DESC:FIELD OF INVENTION
The invention relates generally to a Motor Protection Circuit Breaker (MPCB). More particularly the present invention relates to a Motor Protection Circuit Breaker (MPCB) which will be capable of extinguishing and discharging an arc generated by a fault current. The Motor Protection Circuit Breaker is constructed with increased air gap between the moving contacts and the stationary contacts during the interruption for faster extinguishing of the arc.
BACKGROUND OF INVENTION
In general a Motor Protection Circuit Breaker (MPCB) serves as a switching device which has a function for protecting a motor by interrupting power supply to the motor upon generation of a fault current in a section for starting or stopping the motor, such as power failure, short circuit and deficiency in phase.
Motor Protection Circuit Breaker (MPCB) known in the art generally comprises an upper housing and a lower housing disposed to house the system components of the MPCB. The MPCB essentially provided with a detector disposed to detect the failure of input current to its input terminals from the power source in order to prevent a failure current from flowing to the motor through the motor-side terminals in order to protect the motor. An open/close mechanism opens and closes the circuit breaker in response to a detection signal from the detector. The open/close operation of the circuit breaker is achieved by the separation of movable contact fitted to a movable contact bar from the stationary contacts fitted to a stationary contact bar by the operation of the open/close mechanism.
The stationary contacts and moveable contacts are fitted to stationary contact bar and moveable contacts bar and are located both in the power source side and motor side.
At the time when the movable contacts of the movable contact bar is separated from the stationary contacts of the stationary contact bar, high pressure and high temperature arc is generated between the movable and stationary contacts which may damage the movable and stationary contacts. In certain occasions the arc may result in failure of interruption of the fault current which in turn damages the MPCB. In order to prevent the movable and stationary contacts from the possible damage from the high pressure and high temperature arc, as well as from failure of interruption of the fault current, it is necessary to swiftly extinguish and discharge the same outside the MPCB. The arc extinguishing device of MPCB normally comprises plurality of magnetic plates and side wall in which the plurality of magnetic plates are packaged. Each magnetic plate may have a U-shaped member opened in the direction of arc generation, and induce the arc in response to the electromagnetic force.
When a fault current is introduced, the movable contacts are separated from the stationary contacts by the open/close mechanism. By this time a high pressure and high temperature arc is generated and part of the fault current flows through the arc between the stationary and moveable contacts. The arc which is induced in the arc chamber is extinguished by cathode effect and cooling effect of the magnetic plates finally interrupt the flow of the fault current and is discharged via an arc outlet there by the flow of fault current is arrested.
The air gap is the effective distance between the rivets fitted on the stationary contact and moving contact when the MPCB is in OFF condition. This is key parameter in deciding short circuit current breaking capacity of the MPCB. An increased air gap lengthens the arc which facilitates the faster extinguishing of the arc. Also the increased air gap requires more re- striking voltage to reignite the arc. Increased air gap provides MPCB with increased short circuit current rating.
Accordingly there is a need to provide Motor Protection Circuit Breaker (MPCB) with increased air gap between the rivets fitted to the stationary contact and moving contact when the MPCB is in OFF condition.
OBJECTS OF INVENTION
One or more of the problems of the conventional prior art may be overcome by various embodiments of the present invention.
It is the primary object of the present invention to provide a Motor Protection Circuit Breaker with air gap between the rivets fitted to the stationary contact and moving contact in the range 4 to 4.5 mm when the MPCB is in OFF condition.
It is another object of the present invention to add material in the moving contact holder of Motor Protection Circuit Breaker to facilitate the extra movement of the moving contact bar in order to increase the air gap between the rivets fitted to the stationary contact and the moving contact.
It is another object of the present invention to provide Motor Protection Circuit Breaker with increased air gap wherein the height of the rivets fitted on the moving contact and the rivets fitted on the stationary contact is in the range 1mm to 1.40 mm.
SUMMARY OF INVENTION
Thus according to the embodiment of the present invention there is provided a Motor Protection Circuit Breaker with increased air gap between the rivets fitted to the stationary contact and moving contact comprises a detector detecting a fault current; an open/close mechanism that includes moving contact holder operating in response to a detection signal of the detector; stationary contact bars having a stationary contacts arranged both on the power source side and motor side and is fitted with rivets; a movable contact bar having a movable contact arranged both on the power source side and motor side and is fitted with rivets that make the contact; an arc extinguishing device and an air gap provided between rivets fitted on the moving contact and rivets fitted on the stationary contact when the MPCB is in OFF condition,
It is another aspect of the present invention, characterized in that the air gap is in the range 4.0 mm to 4.50 mm, preferably 425mm.
It is another aspect of the present invention, wherein the height of the rivets fitted on the moving contact and the rivets fitted on the stationary contact is in the range 1mm to 1.40mm, preferably 1.2 mm.
It is another aspect of the present invention, wherein approximately 1.0mm of additional material is added in the moving contact holder to facilitates the extra movement of the moving contact bar
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: schematically illustrate the Motor Protection Circuit Breaker according to the present invention.
Figure 2: schematically illustrates partial cross sectional view of the Motor Protection Circuit Breaker with enhanced air gap according to the present invention.
Figure 3: schematically illustrates the contacts bars of the Motor Protection Circuit Breaker with enhanced air gap according to the present invention.
Figures 4: schematically illustrates the arc extinguishing device of Motor Protection Circuit Breaker.
