[005] The above-described deficiencies of today's current sharing or current distribution among the multiple fingers of a pole or of a phase of multiphase switch or circuit breaker are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.

SUMMARY OF THE INVENTION

[006] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[007] An object of the present invention is to provide a multiple finger contact assembly in a circuit breaker, which by virtue of its design helps in better current sharing and comparably more uniform current distribution among the multiple contact fingers of single phase in circuit breakers. This unique design thus improves the Rated short-time withstand current or Icw performance of a circuit breaker, improves temperature rise performance of a circuit breaker, and improves fault current breaking capability and performance of a circuit breaker. The present invention is of use in the switchgear industry.

[008] Accordingly, the present invention provides a contact finger assembly having finger combination of different cross section in a pole or in a phase in a multiple phase circuit breaker helps in better current sharing and comparably more uniform current distribution among the multiple contact fingers The unique design of this multiple contact finger assembly or pole assembly having combination of fingers of same and different cross section or having fingers of different cross section in a pole or in a single phase in a multiphase circuit breaker improves the Rated short-time withstand current or Icw performance of a circuit breaker, improves temperature rise performance of a circuit breaker, and improves fault current breaking capability and performance of a circuit breaker.

[009] In contrast to the prior-art contact assembly, the present invention provides a moving contact finger assembly having finger combination of different cross section in a pole or in a phase in a multiple phase circuit breaker helps in better current sharing and comparably more uniform current distribution among the multiple contact fingers. The unique design of this multiple contact finger assembly or pole assembly having combination of fingers of same and different cross section or having fingers of different cross section in a pole or in a single phase in a multiphase circuit breaker improves the Icw performance of a circuit breaker, improves temperature rise performance of a circuit breaker, and improves fault current breaking capability and performance of a circuit breaker. The moving contact finger assembly of the present invention having finger combination of different cross section in a pole or in a phase in a multiple phase circuit breaker helps in better current sharing and comparably more uniform current distribution among the multiple contact fingers of single phase in multiphase circuit breakers that is, it helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform.

[0010] The variation of cross section can be there along the finger length of any finger and any number of such fingers along with finger or fingers, having lengthwise uniform cross section, can be assembled to form such a pole or multiple fingers moving contact assembly. Also the variation of cross section can be there along the finger length in multiple fingers in a pole or in a single phase. In that case current invention uses a moving contact finger assembly having finger combination of different average cross section in a pole or in a phase in a multiple phase circuit breaker.

[0011] In case of the Rated short-time withstand current performance or Icw performance, the moving contact finger has to withstand and maintain required contact pressure to carry that particular magnitude of current against the electrodynamic force especially against the repulsive Holmes force. If the repulsion force is greater than the finger closing force the particular finger repels open and leads to withstand failure of that breaker. The magnitude of the Holmes force is dependent upon the magnitude of current, the higher the current magnitude the higher the repulsion force.

[0012] Due to proximity effect of intra phase and inter phase current carrying fingers, this current sharing by the multiple fingers in a single phase is not uniformly distributed. Thus for each finger the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude for an alternating current cycle. So the current carrying capability and fault current withstand capability a circuit breaker is limited by that single finger which carries the maximum instantaneous current, because current withstand failure of single moving contact finger leads to current withstand failure of all the adjacent finger in that poles of one particular phase due to cascading effect.

[0013] Due to proximity effect of intra phase and inter phase current carrying fingers, this current sharing by the multiple fingers in a single phase is not uniformly distributed. Thus for each finger the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude for an alternating current cycle (like sine waveform, short circuit current waveform). So in addition to current carrying capability and fault current withstand capability, the fault current breaking capability and performance, the temperature rise performance and electrical life also get affected and due to the non-uniform distribution of current among current carrying moving contact fingers. The higher the current the higher the temperature rise effect in any particular finger. In case of fault withstand or in Icw performance due to temperature rise that particular finger with maximum instantaneous current value over a full cycle of current wave from gets more affected and more deteriorated in terms of contact surface than the other adjacent fingers. Thus following temperature rise performance of that finger gets deteriorated. Thus also affecting the electrical life of the circuit breaker. In case of following fault current breaking the performance of that particular finger gets deteriorated if last open. The make carry and break performance for rated current also get affected and thus electrical life of circuit breaker gets deteriorated.

