Method for adapting a target voltage value for controlling a tap-changing transformer, and device for adapting a target voltage value for controlling a tap-changing transformer
Patent Information
- Application Number
- EP2023722264
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-02
- Filing Date
- 2023-04-19
- Publication Date
- 2025-01-29
AI Technical Summary
In power networks with step-up transformers, maintaining constant voltage across consumers while managing reverse active power flows and maximizing system utilization is challenging, especially with increasing generator presence on the low-voltage side, as traditional fixed voltage setpoints fail to adapt to changing conditions.
A method and device for adjusting the voltage setpoint of a step transformer using an on-load tap changer, which determines reverse power flow by measuring current and voltage, calculates a slope value (m) based on power measurements at different tap positions, and actuates the tap changer to maintain voltage within a predetermined band, ensuring efficient voltage regulation and preventing overvoltages.
This approach allows for quick and efficient adaptation of the voltage setpoint, preventing overvoltages and ensuring maximum feed-in power, even with changing network conditions, such as the integration of PV systems, without negative effects.
Smart Images
Figure 1.1
Abstract
Description
[0001] METHOD FOR ADJUSTING A VOLTAGE SETPOINT FOR THE CONTROL OF A TAP TRANSFORMER AND DEVICE FOR ADJUSTING A VOLTAGE SETPOINT FOR THE CONTROL OF A TAP TRANSFORMER The invention relates to a method for adapting a voltage setpoint for the control of a tap transformer by means of an on-load tap changer.
[0002] Furthermore, the invention relates to a device for adjusting a voltage setpoint for the control of a tap transformer.
[0003] Typically, active power is consumed by consumers on the low-voltage side of a tap-changer in a network. To keep the voltage constant as consumption increases or decreases, voltage regulation is carried out using an on-load tap-changer. However, since more and more generators are located on the low-voltage side, a negative active power flow can occur. This requires a new control concept. The object of the present invention is therefore to create a method for adjusting a voltage setpoint for controlling a tap-changer with an on-load tap-changer, by means of which the voltage at the end consumer does not slip out of a predetermined voltage range and, in addition, the maximum system load, which corresponds to the current through the lines, is not exceeded.
[0004] This task is solved by a method for adjusting a voltage setpoint for voltage regulation of a tap transformer using an on-load tap changer, the method comprising the following steps: determining a reverse power flow on a low-voltage side of the tap transformer by measuring a current and a voltage; actuating the on-load tap changer from a current tap position to another tap position and measuring the voltage and current in the next tap position; determining a value m from the power of the different tap positions; using the determined value m as the gradient for a first section of a straight line of a voltage setpoint.
[0005] The method makes it easy to adjust the voltage setpoint, which is used to control the on-load tap changer in the tap transformer, particularly efficiently and quickly in the event of reverse power flow, thus preventing overvoltages for consumers in the grid. Furthermore, the method ensures maximum feed-in power. A fixed voltage setpoint does not allow for response to changes in the grid on the low-voltage side. The method makes it possible, for example, for a PV system to be easily connected to the grid without this having a negative impact. The method then adjusts the voltage setpoint to the new grid conditions. For this purpose, the power (apparent power and / or active power) at different tap positions is determined after the reverse power flow has been determined.The powers are based on measured currents and voltages on the low-voltage side of the tap-changer when the on-load tap-changer moves to different tap positions. Once determined, the quotient of the powers then represents the value m of the slope of the straight line that represents the voltage setpoint.
[0006] The power can be determined in any way, for example, as apparent power and / or active power. The reverse power flow can be determined in any way, for example, by measuring the current and voltage on the low-voltage side of the tap-change transformer. In particular, when reverse power flow is detected, the active current flows from the consumers and generators, i.e., from the low-voltage side, via the tap-change transformer to the high-voltage side.
[0007] The on-load tap-changer can be designed in any way and, for example, be an on-load tap-changer with a diverter switch and selector or load selector. Furthermore, the on-load tap-changer can have mechanical switching elements such as contacts and vacuum interrupters or semiconductor switching elements. The on-load tap-changer can be operated via a motor drive or electronic control of the semiconductor switching elements.
[0008] Power can be determined in any way, for example, as the product of measured current and measured voltage. Either apparent power or active power can be determined.
[0009] The value m for the gradient for the first section of a straight line of a voltage setpoint is determined as a quotient of the power of different tap positions of the on-load tap changer.
[0010] The procedure can be carried out in any way, whereby the
[0011] Value m is used after its determination as the gradient in the first section of the straight line of the voltage setpoint.
