Method for operating on-load tap changer and on-load tap changer arrangement

Abstract

The invention relates to a method for operating an on-load tap changer (4) by means of a drive (3), a sensor (5) and a control device (2), the control device (2) receiving a switching command for operating the on-load tap changer (4); the current change trend is detected through the sensor (5); determining a starting time (T0) in the course of the current change, at which starting time a switching command for operating the on-load tap changer (4) is received; adding the time deviation (TV) to the starting time (T0) and determining therefrom the time (TB) at which the operation may be started; determining a moment (TG) of a next current zero crossing after the moment (TB) at which the operation is likely to start; determining a time difference (TD) between the time (TB) at which the operation may start and the time (TG) of the next current zero crossing; adding said time difference (TD) to the starting time (T0) in order to determine therefrom a new starting time (T1) for operation; the operation of the on-load tap changer (4) by the drive (3) begins at the new starting time (T1).

Description

Technical Field

[0001] The invention relates to a method for operating an on-load tap changer and an on-load tap changer device. Background Art

[0002] In transformer substations there are a large number of switches for different tasks and with different requirements. In order to operate the respective switches, they must be driven by a drive system. Among other things, these switches are on-load tap changers, load changeover switches, selectors, double commutators, commutators, preselectors, power switches, load switches or disconnect switches.

[0003] Therefore, the on-load tap changer is used, for example, for the interruption-free switching between different winding taps of an electrical device such as a power transformer. For example, the transformation ratio of the transformer or the inductance of the choke can be changed thereby.

[0004] On-load tap changers are usually operated by a combination of a motor drive and a spring accumulator. The operation takes place immediately after the switching command, i.e. at any time. Summary of the invention

[0005] It is therefore an object of the present invention to provide a method for operating an on-load tap changer which is more precise, checks the state of the on-load tap changer before switching and protects the vacuum switching tube.

[0006] This object is achieved by the corresponding technical solutions of the independent claims. Other embodiments are the technical solutions of the dependent claims.

[0007] The invention proposes a method for operating an on-load tap changer by means of a drive, a sensor and a control device, wherein:

[0008] - the control device receives a switching command for operating the on-load tap-changer;

[0009] - Detect the direction of current changes through sensors;

[0010] - determining a starting time in the course of the current change at which a switching command for operating the on-load tap changer is received;

[0011] - add the time offset to the start time and determine from this the possible start time of the operation;

[0012] - determining the time of the next current zero crossing after the time of the possible start of operation;

[0013] - determining the time difference between the moment of possible start of operation and the moment of the next current zero crossing;

[0014] - adding the time difference to the starting time in order to thereby determine a new starting time for the operation;

[0015] - The on-load tap-changer is operated by the drive starting at this new starting time.

[0016] The method is based on the idea of ​​monitoring the current variation in the on-load tap changer, more precisely the current variation in the vacuum switching tube, and starting to operate the on-load tap changer or opening the vacuum switching tube precisely at or shortly before the current zero crossing. As a result, the arc burning duration in the vacuum switching tube during opening is shortened as much as possible. As a result, the vacuum switching tube and, in particular, the contacts in the vacuum switching tube can be protected to the greatest extent. In addition, by predicting future current zero crossings and thus opening or switching or operating the on-load tap changer based on these current zero crossings, accurate opening or switching or operation can be achieved. Since the inertia of the drive train and, therefore, the time deviation between the switching command and the actual operation are known, they are coordinated with the future and suitable current zero crossing. Therefore, the actual operation does not start immediately after the switching command, but is delayed accordingly in consideration of the time deviation in the drive train. As a result, the inertia of the drive train (mechanical mechanism) is taken into account during operation, so that the operation of the vacuum switching tube is always carried out at or shortly before the current zero crossing. Operating the on-load tap changer can also be understood as opening a vacuum switching tube which is a component of the on-load tap changer.

[0017] The control unit is connected to the drive and at least one sensor. The control unit controls the drive, which in turn operates the on-load tap changer. In addition, the control unit detects the current change trend by means of at least one sensor. The sensor detects the current change trend and can be arranged at different locations, for example, on the vacuum switching tube and / or on the on-load tap changer and / or on the low-voltage side and / or high-voltage side of the tapped transformer.