[0014] Due to proximity effect of intra phase and inter phase current carrying fingers, this current sharing by the multiple fingers in a single phase is not uniformly distributed. Thus for each finger the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude for an alternating current cycle (like sine waveform, short circuit current waveform). If there are n fingers in a particular phase in a multiphase circuit breaker, it is observed that mostly the corner most or side most finger that is the 1st finger or nth finger of the construction wise in-between phase, carries the maximum magnitude of instantaneous current for an non uniform current distribution among the moving contact fingers in that particular phase. If there are 3 phases with 120 degree phase shift, that is R, Y and B and circuit breaker construction wise they are so placed that Y phase is the in-between phase, then due to proximity effect, it is observed that mostly the corner most or side most finger that is the 1st finger or nth finger of the construction wise in-between phase, carries the maximum magnitude of instantaneous current for an non uniform current distribution. In a phase it is mostly the corner most finger which has the maximum proximity to the other phase, carries the maximum instantaneous current for that phase.

[0015] This current distribution pattern and the finger in which the maximum instantaneous current flows depends upon many factors like, number of phases, number of poles per phase, phase angles, phase shift angle between phases, breaker closing point on wave, frequency of alternating current, waveform shape, breaker construction, pole width, gap between fingers, gap between poles of same phase, inter-phase pole gap, finger profile, number of fingers in a particular phase, proximity of ferromagnetic material and other potential and influential factors that can effect magnetic flux lines distribution and magnitude.

[0016] Depending upon these factors the current distribution pattern and maximum instantaneous current magnitude in a particular moving contact finger in multiphase circuit breaker can change due to variation of self and mutual inductance and due to proximity effect of intra phase and inter phase current carrying fingers.. But for a non-uniform current distribution among the multiple fingers due to proximity effect of intra phase and inter phase current carrying fingers and for each finger the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude for an alternating current cycle limits and decreases the current carrying capability, fault current withstand capability and fault current breaking capability and performance of a circuit breaker. This uneven instantaneous current distribution among the multiple fingers of multiphase circuit breaker also decreases the temperature rise performance and electrical life as well. So If there are m phases and If there are n fingers in a particular phase, where m and n are any positive integers, then due to intra phase and inter phase proximity effect any finger that is the 1st finger or the 2nd or 3rd or n-1th or nth finger of any particular phase, can carry the maximum magnitude of instantaneous current for an non uniform current distribution.

[0017] However, for a non-uniform current distribution among the multiple fingers due to proximity effect of intra phase and inter phase current carrying fingers and for each finger the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude for an alternating current cycle limits and decreases the current carrying capability, fault current withstand capability and fault current breaking capability and performance, temperature rise performance and electrical life of a circuit breaker.

[0018] In the present invention using moving contact fingers with different cross section, especially moving contact fingers with comparatively lower cross section in the side most or corner most 1 or 2 fingers on both sides of the pole or in the single side of the pole and moving contact fingers with comparatively higher cross section in the middle most remaining fingers in each phase in a multiphase circuit breaker helps in a more uniform current distribution among the fingers. The increase in the resistivity in the fingers with lesser cross section and due to the constructional feature of each pole having fingers with different cross sections, the variation in self and mutual inductance and the variation in the distribution of the magnetic field lines due to rated or fault current and corresponding eddy current and the intra phase and inter phase proximity effect leads to a comparatively lesser current pass through that finger and to balance the phase current other fingers with higher cross section carries comparatively higher current than the current, which otherwise could have been flown if all the fingers in a phase in a multiphase circuit breaker would have same cross section. Ultimately it helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform. For n fingers in a pole or in a phase in a multiphase circuit breaker 1 or 2 side most corner fingers on one or both side of the pole having comparatively lesser cross section ‘d1’ than the remaining (n - no. of fingers with lower cross section) fingers with comparatively higher cross section ‘d2’, where d2>d1 and d1 and d2 are any non-zero and non-negative values or numbers.