[0012] The method can be carried out in any way, whereby the power in the current tap position is determined as the product of the measured current and the measured voltage in the current tap position; the on-load tap-changer is operated and moved from a current tap position to a higher tap position; the power of the higher tap position is determined as the product of the measured current and the measured voltage of the higher tap position; the value m is determined as the quotient of the power of the higher tap position and the power of the lower tap position.
[0013] After its determination, the value m is then used as the gradient in the first section of the straight line of the voltage setpoint and thus replaces the previous first section of the straight line.
[0014] The method can be carried out in any way, whereby the power in the current tap position is determined as the product of the measured current and the measured voltage in the current tap position; the on-load tap-changer is operated and moved from a current tap position n to a lower tap position; the power of the lower tap position is determined as the product of the measured current and the measured voltage of the lower tap position; the value m is determined as the quotient of the power of the higher tap position n and the power of the lower tap position n-1. The method can be carried out in any way, whereby the on-load tap-changer is operated and moved from a current tap position to a higher tap position; - the power of the higher tap position is determined as the product of the measured
[0015] current and the measured voltage of the higher tap position; the on-load tap-changer is operated twice and moved from a current tap position to the lower tap position; - the power of the lower tap position is determined as the product of the measured current and the measured voltage of the lower tap position; the value m is determined as the quotient of the power of the higher tap position and the power of the lower tap position.
[0016] The procedure can be carried out in any way, whereby the on-load tap-changer is operated and moved from a current tap position to a lower tap position; the power of the lower tap position is determined as the product of the measured current and the measured voltage of the lower tap position; the on-load tap-changer is operated twice and moved from a current tap position to the higher tap position; the power of the higher tap position is determined as the product of the measured current and the measured voltage of the higher tap position; the value m is determined as the quotient of the power of the higher tap position and the power of the lower tap position. When determining the voltage setpoint, the on-load tap-changer is always switched from the current tap position to an adjacent tap position. The voltage and current are measured in the respective tap positions.The quotient of the power of the higher tap position and the lower tap position forms the slope of the straight line that represents the voltage setpoint. Higher and lower tap position here means that the numerical value of the higher tap position of the on-load tap-changer is higher than the numerical value of the lower tap position. Furthermore, switching can be performed from a current tap position to a higher tap position. The tap position is then switched to the lower tap position twice. The voltage and current are measured accordingly in the tap positions reached. The value m for the slope of the voltage setpoint thus becomes more precise. The slope triangle becomes larger, and thus the determined value m more precise.
[0017] Furthermore, it is an object of the present invention to provide a device for adjusting a voltage setpoint for voltage regulation of a tapped transformer, comprising: at least one measuring device for measuring a current and a voltage on the low-voltage side of the tapped transformer; a control device connected to the at least one measuring device for receiving the measured current and voltage.
[0018] The measuring device can be designed in any way, for example it can have a current sensor and a voltage sensor.
[0019] These sensors are connected to the control device via cable or wirelessly. The device is designed and configured to carry out the previously described improved method for adjusting a voltage setpoint for voltage regulation of a tap-changer by means of an on-load tap-changer and, in particular, to record the measured currents and voltages, to determine a reverse power flow, to calculate the respective powers, to control the drive of the on-load tap-changer so that the on-load tap-changer moves to different tap positions, to determine a value for the gradient of the
[0020] To determine the straight line of the voltage setpoint and to change the straight line of the voltage setpoint accordingly and to save it.
[0021] The device can be designed in any desired manner, wherein the step transformer is a series regulator with variable impedance, in particular a
[0022] High-voltage transformer. is.
[0023] The invention is explained in detail below using exemplary embodiments with reference to the drawings. Components that are identical or functionally identical or have an identical effect may be provided with identical reference numerals. Identical components or components with identical functions may only be explained with reference to the figure in which they first appear. The explanation is not necessarily repeated in subsequent figures.
[0024] Figure 1 shows a power supply system;
[0025] Figure 2 shows a circuit diagram of an idealized network;
[0026] Figure 3 is a diagram to visualize voltage regulation.
