FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003 As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Double break circuit breaker
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Roy Deosharan, Crompton Greaves Limited, Global R&D Centre, Bhaskara, Kanjur Marg (East), Mumbai 400 042, Maharashtra, India and Kumar Roop, 683 Sector 8, R K Puram, New Delhi 110 022, India, both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed

FIELD OF THE INVENTION
The invention relates to a double break circuit breaker.
BACKGROUND OF THE INVENTION
Circuit breakers are protective electrical switching devices for connecting and disconnecting power supply. Under fault conditions, the circuit breakers trip and clear fault currents thereby preventing damage to electrical loads and accidents. There are various types of circuit breakers. Double break circuit breakers are generally high voltage capacity breakers and are used in power stations. They may be gas insulated breakers or vacuum breakers. SF6 gas (sulfur hexafluoride gas) is generally used in gas insulated circuit breakers.
A double break circuit breaker comprises a hollow porcelain perpendicular limb and a connector tank mounted at the top of the perpendicular limb. A pair of hollow porcelain side limbs extend from the opposite sides of the connector tank along a common axis. An interrupter is housed in each of the side limbs, a linkage and a passive insertion resistor (PIR) are housed in the connector tank and a drive rod is vertically reciprocally disposed in the perpendicular limb. The drive rod is connected to a spring operated drive mechanism at the lower end thereof. The linkage disposed in the connector tank comprises a pair of driver links and a pair of bell crank levers pivoted in the connector tank at their corners. One end of each of the driver links is pivoted to one end of each of the bell crank levers. The other end of each of the bell crank levers is pivoted to each of the moving electrodes of each of the moving contacts of each of the interrupters housed in each of the porcelain side limbs.

Responsive to compression and expansion of the spring of the drive mechanism, the drive rod reciprocates up and down in the perpendicular porcelain limb. During the up and down movements of the drive rod, the driver links move up and down with the drive rod and the bell crank levers rotate about their pivots and cause the moving electrodes to describe the forward and reverse strokes thereby closing and opening or tripping the contacts of the interrupters. The linear motion of the driver links is converted into rotary motion of the bell crank levers and the rotary motion of the bell crank levers is converted into linear motion of the moving electrodes. Due to rotation of the bell crank levers, average velocity or C2 speed of the moving electrodes reduces. As a result there is delay in tripping and closing the contacts of the interrupters. Delay in tripping the contacts is more critical as compared to delay in closing the contacts. Tripping delay may cause damage to the electrical loads and accidents. In order to avoid speed reduction of the moving electrodes and improve performance efficiency of the circuit breaker, spring force or energy is increased. Increase in the spring force or energy cause fatigue to the spring and reduces its life. Also increased spring energy introduces increased stresses in the linkage and in order to withstand the increased stresses the thickness of the components of the linkage has to be increased. This not only increases material cost of the linkage but also the mass inertia. Increased mass inertia also causes speed reduction.
In order to diffuse the stresses on the linkage, the size and volume of the connector tank is increased so to contain increased volume of gas. As a result, the cost of the connector tank increases. The connector tank comprises a bottom opening and a top opening along the same axis and a pair of side openings along the same axis. The bottom opening is aligned with the perpendicular limb. The side openings are aligned with the side limbs. The passive insertion

resistor is introduced in the connector tank through the top opening thereof. The connector tank also comprises a front opening and a back opening along the same axis. The connector tank further comprises a pair of pivots one pivot for one bell crank lever accessible through the front opening and the other pivot for the other bell crank lever accessible through the back opening. Because of the two pivots and front and back openings, the cost of fabrication of the connector tank further increases.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a double break circuit breaker comprising a hollow porcelain perpendicular limb, a connector tank mounted at the top of the perpendicular limb and a pair of hollow porcelain side limbs extending from opposite sides of the connector tank along a common axis, an interrupter housed in each of the side limbs, a linkage housed in the connector tank and a drive rod vertically reciprocally disposed in the perpendicular limb and connected to a spring operated drive mechanism at the lower end thereof, wherein the connector tank comprises a front opening, a bottom opening and a top opening along a common axis and a pair of side openings along a common axis, the common axis of the bottom and top openings and the common axis of the side openings intersecting with each other and the axis of the front opening passing through the point of intersection between the common axes of the bottom and top openings and the side openings, the bottom opening of the connector tank being aligned with the perpendicular limb and the side openings of the connector tank being aligned with the side limbs and wherein the linkage comprises a pair of straight driver links pivoted at the top of the drive rod at one ends thereof, a pair of straight driven links each having a straight perpendicular