[0019] The variation of cross section can be there along the finger length of any finger and any number of such fingers along with finger or fingers, having lengthwise uniform cross section, can be assembled to form such a pole or multiple finger moving contact assembly. Also the variation of cross section can be there along the finger length in multiple fingers in a pole or in a single phase. In that case present invention using moving contact fingers with different average cross section, especially moving contact fingers with comparatively lower average cross section in the side most or corner most 1 or 2 fingers on both sides of the pole or in the single side of the pole and moving contact fingers with comparatively higher average cross section in the middle most remaining fingers in each phase in a multiphase circuit breaker helps in a more uniform current distribution among the fingers. It helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform.

[0020] The same can be achieved by varying the resistivity or by varying the flux line distribution and linkages in a way so that comparatively more uniform current distribution can be achieved among the multiple fingers of a pole or of a single phase in a multiphase circuit breaker by using different material and by any other probable means. Different material can be used for the same purpose in a single finger or in multiple fingers in a pole or in a single phase of a multiphase circuit breaker.

[0021] In a multiphase circuit breaker for each phase or each pole, the lesser cross section in finger can be achieved by reducing the width of the finger than the remaining fingers in the pole having thickness constant in all the fingers. For n fingers with equal finger thickness in a pole or in a phase in a multiphase circuit breaker 1 or 2 side most corner fingers on one or both side of the pole having comparatively lesser cross section ‘d1’ by having lesser finger width w1 than the remaining (n - no. of fingers with lower cross section) fingers with comparatively higher cross section ‘d2’ by having comparatively higher finger width w2, where d2>d1, w2>w1 and d1, d2, w1 and w2 are any non-zero and non-negative values or numbers.

[0022] The current distribution pattern and the finger of the present invention in which the maximum instantaneous current flows depends upon many factors like, number of phases, number of poles per phase, phase angles, phase shift angle between phases, breaker closing point on wave, frequency of alternating current, waveform shape, breaker construction, pole width, gap between fingers, gap between poles of same phase, inter-phase pole gap, finger profile, number of fingers in a particular phase, proximity of ferromagnetic material and other potential and influential factors that can effect magnetic flux lines distribution and magnitude. Depending upon these factors the current distribution pattern and maximum instantaneous current magnitude in a particular moving contact finger in multiphase circuit breaker can change due to proximity effect of intra phase and inter phase current carrying fingers and due to variation of self and mutual inductance. So If there are m phases and If there are n fingers in a particular phase, then due to intra phase and inter phase proximity effect any finger that is the 1st finger or the 2nd or 3rd or n-1th or nth finger of any particular phase, can carry the maximum magnitude of instantaneous current for an non uniform current distribution. For this after identifying the current distribution pattern in a pole or in each phase among the moving contact fingers, the concept of this invention can be applied and the respective finger which sees the maximum instantaneous current magnitude for an alternating current cycle can be made of lower cross section having other influential factors constant so that the current sharing pattern among the fingers in a phase can change and leads to more uniform current distribution so that current shared by each finger in a phase tends more towards the average current distribution. For this after identifying the current distribution pattern in a pole or in each phase among the moving contact fingers, the concept of this invention can be applied and the respective finger which sees the maximum instantaneous current magnitude for an alternating current cycle can be made of lower cross section along with changes in other influential factors in any probable way and combinations so that the current sharing pattern among the fingers in a phase can change and leads to more uniform current distribution so that current shared by each finger in a phase tends more towards the average current distribution.

[0023] This current distribution pattern and the finger of the present invention in which the maximum instantaneous current flows depends upon many factors like, number of phases, number of poles per phase, phase angles, phase shift angle between phases, breaker closing point on wave, frequency of alternating current, waveform shape, breaker construction, pole width, gap between fingers, gap between poles of same phase, interphase pole gap, finger profile, number of fingers in a particular phase, proximity of ferromagnetic material and other potential and influential factors that can effect magnetic flux lines distribution and magnitude. Depending upon these factors the current distribution pattern and maximum instantaneous current magnitude in a particular moving contact finger in multiphase circuit breaker can change due to variation of self and mutual inductance and due to proximity effect of intra phase and inter phase current carrying fingers.