[0027] Figure 1 shows a power supply system 100 comprising a tapped transformer 200 with a plurality of primary windings 300 and a plurality of secondary windings 400 that are inductively coupled. An on-load tap-changer 10 is coupled to the primary windings. The primary windings 300 have a plurality of taps. The on-load tap-changer 10 is connected to the primary windings 300 via the taps. The on-load tap-changer 10 is designed to switch the taps and thus to control the tapped transformer 200. A motor drive 11 actuates the on-load tap-changer 10, whereby the taps are switched to control the tapped transformer 200. Furthermore, a device 20 for voltage regulation is provided. The device 20 has a control device 21 that is connected to the motor drive 11 and a measuring device 15.The control device 21 is designed and configured to control the motor drive 11 and thus the actuation of the on-load tap changer 10, whereby the tap transformer 200 is controlled.
[0028] The tap transformer 200 is connected to the high-voltage grid on its first side 30, the high-voltage side. Furthermore, the tap transformer 200 is connected to the low-voltage grid on its second side 40, the low-voltage side. For example, 110 kV is present on the high-voltage side and 20 kV on the low-voltage side. These grids are preferably three-phase grids. The tap transformer 200 is typically used to convert the voltage of the first grid into a lower voltage of the second grid. The tap transformer 200 is preferably designed as a series regulator with variable impedance or a high-voltage transformer.
[0029] The control device 21 of the device 20 on the tap-change transformer 200 is intended for voltage regulation. This control device 21 can be arranged directly on the transformer housing or separately in a control room.
[0030] On the second side 40, i.e., the low-voltage side, generators can also be connected in addition to consumers, which is why the voltage on this side or in this network can fluctuate. By operating the on-load tap-changer 10 on the first side 30 of the first network (high-voltage network), these voltage fluctuations on the second side 40 can be compensated for. For this purpose, at least one measuring device 15 is arranged on the low-voltage side, which measures these voltage and current changes. Specifically, this is at least one current sensor and at least one voltage sensor arranged on at least one line 16 of the second network (low-voltage network). This measuring device 15 transmits the measured voltage and current to the control device 21. Furthermore, the measuring device 15 can also be arranged on the high-voltage side, i.e., the first side 30.
[0031] Based on these transmitted currents and voltages, voltage regulation and thus in particular the actuation of the on-load tap-changer 10 via the motor drive 11 takes place according to a method for voltage regulation.
[0032] The device 20 with the control device 21 has means or is designed and configured to additionally carry out the method according to the invention.
[0033] Figure 2 shows a circuit diagram of an idealized network 41 with the power supply system 100. The tap-change transformer 200 is connected to the network. The circuit diagram of the network 41 also shows a line with a line impedance 45, a load with a load impedance 46, a high-voltage network with a network impedance 43, and a generator 47. The generator 47 represents old elements (generators) that feed power into the grid and do not withdraw it. These can be, for example, photovoltaic systems, wind turbines, and thus, more generally, renewable energy generators.
[0034] The line impedance 45 represents the impedance of all lines (or high-voltage lines or cables).
[0035] The network impedance 43 represents the impedance of the higher-level network (high-voltage network) at the connection point of the tap transformer.
[0036] The tap transformer 200 represents an adjustable longitudinal impedance.
[0037] Since both consumers and producers are connected to the grid 41, it can happen that energy is not only taken from the high-voltage grid by the consumers, but also fed into it by the producers. Taken out here means that on the second side 40 - i.e. the low-voltage side - it is mainly power (active power) that is consumed by the consumers. This is the so-called forward power flow (FPF). When fed in, power (active power) is supplied to the grid 41 from a source (47) on the second side 40 by PV systems or similar. In other words, the active power flows from the consumer side, i.e. the second side 40, to the higher-level grid, or power is transported from the low-voltage side to the high-voltage side. This is the so-called reverse power flow (RPF).
[0038] To determine whether an RPF or an FPF is present, a voltage U20 is measured between points A and B of the network. Point A is located between the tapped transformer 200 and the line impedance 45, the load impedance 46, and the generator 47. Point B is after the line impedance 45, the load impedance 46, and the generator 47. Furthermore, a current I20 is measured directly at point A. All measurements, and in particular the measurements at point A, are carried out using measuring device 15. In an FPF, the current I20 (active current) flows from the high-voltage network via the tapped transformer 200 and the lines to the loads. At RPF, the current (active current) 120 flows from the combination of consumers and producers via lines into the high-voltage network via the tap transformer 200. When measuring an RPF at points A and B, the sign of the measured power (active power) is negative.When measuring an FPF at points A and B, the sign of the measured power (active power) is positive. Thus, the sign can be used to determine whether a reverse power flow or a forward power flow is present.