portion projecting from the center thereof, one end of each of the driven links being pivoted to the other end of each of the driver links and the perpendicular portions of the driven links being pivoted on a common pivot provided in the connector tank at the inner side of the back wall thereof along the axis of the front opening and a pair of straight drive transmitter links one end of each of which is pivoted to the other end of each of the driven links and the other end of each of which is pivoted to each of the moving electrodes of each of the moving contacts of each of the interrupters in each of the porcelain side limbs.
The following is a detailed description of the invention with reference to the accompanying schematic drawings, in which:
Fig 1 is a partial elevation of a double break circuit breaker according to an embodiment of the invention;
Fig 2 is a partial crossectional view of the circuit breaker of Fig 1;
Fig 3 is a view of the linkage in the connector tank of the circuit breaker of Fig 1; and
Figs 4, 5 and 6 are plan view, front view and crossectional view of the connector tank of the circuit breaker of Fig 1.
The double break circuit breaker 1 as illustrated in Figs 1 to 6 of the accompanying drawings comprises a hollow porcelain perpendicular limb 2 and a connector tank 3 mounted at the top of

the perpendicular limb. A pair of hollow porcelain side limbs 4, 4 extend from opposite sides of the connector tank along a common axis. An interrupter 5 is housed in each of the side limbs. 6, 6 are moving electrodes of the moving contacts (not shown) of the interrupters located in the side limbs. 7 is a linkage housed in the connector tank. 8 is a drive rod vertically reciprocally disposed in the perpendicular limb and connected to a spring operated drive mechanism (not shown) at the lower end thereof. The spring operated drive mechanism has not been illustrated and described as such is not necessary for understanding the invention. The connector tank comprises a front opening 9 and a bottom opening 10 and a top opening 11 along a common axis. The connector tank also comprises a pair of side openings 12 and 13 along a common axis. The common axis of the top and bottom openings and common axis of the side openings intersect with each other. The axis of the front opening passes through the point of intersection between the common axes of the bottom and top openings and the side openings. The bottom opening of the connector tank is aligned with the perpendicular limb and the side openings of the connector tank are aligned with side limbs. A passive insertion resistor (not shown) is introduced in the connector tank 3 through the top opening 11 thereof.
The linkage comprises a pair of straight driver links 14, 14 pivoted (pivot 15) at the top of the drive rod at one ends thereof. Only one driver links is seen in Figs 2 and 3 as the other link is behind the one driver link. The linkage also comprises a pair of straight driven links 16,16 each having a straight perpendicular portion 17 projecting from the centre thereof. One end of each of the driven links is pivoted (pivot 18) to the other end of each of the driver links. The perpendicular portions of the driven links are pivoted on a common pivot 19 provided in the connector tank at the inner side of the back wall thereof along the axis of the front opening. The