[0024] If there are m phases and If there are n fingers in a particular phase, then due to intra phase and inter phase proximity effect any finger that is the 1st finger or the 2nd or 3rd or n-1th or nth finger of any particular phase, can carry the maximum magnitude of instantaneous current for an non uniform current distribution. For this construction wise and position wise symmetrically or asymmetrically any finger and any number of fingers p in a phase or in a pole can be of lower average cross section A1 as per requirement and other (n-p) number of fingers can be of comparatively higher average cross section A2 where A2>A1 [Where n and p are any positive integer and n>p]. Also as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section like a1, a2, a3…..an and a1?a2?a3?……?an. In a multiphase circuit breaker for each phase or each pole, the lesser average cross section in finger can be achieved by reducing the average width of the finger than the remaining fingers in the pole having average thickness constant in all the fingers. For this for n fingers with equal finger average thickness in a pole or in a phase in a multiphase circuit breaker, construction wise and position wise any finger and any number of fingers p in a phase or in a pole can be of lower average cross section A1 by having lesser finger average width B1 as per requirement and other (n-p) number of fingers can be of comparatively higher average cross section A2 by having higher finger average width B2 where A2>A1 and B2>B1. Also as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section like a1, a2, a3…..an and a1?a2?a3?……?an. For this for n fingers with equal finger average thickness in a pole or in a phase in a multiphase circuit breaker, as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section a1, a2, a3…..an where a1?a2?a3?……?an by having corresponding different finger average width like b1, b2, b3……bn where b1?b2?b3?……?bn. In a multiphase circuit breaker for each phase or each pole, the lesser average cross section in finger can be achieved by reducing the average thickness of the finger than the remaining fingers in the pole having finger average width constant in all the fingers. For this for n fingers with equal finger average width in a pole or in a phase in a multiphase circuit breaker, construction wise and position wise any finger and any number of fingers p in a phase or in a pole can be of lower average cross section A1 by having lesser finger average thickness C1 as per requirement and other (n-p) number of fingers can be of comparatively higher average cross section A2 by having higher finger average width C2 where A2>A1 and C2>C1. Also as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section like a1, a2, a3…..an and a1?a2?a3?……?an. For this for n fingers with equal finger average width in a pole or in a phase in a multiphase circuit breaker, as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section a1, a2, a3…..an where a1?a2?a3?……?an by having corresponding different finger average thickness like c1, c2, c3……cn where c1?c2?c3?……?cn. In a multiphase circuit breaker for each phase or each pole, the different average cross section in fingers can be achieved by varying the average thickness or the average width of the finger or varying both simultaneously or by having any probable finger average width and average thickness combinations. For this for n fingers in a pole or in a phase in a multiphase circuit breaker, as per requirement each finger in a pole or in a phase in a multiphase circuit breaker can be of different average cross section a1, a2, a3…..an where a1?a2?a3?……?an by having corresponding different finger average thickness and different finger average width or by having any probable finger average width and average thickness combinations. [Here A1, A2, B1, B2, C1, C2, a1, a2, a3.. an, b1, b2, b3.. bn, c1,c2, c3.. cn are non-zero and non-negative values or numbers].

[0025] In a multiphase circuit breaker for each phase or each pole, the different cross section in any finger can also be achieved by varying the thickness or the width of the finger vertically or along the length wise of the finger or varying both simultaneously or by having any probable finger width and thickness combinations vertically or along the length wise of the finger. In a multiphase circuit breaker for each phase or each pole, the different cross section in fingers can be achieved by varying the thickness or the width of the finger or varying both simultaneously or by having any probable finger width and thickness combinations in single finger and in among the fingers.

