FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
SPRING DISCHARGE MECHANISM FOR CIRCUIT BREAKERS;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF THE INVENTION
The invention relates to circuit breakers, and more particularly to a spring discharge mechanism for withdraw-able circuit breakers. BACKGROUND OF THE INVENTION
A circuit breaker is a switch that automatically interrupts flow of electrical current when the rated current is exceeded due to an electrical overload or fault. Typically, a circuit breaker comprises a housing, contacts enclosed within the housing, an operating mechanism to operate the contacts, and an arc chute.
The operating mechanism of a circuit breaker primarily consists of two springs, a main spring (or a closing spring) and an opening spring (or a return spring). The main spring is used for closing operation, wherein the spring is held in a charged condition by a closing (atch. On releasing the closing latch, the spring releases energy, and this turns ON the circuit breaker. The closing spring generates required driving force to close the circuit breaker and charge the opening spring, and energy needed for the vital opening operation is stored in the opening spring when the circuit breaker is in closed position.
Based upon their construction, circuit breakers are broadly categorized as fixed circuit breakers and withdraw-able circuit breakers. A withdraw-able circuit breaker has a breaker (withdraw-able part) mounted inside a cradle (fixed part). The breaker can be racked in and racked out for connecting, testing, disconnecting, or for maintenance. When the circuit breaker is racked out for maintenance, circuit breaker is switched OFF and contacts are separated. However, switching OFF the circuit breaker doesn't ensure discharging of the charged spring. Accidental discharge of charged spring poses a great risk to the operator and can also severely damage the circuit breaker and surrounding equipments.

In view of the above, there is a need to prevent accidental discharge of charged spring of a circuit breaker. SUMMARY OF THE INVENTION
Accordingly the present invention in one aspect provides a system for automatic discharge of a charged spring of a withdraw-able circuit breaker in a maintenance position, the system comprising a racking mechanism, the racking mechanism racks out the circuit breaker to the maintenance position, the circuit breaker in maintenance position is in OFF condition and the spring is in charged condition; and a spring discharge mechanism includes a control circuit, the control circuit comprising an under-voltage release, a closing release and a shunt release, wherein the control circuit receives supply from a disconnected secondary isolated contact and the common terminal of the circuit breaker, the supply drives the closing release to switch ON the circuit breaker triggering the shunt release to trip a switch switching OFF the circuit breaker thereby discharging the charged spring.
In one another aspect, the present invention provides a spring discharge mechanism capable of being retrofitted to existing circuit breakers.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a withdraw-able circuit breaker in accordance with an embodiment of the
invention, where
Figure 1A is a withdraw-able circuit breaker in connected position in accordance
with an embodiment of the invention;

Figure 1B is a withdraw-able circuit breaker racket out in maintenance position in accordance with an embodiment of the invention.
Figure 2 shows interface of breaker and cradle in accordance with an embodiment of the invention.
Figure 3 shows interface of breaker and cradle illustrating position of racking shutter and racking interlock where,
Figure 3A shows the racking shutter in a closed position and the racking interlock in a first position in accordance with an embodiment of the invention.
Figure 3B shows the racking shutter in an open position and the racking interlock in a second position in accordance with an embodiment of the invention. Figure 4 shows a control circuit for spring discharge in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the present invention provide a system for automatic discharge of a charged spring of a withdraw-able circuit breaker in a maintenance position, the system comprising a racking mechanism, the racking mechanism racks out the circuit breaker to the maintenance position, the circuit breaker in maintenance position is in OFF condition and the spring is in charged condition; and a spring discharge mechanism includes a control circuit, the control circuit comprising an under-voltage release, a closing release and a shunt release, wherein the control circuit receives supply from a disconnected secondary isolated contact and a common terminal of the circuit breaker, wherein the supply drives the closing release to switch ON the circuit breaker triggering the shunt release to trip a switch switching OFF the circuit breaker thereby discharging the charged spring.
Figure 1A and figure 1B show a withdraw-able circuit breaker 100, in accordance with an embodiment of the invention. Withdraw-able circuit breaker 100 has a breaker 102 mounted inside a cradle 104, wherein breaker can be 'racked in' as shown in figure 1A and 'racked out' as shown in figure 1B. Accordingly, breaker 102 can take three positions in cradle 104 i.e. a connected position, a test position, and a disconnected position, and then, a maintenance position, wherein the breaker is lifted from the cradle for maintenance.
The present invention provides a system for automatic discharge of a charged spring of such a circuit breaker. In an embodiment of the invention, the system for automatic discharge of a charged spring includes a racking mechanism and a spring discharge mechanism (as shown in figure 4).
Figure 2 through figure 3 shows racking mechanism of the circuit breaker. Racking mechanism enables breaker to be 'racked in' and 'racked out of cradle. Racking mechanism includes a racking shutter 106, a racking interlock 108, a tripping link 110 coupled to racking interlock 108 and a racking handle (not shown).