[0018] The current profile preceding a switching command for operating the on-load tap changer can be detected in various ways, in particular the frequency and past current zero crossings can be determined and detected. The current profile is preferably evaluated in the control device.

[0019] The time of the next current zero crossing is the future current zero crossing and is based on the past current zero crossing of the current change trend.

[0020] A future current zero crossing or all future current zero crossings are determined by one or more mathematical methods, in particular a fast Fourier transform. In addition, a future current zero crossing or all future current zero crossings can be determined by means of analog electronics.

[0021] The current profile can be detected, for example, by means of sensors at the vacuum switching tube and / or the on-load tap changer and / or at the low-voltage side and / or the high-voltage side of the tapped transformer.

[0022] The time deviation is a value caused by or dependent on the mechanical structure of the drive train. The value of the time deviation can be adjusted automatically and / or manually. In addition, the value of the time deviation can also be adjusted according to the arc burning duration in the vacuum switching tube of the on-load tap changer. In addition, the value of the time deviation can also be adjusted according to the arc burning duration of the on-load tap changer in the vacuum switching tube of the on-load tap changer in the past switching.

[0023] After determining the time offset, another time offset can be subtracted in order to thereby move to a new starting time. Thus, the on-load tap changer is operated not before the zero crossing, but at an earlier time, which is not the time of the next current zero crossing.

[0024] The control device can be designed in any desired manner and in particular comprise means for controlling a drive in order to operate the on-load tap changer and to carry out the method according to the invention.

[0025] In addition, the present invention provides an on-load tap changer device, comprising:

[0026] - On-load tap-changer;

[0027] - sensor;

[0028] - drive unit;

[0029] - control devices;

[0030] Wherein, the control device is configured to:

[0031] - receiving switching commands for operating the on-load tap-changer;

[0032] - Detect the direction of current changes through sensors;

[0033] - determining a starting time in the course of the current change at which a switching command for operating the on-load tap changer is received;

[0034] - add the time offset to the start time and determine from this the possible start time of the operation;

[0035] - determining the time of the next current zero crossing after the time of the possible start of operation;

[0036] - determining the time difference between the moment of possible start of operation and the moment of the next current zero crossing;

[0037] - adding the time difference to the starting time and determining therefrom a new starting time for the operation;

[0038] - At this new starting time, the on-load tap changer is operated by means of the drive.

[0039] An on-load tap changer arrangement, which comprises an on-load tap changer with a vacuum switching tube, a drive, a sensor and a control device, allows taking into account the time delays of the mechanical mechanism during load switching and thus opens the vacuum switching tube at a current zero crossing.

[0040] Furthermore, the on-load tap changer arrangement can have a further sensor for measuring the arc burning duration. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The present invention will be described in detail below by way of exemplary embodiments with reference to the accompanying drawings. The accompanying drawings are as follows:

[0042] Figure 1 A variable transformer with an on-load tap changer is shown;

[0043] Figure 2 Show the method flow;

[0044] Figure 3 A diagram for illustrating the method is shown;

[0045] Figure 4 Another diagram is shown to illustrate the method. DETAILED DESCRIPTION

[0046] Figure 1 An on-load tap changer device 1 for carrying out load switching is shown. The on-load tap changer device 1 comprises a control device 2, at least one sensor 5 and an on-load tap changer 4. The control device 2 is connected to a drive device of the on-load tap changer 4. The control device 2 is provided and constructed to control the drive device 3 so that the drive device operates the on-load tap changer 4. In addition, the control device 2 is connected to a sensor 5 or a plurality of sensors 5, which measure the current flowing through the vacuum switching tube 6 and thus through the on-load tap changer 4 and the tapped transformer 7. The control device 2 is constructed and arranged to measure and evaluate the current detected by the sensor 5 or the plurality of sensors 5. In particular, the control device 2 determines the course of the current change, that is, when the current has or takes a zero value and how often this occurs. The sensor 5 can be arranged, for example, on the tapped transformer 7, in particular on the high voltage side 8 or the low voltage side 9. In addition, the sensor 5 can be arranged in the on-load tap changer 4, directly on the vacuum switching tube 6, or at any other position suitable for detecting the course of the current change.

