KR20130036119A - Method and system for a pre-selector in a tap changer - Google Patents

Abstract

The pre-selector of the tap-changer is equipped with an operating device for changing the speed for the movable contact of the pre-selector. The apparatus is provided in a cylindrical tap changer 10 that includes a cylinder 24 formed with pre-selector contacts 25-27 and tab contacts, which extend into the cylinder, the apparatus having the cylinder 24. A contact carrier (9) formed with at least one movable contact (8) engaging with said pre-selector contacts, and a drive mechanism (21) for providing rotational motion to said contact carrier (9), said contactor The carrier 9 is rotated by the drive mechanism 21 in use, such that the movable contact 8 selectively engages the pre-selector contacts 25 to 27 inside the cylinder. In the device, the drive mechanism 21 is characterized in that it is operatively connected to the contact carrier 9 via a swing mechanism 1 arranged to provide a swing motion to the contact carrier 9.

Description

METHOD AND SYSTEM FOR A PRE-SELECTOR IN A TAP CHANGER}

The present invention relates generally to a tap changer for a transformer, and more particularly to an apparatus for operating a pre-selector of a tap changer of a transformer.

In power transformers, on-load tap changers (OLTC) are used to switch the tapping connection of the windings of the transformer while energizing the transformer. Since the transformer is in use, an arc will occur when the tapping connection is switched. Pre-selectors are used in the on-load tap-changer to enable connection or disconnection turns of the windings of the transformer. This pre-selector can also be used to connect the entire part of the winding. In addition, for contacts of the pre-selector, an arc will occur when the contacts move. If this arc is not limited, not only does contact wear increase, but there is also a risk of damage to the windings of the transformer, resulting in reduced duty operational time for both the tap-changer and the transformer. In the worst case, the arc in the pre-selector will be found to be a short circuit, causing severe damage to the transformer.

In order to limit the arc at the contacts of the pre-selector, so-called tie-in-resistors are used. Instead of causing an arc, the stored energy is released in the form of a controlled current through the tie-in resistor when blocking the contactor of the pre-selector. Although used in good operating mode, there are some disadvantages in tie-in resistors. This tie-in resistor is only installed in certain environments which are expensive, bulky and preferably require installation. There is a risk that the situation in the field may not be fully known or changed, resulting in damage to the transformer if no tie-in resistor is installed. In addition, if a tie-in resistor is installed, there will still be energy in the form of heat in the resistor.

In addition, to ensure proper functionality, it is important to ensure that the pre-selector is securely locked when placed in a suitable position. There are known systems in which the locking function of such a pre-selector is achieved by bringing two surfaces into contact with each other with high friction. However, since the locking function is caused by the two surfaces in contact, high friction between these surfaces is also caused when it is not desired, ie when the contacts of the pre-selector have to be separated. If the contacts are not disconnected quickly, more arcs will occur during separation, which will cause unnecessary wear of the contacts and the risk of damaging the windings of the transformer.

It is an object of the present invention to provide a device for a pre-selector on a tap changer of a transformer without the above mentioned disadvantages. In particular, it is an object of the present application to provide a quick separation of the contacts of the pre-selector.

The object is achieved by providing an apparatus for actuating a pre-selector of a cylindrical tap changer comprising a cylinder formed with a tap contact and pre-selector contacts extending into the cylinder, the apparatus comprising: the pre-selection of the cylinder; A contact carrier having at least one movable contact engaged with the selector contacts, and a drive mechanism for providing rotational motion to the contact carrier, the contact carrier being rotated by the drive mechanism in use such that the movable contact And selectively engages with the pre-selector contacts inside the cylinder. In the pre-selector device, the drive mechanism is operatively connected to the contact carrier via a swing mechanism arranged to provide rotation of the angular velocity to the contact carrier. Preferably, the geometrical positioning of the contacts is provided such that the varying angular velocity is the highest when separating the movable contact from the corresponding cylinder contact.

In a preferred embodiment, the oscillating mechanism comprises a cam structure and a cam follower, the cam follower acting on the cam structure upon rotation. Preferably, the cam follower is spring loaded against the cam structure.

In one embodiment, the swing mechanism is at least one end groove arranged to provide a first resting position for the swing mechanism in accordance with a movable contact in contact with one of the cylinder contacts. It includes.

In one embodiment, the cam structure and the cam follower provide a rest position and the cam follower comprises a first groove and a second groove providing a first locking position and a second locking position for the cam follower. Wherein the locking positions provide a first rest position and a second rest position of the swing mechanism.

In these positions, the cam follower can rest, the positions corresponding to the contact positions of the corresponding and movable contacts of the cylinder.

Advantageously, said cam structure comprises a first cam and a second cam and provides a groove between said first cam and said second cam.

The groove is an intermediate groove that controls and limits the rotational speed of the movable contact (cam follower and thereby) during the movement between two successive fixed contacts of the cylinder.

In one embodiment, the movable tap change contacts of the tap changer are driven essentially at constant speed by a drive mechanism. The speed of change in the operation of the pre-selector is essentially provided only by the swinging mechanism, for example by the cam structure and the cam follower structure.