Racking shutter 106 is capable of moving between a closed position as shown in figure 3A and an open position 3B. Racking shutter 106 is moved to the open position, once circuit breaker is in OFF condition.
Racking interlock 108 is provided between racking shutter 106 and a breaker contact. Racking interlock 108 is capable of moving between a first position as shown in figure 3A and a second position as shown in figure 3B depending on position of racking shutter 106. Racking interlock prevents racking of circuit breaker when the racking shutter 106 is closed. Advantageously, racking shutter 106 and racking interlock 108 prevents accidental racking of circuit breaker 100.
In an embodiment of the invention, to 'rack out' circuit breaker, the racking handle is inserted through racking shutter 106, wherein the racking shutter 106 is in the open position and the racking interlock 108 is in the second position as shown in figure 3B, allowing the racking handle to be rotated thereby racking the breaker out of the cradle.
In an embodiment of the invention, the spring discharge mechanism includes a control circuit 400 as shown in figure 4. Control circuit 400 as shown in figure 4 includes accessories such as an under-voltage release 402, a closing release 404, a shunt release 406 and control supply terminals 408, wherein control supply terminals 408 provides supply through secondary isolated contacts to the accessories when the breaker is in connected position.
In an embodiment of the invention, control circuit is activated in the maintenance position to discharge the spring. In this regard, once contacts are separated, racking handle is withdrawn and panel door of the circuit breaker is opened, control circuit 400 is activated. However during maintenance position since breaker is lifted from cradle 104, no supply is available to the breaker 102. In an embodiment of the invention, during maintenance position control circuit 400 receives supply from a disconnected secondary isolated contact and a common terminal 410 of the circuit breaker as shown in figure 4.

In an embodiment of the invention, control circuit 400 on receiving supply from disconnected secondary isolated contact and common terminal 410 of the circuit breaker drives the closing release 404 to switch ON the circuit breaker triggering shunt release 406 to trip a switch 412, switching OFF the circuit breaker thereby discharging the charged spring.
Advantageously, the spring discharge mechanism discharges the spring, allowing safe transition from disconnected position to a hazard-free maintenance operation.
In an embodiment of the invention, the system for automatic spring discharge further comprises of a spring charge indicator 414 for indicating a charge or discharge condition of the spring.
In an embodiment of the invention, the system for automatic spring discharge further comprises of a ready to close micro switch, the ready to close micro switch allows the circuit breaker to close only if all necessary operating conditions are in normal condition.
In an embodiment of the invention, the accessories of the control circuit in connected and test position perform their normal functions.
In an embodiment, the present invention provides a spring discharge mechanism capable of being retrofitted to existing circuit breakers without major modifications to the circuit breakers for automatic discharge of the charged spring when a withdraw-able circuit breaker is racked out for maintenance.
Advantageously, the spring discharge mechanism of the present invention provides:
Automatic discharge of charged spring during rack out operation.
Adaptability to existing circuit breakers.
Use of existing accessories without affecting their desired function.
Safety to the operator, circuit breaker and surrounding equipment.
Reduced stresses on the mechanism by having delay in closing & opening operation.
Discharge of spring with panel door closed, and further discharging of spring if manually
charged.

Higher mechanical life due to elimination of stresses (avoiding close-trip operation).
While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.

WE CLAIM:
1. A system for automatic discharge of a charged spring of a withdraw-able circuit breaker
in a maintenance position, the system comprising:
a racking mechanism, the racking mechanism racking out the circuit breaker to the maintenance position, the circuit breaker being in an OFF condition and the spring being in charged condition; and
a spring discharge mechanism, the spring discharge mechanism having a control circuit, the control circuit comprising an under-voltage release, a closing release, and a shunt release,
wherein the control circuit receives supply from a disconnected secondary isolated contact, the supply driving the closing release to switch ON the circuit breaker and triggering the shunt release to trip a switch switching OFF the circuit breaker thereby discharging the charged spring.
2. The system as claimed in claim 1, wherein the switch is connected in series with the shunt release.
3. The system as claimed in claim 1 further comprises of a spring charge indicator for indicating a charge and discharge condition of the spring.
4. The system as claimed in claim 1 further comprises of a ready to close micro-switch.
5. The system as claimed in claim 1, wherein the spring discharge mechanism can be adapted to existing circuit breakers.
6. The system as claimed in claim 1, wherein the racking mechanism comprises:
a racking shutter capable of moving between an open position and closed position;

a racking interlock, the racking interlock being provided between the racking shutter and a breaker contact, the racking interlock capable of moving between a first and a second position depending upon position of the racking shutter;
a tripping link coupled to the racking interlock, and
a racking handle, the racking shutter in the open position allows the racking handle to be inserted into separate contacts of the circuit breaker, wherein when the handle is pulled out after racking the circuit breaker to the maintenance position, the spring discharge mechanism is activated.