[0026] In the current invention the increase in the resistivity in the fingers with lesser cross section and due to the constructional feature of each pole having fingers with different cross sections, the variation in self and mutual inductance and the variation in distribution of the magnetic field lines due to rated or fault current and corresponding eddy current and the intra phase and inter phase proximity effect leads to a comparatively lesser current pass through that finger and to balance the phase current other fingers with higher cross section carries comparatively higher current than the current, which otherwise could have been flown if all the fingers in a phase in a multiphase circuit breaker would have same cross section. Ultimately it helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform. The same effect can be achieved by variation in the self inductance, mutual inductance of a finger in a phase or in a pole in a multiphase circuit breaker by any probable means and variation in magnetic field distribution pattern by any probable means, which leads to a comparatively lesser current pass through that finger and to balance the phase current, other fingers with higher cross section carries comparatively higher current than the current, which otherwise could have been flown if all the fingers in a phase in a multiphase circuit breaker carries equal current and ultimately it helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform.

[0027] In contrast to the prior-art, the electrical contact assembly of the present invention is adapted to provide current sharing and more uniform current distribution among the multiple contact fingers. It helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform.

[0028] In contrast to the prior-art, the electrical contact assembly of the present invention is adapted to provide current sharing and more uniform current distribution among the multiple contact fingers which can be achieved by varying the resistivity or by varying the flux line distribution and linkages in a way so that comparatively more uniform current distribution can be achieved among the multiple fingers of a pole or of a single phase in a multiphase circuit breaker by using different material and by any other probable means. Different material can be used for the same purpose in a single finger or in multiple fingers in a pole or in a single phase of a multiphase circuit breaker.

[0029] In contrast to the prior-art, in the electrical contact assembly the variation of cross section can be there along the finger length of any finger and any number of such fingers along with finger or fingers, having lengthwise uniform cross section, can be assembled to form such a pole or multiple finger moving contact assembly. Also the variation of cross section can be there along the finger length in multiple fingers in a pole or in a single phase. In that case present invention using moving contact fingers with different average cross section, especially moving contact fingers with comparatively lower average cross section in the side most or corner most 1 or 2 fingers on both sides of the pole or in the single side of the pole and moving contact fingers with comparatively higher average cross section in the middle most remaining fingers in each phase in a multiphase circuit breaker helps in a more uniform current distribution among the fingers. It helps in reducing the magnitude of the maximum instantaneous current seen by any single finger in a phase in a full cycle of the current wave form so that current shared by each finger in a phase tends more towards the average current distribution. It helps in better current sharing by reducing the current peak seen by that finger in which the highest peak current flows otherwise and by increasing the current in such a finger in which comparatively lower peak current flows otherwise for a full cycle current waveform.

[0030] The advantages and salient features of the present invention can be applied to any electrical switching apparatus or current carrying devices that use multiple electrical contact assembly or parallel electrical paths.

[0031] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0032] Figure 1a shows isometric view of breaker assembly.

[0033] Figure 1b shows front view of breaker assembly (partial), showing arc chute assembly, contact assembly.

[0034] Figure 2a, 2b and 2c shows side view, top view and isometric view of a pole assembly of circuit breaker, in accordance with an embodiment of the present subject matter.

[0035] Figure 3a and 3b shows the side view and top view and 3c to 3e shows the isometric view of a partial pole assembly and 3c, 3d and 3e shows the isometric views of that partial pole assembly, in accordance with an embodiment of the present subject matter.

[0036] Figure 3f and 3g shows the isometric view and top view of a pole assembly in which fingers of different cross section are assembled, in accordance with an embodiment of the present subject matter.

[0037] Figure 3h and 3i shows the isometric view and top view of a pole assembly in which fingers of different cross section are assembled, in accordance with an embodiment of the present subject matter.

[0038] Figure 3j and 3k shows the isometric view and top view of a pole assembly in which fingers of different cross section are assembled, in accordance with an embodiment of the present subject matter.

[0039] Figure 3l and 3m shows the isometric view and top view of a pole assembly in which fingers of different cross section are assembled, in accordance with an embodiment of the present subject matter.

[0040] Figure 3n and 3q shows the isometric view of a partial pole assembly, in accordance with an embodiment of the present subject matter.

[0041] Figure 4a, 4b and 4c shows isometric, side and top schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter..

[0042] Figure 5a, 5b and 5c shows isometric, side and top schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter.

[0043] Figure 6a, 6b and 6c shows isometric, side and top schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter.

[0044] Figure 7a, 7b and 7c shows isometric, side and top schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter.

[0045] Figure 8a and 8b shows isometric and side schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter.

[0046] Figure 8d shows top schematic view of finger arrangement in a pole in which fingers of different cross section are used, in accordance with an embodiment of the present subject matter.

[0047] Figure 9a to 9d shows the top schematic view of finger arrangements and pole arrangements (1pole/phase) for 3 phase circuit breaker for different combination and arrangement of fingers, having same and different cross section, in a single pole, in accordance with an embodiment of the present subject matter.

[0048] Figure 10a to 10d shows the top schematic view of finger arrangements and pole arrangements (2pole/phase) for 3 phase circuit breaker for different combination and arrangement of fingers, having same and different cross section, in a single pole, in accordance with an embodiment of the present subject matter.

[0049] Figure 11a to 11d shows the top schematic view of finger arrangements and pole arrangements (2pole/phase) for 3 phase circuit breaker for different combination and arrangement of fingers, having same and different cross section, in a single pole, in accordance with an embodiment of the present subject matter.

[0050] Figure 12a and 12b shows, for the same current, the different current sharing or current distribution patterns in fingers of single phase for a simulation for 3 phase sinusoidal current (2Pole/phase), having total 16 fingers/phase and 8 fingers/pole (Where no other influential factors are included), in accordance with an embodiment of the present subject matter.

[0051] Figure 12e and 12f shows, for the same current, the different, the current sharing or current distribution patterns in fingers of single phase for a simulation for 3 phase sinusoidal current (2Pole/phase), having total 16 fingers/phase and 8 fingers/pole for the finger arrangement and design referred to 12c and 12d respectively (Where no other influential factors are included), in accordance with an embodiment of the present subject matter.

[0052] Figure 12i and 12j shows, for the same current, the different, the current sharing or current distribution patterns in fingers of single phase for a simulation for 3 phase short circuit current (1Pole/phase), having total 6 fingers/phase and 6 fingers/pole for the finger arrangement and design referred to 12g and 12h respectively (Where no other influential factors are included), in accordance with an embodiment of the present subject matter.

[0053] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0054] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0055] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0056] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0057] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0058] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0059] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0060] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0061] Current technology trend in modern circuit breakers uses multiple fingers moving contact assembly, where fingers are of same material, example Copper, and of same average cross section, to carry the rated current, to withstand the fault current and to break the fault current. To minimize the high repulsive force, current sharing technology using multiple finger assembly is being used in the modern day switchgear, especially in circuit breakers. Due to proximity effect of intra phase and inter phase current carrying fingers, this current sharing by the multiple fingers in a single phase is not uniformly distributed. Thus for each finger for an alternating current cycle the maximum instantaneous current magnitude is different so each finger carries a maximum current of different magnitude. Also for each finger at a particular time instant the instantaneous current magnitude is different so each finger carries a current of different magnitude in a multiphase alternating current circuit breaker. In other terms the rms value and the peak value of current flown through each finger for a full cycle of current waveform is different and at a particular time instant the instantaneous value of the current flown through each finger is also different. This non-uniform distribution of current limits and decreases the current carrying capability, fault current withstand capability and fault current breaking capability and performance of a circuit breaker. This uneven instantaneous current distribution among the multiple fingers of multiphase circuit breaker also decreases the temperature rise performance and electrical life as well.

[0062] If in a multiphase alternating current circuit breaker maximum instantaneous current per phase stands as I, then for n fingers for that instant average current per finger will be I/n, but due to proximity effect of intra phase and inter phase current carrying fingers, it is observed that the maximum instantaneous current in each finger in a single phase is either I/n and also each finger carries a current of different magnitude at a particular time instant. In a phase among the n numbers of contact finger, only 1 finger sees the maximum instantaneous current in a full cycle current wave form, other fingers experience comparatively less maximum instantaneous current in a full cycle current wave form. In some fingers in a phase, the maximum current can be as high as 2 to 3 times of the average per finger current and in some fingers in a phase, the maximum current can be as low as 0.5 times of the average per finger current. The factor x that is [current in any particular finger/(I/n)] can vary from fraction to n depending upon the other influential factors.