EP0009287A1 - Electrical apparatus comprising a series of voltage taps and a tap selector and/or a circuit breaker - Google Patents

Abstract

A circuit for switching electrical winding taps (3, 4) which are seats of electromotive forces comprising impedances (8) of transition on passing from one tap to the next. The circuit of the impedance (8) of transition comprises an inverter (9) for connecting the impedance of transition to one (3) or the other tap (4), so as to permit the switching circuit to operate in one direction or the other. It applies to on-load tap changers and to load selector switches for stepped electric transformers. <IMAGE>

Description

The present invention relates to an electrical appliance comprising a series of sockets and a selector unit and / or a set of switches provided with contacts cooperating with the sockets and connected to a circuit comprising at least one transition impedance, as well as a connection to a main conductor. The selector unit and / or the set of switches are actuated by a control device. A typical example of such a plug-in electrical appliance is a step-type electrical transformer equipped with a tap-changer switch or load selectors. The invention is not however limited to transformers but can be applied to other electrical devices such as compensation inductors, resistance banks or capacitor banks. These devices can be single-phase or can be designed for several phases. As in the vast majority of cases the circuits of the selector crew or the sets of switches of the different phases are identical between them and present differences only when special effects are envisaged, the description below is limited to the single-phase case.

Step transformers operating using selector assemblies and / or breaker assemblies for switches, on-load tap-changers are well known and described in numerous patents and other prior documents. In these known transformers, during a tap change cycle, a portion of a winding, seat of an electromotive force which one wants to add or subtract, is short-circuited by one or more transition impedances set in service during one or more intermediate positions the selector crew or the set of breakers. This known state of the art is represented in FIGS. 1, 2 and 3 of the appended drawing which are electrical diagrams of the selector or switch apparatus, tap changer.

FIGS. 1 and 2 represent two successive positions of a switch and on-load tap-changer equipment and FIG. 3 represents a set of switches, all known per se.

In the switch according to Figures 1 and 2, the two taps of a winding, seat of an electromotive force are connected to two main contacts W and Z and, through resistors R, to two auxiliary contacts, intermediate X and Y A movable contact M connected to a main conductor I can move from a fixed contact W to a contact Z also fixed. The contact M is actuated by a control mechanism, not shown. Starting from contact W (Figure 1), the movable contact M first connects the fixed contact X. Leaving the contact W, the movable contact M connects the contact X to the fixed contact Y (Figure 2). On leaving contact X, the movable contact M connects contact Y to contact Z and finally, contact M ends its course when it connects conductor I to contact Z alone.

In the intermediate position, represented in FIG. 2, when the movable contact M leaves contact X, it must cut off a current intensity equal to approximately half of the current passing through the conductor I increased by a supplement constituted by the circulating current from one tap to the other of the winding portion and through the two resistors R. If E is the voltage difference between the taps of the winding portion, this supplement is equal to E / 2R.

If i denotes by i the current flowing in the conductor I, the current cut when the contact M leaves the contact X is 1/2 (i + ^{E /} R) and the recovery voltage which appears between the contacts X and M is (E + Ri). This additional current on the one hand and the increase by the component Ri of the recovery voltage on the other hand require a higher breaking capacity for the contact M, which can be obtained by a shortening of the maintenance periods or replacement of the contacts and / or by the use of more expensive contacts and / or dielectric liquids.

A known way to reduce these drawbacks is to separate the line current and the circulation current and cut them separately in different circuits.

Such a circuit is shown in Figure 3 of the accompanying drawings. The opening and closing sequence of the contacts can for example be as follows:

It is easy to see that the contacts A and D never cut only the line current while the contacts B and C never cut only the circulation current through the resistor R.

Such asymmetric sequences are achievable using complicated mechanics including particular linkages of the contact control mechanism derived from parallelogram, pantograph, etc. systems.

In the particular case of rotary switches of the Jansen type composed of three symmetrical sectors furnished with movable contacts rolling on fixed contacts at the periphery of an insulating cylinder, it is not practically possible to use the diagram of FIG. 3, unless the switch could always turn in the same direction, which is not possible, neither in the case of a on-load tap-changer switch, nor in the case of a selector crew under load, since, according to the In this case, winding portions must be added or subtracted.

