Claims:We claim:

1. An auxiliary trip device for under voltage and shunt release in a circuit breaker comprising:
a frame having a moving core and a fixed core configured therein;
a guide-pin being divided into longer body and shorter body by means of ridge configured thereon, the guide pin is capable of being fixed to the moving core by enclosing the longer body for use in the under-voltage condition and by enclosing shorter body for use in the shunt release, wherein the guide pin moves along with the moving core;
at least one compression spring arranged in-between the moving core and the fixed core for separating the moving core from the fixed core;
a bobbin configured outside of the moving core as a guide for the moving core; and
a coil accommodated in the bobbin, wherein upon applying rated voltage across the terminals of the coil, the electromagnetic force pulls the moving core towards the fixed core against the compression spring force,
wherein during the under-voltage condition, when the moving core encloses longer body of the guide pin, the compression spring force overrides the electromagnetic force and pushes the moving core out, aiding the tripping of the circuit breaker, and during the shunt release operation when the moving core encloses shorter body of the guide pin, the movement of the moving core towards the fixed core is converted to a pushing action on the other side of the ferromagnetic frame thereby providing a stroke for tripping the circuit breaker.

The auxiliary trip device of claim 1, wherein the frame is ferromagnetic frame for completing the magnetic flux path for the electromagnet.

3. The auxiliary trip device of claim 1, wherein the guide pin is non-magnetic pin.

4. The auxiliary trip device of claim 1, wherein ridge of the guide pin is placed closer to one end of the guide pin dividing it into longer and shorter body.

5. The auxiliary trip device of claim 1, wherein the coil is electromagnetic coil.

, Description:Field of the invention

The present invention relates to switchgear applications and more particularly to moulded case circuit breaker and air circuit breakers having internal auxiliary trip device for UV & shunt release.

Background of the invention

An under-voltage (UV) release is used in a circuit breaker to offer protection against under voltage or zero voltage condition. The under voltage release trips the circuit breaker mechanism when voltage across terminals of the under voltage release falls below a predetermined value. Hence, the under voltage release goes along with the circuit breaker module as internal accessories.

A shunt release is used for electrical tripping of the circuit breaker by a control supply voltage, mainly for remote tripping. Both the under-voltage and the shunt release uses electromagnetic coil to provide the trip signal. In high rated moulded case circuit breaker and air circuit breakers, providing means to reset the under-voltage/shunt release from the circuit breaker mechanism is difficult. Such applications demands for self-resetting type under-voltage/shunt release with high force output. The size of the electromagnetic coil with continuous duty required to generate adequate trip force is larger. Considering space constraints in a circuit breaker, a compact electromagnetic coil to provide continuous duty hold-on force and same coil that can be used to generate high pick up force (to satisfy self-resetting) with intermittent duty is desirable. Further, having the space constraint in the circuit breaker module, separate mechanisms for UV release and shunt release cannot be provided.

US Patent No. 4641117 discloses a modified electronic trip unit actuator provides remote trip and undervoltage release function without impairing the actuator reliability. One embodiment replaces the permanent magnet of a flux shift trip unit actuator with an undervoltage release coil for undervoltage facility and a further embodiment uses the combination of a permanent magnet with a shunt trip coil for remote tripping function. However, the US Patent 4641117 uses permanent magnet and also it acts as FSD/Shunt or UV at the same time which is undesirable at times.

Another US Patent No. 5512720 discloses an auxiliary trip device for a circuit breaker which includes an electromechanical actuating device and an energy storage system. The electromechanical actuating device includes a coil housed in a sheath which has a central bore containing a plunger fixed to a push-rod, and a fixed core spaced apart from the plunger, via a first spring. The push-rod is slidable within the bore to actuate a latch device of the energy storage system, which in turn releases a blade which is cooperable with a trip bar of the circuit breaker on which the auxiliary trip device is placed. The blade is biased by a second spring which releases and stores energy greater than released and stored energy of the first spring. In US Patent No 5512720 if fixed core is assembled in first bore and plunger in second bore, then acts as a UV release and if position of the fixed core and the plunger reversed, then it acts as a shunt release. However, the construction and assembly of device disclosed above is not cost effective and complicated.

Accordingly, there exists a need to provide an auxiliary trip device for under voltage and shunt release in a circuit breaker, which overcomes abovementioned drawbacks.

Objects of the invention

An object of the present invention is to protect downstream devices from under-voltage condition or zero voltage conditions.

Another object of the present invention is to use common electromagnet for both shunt and under-voltage release in a circuit breaker.

Summary of the invention

Accordingly, the present invention provides an auxiliary trip device for under voltage release and shunt release in a circuit breaker. The auxiliary trip device comprises a frame having a moving core and a fixed core configured therein. The auxiliary trip device further comprises a guide-pin. The guide pin is divided into longer body and shorter body by means of ridge configured thereon. Specifically, the guide pin is capable of being fixed to the moving core by enclosing the longer body for use in the under-voltage condition and by enclosing shorter body for use in the shunt release. The guide pin moves along with the moving core.

