FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Lockable close push button (LCPB] interlock with trip push button
2. APPLICANT(S)
(a) NAME : Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c)ADDRESS : L&T House, Ballard Estate, Mumbai-400 001, India.
3. PREAMBLE TO THE DESCRITION
COMPLETE
The following specification particularly describes the
invention and the manner in which it is to be performed
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble -"I/We claim" on separate page)
6. DATE AND SIGNATURE (to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on the separate page)
Note:
*Repeat boxes in case of more than one entry
*To be signed by the applicant(s)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and
country
*Strike out the column which is/are not applicable

Field of the invention
The invention generally relates to mechanical interlocking mechanism in air circuit breaker(ACB) which prevents unnecessary tripping of air circuit breaker and maintains continuous power supply.
Background of the invention
DC Supply at power plant is very critical as it feeds the turbine lubrication systems along with other functions. If there is discontinuity of supply for more than the recommended duration then it has cascading effect of tripping VFDs etc. which results into tripping of power plant and may damage the turbine. There is need to provide a mechanical interlock configuration designed such that, an 'ON' ACB cannot be tripped unless other tripped ACB is switched 'ON'. Trip push button is in defeated state when close push button is in locked condition.
During changeover operation all ACB's would remain 'ON'. There would be no discontinuity in the DC supply. The changeover operation for configuration of two I/C and one B/C is explained below. Operating Principal : For 2:I/Cs and 1 :B/C

Config. I/C :
1 B/C I/C :
2 I/C : 1 B/C I/C : 2
A 1 1 0
1 0 1
B 1 0 1
0 1 1
C 0 1 1
1 1 0
1 =ON
0 = OFF
Configuration: (A)

I/C:l B/C I/C: 2 Result
ON ON OFF - Key trapped Supply from I/C system 1 to the

ON
ON Press & remove key to switch 'ON' Changeover operation
ON ON ON I/C : 1 & I/C : 2 supply in parallel
ON Insert key & press trip PB. ON B/C is switched OFF
ON OFF - Key trapped ON Individual supply from I/C : 1 &2
Configuration: (B)

I/C:l B/C I/C: 2 Result
ON OFF - Key trapped ON Individual supply from I/C : 1 &2
ON
ON
Insert key & press trip PB. Press & remove key to switch 'ON'
ON ON ON ON ON Changeover operation
I/C : 1 & I/C : 2 supply in parallel
I/C : 1 is switched OFF
OFF - Key trapped ON ON Supply from I/C : 2 to the system
Configuration: (C)

I/C:l B/C I/C: 2 Result
OFF - Key trapped ON ON Supply from I/C system 2 to the

Press & remove key to switch 'ON' ON ON Changeover operation
ON ON ON I/C : 1 & I/C : 2 supply in parallel
ON ON Insert key & press trip PB. I/C : 2 is switched OFF
ON ON OFF - Key trapped Supply from I/C : 1 to the
system
Module type HD shall have key interlock with module type DC on both sections in such a way
that when switch HD is in open condition the key shall be trapped. On closing module HD the
key shall be released. Module type DC can only be opened on inserting the above key in any one
of the section.
Object of the invention
One object of the invention is to provide an anti-tripping mechanism for electrical devices which
will prevent tripping unless the alternative power supply is available thus maintain continuous
power supply.
Another object of the present invention is to provide a lockable close push button (LCPB)
interlock with trip push button which can be locked using key to maintain continuous supply.
Summary
An anti-tripping mechanism for electrical devices has a lockable type push switch having close button for inserting key on one surface and a threaded pin is connected on another surface of the -lockable type push switch. An anti-tripping lever mounted on the said threaded pin. Tripping mechanism of the electrical device having a tripping shaft connected to trip push button is mounted near anti-tripping mechanism at a distance not exceeding the length of the anti-tripping lever. The anti-tripping lever prevents the motion of the tripping pin when the electrical device is locked by close button.
Description of drawings
Figure 1 shows single line power distribution in power plant

Figure 2 shows air circuit breaker in open condition
Figure 3 shows air circuit breaker in closed condition
Figure 4(a) shows interlock assembly with key trapped in lock (ACB can be closed or tripped)
Figure 4(b) shows interlock assembly with key removed (ACB is closed. Trip function defeated)
Figure 4(c) shows Schematic diagram with key trapped in lock.
Components:
1: Threaded pin
2: Locakable type push switch/lock/button
3: Key
4 and 5: Nut/Nylo nut
Detailed description
The description of specific embodiments of the present invention has 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, 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 omission and substitutions of equivalents are contemplated as
circumstance may suggest or render expedient, but such are intended to cover the application or
implementation without departing from the spirit or scope of the present invention.
Some of the common terms used in the field of electrical devices are as follows:
LCPB Lockable Closed Push Burton
ACB Air circuit breaker
VFD Variable Frequency Drive
DC Direct Current
I/C Incomer
B/C Bus-coupler
PB Push button
ATL Anti tripping lever

To achieve above I/L, 3 number ACBs having Spring Charging Motor, Lockable Close PB with key trapped in ACB in Open Condition and released after Closing the ACB. The mechanical interlock within ACB is such that once the Key of Lockable Close PB is released, the Tripping function is disabled.
In Normal Operation both HD type Incomers are in closed condition with disabled Trip PB and DC Buscoupler is in open condition with lockable key trapped. In case any HD Incomer is required to be made Open, one needs to Close the DC Buscoupler first with the help of Close PB and take out the Key. The discharged Spring of DC Buscoupler would get charged with the help of Spring Charging Motor to keep it ready for next close Operation. This key is used in HD Incomer for enabling the operation of Trip PB and then the ACB is made Open.
In the above operation the supply of Bus-A & Bus-B would be paralleled till the 3rd ACB is made Open. The closing of any of the breaker will make the spring discharged, which shall be charged again automatically through the spring charging motor for making the ACB ready for next close operation.
Prior art design consisted of racking interlock on cradle where two ACB's would be maintained in 'ON: condition. This configuration had three locks and two keys. The ACB in which the key is trapped can be switched 'ON'. It was not possible to switch on the third ACB.
In the present invention, the lockable type switch along with key is mounted on front facia of the breaker in the section for close switch. Pin is connected to lockable type switch with nut. It can be a single nut or lock-nut arrangement. The pin can be fully threaded or partly threaded on either sides to have engagement with lockable type switch and ATL. The anti tripping lever is mounted on the pin with nuts on either side or one side depending upon the threading of pin. An anti-tripping mechanism for electrical devices has a lockable type push switch having close button for inserting key on one surface and a threaded pin is connected on another surface of the lockable type push switch. An anti-tripping lever mounted on the said threaded pin. Tripping mechanism of the electrical device having a tripping shaft connected to trip push button is

mounted near anti-tripping mechanism at a distance not exceeding the length of the anti-tripping lever. The anti-tripping lever prevents the motion of the tripping pin when the electrical device is locked by close button.

Claims:
1) An anti-tripping mechanism for electrical devices comprising;
a lockable type push switch having close button for inserting key on one surface and a threaded pin connected on another surface,
an anti-tripping lever mounted on the said threaded pin,
tripping mechanism of the electrical device having a tripping shaft connected to trip push
button and mounting the tripping mechanism near anti-tripping
mechanism at a distance not exceeding the length of the said anti-tripping lever
wherein the anti-tripping lever blocks the tripping shaft from actuating the trip mechanism in the case of accidental attempt of tripping.