It is therefore necessary, and this is the aim of the present invention, to adapt the operating cycle to the movement of addition or to the movement of subtraction of winding portions. However, according to another object of the invention, this intervention in the operating cycle must be carried out economically by means of a simple element, not subject to particular constraints.

The invention is characterized in that in the selector unit or in the set of switches, at least one inverter is connected in series with at least one of the transition impedances and this between one of the contacts connected to the sockets of the device and the main conductor, and in that the reverser is positioned as a function of the movement of the selector equipment or of the operating cycle of all the switches imposed by the control device. at a time in the operating cycle when its reversal does not cause circulation or a cut in current through its contacts. Thanks to such an arrangement, when switching from a first to a second tap, the transition impedance is connected, generally before the start of the operating cycle, so that when the contacts are switched, the impedance transition is connected to the contact cut last and this regardless of whether the second tap is reached by an addition or subtraction movement of a winding part.

Other characteristics of the invention will appear during the description below of some examples of embodiments of the invention illustrated in the accompanying drawings.

Figures 1, 2 and 3 of the drawings showing, known arrangements already described above. 4 shows a diagram of a _'tapped transformer according to the invention equipped with a switch for on-load tap changer.

Figures 5a to _5f show the various successive phases of the operating cycle of a selector on load for step transformers. FIG. 6 is a variant of a selector under load according to FIG. 5.

FIGS. 7a to 7i show the different stages of an operating cycle of a on-load switch equipped with a set of switches and comprising at least one non-linear element.

Figures 8, 9 etio _a show alternative circuits according to Figures 7a to 7i. Figures 11 to ₁₅ are various diagrams of on-load selectors comprising at least one non-linear element.

In FIG. 4, a step transformer is represented diagrammatically by its main winding 1 and its adjusting winding 2, of which only the taps 3 and 4 of the steps are identified. A selector unit is connected to two sockets of the adjustment winding 2 and includes two main contacts 5 and 6 connected respectively to sockets 3 and 4 of the winding 2. An auxiliary contact 7 of this crew is connected via a transition impedance , in this case a resistor 8, to the movable contact of an inverter 9 whose fixed contacts are connected to the sockets 3 and 4. In the position of the inverter shown in the drawing, the impedance 8 is connected to the socket 3.

The bottom of FIG. 4 represents, offset with respect to each other, the successive positions a, b, c, d, e of a movable contact 10 which cooperates with the contacts 5, 6 and 7. This movable contact 10 is actuated by a control device II consisting of a mechanism 11 set in motion from a reference transmitter 12 which can also control the switching of the inverter 9. The switching of the inverter 9 must take place at a moment of the operating cycle when its reversal causes neither a circulation nor a cut of a current through its contacts, that is to say, for example, before or at the very beginning of the movement of the movable contact 10 when the latter is in position a.

In position a, the movable contact 10 cooperates with the contact 5 and the line current, coming from the socket 3, is transmitted directly to the main conductor I of the use network. In position b, the movable contact 10 cooperates with the contacts 5 and 7, which has the effect of activating the transition impedance 8. In position c, where the movable contact 10 cooperates only with the intermediate contact 7, the line current also crosses the transition impedance 8, but the break between the contacts 10 and 5 only affects the line current. In position d, where the movable contact 10 cooperates with the contacts 6 and 7, the line current is transferred from the socket 3 to the socket 4. Finally, in position e, the movable contact 10 cooperates only with the contact 6 for the direct line current transfer.

In FIG. 4, it can easily be seen that the break between the movable contact 10 and the contact 5 only concerns the part of the line current not derived through the transition impedance 8. Next, the break between the movable contact 10 and the contact 7 only concerns the current flowing through the impedance 8, We have thus achieved, in this way, a separation of the break between the lignet current and the circulation current through the impedance 8, which makes it possible to improve the breaking capacity of the contacts and their resistance against deterioration, as well as to reduce the decomposition of the dielectric liquid in which the separation of the contacts is carried out.

When it is necessary to reverse the operating cycle, it suffices to maneuver the reverser 9 to carry out a "rear" sequence from socket 4 to socket 3 identical to that which was carried out "before" from socket 3 to socket 4.

In the case of FIG. 4, the reverser has been represented directly 9 in series with the transition impedance 8. In this case, the contacts of the inverter 9 are in direct connection with the sockets 3 and 4 of the adjustment winding 2. An identical result would be obtained if the inverter 9 was connected directly to the auxiliary contact 7, and if a transition impedance was inserted in each circuit separating the contacts of the inverter 9 with the sockets 3 and 4 of the adjustment winding 2.