[0047] Furthermore, the control device 2 is designed and arranged to predict or calculate the future current zero crossing time. The control device 2 therefore correspondingly has a computing unit and / or a processor and / or a memory.

[0048] The drive device 3 is mechanically connected to the on-load tap changer 4 and thus also to the vacuum interrupter 6 via a drive train 10. The drive train 10 can be understood as the sum of mechanical elements or mechanical mechanisms between the motor drive device 3 and the vacuum interrupter 6, such as shafts, toggle levers, rollers, etc.

[0049] The control device 2 can be arranged as an independent device on the variable transformer 7 or in a control room. In addition, the control device 2 can be part of the drive control device of the on-load tap changer 4 or be designed as part of a voltage regulator. The control device 2 is designed and arranged to control the drive device 3.

[0050] In addition, another sensor 15 is provided, which is connected to the control device 2. The other sensor 15 is provided and constructed to detect the arc burning duration in the vacuum switching tube 6. The control device 2 then evaluates the detected arc burning duration. Ideally, the vacuum switching tube 6 opens when the current passes through the zero point, so that no arc is generated inside the vacuum switching tube 6 and the arc burning duration is equal to zero. If the vacuum switching tube 6 is operated while the current is still flowing through the vacuum switching tube 6, an arc is generated until the arc is disconnected and extinguished. The arc burning duration also depends on the time deviation TV. Therefore, the arc burning duration from the past switching is also used to adjust the time deviation TV. The evaluation and adjustment are performed in the control device 2.

[0051] The tapped transformer 7 has a main winding 11 and a regulating winding 12. The on-load tap changer 4 is connected to the regulating winding 12 via a winding tap 13. The main winding 11 and the regulating winding 12 are arranged on the high-voltage side 8 (in rare cases, also on the low-voltage side). In addition, the tapped transformer 7 has a low-voltage winding 14 inductively coupled to the main winding 11 and the regulating winding 12.

[0052] Figure 2 The flow chart of the method for carrying out a load changeover by means of an on-load tap changer 4 is shown. In a first step 30, the control device 2 receives a signal or a switching command for carrying out a load changeover by means of the on-load tap changer or a switching command for starting the operation of the on-load tap changer 4. The signal or the switching command is generated, for example, manually or by a voltage regulator.

[0053] In the next step 31, the current change trend is detected by means of the sensor 4, in particular, when the current flowing through the vacuum switching tube 5 of the on-load tap changer 4 has or takes a zero value and the frequency F at which this occurs. The past current zero-crossing moments and the intervals between them are determined. This is continuously carried out during the operation of the tapped transformer, in particular before the switching command and before the on-load tap changer is started. Ideally, the current has a sinusoidal change trend, whereby regular current zero-crossings occur. Thus, the future current zero-crossings or the moments in the current change trend are predicted based on moments from the past or based on past current zero-crossings. This can be done in different ways, for example by using mathematical methods such as fast Fourier transforms to calculate. The calculation is carried out in the control unit 2, which is constructed and arranged for this purpose. The control unit 2 therefore has a calculation unit and / or a processor and / or a memory accordingly. The determination of the current zero-crossing moments in the present and future is carried out by means of the signal of the sensor, which, according to its design, only detects or outputs the current zero-crossing or the entire sinusoidal change trend.

