Title of Invention

MECHANISM FOR SEALABILITY OF OVERLOAD RELAY IN OFF CONDITION

Abstract A mechanism for sealability of overload relay in off condition, the said mechanism comprising interrupter means (3 and 4) adapted for interrupting the flow of pick up current in the contactor coils through the normally close contact (1) of the relay and means (7) adapted for holding the said interrupter means (3) permanently in its depressed position interrupting the flow of pick up current in the contactor coils. The mechanism sealability mechanism can be sealed by any type of seal for sealing the slider (7) with the relay shroud (5).
Full Text FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION (See section 10; rule 13)

1.Title of the invention. -

MECHANISM FOR SEALABILITY OF OVERLOAD RELAY IN OFF CONDITION

2. Applicant
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : Indian Company
(e) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001, State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be
Performed: -
Field Of Invention
The present invention relates to a mechanism for sealability of overload relay. More particularly, it relates to a mechanism for sealability of overload relay in OFF condition adapted for safety during maintenance operation on motor starters by sealing the normally close contact of the relay in off condition thereby freezing the operation/pick-up of the coil of the contactors.
Background Art
As a safety feature during maintenance operations on the motor starters, it is extremely important to ensure that no one can inadvertently start the motor by pressing the ON push button.
In the known device, the normally closed (NC) contact of the overload protection device like an overload relay is connected in series with the contactor coil. In case of overloads, the normally closed contact opens thereby de-energizing the contactor coil and the contactor breaks the motor current. This NC contact can also be actuated by a push button (STOP) provided on the relay to stop the motor, or some cases to even reset the relay after it has tripped (STOP/ RESET). This stop pushbutton is spring-loaded and so when the push button is released, it comes back to the original position. So, when the stop button is pushed, it de-energizes the circuit by opening the normally closed contacts and when the push button is released the normally closed contacts close.
US 4219714 teaches a lock-off switch comprising a switch case, a trigger like slider and a lock plate rockably attached to the slider and engageable therewith in a locking position so as to prevent a pulling of the trigger like slider. A release shaft slidably penetrates into the switch case through one side thereof and is coupled to the lock plate by coupler member.
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EP 1376632 teaches a lockable switch mechanism for use in association with for example machine guards where a door of a machine must be secured in a locked condition until the guarded machine has stopped operating. A switch plunger is mounted in a housing and is displaceable relative to the housing along a predetermined axis between first and second positions. The switch plunger is displaced as a result of insertion of an actuator, which causes a cam to rotate from a datum position, rotation of the cam locking the actuator in engagement with the cam. A locking mechanism is provided for locking the switch plunger is provided with first locking member and second locking member. The second locking member in its locking position prevents movement of the switch plunger against which the first locking member is biased. Thus removal of the actuator is prevented unless the second locking member has been moved to the unlocked position by for example a solenoid, which is energized when guarded machine is in safe condition.
US 3604868 teaches a toggle switch designed to prevent accidental actuation wherein the switch may be locked against operation by pushing the toggle into the switch body and turning it through 90°. The mechanism by which the locking feature is obtained utilizes the toggle pivots and operating grooves normally found in toggle switches but adds a second set of grooves perpendicular to the normal operating grooves and into which the toggle pivots may be shifted to the conventional spring used for plunger pressure in a toggle switch serves to hold the toggle pivots in either set of grooves. Here means for locking the switch is by rotating the lever and this is for a single toggle switch comprising only one set of contacts. There is no arrangement for locking of more than one set of contacts. The sliding motion and arrangement is not present in US 3604868.
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US 5103107 teaches an electro magnetic switch in a starter motor having a
movable contact cooperating with normally open contact member and normally closed contact member and a part of a stationery contact in the normally closed contact member is formed into a locking piece to prevent the movable contact from contacting the passage formed in the cap of the switch or the electro magnetic switch has a first movable contact cooperating with normally open contact member and a second movable contact member cooperating with normally closed contact member and an insulating partition wall is disposed between the first and second movable contacts whereby the gripping distance between the normally open member and the normally closed contact member is increased as much and the occurrence of current leakage is prevented.
