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: A METHOD AND AN APPARATUS FOR
MEASUREMENT OF CONTACT LOADING FORCE IN A CIRCUIT
BREAKER
2. Applicant(s):
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) 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 THE INVENTION
The present invention relates to circuit breaker force measurement. More particularly, the invention is concerned about a method and an apparatus for direct measurement of contact loading force in a vacuum circuit breaker.
BACKGROUND OF THE INVENTION
Various known techniques have been used for measurement of contact loading force in a circuit breaker. For example in case of direct contact loading force mechanism, theoretically calculating force based on spring characteristics like spring constant, spring compression has been used. In designs where linkages are used to take the mechanical advantage, linkage ration has to be considered also for mechanism forces losses needs to be considered and calculated. To validate these calculations, contact loading springs are required to be tested separately to cross check the actually exerted force for a given compression limit.
For measurement of contact loading force various techniques are used for example in case of direct contact loading force mechanism, theoretically calculating the force based on spring characteristics like spring constant, spring compression. In designs where linkages are used to take the mechanical advantage, linkage ration has to be considered also for mechanism forces losses needs to be considered & calculated. To validate these calculations, contact loading springs are required to be tested separately to cross check the actually exerted force for a given compression limit.
In the above mentioned methods, the disadvantages are such that losses in the mechanism are not practically verified or displayed and the mechanism involves component level and product level verifications.

For measurement of contact loading force various techniques are used for example in case of direct contact loading force mechanism, theoretically calculating the force based on spring characteristics like spring constant, spring compression. In designs where linkages are used to take the mechanical advantage, linkage ration has to be considered also for mechanism forces losses needs to be considered & calculated. To validate these calculations, contact loading springs are required to be tested separately to cross check the actually exerted force for a given compression limit.
In the above mentioned methods, losses in the mechanism are not practically verified or displayed and is involves component level & product level verifications.
Thus, there is a need to overcome the problems of the prior art. Therefore, present inventors have developed a method and an apparatus for measurement of contact loading force in a circuit breaker. In which, a direct contact loading force measurement is done easily and it is not required to test the contact loading springs separately for checking individual spring characteristics.
OBJECTS OF THE INVENTION
An object of the present invention is to overcome the problems/disadvantages of the prior art.
Another object of the present invention is to provide a method for measurement of contact loading force in a circuit breaker.
Another object of the present invention is to provide an apparatus for measurement of contact loading force in a circuit breaker
These and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawing(s):
Figure J illustrates an apparatus for measurement of contact loading force. Figure 2 illustrates simulated vacuum interrupter.
SUMMARY OF THE INVENTION
According to one of the aspect of the present invention there is provided an apparatus
for direct measurement of contact loading force in a vacuum circuit breaker(VCB),
said apparatus comprising :
plurality of spring;
plurality of simulated vacuum interrupter, said interrupter comprising :
mounting stem;
a main contact means comprising :
a fixed contact connected with said mounting stem;
a moving contact connected with said moving electrode;
a moving electrode operatively connected with said spring;
plurality of balloon placed on said electrode for its movement; and
a load cell placed between said fixed and moving contact adapted for load
measurement;
a digital load indicator operatively connected with said load cell;
wherein said circuit breaker is close said moving contact is pressed against fixed
contact such that said spring gets compressed and exerting force on said main contact

means so that said force is measured by said load cell and said force is transferred from said load cell to digital load indicator.
According to another aspect of the p[resent invention there is provided a method for
direct measurement of contact loading force in a vacuum circuit breaker(VCB), said
method comprising steps of:
closing of said VCB;
opposite movement of the moving contact from the fixed contact;
compression of spring due to the operative connection of said moving contact with
said spring;
exerting force on said fixed and moving contact;
measuring of force by a load cell; and
transferring of measured force from said load cell to a digital load indicator.
displaying the measured force through digital load indicator.
DETAILED DESCRIPTION OF THE INVENTION
An apparatus is developed with a load cell and simulated Vacuum Interrupter Tube, which is having similar moving mass as of the actual Vacuum Circuit Breaker. This apparatus is fixed in place of original vacuum Interrupter Tube and typical vacuum circuit breaker settings are done for contact gap & contact loading spring. When vacuum circuit breaker (VCB) is given close command, main contacts close against each other and contact loading spring gets compressed exerting force on the main contacts. This exerted force is measured by the load cell arrangement and which in turn is transferred to the digital display on the meter.
Present invention practically checks the contact loading force in actual condition & do not depend only on theoretical calculation. It uses a load cell assembly for conversion & display of measured force value.

