EP0637829B1 - Tap changer for tapped transformer - Google Patents

Abstract

A stage switching unit for use in transformers has a number of fixed contacts (Kn) mounted on a frame. Auxiliary contacts (5) are mounted on a slide element (3) that is subjected to the force applied by a spring (4) when a leadscrew (2) is rotated by a geared drive (1). The movable contact is mounted on a coupled mass (7) that is subjected to a separate spring force. The changeover between contacts occurs with a snap action.

Description

The invention relates to a tap changer for a tap changer according to the preamble of the first claim.
Such tap changers are known from WO 94/02955.

Typically, tap changers are constructed according to the principle of fast resistance switching for uninterrupted switching from one tap of a tap transformer to another in such a way that the fixed tap contacts, which are electrically connected to the leads of the tap windings, are circular in one or more horizontal planes or planes on an insulating frame or cylinders are arranged and can be connected by rotating contact bridges actuated by concentric drive shafts.
In the case of load selectors in which the stage selection and the actual load changeover are combined, the contact bridges are operated abruptly after triggering an energy store, usually a spring force store, which is pulled up by the drive shaft of the switch.

In WO 94/02955, in deviation from these conventional constructions, a tap changer with linear contact actuation is described, the fixed tap contacts along a path extending into the interior of the switch and being switchable by a sliding switching mechanism, which in turn is driven by the drive shaft .

The vertically displaceable switching mechanism consists of an elevator carriage that can be driven continuously by the drive shaft, which preselects the new fixed step contact, and an output part that can be pulled up by the elevator carriage by means of an energy store, which after triggering runs after the elevator carriage and thereby the Actual load switchover from the previous tap of the step winding to the preselected new tap. The switching elements required for this are part of the driven part.

A disadvantage of this tap changer is that the driven part necessarily has a number of different mechanical guide and electrical contact elements, as well as the switching elements and means for their actuation, and thus overall a not inconsiderable mass. From this it follows inevitably that since the spring energy storage releases the same energy each time it is triggered, the abrupt movement of the stripping part takes place more slowly than downwards, since in the first case the energy content of gravity of the stripping part counteracts the energy content of the spring energy storage while it adds to this in the second case. Such a different switching speed depending on the switching direction is undesirable; rather, it is desirable that, as in the known step switches operated by rotatable horizontal contact bridges, each changeover takes place with at least approximately the same switching speed.

The object of the invention is therefore to provide a way to compensate for the weight of the abruptly tracked output part in the aforementioned vertically moved linear tap changers, such that it does not affect the switching speed depending on the direction.

This is achieved according to the invention by the means listed in the characterizing part of the first claim. The subclaims contain advantageous developments of the invention.

The additional spring according to the invention between the elevator carriage and the driven part is, as in Embodiment will be explained in more detail, a simple way to compensate for the dead weight of the output part and thus an equalization of the switching speed regardless of the switching direction with little additional design effort.
Both tension and compression springs are suitable as additional springs. If a tension spring is used, it must be arranged between the elevator carriage and the driven part in such a way that when a shifting movement is prepared downwards, i.e. the elevator carriage has already been moved vertically downwards to the next fixed step contact, and the driven part before the energy storage device is triggered, the previous one (Overlying) fixed step contact remains, the tension spring is in the rest position, ie without or with little pretension, and is pulled open during the subsequent abrupt follow-up of the driven part, ie it is tensioned.
If, on the other hand, a compression spring is used, it must be arranged in such a way that it is also in the rest position, ie in the relaxed or largely relaxed state, when the parts are in the described position and is compressed, that is also tensioned, during the subsequent abrupt succession of the driven part.
This can be achieved by means of correspondingly selected articulation points for fastening the corresponding spring.

The use of tension springs is more advantageous in that tension springs do not need an additional longitudinal guide, while compression springs of a certain length are at risk of kinking when being compressed, which makes additional longitudinal guidance, for example by a surrounding tube, necessary.
It has been shown that, in particular when using a tension spring as an additional spring, an almost complete compensation of the kinetic energy caused by gravity is possible. In addition to an appropriately selected spring characteristic, adjustment is also made by simply varying the spring length Different weight and kinematic ratios of the energy storage possible.

Fig. 1

zeigt einen erfindungsgemäßen Stufenschalter mit einer Zugfeder als Zusatzfeder in seitlicher Schnittdarstellung

Fig. 2

zeigt in schematischer Darstellung eine Schaltsequenz eines solchen Stufenschalters

Fig. 3

zeigt, ebenfalls schematisch, die entsprechenden Kennlinien der bei dieser Schaltsequenz wirksamen Kräfte

Fig. 4

zeigt die vereinfachte Energiebilanz bei dieser Schaltsequenz

Fig. 5

zeigt wiederum in schematischer Darstellung eine zweite Schaltsequenz eines anderen Stufenschalters, bei dem statt einer Zug- eine Druckfeder als Zusatzfeder verwendet wird.

The invention will be explained in more detail below with reference to drawings.

Fig. 1

shows a tap changer according to the invention with a tension spring as an additional spring in a side sectional view

Fig. 2

shows a schematic representation of a switching sequence of such a tap changer

Fig. 3

shows, also schematically, the corresponding characteristic curves of the forces effective in this switching sequence

Fig. 4

shows the simplified energy balance for this switching sequence

Fig. 5

again shows a schematic representation of a second switching sequence of another tap changer, in which a compression spring is used as an additional spring instead of a tension spring.

