Form - 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES ,2003
COMPLETE SPECIFICATION (Section 10; rule 13)
"AN AUTO TRANSFER SWITCH WITH ELECTRICAL INTERLOCK MECHANISM CAPABLE OF SUPPLYING POWER FROM A PREFERRED ELECTRICAL SOURCE"
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate,
Mumbai - 400 001,Mharashtra State, India
An Indian company duly registered and incorporated under
Company's Act, 1956.
The following specification particularly describes and ascertains the nature of the invention and the manner in which it is to be performed:-

TITLE
An Auto Transfer Switch with electrical interlock mechanism capable of supplying power from preferred electric source.
PRIOR ART
US2002/0079741 Al: - describes ATS with engine control. ATS is pair of double pole switch operated by servo motor. An actuator is mounted on servomotor that acts as interlock to prevent line-to-line short. System ensures break before make function. ATS includes logic section to control its operation and to communicate with engine controller; in addition it detects AC voltage from utility.
Power supply is included in ATS and provides power to the logic section, engine controller, and also for a battery charger. ATS includes bi-directional communication with engine controller, this helps in sending information between ATS and engine controller. ATS may be manually operated.
US 6172432 B1: - describes the ATS apparatus for use in association with stand along generator, enabling stand alone generator to supply electrical power to plurality of electrical circuits in event of failure of electric power being supplied to the structure by an electric utility. The ATS apparatus comprises a plurality of electric utility inputs. A controller is operable configured, following installation of ATS. A controller is further operable configured to transmit actuation signal to corresponding ones of switches. A controller is operable configured to substantially monitor total loading on the generator. Controller further comprises a display and input panel for enabling as operator to input into programmable memory instructions for plurality of control parameters.
US6825578 B2: an ATS system controls switching of power from a main source (utility source) to back up source (generator) using a state machine controller and low cost relay switches housed in a single electrical panel. The low power automated transfer switch system is well-suited for residential use and is less expensive and easier to install than conventional ATSes. The key to a low cost transfer switch is delivering power with low cost relays. This is accomplished by employing relay drive techniques that enable these devices to survive rigorously standards compliance testing. Preferably, the state machine controller measures utility and generator source compliance using an optical coupling arrangement, rather than a transformer. The automated transfer switch disconnects the utility and generator by means through a circuit breaker providing for fast protection. The relay drive techniques disclosed provide a form of an electrical interlock. This is key feature when seeking compliance standard approval. Essentially, an automated transfer system should not continuously be capable of back feeding power from generator to utility, and the electrical interlock of the relays as taught by this invention prevents any such back feeding.
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US Patent 20040233602: The ATS system includes at least one input port capable of being coupled to at least one power source to receive an input power, a first internal component that requires internal power satisfying first criterion in order to properly operate, and a power converter such as switch mode power supply that is coupled to the first internal component and to the at least one input port. The power converter is capable of receiving the input power by the way of the at least one input port and converting the input power into internal power to be provided to the first internal component. The internal power provided by the power converter satisfies the first criterion, even though at least one characteristic of the input power varies within range.
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FIELD OF INVENTION
[001] The present invention relates to auto source transfer system employed to switch between two power sources namely Normal and Alternate. The power sources include two different feeders of same utility, or two different utility feeders, or utility and stand alone generator combination.
BACKGROUND OF INVENTION
[002] Process industries, hospitals, Airports, buildings receive power from utility company. For maintaining continuity of supply for important loads, owners may desire second source, as back up, may be second feeder of same utility or another feeder utility or stand-alone generator.
[003] The source transfer systems are of two types manual and automatic.
[004] In manual source transfer systems operator's intervention is required for changing over to second healthy source. Auto Transfer Switch is able to automatically switch from one power source (e.g. utility) to another power source (e.g. second feeder of same utility, feeder another utility, stand alone generator) when it detects first power source is in unhealthy condition.
[005] Components of ATS are microprocessor, relays, and application specific circuits power source for operation of these components with voltage level of 12 Volt DC or 24 Volt DC referred as control circuit
[006] An another major component of ATS is power circuit made up of Switching devices and operators for operating switching devices. Switching devices are capable of breaking, making and/or withstanding short circuit currents.
[007] Function of ATS is fully dependent on the power source as any variation in this may cause system to malfunction. Thus it is necessary that power source must full fill requirements of all components at any given moment of time.
[008] The power sources that are coupled to given ATS can vary significantly in terms of characteristic, for example sags and unbalance in phase and undervoltage. ATS should take all this factors into consideration during operation.
[009] It is therefore advantageous if new ATS could be designed capable of receiving power from various combination, selecting preferred source out of these two sources, to take care of source parameter variations, capable of supplying power to internal components.
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[0010] In addition this new ATS should meet all the requirements of residential sector in addition this should meet the requirements of industries by providing phase sensitive sensing and selection of preferred supply facility, where most industries are fed via dual supply.
[0011] It is advantageous if an new ATS provides protection from faults at load side. The ATS system should include such switching devices capable of protection against overloads and protection against short circuit.
OBJECT OF INVENTION
[0012] The basic objective of the present invention is to provide ATS for two sources namely Normal and Alternate with selection of preferred supply source facility.
[0013] As far as Normal and Alternate supply is considered both can be utility, one utility second stand alone generator or both can be stand alone generator supply there is no restriction on connected supply.
[0014] Another objective of the present invention is that controller with settable under voltage and settable source failure time for normal source will give commands only to interlocking unit for further operations.
[0015] Physical position of said switching devices is sensed by auxiliary switches mounted on said switching devices and is connected to Interlocking unit.
[0016] Interlocking unit receives signals from controller as well as from electrical switching devices regarding their status. Interlocking unit controls operation of ATS thereby making ATS less dependent on controller. With inclusion of interlocking unit there are chances of complete elimination of controller.
[0017] Test Switch is part of ATS, provided in order to simulate the whole source transfer condition.
[0018] When both sources namely Normal and Alternate are available and ATS is set for said Normal as preferred then it will only switch ON Normal switching device, by keeping alternate switching device in OFF state.
[0019] Interlocking functions such that break before make operating sequence is followed under any sequence of operation, there by ensuring safety.
[0020] Driving mechanism for Breaker includes direct drive or stored energy
[0021] Power Supply required for operation of controller, interlocking unit and for driving switching devices is generated internally through connected power sources.
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[0022] Battery backup is possible but power supply will take battery into consideration only after Normal, Alternate failed condition. When normal source fails supply will be generated from alternate if alternate fails then only supply will be provided by battery. Normal supply set at highest priority this means at any moment Normal becomes healthy supply will be generated from Normal.
WORKING
[0023] The present invention is hereforth illustrated specifically with reference to a moulded case circuit breaker (MCCB). This does not restrict the scope of the embodiment of the invention to MCCBs but also may apply to other Low Voltage switching system.
[0024] A further enhancement or improvement of the said invention may also apply to MV system or HV system devices.
[0025] In further embodiment of the said invention is also possible to add more than two sources by cascading arrangement thereby addressing plurality of electrical supply problem.
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Complete Description of Invention
Description of Drawing
Figure 1 Auto Transfer Switch (ATS) Scheme Figure 2 ATS present Scheme Figure 3 ATS with MCCB - Control Unit Figure 4 ATS with MCCB - Power Unit
Referring to Fig 1 Auto Transfer Switch general schematic is shown.
A more detailed scheme explaining present scheme is shown in Fig 2.
