-2-FIELD OF INVENTION
The invention relates to a fail-safe device for automatic switching of circuit breakers and restoration of power supply.
BACKGROUND OF THE INVENTION
Circuit breaker is a switch used in high/medium voltage electrical power system to protect the system, the operating plant and machinery, including human life.
As a part of protection, the circuit breaker takes care of any kind of fault in the system, namely; earth fault, short circuit, leakage current single phasing, under voltage etc. The circuit breaker trips the circuit to disconnect supply in case of electrical fault and allows restoration of power supply till the fault is detected and rectified. The total activity results in considerable idle time and cost in respect of maintenance and man power deployment.

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In case of a transition fault of very short duration, disruption of power supply is not desirable for a long period to avoid loss of production and idle man hours.
In mining electrical system, where a plurality of circuit breakers are disposed at various locations covering a large area both underground and open cast providing supply to pumps, crushers, pit lighting, crane weigh bridge, it may take minimum 2-3 hours to switch on all the breakers after it has been tripped due to temporary and transition fault. Such a situation is quite common and frequent in the mining area. The manual switching of the circuit breakers, particularly when disposed at different distant locations, add-on to the already loss of production due to lack of power supply owing to transitional fault.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to develop a failsafe device for automatic switching on the circuit breakers without any man power requirement to reconnect the load with the power source after restoration of power.

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Another object of the invention is to propose a fail-safe device for automatic switching on the circuit breakers which is capable of presetting a time gap, between any possible tripping of the circuit breaker, and switching on the breaker after restoration of power supply.
A still another object of the invention is to propose a fail-safe device for automatic switching on the circuit breakers which can protect the circuit breaker contacts from burning due to frequent on-off operation during permanent/major fault.
A further object of the invention is to propose a fail-safe device for automatic switching on the circuit breakers which is operable both in auto and manual mode as per demanding situation.
A still further object of the invention is to propose a fail-safe device for automatic switching on the circuit breakers which includes a fault-indicator to visibly project the nature of the fault.

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SUMMARY OF THE INVENTION
Accordingly there is provided a fail-safe device for automatic switching of circuit breakers in a power system to protect the system. The device comprises a timer provided in the circuit between the neutral phase and an on-off switch. A contactor MM-00 having NC-contact (16) is arranged which disallows the timer to operate and switch on a closing coil (3) in case of a permanent fault. A selector switch is provided for selection of the operation between the automatic or manual mode. An indicator is provided in series with the contact of MMOO contactor and a micro switch is coupled with a thermo magnetic release means to energize the MMOO contactor coil when the circuit breaker trips.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1- Shows a schematic diagram of the circuit in operational mode of a circuit breaker according to prior art.
Figure-2 Schematically shows the closing of the circuit of a circuit breaker according to the present invention

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DETAIL DESCRIPTION OF THE INVENTION
Figure-1 shows a main pole contacts (1) of the circuit breaker with three phases and neutral (R,Y,B and N ) (2), according to prior art.
From each phase, one tapping comes through a fuse (8) to a single phasing preventor (7). One phase from the single phasing preventor (8) is tapped through a Reset button (6) to an under voltage release coil (5) and then to a spring charge motor (not shown).
As power comes in to the coil (5) it will pick up and pull a mechanical lock of the main pole contact (1). At the same time, the spring charge motor will charge the main pole contactor spring.
As the main contactor spring is charged, the circuit breaker is ready to be switched on.
As the operator presses a "ON" switch (10), a closing coil (3) gets the power and open the charged spring which switches on the main pole contact (1).

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The main pole contact (1) gets locked by another mechanical device at the top end which is operated by a Thermo magnetic release means (11). Whenever any fault occurs in the system, the release means (11) will sense it and operate the locking device, so that the main pole contact trip within a fraction of second.
Now to restart the system, individually each circuit breaker has to be switched on at various locations and would take at least 2-3 hours.
If the fault is of permanent in nature, the thermo magnetic release means (11) would again trip the circuit, even after manual switching on of the circuit breakers.
As shown in Fig. (2), a timer (12), has been provided to close the circuit within a preset timing without indulging any manual operation in case of tripping of the circuit breaker due to any fault.
Although the timer (12) makes the circuit breaker on, in case of any permanent fault in the line like short circuit, earth fault or leakage due to insulation failure, the thermo magnetic release means (11)

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would instantaneously trip the breaker. But at the end of the preset time, the circuit breaker will be automatically switched on. Thus, in the event of a permanent fault, this cycle of ON-OFF operation will continue leading to burn out of the circuit breaker contacts.
To alleviate this problem, the invention provides a micro switch (15) and a MM-00 contactor (14), both being incorporated in the circuit with NO/NC contacts.
In case of any permanent fault, the thermal magnetic release means (11) will trip the circuit breaker and simultaneously press the micro switch contact (15) mechanically to energize the coil of the contactor (14) when NO/NC contacts of the contactor (14) will change their positions to NC/NO.
In that case, the timer circuit (12) and the closing coil (3) of the circuit breaker will not have any power to energize the main pole contacts.
With a view to ensure both mode of operation of the device for example manual and auto,, a selector switch (13) has been provided in the closing circuit so that the same can be switched "on" either through auto mode or manual mode.

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Finally to ensure that the device is fail safe, the invention provides an indicator (16) arranged in series with the MM-00 contactor (14) to indicate that the breaker has been tripped due to certain permanent fault. When the fault is rectified, the Reset Button (6) is pressed to deenergize the contactor coil (14) of the contactor MMOO, and the timer (12) again gets power directly to energize the closing coil (3), and the main pole contacts (1) is switched on to provide power supply at load end.

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WE CLAIM
1. A fail-safe device for automatic switching of circuit breakers in a power system to protect the system, characterized by comprising:
a timer (12) provided in the circuit between the neutral phase (N) and the on-off switch (10);
a contactor MM-00 (14) having NC-contact (16) which disallows the timer (12) to operate and switch on the closing coil (3) in case of a permanent fault;
a selector switch (13) provided for selection of the operation mode between the automatic or manual mode;
an indicator (16) provided in series with the contact of MMOO contactor (14); and
a micro switch (15) coupled with a thermo magnetic release means (11) to energize the MMOO (14) contractor coil when the circuit breaker trips.

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2. A fail-safe device for automatic switching of circuit breakers in a power system to protect the system, as substantially described and illustrated herein with reference to the accompanying drawings.
Dated this 2nd day of JANUARY 2007

Accordingly there is provided a fail-safe device for automatic switching of circuit breakers in a power system to protect the system. The device comprises a timer provided in the circuit between the neutral phase and an on-off switch. A contactor MM-00 having NC-contact (16) is arranged which disallows the timer to operate and switch on a closing coil (3) in case of a permanent fault. A selector switch is provided for selection of the operation between the automatic or manual mode. An indicator is provided in series with the contact of MMOO contactor and a micro switch is coupled with a thermo magnetic release means to energize the MMOO contactor coil when the circuit breaker trips.