WO2022117549A1

WO2022117549A1 - Method and measuring device for determining a resistance of a transformer winding

Info

Publication number: WO2022117549A1
Application number: PCT/EP2021/083535
Authority: WO
Inventors: Jakob HÄMMERLE; Dirk FLAX
Original assignee: Omicron Electronics Gmbh
Priority date: 2020-12-03
Filing date: 2021-11-30
Publication date: 2022-06-09
Also published as: AT524529A1

Abstract

The present invention relates to a measuring device (20) for automatically determining a resistance of a transformer winding of a transformer (70). The measuring device comprises at least one direct current source (21A, 21B). Each of the at least one direct current sources (21A, 21B) can provide a measuring current. The measuring device also comprises a coupling assembly (22) which is coupled to the at least one direct current source (21A, 21B) and can be coupled to terminals (81 to 84) of at least one high-voltage winding (71-73) of the transformer (70) and terminals (91 to 94) of at least one low-voltage winding (75-77) of the transformer (70). The coupling assembly (22) is designed to simultaneously conduct a measuring current from one direct current source of the at least one direct current source (21A, 21B) through the at least one high-voltage winding (71-73) and to conduct a measuring current from one direct current source of the at least one direct current source (21A, 21B) through the at least one low-voltage winding (75-77).

Description

METHOD AND MEASURING DEVICE FOR DETERMINING A RESISTANCE OF A TRANSFORMER WINDING

FIELD OF THE INVENTION

The present invention relates to a measuring device for automatically determining a resistance of a transformer winding of a transformer and a corresponding method for automatically determining a resistance of a transformer winding of a transformer. The present invention relates in particular to a measuring device and a method, respectively, which enable the resistance of the transformer winding to be determined quickly.

BACKGROUND OF THE INVENTION

The resistance of a transformer winding is a commonly checked quantity to determine the proper condition of the transformer. In the case of power transformers in particular, checking the winding resistance is very time-consuming. In the case of transformers with a high ratio, determining the winding resistance on the low-voltage side winding, which is also referred to as the low-voltage winding, can take a long time. The reason for this is that for the accurate measurement of the winding resistance, a saturation of the

Transform atorkerns is required. In order to reach the saturation of the transformer core, high measuring currents are required, which require powerful measuring devices and heavy cables. Alternatively, with lower currents, saturation of the transformer core can be achieved over a longer measurement interval.

In detail, to measure a winding of a transformer, a direct test current is usually applied to the winding to be measured. It then takes some time before the inductance is saturated and the resistance value no longer changes and can be reliably read. The low-voltage winding in particular usually has a low number of turns, so that the test current combined with the low number of turns in the low-voltage winding has little magnetic flux in the Transformer core generated, which is necessary for saturation. Therefore, it takes a very long time for the core to saturate and a stable resistance measurement to be possible. The measurement can be accelerated by increasing the test current. However, this requires a test device with a high-current output and heavy and unwieldy connection cables that are able to permanently conduct the high test current. The maximum test current is subject to practical limits due to the length and power loss of the cable, which can be in the range of 70 to 100 A, for example. To measure the high-voltage winding, these heavy and unwieldy connection cables must be connected to the high-voltage winding by manual rewiring, for example. Alternatively, a corresponding measuring device can include an internal or external automated switching matrix, a so-called switch box, which replaces manual rewiring and automatically couples the direct test current to either the high-voltage winding or the low-voltage winding.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to enable the resistance of the transformer windings to be determined quickly and easily.

This object is achieved according to the present invention by a measuring device for automatically determining a resistance of a transformer winding of a transformer according to claim 1 and a method for automatically determining a resistance of a transformer winding of a transformer according to claim 17. The dependent claims define embodiments of the invention.

According to one aspect of the present invention, a measuring device for automatically determining a resistance of a transformer winding of a transformer is provided. The measuring device comprises at least one direct current source and a coupling arrangement. The measuring device can, for example, only have one direct current source or several direct current sources include, for example, the measuring device may include two direct current sources. The term "DC power source" as used herein refers to an electrical power source that provides a direct current. The direct current source can be designed, for example, to supply direct current with an adjustable current intensity or adjustable voltage. Each direct current source of the at least one direct current source is thus designed to provide a respective measurement current. The respective measurement current can include, for example, a direct current of a defined size, for example a direct current in the range from 30 A to 100 A, for example 70 A or 100 A. Larger or smaller currents are possible depending on the type of transformer. The coupling arrangement is coupled to the at least one direct current source and can be coupled to terminals of at least one high-voltage winding of the transformer and terminals of at least one low-voltage winding of the transformer. The coupling arrangement is designed to simultaneously conduct a measuring current from a direct current source of the at least one direct current source through the at least one high-voltage winding and a measuring current from a direct current source of the at least one direct current source through the at least one low-voltage winding.

Thus, for example, when determining the resistance of the low-voltage winding, not only is a measurement current passed through the low-voltage winding, but at the same time a measurement current is also passed through the high-voltage winding. The high-voltage winding has a higher number of turns than the low-voltage winding by the transformation ratio of the transformer. As a result, the high-voltage winding generates a significantly higher flux in the transformer core and can thus accelerate the saturation of the transformer core. This means that the resistance of the low-voltage winding can be determined more quickly.

According to a preferred embodiment, the switching arrangement is a controllable switching arrangement. In particular, the coupling arrangement can be such a controllable coupling arrangement in which an interconnection of the connections for the at least one high-voltage winding and the at least one low-voltage winding and the at least one current source can be changed via a corresponding control. The control can be provided, for example, via control information for the controllable coupling arrangement. The control information can be supplied, for example, via appropriate control signals, for example analog or digital control signals.

The controllable coupling arrangement can be designed, for example, to automatically conduct a measurement current from one of the at least one current source into a series circuit consisting of the at least one high-voltage winding and the at least one low-voltage winding based on the control information. For this purpose, the controllable coupling arrangement can comprise, for example, electronic or electromechanical switches.

The measuring device thus makes it possible to connect the high-voltage winding and the low-voltage winding in series and to conduct the measuring current through this series connection. It is clear that in this case only one direct current source is required, which supplies a measuring current which is conducted through the series circuit and thus simultaneously excites the at least one high-voltage winding and the at least one low-voltage winding.

Since the controllable coupling arrangement can be coupled to both the high-voltage winding and the low-voltage winding and can automatically conduct the measurement current through these windings based on the control information, there is no need for manual rewiring for different measurements, for example for a subsequent measurement of only the high-voltage winding or for a subsequent measurement of only the low-voltage winding is required when the transformer core is already largely pre-magnetized.

According to an embodiment in which the high-voltage winding and the low-voltage winding are to be connected in series and therefore only one Direct current source is required, the controllable coupling arrangement comprises a first controllable switching arrangement which is coupled to the direct current source and can be coupled to the terminals of the at least one high-voltage winding. The controllable coupling arrangement also includes a second controllable switching arrangement which is coupled to the direct current source and can be coupled to the terminals of the at least one low-voltage winding. The controllable coupling arrangement also comprises a controllable switching device which is coupled to the first switching arrangement and the second switching arrangement. The controllable switching device can include an electronic or electromechanical switch, for example. The controllable switching device is designed to provide an electrical connection between the first controllable switching arrangement and the second controllable switching arrangement on the basis of the control information.

The first and second controllable switching arrangement can, for example, be constructed similarly to the switch box mentioned at the outset, which is able to selectively couple a measurement current to either the high-voltage winding or the low-voltage winding. Due to the additional controllable switching device between the first switching arrangement and the second switching arrangement, the measuring current can be routed in a simple manner either only through the high-voltage winding, only through the low-voltage winding or through a series circuit consisting of the high-voltage winding and the low-voltage winding. This makes it possible to implement the measuring device by modifying known switch boxes.

For example, the controllable coupling arrangement can be designed to automatically conduct the measurement current in a series circuit based on the control information as follows: the measurement current is conducted through the at least one high-voltage winding by means of the first controllable switching arrangement and then from the first controllable switching arrangement to the second controllable one by means of the controllable switching device Switching arrangement directed. The measurement current is conducted through the at least one low-voltage winding by means of the second controllable switching arrangement. A coupling of the high-voltage winding with the first switching arrangement and a coupling of the low-voltage winding with the second switching arrangement is set up only once and the measurement of the series connection of high-voltage winding and low-voltage winding can be carried out using suitable control information without rewiring.

In a further example, the measurement current can be automatically conducted only through the at least one high-voltage winding by means of further control information by means of the first controllable switching arrangement. In other words, based on first control information, the measurement current in the series circuit can be conducted through the at least one high-voltage winding and the at least one low-voltage winding, and based on second control information, the measurement current can only be conducted through the at least one high-voltage winding. It is clear that the first piece of control information and the second piece of control information are different and are used one after the other, in particular the first piece of control information can be used first and then the second piece of control information. For example, the first actuation information can set the controllable switching device to a conductive state, so that the measurement current is conducted from the first controllable switching arrangement into the second controllable switching arrangement. In contrast, the second control information can set the controllable switching device to a non-conductive state, for example by opening an electromechanical switch, so that the first controllable switching arrangement and the second controllable switching arrangement are decoupled. The controllable switching device therefore makes it possible to carry out different measurements including the at least one high-voltage winding and/or the at least one low-voltage winding without the cabling between the controllable coupling arrangement and the windings of the transformer having to be changed manually.

In a further embodiment, based on the first control information, the measurement current is conducted through the at least one high-voltage winding with the same polarity as based on the second control information. Expressed differently the transformer core is magnetized in the same direction in a measurement based on the first control information as in a measurement based on the second control information. As a result, magnetization reversal in the transformer core can be avoided and the measurements can be carried out in rapid succession.

In a further example, the controllable coupling arrangement is designed to automatically conduct the measurement current only through the at least one low-voltage winding by means of the second controllable switching arrangement on the basis of third control information. The third piece of control information can be used, for example, after the first piece of control information has been used. In particular, the controllable coupling arrangement can be designed to conduct the measurement current through the at least one low-voltage winding with the same polarity on the basis of the first control information as on the basis of the third control information.

In summary, the controllable coupling arrangement allows the measurement current to be conducted for different measurements either only through the at least one high-voltage winding or only through the at least one low-voltage winding or through the series connection consisting of the at least one high-voltage winding and the at least one low-voltage winding, with the Measuring current flows in the same direction through the high-voltage winding and/or low-voltage winding, so that the transformer core is not remagnetized when the measurement changes. As a result, these three different measurements can be carried out in quick succession, each with a short measurement duration.

In a further embodiment of the measuring device, the at least one direct current source comprises at least a first direct current source and a second direct current source. The coupling arrangement is a controllable coupling arrangement, ie an interconnection of the connections for the at least one high-voltage winding and the at least one low-voltage winding as well as the first and second a current source can be changed via a corresponding control. For this purpose, the controllable coupling arrangement can comprise, for example, electronic or electromechanical switches. The control can be provided, for example, via control information for the controllable coupling arrangement. The control information can be supplied, for example, via appropriate control signals, for example analog or digital control signals.

The controllable coupling arrangement can be designed, for example, to automatically conduct a measurement current from the first DC source through the at least one high-voltage winding based on control information and at the same time to conduct a measurement current from the second DC source through the at least one low-voltage winding. A polarity of the measurement current from the first DC source and a polarity of the measurement current from the second DC source are set such that the resulting magnetic fluxes of the current-carrying at least one high-voltage winding and the current-carrying at least one low-voltage winding in a transformer core of the transformer add up.

The measuring device thus makes it possible to conduct a measuring current through the high-voltage winding and a measuring current through the low-voltage winding at the same time. It is clear that, particularly in the event that the high-voltage winding and/or the low-voltage winding comprises a plurality of windings, for example in a multi-phase transformer, a plurality of direct current sources can be provided to supply the multiple high-voltage windings and a plurality of direct current sources to supply the multiple low-voltage windings. It is further clear that in the case that the high-voltage winding comprises a plurality of windings, at least some of the plurality of high-voltage windings can be connected in series, for example, and a measuring current from the first direct current source can be passed through this series connection. Likewise, in the event that the low-voltage winding comprises multiple windings, at least some of the multiple low-voltage windings can be connected in series, for example and a measurement current from the second direct current source can be passed through this series connection.

Due to the measuring current through the high-voltage winding, a significantly higher magnetic flux can be generated in the transformer core and magnetic saturation of the transformer core can thus be accelerated. This means that the resistance of the low-voltage winding can be determined more quickly.

Especially when using at least two current sources separately for the high-voltage winding and the low-voltage winding, it is clear that the above measuring current for the high-voltage winding is not necessarily a measuring current to determine a resistance of the high-voltage winding, but rather can be viewed as a magnetizing current to determine a to achieve rapid magnetization of the iron core of the transformer. The term "measuring current" is therefore not limited here to a current which is used in a calculation of a resistance of a transformer winding, but can also refer to a current which is used when measuring the resistance of a transformer winding (e.g. low-voltage winding) for faster saturation of the iron core of the transformer is fed into another transformer winding (e.g. high-voltage winding).

Since the controllable coupling arrangement can be coupled to both the high-voltage winding and the low-voltage winding and can automatically conduct the measurement currents through these windings based on the control information, there is no need for manual rewiring for different measurements, for example for a subsequent measurement of only the high-voltage winding or for a subsequent measurement of only the low-voltage winding is required when the transformer core is already largely pre-magnetized.

The control information for the controllable coupling arrangement can be determined and made available by a control device, which is part of the measuring device or is assigned to the measuring device. The control device can be, for example, an electronic controller, in particular a microprocessor controller. The controller may further include a user interface, such as a keyboard and display, through which a user selects one or more measurements and initiates the measurements. Additional instructions for coupling the measuring device to the transformer can be provided to the user via the display of the user interface.

According to a further embodiment, the control device can be designed to determine a vector group of the transformer and to determine the control information for the controllable coupling arrangement as a function of the vector group. In the case of a three-phase transformer, the vector group can designate, for example, the connection of the high-voltage windings and the low-voltage windings, for example whether the windings on the relevant side are connected in a star connection, a delta connection or a zigzag connection. For example, the control device can be configured to capture information from the transformer, for example by entering the type plate information from a user or by capturing the type plate information using a detection device of the control device, for example a camera or a scanner, for example a barcode scanner or a QR code scanner. Based on the information on the nameplate, the control device can issue an instruction for coupling the controllable coupling arrangement to the terminals of the high-voltage windings and the low-voltage windings and generate control information for carrying out resistance measurements. Information about the transformer can also be determined by the control device in a different way, for example corresponding information can be retrieved automatically from an electronic data processing system, for example ERP or a cloud-based database, after the transformer has been identified.

The control device can be designed to determine a plurality of different items of control information which are used to determine resistances different transformer windings of the transformer can be used. The control device can also be designed to provide the plurality of different pieces of control information to the controllable coupling arrangement in chronological succession. As a result, resistance measurements on the windings of a transformer can be carried out quickly in several measurement processes without an operator having to carry out complex rewiring.

According to a further embodiment, the measuring device comprises a voltage measuring device which is coupled to the controllable coupling arrangement. The controllable coupling arrangement is designed to automatically provide the voltage measuring device with a voltage across the at least one low-voltage winding on the basis of the control information. Furthermore, the measuring device can be designed to automatically provide the voltage measuring device with a voltage across the at least one high-voltage winding on the basis of additional control information. With a known measuring current through the low-voltage winding or high-voltage winding, the resistance of the low-voltage winding or high-voltage winding can be determined from corresponding voltage measurements of the voltage measuring device.

A further aspect of the present invention relates to a method for automatically determining a resistance of a transformer winding of a transformer. At least one measurement current is provided in the method. A coupling arrangement is coupled to terminals of at least one high-voltage winding of the transformer and terminals of at least one low-voltage winding of the transformer. A measuring current of the at least one measuring current is conducted through the at least one high-voltage winding by means of the coupling arrangement, and at the same time a measuring current of the at least one measuring current is conducted through the at least one low-voltage winding.

For example, a measurement current in a series circuit consisting of the at least one high-voltage winding and the at least one Low-voltage winding are routed by means of the coupling arrangement. It is clear that in this case it is sufficient to provide only one measuring current. By measuring a voltage across the at least one low-voltage winding or the at least one high-voltage winding, the resistance of the corresponding winding of the transformer can be determined in conjunction with the measuring current, which is assumed to be known or is measured. By passing the measurement current through the series circuit of the at least one high-voltage winding and the at least one low-voltage winding, a high magnetic flux is generated in the transformer core, so that the transformer core is quickly led to magnetic saturation. Since the resistance measurement should preferably be carried out in the saturated state of the transformer core, the measurement can also be carried out quickly due to the rapid magnetic saturation.

In another example, a first measurement current is conducted through the at least one high-voltage winding and a second measurement current is conducted through the at least one low-voltage winding by means of the coupling arrangement. The resistance of the corresponding winding of the transformer can be determined by measuring a voltage across the at least one low-voltage winding or the at least one high-voltage winding in connection with the corresponding measuring current, which is assumed to be known or is measured. By passing current through both the at least one high-voltage winding and the at least one low-voltage winding, a high magnetic flux is generated in the transformer core, so that the transformer core is quickly led to magnetic saturation. Since the resistance measurement should preferably be carried out in the saturated state of the transformer core, the measurement can also be carried out quickly due to the rapid magnetic saturation.

The method can, for example, be carried out automatically using the measuring device described above. As a result, rewiring can be avoided and different measurements can be carried out automatically in quick succession. BRIEF DESCRIPTION OF THE FIGURES

The present invention will be explained below with reference to the drawings using preferred embodiments.

1 schematically shows a measuring device for automatically determining a resistance of a transformer winding according to an embodiment of the present invention in connection with a transformer.

2 schematically shows a measuring device for automatically determining a resistance of a transformer winding with a current source according to an embodiment of the present invention in connection with a transformer.

FIG. 3 schematically shows an interconnection of windings of a transformer during a resistance measurement according to an embodiment of the present invention.

FIG. 4 schematically shows an interconnection of windings of an autotransformer with a tertiary winding according to an embodiment of the present invention.

5 schematically shows a measuring device for automatically determining a resistance of a transformer winding according to an embodiment of the present invention in connection with a three-phase transformer.

6 schematically shows details of a controllable coupling arrangement of a measuring device according to an embodiment of the present invention.

FIGS. 7 to 9 show schematic interconnections of windings of a three-phase transformer during a resistance measurement according to an embodiment of the present invention. FIGS. 10 to 12 show schematic interconnections of windings of a further three-phase transformer during a resistance measurement according to an embodiment of the present invention.

FIGS. 13 to 15 show schematic interconnections of windings of a further three-phase transformer during a resistance measurement according to an embodiment of the present invention.

16 schematically shows a measuring device for automatically determining a resistance of a transformer winding with two current sources according to an embodiment of the present invention in connection with a transformer.

FIGS. 17 to 19 show schematic interconnections of windings of a three-phase transformer during a resistance measurement according to an embodiment of the present invention.

20 shows steps of a method for automatically determining a resistance of a transformer winding according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following, embodiments will be described in detail with reference to the accompanying drawings. It is clear that the following description of embodiments is not to be construed as limiting. The scope of the invention should not be limited by the embodiments described herein or by the drawings. The drawings are schematic representations only, and elements depicted in the drawings are not necessarily shown to scale. Connections or couplings between functional blocks, devices, components, or other physical or functional entities shown in the drawings or described herein may also be through an indirect connection or coupling can be realized. Functional blocks can be implemented in hardware, firmware, software or a combination of these.

Fig. 1 shows schematically a measuring device 20 for automatically determining a resistance of a transformer winding of a transformer, for example the transformer 70 shown in Fig. 1. The measuring device comprises at least one direct current source 21A, 21B and a coupling arrangement 22. Each of the direct current sources 21A, 21B is designed to provide a respective measurement current, which can be measured and monitored, for example, with a respective current measuring device 23A, 23B. The direct current sources 21A, 21B can each supply an adjustable measuring current, which can be adjusted, for example, by means of a control device 24 via a suitable control. A first direct current source 21A and a second optional direct current source 21B are shown in dashed lines in FIG. 1 as an example. The multiple direct current sources 21A, 21B can provide different or the same measurement currents. In particular, the use of multiple direct current sources 21A, 21B will be described below with reference to FIGS. 16 to 19. FIG. However, the use of multiple direct current sources 21A, 21B is optional, and the measuring device 20 can also be operated with a single direct current source 21A, as will be described below with reference to FIGS. 2 to 15.

Coupling assembly 22 is coupled to one or more power sources 21A, 21A, 21B and has terminals 31 , 32 , 41 , and 42 for coupling coupling assembly 22 to terminals 81 , 82 , 91 , and 92 of transformer 70 . The connections 31, 32, 41 and 42 of the coupling arrangement 22 can be coupled to the connections 81, 82, 91 and 92 of the transformer 70, for example, via connection lines 51, 52, 61 and 62, as shown in FIG .

The transformer 70 can have, for example, a high-voltage winding 71 and a low-voltage winding 75, which are magnetically coupled to one another via a transformer core 74, for example an iron core. The high-voltage winding 71 typically has more turns than the Low-voltage winding 75. The transformation ratio of the transformer is determined by the turns ratio of high-voltage winding 71 to low-voltage winding 75.

The coupling arrangement 22 is designed to simultaneously supply a measurement current from the one direct current source 21 A or the multiple direct current sources 21 A, 21 B through the at least one high-voltage winding 71 and a further measurement current from one or more of the direct current sources 21 A, 21 B through the at least one low-voltage winding 75 to direct.

FIG. 2 shows an example in which a measurement current can be conducted through the high-voltage winding 71 and a measurement current through the low-voltage winding 75 at the same time using only one direct current source 21 A. The coupling arrangement 22 can be a controllable coupling arrangement which is configured, on the basis of control information from the control device 24, to automatically direct the measurement current from the direct current source 21 A into a series circuit consisting of the at least one high-voltage winding 71 and the at least one low-voltage winding 75.

The controllable coupling arrangement 22 can, for example, as shown in FIG. 2 , comprise a first controllable switching arrangement 25 and a second controllable switching arrangement 26 . The first controllable switching arrangement 25 is coupled to the direct current source 21A and provides the terminals 31 and 32 for coupling to the high-voltage winding 71 of the transformer 70 . The second controllable switching arrangement 26 is coupled to the direct current source 21A and provides the terminals 41 and 42 for coupling to the low-voltage winding 75 of the transformer 70 . The controllable coupling arrangement 22 can also include a controllable switching device 27 which, depending on control information from the control device 24, selectively provides or disconnects an electrical connection between the first controllable switching arrangement 25 and the second controllable switching arrangement 26 . The first controllable switching arrangement 25 and the second controllable switching arrangement 26 each comprise a plurality of switching elements which are able to connect the terminals 31, 32, 41 and 42 to be electrically connected or disconnected either to one of the terminals of the power source 21 A and/or to the controllable switching device 27 as a result of activation by the control device 24 . The switching elements can include, for example, electromechanical or electronic switches. The switching elements can include, for example, on switches, changeover switches and/or step switches or a combination thereof. The switching elements can form a switching matrix which is able to provide the electrical connections described below between the direct current source 21 A, the terminals 31, 32, 41 and 42 and the terminals of the controllable switching device 27 due to suitable activation by the control device 24.

The measuring device 20 also includes a voltage measuring device 28 which is also coupled to the controllable coupling arrangement 22 . In particular, as shown in FIG. 2 , the voltage measuring device 28 can be coupled both to the first controllable switching arrangement 25 and to the second controllable switching arrangement 26 . The switching elements of the first controllable switching arrangement 25 and the second controllable switching arrangement 26 can be designed in such a way that by means of suitable activation of these switching elements by the control device 24, a voltage between two of the terminals 31, 32, 41 and 42 of the voltage measuring device 28 can be supplied.

Although not shown in FIG. 2, one or more of the lines 51, 52, 61 and 62 can each be formed as double lines so that voltage measurements can be made directly at the transformer 70, i.e. at the terminals 81, 82, 91 and 92. perform can be performed. With such a so-called 4-wire measurement, small resistances in particular can be precisely determined, since due to the double design of the lines, a voltage drop due to the measuring current across the lines is not also measured during the voltage measurement. The use of such double lines is possible in all of the embodiments described herein, even if not explicitly mentioned in each of the different embodiments is pointed out. For the sake of clarity, these double lines are not shown in the figures.

The control device 24 can include, for example, a microprocessor control and a user interface. The user interface may include, for example, a display, such as a screen, and an input device, such as a touch-sensitive surface on the screen or a keyboard. Furthermore, the control device 24 can comprise an optical detection device (not shown), for example a camera or a scanner. By means of the optical detection device, the control device 24 can, for example, detect information about the transformer 70, for example by detecting a type plate of the transformer or a barcode or QR code attached to the transformer. Information about the transformer 70 can include, for example, a transformation ratio, a rated power, a rated current, a rated voltage and, in particular, a vector group. The information about the transformer can also be entered by a user via the user interface instead of using the optical detection device.

The controller 24 is coupled to the controllable coupling arrangement 22 and is capable of driving the switching elements of the controllable coupling arrangement 22 in order to carry out resistance measurements in order to determine the resistances of the windings of the transformer 70, as will be described in detail below using various examples.

The measurement of the resistances of the windings 71, 75 of the transformer 70 can be carried out, for example, as follows.

First, the control device 24 controls the first controllable switching arrangement 25 in such a way that the measurement current is output from the current source 21A at the connection 31 and is fed back to the current source 21A via the connection 32 . The controllable switching device 27 is open. The measuring current thus flows from the connection 31 through the line 51 and the connection 81 through the High-voltage winding 71 and from there via the connection 82, the line 52 and the connection 32 back to the power source 21 A. The first controllable switching arrangement 25 is also controlled in such a way that the voltage measuring device 28 is coupled to the connections 31 and 32. The measuring current thus flows through the high-voltage winding 71 and the voltage drop across the high-voltage winding is measured with the voltage measuring device 28 . The resistance of the high-voltage winding 71 can be determined from the size of the measuring current, which is measured, for example, by means of the current measuring device 23, and the size of the voltage drop.

After the resistance of the high-voltage winding 71 has been determined, the control device 24 controls the first switching arrangement 25 in such a way that the measurement current is decoupled from the connections 31 and 32 . The second controllable switching arrangement 26 is then controlled by the control device 24 in such a way that the measurement current is output from the current source 21A at the connection 42 and is fed back to the current source 21A via the connection 41 . The controllable switching device 27 remains open. The measuring current therefore flows from the connection 42 through the line 62 and the connection 92 through the low-voltage winding 75 and via the connection 91, the line 61 and the connection 41 back to the current source 21 A. Via a corresponding activation of the second controllable switching arrangement 26 by means of the Control device 24 couples voltage measurement device 28 to terminals 41 and 42 so that voltage measurement device 28 measures the voltage drop across low-voltage winding 75 while the measurement current flows through low-voltage winding 75 . The resistance of the low-voltage winding 75 can be determined from the quotient of the voltage drop and the measurement current.

A reliable measurement of the winding resistance usually requires magnetic saturation of the transformer core. In particular when measuring the resistance of the low-voltage winding 75, the measuring current combined with the low number of turns generates only a small magnetic flux in the transformer core 74, so that it takes some time before magnetic saturation occurs is reached. With normal measuring currents, this can take 1 to 2 minutes for medium-sized transformers, 10 to 20 minutes for large transformers and, in exceptional cases, up to 1 hour per phase. To speed up the measurement, the measurement current can be increased. However, the size of the measuring current is limited in many measuring devices. In the method described above, the measurement of the low-voltage winding can be accelerated by first measuring the high-voltage winding and then the low-voltage winding, with the measuring current when measuring the high-voltage winding being passed through the high-voltage winding with the same polarity as the measuring current when measuring the Low-voltage winding is passed through the low-voltage winding. A magnetic reversal of the transformer core is therefore not necessary. Rather, the transformer core is already suitably pre-magnetized at the beginning of the measurement of the low-voltage winding.

The measurement of the winding resistances can be further accelerated by the procedure described below. The control device 24 controls the first controllable switching arrangement 25 in such a way that the measurement current is conducted from the direct current source 21A to the connection 31 . Furthermore, a connection between the terminals 32 and 42 is established by means of suitable activation by the control device 24 by establishing a connection between the terminal 32 and the controllable switching device 27 in the first controllable switching arrangement 25, and in the second controllable switching arrangement 26 a connection between the controllable switching device 27 and the connection 42 is produced and the controllable switching device 27 is closed. Finally, the connection 41 is coupled to the current source 21A by means of a suitable activation by the control device 24 so that the measurement current is fed back from the connection 42 through the second controllable switching arrangement 26 to the current source 21A. The measurement current thus flows through the first controllable switching arrangement 25 and the line 51 through the high-voltage winding 71 and from there via the line 52, the first controllable switching arrangement 25, the controllable switching device 27, the second controllable switching arrangement 26 and the line 62 through the low-voltage winding 75 The measurement current flows from the low-voltage winding 75 through the line 61 and the second controllable switching arrangement 26 back to the current source 21 A. The flow of the measuring current is indicated schematically in FIG. 2 by the arrows. It should be noted that the high-voltage winding 71 and the low-voltage winding 75 are traversed in the same direction, so that the transformer core 74 is magnetized by both windings in the same direction. 3 shows this interconnection schematically. Due to the higher number of turns of the high-voltage winding 71, the magnetization of the transformer core 74 reaches saturation very quickly, so that the voltage drop remains constant both at the high-voltage winding and at the low-voltage winding and for the determination of the resistances of the high-voltage winding and the low-voltage winding using the voltage measuring device 28 can be measured. For this purpose, the voltage measuring device 28 can, for example, first be coupled to the terminals 31 and 32 by suitably activating the first controllable switching arrangement 25 and then coupled to the terminals 41 and 42 by suitably activating the second controllable switching arrangement 26 . The measuring current can flow continuously through the high-voltage winding 71 and the low-voltage winding 75 as shown in FIG. 3 during these two voltage measurements.

The procedure described above and the measuring device 20 are also suitable for measuring the winding resistance of an autotransformer if it has a tertiary winding. 4 shows a schematic connection of an autotransformer with a main winding 71 and a tertiary winding 78. The main winding 71 and the tertiary winding 78 are connected in series by suitably controlling the first and second controllable switching arrangement 25, 26. Due to the additional turns of the tertiary winding 78, a magnetic saturation of the transformer core can be reached more quickly with the same measuring current than in the case in which the measuring current is only conducted through the main winding 71. As a result, the resistance of the tertiary winding 78 and/or the main winding 71 can be measured quickly and reliably.

As shown in Figures 5 and 6, the controllable coupling arrangement 22 may have further terminals 33 and 43 to be able to make resistance measurements of windings of polyphase transformers, for example a three-phase transformer 170. Based on information about the transformer 170, for example based on a scanned nameplate of the transformer 170, the controller 24 can issue an instruction on its user interface to connect the transformer 170 to the terminals 31-33 and 41-43. The transformer 170 can have, for example, three high-voltage windings 71 to 73 which are connected, for example, in a star configuration. Furthermore, the transformer can have, for example, three low-voltage windings 75 to 77 which are connected, for example, in a delta configuration. An iron core 74 of the three-phase transformer 170 conducts energy transmission between the high-voltage windings 71 to 73 and the low-voltage windings 75 to 77. According to the instruction for connecting the transformer 170, terminals 81 to 83 of the high-voltage windings 71 to 73 can be connected by means of lines 51 to 53 to the terminals 31 to 33 to be coupled. Likewise, connections 91 to 93 of the low-voltage windings 75 to 77 can be coupled to the connections 41 to 43 via lines 61 to 63 .

The first controllable switching arrangement 25 can be configured, for example, to output the measurement current from the direct current source 21 A at any one of the connections 31 to 33 to the high-voltage windings 71 to 73 and from any other connection 31 to 33 to output current from the high-voltage windings 71 to 73 of the direct current source 21A. Alternatively, the first controllable switching arrangement 25 can conduct current from the high-voltage windings 71 to 73 from any one or more of the terminals 31 to 33 to the controllable switching device 27 . If the controllable switching device 27 is switched on, this current is passed to the second controllable switching arrangement 26 .

The second controllable switching arrangement 26 can be designed, for example, to output the measurement current from the direct current source 21 A to any of the connections 41 to 43 to the low-voltage windings 75 to 77 and from one other any of the terminals 41-43 to shunt current from the low-voltage windings 75-77 back to the DC source 21A. Alternatively, the second controllable switching arrangement 26 can receive current from the controllable switching device 27 and output it to any one or more of the terminals 41 to 43 on the low-voltage windings 75 to 77 .

6 shows an exemplary embodiment of the controllable coupling arrangement 22 in detail. The controllable coupling arrangement 22 shown in FIG. 6 comprises four connections 31 to 34 for coupling to high-voltage windings of a three-phase transformer 270. The fourth connection 34 can be used, for example, for coupling the controllable coupling arrangement 22 to the star point of the high-voltage windings 71 to 73 in a star configuration. The controllable coupling arrangement also includes four connections 41 to 44 for coupling to low-voltage windings 75 to 77 of the three-phase transformer 270. The fourth connection 44 can, for example, be used to couple the controllable coupling arrangement 22 to the neutral point of the low-voltage windings 75 to 77 in a star configuration.

The first controllable switching arrangement 25 comprises four switching elements 251 to 254 which each selectively couple a respective connection of the connections 31 to 34 to a first side of the controllable switching device 27 . Furthermore, the first controllable switching arrangement 25 includes two step switches 255 and 256. Using the step switch 255, a first side of the current source 21 A can be coupled to any one of the connections 31 to 34. Additionally, tap changer 255 allows none of terminals 31-34 to be coupled to the first side of current source 21A. Tap changer 256 is capable of coupling a second side of current source 21A to any one of terminals 31-34 or decoupling the second side of current source 21A from terminals 31-34.

The second controllable switching arrangement 26 also includes four switching elements 261 to 264, which each optionally have a respective connection of the connections 41 to 44 to a second side of the controllable switching device 27 couple. Furthermore, the second controllable switching arrangement 26 includes two step switches 265 and 266. The step switch 265 can be used to couple the first side of the current source 21A to any one of the connections 41 to 44. Additionally, tap changer 265 allows none of terminals 41-44 to be coupled to the first side of current source 21A. Tap changer 266 is capable of coupling the second side of current source 21A to any one of terminals 41-44 or decoupling the second side of current source 21A from terminals 41-44.

It is clear that the step switches 255, 256, 265 and 266 can also each be implemented by several on switches or changeover switches. All switches of the controllable coupling arrangement 22 can comprise electromechanical or electronic switches. The switches of the controllable coupling arrangement 22 can be controlled individually by means of control information from the control device 24, i.e. each of the switches can be set individually under the control of the control device 24, for example switched on, switched off or, in the case of the step switch, set to a specific position .

The controllable coupling arrangement 22 further comprises switching elements in order to couple the voltage measuring device 28 (not shown in FIG. 6 ) to two of the terminals 31 to 34 or to two of the terminals 41 to 44 in order to determine a corresponding voltage between the coupled terminals. Alternatively, several voltage measuring devices can also be provided in order to determine voltages between any two of the connections 31 to 34 and/or any two of the connections 41 to 44 .

Referring to Figures 7 through 15, automated resistance measurements on various three-phase transformers will now be presented. The automated resistance measurements are carried out with a current source, for example with the current source 21 A of the measuring device 20 of FIG 5 and 6. In FIG. 20 method steps of the automated resistance measurements are shown.

7 to 9 relate to measurements on a three-phase transformer 370 with a vector group Yd1 , i.e. the high-voltage windings 71 to 73 are star-connected and the low-voltage windings 75 to 77 are delta-connected. A phase shift between a voltage on the high-voltage windings and a voltage on the low-voltage windings is 30°. This information from the three-phase transformer 370 and further information, for example a rated current of the three-phase transformer 370, can be provided to the control device 24 via, for example, a user input or by detecting a rating plate (step 301). Furthermore, the control device 24 can output instructions for connecting the three-phase transformer 370 to the measuring device 20 for a user on its display. The three-phase transformer 370 is connected at step 302 accordingly. The connections 81 to 83 of the high-voltage windings 71 to 73 are coupled to the connections 31 to 33 of the first controllable switching arrangement 25, for example. The connections 91 to 93 of the low-voltage windings 75 to 77 are coupled to the connections 41 to 43 of the second controllable switching arrangement 26, for example. A suitable measurement current can be set and provided in step 303 by the control device 24 using the direct current source 21A.

In step 304, the control device 24 generates control information for the controllable coupling arrangement 22 in order to let the measuring current flow through the three-phase transformer 370 according to the configuration shown in FIG. In step 305 the controllable coupling arrangement 22 is controlled by the control device 24 in such a way that the current is output from the direct current source 21A at the connection 31 and thus flows through the high-voltage winding 71 . For example, the step switch 255 can be controlled accordingly. Due to the delta connection, the measuring current flowing through the high-voltage winding 71 is divided and flows through the high-voltage windings 72 and 73 and is switched off by means of the switching elements 252 and 253 passed to the controllable switching device 27. The controllable switching device 27 is switched through and the measuring current is fed into the delta connection of the low-voltage windings between the low-voltage winding 75 and the low-voltage winding 77 by means of the switching element 261 . The measurement current flows through the delta connection and is conducted back to the direct current source 21 A via the terminals 92 and 42 by means of the tap changer 266 between the low-voltage winding 75 and the low-voltage winding 76 .

In summary, the measurement current is passed into a series circuit consisting of the high-voltage windings 71 to 73 and the low-voltage windings 91 to 93 by means of the controllable coupling arrangement 22 . The configuration of the measurement current described above causes a magnetic flux in the transformer core due to the measurement current through the high-voltage windings 71 to 73 to have the same direction as a magnetic flux in the transformer core due to the measurement current through the low-voltage windings 75 to 77. Due to the significantly higher number of turns of the high-voltage windings 71 to 73 compared to the low-voltage windings 75 to 77, the transformer core can be saturated more quickly with the same measurement current than in the case where the measurement current is only passed through the low-voltage windings 75 to 77.

As soon as the saturation of the transformer core is essentially reached, voltage measurements can be carried out in step 306 using the voltage measuring device 28 . For example, a voltage across the low-voltage winding 75 can be measured at the terminals 91, 92, a voltage across the low-voltage winding 76 can be measured at the terminals 92, 93, and a voltage across the low-voltage winding 77 can be measured across the terminals 93, 91. Due to the known connection of the low-voltage windings 75 to 77 in a delta circuit, the voltages across the individual low-voltage windings and the measuring current, corresponding equations can be set up in which the individual resistances of the individual low-voltage windings 75 to 77 as unknowns are included and solved (step 307). In addition, voltages on the high voltage windings 71-73 can be measured at the terminals 81-83 in order to set up and solve equations for the individual resistances of the individual high voltage windings 71-73 in the same way. The voltage measurements can be carried out automatically by the control device in that the control device couples the voltage measuring device 28 to the respective connections 31 to 33 or 41 to 43 via the controllable coupling arrangement 22 .

Further measurements can be carried out in a changed configuration (step 308). For example, according to another measurement according to the configuration shown in FIG. 8 , the measurement current can be routed through the three-phase transformer 370 . In yet another measurement, the measurement current may be routed through the three-phase transformer 370 according to the configuration shown in FIG. 9 . In these measurements, too, the measurement current is conducted by means of the controllable coupling arrangement 22 into a series circuit consisting of the high-voltage windings 71 to 73 and the low-voltage windings 91 to 93 . The configurations of Figs. 8 and 9 also cause a magnetic flux in the transformer core due to the high-voltage windings 71 to 73 to have the same direction as a magnetic flux in the transformer core due to the low-voltage windings 75 to 77, so that rapid saturation of the transformer core can be achieved can and the voltage measurements can be carried out after a relatively short time after applying the measuring current. On the basis of the further measurements of FIGS. 8 and 9, further equations can be set up in which the individual resistances of the individual low-voltage windings 75 to 77 or the individual resistances of the individual high-voltage windings 71 to 73 are contained as unknowns. The individual resistances of the individual low-voltage windings 75 to 77 and/or the individual resistances of the individual high-voltage windings 71 to 73 can be determined by solving the system of equations. This can likewise be carried out automatically by the control device 24 . It should be noted that measurements of FIGS. 7 to 9 are sequentially automated from the Control device 24 can be carried out so that no complex rewiring is required when determining the resistance values of the windings of the three-phase transformer.

10 to 12 show connection configurations for a three-phase transformer 470 with a vector group Yd5 in order to carry out a resistance measurement of high-voltage windings 71 to 73 and/or low-voltage windings 91 to 93. In a vector group Yd5, the high-voltage windings 71 to 73 are star-connected and the low-voltage windings 75 to 77 are delta-connected, and a phase shift between a voltage at the high-voltage windings and a voltage at the low-voltage windings is 150°. In these measurements, too, the measurement current is conducted by means of the controllable coupling arrangement 22 in a series circuit consisting of the high-voltage windings 71 to 73 and the low-voltage windings 91 to 93. The configurations of FIGS. 10 to 12 each cause a magnetic flux in the

Transform atorkern due to the measurement current through the high-voltage windings 71 to 73 has the same direction as a magnetic flux in the transformer core due to the measurement current through the low-voltage windings 75 to 77, so that rapid saturation of the Transform atorkern can be achieved. Consequently, the voltage measurements can be carried out after a relatively short time after the measurement current has been applied, so that the resistances of the high-voltage windings 71 to 73 and/or the low-voltage windings 75 to 77 can be determined quickly and reliably.

13 to 15 show connection configurations for a three-phase transformer 570 with a vector group Yd11. In a vector group Yd11, the high-voltage windings 71 to 73 are star-connected and the low-voltage windings 75 to 77 are delta-connected. A phase shift between a voltage across the high-voltage windings and a voltage across the low-voltage windings is 330°. The connection configurations shown in Fig. 13 to 15 are for a resistance measurement of high-voltage windings 71 to 73 and/or low-voltage windings 91 to 93 suitable. Due to the connection configurations shown in Fig. 13 to 15, the measurement current is conducted by means of the controllable coupling arrangement 22 in a series circuit consisting of the high-voltage windings 71 to 73 and the low-voltage windings 91 to 93, with a magnetic flux in the transformer core due to the measurement current flowing through the high-voltage windings 71 to 73 have the same direction as a magnetic flux in the transformer core due to the measuring current through the low-voltage windings 75 to 77. As a result, both the measuring current through the high-voltage windings and the measuring current through the low-voltage windings contribute to the saturation of the transformer core, so that this is reached quickly. Voltage measurements can be carried out after a short time after the measurement current has been applied, so that the resistances of the high-voltage windings 71 to 73 and/or the low-voltage windings 75 to 77 can be determined quickly and reliably.

Fig. 16 shows an example in which with two direct current sources, i.e., a first direct current source 21 A and a second direct current source 21 B, a measuring current can be passed through the high-voltage winding 71 and a measuring current through the low-voltage winding 75 at the same time. The coupling arrangement 22 can be a controllable coupling arrangement which is configured to automatically conduct a measurement current from the first DC source 21 A through the high-voltage winding 71 on the basis of control information from the control device 24 and at the same time to conduct a measurement current from the second DC source 21 B through the low-voltage winding 75 conduct.

A polarity of the measurement current from the first DC source 21 A and a polarity of the measurement current from the second DC source 21 B are set in such a way that the resulting magnetic fluxes of the current-carrying high-voltage winding and the current-carrying low-voltage winding in the transformer core 74 of the transformer 70 add up.

The controllable coupling arrangement 22 can, for example, comprise electrical or electronic switching elements. With these switching elements For example, the polarity of the measurement currents from the first and second direct current sources 21A and 21B can be adjusted. In the event that the controllable coupling arrangement 22 has further connections for connecting a polyphase transformer, as is shown, for example, in FIGS the high-voltage windings and the low-voltage windings of the polyphase transformer are conducted.

The measuring device 20 also includes a voltage measuring device 28 which is also coupled to the controllable coupling arrangement 22 . Switching elements of the controllable coupling arrangement 22 can be designed in such a way that a voltage between two of the terminals 31 , 32 , 41 and 42 can be supplied to the voltage measuring device 28 by suitable activation of these switching elements by the control device 24 .

The control device 24 is coupled to the controllable coupling arrangement 22 and is able to control the switching elements of the controllable coupling arrangement 22, to make resistance measurements to determine the resistances of the windings of transformer 70, as will be described below.

The control device 24 controls the controllable coupling arrangement 22 in such a way that the measurement current is output from the first direct current source 21A at the connection 31 and is fed back to the first direct current source 21A via the connection 32 . The measuring current thus flows from the connection 31 through the line 51 and the connection 81 through the high-voltage winding 71 and from there via the connection 82, the line 52 and the connection 32 back to the first direct current source 21 A. In addition, the control device 24 controls the controllable coupling arrangement 22 in such a way that the measurement current is output from the second direct current source 21B at the terminal 42 and fed back to the second direct current source 21B via the terminal 41 . The measurement current thus flows from the connection 42 through the line 62 and the connection 92 through the low-voltage winding 75 and from there via the connection 91, the line 53 and the connection 41 back to the second direct current source 21B.

A reliable measurement of the winding resistance usually requires magnetic saturation of the transformer core. In particular when measuring the resistance of the low-voltage winding 75, the measuring current combined with the low number of turns generates only a small magnetic flux in the transformer core 74, so that it takes some time before magnetic saturation is reached. With normal measuring currents, this can take 1 to 2 minutes for medium-sized transformers, 10 to 20 minutes for large transformers and, in exceptional cases, up to 1 hour per phase. To speed up the measurement, the measurement current can be increased. However, the size of the measuring current is limited in many measuring devices. The measuring current from the first direct current source 21 A and the measuring current from the second direct current source 21 B flow simultaneously through the high-voltage winding or low-voltage winding, so that the resulting magnetic fluxes of the current-carrying high-voltage winding 71 and the current-carrying low-voltage winding 75 in the transformer core 74 of the transformer 70 add up. This allows the transformer core 74 to quickly become magnetically saturated so that resistance measurements on the high voltage winding 71 and the low voltage winding 75 can be made quickly and accurately.

For this purpose, the controllable coupling arrangement 22 is controlled, for example, in such a way that the voltage measuring device 28 is coupled to the terminals 31 and 32 . The measuring current of the first direct current source 21 A flows through the high-voltage winding 71 and the voltage drop across the high-voltage winding is measured with the voltage measuring device 28 . The resistance of the high-voltage winding 71 can be determined from the size of the measuring current, which is measured, for example, by means of the current measuring device 23A, and the size of the voltage drop.

After the resistance of the high-voltage winding 71 has been determined, the control device 24 controls the controllable coupling arrangement 22 in such a way that the voltage-measuring device 28 is coupled to the connections 41 and 42, so that the voltage-measuring device 28 measures the voltage drop across the low-voltage winding 75, while the measuring current flows from the second DC source 21 B through the low-voltage winding 75 flows. The measurement current from the second direct current source 21B is either known from the setting of the second direct current source 21B or can be measured with the current measuring device 23B. The resistance of the low-voltage winding 75 can be determined from the quotient of the voltage drop and the measurement current.

Referring to Figures 17-19, automated resistance measurements on a three-phase transformer will now be presented. The automated resistance measurements are made using multiple current sources carried out, for example with the direct current sources 21 A and 21 B of the measuring device 20 of FIG the coupling arrangement 22 in FIGS. 5 and 6. In FIG. 20 method steps of the automated resistance measurements are shown.

17 to 19 relate to measurements on a three-phase transformer 370 with a vector group Yd1, ie the high-voltage windings 71 to 73 are star-connected and the low-voltage windings 75 to 77 are delta-connected. A phase shift between a voltage on the high-voltage windings and a voltage on the low-voltage windings is 30°. This information from the three-phase transformer 370 and further information, for example a rated current of the three-phase transformer 370, can be provided to the control device 24 via, for example, a user input or by detecting a rating plate (step 301). Furthermore, the control device 24 can output instructions for connecting the three-phase transformer 370 to the measuring device 20 for a user on its display. The three-phase transformer 370 is connected at step 302 accordingly. The connections 81 to 83 of the high-voltage windings 71 to 73 are connected to corresponding connections of the controllable coupling arrangement 22 . The connections 91 to 93 of the low-voltage windings 75 to 77 are also connected to corresponding connections of the controllable coupling arrangement 22 . A suitable measurement current is set and made available in step 303 by the control device 24 using the first direct current source 21 A for the high-voltage windings 71 to 73 . At the same time, in step 303, a suitable measurement current is set and made available by the control device 24 using the second direct current source 21B for the low-voltage windings 75 to 76 . The measurement current from the first DC power source 21A may be different than the measurement current from the second DC power source 21B. Depending on the properties of the low-voltage windings 75 to 77 and High-voltage windings 71 to 73 are set appropriately. For example, the measurement current from the second direct current source 21B can be greater than the measurement current from the first direct current source 21A since the high-voltage windings 75 to 77 usually have a greater resistance than the low-voltage windings 71 to 73.

In step 304, the control device 24 generates control information for the controllable coupling arrangement 22 in order to let the measuring currents flow through the three-phase transformer 370 according to the configuration shown in FIG. In step 305 the controllable coupling arrangement 22 is controlled by the control device 24 in such a way that the current is output from the first direct current source 21A to the connection 81 and thus flows through the high-voltage winding 71 . Due to the delta connection, the measuring current flowing through the high-voltage winding 71 is divided and flows through the high-voltage windings 72 and 73 and is fed back from the controllable coupling arrangement via the terminals 82 and 83 to the first direct current source 21A. At the same time, the controllable coupling arrangement is controlled by the control device 24 via the control information in such a way that the measurement current is output from the second direct current source 21B to the connection 91 of the transformer 370 . As a result, the measurement current is fed from the second direct current source 21B into the delta connection of the low-voltage windings between the low-voltage winding 75 and the low-voltage winding 77 . The measurement current flows through the delta circuit and is routed back to the second direct current source 21B via the connection 92 by means of the controllable coupling arrangement 22 between the low-voltage winding 75 and the low-voltage winding 76 .

In summary, a measurement current from the first DC source 21A through the high-voltage windings 71 to 73 and a measurement current from the second DC source 21B through the low-voltage windings 91 to 93 are simultaneously conducted by means of the controllable coupling arrangement 22 . The configuration of the measurement current described above causes a magnetic flux in the transformer core due to the measurement current through the High-voltage windings 71 to 73 have the same direction as a magnetic flux in the transformer core due to the measuring current through the low-voltage windings 75 to 77. As a result, saturation of the transformer core can be reached more quickly than in the case where the measuring current is only passed through the low-voltage windings 75-77.

As soon as the saturation of the transformer core is substantially reached, voltage measurements can be carried out using the voltage measuring device 28 in step 306 . For example, a voltage across the low-voltage winding 75 can be measured at the terminals 91, 92, a voltage across the low-voltage winding 76 can be measured at the terminals 92, 93, and a voltage across the low-voltage winding 77 can be measured across the terminals 93, 91. Based on the known connection of the low-voltage windings 75 to 77 in a delta circuit, the voltages across the individual low-voltage windings and the measurement current, appropriate equations can be set up in which the individual resistances of the individual low-voltage windings 75 to 77 are contained as unknowns and can be solved (step 307 ). In addition, voltages on the high voltage windings 71-73 can be measured at the terminals 81-83 in order to set up and solve equations for the individual resistances of the individual high voltage windings 71-73 in the same way. The voltage measurements can be carried out automatically by the control device in that the control device couples the voltage measuring device 28 to the respective connections 81 to 83 or 91 to 93 via the controllable coupling arrangement 22 .

Further measurements can be carried out in a changed configuration (step 308). For example, according to another measurement according to the configuration shown in FIG. 18 , the measurement current can be routed through the three-phase transformer 370 . In yet another measurement, the measurement current may be routed through the three-phase transformer 370 according to the configuration shown in FIG. In these measurements, too, a measurement current from the first direct current source 21 A through the High-voltage windings 71 to 73 and a measuring current from the second direct current source 21B are passed through the low-voltage windings 91 to 93 . The configurations of FIGS. 18 and 19 also cause a magnetic flux in the transformer core due to the high-voltage windings 71 to 73 to have the same direction as a magnetic flux in the transformer core due to the low-voltage windings 75 to 77, so that the transformer core saturates quickly can be and the voltage measurements can be carried out after a relatively short time after applying the measuring current. On the basis of the further measurements in FIGS. 18 and 19, further equations can be set up in which the individual resistances of the individual low-voltage windings 75 to 77 or the individual resistances of the individual high-voltage windings 71 to 73 are contained as unknowns. The individual resistances of the individual low-voltage windings 75 to 77 and/or the individual resistances of the individual high-voltage windings 71 to 73 can be determined by solving the system of equations. This can likewise be carried out automatically by the control device 24 . It should be noted that measurements in FIGS. 17 to 19 can be carried out automatically in sequence by the control device 24, so that no complex rewiring is required when determining the resistance values of the windings of the three-phase transformer.

Claims

37 CLAIMS

1 . Measuring device for automatically determining a resistance of a transformer winding of a transformer, comprising: at least one direct current source (21 A, 21 B), each of the at least one direct current source (21 A, 21 B) being designed to provide a respective measuring current, a coupling arrangement (22) , which is coupled to the at least one direct current source (21 A, 21 B) and is connected to terminals (81-84) of at least one high-voltage winding (71-73) of the transformer (70) and terminals (91-94) of at least one low-voltage winding (75- 77) of the transformer (70) can be coupled, the coupling arrangement (22) being designed to simultaneously carry a measuring current from a direct current source of the at least one direct current source (21 A, 21 B) through the at least one high-voltage winding (71-73) and a measuring current from a direct current source of the at least one direct current source (21 A, 21 B) through the at least one low-voltage winding (75-77).

2. Measuring device according to claim 1, wherein the coupling arrangement (22) is a controllable by a control information coupling arrangement.

3. Measuring device according to claim 2, wherein the controllable coupling arrangement (22) is designed to automatically conduct the respective measurement current through the at least one high-voltage winding (71-73) and the respective measurement current through the at least one low-voltage winding (75-77) on the basis of the control information .

4. Measuring device according to claim 2 or claim 3, wherein the controllable coupling arrangement (22) is designed, on the basis of the control information, to automatically transfer a measuring current from a direct current source (21 A) of the at least one direct current source (21 A, 21 B) to a series circuit consisting of the at least to conduct a high-voltage winding (71-73) and the at least one low-voltage winding (75-77). 38

5. Measuring device according to claim 4, wherein the controllable coupling arrangement (22) comprises: a first controllable switching arrangement (25) which is coupled to the direct current source (21 A) and connected to the terminals (81-84) of the at least one high-voltage winding (71- 73) can be coupled, a second controllable switching arrangement (26) which is coupled to the direct current source (21 A) and can be coupled to the terminals (91-94) of the at least one low-voltage winding (75-77), and a controllable switching device (27 ), which is coupled to the first controllable switching arrangement (25) and the second controllable switching arrangement (26), the controllable switching device (27) being designed to provide an electrical connection between the first controllable switching arrangement (25) and the second controllable one on the basis of the control information To provide switching arrangement (26).

6. Measuring device according to claim 5, wherein the controllable coupling arrangement (22) is designed, on the basis of the control information, to automatically transfer the measuring current into a series circuit by means of the first controllable switching arrangement (25) through the at least one high-voltage winding (71-73), by means of the controllable switching device ( 27) from the first controllable switching arrangement (25) to the second controllable switching arrangement (26), and by means of the second controllable switching arrangement (26) through the at least one low-voltage winding (75-77).

7. Measuring device according to claim 5 or claim 6, wherein the control information is a first control information and wherein the controllable coupling arrangement (22) is designed, based on a second control information automatically the measurement current by means of the first controllable switching arrangement (25) only through the at least one high-voltage winding ( 71-73).

8. Measuring device according to claim 7, wherein due to the first control information, the measurement current is passed through the at least one high-voltage winding (71-73) with the same polarity as due to the second control information.

9. Measuring device according to one of claims 5-8, wherein the control information is a first piece of control information and wherein the controllable coupling arrangement (22) is designed, on the basis of third control information, to automatically transfer the measuring current by means of the second controllable switching arrangement (26) only through the at least one low-voltage winding (75-77) to direct.

10. Measuring device according to claim 9, wherein the controllable coupling arrangement (22) is designed to conduct the measurement current through the at least one low-voltage winding (75-77) with the same polarity as based on the third control information based on the first control information.

11 . Measuring device according to claim 2 or claim 3, wherein the at least one direct current source (21 A, 21 B) comprises a first direct current source (21 A) and a second direct current source (21 B), the controllable coupling arrangement (22) being configured on the basis of the control information to automatically conduct a measurement current from the first direct current source (21A) through the at least one high-voltage winding (71-73) and at the same time a measurement current from the second direct current source (21B) through the at least one low-voltage winding (75-77) with such a polarity that the resulting magnetic fluxes add up in a transformer core of the transformer.

12. Measuring device according to one of claims 2-11, wherein the measuring device (20) further comprises a control device (24) which determines the control information for the controllable coupling arrangement (22).

13. Measuring device according to claim 12, wherein the control device (24) is further configured to determine a vector group of the transformer (70) and the To determine control information for the controllable coupling arrangement (22) depending on the switching group.

14. Measuring device according to claim 12 or claim 13, wherein the control device (24) is designed to determine a plurality of different pieces of control information, which are used to determine resistances of different transformer windings of the transformer (70), and the plurality of different pieces of control information in chronological succession to the controllable coupling arrangement (22) to provide.

15. Measuring device according to one of claims 2-14, wherein the measuring device (20) further comprises a voltage measuring device (28) which is coupled to the controllable coupling arrangement (22), wherein the controllable coupling arrangement (22) is configured based on the control information of the Voltage measuring device (28) automatically provide a voltage across the at least one low-voltage winding (75-77).

16. Measuring device according to one of claims 2-15, wherein the measuring device (20) further comprises a voltage measuring device (28) which is coupled to the controllable coupling arrangement (22), wherein the controllable coupling arrangement (22) is configured based on the control information of the Voltage measuring device (28) automatically provide a voltage across the at least one high-voltage winding (71-73).

17. A method for automatically determining a resistance of a transformer winding of a transformer, the method comprising:

Generating (303) at least one measuring current, coupling (302) a coupling arrangement (22) with connections (81-84) of at least one high-voltage winding (71-73) of the transformer (70) and connections (91-94) of at least one low-voltage winding (75- 77) of the transformer (70), simultaneously conducting (305) a measurement current of the at least one measurement current through the at least one high-voltage winding (71-73) and one Measuring current of the at least one measuring current through the at least one low-voltage winding (75-77) by means of the coupling arrangement (22).

18. The method according to claim 17, wherein the method is carried out by means of a measuring device (20) according to any one of claims 1-16.