The tap change contacts are actuated by a switching shaft, which is a suitable and preferred embodiment of the tap changer, which is arranged axially and vertically in the center of the cylinder and is driven by a drive mechanism.

Moreover, in a preferred embodiment, the tap changer comprises vacuum interrupters which cut off the current in the tap changer during switching.

1 shows a mechanism in which a cam follower is positioned at a first locking end position;
2 shows a mechanism in which a cam follower is moved to a first cam position;
3 shows a mechanism in an intermediate position,
4 shows a cam follower moved to a second cam;
5 shows a system in which a cam follower is located in a second locking end position;
6 is a perspective view showing a part of a pre-selector;
7 shows a transformer with a tap changer, and
8 shows the main part of the tap changer and the means for switching the tap changer.

FIG. 7 shows a schematic diagram of a transformer 11 with a first terminal set 12 and a second terminal set 13 for transforming electricity between a first voltage level and a second voltage level. The transformer 11 is formed with a tap-changer 10, which has three sets of tap-changing contacts (one for each stage) under a pre-set with three output contacts 26, 27, 28. Symbolically indicated). 7 shows a transformer tap changer of known type which may benefit from mounting the pre-selector device of the present application. 8 shows the main part of a tap changer comprising a pre-selector device according to the invention. The tap changer 10 includes a motor 22 for driving the tap changer, which is connected to be operated by the drive mechanism 21 of the tap changer via the connecting means 23. The tap changer also includes an insulated cylinder 24 arranged inside the transformer housing, which is provided with an annular tap change contact, which is arranged inside the cylinder. The switching shaft 25 supports the movable contact, ie this contact moves with the switching shaft, and the contacts of this contact are arranged to selectively engage with the corresponding contact of the cylinder. The drive mechanism 21 is arranged to provide a drive torque for rotating the switching shaft 25 so that the contacts of the tap changer of the tap changer are manoeuvred. The drive mechanism is also connected to actuate the pre-selector and arranged to drive the contact carrier 9 of the pre-selector supporting the contacts 8 of the movable pre-selector. The contacts 8 of the movable pre-selector are arranged to selectively engage the contacts 26, 27, 28 of the fixed pre-selector of the cylinder when rotated by the drive mechanism 21. The drive mechanism 21 can comprise a Malteser wheel gear that provides rotation to both the changeover shaft 25 of the tap changer and the contact carrier 9 of the pre-selector. The tap-changer with Malteser wheel gear is provided in several versions by ABB AB (for example UC tap-changer with BUE or BUL drive mechanism or UZE / UZF type with drive BUF 3) Will not be described in more detail below.

The pre-selector also includes a mechanism 1 for changing the speed of the movable contact. The mechanism 1 is provided for converting a constant rotational motion input from the drive mechanism 21 into a staggered rotational motion applied to the contact carrier 9. The swing mechanism 1 provides a swing rotation, the speed is varied and the swing mechanism 1 is connected to be operated on the contact carrier 9 so that the maximum speed is the separation moment for the movable contact 8, namely the movable contact ( 8) corresponds to the moment exiting the fixed cylinder contact 26, 27, or 28. Thus, the swing mechanism allows for faster detachment of the contact.

An example of the swinging mechanism 1 according to the present application will be described with reference to FIGS. 1 to 5. It should be appreciated that other devices that provide oscillatory motion may be used without departing from the scope of the invention as defined in the claims. However, the figures show preferred instruments with reliable structures. The swing mechanism of the preferred embodiment comprises a cam structure 5 and a cam follower 2 arranged to cooperate with the cam structure to alternately provide stop and acceleration motions. The cam follower 2 is fixed to a shaft 3 connected to the drive mechanism 21, which is also arranged to impart rotational movement to the cam follower 2 from the drive mechanism 21. The cam follower 2 is subjected to an elastic load by the spring 4 in contact with the surfaces of the cam structure. The cam structure 5 comprises a first groove 16 and a second groove 18 which provide first and second end positions for cam followers in the cam structure. A first cam 5a and a second cam 5b are arranged between these end positions 16, 18, and a third groove 17 is arranged between these cams 5a, 5b to provide a cam follower. It is provided as an intermediate position for (2). The rocking motion is formed by moving the cam follower 2 between the grooves 16, 17, 18 passing through these cams 5a, 5b.

6 shows a partial perspective view of a pre-selector device with movable contact 8 and swing mechanism. The tap-changer cylinder has an external dictionary which provides an inner cylinder contact 26 to 28 of the pre-selector which is arranged to selectively engage with the movable contact 8 which extends into this cylinder and is supported by the contact carrier 9. A selector tap contact 7 is formed. In figure 6 it is shown how the swinging mechanism comprising the cam structure 2 and the cam follower 5 can be arranged on the upper surface of the cylinder. The function of the swinging mechanism will be described with reference to FIGS. 1 to 5.

