FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention : "A DC MINIATURE CIRCUIT BREAKER (MCB) FOR
CONTROL PANELS AND RAILWAY APPLICATIONS"
2. Applicants) : INTEGRA SWTTCHGEAR LIMITED.,
Name, Nationality 10, POR-RAMANGAMDI, POR, OIST. VADODARA,
Address : INDIA , AN INDIAN COMPANY
AND
ELECTRICAL RESEARCH AND
DEVELOPMENT ASSOCIATION., ERDA ROAD,
P.B. NO. 760, MAKARPURA INDUSTRIAL ESTATE, MAKARPURA, VADODARA - 390 010,
INDIA, AN INDIAN COMPANY
3. Preamble to the description
PROVISIONAL : The following speciflcation describes the invention .
COMPLETE : The following specification pa-rticularly describes the invention and the manner in which it is to be performed.

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FIELD OF APPLICATION
The present invention relates to a DC miniature circuit breaker (MCB) for control panels and railway applications.
BACKGROUND OF THE INVENTION
AC MCBs are widely used in utilities and industries and have short circuit breaking capacity upto 10 kA. Short circuit breaking capacity of DC MCBs available in the market are mostly 1 kA and upto a maximum of 3 kA at 130V DC. For railway applications and some control panels, DC MCBs are required and the short circuit breaking capacity required is 5 kA at 130 V DC, in addition to their ability to withstand the vibrations.

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SUMMARY OF THE INVENTION
The main object of the present invention therefore is to provide a DC miniature circuit breaker for control panels and railway applications with a fault level of 5 kA at 130 V DC.
This and other objects of the present invention are achieved by increasing the contact gap for faster extinguishing of the arc, increasing the area of the arc chamber, designing the arc chute to elongate the arc and increasing the force of the spring for increasing the speed of opening.
Thus the present invention provides a DC miniature circuit breaker (MCB) for control panels and railway applications, comprising: an appropriate housing and cover for providing an increased gap between the moving and fixed contacts for extinguishing the arc faster; a throw-off spring with higher spring force required for longer distance of travel; an arc chamber with increased area having an arc chute to elongate the arc; and a pair of permanent magnets for guiding the arc towards the arc chamber.

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BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described with reference to the figures of the accompanying drawings where
Figure 1 shows schematically the DC MCB of the present invention in open condition.
Figure 2A shows the housing of the MCB illustrated in figure 1.
Figure 2B shows the cover for the housing of MCB.
Figure 3 shows the comparative dimensions used in the spring of the present invention and that of the known MCB.
Figure 4 shows details of arc chamber for increasing the arc length.

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Figure 5 shows details of the contact gap of C between the fixed and the moving contacts.
Figure 6 shows details D of the arc pulling magnets of the present invention.
DETAILED DESCRIPTION
It is necessary to extinguish fast the arc generated in the MCB and in order to achieve this the contact gap between the moving contact and the fixed contact should be increased. In the present invention for achieving faster extinguishing of the arc the contact gap C, as shown in Figure 1 and Figure 5 is increased by about 30 %.
As shown in Figure 5 the gap is more than 6 mm.

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In order to achieve this first requirement of increasing the gap between the contacts it will be necessary to have an appropriate geometry of the housing and cover of the MCB as illustrated in Figures 2A and 2B respectively.
For achieving the required speed of extinguishing the arc, 30% increase in the contact gap is provided.
Providing a higher contact gap would mean more distance to be travelled by the moving contact. This increase in the distance travelled would increase the time taken to travel the same. Hence, it becomes important to increase the speed of the mechanism. So, the opening spring A (Figures 1 and 3) of the present invention has been designed accordingly with higher force. The force of the spring has been increased by about 36% to meet the need. This was possible to achieve by providing appropriate wire diameter of the spring and the number of turns and the hook geometry as shown in Figure 3. The throw-off spring has a spring rate of 0.47 grams / mm.

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Once the contact separates the arc produced should be guided into the arc chamber so that arc extinguishing takes place faster and effectively. In case of DC current, the arc produced has to be pulled or pushed for driving the arc into the arc chamber. For this purpose, two numbers of permanent magnets D are fixed up on the protective plates. The polarity of the magnets is kept in such a way that the magnetic field produced would attract the arc towards the arc chamber. Figure 6 shows detail D of the permanent magnet (arc pulling magnet).
The detail B of the arc chamber of Figure 1 is shown in Figure 4. The insulated arc plate is longer in length as shown and projects outside to increase the arc travel path. This provides insulating barrier between two adjacent metallic de-ion plates. This will increase the arc length by 40% to break the DC current and the arrangement provides satisfactory contact opening during the DC breaking.

