Claims: 1. A variable setting electromagnetic release (300) for a circuit breaker comprising:
a stationary magnet (210) holding a current carrying conductor (220); 5
a moving magnet (230) arranged adjacent to the stationary magnet (210) such that the moving magnet (230) maintains an air gap (240) there between, wherein the air gap (240) is set to trip the mechanism of release for a threshold value of current flowing through the current carrying conductor (220); 10
a magnetic slider (250) slidably mounted within the variable setting electromagnetic release (300); and
a shunting magnet (260) held by the magnetic slider (250) between the moving magnet (230) and the stationary magnet (210), wherein the magnetic slider (250) moves the shunting magnet (260) near to 15 and away from the moving magnet (230);
wherein, the air gap (240) is set for the current less than the threshold value, by moving the shunting magnet (260) near the moving magnet (230) and the air gap (240) is set for the current higher than the threshold value, by moving the shunting magnet , Description:Field of the invention:
The invention relates generally to circuit breakers, and more particularly to adjustment of electromagnetic release settings in circuit breakers. 5
Background of the invention:
When an electric current flows through a conductor, a magnetic field is developed around it. During normal current flow, the magnetic field created by the electromagnet is not strong enough to attract the moving magnet or armature. When a short circuit current flows, the strong magnetic field developed around the 10 current carrying conductor (or stationary magnet) attracts the moving magnet or armature towards it, tripping the magnetic release. If In is the rated continuous or uninterrupted current that the circuit breaker can carry then the tripping phenomenon occurs at a particular maximum magnetic setting of the release, i.e. X times of rated current In i.e X × In 15
If this magnetic release setting needs to be changed to (X-n) × In (where 0 < n < X), then this can be achieved through various ways:
Case 1: Changing the spring extension or compression i.e. spring tension, where spring is connected to moving magnet and helps to control the movement of moving magnet at different magnetic force generated by stationary magnet. 20
Referring to figure 1, a magnetic release system (100) of a circuit breaker where magnetic settings are changed by varying spring tension is shown, in accordance with the prior art. In the system (100), spring (10) is controls the movement of the moving magnet (30) at different magnetic force generated by the stationary magnet (40). The magnetic setting can be changed by moving the slider (20) 25 which will change the load value of spring (10). In figure 1, (50) is the current carrying conductor.
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Case 2: Changing the spring tension as in case 1 as well as adjusting the air gap between moving and stationary magnet by moving the moving magnet close to the stationary magnet in relation to desired current setting (X-n)
Referring to figure 2, an electromagnetic release system (200) of a circuit breaker in accordance with the prior art is shown. In system (200), magnetic settings are 5 changed by pressing support (110) in downward direction using the calibration screw (120). This pushes the moving magnet (160) towards stationary magnet (150) changing the air gap between them. In this case, compression of spring (130) also changes as the support (110) moves down. In the figure, (170) is the current carrying conductor while (140) is the support for stationary magnet (150) 10
The same is applicable for the calibration of releases. When moving magnet is attracted towards stationary magnet because of the magnetic force, it trips the mechanism of the release. This phenomenon occurs at a particular current setting that is X times the rated current In i.e., X × In
The tripping band is from 0.8 × X × In to 1.2 × X × In 15
The non tripping of the release is observed below 0.8 × X × In
To achieve the release performance, it has to be calibrated to obtain the desired performance it has to be calibrated to obtain the desired performance for the above mentioned band. To perform calibration two parameters are considered:
1. If Non-tripping of release is observed, air gap is reduced between moving 20 magnet and stationary magnet to increase the effect of magnetic force and calibrate the release as per requirement.
2. If Early-tripping of release is observed, air gap is increased between moving magnet and stationary magnet to reduce the effect of magnetic force and calibrate the release as per requirement. 25
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However, there are certain drawbacks with the existing technology such as in case 1, as the spring manufacturing tolerance is wide, consistency is not achieved for the given design of magnetic release. Secondly, in Case 2, adjusting the air-gap between moving and stationary magnet by moving the moving magnet close to stationary magnet in relation to change in current setting (X-n) also affects change 5 in the load value of the spring connected to moving magnet. In this case, release function depends upon the change in air gap as well as change in load value of the spring. Thus, the overall travel of mechanism is compromised
Accordingly, there exists a need to provide an arrangement for adjustment of magnetic release setting in the circuit breakers, without the need to change 10 position of moving magnet or change the spring tension, that overcomes above mentioned drawbacks in the prior art.
Objects of the invention:
An object of the present invention is to provide a system for adjusting a electromagnetic release setting without changing spring tension settings in a 15 circuit breaker.
Another object of the present invention is to provide a system for adjusting a electromagnetic release setting without changing position of moving and stationary magnets in the circuit breaker.
Still another object of the present invention is to provide a system for adjusting a 20 electromagnetic release setting varying threshold current values without compromise in the travel of release mechanism.