[0054] In the next step 32, the current starting time T0 is determined. This starting time T0 corresponds to the time when the signal for operating the on-load tap changer 4 is generated in the control device 2 or obtained by the control device 2. The starting time is marked in the change trend of the current. Since the drive train 10 has a time deviation TV caused by the mechanical mechanism, this time deviation must be taken into account when operating the on-load tap changer 4 or opening the vacuum switching tube 6. The deviation TV caused by the mechanical mechanism is preset by the structural realization of the drive train 10. This includes, for example, the rotation movement of a cam or a lever, which, for example, must first move a certain distance until, for example, the force or movement can be transmitted to the vacuum switching tube 6. Based on these mechanical conditions, the operation or opening of the vacuum switching tube 6 is not carried out immediately after the signal for operation or at the beginning, but with a corresponding time deviation TV. However, the goal of each operation of the on-load tap changer 4 is to open the vacuum switching tube 6 at or close to the current zero point, that is, shortly before the current zero point. Since the information about the future current zero crossing instants or current zero crossings, the starting instant T0 and the deviation TV are known in the control device 2, the corresponding starting instant T1 for starting the switching is calculated. In other words, the operation is only started when there is a current zero crossing in the vacuum switching tube 6 at the end of the time deviation TV of the drive train 10. Therefore, in the next step 33, the time deviation TV is added to the starting instant T0 and the instant TB at which the vacuum switching tube 6 will actually be opened is determined from this.

[0055] In the next step 34, the time TG is determined at which the next current zero crossing (future current zero crossing) will occur after the time TB at which the operation may start. Based on the times TB and TG, the time difference TD between the times is determined in the next step 35. This difference TD is in turn used to shift the start time T0 to a new start time T1 in the next step 36.

[0056] In a final step 37 , the operation is started or carried out at the newly determined start time T1 . The drive device 3 is controlled by the control unit 2 .

[0057] The time deviation TV has a value of a few milliseconds adapted to the drive train 10. This value can be fixed and predetermined or can also be adjusted. The adjustment can be automatic or manual. For example, if wear or replacement of components occurs in the drive train, the adjustment can be very meaningful. In addition, the arc burning duration can also be used to adjust the time deviation.

[0058] Figure 3 For illustrating the method according to the invention. The time current change trend t (in ms) in the closed vacuum switching tube 6 or the on-load tap changer 4 is plotted on the X-axis. The Y-axis represents the magnitude of the current I in amperes. The change trend of the current or the change trend of the current is sinusoidal or approximately sinusoidal here. The curve of the current change trend intersects the X-axis at the zero crossing point (current zero crossing point). Therefore, no current flows through the vacuum switching tube 6 or the on-load tap changer 4 at these moments. At any time T0, a switching command for operating or starting to operate the on-load tap changer 4 is received in the control unit 2. This moment is assumed to be a possible starting time T0 of the load conversion. Starting from this starting time T0, the time deviation TV is added to the starting time T0. The time deviation TV has a fixed value in principle. After the starting time T0 is added to the time deviation TV, the time TB is obtained, at which the vacuum switching tube 6 may be operated or opened. However, since there is still current at this time, that is, the current is not zero, an arc will be generated when the vacuum switching tube 6 is operated, especially when the vacuum switching tube 6 is opened. And this is exactly what should be avoided.

[0059] As shown in the diagram, the time TB at which the operation may start is not the current zero crossing point. Therefore, a suitable time TG should be determined at which no current flows through the vacuum switch tube 6 when it is turned on. This time TG is the next current zero crossing point after the time TB. The next current zero crossing point is determined based on the past current zero crossing points.

[0060] Based on the possible start time TB of opening or operation and the suitable time TG, the duration TD between these two times is calculated, for example as a difference. This duration TD is then added to the start time T0 and a new start time T1 is thus formed, at which the actual operation or opening is then started. This ensures that the vacuum switch tube 6 starts to be opened or operated when the current crosses the zero point.

[0061] according to Figure 4 In another embodiment of the invention, a further deviation TD1 is subtracted after determining the time deviation TV. This deviation TD1 ensures that the vacuum switching tube is opened not directly at the current zero crossing, but at a time (TF) a few milliseconds earlier, ie shortly before the current zero crossing. Reference numerals list