Figure 3 Illustrates Control Unit of ATS, wherein the components are as follows
3.1 Front Facia
3.2 Controller
3.3 Interlocking Unit
3.4 Normal Breaker ON LED Indication
3.5 Alternate Bkr On LED indication
3.6 Test Switch 3.7Manual Operation Switch 3.8Auto/Manual switch
3.9 Connector
3.10 Enclosure
3.1 l.MPCB covering
3.12 Motor Protection Circuit Breaker
Similarly Figure 4 gives components of power unit of ATS
4.1 Moulded Case Circuit Breaker
4.2 Electrical Operating Mechanism (EOM)
4.3 Terminal Block
4.4 Mechanical Interlock with base plate.
The present invention is hereforth illustrated specifically with reference to a moulded case circuit breaker (MCCB). Figure 3 and Figure 4 explains present ATS system. Power supplies are connected to controller 3.2 via motor protection circuit breaker (MPCB) 3.12. To prevent accidental access to MPCB it is covered with MPCB covering 3.11. The controller is connected electrically to Electrical interlocking unit 3.3. The status of circuit breaker is given to electrical interlocking unit via connector 3.9. The normal and alternate status indicating LED's 3.4 and 3.5 also receives status from connector. The selector switches are AUTO/ MANUAL switch 3.8 and manual operating switch 3.7 works as per mode selection. The TEST switch 3.6 is connected to electrical interlocking unit, this unit detects state of TEST switch.
All these functional components controller, electrical interlocking unit, LED's, selector switches and TEST switch are mounted in front facia 3.1 and are electrically connected.
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The control unit figure 3 is connected to power unit figure 4. The components of power unit are MCCBs 4.1, electrical operating mechanism 4.2 terminal block 4.3 for shorting two outputs of MCCBs for common load connection and mechanical interlock 4.4 implemented with MCCBs.
Component
Component No 1: Controller Operation of the controller is detection of two sources and displays it through LED indications.
Component No 2: Interlocking Unit
Interlocking Unit is logical device and works in conjunction with controller and MCCB status. It has in built LCD display to give system status, display includes ON status of MCCB, in addition it gives indication of faulted condition; these indications are of flashing nature.
Component no 3: AUTO/MANUAL selector switch. System has two independent operating modes termed as
1. Auto Mode: Under this mode there are three different modes & one Test Mode.
2. Manual Mode: Forced operation is possible on individual MCCBs.
The present invention further comprises of components Front Facia, Normal MCCB ON LED Indication, Alternate MCCB ON LED indication, Manual Operation Switch, Connector, Enclosure, MPCB covering, MPCB, MCCBs, Electrical Operating Mechanism (EOM), Terminal Block, Mechanical Interlock with base plate.
For the sake of brevity of the application above mentioned components though integral parts of the ATS have not been described to maintain status quo of the application without limiting the scope of application.
WORKING PRINCIPLE OF INVENTION
The Auto Source Transfer System monitors the voltage availability of Normal Source. If normal supply voltage level falls below the preset value then it Switches OFF Normal MCCB and gives command to Alternate source MCCB to switch ON, with pre settable delay, provided that voltage and frequency of Alternate source is within the limits and vice versa.
Main components of ATS are controller and interlocking unit as these components are involved in system status detection and operation. Controller detects Normal source in healthy condition and gives signal to interlocking unit, in a digital format.
The modes associated with controller include Normal preferred, Alternate preferred and change over to alternate with no return to normal even if normal returns to healthy state. Out of two supplies Normal and Alternate, Normal source is default-
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preferred mode, so whenever both sources are present then, always Normal source MCCB will be switched ON keeping Alternate source MCCB in off state. All these operations are carried out by interlocking device based on signals received from controller and from MCCB.
AUTO MODE- Normal Preferred Supply
This mode is referred as 'Normal supply preferred' mode whenever system is powered on; this is default mode of system, an LED indicator on controller confirms this status.
Controller will detect Normal source indicated by LED. In this mode alternate source will be detected only when normal source fails. When Normal fails following sequence is followed - LED will stop glowing, alternate source will be detected. After completion of normal fail preset delay system will switch OFF normal source MCCB and switches ON alternate source MCCB.
On the return of the Normal supply, it switches OFF alternate source MCCB and switches ON normal source MCCB with set preset delay.
AUTO MODE Alternate Supply Mode
This mode supports for reliable alternate source operation selected via push button. If Normal source fails, the load will be transferred to the Alternate source. However, the ATS will NOT return the load to the Normal source even if normal returns. The load will stay with the Alternate source until another mode is selected.
AUTO MODE Alternate Supply as preferred.