[0039] Figure 3 shows a diagram visualizing voltage regulation on a tap-change transformer 200. The power (active power) P that is drawn from, fed into, or supplied to the tap-change transformer 200 is plotted on the x-axis. "Drawn out" here means that power (active power) is primarily consumed by the loads on the second side 40, i.e., the low-voltage side. This is the so-called forward power flow (FPF).
[0040] When fed in, power (active power) is supplied to the power supply system 100 on the second side 40 by PV systems or similar. In other words, power (active power) flows from the consumer side, i.e. the second side 40, to the grid, or power is transported from the low-voltage side to the high-voltage side. This is the so-called reverse power flow (RPF). The zero point of the x-axis is entered in the center of the diagram so that a corresponding power state of the grid, i.e. an FPF or RPF, can be displayed. The diagram can thus be divided into a first area in which FFP is present and a second area in which RPF is present. With an FPF, the measured power on the low-voltage side is plotted as positive. With an RPF, the measured power is given a negative sign.
[0041] A reference voltage Uref is plotted on the Y-axis. For example, a reference voltage of 100 V is specified here, although this can deviate by 10%, i.e., between 90 V and 110 V. Alternatively, any voltage value can be plotted here. In principle, the reference voltage Uref directly or indirectly reflects the measured voltage on the second side 40 in the low-voltage network.
[0042] A straight line 50 is drawn in the diagram, which serves as the setpoint for the voltage regulation device 20; this straight line 50 represents the voltage setpoint Usoll. During operation, the voltage Uist of the tap-changer 200 on the second side 40 is therefore continuously monitored by at least one measuring device 15. These measured values of the voltages Uist are plotted in the diagram. Depending on where the measured values are located in the diagram, the on-load tap-changer 10 is actuated via the motor drive 11 until the measured actual value of the voltage Uist is at or immediately near the voltage setpoint Usoll, represented by the straight line 50. In this case, a voltage band or a tolerance range is specified around the voltage setpoint Usoll, and therefore also around the straight line 50, within which the actual value of the voltage Uist may lie without any actuation being necessary.
[0043] The straight line 50 of the voltage setpoint Usoll is divided into a first section and a second section and can have a different gradient in each of the sections.
[0044] In the FPF range, i.e., when power is drawn by the loads, the line 50 in the second section 50.2 of the voltage setpoint Usetpoint of the control system has a defined, predefined gradient. This gradient depends on certain grid parameters. These parameters are specified by the transmission lines (Rline, Lline) and the loads (Rload, Lload). These parameters can be easily determined and thus stored in the device 20 before commissioning.
[0045] This ensures that the voltage on the consumer side always remains within a specified range, despite increasing load. The voltage is typically between 360V and 440V.
[0046] In the RPF area, i.e. when power is fed in on the low-voltage side, the straight line 50 in the first section 50.1 of the voltage setpoint Usoll has a different gradient in this section of the control, which, however, differs from the gradient in the FPF area. This gradient can also be determined based on the grid parameters before commissioning. For this to happen, however, the parameters for the transmission line and the generators must be known. However, these parameters are often not available or can change over time. The method according to the invention, however, enables the gradient of the straight line of the voltage setpoint Usoll to be dynamically adjusted. This is symbolized by the double arrow 50.3. The grid parameters do not have to be specified here.
[0047] In the following, an exemplary method sequence for adjusting a voltage setpoint Usoll for voltage regulation of a tap transformer 200 by means of an on-load tap changer 10 is described.
[0048] The first step is to determine the power flow. Specifically, it is determined whether a reverse power flow or a forward power flow is present. For this purpose, the direction of the current I20 or the sign of the active current and the voltage U20 are determined, and from this it is deduced whether a reverse power flow or a forward power flow is present. The current I20 and the voltage U20 measured at point A of a network are recorded by the measuring device 15 and determined in the device 20. Furthermore, the power L20 is determined as the product of the measured voltage U20 and I20. The power can be apparent power or active power.
[0049] A reverse power flow occurs when the voltage U20 and the
[0050] The active power derived from current I20 is negative (has a negative sign), i.e., the active current at point A flows from the generator into the grid via transformer 200. A forward power flow occurs when the active power derived from the voltage and current is positive, i.e., the active current at point A flows from the grid to the consumer via transformer 200.
[0051] In a further step, the on-load tap changer 10 in the tap-changer transformer 200 is actuated such that it is moved from the current output tap position n to the next higher tap position n+1 or, alternatively, to the next lower tap position n-1. Here, the first current 121 and a first voltage U21, and the resulting power L21, are determined if a switch to a higher tap position has been made. However, if a switch to a next lower tap position n-1 has been made, a second current 119 and a second voltage 119 and the resulting power L19 are determined.
