Electrical equipment with a load tap changer

Abstract

- At least one control winding 3 having winding taps n, n + 1 and at least one partial winding 4, 5, - An electrical function 1 including a on-load tap changer 6 for changing the transformation ratio, impedance or voltage used for excitation of the electrical function 1, - The on-load tap changer 6 includes a first module 7 for switching the winding taps n, n + 1 of the control winding 3 and a second module 8 for quickly connecting, reversely connecting or bypassing the at least one partial winding 4, 5, - The second module 8 includes at least one sub-module 9 having semiconductor switching elements and a bypass switch 10 of the electrical apparatus 1.

Description

Technical Field

[0001] The present invention relates to an electrical device including at least one control winding having a winding tap and at least one partial winding, and a load tap changer for changing a transformation ratio, an impedance, or a voltage used for excitation of the electrical device.

Background Art

[0002] When controlling an energy supply network (power supply network), it is distinguished into two different time domains. Within the so-called steady state region, a static operating point that enables reliable operation of the energy supply network during small load fluctuations and power fluctuations is set in the energy supply network by an appropriate electrical device. In this case, the control is executed in a sub-range. Within the dynamic region, an appropriate electrical device responds to dynamic fluctuations in the energy supply network that can be caused, for example, by a fault or by a fast and in some cases only temporary change in the power situation and the load situation. In this case, in order to maintain the stability of the energy supply network, a very fast control within the range of milliseconds is required.

[0003] Since the reactive power amount also changes depending on the power situation and the load situation each time, reactive power control is an important element of the management of the energy supply network that is reliable, efficient, and minimizes losses.

[0004] Electrical devices suitable for both the control of the energy supply network within the steady state region and the dynamic voltage control are already known from the prior art. That is, for controlling the static operation of the energy supply network, for example, a controllable transformer, a phase shifter, or a controllable shunt reactor is used. For controlling the dynamic behavior of the energy supply network, for example, a static synchronous compensator (STATCOM) or a static var compensator (SVC) is used.

[0005] Due to the integration of power conversion and distributed power generation facilities into the facilities of the energy supply network, in particular, electrical equipment for control within the dynamic region will continue to be more important in the near future for the management of the energy supply network that ensures reliable power supply. This is because the power supply from renewable energy is difficult to predict.

[0006] In addition to the control of the energy supply network, the above different time regions also play an important role in the energy supply (power supply) of the arc furnace. Generally, a transformer for an electric furnace suitable for supplying an arc includes a load tap changer. The power control of the transformer for an electric furnace can be achieved within a range of several seconds to several minutes by the load tap changer. However, due to the rapidly changing operating conditions in the arc furnace, such as the disappearance of the arc used for melting, undesirable effects such as flicker having a time constant in the millisecond range occur in the arc furnace. In order to suppress the influence on the energy supply network, generally, a complex and high-cost compensation device (SVC) is used.

[0007] Another application field in which the above time regions play a role is the electrolysis facility for generating hydrogen. In the case of the electrolysis facility, the rectifier transformer is controlled by a load tap changer. In order to enter the energy management market, it is particularly important that it can be controlled within a dynamic time region so that controlled positive or negative power can be supplied to the power grid as quickly as possible.

[0008] Electrical equipment that enables the combination of control in the steady-state region or the second range to the minute range and control in the dynamic region or the millisecond range is not yet known from the prior art. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] Therefore, an object of the present invention is to provide combined flexible control means for operating in both time domains, and further to provide an improved concept for controlling an energy supply network or an energy supply facility that is low-cost, space-saving and low-loss in operation and manufacturing.

Means for Solving the Problem

[0010] This problem is solved by the electrical device described in the independent claims. Other embodiments are described in the dependent claims.

[0011] The improved concept is based on the idea of combining a typical on-load tap changer well known from the prior art with a power electronics-based on-load tap changer existing in series therewith. The power electronics-based on-load tap changer can quickly, i.e., within the range of milliseconds, change its switching position and can then take any position, enabling it to quickly adapt to load behavior and power supply behavior with quickly changing voltages. The steady-state region is controlled by the typical on-load tap changer. In this case, as large a control range as possible is covered. Thus, the energy supply network and facilities or processes can be managed very flexibly.

