A DOUBLE BREAK POWER TRANSFER SWITCH
FIELD OF THE INVENTION
[0001] The present invention generally relates to the field of electrical engineering and more particularly to a double break transfer switch for powerally transferring an electrical load from a normal source of electric power to an emergency source of electric power.
PRIOR ART [0002] Power transfer switches are typically multi-phase switches. Thus, an power transfer switch used with a three phase, four wire system will always include three phases for switching the three phase conductors of the load between the three phase conductors of the normal power source and the three phase conductors of the emergency power source. The fourth, neutral conductor of the load is, often permanently connected to the neutral conductors of the normal and emergency sources.
[0003] The following problems occur when neutral of the load is connected permanendy to the neutral of the two supplies through an ATS. Ground fault sensor is connected with one of the sources. Permanent connection of the neutral may affect the sensing of ground fault sensor. It may also lead to nuisance tripping of the ground fault sensor on overload. To take care of above problem ATS are provided with a separate phase for neutral.
[0004] US Patent No.3936782 assigned to Power Switch Company discloses an power transfer switch having two sets of phase switches, one set for connection between a normal power source and a load and the other set fov connection between an emergency power source and the load. The transfer switch also includes two neutral switches, one for connection between the normal source neutral and the load neutral, and the other for connection between the emergency source neutral and the load neutral. Only one set of the phase switches can be closed at any one time, and during transfer of the load from one source to the other both sets of phase switches are open. Prior to a transfer operation, the neutral switch corresponding to the closed set of phase switches is closed and the neutral

switch corresponding to the open set of phase switches is open. During transfer of the load, both neutral switches are closed before the closed set of phase switches open and both neutral switches remain closed until after the closed set of phase switches open and the open set of phase switches close. Thereafter, the neutral switch, which had originally been open remains closed, and the neutral switch which had originally been closed opens.
[0005] But the provision of a separate phase results in another problem. Practically the opening and closing time of all phases during transformation will not be same. This can cause over voltage between phases that make a late contact. So the advanced neutral i.e. early make and late break in neutral conductor was introduced. However, during the transition between sources the neutral conductors of both sources are open for some time. If arc re-strikes in any one of the phases during this time, overvoltage occurs and it may damage the system. [0006] This problem is overcome in U.S. Patent No.5070252 assigned to Power Switch Company wherein an power transfer switch having two sets of phase switches, one set for connection between a normal source of power and a load, and the other set for connection between an emergency power source and the load is shown and described. The transfer switch includes two pairs of neutral switches, one pair for connection in parallel between the normal source neutral and the load neutral, and the other pair for cotmection in parallel between the emergency source neutral and the load neutral. The phase switches can operate to provide either an "open transition" transfer or a "closed transition" transfer. Prior to transfer operation, the pair of neutral switches corresponding to the closed set of phase switches are closed and the pair of neutral switches corresponding to the open set of phase switches are open. During transfer of the load, whether by open or closed transhion transfer, one neutral switch of each pair are closed before the open set of phase switches close and those neutral switches remain closed until after the closed set of phase switches opens. Thereafter, the pair of neutral switches, which had originally been open, are both closed, and the pair of neutral switches which had originally been closed are both opened.

[0007] The transfer switch as disclosed in the switch provides an power transfer switch for a single break contact system with an advanced neutral mechanism. The single break transfer switches have complexed construction and increased size. Further, in single break transfer switches efficient contact cleaning is not achieved. [0008] Heretofore, many transfer switches have been unreliable for such reasons as overheating, complex construction, contact destruction due to arcing during normal operations, and susceptibility to contact damage during short circuit condition. Thus, there has been a need for a transfer switch that obviates many of the unreliable circumstances. Although U.S. Patent No. 4791255 assigned to Westinghouse Electric Corporation provides a double break transfer switch having a sliding contact for enabling transfer of power from the emergency and/or alternate power source, the need for a transfer switch with advanced neutral mechanism is desired,
SUMMARY OF THE INVENTION
[0009] One aspect of the invention includes a double break power transfer switch comprising a contact assembly and a power transfer mechanism. The contact assembly includes a movable pole contact housing having a first elongate slot and a movable neutral contact housing having a second elongate slot oriented substantially perpendicular to the first elongate slot wherein the movement of movable neutral contact housing is achieved subsequent to the completion of the movement of the movable pole contact housing. The contact assembly is co-ordinatingly coupled to the power transfer mechanism. Further, the power transfer mechanism includes a first link member having a first end coupled to a solenoid and a second end coupled to a second link member. The second link member has a first end rotatably supported on a pivot member and a second end configured to have an elongate pin member.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly

summarized above, may be had by reference to various embodiments, some of
which are illustrated in the appended drawings. It is to be noted, however, that the
appended drawings illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, for the invention may admit to
other equally effective embodiments.
[0010] FIG. 1 shows a double break power transfer switch according to an
embodiment of the invention,
[0011] FIG 2 shows a double break power transfer switch along with a contact
mechanism according to an embodiment of the invention.
[0012] FIG. 3 shows the contact position of the moving conductors of phase and
neutral of the primary source SI during initiation of transfer, according to an
embodiment of the invention.
[0013] FIG. 4 shows the initiation of movement of the moving contact alter the
linear disposition of the rotating secondary link along the slot, according to an
embodiment of the invention.
[0014] FIG. 5 shows the contact position of moving neutral conductors in relation
to fixed neutral conductors prior to transfer of power from either of the source to
the load, according to an embodiment of the invention.
[0015] FIG, 6 shows the mechanism by which the delay in transferring neutral
contacts is achieved, according to an embodiment of the invention,
[0016] FIG. 7 shows the relative positions of the moving neutral conductors at the
termination of transfer of power from one source to the other, according to an
embodiment of the invention.
[0017] FIG. 8 shows a schematic representation of relative contact positions of
moving conductors of phase and neutral during various stages of transfer of power
from either of the source to a load, according to an embodiment of the invention,
DETAILED DESCRIPTION OF INVENTION
[0018] Various embodiments of the invention provide a double break power transfer switch with an advanced neutral mechanism. FIG. 1 shows a double break power transfer switch according to an embodiment of the invention, A double

break power transfer switch for transferring power to a load from either a primary source of power S1 or a secondary source of power S2 includes a housing 1. A first pair of fixed conductors is disposed on proximal end of the housing for connecting to phase 11 and neutral 21 of primary source of power S1. A first pair of moving conductors moving phase conductor 31 and moving neutral conductor 41 are disposed in an opposing manner to first pair of fixed conductors. The moving phase conductor 31 and moving neutral conductor 41 are biased to establish connection with the phase 11 and neutral 21 of the primary source of power Si. A second pair of fixed conductors is disposed on distal end of the housing. The second pair of fixed conductors are configured to establish connecfion with the phase 12 and neutral 22 of a secondary source of power S2. Further, a second pair of moving conductors, namely a moving phase conductor 32 and a moving neutral conductor 42 are disposed in an opposing manner to second pair of fixed conductors 12 and 22.
[0019] The double break power transfer switch also includes at least two pairs of fixed conductors disposed on opposite end of the housing. The first conductor of each of the pair, namely, Lll and L12 are connected to phase of the load corresponding to the primary source SI and the secondary source S2 respecfively. The second conductor of each of the pair, namely, L2I and L22 are connected to the neutral of the load corresponding to the primary source SI and the secondary source S2. At least two pairs of moving conductors is disposed in in opposing manner to the two pairs of fixed conductors of the load to establish connection with each of the phase and neutral of the load corresponding to the primary and secondary source of power.
[0020] FIG. 2 shows the contact assembly along with the power transfer mechanism incorporated into a double break power transfer switch according to an embodiment of the invention. The power transfer mechanism includes a first link member 3 having a first end and a second end. The first end is coupled to a solenoid 2 and the second end coupled to a second link member 4. Th;. second link member 4 has a first end rotatably supported on a pivot member 5 and a second end configured having an elongate pin member 13. An user operable power

transfer switch 10 is connected to the solenoid 2. The contact assembly includes a movable pole contact housing 6 having a first elongate slot 7 and a movable neutral contact housing 8 having a second elongate slot 9 oriented substantially perpendicular to the first elongate slot 7. The movable pole contact housing has a plurality of pole conductors mounted to establish contact with the fixed pole conductors. The elongated pin member 13 is slidingly engaged to the first elongated slot 7 and the second elongate slot 9;
[0021] A plurality of energizing members 15 are connected to the movable pole contact housing 6 and the movable neutral contact housing 8. In an example of the invention, the energizing members can be a spring. Each of spring is being coupled with one of the moving conductor for rotating the secondary link 4 between a first desired position and a second desired position. The movable pole contact housing 6 is provided with an elongated slot 6 to engage the secondary link 4 for linear disposition.
[0022] FIG. I shows a double break power transfer switch according to an embodiment of the invenfion. During the initial position of the power traiisfer switch, the load connected initially with source SI. Fixed conductor 11 of source S1 is connected with fixed conductor of load L11 through moving conductor of the phase 31. Neutral of the load L21 is connected with the neutral conductor 21 through moving conductor of the neutral conductor 41. Rotating secondary link 4 is at maximum position. Source SI is supplying power to the load L. [0023] FIG. 3 shows the contact position of the moving conductors of phase and neutral of the primary source SI during initiation of transfer, according to an embodiment of the invention. The primary link 4 is made to rotate. This drawing shows that neutral moving conductor 41 is not moving whereas the moving conductor 31 starts. FIG, 4 shows the initiation of movement of the moving contact after the linear disposition of the rotating secondary link 4 along the slot, according to an embodiment of the invention. At this position of the secondary link 4, neutral moving conductor 42 is closed.
[0024] FIG. 5 shows the contact position of moving neutral conductors in relation to fixed neutral conductors prior to transfer of power from either of the sourc;e lo

the load, according to an embodiment of the invention. The neutral moving conductor 42 is closed with neutral fixed conductor of neutral 22 and neutral moving conductor 41 is also in contact with neutral fixed conductor 21. But both the sources SI and S2 are not connected with load L in this stage. This avoids the problem of overvoltage raise due to incomplete quenching of arc at any one of the poles.
[0025] FIG. 6 shows that the moving conductor of phase 32 starts to make contact with fixed conductor of phase 12 of source 2, whereas the neutral moving conductor 41 tends to open from fixed neutral conductor 21, but both of the neutral conductors 41 and 42 are still in contact with their respecfive neutral fixed conductors of their respective sources. Now the phase moving conductor 31 is fully opened from fixed phase conductor 11.
[0026] FIG 7 shows the relative positions of the moving neutral conductors at the terminafion of transfer of power from one source to the other, according to an embodiment of the invention. The fixed conductor 12 is connected with load L through moving phase conductor 32 and the neutral fixed conductor 22 is connected fully with load neutral conductor L by moving neutral conductor 42. Now both phase and neutral conductors of source 1 is opened and load is totally transferred from source I to source 2 successfirlly.
[0027] Figure 8 shows a schematic representation of relative contact positions of moving conductors of phase and neutral during various stages of transfer of power from either of the source to a load, according to an embodiment of the invention FIG 8a. shows the initial condition of the ATS. Load is connected with source 1 through fixed contact (11) and Moving contact (31) and load neutral is connected with the source 1 through fixed neutral contact (21) and Movable Contact (41). FIG. 8b shows source 1 is open but neutral conductor (41) of the source I is not open, at the same time neutral (42) of is closed. FIG. 8c shows that the phase conductor (32) of source 2 lends to close and at the same time both the source neutral conductors (41) and (42) are still closed. FIG. 8d shows that phase conductor (32) is connected with the load and both of the neutral conductors (41)