Compression Type Load Cell is used for the force measurement & is kept in between the main contacts of the simulated Vacuum Interrupter device. On closing of the VCB, moving contact is pressed against fixed contact, the force is exerted by the contact loading spring, and magnitude of the force exerted depends on the spring characteristics and corresponding compression length.
Generally, Contact loading springs are compression Type.
A mechanical linkage is used to operate the Vacuum Interrupter moving stem. Location of these contact loading spring is either (a) Vacuum Interrupter side second end of the linkage or (b) other side of the Vacuum Interrupter (mechanism side of the linkage).
Theoretical formula used for force calculation is as below
(a) Contact loading spring at Vacuum Interrupter side
Contact Loading force = (Free Length - Compression Length) x Spring Constant
(b) Contact loading spring at mechanism side
Contact Loading force = (Free Length - Compression Length) x Spring Constant x Linkage Ration
According to one of the embodiment of the present invention there is provided an apparatus for direct measurement of contact loading force in a vacuum circuit breaker (VCB). The apparatus comprising plurality of spring; plurality of simulated vacuum interrupter, a digital load indicator operatively connected with the load cell;
The interrupter comprising mounting stem; a main contact means comprising a fixed contact connected with the mounting stem and a moving contact connected with the

moving electrode; a moving electrode operatively connected with the spring; plurality of balloon placed on the electrode for its movement; and a load cell placed between the fixed and moving contact adapted for load measurement;
The circuit breaker is close the moving contact is pressed against fixed contact such that the spring gets compressed and exerting force on the main contact means so that the force is measured by the load cell and the force is transferred from the load cell to digital load indicator.
The mounting stem is fixed. The spring is compression spring. The load cell is compression type.
According to the second embodiment of the present invention there is provided a
method for direct measurement of contact loading force in a vacuum circuit
breaker(VCB), the method comprising steps of:
closing of the VCB;
opposite movement of the moving contact from the fixed contact;
compression of spring due to the operative connection of the moving contact with the
spring;
exerting force on the fixed and moving contact;
measuring of force by a load cell; and
transferring of measured force from the load cell to a digital load indicator.
displaying the measured force through digital load indicator.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to a preferred embodiment of the invention, there is provided an apparatus for measurement of contact loading force in a circuit breaker.

As shown in figure 1, an apparatus is developed with a load cell (2) and simulated Vacuum Interrupter Tube, which is having similar moving mass as of the actual Vacuum Circuit Breaker. This apparatus is fixed in place of original vacuum Interrupter Tube and typical vacuum circuit breaker settings are done for contact gap and contact loading spring. When vacuum circuit breaker is given close command, main contacts close against each other and contact loading spring (4) gets compressed exerting force on the main contacts. This exerted force is measured by the load cell (2) arrangement and which in turn is transferred to the digital display on the meter
(3).
Load cell is kept between fix & moving contact of simulated vacuum interrupter as
shown in figure & it is connected through a measurement cable & a data connector to
digital display unit.
Contact loading force was measured with
■ Springs having different loading force
■ Mechanical link with different ratios
These measurements were done to verify accuracy of the results & were cross
checked with traditional measurement method & found ok.
According to the invention there is provided a method for measurement of contact
loading force in a circuit breaker. The method doesn't require a separate testing of
spring assembly. It avoids calculation errors and mechanism losses are automatically
considered.
ADVANTAGES OF THE INVENTION
• Avoids calculation errors
• Avoids separate spring testing for force measurement & reduces man fatigue
• Mechanism losses are automatically considered

• Faster, accurate & reliable results are achieved for measurement of contact loading force.
• As this method does not require theoretical verification of the load & the linkage calculation, it avoids the calculation errors for load measurement.
• Does not require to check the springs separately.
• Design work involved in the invention
• V1 equivalent apparatus developed simulating the moving mass & contact structure
• Load cell is used with a fixing arrangement between contacts for direct force measurement.
• Present invention gives more accurate values as compared to theoretical calculations
The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.

WE CLAIM
1. An apparatus for direct measurement of contact loading force in a vacuum circuit breaker(VCB), said apparatus comprising : plurality of spring; plurality of simulated vacuum interrupter, said interrupter comprising:
mounting stem;
a main contact means comprising :
a fixed contact connected with said mounting stem; a moving contact connected with said moving electrode;
a moving electrode operatively connected with said spring;
plurality of balloon placed on said electrode for its movement; and
a load cell placed between said fixed and moving contact adapted for load measurement;
a digital load indicator operatively connected with said load cell; wherein said circuit breaker is in closed position, said moving contact is pressed against fixed contact such that said spring gets compressed and exerting force on said main contact means so that said force is measured by said load cell and said force is transferred from said load cell to digital load indicator.
2. Apparatus as claimed in claim 1 wherein said mounting stem is fixed.
3. Apparatus as claimed in claim 1 wherein said spring is compression spring.
4. Apparatus as claimed in claim 1 wherein said load cell is compression type.
5. A method for direct measurement of contact loading force in a vacuum circuit breaker(VCB), said method comprising steps of:

closing of said VCB;
opposite movement of the moving contact from the fixed contact;
compression of spring due to the operative connection of said moving contact
with said spring;
exerting force on said fixed and moving contact;
measuring of force by a load cell; and
transferring of measured force from said load cell to a digital load indicator.
displaying the measured force through digital load indicator.