In FIGS. 5a to 5 _f , a winding part of a transformer ending in sockets 13 is connected to fixed contacts 14 and 15. The selector assembly is movable relative to the contacts 14 and 15 and comprises three contacts associated 16, 17 and 18. The two extreme contacts 16 and 17 are directly connected to the terminals of the inverter _'19 , while the common terminal of this inverter 19 is connected via a transition impedance 20 to the main conductor or to the line direct from use, itself in direct connection with the middle contact 18.

From the examination of FIGS. 5a to 5 _f , it can easily be deduced that, in the phase of the operating cycle represented in FIG. 5 _c , the contact 18 cuts the line current, while the recovery voltage is equal to the voltage drop in the transition impedance 8. In the phase shown in FIG. 5 _d , a circulating current flows through the transition impedance 8 in relation to the potential difference between two successive taps 13 and the value of the transition impedance 8. Finally, in the phase represented in FIG. 5 _e , only the circulation current is cut by the contact 16.

As in the case of FIG. 4, it can be seen that during the reversal of the movement of the selector assembly the operating cycle can be easily reversed by simple tilting of the movable contact of the reverser 19.

Figure 6 shows an equivalent circuit similar to that of Figures 5a to _5f in which the inverter is replaced by two reversers mechanically coupled. The transition impedance 8 is connected to a "+" terminal of a contact of the inverter 21 and to a "-" terminal of a contact of the other inverter 22.

In this exemplary embodiment, the transition impedance 8 is connected to a contact of the first inverter in the "front" sequence and is on the other hand connected to a contact of the second inverter in the "back" sequence.

A significant improvement in the breaking qualities of a device according to the invention can be obtained by the use in the circuits of the selector equipment and / or of all the switches of elements with non-linear characteristic such as thyristors, transistors, rectifiers, diodes, triac, GTO, GAT, Zener diodes, either any element having the characteristics of one of the elements mentioned or of a combined set of two or more of these elements such as a thyristor-diode.

To obtain the desired result, at least one non-linear element as defined above is placed in the selector assembly or all of the breakers and connected in series with at least one of the reversers.

Figures 7a to 7i show successive stages of positions of six switches 23 to 28 of a typical assembly. A winding portion delimited by two taps 29 is connected to the breakers, tap selectors 23 and 24 of the assembly. Each breaker 23 and 24 is connected to a socket of an inverter 30 and a socket of an inverter 31 which are coupled between them either mechanically or electromagnetically or in any other suitable manner. The breaker 23 is further connected via the breaker 27 to a main conductor 32. Likewise, the breaker 24 is connected via the breaker 28 to the main conductor 32. The inverter 30 is connected via the breaker 25 and a thyristor 33 to the main conductor, so that any current which is to be cut by the breaker 25 can be cut beforehand by the thyristor 33. The inverter 31 is connected via the breaker 26 and an impedance 34, generally a resistor, to the main conductor 32 This circuit works as follows:

In step 7a, one of the taps 29 of a step transformer is connected via the breaker 23 and the breaker 27, both closed • to the main conductor 32 which is therefore at the potential of the tap at the input of the breaker 23. At this time, at the input of the breaker 24, a socket 29 can be chosen either to add or to subtract a portion of winding from the step transformer. In step 7b, this socket 29 is chosen and the inverters 30 and 31 are switched to the position shown, valid in the case where the switching passes from a socket 29 at the input of the breaker 23 to another socket 29 to the input of the switch 24. The switch 24 is then closed. In step 7 _c , the breaker 26 closes and allows the flow of a current through the impedance transition 34. The thyristor 33 is made conductive and the breaker 25 is also closed. In step 7 _d , the breaker 27 opens without a recovery voltage appearing at its terminals since it is short-circuited by the breaker 25 and the thyristor 33. In step 7 _e the thyristor control 33 is interrupted and, after the current has passed through zero, the latter remains blocked. In step 7 _f , the breaker 25 is opened without having to cut the current already interrupted by the thyristor 33. However, the current continues to flow via the impedance 34, but now takes its source in the socket 29 at the input of the breaker 24. At step 7g, the breaker 28 closes and short-circuits the breaker 26. At step 7 _h , the breaker 26 opens without having to cut the current which now flows directly through the breaker 28. Finally in step 7i, the breaker 23 opens after all current has stopped flowing through its contacts.

At this moment we are in a position similar to that of FIG. 7a, but instead of supplying the current by the switches 23 and 27 to the main conductor 32, the latter is supplied by the switches 24 and 28. A new outlet 29 can then be selected at the input of the breaker 23 and the inverters 30 and 31 must be switched. Thanks to this switching, the operating cycle takes place again in the same manner as described above.

The diagram of Figure 8 differs from celuides Figures _7a-i 7 in that an additional breaker 35 is disposed between the common point of resistor 34 and thyristor 33 and the main conductor 32. The breaker 35 is closed only during the transition from one outlet to another and performs a safety function. Otherwise everything remains identical to the circuit according to Figures 7a to 7i.

The diagram of FIG. 9 is a variant of the diagram according to FIGS. 7a to 7i. The breaker 25 is replaced there by two breakers 36 and 37 connected to the contacts of the reverser 30.

The diagram in Figure 10 is equivalent to the diagram in Figure 9. Indeed, the inverter 30 and the breaker 26 are replaced by two breakers 30 'and 30 "and the breakers 36' and 37 'assume here the function of l 'inverter 31. For greater safety, the thyristor 33 is split and replaced by two thyristors 33' and 33 ". It is obvious that in all cases, a set of four breakers suitably coupled mechanically or electromagnetically can replace a set of two inverters.

The following figures relate to catch selector crews. FIG. 11 shows a selector system with four mobile contacts 38, 39, 40, 41 which move together in front of fixed contact pads of which 42 and 43 are identified. The movable contact of an inverter 44 is connected to a main conductor 32. The fixed contacts of the inverter 44 are connected to two groups of selector contacts 38, 39 and 40,41. Between the fixed contact of the inverter 44 and the selector contact 39 is arranged an impedance 45 and in parallel on this impedance a thyristor 46. Between the other fixed contact of the inverter 44 and the selector contact 40 is arranged a impedance 47 and a thyristor 48 in parallel with this impedance. A thyristor 49 is disposed between the two groups of selector contacts, ie between contacts 39 and 40. The crew moves from one fixed contact to the other, by example of contact 42 to contact 43. In this case the reverser 44 is put in the position shown. At the start of the movement of the crew, even before the contact 41 leaves the contact 42, the thyristors 46, 48 and 49 are made conductive. As soon as the contact 40 leaves the contact 42, the control of the thyristor 48 is interrupted so that it blocks before the contact 39 leaves the contact 42. As soon as the contact 39 leaves the contact 42, the control of the thyristor 46 is interrupted so that it blocks before contact 41 reaches contact 43. As soon as contact 41 reaches contact 43, the thyristor 49 control is interrupted so that it blocks before contact 38 leaves the contact 42. In this way none of the contacts 38, 39, 40, 41 has any current to be cut, all the cuts being made using the thyristors 46, 48, 49. During the reverse movement for example of the contact 43 towards the contact 42 the inverter 44 is put in the other position and the thyristors are blocked in the following order: 46,48,49.

Whatever the position of the inverter 44, the thyristors 46, 48, 49 are arranged so as to be connected in series with the inverter 44 since the distance between two fixed contacts such as 42 and 43 is always greater than the distance between contacts 38 and 40 or 39 and 41.

The selector device according to Figure 11 is suitable in cases where the voltage difference between two fixed contacts 42 and 43 is relatively large. For lower voltage differences, the circuit according to Figure 10 can be simplified.

FIG. 12 shows a selector unit comprising the selector contacts 39, 40 and 50 which move in front of the fixed contacts 42 42 and 43. During a movement of the selector equipment, for example from contact 42 to the 43 43 two reversers 51 and 52 mechanically coupled connect the contacts 39 and 40 in series. In such an intermediate position, the impedance 47 is interposed between the reverser 52 in series with the contact 40 and the main conductor 32 and the impedance 45 between the main conductor 32 and the contact 39 in series with the inverter 51. The inverter 51 is connected to a circuit comprising a thyristor 53 in series with an impedance 45 and a thyristor 46 placed in parallel.

As the distance between contacts 39 and 50 or 50 and 40 is less than the distance between contacts 42 and 43, thyristors 53 and 46 are made conductive before contact 50 leaves contact 42. As soon as contact 50 has left contact 42 the control of thyristor 46 is interrupted so that the latter blocks on the next zero current pass. Then, the control of the thyristor 53 is interrupted so that the latter blocks before the contact 39 leaves the contact 42. In this way one of the contacts 39, 50 and 40 does not have to cut off a current. These contacts therefore wear very little.

A variant of the selector device according to FIG. 11 is shown in FIG. 12. In this variant a thyristor 54 is connected in series with the impedance 45 and a thyristor 55 is connected in parallel on the impedance 45 and the thyristor 54. The operation of this circuit is identical to that of FIG. 11, if the thyristor 55 is controlled like the thyristor 46 and the thyristor 54 like the thyristor 53.

An even greater simplification is obtained according to FIG. 13 where the impedance 45 and the thyristor 46 of FIG. 11 are deleted and where only the thyristor 53 is maintained.

Another simplification is that obtained by removing impedance 47 from FIG. 11, it is shown in FIG. 14.

The opportunity to take advantage of these latest simplifications is influenced by the degree of reliability and safety that these circuits guarantee.

Claims (10)

1. An electrical appliance (1,2) comprising a series of sockets (3,4,13, 29) and a selector unit and / or a set of switches provided with contacts (5,6,7; 16,17,18; 23.24; 42.43) cooperating with the sockets (3,4,13,. 29) and at least one transition impedance (8,20,34,46,47), as well as a connection to a main conductor (1,32), the selector unit and / or the set of switches being actuated by a control device (11,12), characterized in that at least one reverser (9,19; 21,22; 30,31; 44; 51,52) is connected in series on the selector assembly or in all of the breakers with at least one of the impedances of transition (8,20,34, 46,47) between one of the sockets (3,4,13,29) of the device and the main conductor (1,32) and in that the position of the inverter (9 , 19,21,22,30, 31,44,51,52) is determined as a function of the movement of the selector assembly or of the operating cycle of all the switches imposed by the control device (11,12) . 2. Electrical device according to claim 1 characterized in that the inverter 9 and the impedance 8 are connected in series between one of the taps of the device and a selector contact (7) swept by a movable contact (10) to which is connected the main conductor (I). 3. Electrical device according to claim 1 characterized in that the inverter is composed of two inverters (21,22; 30,31; 30 ', 30 "; 36', 37 '; 51, 52) each suitably coupled connected to a selector contact (16,17; 23,24; 39,40). 4. Electrical device according to one of the preceding claims, characterized in that at least one non-linear element (33; 46,48,49; 53, 54,55) disposed on the selector assembly or in the set of switches is connected in series with at least one of the inverters (30; 30 ', 30 "; 36', 37 '; 44,51). 5. Electrical device according to claim 4, characterized in that the inverter (44) whose movable contact is connected to the main conductor (32) and whose two fixed contacts are connected to two groups of selector contacts (38,39 and 40,41) connected together by a non-linear element (49). 6. An electrical appliance according to claim 5, characterized in that one of the selector contacts (38,41) of each group is connected directly to the corresponding fixed contact of the selector (44) and in that the other selector contact (39,40) is connected to the corresponding fixed contact of the selector through an impedance (45,47) on which a non-linear element (46,48) is placed in parallel. 7. Electrical device according to claim 4, characterized in that the inverter is composed of two inverters (30,31; 30 ', 30 "; 36', 37 '; 51,52) suitably coupled in that each reversers is connected on one side to one of the selector contacts (23,24; 39,40) in that one of the two reversers is connected on the other side through a transition impedance (34,47) to the conductor main 32, and in that the other of the inverters is connected through a non-linear element (33, 53, 55) to the main conductor 32. 8. Electrical apparatus according to claim. 7 characterized in that a third selector contact (50) is connected directly to the main conductor (32). 9. Electrical apparatus according to claim 4, characterized in that the reverser is composed of two reversers (51,52) suitably coupled, in that each reverser is connected on one side to one of the selector contacts (39 , 40), in that one of the inverters is connected on the other side to a circuit composed of a non-linear element (53) put in series with an impedance (45) and a non-linear element put in parallel, this circuit being connected to the main conductor (32) and in that the other inverter is connected directly to the main conductor (32) together with a third selector contact (50). 10. An electrical device according to one of claims 7 to 9 characterized in that the inverter is composed of two inverters each made with two switches (30 ', 30 "; 36', 37 ').

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