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The DC MCB, 130V of the present invention was evaluated for the required duty as follows:
1. First a temperature rise test at the rated current had been carried out on the MCB. The temperature rise measured after stabilization.
Temperature rise of terminals = 20.7° C (< 50° C*) Temperature rise of body = 15.1° C (< 25° C*) * Requirement as per standard
The temperature rise observed was well within limits specified by the standard.
The milli-voltage drop of the contacts were measured at rated current around 120 millivolts. Power loss measured was Is 2.4 watts.

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2. The prototype DC MCB withstood high voltage withstand test successfully at 2000V 50Hz for one minute between incoming and outgoing terminals with MCB in open position and between terminals and earth with MCB is closed position.
3. Insulation resistance was measured at 500V DC and the resistance measured was found more than 200MQ.
4. Then the prototype was subjected to short circuit breaking capacity test. The prototype was tested first at 1kA 130V DC then it was tested at 3kA 130V DC successfully. Finally, the MCB was subjected short circuit breaking capacity at 5kA 130 V DC. The test duty cycle is an opening operation followed by one close open operation at an interval of 3 minutes in between.
O -1 - CO
O - represent breaking operation
CO - represents a making operation followed by a breaking operation.
T - represents the specified time interval of 3 minutes or the resetting
time of the breaker, whichever is longer.

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The oscillograms of O & CO operation is given in Oscillogram No. 1 and 2 along with cut-off current, operating time, 12t (let through current in A2s).
The time constant of the circuit was 10 msec. The MCB has successfully completed 10 cycles of operations consecutively as above. Within 3 of conclusion of the test, the insulation resistance of the MCB was measured at 500V DC and found above 20 MQ. Then the samples were subjected to over-current calibration test at 2.0 times the rated current at 40° C and the MCB tripped within the limits. After cooling down to the ambient temperature, this test was repeated 4 more time and the samples tripped within the limits specified by the standards.
5. Then the MCB was tested for the over load performance test. The test parameters were as below:
Test Current - 6In
Test Voltage-rated voltage = 130V
Time constant - 10m.sec.

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The MCB was subjected to 35 make and break operation by closing and opening manually and 15 make and break operations by closing manually and opening automatically at the rate of 4 make-break operations per minute.
On successful completion of the above test, the samples were subjected to temperature rise test and over current calibration tests at 2In and the test results were well within limits as per the standards.
6. Two samples of prototype MCBs were successfully cleared electrical endurance test, 6000 close-open operation with full load current at rated voltage at the rate of 240 Cycles/hour followed by 4000 operations without current at the same rate. After the test, the MCB was subjected to calibration test at 2In and mili-volt drop test at rated current and found within the limits specified.

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7. The MCB was subjected to a vibration test at the level of 3g at frequency of 50 cycles for two hours mounted on a vertical plane with 1.15 times the rated current passing through it. There was no tripping observed during the test.

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WE CLAIM
1. A DC miniature circuit breaker (MCB) for control panels and railway applications, comprising:
- an appropriate housing and cover for providing an increased gap between the moving and fixed contacts for extinguishing the arc faster;
- a throw-off spring with higher spring force required for longer distance of travel;
- an arc chamber with increased area having an arc chute to elongate the arc; and
- a pair of permanent magnets for guiding the arc towards the arc chamber.

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2. The DC MCB as claimed in claim 1, wherein the gap between moving and fixed contacts is increased by about 30% for extinguishing the arc faster.
3. The DC MCB as claimed in claim 1, wherein said throw-off spring is with about 36% more strength required for longer distance of travel.
4. The DC MCB as claimed in claim 3, wherein said throw-off spring has a spring weight of 0.47 gm/mm.
5. The DC MCB as claimed in claim 1, wherein said arc chamber is provided with longer arc plates between metallic de-ion plates for increasing the arc travel path.
6. The DC MCB as claimed in claim 5, wherein the arc length is increased by about 40% to break the DC current.

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7. The DC MCB as claimed in claim 1, wherein the magnets are arranged on protective plates in such a way that the magnetic field produced would attract the arc towards the arc chamber.
8. A DC miniature circuit breaker (MCB) for control panels and railway applications, substantially as herein described and illustrated in the accompanying drawings.
Dated this 10* day of October 2006.