In this mode of operation Alternate source is the preferred supply selected via push button. When alternate source fails then it will switch OFF alternate source MCCB and will switch ON normal source MCCB, when alternate supply returns then system will switch OFF normal source MCCB and will switch ON alternate source MCCB.
All these modes are functional under AUTO mode of system, selected via AUTO / MANUAL selector switch. AUTO/ MANUAL switch is two-pole two-position switch used to perform above function.
Manual Mode
This mode is selected via AUTO / MANUAL selector switch, this action activates manual operation switch to carry out forces operation on breaker.
Switch on Normal breaker by keeping manual operation switch in Normal ON condition, similarly for other conditions. Electrical interlock works in such a way that no two breakers can be switched on simultaneously.
Controller has built in timer namely normal fail timer and normal return timer with default setting. Controller, in addition to these timers has built in function of undervoltage setting with default setting and built in hysteresis. For example setting is 180V /200V then, the load will be transferred to Alternate if any phase falls Below 180 V with respect to the neutral for the duration of the set delay time. The load will be transferred back to Normal when voltage of Normal Returns to 200V or higher for
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duration of normal return timer. The under voltage setting is available from 80% to 30% with associated hysteresis values. In addition controller also takes into account voltage dips issue.
When normal source fails means value is less than undervoltage set value and normal fail time is elapsed then only ATS unit will start operation of switching OFF and ON of MCCBs and vice versa.
Interlocking devices is a logic device that works in conjunction with controller and MCCB. Interlocking unit receives signals from controller; in addition this receives signals from MCCBs regarding there on off status. This logic device controls the MCCB switching off and on operation. This interlocking unit is mounted in control unit. In addition this detects physical position of MCCBs via trip alarm and auxiliary contacts. The functions such as test mode, sensing position of MCCBs and controlling operation of MCCB was controller's function but present invention comprises of interlocking device, which takes over all these functions thereby reducing controller dependency.
For ATS, system simulation is one more important function; TEST switch is switch available for whole system simulation. Interlocking device also detects physical status of TEST switch; this logic device executes TEST sequence. Test switch is normally open contact when pressed this gives command to interlocking unit to execute system simulation function.
This device has built in LCD display that gives MCCB ON status along with flashing TEST MODE and MCCB TRIPPED status.
Power supply required for driving MCCB and other system components is generated internally from normal and alternate source despite variations in sources. When both sources are in failed condition then battery connected to system will take care of supply requirement. If any of normal or alternate returns to healthy status system will be transferred from battery to respective source automatically, with normal supply set at highest priority.
SUMMERY OF INVENTION
[0011] The present invention is improved ATS system that is able to offer two distinct modes of system operation named AUTO and MANUAL.
[0012] The present invention additionally relates AUTO mode with other four distinct modes of operation Normal Preferred, Alternate preferred, Changeover to Alternate mode and no return back to normal and TEST mode for system simulation.
[0013] The mode Normal preferred is default mode of system. Working is such that ATS is in AUTO mode and both sources are in healthy condition then, ATS will switch on Normal switching device for example MCCB only.
[0014] The present invention further relates to ATS with sensing circuit capable of sensing phase unbalance, settable undervoltage levels, settable timer and voltage dips effects.
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[0014] The present invention further relates to ATS with separate device referred as Interlock device that will act as interface between controller and position sensors of MCCB. This devices will reduce dependency on microprocessor based circuits making system more simple.
[0015] The present ATS system is able to supply power to its respective internal components despite variations in sources. In addition internal power source will switch over to third source to battery under both sources failed condition.
[0016] The present invention further relates ATS with inclusion of Mechanical Interlocking acting as back up to whole system. Mechanical interlock will come into operation under electrical interlock unit fail condition only. This acts as backup such that no two switching devices can be switched on simultaneously
ADVANTAGES
[0017] The present ATS takes into account different kinds of source that includes two feeders of same utility, two different utility and utility generator combination. User
[0018] The present ATS system connects only preferred source MCCB when both sources are available in healthy state.
[0019] The present ATS provides facility for selection of preferred source.
[0020] The present ATS also takes into account of plurality of electrical sources.