The tap changer shown in FIG. 1 will first be described in more detail below.
Laterally, vertically one above the other, the fixed step contacts K (n-1), K (n), K (n + 1), ..., each consisting of two parallel contact cheeks, extend into the interior of the switch. From the drive 1 arranged above, a threaded spindle 2 leads into the interior of the tap changer. This also has a spring energy store, which consists of a tubular elevator slide 3, which is enclosed by a compression spring 4 and in turn encloses the threaded spindle 2, by which it is driven. A preselecting auxiliary contact 5, each with a contact cheek, is insulated on the elevator slide 3 of the selected fixed step contact K (...), and a vertically extending trigger contour 6 is also attached. The spring energy store also consists of an essentially U-shaped output part 7. Another component of the output part 7 and thus its jump-like movement after triggering is a switching contact that connects the other contact part of each fixed step contact K (...); This switch contact is not visible in the figure, since in the rest position shown it is in the same horizontal plane behind the preselecting auxiliary contact 5. A tension spring 11 is clamped at the top at an attachment point 11.1 of the elevator carriage 3 and at the lower end at an attachment point 11.2 of the driven part 7 in such a way that it is at rest, ie when the leading auxiliary contact 5 and the trailing switching contact are applied to the same fixed step contact, below Preload is present, ie pulled apart from its rest position by a certain amount.

If a switchover is to take place, the threaded spindle 2 performs a rotary movement and moves the tubular elevator slide 3, which surrounds it, continuously up or down, depending on the direction of rotation. As a result, the compression spring 4 of the energy store, which is supported against an upper abutment 4.1 or a lower abutment 4.2, is tensioned; the spring energy storage is pulled up.

During this movement of the elevator carriage 3 relative to the still stationary output part 7, a roller 8 of a trigger bar 9 of the output part 7 runs on the likewise vertically moving trigger contour 6, which has slopes 6.1, 6.2.
At the same time, the preselecting auxiliary contact 5, which is fixedly connected to the elevator carriage 3, moves; it leaves the original fixed step contact K (n) and reaches the next, above or below the fixed step contact K (n + 1), K (n-1).
Then the roller 8 reaches the respective slope 6.1 or 6.2; the trigger bar 9 is shifted horizontally out of the lock 10.n assigned to the fixed step contact K (n) and the complete stripping part 7 abruptly follows the previous movement of the elevator carriage 3 until the release bar 9 is in the lock 10 assigned to the newly reached fixed step contact. n + 1 or 10.n-1 locked again. The switching contact now also leaves the previous fixed step contact and reaches a contact cheek of the new step contact, on the other of which the auxiliary contact 5 already rests.
When switching from K (n) to K (n + 1), the tension spring 11 is deflected further by the preselecting elevator slide 3 in addition to its pre-tension already present in the rest position, so that when the output part 7 follows, the energy of the compression spring 4 of the triggered energy storage and add the partially relaxing tension spring 11.

In the case of a shift from K (n) to K (n-1), on the other hand, the tension spring 11 is relaxed by the preselecting elevator slide 3, so that a part of the kinetic energy is required for a partial tensioning of the tension spring 11 when the output part 7 is followed - the influence the weight is balanced.

FIG. 2 shows the switching processes described again schematically; the corresponding characteristic curves of the force profiles can be seen from FIG. 3. It can be seen that the same conditions prevail regardless of the switching direction. Fig. 4 shows the resulting energy balance in the tap changer described.
E1 is the energy content of the energy storage spring 4, E2 that of the gravity acting on the driven part 7 and E3 that of the additional spring 11, namely E3 'for the downward and E3'' when shifting up. E 'is the respective resulting total content with downshift, E''with upshift. E '= E''andE3' + E3 '' = 2 E2 apply.

5 schematically shows the relationships that result when using a compression spring instead of a tension spring. As already explained, when using a compression spring, its articulation or fastening points on the elevator carriage 3 or driven part 7 must be selected differently; otherwise the characteristics of the acting forces and the energy balance remain unchanged.

For the invention, it is irrelevant overall whether the respective additional spring is completely or only partially relaxed during the switching process; the relative change in the preload of the additional spring depending on the switching direction is decisive in order to achieve the desired compensation effect.

Claims (3)

1. Tap selector switch for tapped transformers, wherein fixed tap contacts are arranged along a linear path and switchable to by a displaceable switching mechanism which consists of a continuously drivable tensioning carriage and a drive part which is tensionable through this by means of an energy storage device and which after release rapidly follows the tensioning carriage, characterised thereby, that an additional spring (11) is arranged between the tensioning carriage (3) and the drive output part (7) in such a manner that the additional spring (11) is tensioned during a downward movement of the drive output part (7) and relieved during an upward movement of the drive output part (7).
2. Tap selector switch according to claim 1, characterised thereby, that the additional spring (11) is arranged nearly vertical and fastened by its upper end at the tensioning carriage (3) and by its lower end at the drive output part (7).
3. Tap selector switch according to one of the preceding claims, characterised thereby, that the additional spring (11) is a tension spring.

Images