Patent CA-2255283-A1 (CA)
Inventor: CHISHOLM KEVIN
IPC: H02J9/04
Filed: 1998-12-11
Abstract: The transfer switch assembly typically transfers electrical loads from a normal electrical power source to an emergency electrical power source upon reduction or loss of normal power source voltage. It can also re-transfer the load to the normal power source when the normal voltage has been restored within acceptable limits. The transfer switch assembly can also be caused to operate in several modes. For example it can operate automatically in the manner described above, by providing a suitable control circuit of a type well known to those versed in the art. It can also be operated manually by means of an electrical interface. Furthermore, in the case of an electrical operator fault, the switch may be operated completely by manual means. The device includes a number of over-center spring mechanism type molded case electric switches disposed in horizontal alignment. The switches are each multi-pole switches and each includes a single operating handle of the reciprocating toggle type. The handle of each of the switches must travel a greater portion of the possible full length of travel in going from off toward on position in order to operate the contacts than the same handle has to when moving from on toward off position in order to operate the contacts. As a result, when both handles are operated simultaneously by a lever mechanism, the switch which was in on condition at the beginning of travel is moved to off condition before the switch which was in off condition at the beginning of travel moves far enough to actuate its mechanism to on condition. Accordingly, the initially closed switch is opened before the initially open switch is closed, thereby avoiding any possibility of an overlap condition in which both switches may be closed at the same time, which might cross connect the power sources, and would be an undesirable condition. The switches are supported on a generally planar supporting base by suitable means, such as by bolts extending through mounting holes, provided in the switch casing. A  bracket is mounted on the supporting base mid-way between the switch operating handles. This bracket serves to hold a shaft which carries the operating arm. The shaft is located at the centre between the switch operating handles and vertically on a line connecting the centre of the total switch handle travel. Another bracket supports a gear motor, the shaft of which is located horizontally in-line with the aforementioned shaft. The gear motor is an electric unidirectional type which does not incorporate any type of brake mechanism. A crank arm attached to the gear motor shaft holds a pin and sliding member.  This sliding member moves within the confines of an operating arm as the crank is rotated.  The operating arm pivots on the shaft previously mentioned, thus as the crank rotates an oscillating motion is imparted to the operating arm. Within this arm is incorporated a cantilever spring element, complete with friction reducing means, so as to impart a uniform application of force to the molded case switch operating handle. The spring element mentioned above, by virtue of its flexibility, also ensures that the switch operating handle is moved to the extreme limits of its travel, in both the on and off positions. Thus as the arm moves from one extreme to another, the switches are caused to operate. Limit switches are disposed in such a manner as to remove power from the gear motor at the extreme positions of the operating arm.     The switches are each of the type having an over-center spring mechanism which is of such a design that the handle of each of the switches must travel a greater portion of the possible full length of travel in going from off towards on position in order to operate the contacts than the same handle has to when moving from on towards off position in order to operate the contacts. As a result, when both handles are operated simultaneously by the mechanism described above, the switch which was in on condition at the beginning of travel is moved to off condition before the switch which was in off condition at the beginning of travel moves far enough to actuate its mechanism to on condition. Accordingly, the initially closed switch is opened before the initially open switch is closed, thereby avoiding any possibility of an overlap condition in which both switches may be closed at the same time, which might cross connect the power sources.  By virtue of the resiliency afforded by the mechanism described previously, the switches referred to in this invention can be of any type and grade classification, without special consideration for the overall strength of materials or degree of manufacturing tolerance utilized in these switching elements. This enables inexpensive, commonly available switching elements to be used in the embodiment, that may be vulnerable to failure in such modes as sensitivity to extreme over-extension of the switch handle, sensitivity to variations in production tolerance of the transfer switch actuating mechanism as a whole, wearing of internal mechanical components, pitting and wearing of the external handle of the switching element, and shock stress on the handle of the switching element caused by actuation. The front surface of the operating arm is completely enclosed with two covers.  The first cover is fixed in position, and serves to protect the switch actuating mechanism. The second cover is allowed to pivot about a point at its lower right corner, which permits it to be swung away to expose the pin slider. This cover is retained in the closed position by means of a retaining plate fixed to the left end of the first cover or by a suitable latch. When the second cover is opened, the pin slider may be removed from its confines in the crank and arm to permit the arm to be operated manually, thus actuating the switches to any desired condition. With the pin slider inserted in position and the cover closed, the pin slider is retained behind this cover and thus prevented from moving out of position while still able to move within the confines of the arm. Since the operating arm is supported on a central shaft attached to a bracket which in turn is supported on the generally planar support independently of the switches, it is possible to remove the switches in order to replace or repair them, merely by removing the operating arm shaft. Suitable control circuitry is provided to accomplish the desired operation to disconnect the power consuming apparatus from a first "normal" power source and then to connect it to an emergency or stand-by power source.