Patent Application
20130140275
1. Field
The disclosed concept relates generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers. The disclosed concept also relates to trip mechanisms for electrical switching apparatus.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions as detected, for example, by a trip mechanism, such as a trip unit.
Latches are an important part of electrical switching apparatus, such as circuit breakers. A latch assembly typically includes three components: a pivotable D-shaft, a latch plate and a latch shaft. The latch plate and the latch shaft are suitably joined together and the latch plate rotates about a longitudinal axis of the latch shaft. The D-shaft blocks or allows movement of the latch plate through a D-shaft slot when in a corresponding suitable axial position as the D-shaft rotates on its longitudinal axis. The latch shaft and the D-shaft both rotate about their respective longitudinal axes, which are disposed a fixed distance apart. The latch assembly can only rotate when the D-shaft is suitably oriented to allow the latch plate to pass through the D-shaft slot. The D-shaft can include a number of arms for interface, for example, by a trip plunger of a trip solenoid that is energized in response to a trip condition, as detected by the trip unit.
During an interruption event, the trip latch load is increased during excessive current flow because of magnetic forces generated on the operating mechanism and the movable contact arms. These magnetic forces translate to the operating mechanism and create the need for relatively higher trip latch forces. For example, sometimes the contact carrier can begin to open prior to the trip unit tripping the circuit breaker. In other words, the magnetic forces lift the contact carrier and require an additional latch force to trip open the operating mechanism. As a result, during a relatively high fault current, the trip solenoid must either have sufficient operating force to operate the trip latch lever, or the desired trip might be delayed or inhibited, which would be completely undesirable.
There is room for improvement in electrical switching apparatus. There is also room for improvement in trip mechanisms for electrical switching apparatus.
These needs and others are met by embodiments of the disclosed concept where a trip member is disposed in an opening of a barrier of an arc chamber. During interruption of current flowing through separable contacts, pressure arising from an arc in the arc chamber pushes the trip member away from the barrier of the arc chamber to engage a trip latch and cause a trip mechanism to trip open the separable contacts.
In accordance with aspects of the disclosed concept, an electrical switching apparatus comprises: separable contacts; an operating mechanism structured to open and close the separable contacts; a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, the trip mechanism comprising a trip latch; an arc chamber operatively associated with the separable contacts, the arc chamber comprising a plurality of arc plates and a barrier disposed between the arc plates and the trip latch, the barrier having an opening therein; and a trip member disposed in or about the opening of the barrier of the arc chamber, wherein during interruption of current flowing through the separable contacts, pressure arising from an arc in the arc chamber pushes the trip member away from the barrier of the arc chamber to engage the trip latch and cause the trip mechanism to trip open the separable contacts.
The opening may be a cylindrical opening; the trip member may be a cylindrical piston slidably positioned within the cylindrical opening; and gas pressure may arise from the arc in the arc chamber and push the cylindrical piston along the cylindrical opening to engage the trip latch.
During flow of the current through the separable contacts, a mechanical load on the trip latch may increase from magnetic forces generated on the operating mechanism by the flow of the current; and the cylindrical piston may be structured to overcome the mechanical load.
The trip member may be a piston aligned with the trip latch; and the piston may include a spring structured to return the piston to a seated position within the opening of the barrier after interruption of the current flowing through the separable contacts.
As another aspect of the disclosed concept, a trip mechanism is for an electrical switching apparatus comprising separable contacts, an operating mechanism structured to open and close the separable contacts, and an arc chamber operatively associated with the separable contacts, the arc chamber comprising a plurality of arc plates and a barrier. The trip mechanism comprises: an opening in the barrier of the arc chamber; a trip latch, the barrier being disposed between the arc plates and the trip latch; and a trip member disposed in or about the opening in the barrier of the arc chamber, wherein the trip mechanism cooperates with the operating mechanism to trip open the separable contacts, and wherein during interruption of current flowing through the separable contacts, pressure arising from an arc in the arc chamber pushes the trip member away from the barrier of the arc chamber to engage the trip latch and cause the trip mechanism to trip open the separable contacts.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
The disclosed concept is described in association with a circuit breaker, although the disclosed concept is applicable to a wide range of electrical switching apparatus.
Referring to
As is conventional, the example circuit breaker 2 includes an operating mechanism 16 structured to open and close the separable contacts 10, and the trip mechanism 14 cooperating with the operating mechanism 16 to trip open the separable contacts 10. The trip mechanism 14 includes the trip latch lever 4. The arc chamber 6 is operatively associated with the separable contacts 10 and includes a plurality of arc plates (not shown, but see the arc chamber 62 and the plurality of arc plates 20 of
In accordance with aspects of the disclosed concept, the barrier 22 has the opening 12 therein and forms a cylindrically shaped port 24. The trip member 8, which can have, for example and without limitation, a shape resembling a piston, is disposed in the port 24. The trip member 8 is suitably aligned with the trip latch lever 4. During interruption of current flowing through the separable contacts 10, gas pressure 25 arising from the arc 11 in the arc chamber 6 pushes the trip member 8 away from the barrier 22 to engage the trip latch lever 4 and cause the trip mechanism 14 to trip open the separable contacts 10. Preferably, a spring (not shown, but see spring 26 of
As is also conventional, the trip mechanism 14 further includes a trip solenoid 28 and a trip circuit 30 structured to sense the current flowing through the separable contacts 10 and responsively energize the trip solenoid 28. The trip solenoid 28 includes a plunger 32 structured to engage the trip latch lever 4 and cause the trip mechanism 14 to trip open the separable contacts 10.
As shown in
During flow of current through the separable contacts 64, a mechanical load on the trip latch lever 52 increases from magnetic forces generated on operating mechanism 80 by the flow of the current. The trip member 54, as moved by the gas pressure arising from the arc in the arc chamber 62 against the force of the spring 26 (
The separable contacts 64 include a fixed contact 82 and a movable contact 84. The operating mechanism 80 includes a contact carrier 86 carrying the movable contact 84. Prior to interruption of the current flowing through the separable contacts 64, a magnetic force arising from the current lifts the contact carrier 86 and causes a mechanical load on the trip latch lever 52, which requires additional force from the trip member 54 to cause a trip mechanism 88, when released by the trip latch lever 52, to trip open the separable contacts 64.
A non-limiting example of a circuit breaker including a D-shaft, which can be rotated by the disclosed trip latch lever 52, and a latch mechanism is disclosed by U.S. Patent Application Publication No. 2011/0062006, which is incorporated by reference herein.
The disclosed arc pressure assisted trip members 8,54 preferably provide sufficient tripping force to independently ensure that the corresponding electrical switching apparatus 2,50 does trip.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof
