OF ON-LOAD TAP CHANGER

TECHNICAL FIELD

The spring-energy accumulator is used to realize the switching of the contact system of a power diverter switch for an on-load tap changer. The on-load tap changers are embedded in power transformers and used to regulate their high voltage under load, i.e. without interruption of the power supply to the consumers. BACKGROUND ART

There is a very wide variety of spring-energy accumulators for power diverter switches of on-load tap changers. They are used both in power diverter switches with arcing in transformer oil and in vacuum-arc cameras.

A spring energy storage device (1) is known, comprising two tensioning spring operating in tensile mode. One nozzle of these springs is connected to the end of a lever mounted on a bush located along the axis of a power diverter switch. The other end is connected by a slider with one end of a switching lever, the other end of which is held in both end positions by a locking mechanism. An axle at the end of the rotatable central lever, to which the one end of the springs . is attached, has a stem connected to the lever. This lever is rotated by a hinged four-stroke mechanism, mounted on the bottom of an oil container. Tensioning of the springs is done in this way.

The disadvantage of this spring-energy accumulator is that it occupies a lot of space, as the mechanisms rotate within the whole circle. Another disadvantage is that charging mechanisms are in an uncomfortable location and are difficult to access for surveillance and revision.

For some power diverter switches with vacuum interrupters it is necessary to start the switching with a greater motor torque for a relatively short interval. This means that the force characteristic of the springs must be stepped. In (2) such a spring block as applied in (1) is shown. In this construction, there is one short spring connected to a rod in the interior of each of the two springs, which at the beginning of the switching has an idle movement.

Here the disadvantages of (1) are retained, with another one appearing. The location inside the springs is limited, which does not allow the realizing of larger additional forces.

Also it is known another spring-energy accumulator (3) which takes up less space, because the movement of the springs is linear. It contains a carrying housing, at the ends of which two parallel axes are attached. There are two sleds which slides along the edges of which two switching springs, operating in pressure mode are mounted. The springs are loaded from a shaft with an eccentric that contacts straight rails on the upper sled. The output shaft, which is connected with contact system of the power diverter switch, is coaxial ly mounted on the charging shaft. The output shaft has an arm with a pin and a roller located in a transversal groove of the lower sled, through which a jump switching occurs. The arm has also two locking teeth, which are held in the end positions by a locking mechanism.

The disadvantage of this spring-energy accumulator is that the friction between the sleds and the axles is increased due to eccentric charging and releasing. Sprain of compression springs contributes for increasing of a friction since they are mounted coaxially around the axes. This is particularly unfavorable for power diverter switches operating in the gaseous environment. Another disadvantage is that the connection between the output shaft and the contact system is complicated. High precision is required in designing and assembling.

Therefore, there is another construction of a spring-energy accumulator (4), in which the two guiding axes and coaxially mounted springs on them, operating in pressure mode are arranged sideways one below the other. The charging is also done by a shaft with an eccentric. The movement from the sled to the output shaft is transmitted via a toothed rack, attached to the sled and a gear wheel. There is also a locking mechanism and elements for releasing attached to the sled.

A disadvantage of this spring-energy accumulator is that the construction is complicated, especially the locking mechanism and the associated elements. Another disadvantage is that the friction is greater, as the toothed gear loads the sled eccentrically and the springs work under pressure. This is also disadvantageous for power diverter switches operating in the gaseous environment.

A further spring energy storage device (5) is known in which charging and release loading is more advantageous. It has a carrying housing to which two parallel carrying axes are mounted. Two sleds are sliding on both sides mirror-mounted. Two springs operating in tension mode are mounted coaxial ly on the axles and are attached to the outer edges of the axles. There are two rolling bearings situated one under another between the internal faces of the sleds. One of them is mounted on the end of a lever which is connected to a charging rod and an eccentric located on the carrier housing. The other roller bearing is mounted on the one side of a shift lever connected to the drive shaft of the contact system. The other arm is locked at the end positions by a locking mechanism.

A disadvantage of this spring-energy accumulator is that it requires a great deal of accuracy in the making and assembly of the elements in order to limit sliding friction, which will nevertheless be great. Another disadvantage is that the rolling bearings are loaded locally in the charging and in the switching, which is not beneficial to them.

A step power characteristic can be achieved in the construction shown on (5). This is done according to (6). On both sides of the housing, parallel between the axles are mounted by one piston with a spring, operating in pressure mode, which is tightened in the end of the charging.

The disadvantage is that, regardless of the use of the step power characteristic, the construction is complicated and the friction is increasing. Another disadvantage is that the additional springs work with a little useless move, so their initial force is not used, but it is the greatest.

DISCLOSURE OF INVENTION

The task of the invention is to provide a spring-energy accumulator for a power diverter switch of an on-load tap changer, having a simple design without sliding pairs of contact elements. The connections between the elements must only be done by rolling bearings. The spring blocks must be independent and accessible for installation, allowing for easy replacement of springs with others. The charging mechanism must be simple and the shifting roller bearings must not load in one place only.

The task is solved with spring-energy accumulator for a power diverter switch of an on-load tap changer, containing a carrying flange, on which are mounted a charging system and a switching system. The switching system is equipped with switching springs in the end positions, and locking mechanisms for unlocking to start the switching.

According the invention, three pivots are mounted on the carrying flange. On the left pivot is mounted a hub of the left lever and on right pivot - a hub of the right lever. A charging lever is mounted on the third pivot. The two levers have widened front parts, with located between them an upper rolling-contact bearing, connected to the end of the charging lever and a lower rolling-contact bearing, connected to one end of the double-armed switching lever. The other end of this lever has a stem, held in the two extreme positions by two locking pawls. Between the ends of the two levers are mounted switching springs operating in tensile mode. The charging system comprises a gear wheel performing half the switching cycle and rod connected between this gear wheel and the charging lever.

The three pivots are mounted in the lower parts of the carrying flange and in the upper parts are reinforced with a common triangular plate. The locking system comprises a left locking pawl and a right locking pawl connected to a spring. They are mounted on the lower part on pivot, on which part upper is mounted the charging lever. The shaft of the charging gear wheel is mounted in a bush, fixed on the carrying flange. The shaft of the double-armed lever is mounted in the middle of the carrying flange and is coupled to a shaft which drives the contact system. A semi-cardan connector can be used of missing the coaxially. In order to achieve greater force at the start of the switching, an additional spring can be used between the ends of the two levers. This spring has a piston with a spindle, and the piston may perform an idle stroke until it begins to stretch the spring. An advantage of the spring-energy accumulator according to the invention is that, it has a very simple construction, convenient for monitoring and control. There are no sliding pairs of elements in it. All joints are hinged on the basis of rolling bearings. Another advantage is that the springs are opened and accessible and can be easily changed depending on the type of power diverter switch they are switching on. It is also advantageous that a step power characteristic with an independent spring can be achieved if necessary. It is also an advantage that the charging system is very simple and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

On example embodiment of the spring-energy accumulator, according to the invention is shown in the attached figures, of which:

Figure 1 is a longitudinal section through the center of the spring-energy accumulator.

Figure 2 is a top view of the spring-energy accumulator presented in the middle position for better understanding of the construction.

Figure 3 is a cross-sectional view of the double-armed switching lever and blocking fingers.

Figure 4 is a longitudinal section perpendicular to Fig. 1.

Figure 5 is a longitudinal section through the bearing of the switching levers and through the charging lever.

Figure 6 is a cross-section through the switching springs.

Figure 7 is a section through the additional spring, providing a step force characteristic with a large initial force.

The spring-energy accumulator is mounted on a carrying flange 1. Three axes 2,

3 and 4 are attached on it and they are secured on top by a plate 5. On the axis 2 is mounted the hub 6 of the left lever 7 and on the axis 3 is mounted the hub 8 of the right lever 9. For easier depiction of the sections and views, the spring-energy accumulator is given in the middle, intermediate position. The switching springs 12 are mounted between the ends 10 and 11 of the two levers 7 and 9. If a greater initial force is required, an additional spring 13 with a special force characteristic is also possible to be mounted. On its inner side, the lever 7 has a widened front part 14 and a lever 9 has a widened front part 15. Between these front parts are located an upper rolling-contact bearing 16 and a lower rolling-contact bearing 17. A bearing 16 is mounted at the end of the charging lever 18, axis 4 (Figure 4, Figure 5). A bearing 17 is mounted on the one arm of a double-armed switching lever 19 with a shaft 20, mounted in the center of the carrying flange 1. A lever 19 has on its other arm a stem 21 which is locked in the shifts in extreme positions by a left locking pawl 22 and right locking pawl 23. These pawls are mounted at the bottom of axis 4. A tcnsioncd spring 24 is stretched between their outer edges. To start the switching process, the unlocking of the stem 21 is made by the pawls 25, fixed to the charging lever 18.

The driving of the charging lever 18 is released by a rod 26 which is mounted in its one end on a lever 18 and in the other end - on a gear wheel 27. The shaft 28 of this gear wheel is mounted in a bush 29, which is mounted on the carrying flange 1. A gear wheel 27 rotated by an external gear wheel 30, shown schematically. It makes one switching turnover, and the gear wheel 27 makes a half of switching turnover.

The carrying flange 1, most often is mounted on a non-shown flange of the carrying head of the oil container of the on-load tap changer. This happens by bolts, passing through the holes 31. The shaft 20 is connected to a shaft 32 which actuates a known, not-shown contact system. Most often the shaft 32 has an insulating part, as the contact system is at the star center potential. It is fastened to carrying flange 1 by not-shown insulating reeds. The power diverter switch is lifted by hooks 33. In order to compensate some deviations of the coaxial placement it is possible for a semi- carded clutch 34 to be used in the connection between shaft 20 and shaft 32.

The switching springs 12 (Fig. 6) have nozzles 35 in which there are threaded holes connected with screws 36 with hubs 37. They are joined to the ends 10 and 1 1 of the levers 7 and 9 by pins 38. By the screw connections it can be adjusted within certain limits the tension of the springs 12. The locking is made by means of counter nut 39.

The additional spring 13 (Fig. 7) is connected to the end 10 by a nozzle 40 with a stem 41. The nozzle 42 on the other side is free. An axle 23 is sliding in its opening, which at one end has a piston 44 and in the other - a stem 45, attached to a nozzle 11. The free stroke x determines at what point of the stretching the additional system will appear.

The action of the spring energy accumulator is as follows:

In the starting position, the switching lever 19 is rotated, for example 45° counter clockwise (Fig.2, Fig.3) and its stem 21 is locked by the right locking pawl 23. The levers 7 and 9 are turned to the left and the charging lever 18 too. The gear wheel 27 is in a left dead point and the rod 26 is fixed along the diameter.

When the switch command is submitted, the gear wheel 30 is rotated by a not-shown gear. It rotates a gear wheel 27, for example in a clockwise direction. The rod 26 moves to the right the charging lever 18 and its bearing 16, acts on the widened front part 15 of the lever 9 and moves it to the right. At the same time the bearing 17 holds the lever 7 in the starting position and the springs 12 begin to tighten. At a certain angle before the gear wheel 27 to reach its right dead point, the corresponding pawl 25 from the charging lever 18 releases the right locking pawl 23 and the left lever 7 by the action of the springs 12, jogs to the right and, via a bearing 17 acts on the double-armed lever 19 and performs the switching of the contact system. The stem 21 of the switching lever 19 is locked by the left locking pawl 22. The spring-energy accumulator is ready for the next switching. This happens in a similar manner by turning the gear wheel 27 clockwise or vice versa. It rotates to 180° from a right dead point to a left dead point.