Thus there is need to provide for a mechanism for sealability of the overload relay in OFF condition that would give safety to the operator during maintenance operation and prevent inadvertently switching on the motor starter by actuation of the start button.
Objects Of Invention
The basic object of the present invention is to provide safety to operator from inadvertent starting of the motor during maintenance operation by sealing the normally close contact of the relay.
Another object of the present invention is to keep the normally closed contacts of the relay in permanently open conditions, till the maintenance operation is carried out.
The other object of the present invention is to provide sealing of the slider with the relay housing, thereby keeping the OFF push button in depressed condition
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Summary Of Invention
Thus according to the basic aspect of the present invention there is provided a mechanism for sealability of overload relay in off condition, the said mechanism comprising:
(i) interrupter means adapted for interrupting the flow of pick up
current in the contactor coils through the normally close contact of
the relay; and
(ii) means adapted for holding the said interrupter means permanently
in its depressed position interrupting the flow of pick up current in
the contactor coils.
According to another aspect of the present invention there is provided a mechanism adapted for sealability of overload relay, wherein further sealing can be provided by any type of seal for sealing the slider with the relay shroud.
Detailed Description Of Invention
In overload relay there are mainly two contacts i.e. the normally open (NO) contact and normally closed contact (NC). The normally closed contact incorporated in the relay device actuates the coil of the contactor. The normally close contact is actuated by the relay mechanism and also can be actuated by stop push button.
In the present invention mechanism adapted for sealability of overload relay
in OFF condition comprises means for interrupting the flow of pick up current to actuate the contactor coils through the normally close contact of relay. The said means for interrupting the flow of pick current comprises
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protrusion from stop push button, which locates the upper part of the
normally closed moving contact. The stop push button protrudes from the shroud comprising a cap-like profile on the outer surface of the housing of the relay. The stop push button being spring loaded returns to its original position. The said cap of the stop push button comprises grooved portion adapted for locating means to hold the stop push button in depressed position. The groove of the push button is so provided that it is able to accommodate the means to hold the stop push button.
The said means for holding the stop push button comprises slider, which is click-fitted on the shroud and is movable in vertical direction. The slider being operatively connected to the shroud such that when it is moved downwards with stop push button depressed, it locates the groove of the push button, thus locking the push button in the depressed condition adapted for providing discontinuity in the flow of coil actuating entity in the relay circuit. The protruded stop push button being so located that when the stop push is pushed, the center plane of the groove of the stop push button coincides with the center plane of the slider adapted for proper accommodation of the slider in the stop push button. During normal operation the slider allows the stop push button to be operated - to stop or reset the relay as and when required.
The stop button comprises protrusion adapted for locating the upper part of the contacts so that the normally close contacts open. The contactor coil being placed in series with these contacts keeps the contactor coil in de-energized condition adapted to prevent pick up of the contactor even if somebody pushes the start button.
The locking of the stop push button by the slider at the depressed position is adapted for operative transformation of the normally closed (NC) contact to
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normally open (NO) contact thus preventing unauthorized restarts of the
motor.
Further the slider comprises of hole, which is so located that the axis of it coincides with holes axis of the shroud and the transparent cover adapted for sealing the slider with the relay adapting a seal.
Brief description of accompanying figures
Figure 1 illustrates the relay NC contacts in the closed position.
Figure 2 illustrates the relay NC contacts in the open position by pressing stop push button.
Figure 3 illustrates the lay out profile of the stop push button in normal condition in the present invention.
Figure 4 illustrates the relay stop push button in pressed condition with the help of the slider in the present invention.
Detailed description of accompanying figures
In figure 1 the normally closed contacts of the relay in the closed position is illustrated. The normally closed contact (1) is adapted to actuate the coil of the contactor. The normally open contact (2) is not connected to the contactor coil. The stop push button (3) is operatively connected to the normally closed contact (1).