and (42) are still closed. FIG. 8e shows that after closing the phase conductor (32), the neutral conductor 41 is opened.
[0028] In an aUemate embodiment of the system, a double break power transfer switch includes a contact mechanism wherein the pole conductors and neutral conductors are sliding type conductors.
Industrial applicability:
[0029] FIG 1 - 8 generally refers to a double break power transfer switch according to an embodiment of an invention. Initially load is connected with source SI. Fixed conductor 11 of source SI is connected with fixed conductor of load LI I through moving conductor of the phase 31. Neutral of the load L21 is connected with the neutral conductor 21 through moving conductor of the neutral conductor 41. Rotating secondary link 5 is at maximum position. Source SI is supplying power to the load L. Rotating secondary link 5 is made to rotate. This drawing shows that neutral moving conductor 41 is not moving whereas the moving conductor 31 starts after which the neutral moving conductor holder 8 starts to move. The neutral moving conductor 42 is closed with neutral fixed conductor of neutral 22 and neutral moving conductor 41 is also in contact with neutral fixed conductor 21. But both the sources (SI & S2) are not connected with load L in this stage. This avoids the problem of overvoltage raise due to incomplete quenching of arc at any one of the phases. The moving conductor of phase 32 starts to make contact with fixed conductor of phase 12 of source 2, whereas the neutral moving conductor 41 tends to open from fixed neutral conductor 21. but both of the neutral conductors 41 and 42 are still in contact with their respective neutral fixed conductors of their respective sources. Now the phase moving conductor 31 is fully opened from fixed phase conductor II. The fixed conductor 12 is connected with load L through moving phase conductor 32 and neutral l"ixcd conductor 22 is connected fully with load neutral conductor L by moving neutral conductor 42. Now both phase and neutral conductors of source 1 is opened and load is totally transferred from source 1 to source 2 successftilly.

[0030] The advanced neutral is achieved by making slot in the moving contact housing 7 (refer FlG.l). During the switching the neutral conductors of ATS is in contact with the neutral of the source supplying power, though the main contacts are open. In this invention neutral contacts of both the sources are in closed condition during the transition between sources. Due to movemenl o!' the rotating secondary link, phase conductors tend to make contact with another source, at this time the neutral of the source which is supplying power, is starts to open. Hence, the load (system) is always connected with neutral.
[0031] The invention provides a double break power transfer switch which includes a contact assembly and power transfer mechanism. The contact assembly, includes a movable pole contact housing having a first elongate slot and a movable neutral contact housing having a second elongate slot oriented substantially perpendicular to the first elongate slot wherein the movement of movable neutral contact housing is achieved subsequent to the completion of the movement of the movable pole contact housing.
[0032] The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of me invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
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CLAIMS:
What is claimed is:
1. A double break power transfer switch comprising;
i. a contact assembly, including
a. a movable pole contact housing having a first elongate slot
and
b. a movable neutral contact housing having a second
elongate slot oriented substantially perpendicular to the first
elongate slot;
ii. the contact assembly co-ordinatingly coupled to a power transfer
mechanism; and iii. the power transfer mechanism including:
a) a first link member having a first end and a second end;
b) the first end coupled to a solenoid and the second end coupled to a second link member;
c) the second link member having a first end rotatably supported on a pivot member and a second end configured having an elongate pin member; and
d) the pin member slidingly engaged to the first and second elongate slots;

2. A double break power transfer switch according to claim 1, wherein movable neutral contact housing is configured for movement between a first desired position and a second desired position subsequent to compilation of the movement of the movable pole contact housing.
3. A double break power transfer switch according to claim 1, further including a plurality of energizing members coupled to the movable pole contact housing and the movable neutral contact housing, wherein the movement of the contact housings is against the energizing force of the energizing members.
4. A double break power transfer switch according to claim 1. wherein the pole conductor and neutral conductor is a button type conductor.
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5. A double break power transfer switch according to claim 1, wherein the pole conductor and neutral conductor is a sliding type conductor.
6. A contact assembly, including
i, a movable pole contact housing having a first elongate slot r.nd ii. a movable neutral contact housing having a second elongate slot,
characterized in that the first and second elongate slots are oriented
substantially perpendicular to each other.
7. A contact assembly according to claim 6, wherein a pin member of a power transfer mechanism slidingiy engages with the first and second elongate slots, wherein the movable neutral contact housing moves subsequent to the completion of movement of the movable pole contact housing.
8. A power transfer mechanism including
i. a first link member having a first and a second end; ii. the first end coupled to a solenoid and the second end coupled to a
second link member: and iii. the second link member having a first end rotatably supported on a pivot member and a second end configured having an elongate pin member.
9. A contact transfer mechanism according to claim 8, wherein the solenoid is
coupled to an user operable power transfer switch wherein *he solenoid
reciprocates in response to operation of the power transfer switch.
10. A contact transfer mechanism according to claim 8, wherein the first link
member is pivotally connected to a substantial central location of the second
link member.

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