[0052] In a subsequent step, the on-load tap-changer 10 is switched to the original tap position n. In a next step, a value m is determined from the measured power in the tap position approached and the current tap position. The value m is always calculated as the quotient of the power of the higher tap position and the lower tap position. Higher and lower tap position here means that the numerical value of the higher tap position of the on-load tap-changer is higher than the numerical value of the lower tap position. In the case of the previous upshift, the value m is therefore the quotient of the power L21 of the higher tap position n+1 and the power L20 of the current tap position n, or when downshifting or approaching a lower tap position or tap-changer position, the quotient of the power L20 of the current tap position n and the power L19 of the lower tap position n-1.
[0053] In the next step, the determined value m is used as the gradient for the straight line 50 of the voltage setpoint Usoll in the first section 50.1 of the RPF. This new straight line section forms the voltage setpoint Usoll and is used to control the on-load tap changer 10. The equation for the straight line of the voltage setpoint Usoll is then y=m * x. This voltage setpoint Usoll is determined by means of the device 20 for voltage regulation and in particular a regulation device 21. Thus, the device 20 not only serves to regulate the voltage of the tapped transformer 200 but is also able to adjust the voltage setpoint Usoll. This adjustment can be carried out as often as required, particularly when weather conditions change. For example, when clouds pass over large PV systems; when the feed-in power changes, i.e. reverse power flow with a high gradient, or when grid configurations are switched on or off.
[0054] In the following, a further exemplary method sequence for adjusting a voltage setpoint Usoll for voltage control of a tap transformer 200 by means of an on-load tap changer 10 is described.
[0055] Here, too, the first step is to determine the power flow. Specifically, it is determined whether a reverse power flow or a forward power flow is present. For this purpose, the direction of the current (active current) I20 and the voltage U20 are determined, and from this, it is deduced whether a reverse power flow or a forward power flow is present. The current I20 and the voltage U20 measured at point A of a network are recorded by measuring device 15 and determined in device 20.
[0056] A reverse power flow occurs when the active power derived from the voltage U20 and the current I20 is negative (or has a negative sign), i.e. the current at point A flows from the generator into the grid via the transformer 200.
[0057] A forward power flow occurs when the power derived from the voltage and current is positive, i.e. the current flows at point A from the grid to the consumer via the transformer 200. In a further step, the on-load tap changer 10 in the tap transformer
[0058] 200 is actuated in such a way that it is moved from the current output tap position n to the next higher tap position n+1. Here, the first current 121 and a first voltage U21, and the resulting power L21, are determined. The power can be apparent power or active power.
[0059] In a further step, the on-load tap changer 10 in the tap-changer transformer 200 is actuated such that it is moved down two steps from the current output tap position n+1 to a lower tap position n-1. Here, the second current U19 and a second voltage U19, and the resulting power L19, are determined. The power can be apparent power or active power.
[0060] In a subsequent step, the on-load tap-changer 10 is switched to the original tap position n.
[0061] In the next step, a value m is determined from the measured power L21 in the tap position n+1 reached and the measured power L19 of the second tap position n-1 reached. The value m is always calculated as the quotient of the power of the higher tap position and the lower tap position. Higher and lower tap position here means that the numerical value of the higher tap position of the on-load tap-changer is higher than the numerical value of the lower tap position. In this case, the value m is the quotient of the power L21 of the higher tap position n+1 and the power L19 of the tap position n-1.
[0062] In the next step, the determined value m is used as the gradient for the straight line 50 of the voltage setpoint Usoll in the first section 50.1 of the RPF. This new straight line forms the voltage setpoint Usoll. The equation for the straight line of the voltage setpoint is then y=m * x. This voltage setpoint U-soll is determined by means of the device 20 for voltage regulation and in particular a control device 21. Thus, the device 20 not only serves to regulate the voltage of the tap-change transformer 200 but is also capable of adjusting, changing, and saving the voltage setpoint Usoll. This adjustment can be performed as often as required.
[0063] Alternatively, the power can be switched down once to tap position n-1 and up twice to tap position n+1. Compared to the previously described method, the quotient of the powers of the tap positions that are further apart is more accurate than the quotient of the powers of the tap positions that are closer together.