Summary of the invention:
The present invention provides a system for adjusting a electromagnetic release setting without changing the spring tension settings or positions of moving magnet 25 and stationary magnet in a circuit breaker. When a current higher than a set value (X times the rated current In) flows through the circuit breaker, a magnetic field
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strong enough to attract the moving magnet is developed around the current carrying stationary magnet which further trips the mechanism of release in the circuit breaker. To change the electromagnetic release setting to (X-n) times the rated current In, where 0 < n < X, a shunting magnet is introduced near moving and stationary magnet or in the air gap between moving and stationary magnet. By 5 moving the shunting magnet, air gap between the stationary and moving magnet can be altered as per the requirement, without affecting spring tension and air gap settings.
Brief description of the drawings:
Figure 1 shows a perspective view of a electromagnetic release of a circuit breaker 10 where electromagnetic settings are changed by varying spring tension, in accordance with the prior art;
Figure 2 shows a perspective view of an electromagnetic release of a circuit breaker where electromagnetic settings are changed by varying air gap between magnets, in accordance with the prior art; 15
Figure 3 shows a perspective view of a variable setting electromagnetic circuit breaker, in accordance with the present invention;
Figure 4 shows a perspective view of an adjustment in electromagnetic setting of a a variable setting electromagnetic circuit breaker, in accordance with the present invention. 20
Detailed description of the embodiments:
The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments. 25
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The present invention provides a system for adjusting a electromagnetic release setting without changing spring tension settings or positions of moving magnet and stationary magnet in a circuit breaker. When a current higher than a set value (X times the rated current In) flows through the circuit breaker, a magnetic field strong enough to attract the moving magnet is developed around the current 5 carrying stationary magnet which further trips the mechanism of release in the circuit breaker. To change the magnetic release setting to (X-n) times the rated current In, where 0 < n < X, it is a common practice to adjust the electromagnetic setting through either changing the spring tension or adjusting air gap between moving magnet and stationary magnet. In view of the above, changing the spring 10 tension can result into inconsistency in the system as spring manufacturing tolerances are wide. Also, adjusting the air-gap between moving and stationary magnet by moving the moving magnet close to the stationary magnet in relation to change in current setting (X-n) also affects the change in the load value of the spring connected to the moving magnet. In this case, release function depends 15 upon the change in air gap as well as change in load value of the spring. Moreover, the overall travel of the mechanism is compromised with change in magnetic setting. The present invention overcomes the limitation by changing the air gap between moving magnet and fixed magnet by introducing a shunting magnet near the moving and the stationary magnet or in the air gap between the 20 moving and the stationary magnet. With this, at the time of change in electromagnetic setting, only one shunted magnet will be introduced in the system. This will not affect consistent performance of the release. Also, overall travel of MCCB mechanism is not compromised.
The present invention is illustrated with reference to the accompanying drawings, 25 throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in bracket in the following description.
Referring to Figure 3 and Figure 4, a variable setting electromagnetic release (300) for a circuit breaker in accordance with the present invention is shown. The 30
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variable setting electromagnetic release (300) for a circuit breaker comprises of a stationary magnet (210) holding a current carrying conductor (220), a moving magnet (230) adjacent to the stationary magnet (210) such that the moving magnet maintains a predefined air gap (240) there between; a magnetic slider (250) holding a shunting magnet (260) and slidably mounted within the variable setting 5 electromagnetic release (300) such that the shunting magnet (260) is capable of changing the air gap (240) when the magnetic slider (250) moves.
The air gap (240) is set for a threshold value of current flowing through the current carrying conductor (220) at which the magnetic force produced in the stationary magnet (210) attracts the moving magnet (230) and trips the mechanism 10 of release. To adjust the air gap (240) for a current less than the threshold value, the shunting magnet (240) is moved near or in between the air gap (240) and to adjust the air gap (240) for a current higher than the threshold value, the shunting magnet (240) is moved away from the air gap (240) such that the change in magnetic force due to changed threshold current is compensated by change in the 15 air gap (240). This is also applicable for the calibration of release.
Referring to figure 3, the air gap (240) is set for a threshold value of current (i.e. X times the rated current In) flowing through the current carrying conductor (220). When current higher than the set value flows through the current carrying conductor (220), the magnetic field produced in the stationary magnet (210) 20 attracts the moving magnet (230) towards it with a certain magnetic force, tripping the mechanism of release. Now referring to figure 4, to adjust the air gap (240) for a current less than the set value i.e. (X-n) times the rated current In where 0 < n < X, the shunting magnet (260) is moved in the air gap (240) wherein the change in magnetic force due to changed current is compensated by change in the air gap 25 (240) without compromise in the travel of release mechanism.
The force generated by shunting magnet (260) will remain same in both the X × In setting and (X-n) × In setting. The same can be achieved by selecting the position of placement of shunting magnet (260) with change in magnetic setting; this will
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change the air gap path (240). The desired shunting property can be achieved by selecting the shunting magnet (260) of any suitable shape, size and magnetic material.
Advantages of the invention:
? Adjustment in electromagnetic release setting for varying threshold current 5 is achieved without changing positions of moving magnet (230) or stationary magnet (210) in a circuit breaker.
? Adjustment in electromagnetic release setting for varying threshold current is achieved without changing spring tension settings in a circuit breaker.
? Introduction of shunting magnet (260) does not affect the overall 10 mechanism of travel of the trip release in the circuit breaker.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in 15 light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, and to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various 20 omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but such omissions and substitutions are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present invention.