[0062] 1On-load tap-changer equipment

[0063] 2 Control device

[0064] 3. Drive device

[0065] 4On-load tap changer

[0066] 5 Sensors

[0067] 6 Vacuum switch tube

[0068] 7Adjustable transformer

[0069] 8 High voltage side

[0070] 9 Low voltage side

[0071] 10 Drivetrain

[0072] 11 Main winding

[0073] 12 Adjustment winding

[0074] 13 Winding taps

[0075] 14 Low voltage winding

[0076] 15 Another sensor

[0077] T0 start time

[0078] T1 new starting time

[0079] TV Time Deviation

[0080] TD1 Another Deviation

[0081] Moments when TB may start operating

[0082] The moment when the next current crosses zero in TG

[0083] TD Time Difference

[0084] TF earlier moments

[0085] F Frequency

Claims

1. A method for operating an on-load tap changer (4) by means of a drive device (3), a sensor (5) and a control device (2), wherein: - the control device (2) receives a switching command for operating the on-load tap changer (4); - Detecting the direction of current change through the sensor (5); - determining a starting time (T0) in the course of the current change, at which a switching command for operating the on-load tap changer (4) is received; - add the time deviation (TV) to the start time (T0) and determine from this the possible start time of the operation (TB); - determining the time (TG) of the next current zero crossing after the time (TB) of the possible start of operation; - determining the time difference (TD) between the moment of possible start of operation (TB) and the moment of the next current zero crossing (TG); - adding the time difference (TD) to the starting time (T0) in order to thereby determine a new starting time (T1) for the operation; - At the new starting time (T1), the on-load tap changer (4) is operated by the drive (3).

2. The method for operating an on-load tap changer (4) according to claim 1, wherein: Prior to a switching command for operating an on-load tap changer (4), a current profile is detected; when detecting the current profile, a frequency and a past current zero crossing are determined.

3. The method for operating an on-load tap changer (4) according to claim 1, wherein: The time point (TG) of the next current zero crossing is a future current zero crossing, and the future current zero crossing is based on past current zero crossings of the current variation trend.

4. The method for operating an on-load tap changer (4) according to claim 3, wherein: The future current zero crossing is determined by mathematical methods, in particular a fast Fourier transformation, or with the aid of analog electronics.

5. Method for operating an on-load tap changer (4) according to any one of claims 1 to 4, wherein: The current profile is detected at the vacuum switching tube (6) and / or the on-load tap changer (4) and / or at the low-voltage side (9) and / or the high-voltage side of the tapped transformer (7) by one or more sensors (5).

6. Method for operating an on-load tap changer (4) according to any one of claims 1 to 5, wherein: The time deviation (TV) is a value which is caused by the mechanics of the drive train (10) or is dependent on the mechanics of the drive train.

7. Method for operating an on-load tap changer (4) according to claim 6, wherein: The value of the time deviation (TV) can be adjusted automatically and / or manually.

8. Method for operating an on-load tap changer (4) according to any one of claims 1 to 6, wherein: The value of the time deviation (TV) can be adjusted as a function of the arc burning duration in the vacuum switching tube (6) of the on-load tap changer (4).

9. Method for operating an on-load tap changer (4) according to any one of claims 1 to 8, wherein: After determining the time offset (TV), a further time offset (TD1) is subtracted and the process moves to a new starting time (T1) and starts operating the on-load tap changer (4) before the zero crossing at an earlier time (TF) which is not the time (TG) of the next current zero crossing.

10. Method for operating an on-load tap changer (4) according to any one of claims 1 to 9, wherein: The control device (2) controls a drive device (3) which operates an on-load tap changer (4).

11. On-load tap-changer device (1), comprising: - On-load tap-changer (4); - Sensors (5); - drive device (3); - control device (2); Wherein, the control device (2) is configured to: - receiving a switching command for operating the on-load tap changer (4); - Detecting the direction of current change through the sensor (5); - determining a starting time (T0) in the course of the current change, at which a switching command for operating the on-load tap changer (4) is received; - add the time deviation (TV) to the start time (T0) and determine from this the possible start time of the operation (TB); - determining the time (TG) of the next current zero crossing after the time (TB) of the possible start of operation; - determining the time difference (TD) between the moment of possible start of operation (TB) and the moment of the next current zero crossing (TG); - adding the time difference (TD) to the start time (T0) and determining therefrom a new start time (T1) for the operation; - At the new starting time (T1), the on-load tap changer (4) is actuated by means of the drive device (3).

12. The on-load tap changer (1) according to claim 11, comprising a further sensor (15) for measuring the arc burning duration.

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