, low power consuming, economical, compact and meets the various national and international standards.
A still further object of the present invention is to propose a device for automatic changeover of electric power supply between the primary and secondary including current limiting features for both the power/sources, which is capable of consistently indicating the ooerational status.
SUMMARY OF THE INVENTION
In accordance with the present invention, the device constitutes an electronic circuit connected to a primary power source such as mains, and a secondary
power source such as generator. The device is provided with a controlling circuit comprising of a current sensing means a microcontroller, a tripping circuit, phase sensing circuits ,a status indication circuit, a voltage regulator and a switching device section comprising a number of switching devices.
The device is provided with additional features for example, an ON/OFF switch, and LED status indicator, a reset button and a multiple current rating adjuster. By using the multiple current rating adjusters, user can set the current rating according to the changing needs. The ON/OFF switching is synchronized with the secondary supply with the help of a microcontroller.
The microcontroller allows increase in efficiency and reliability of the device. With the help of the micro controller, the components can be accommodated in a compact form which makes the device reliable and efficient than the existing devices.
The invented device is enabled to automatically change the Load supply from the primary supply source to a secondary supply sources and vice versa corresponding to the load availability including predefined priorities. Moreover the device provides current limiting feature on both the supply sources. In addition, means for multiple current rating adjustment has been provided. Accordingly, an user can adjust the current rating in predefined steps on the secondary supply source in case, the installed load increases or decreases which ensures a safe operation of the device. Further, the device is configured in a
compact module which is DIN rail mountable and compatible with Domestic range of devices.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 shows a block diagram of a device for automatic changeover of power supply between the mains and a generator according to the present invention.
Figure 2 shows an outer view of the device of Figure-1;
Figure 3 shows a side view of the device of Figure-1;
Figure 4 shows the provision for din rail mounting of automatic device to shift Electrical supply between two different sources.
Detailed description of the invention
Figure 1 shows that the inventive device is connected to two different power sources (10, 11), and constitutes an electronic circuit, the device being further connected to the load. The two different supplies (10,11) are a primary power supply (10) such as mains and a secondary power supply (11) such as generator. The device is being provided with a controlling circuit comprising a current sensing circuit 12A, 12B, a microcontroller (13), tripping circuit (14), a phase sensing circuit (15A and 15B) a status indication circuit (16), a voltage regulator
(17), and a switching device section (18) comprising a number of switching devices as Rl, R2, R3 and R4. The changeover step is implemented basically by operating the switching devices through microcontroller.
The primary power supply (10) and secondary power supply (11) provide the power to the electronic circuit. The conditioned power provided to the electronic circuit is used by the controller (13) and the switching device section (18). When the primary supply (10) is available it is sensed by the phase sensing circuit (15A) which sends a signal to the microcontroller (13). The microcontroller (13) in turn changes the status of the switching devices Rl, R2, R3 and R4 to the primary side and also indicates the system status through the status indication circuit (16). Similarly when primary supply (10) fails and the secondary supply (11) commences, the secondary supply (11) is sensed by the phase sensing circuit (15B) which sends a signal to the microcontroller (13). The microcontroller (13) in turn changes the status of the switching devices Rl, R2, R3 and R4 to secondary side.
A single current sensor (19) has been used to sense the current flowing to the load. The signal from the current sensor is proportional to the current flowing through the mains and the signals are fed to the signal conditioning circuit (12A, 12B). The signal is then fed to the microcontroller (13) after conditioning it through one of the signal conditioning circuit (12A). The microcontroller (13) receives the signal from the signal conditioning circuit (12A, 12B) and monitors it. When the received signal exceeds from a predefined threshold limit, then the
microcontroller (13) generates an output signal, which in turn activates the trip circuit (14) which commands the switching means to operate. When the primary supply (10) fails it is sensed by the microcontroller (13), and with the help of the phase sensing circuit (15A), the microcontroller (13) immediately sends a signal to operate the switching device which in turn starts the secondary supply source. Similarly, when the primary supply (10) becomes active, the microcontroller (13) immediately sends a signal to the switching means which stops the secondary supply source.
A multiple current rating adjuster is provided such that the user can adjust any intermediate current rating in predefined steps on the secondary supply (11), in case the installed load increases or decreases. Overload tripping is done by the switching devices RL3.
Figure 2 shows an outer view of the inventive device. As shown, a reset button (21) to reset the ACCL from a sleep mode condition, a load adjuster button (22) for adjustment by the user as per the requirement and a plurality of indicators (23) for status indication of the Mains supply, Generator supply, load and overload, are provided to the device.
Figure 3 shows the bottom view of the inventive device having a staggered terminal 31 for proper isolation between the phase and neutral wires which facilitates the connection of the wires.
Figure 4 shows a DIN rail mounting of the so that the device can be fitted in the existing boards.
A method of working of the device is now described based on the availability of supply source :-
1. When the primary source i.e. the mains is available
When the primary source (10) is available, the power for the electronic processing is generated by the primary power supply. The availability of the primary supply (10) is sensed by the microcontroller (13) with the help of the phase sensing circuit (15A) which generates a 5V signal at the microcontroller pin when primary supply source is available and a 0V when the primary supply source (10) fails. After receiving this signal the microcontroller (13) sends a 5V signals to the respective driving circuit of switching devices RL1, RL2, RL3 and RL4; when the 5V signal is sent to the base of the NPN transistor, a 12V power flows through the relay coil which is turn changes the switching devices contact from NC (normally closed) to NO (normally open) position. Hence at this stage all the switching devices RL1, RL2, RL3 and RL4 contacts remain at NO position.