Figure 5: schematically illustrates the moving contact bar of the Motor Protection Circuit Breaker with enhanced air gap according to the present invention.
Figure 6: schematically illustrates the stationary contact bar of the Motor Protection Circuit Breaker with enhanced air gap according to the present invention.
Figure 7: schematically illustrates the moving contact holder of the Motor Protection Circuit Breaker with enhanced air gap according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
As shown in figure 1, the Motor Protection Circuit Breaker MPCB (1) comprises an upper housing (1a) and a lower housing (1b) within which the system components of the MPCB (1) are assembled. As shown in figure 2, the MPCB (1) is provided with an open/close mechanism (2) that opens and closes the MPCB (1) in response to a detection signal from the detector in order to prevent a failure current from flowing to the motor through the motor-side terminals to protect the motor that is connected to the MPCB. The open/close operation of the circuit breaker is achieved by the separation of movable contact (3) fitted to a movable contact bar from the stationary contacts (4) fitted to a stationary contact bar by the operation of the open/close mechanism (2).
The stationary contact bars and the moveable contact bars are located both in the power source side and motor side of the Motor Protection Circuit Breaker (1) and separated from each other.
At the time when the movable contacts (3) of the movable contact bar separated from stationary contacts (4) of the stationary contact bar, high pressure and high temperature ‘arc’ is generated. In certain circumstances the ‘arc’ may result due to failure of interruption of the fault current. The ‘arc’ generated between the movable contacts (3) and stationary contacts (4) may damage the movable contacts (3) and stationary contacts (4) of the Motor Protection Circuit Breaker (1).
It is necessary to prevent the movable contacts (3) and stationary contacts (4) from the possible damage caused by the high pressure and high temperature arc. Equally it is important that movable contacts (3) and stationary contacts (4) are to be prevented from failure of interruption of the fault current.
This is achieved by swiftly extinguishing and discharging the ‘arc’ by the arc extinguishing device (5). As shown in figure 4, the arc extinguishing device (5) comprises plurality of magnetic plates (5a) and side wall (5b) and the magnetic plates (5a) are packaged within the side wall (5b). Each magnetic plate (5a) may have a U-shaped member opened in the direction of arc generation, and induce the arc in response to the electromagnetic force.
When a fault current is introduced, the movable contacts (3) are separated from the stationary contacts (4) by the open/close mechanism (2). The high temperature ‘arc’ induced in the arc chamber is extinguished by cathode effect and cooling effect of the magnetic plates (5a) and the flow of the fault current is interrupted and discharged via an arc outlet there by the flow of fault current is arrested.
As shown in figure 2 and 3, the air gap (A) is the effective distance between the rivets (3a) fitted on the moving contact (3) as shown in figure 5 and the rivets (4a) fitted on the stationary contact (4) as shown in figure 6 when the MPCB (1) is in OFF condition.
The air gap (A) is key parameter in deciding short circuit current breaking capacity of the MPCB (1). In order to facilitate faster extinguishing of the arc, the air gap (A) is enhanced in the Motor Protection Circuit Breaker (1) according to the present invention so that arc is lengthened. Advantageously the increased air gap (A) enables the MPCB (1) with increased short circuit current rating due to the fact that increased air gap require more re-striking voltage to reignite the ‘arc’.
In a preferred embodiment the air gap (A) between the rivets (3a) fitted on the moving contact (3) and the rivets (4a) fitted on the stationary contact (4) when the MPCB (1) is in OFF condition is in the range 4.0 mm to 4.50 mm, preferably 4.25mm .
Increased air gap (A) calls for extra movement of the moving contact bar of about 1.0mm. To achieve the extra movement of the moving contact bar, in a preferred embodiment approximately 1.0mm of material is added to the moving contact holder (6) such a manner that moving contact bar moves the required extra distance to maintain the same rivet erosion. The moving contact holder (6) is shown in figure 7,
In order to achieve the increased air gap (A) the height (H) of the rivets (3a) fitted on the moving contact (3) and the rivets (4a) fitted on the stationary contact (4) is maintained in the range 1.00 mm to 1.40 mm, preferably 1.2 mm.
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. Motor Protection Circuit Breaker with increased air gap between the rivets fitted to the stationary contact and moving contact comprising of:
a detector detecting a fault current;
an open/close mechanism (2) that includes moving contact holder (6) operating in response to a detection signal of the detector;
stationary contacts bars having a stationary contacts (4) arranged both on the power source side and motor side and is fitted with rivets (4a);
a movable contact bar having movable contact (3) arranged both on the power source side and motor side and is fitted with rivets (3a); and
an arc extinguishing device (5)
wherein an air gap (A) is provided between rivets (3a) fitted on the moving contact (3) and rivets (4a) fitted on the stationary contact (4) when the MPCB (1) is in OFF condition ,
characterized in that the air gap (A) is in the range 4.0 mm to 4.50 mm, preferably 425mm.

2. The Motor Protection Circuit Breaker with increased air gap as claimed in claim 1, wherein the height (H) of the rivets (3a) fitted on the moving contact (3) and the rivets (4a) fitted on the stationary contact (4) is in the range 1mm to 1.40mm, preferably 1.2 mm.

3. The Motor Protection Circuit Breaker with increased air gap as claimed in claim 1, wherein approximately 1.0mm of additional material is added in the moving contact holder (6) to facilitate the extra movement of the moving contact bar.