1 to 5 show the passages of the cam follower 2 over the cam structure 5 in the switching operation of the pre-selector. In FIG. 1, the cam follower 2 is located in a first groove 16 which provides a first end position for the swing mechanism. The end position corresponds to the contact position for the movable contact of the pre-selector, so that the movable contact 8 engages with the first fixed contact of the stationary contacts of the cylinder. In FIG. 5, the opposite end position where the movable contact 8 of the pre-selector switch engages with the second fixed contact of the fixed contacts of the cylinder 2 is shown. Normal switching adjustment starts at the position shown in FIG. 1 and ends at the position in FIG. 5. In FIG. 2, the cam follower 2 rotated by the shaft 3 starts its movement in the first end position and meets the first cam 5a of the cam structure 5. When the cam follower 2 meets the first cam 5a in rotation, the spring 4 is compressed, which compresses motion from the contact surface slope between the first cam 5a and the first groove 16. resistance). In this way the movement of the cam follower 2 is slowed down. Resistance to this movement generates torque in the drive mechanism 21 and the motor 22. This resistance keeps the rotational speed constant when the cam follower 2 raises the cam 5a. In Fig. 2, the cam follower reaches the top of the first cam 5a. When passing through the top of the cam, not only the torque in the motor 22 and the drive mechanism 21 but also the elastic force are released, and the angular velocity increases. In FIG. 3, the cam follower 2 enters the intermediate groove 17 of the cam structure 5 between the grooves 5a, 5b. Between the top of the first cam 5a (see FIG. 2) and the intermediate groove 17 (see FIG. 3), the cam follower engages with the second slope of the first cam 5a, and the motor 22 and The compressed spring as well as the torque of the drive mechanism 21 pushes the cam follower, the cam follower moves towards the cam structure 5, and the resilient force and released torque move the cam follower 2 "down the slope. "Accelerate. This acceleration step increases the speed up to the maximum speed, which speed is suitably formed so that the movable contact 8 loses contact and substantially conforms to the transition step, which is separated from the fixed contacts 26, 27, 28 of the cylinder. do. Thus, the angular position with respect to the movable contact of the fixed contact is arranged to make contact separation at the end of the acceleration period when the mutual speed of the movable contact and the fixed contact is high and close to its top. Preferably, the maximum speed is reached slightly after the point of contact detachment to minimize the risk of arcing.

3 shows a cam follower 2 entering the intermediate groove 17, which prevents uncontrollable movement of the cam follower 2, and instead of the groove 17, a second cam ( By providing an intermediate stop for the cam follower 2 upon encountering the slope of 5b), the cam follower 2 slows down when moving on the slope between the intermediate groove 17 and the second cam 5b.

4 shows that the cam follower 2 reaches the top of the second cam 5b in which the rotational speed has again decreased to the minimum. After that, the cam follower 2 will descend below the second cam 5b, the compressed spring 4 again contributes to the rotational speed, and the cam follower 2 into the second end groove 18. Enter. Entry into the second end groove coincides with the entry of the movable contact 8 in contact with the second contact of the fixed contacts on the cylinder. The end position is shown in FIG.

Claims (9)

An apparatus for operating a pre-selector of a cylindrical tap changer 10 comprising a cylinder 24 having pre-selector contacts 25 to 27 extending into the cylinder and a tab contact formed therein,
The apparatus comprises:
A contact carrier 9 formed with at least one movable contact 8 that engages with the pre-selector contacts of the cylinder 24,
A drive mechanism 21 for providing rotational movement to the contact carrier 9,
The contact carrier 9 is rotated by the drive mechanism 21 in use so that the movable contact 8 selectively engages with the pre-selector contacts 25 to 27 inside the cylinder,
The device for operating the pre-selector characterized in that the drive mechanism 21 is operatively connected to the contact carrier 9 via a swing mechanism 1 arranged to provide a swing motion to the contact carrier 9. . The method of claim 1,
The swinging mechanism 1 comprises a cam structure 5 and a cam follower 2, the cam follower 2 acting on the cam structure 5 in rotation. . The method of claim 2,
The cam follower (2) is loaded with a spring (4) against the cam structure (5). The method according to claim 2 or 3,
The cam structure includes a first cam 5a and a second cam 5b and also provides a groove 17 between the first cam 5a and the second cam 5b. Device to operate. The method according to any one of claims 1 to 4,
The swing mechanism 1 is at least one end arranged to provide a first rest position for the swing mechanism in accordance with the movable contact 8 in a contact position with one of the cylinder contacts 25-27. And a groove (16, 18). The compound according to any one of claims 2 to 4, wherein
The cam structure 5 comprises a first groove 16 and a second groove 18 which provide a first locking position and a second locking position for the cam follower 2, the locking positions being the swinging position. Providing a first rest position and a second rest position of the instrument. 7. The method according to any one of claims 1 to 6,
And the movable tap change contacts of the tap changer are driven essentially at constant speed by a drive mechanism. The method of claim 7, wherein
The tap change contacts are actuated by a diverter shaft (25), the diverter shaft being arranged axially and vertically at the center of the cylinder and driven by a drive mechanism. The method according to any one of claims 1 to 8,
And the tap changer comprises vacuum interrupters for interrupting current in the tap changer during switching.

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