After maintaining the status of the switching devices, the microcontroller (13) monitors the signal coming from the current sensor. The voltage developed across the sensor is proportional to the current flowing through the primary side. The signal from the current sensor is conditioned and filtered by using the
filtering circuit and then supplied to ADC input of the microcontroller. When the signals received at the ADC and the input signals is beyond a pre defined threshold limit, then the microcontroller (13) stops the driving signal switching device of RL3 which in turn trips the system. The microcontroller (13) again connects the supply after a predefined delay and senses whether the value received at the ADC is within the predefined limit or not. If it remains within the limit then it continues the 5V signals at the NPN transistor otherwise it again stops 5V signal to the transistor of RL3. This cycle continues for defined time say 5 times, if still the value at the ADC is above the defined limit, the supply is switched off and then the supply can be restored by pressing the Reset button (21) which resets the controller (13) by resetting the power supply of the controller (13).
2. When primary source fails
When the primary source (10) fails then the switching device RL4 by default goes to NC position which in turn activates the secondary supply start circuit and the secondary supply starts.
3. Secondary source is available
When the secondary supply source (11) is available, the power to drive the electronic circuit is generated by the secondary power supply. The availability of the secondary supply is sensed by the microcontroller with the help of the phase
sensing circuit which generates a 5V signal at the microcontroller pin when the secondary supply source (11) is available and a OV when the secondary supply source fails. After receiving this signal, the microcontroller (13) sends the 5V signals to the respective driving circuit of switching device RL3. When the 5V signal is sent to the base of a NPN transistor, a 12V power flows through the switching device coil which in turn changes the switching device contact to NO. Hence in this stage all the contacts of the switching devices RL1, RL2, and RL4 remain in NC position and contacts of the switching device RL3 remain in NO position.
After maintaining the status of the switching devices, the microcontroller (13) monitors the signal coming from the current sensor. The signal from the current sensor is conditioned and filtered by using the filtering circuit and then supplied to the ADC input of the microcontroller. When the signal received at the ADC, and the input signal is beyond a pre defined threshold limit the signal is fed through multiple current rating adjuster, then the microcontroller stops the driving signal of the switching device RL3 which in turn trips the system. The multiple current rating adjuster varies the voltage across it due to change in its position and this changing signal is sensed by the microcontroller which decides the rating according to the voltage developed across the multiple current rating adjuster. The microcontroller again connects the supply after a pre defined delay and senses whether the value received at ADC is within the predefined limit or not. If the rating remains within the limit then it continue the 5V signal at NPN transistor, otherwise it again stops the 5V signal to the transistor of RL3. This
cycle continues 5 times. If still the value at the ADC is above the defined limit, then it switches off the supply and then the supply can be restored by pressing the Reset button (21) which resets the Controller by resetting the power supply of the controller.
4. When both supply sources are available:
When the primary supply is restored and the device is running in secondary supply mode then the primary supply is sensed by the microcontroller with the help of the phase sensing circuit and the microcontroller generates the 5V signal at the base of the driving transistor of RL4 (for generator as a secondary supply source) which in turn move the contact from NC to NO and stops the generator and then automatically goes to the primary supply availability mode.
Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiment, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.

WE CLAIM
1. A device for automatic changeover of electric power supply between a primary and a secondary power source including current limiting for the both power sources in a compact module with provision for fitment in the existing panel boards, the device comprising of the primary power supply generated from primary power source, a secondary power supply from secondary power source, a controlling circuit comprising a current sensing circuit; a microcontroller, a voltage regulation circuit, a tripping circuit, a phase sensing circuit, a status indication circuit, and a relay circuit to interchange the supply between the primary and the secondary source based on the pre-programmed conditions and further connected to the load;, where in the controlling circuit is configured to:
- sense the power sources via the electronic circuit by the current sensing circuit and transmitting a corresponding signal by the electronic circuit, the signal representing the current flowing from the power sources;
- condition the signal by adapting the signal conditioning circuit;
- generate an output signal when the received signal exceeds a predetermined value which in turn activates the tripping circuit enabling the switching means to operate, a status of exceeding the predetermined value representing a failure of the primary supply source to provide required power;
- activate the second power source by operating the switching means; and
- sense the primary supply when resumed and transmit a signal to the switching means which stops the secondary power supply.

2. The device as claimed in claim 1, comprising an in-built synchronization interface to provide a signal for activating or deactivating the secondary power source.
3. The device as claimed in claim 1, further comprising a means for current limiting rating adjustment to adjust the rated current by processing the signals through a potentiometer, and a means for current limiting on both of the supply sources to prevent overheating of the device, the device achieving the tripping on both the primary and secondary sides utilizing a single current sensor.
4. The device as claimed in any of the preceding claims, wherein the switching means each has atleast one NO (Normally Open) or one NC (Normally closed) contact, at least two switching devices operated at no load condition when the number of operations at rated current is less, and wherein the switching at rated current is attained through a third switching device having one NO contact, the third switching device being enabled to perform rated number of operations at rated current, and the fourth switching device used to provide the signal for operating the alternate supply.
5. The device as claimed in claim 1, comprising an indicator means for
visually indicating the conditions in respect of availability of the primary
and/or the secondary power supply, load supply, and overload.
6. The device as claimed in claim 1, comprising a Din clip enabling mounting
of the device to the DIN rail when installed.
7. A device for automatic changeover of electric power supply between the
primary and a secondary source including current limiting for the both the
power sources as substantially described and illustrated herein with
reference to the accompanying drawings.