[0021] The present ATS includes controller with under voltage setting facility with built in hysteresis fiinction. In addition this includes normal source fail and return timer along with voltage dips issues.
[0022] In present ATS controller gives signals to Interlocking device for further operation.
[0023] In present ATS interlocking device being logical device accepts signal from controller, in addition this senses physical position of MCCBs. This logical device based on signal received from controller and status of MCCBs controls sequence of source change over operations.
[0024] TEST switch that simulated whole source transfer system is connected to interlocking device.
[0025] With reference to above three statements interlocking device partly or completely eliminates need for controller in ATS system.
[0026] The power supply requirement of ATS is completed internally generated via two sources despite all variation of sources.
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[0027] When both source are in failed condition then power supply requirement of ATS is catered through battery, on one of source becoming healthy the respective source will take over with normal source set at highest priority.
[0028] The switching devices of ATS provides protection against any abnormal condition. In event of switching devices tripped under fault condition ATS will suspend any further operation as this may violate safety norms.
[0029] The mechanical interlock is incorporated in circuit breakers, so that even if breakers are operated manually then also simultaneous closing of two circuit breaker condition is avoided there by maintaining safety requirements of circuit breaker.
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CLAIMS,
We claim,
1. An ATS with electrical interlock mechanism capable of supplying power from preferred source out of normal and alternate power supplies comprising, circuit breakers capable of connecting electrical source to load, wherein the said circuit breakers further comprise of an operator capable of switching device in ON and OFF state, mechanical interlock capable of preventing said breakers from simultaneously connecting both said sources to load, failure and return timers for detection of healthy state of preferred source, an electrical interlocking device capable of receiving signals from controller and controlling said breakers through said operators, Logical sequence in built in electrical interlocking device thereby governing system operations, power unit capable of receiving power from normal and alternate as well as from battery for fulfilling requirement of internal power, A transfer switch capable of accepting plurality of power supplies, a transfer switch with TEST Switch for source changeover simulation facility
2.A transfer switch according to claim 1 where in said circuit breakers are capable of breaking making and/or withstanding short circuit currents.
3.A transfer switch according to claim 1 wherein the said operator is direct drive motor mechanism or spring charged stored energy drive for circuit breakers as per claim 1.
4.A transfer switch according to claim 1 wherein the said mechanical interlock is incorporated in circuit breaker.
5. A transfer switch according to claim 1 wherein the power supply requirement is internally generated by power unit via normal and alternate sources despite variation in sources, such that when said sources are in failed condition then power supply requirement is catered through battery, on any of source becoming healthy the respective source takes over with normal source set at highest priority.
6. A transfer switch according to claim 1 wherein the said internal power unit further includes battery charging function.
7. A transfer switch according to claim 1 where in said electrical interlocking device receives signals from controller and from circuit breakers, on receipt of signals logical sequence of electrical interlocking device governs the source changeover function, in addition this displays status of circuit breakers on LCD screen of interlocking device.
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8. A transfer switch according to claim 1 where in said electrical interlocking device also receives status of TEST switch and based on status it simulates source changeover operation.
9. A transfer switch according to claim 1 where in said transfer switch enables supply of electrical power to load from plurality of electrical supplies with required number of transfer switches one less than no of said electrical supplies.
10. A transfer switch as described in the complete specification accompanied by
drawings in the complete specification.
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ABSTRACT
Present invention is an ATS (ATS) with electrical interlock mechanism capable of supplying power from preferred source out of Normal or Alternate power sources. Power is supplied to load from two power sources namely Normal and Alternate. Auto Transfer Switch (ATS) based on selection of preferred supply will detect respective source through detection circuit. If selected source is in healthy state as per set values available with ATS, then only ATS will connect this source to load via connecting device. ATS system incorporates controller; this detects two sources and gives command to interlocking unit. Interlocking unit receives signals from controller as well as from electrical switching devices regarding their status. Interlocking unit controls operation of ATS thereby making ATS less dependent on controller. With inclusion of interlocking unit there are chances of complete elimination of controller. Internal power required for operation of ATS is derived for the above said power sources.
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