The auxiliary trip device furthermore comprises at least one compression spring arranged in-between the moving core and the fixed core for separating the moving core from the fixed core. The auxiliary trip device moreover comprises a bobbin configured outside of the moving core as a guide for the moving core. The auxiliary trip device also comprises a coil accommodated in the bobbin, wherein upon applying rated voltage across the terminals of the coil, the electromagnetic force pulls the moving core towards the fixed core against the compression spring force.

During the under-voltage condition, when the moving core encloses longer body of the guide pin, the compression spring force overrides the electromagnetic force and pushes the moving core out, aiding the tripping of the circuit breaker.

Further, during the shunt release when the moving core encloses shorter body of the guide pin, the movement of the moving core towards the fixed core is converted to a pushing action on the other side of the ferromagnetic frame thereby providing a stroke for tripping the circuit breaker.

Brief description of the drawings

Figure 1 shows an auxiliary trip device for under voltage release in a circuit breaker, in accordance with the present invention;

Figure 2 shows an auxiliary trip device for shunt voltage release in a circuit breaker, in accordance with the present invention;

Figure 3 shows a schematic drawing of a guide-pin used in auxiliary trip device of figure 1 and 2;

Figure 4 shows a moving core and guide-pin sub assembly for UV release of figure 1; and

Figure 5 shows a moving core and guide-pin sub assembly for shunt release of figure 2.

Detailed description of the invention

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 embodiment. The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.

Referring to figures- 1-5, there is shown an auxiliary trip device for under voltage and shunt release in a circuit breaker (hereinafter “the auxiliary trip device (100)”).

The auxiliary trip device (100) comprises a frame (80). In an embodiment, the frame is a ferromagnetic frame which serves for completing the magnetic flux path for the electromagnet.

The auxiliary trip device (100) further includes a moving core (10) and a fixed core (20) configured within the frame (80).

The auxiliary trip device (100) furthermore comprises a guide-pin (30). The guide pin (30) is divided into a longer body (30a) and a shorter body (30b) by means of ridge (30c) configured thereon. Specifically, the ridge (30c) of the guide pin (30) is placed closer to one end of the guide pin (30) dividing it into the longer body (30a) and the shorter body (30b).

Specifically, the guide pin (30) is capable of being fixed to the moving core (10) by enclosing the longer body (30a) for use in the under-voltage release and by enclosing the shorter body (30b) for use in the shunt release. The guide pin (30) moves vertically along the moving core (10). In an embodiment, the guide-pin (30) is a stepped nonmagnetic pin as shown in figure 3.

The auxiliary trip device (100) furthermore comprises at least one compression spring (40) arranged in-between the moving core (10) and the fixed core (20) for separating the moving core from the fixed core.

The auxiliary trip device (100) moreover comprises a bobbin (50) configured outside of the moving core (10) as a guide for the moving core (10). The auxiliary trip device (100) also comprises a coil (60) accommodated in the bobbin (50). In an embodiment, the bobbin (50) is hollow cylindrical member configured around the moving core (10) for holding the coil (60) therein.

Upon applying rated voltage across the terminals of the coil (60), the electromagnetic force pulls the moving core (10) towards the fixed core (20) against the compression spring (40) force. Specifically, the coil (60) and the compression spring (40) of the present invention are optimized to work in the required band of operation of under-voltage and shunt release.

When the auxiliary trip device (100) is to be used as under-voltage release, the guide pin (30) is fixed to the moving core (10) with its longer body (30a) enclosed by the moving core (10) as shown in figure 4. During normal voltage condition, the moving core (10) is attracted to the fixed core (20) and remains in hold-on condition. During under-voltage condition, the compression spring (40) force overrides the electromagnetic force and pushes the moving core (10) out, aiding the tripping of the circuit breaker. Specifically, the reset and trip position of the under-voltage release of the auxiliary trip device (100) is shown in figure 1.

When the auxiliary trip device (100) is to be used the shunt release, the guide pin (30) is fixed to the moving core (10) with its shorter body (30b) enclosed by the moving core (10) as shown in figure 5. When voltage is applied, the movement of the moving core (10) towards the fixed core (20) is converted to a pushing action on the other side of the ferromagnetic frame (80) with the help of guide pin (30) and through hole of the fixed core (20).

Specifically, the length of the guide pin (30) is designed in such a way that the stroke available for tripping the circuit breaker is same in both cases i.e. for under voltage release and the shunt release. The position of the moving core (10) before and after the application of voltage is shown in figure 2.

In an embodiment, the auxiliary trip device (100) has to be mounted in an inverted fashion for it to act as shunt release.

The auxiliary trip device (100) is a compact electromagnet developed for under-voltage release and the same can be modified and used as shunt release, as described instead of designing separate electromagnets for under-voltage and shunt applications. No additional components are required for this modification.

Advantages of the invention

1. The auxiliary trip device (100) uses a common electromagnet for both shunt and under-voltage release.

2. No additional components are used for the auxiliary trip device (100) to act for under voltage release and the shunt release.

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 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 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.