[0064] The device 20 with the control device 21 has means or is designed and configured to carry out the methods described above. REFERENCE SYMBOL
[0065] 10 on-load tap-changers
[0066] 11 Motor drive
[0067] 15 Measuring device 16 Line
[0068] 20 Device
[0069] 21 Control device
[0070] 30 first page of 200
[0071] 40 second page of 200 41 network
[0072] 43 Network impedance of the high-voltage network
[0073] 45 Line impedance
[0074] 46 Consumer impedance
[0075] 47 Generator 50 Voltage setpoint Usoll
[0076] 50.1 first section of 50
[0077] 50.2 second section of 50
[0078] 50.3 Double arrow
[0079] 100 Power supply system 200 Step transformer
[0080] 300 primary winding
[0081] 400 secondary winding
Claims
REQUIREMENTS 1. Method for adjusting a voltage setpoint (Usoll) for voltage regulation of a step transformer (200) by means of a load tap changer (10) wherein the method comprises the following steps: determining a reverse power flow on a low-voltage side of the step-down transformer (200) by measuring a current (I20) and a voltage (U20); - actuating the load tap changer (10) from a current tap position n to another tap position (n-1, n+1) and measuring the voltage (U21, U19) of the current (I21, U119) in the further tap position (n-1, n+1); determining a value m from the powers (L19, L20, L21) of the different tap positions (n, n-1, n+1); - using the determined value m as the slope for a first section of a straight line (50) of the voltage setpoint (Usetpoint).
2. Method according to claim 1, wherein the value m is determined as the slope of the line (50) in the first section (50.1) of the target stress value (Usoll) and replaces the existing line (50) in the first section (50.1).
3. Method according to one of claims 1-2, wherein the power (L20) in the current stage position (n) is the product of the measured current (I20) and the measured voltage (I20) in the current The step position (n) is determined; the load tap changer (10) is actuated and moved from a current step position (n) to a higher step position (n+1); the power (L21) of the higher step position (n+1) is calculated as the product of the measured current (121) and the measured voltage (U21) of the higher step position (n+1). The step position (n+1) is determined; the value m is determined as the quotient of the power (L21) of the higher step position (n+1) and the power (L20) of the lower step position (n).
4. Method according to one of claims 1-2, wherein the power (L20) in the current step position (n) is determined as the product of the measured current (I20) and the measured voltage (I20) in the current step position (n). the load tap changer (10) is actuated and moved from a current tap position (n) to a lower tap position (n-1); the power (L19) of the lower tap position (n-1) is determined as the product of the measured current (119) and the measured voltage (LJ19) of the lower tap position (n-1); the value m is determined as the quotient of the power (L20) of the higher tap position n and the power (L19) of the lower tap position (n-1).
5. A method according to one of claims 1-2, wherein: - the load tap changer (10) is actuated and moved from a current tap position (n) to a higher tap position (n+1); the power (L21) of the higher tap position (n+1) is determined as the product of the measured current (121) and the measured voltage (U21) of the higher tap position (n+1); - the load tap changer (10) is actuated twice and moved from a current tap position (n+1) to the lower tap position n-1; the power (L19) of the lower tap position (n-1) is determined as the product of the measured current (119) and the measured voltage (U19) of the lower tap position (n-1); - the value m is determined as the quotient of the power (L21) of the higher tap position n+1 and the power (L19) of the lower tap position (n-1).
6. A method according to any one of claims 1-2, wherein the load tap changer (10) is actuated and moved from a current tap position (n) to a lower tap position (n-1); the power (L19) of the lower tap position (n-1) is determined as the product of the measured current (119) and the measured voltage (U19) of the lower tap position (n-1); the load tap changer (10) is actuated twice and moved from a current tap position (n-1) to the higher tap position (n+1); the power (L21) of the higher tap position (n+1) is determined as the product of the measured current (121) and the measured voltage (U21) of the higher tap position (n+1); the value m is determined as the quotient of the power (L21) of the higher tap position (n+1) and the power (L19) of the lower tap position (n-1). Method according to any one of claims 1-6, wherein the power is either apparent power and / or active power. Device (20) for adjusting a voltage setpoint (Usetpoint) for voltage regulation of a step-down transformer (200), comprising: at least one measuring device (15) for measuring a current (119, 120, 121) and a voltage (U19, U20, U21) on the low-voltage side of the step-down transformer (200); a control device (21) connected to the at least one measuring device (15) for receiving the measured current (119, 120, 121) and voltage (U19, U20, U21); the control device (21) configured to perform a method according to claims 1 to 6. Device (20) for adjusting a voltage setpoint (Usetpoint) for voltage regulation of a step-down transformer (200) according to claim 8, wherein the step-down transformer (200) is an autotransformer.