In figure 2 the normally closed contact of the relay in the open position is illustrated. In the figure the normally closed contact (1) is operatively connected to the stop push button (3) and with the movement of the stop
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push button (3) the connection between the normally closed contact (1) and the contactor coil is interrupted.
In figure 3 the lay out profile of the stop push button in normal condition of the present invention is illustrated. The cap (4) of the stop push button (3) protruding outside the shroud (5) comprises grooved portion (6) adapted for locating the upper part of the contacts and interrupt the flow of pick up current for the actuation of the relay for starting the motor. The slider (7) is click fitted on the shroud (5) of the relay.
In figure 4 the relay stop push button in pressed condition with the help of the slider of the present invention is illustrated. The stop push button (3) with protrusion of the cap (4) outside the shroud (5) is so located that on the outer surface of the housing (8) that when the stop push button (3) is pushed, the center plane of the groove (6) of the stop push button (3) coincides with the center plane of the slider (7). The slider (7) sits within the groove (6) in the cap (4) of the push button (3) adapted for providing locking to the stop push button (3) by not allowing it return back to its original position due to the action of the spring.
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WE CLAIM
1. A mechanism for sealability of overload relay in off condition, the said
mechanism comprising:
(i) interrupter means adapted for interrupting the flow of pick up
current in the contactor coils through the normally close contact of
the relay; and
(ii) means adapted for holding the said interrupter means permanently
in its depressed position interrupting the flow of pick up current in
the contactor coils.
2. Mechanism as claimed in claim 1, wherein interrupter means comprises stop push button protruding from the shroud forming a cap-like profile on the outer surface of the housing of the relay.
3. Mechanism as claimed in claim 2, wherein the cap of the stop push button comprises groove adapted for accommodating the slider when the stop push button is in depressed condition.
4. Mechanism as claimed in claims 1 to 3, wherein the stop push button comprising protrusion adapted for locating the upper part of the normally close contact, thereby operatively transforming the normally closed contact to open contact preventing unauthorized restarts of the motor.
5. Mechanism as claimed in claim 1, wherein the means adapted for holding the stop push button in depressed position comprises slider click fitted on the shroud of the relay housing.
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6. Mechanism as claimed in any preceding claims, wherein the
protrusion of the cap outside the shroud is so located that when the stop push button is pushed, the center plane of the groove of the stop push button coincides with the center plane of the slider adapted for proper accommodation of the slider in the stop push button.
7. Mechanism as claimed in any preceding claims adapted for sealability of overload relay with atleast one set of normally close contacts.
8. Mechanism adapted for sealability of overload relay, wherein further sealing is provided by a seal adapted for sealing the slider with the relay shroud.
9. Mechanism for sealability of overload relay substantially as herein described and illustrated with reference to the accompanying figures.
Dated this 19 th day of May, 2005.
Dr. Sanchita Ganguli
of S. Majumdar & Co.
Applicant's agent
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A B S T R A C T
Title : Mechanism For Sealability Of Overload Relay In Off Condition
A mechanism for sealability of overload relay in off condition, the said mechanism comprising interrupter means (3 and 4) adapted for interrupting the flow of pick up current in the contactor coils through the normally close contact (1) of the relay and means (7) adapted for holding the said interrupter means (3) permanently in its depressed position interrupting the flow of pick up current in the contactor coils. The mechanism sealability mechanism can be sealed by any type of seal for sealing the slider (7) with the relay shroud (5).
Figure 3

Documents:


Patent Number 249143
Indian Patent Application Number 614/MUM/2005
PG Journal Number 40/2011
Publication Date 07-Oct-2011
Grant Date 04-Oct-2011
Date of Filing 20-May-2005
Name of Patentee LARSEN & TOUBRO LIMITED
Applicant Address L & T House Ballard Estate, Mumbai 400 001
Inventors:
# Inventor's Name Inventor's Address
1 CHAUDHARI,Hemant Laxman Switchgear Design & Product Development Centre Larsen & Toubro Limited, Electrical Sector-(EBG), Powai Works (East),Gate No.7, Saki Vihar Road, Mumbai 400 072, Maharashtra State.
2 OCHANI,Deepak Mangharam Switchgear Design & Product Development Centre Larsen & Toubro Limited, Electrical Sector-(EBG), Powai Works (East),Gate No.7, Saki Vihar Road, Mumbai 400 072, Maharashtra State.
PCT International Classification Number H01H51/06 H01H51/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA