METHOD AND DEVICE FOR TESTING A TAP CHANGER OF A TRANSFORMER

Abstract

The following steps are performed in order to test a tap changer (20) of a transformer (5; 6) which tap changer is designed to change a transmission ratio of the transformer (5; 6): generating a test signal which is supplied to a winding (1-3; 10) of the transformer (5; 6) and to the tap changer (20).

Repeatedly actuating the tap changer (20) in order to change the transmission ratio with each actuation.

Determining a curve of an electrical measurement variable (I; I.sub.1; I.sub.2) of the transformer (5; 6) over time (t) for each actuation of the tap changer (20) depending on the test signal.

Filtering the curves (41, 42) in order to prevent at least one of the curves (41, 42) from being output.

Outputting the filtered curves (41; 42).

Claims

1. Method for testing a tap changer of a transformer, wherein the tap changer is designed to change a transmission ratio of the transformer, wherein the method comprises the following steps: generating a test signal which is supplied to a winding of the transformer and to the tap changer, repeatedly actuating the tap changer in order to change the transmission ratio with each actuation, determining a curve of an electrical measurement variable of the transformer over time for each actuation of the tap changer depending on the test signal, filtering the curves in order to prevent at least one of the curves from being output, and outputting the filtered curves.

2. Method according to claim 1, wherein: the transformer is a multi-phase transformer, a separate tap changer is present for each phase of the transformer which is designed to change a transmission ratio of the transformer, respectively one test signal is generated simultaneously for each phase of the transformer which is supplied to a winding of the transformer assigned to the respective phase and to the tap changer assigned to the winding, the tap changers are actuated repeatedly in order to change the transmission ratio with each actuation, the curve of the electrical measurement variable is determined over time respectively during the step of actuating the tap changers for each tap changer depending on the test signal, and the filtered curves of the respective tap changer are output.

3. Method according to claim 2, wherein the test signals for each phase are generated identically in terms of value.

4. Method according to claim 1, wherein the test signal is a direct current signal.

5. Method according to claim 1, wherein the respective winding comprises a plurality of taps, wherein switching from one of the taps to another of the taps takes place in the case of actuating the tap changer, and wherein the filtering of the curves is performed depending on an output tap of the taps away from which switching takes place in the case of actuation and/or depending on a target tap of the taps to which switching takes place in the case of actuation.

6. Method according to claim 5, wherein in the case of actuating the respective tap changer switching takes place from one of the taps at a first side to one of the taps at a second side or from one of the taps at the second side to one of the taps at the first, and wherein in the case of filtering the curves, either the curves in which switching takes place to one of the taps at the second side are eliminated or the curves in which switching takes place to one of the taps at the first side are eliminated.

7. Method according to claim 5, wherein a determined target tap of the taps is predefined and wherein in the case of filtering the curves, the curves in which switching does not take place to the determined target tap are eliminated.

8. Method according claim 5, wherein in the case of filtering the curves, the curves, in which the transmission ratio is increased when actuating respective tap changer, are eliminated, or wherein in the case of filtering the curves, the curves, in which the transmission ratio is decreased when actuating respective tap changer, are eliminated.

9. Method according to claim 2, wherein in the case of filtering the curves, the curves of at least one determined phase are eliminated.

10. Method according to claim 1, wherein in the case of outputting the filtered curves, the curves are illustrated in a temporally-superimposed manner.

11. Method according to claim 10, wherein the curves are illustrated as congruently as possible.

12. Method according to claim 10, in that wherein the curves are plotted in an offset manner.

13. Method according to claim 10, wherein time periods of the curves corresponding to each other are illustrated in a temporally-superimposed manner.

14. Method according to claim 1, wherein the electrical measurement variable comprises one of: a current which flows through the winding and the tap changer, a voltage drop at the winding, and an electrical resistance value which can be calculated depending on the voltage and the current.

15. Apparatus for testing a tap changer of a transformer wherein the tap changer is designed to change a transmission ratio of the transformer, wherein the apparatus comprises a test signal generation device, a measuring device and a control device, wherein the apparatus is designed to supply a test signal to a winding of the transformer to the tap changer by means of the test signal generation device and the control device, wherein the apparatus is designed to determine a curve of an electrical measurement variable of the transformer by means of the measuring device over time respectively during an actuation of the tap changer depending on the test signal, wherein the control device is designed to filter the curves in order to prevent at least one of the curves being output, and wherein the control device is designed to output the filtered curves.

16. Apparatus according to claim 15, wherein the transformer is a multi-phase transformer, wherein a separate tap changer is present for each phase of the transformer which is designed to change a transmission ratio of the transformer, wherein the apparatus is designed to simultaneously generate respectively one test signal for each phase of the transformer by means of the test signal generation device and to supply said test signal to a winding of the transformer assigned to the respective phase and to the tap changer assigned to the winding, wherein the apparatus is designed to determine a curve of an electrical measurement variable of the transformer by means of the measuring device over time respectively during an actuation of the tap changers for each tap changer depending on the test signal, and wherein the control device is designed to output the filtered curves of the respective tap changer.

17. Apparatus according to claim 15, wherein the apparatus comprises a display, wherein the apparatus is designed such that the control device illustrates the filtered curves on the display.

18. (canceled)

Description

[0044] The invention is described in detail below by means of preferred embodiments according to the invention with reference to the figures.

[0045] A plurality of time curves of an electric current is illustrated in FIG. 1 in the case of actuating a tap changer of a transformer according to the invention.

[0046] Only certain time curves of those illustrated in FIG. 1 are illustrated in FIGS. 2 to 4.

[0047] The time curves of an electric current in the case of actuating a tap changer of a transformer are not illustrated in a temporally-superimposed manner in FIG. 5, but rather they are illustrated chronologically.

[0048] A transformer with tap changer is illustrated together with a device according to the invention in FIG. 6.

[0049] A multi-phase transformer is illustrated together with a device according to the invention in FIG. 7.

[0050] A device according to the invention is schematically illustrated in FIG. 8.

[0051] Although one electric current is respectively illustrated in the following figures by way of example both as a test signal and as a measurement variable, it should be noted that according to the invention a voltage can also be applied as the test signal and/or that a voltage, an electrical resistance, an impedance, an output, energy etc can also be used or determined as a measurement variable.

[0052] A plurality of time curves 41, 42 of an electric current are illustrated in a temporally-superimposed manner according to the invention in FIG. 1, wherein each of the curves 41, 42 is determined in the case of the actuation of a tap changer of a transformer. The electric current, the curve of which is determined, flows through the winding and the tap changer arranged in series with the winding. A time period is respectively illustrated for each of the curves which begins at a first time point t.sub.0 and ends at a second time point t.sub.1. In this regard, the first time point t.sub.0 comes shortly after the beginning of the actuation of the tap changer and the second time point t.sub.1 comes after the end of the switching process of the tap changer.

[0053] In the present case, the winding comprises eleven taps or tappings between which the tap changer can be switched, as is explained more precisely in FIG. 6. The curves labelled with the reference numeral 41 respectively show one of ten current curves which are determined when the tap changer switches upwards, whereby the number of the effective coils of winding is reduced. In a similar manner, the curves labelled with the reference numeral 42 respectively show one of ten current curves which are determined when the tap changer switches downwards, whereby the number of the effective coils of the winding is increased.

[0054] As illustrated in FIG. 6, there are left-hand or odd taps 13 and right-hand or even taps 12 of the winding 10. Only the current curves 41, 42 in the case of even switching processes are illustrated in FIG. 2 by eliminating the current curves in the case of odd switching processes by means of filters. An even switching process is then present when switching takes place to an even or right-hand tap 12. In this regard, switching can take place to an even or right-hand tap 12 both in the case of downwards switching and in the case of upwards switching. In other words, the current curves labelled with the reference numeral 41 in FIG. 2 show five even switching processes in the case of downwards switching, while the current curves labelled with the reference numeral 42 in FIG. 2 show five even switching processes in the case of upwards switching.

[0055] In contrast, only the current curves 41, 42 in the case of odd switching processes are illustrated in FIG. 3 by eliminating the current curves in the case of even switching processes by means of filters. An odd switching process is then present when switching takes place to an odd or left-hand tap 13 (see FIG. 6). Like in the case of even switching processes, in the case of odd switching processes, switching can take place to an odd or left-hand tap 13 both in the case of downwards switching and in the case of upwards switching. In other words, the current curves labelled with the reference numeral 41 in FIG. 3 show five odd switching processes in the case of downwards switching, while the current curves labelled with the reference numeral 42 in FIG. 3 show five odd switching processes in the case of upwards switching.

[0056] Only the ten current curves 41 in the case of even switching processes are illustrated in FIG. 4 such that the ten current curves 42 in the case of odd switching processes (see FIG. 1) are not illustrated since they have been filtered out.

[0057] The 20 current curves 41, 42 from FIG. 1 are illustrated in FIG. 5 chronologically side by side. In this connection, a time point (e.g. t.sub.3 or t.sub.6), at which a current curve 41, 42 ends, corresponds to a time point at which a current curve illustrated adjacent thereto begins. In other words, the current curves illustrated in FIG. 5 are not illustrated in a temporally-superimposed manner.

[0058] A transformer 6 with a tap changer 20 and a device 30 according to the invention for testing the tap changer 20 are illustrated in FIG. 6.

[0059] The transformer 6 comprises a winding 10 which has a plurality of taps or tappings 12, 13. The tap changer 20 comprises two tap selectors 14, 15. In this regard, the one tap selector 14 is connected to one of the right-hand or even taps 12 and the other tap selector 15 is connected to one of the left-hand or odd taps 13. Furthermore, the tap changer 20 comprises a first connection 21 and a first resistor 22 which are assigned to the tap selector 15 as well as a second connection 24 and a second resistor 23 which are assigned to the tap selector 14. In the case of the condition illustrated in FIG. 6, a current I flows at connection 11 into the winding 10 and flows out from the winding 10 at the tap 13 which is in contact with the tap selector 15.

[0060] In order to now change the transmission ratio of the transformer 6, a switch 25 of the tap changer 20 is switched from connection 21 to connection 24. The switch 25 here contacts in a first step both the first connection 21 and the first resistor 22 such that the current I flows through the first resistor 22 if the switch 25 loses the contact to the first connection 21 in the second step. In the third step, the switch 25 contacts both the first resistor 22 and the second resistor 23 such that the current I flows both via the first resistor 22 and via the second resistor 23 and thus both via the tap selector 15 and the corresponding tap 13 and via the tap selector 14 and the corresponding taps 12. If the switch 25 is switched further, the switch 25 loses the contact with the first resistor 22 in the fourth step such that the current I flows in the fourth step only via the second resistor 23 and the tap selector 14 and the corresponding tap 12. If the switch 25 is switched further, the switch 25 contacts the second connection 24 in the fifth step such that the second resistor 23 is virtually short-circuited. The current I flows via the second connection 24 as well as the tap selector 14 and the associated tap 12 such that the transmission ratio of the transformer 6 changes correspondingly. If the switch 25 is switched further, the switch 25 loses the contact to the second resistor 23 in the sixth and final step, whereby the switching process or the actuation of the tap changer 20 for changing the transmission ratio of the transformer 6 has finally ended.

[0061] As soon as the tap selector 15 is switched in a currentless manner (i.e. with the fourth step), the tap selector can be connected to another left-hand or odd tap 13. In order to once again change the transmission ratio of the transformer 6, the switch 25 is switched in a similar manner as previously described from the second connection 24 to the first connection 21.

[0062] In order to test the tap changer 20, the device 30 according to the invention is present which has a current source 31 and an ammeter 32. The current I is generated by means of the current source 31 which flows through the winding 10 and the tap changer 20 arranged in series with the winding 10. A time curve of the current I flowing through the winding 10 and the tap changer 20 is in particular determined during the switching over of the tap changer 20 with the corresponding measuring device 9 (see FIG. 8) of the device 30 according to the invention. After determining a plurality of current curves, which are determined during respective switching over processes of the tap changer 20, these current curves are filtered according to predetermined filtering criteria and illustrated in a temporally-superimposed manner.

[0063] A multi-phase transformer 5 is illustrated in FIG. 7 which has three phases with respectively one winding 1-3 in a Y-interconnection. In this regard, each phase or winding 1-3 has a tap changer 20 (not illustrated in FIG. 7) in order to change the transmission ratio of the transformer 5 in the same manner as was previously described with regard to FIG. 6.

[0064] In order to test the tap changer, the device 30 according to the invention generates a first direct current I.sub.1 which is supplied to the end of the first winding 1 facing away from the star point 4 and a second direct current I.sub.2 which is, on the one hand, taken away from the end of the third winding 3 facing away from the star point 4 and, on the other hand, is supplied to the end of the second winding 2 facing away from the star point 4. It can be discerned that the first direct current I.sub.1 also flows away from the star point 4 to the device 30. In other words, the test signals or direct currents I.sub.1, I.sub.2, which are supplied to each winding 1-3, comprise the same value.

[0065] The time curves of the currents through the three windings 1-3 are determined, while the tap changers are repeatedly switched in order to change the transmission ratio of the multi-phase transformer 5. A plurality of determined and filtered current curves are illustrated in a temporally-superimposed manner for each tap changer in order to test the correct operation of the tap changers.

[0066] A further embodiment of the device 30 according to the invention is schematically illustrated in FIG. 8. In addition to a current source 31 which corresponds to the test signal generation means, the device 30 comprises, a controller 7, a display 8 and a measuring means 9 by means of which a time curve 41, 42 of the electrical measurement variable can be determined. The determined and filtered time curves 41, 42 are illustrated on the display 8 in a temporally-superimposed manner.

LIST OF REFERENCE NUMERALS

[0067] 1-3 Winding [0068] 4 Star point [0069] 5 Three-phase alternating current transformer [0070] 6 Transformer [0071] 7 Controller [0072] 8 Display [0073] 9 Measuring device [0074] 10 Winding [0075] 14, 15 Tap selectors [0076] 12, 13 Tap [0077] 20 Tap changer [0078] 11, 21, 24 Connection [0079] 22, 23 Resistor [0080] 30 Device [0081] 31 Current source [0082] 32 Ammeter [0083] 41 Current curve in the case of downwards switching [0084] 42 Current curve in the case of upwards switching [0085] I, I1, I2 Direct current [0086] t Time [0087] t.sub.x Time point