linkage also comprises a pair of straight drive transmitting links 20, 20 one end of each of which is pivoted (pivot 21) to the other end of each of the driven links and the other end of each of which is pivoted (pivot 22) to each of the moving electrodes 6 of each of the moving contacts of each of the interrupters 5 in each of the porcelain side limbs.
The drive rod reciprocates in the perpendicular limb up and down responsive to compression and expansion of the spring of the drive mechanism in the usual manner. During upward and downward movements of the drive rod, the driver links, driven links and drive transmitter links translate linearly and cause the moving electrodes 6 to describe the forward and reverse strokes and close and open or trip the contacts of the interrupters. The perpendicular portions 17 of the driven links 16 rotate about the common pivot 19 to facilitate translation of the driven links. Since all the links describe linear or substantially linear motions, spring force required for moving the links is reduced and motion from one link to another link is transmitted without any delay and without any speed reduction. Therefore, closing and tripping of the contacts of the interrupters is without any delay and performance efficiency of the circuit breaker is improved. As spring force and energy required is reduced spring fatigue is reduced and the life of the spring is increased. Stresses introduced in the linkage are reduced and the links can be made of reduced thickness. As the links are of reduced thickness, the material cost of the links is reduced. Also mass inertia of the linkage is reduced thereby further improving the speed of the linkage and moving electrodes. As the stresses in the connector tank are reduced, the size and volume of the connector tank is reduced. As a result the volume of the gas in the connector tank is also reduced. Both the drive transmitter links are pivoted on the common pivot accessible from the top opening 11 of the connector tank 3. Therefore, the connector tank does not require an

opening at the back thereof. As a result of all this, the material and fabrication cost of the connector tank is reduced.
Comparative simulation studies were conducted using a conventional double break gas insulated circuit breaker and a gas insulated double break circuit breaker of the invention. Rating of the circuit breakers was selected to be 420 KV. Pressure of SF6 gas used in the connector tanks was selected to be 22 bars. Spring energy applied to move the drive rod and the linkage was selected to be 3 KJ. Average velocity or C2 speed of the moving electrodes of the interrupters in the case of the conventional circuit breaker was 6.244 m/s. Average velocity or C2 speed of the moving electrodes of the interrupters in the case of the circuit breaker of the invention was 6.814 m/s. Percentage of increase of average velocity in the case of the circuit breaker of the invention was 9.15% thereby reducing the spring force or spring energy requirement of the linkage by about 10%. The stresses introduced in the connector tank of the conventional circuit breaker were 582 MPa, whereas the stresses introduced in the connector tank of the circuit breaker of the invention was 140MPa. Mass of the connector tank in the case of the conventional circuit breaker was 67.97kg, volume of the connector tank was 25.17L and volume of SF6 gas in the tank was 67.59L. Mass of the connector tank of the circuit breaker of the invention was 51.5kg, volume of the connector tank was 19L and volume of SF6 gas in the tank was 42.9L. It is very quite evident from the comparative study that average velocity of the moving electrodes of the circuit breaker of the invention increased, weight and volume of the connector tank and volume of gas in the connector tank and stresses in the tank all were reduced.

We claim:
1. A double break circuit breaker comprising a hollow porcelain perpendicular limb, a connector tank mounted at the top of the perpendicular limb and a pair of hollow porcelain side limbs extending from opposite sides of the connector tank along a common axis, an interrupter housed in each of the side limbs, a linkage housed in the connector tank and a drive rod vertically reciprocally disposed in the perpendicular limb and connected to a spring operated drive mechanism at the lower end thereof, wherein the connector tank comprises a front opening, a bottom opening and a top opening along a common axis and a pair of side openings along a common axis, the common axis of the bottom and top openings and the common axis of the side openings intersecting with each other and the axis of the front opening passing through the point, of intersection between the common axes of the bottom and top openings and the side openings, the bottom opening of the connector tank being aligned with the perpendicular limb and the side openings of the connector tank being aligned with the side limbs and wherein the linkage comprises a pair of straight driver links pivoted at the top of the drive rod at one ends thereof, a pair of straight driven links each having a straight perpendicular portion projecting from the center thereof, one end of each of the driven links being pivoted to the other end of each of the driver links and the perpendicular portions of the driven links being pivoted on a common pivot provided in the connector tank along the axis of the front opening and a pair of straight drive transmitter links one end of each of which is pivoted to the other end of each of the driven links and the other end of each of which is pivoted to each of the moving electrodes of each of the moving contacts of each of the interrupters in each of the porcelain side limbs.
2. The double circuit breaker as claimed in claim 1, which is a gas insulated circuit breaker.

3. The circuit breaker as claimed in claim 1, which is a vacuum circuit breaker.