[0012] According to the improved concept, there is provided the electrical function including at least one main winding, at least one control winding having winding taps, at least one partial winding, and an on-load tap changer for changing the transformation ratio, impedance or voltage used for excitation of the electrical function.

[0013] The electrical device can be configured as a controllable transformer, as a phase-shifting transformer, as a controllable reactor or as a controllable transformer having a capacitor.

[0014] According to one embodiment, the electrical function is configured as a controllable transformer, and the on-load tap changer is configured to change the transformation ratio of the controllable transformer.

[0015] According to one embodiment, the electrical function is configured as a controllable reactor, and the on-load tap changer is configured to change the impedance of the controllable reactor.

[0016] According to another embodiment, the electrical function includes a first electromagnetic induction device and a second electromagnetic induction device. The second electromagnetic induction device is excited by the actual voltage in the first electromagnetic induction device, thereby increasing the output of the first electromagnetic induction device. In other words, the second electromagnetic induction device, which is a booster transformer, is added to the first electromagnetic induction device, which is an excitation transformer. The voltage used to excite the booster transformer is changed by the on-load tap changer. According to this device, it is possible to flexibly adjust the current and voltage, which are the operating parameters of the on-load tap changer, especially in the case of a high-output device.

[0017] According to another embodiment, the electrical function is configured as a phase-shifting transformer. A phase-shifting transformer is a special power transformer that can appropriately control the phase angle of the voltage or the load current energizing the overhead transmission line by applying an effective voltage or a phase-shifting voltage (Schraegspannung). According to this embodiment, the phase-shifting transformer includes a series transformer and an excitation transformer. Therefore, the on-load tap changer is configured to adjust a predetermined phase shift by changing the transformation ratio of the excitation transformer.

[0018] The on-load tap changer includes a first module for switching the winding taps of the control winding, and a second module having semiconductor switching elements for quickly connecting, reverse-connecting, or bypassing at least one partial winding. The second module includes at least one sub-module having semiconductor switching elements and a bypass switch.

[0019] At least one partial winding has dimensions that are at least comparable to the portion existing between two adjacent winding taps of the control winding. In other words, at least one partial winding has a predetermined number of windings that is at least comparable to the minimum number of windings existing between two adjacent winding taps of the control winding. When the electrical function has a plurality of partial windings, the number of windings of the plurality of partial windings may be an integer multiple of each other.

[0020] According to one embodiment, the first module is configured as a load tap changer for switching between different winding taps of the control winding of an electrical device during load, particularly as a high-speed resistance load tap changer, and has a selector for preselecting, in a no-current state, the winding tap that the electrical device has to be switched to, and a switching switch for actually switching, during load, the already connected winding tap to the newly preselected winding tap. In order to preselect the winding tap in a no-current state, generally, the selector has two movable selector contacts that connect to the winding tap. Generally, the switching switch has a switching contact and a resistor for actually switching. The switching contact is configured as a vacuum valve. The resistor is used to limit, for a short period, the circulating current flowing through the switching switch during the switching process and is also called a current-limiting resistor.

[0021] According to another embodiment, the first module is configured as a reactor switch. According to the principle of the reactor switch, the circulating current flowing through the inductance, also called a reactor, is limited.

[0022] According to one embodiment, the electrical function comprises a plurality of partial windings, and the second module comprises a plurality of sub-modules having semiconductor switching elements. At least one partial winding is attached to each sub-module, and each sub-module is configured to connect, reverse-connect, or bypass the attached partial winding. Specifically, bypassing means that each partial winding is not energized.

[0023] According to one embodiment, one sub-module includes four switching cells configured as, for example, a bridge circuit.

[0024] According to one embodiment, one switching cell includes two anti-parallel connected thyristor paths respectively. In this case, one path may be composed of a plurality of thyristors connected in series.

[0025] According to another embodiment, the bypass switch is configured to bypass a second module including at least one sub-module having a semiconductor switching element.

[0026] According to one embodiment, the bypass switch is configured as a circuit breaker or a load switch.

[0027] According to another embodiment, the on-load tap changer is operable in a predetermined operating mode in which the bypass switch is closed and at least one sub-module having a semiconductor switching element is bypassed.

[0028] According to another embodiment, when the on-load tap changer is in the predetermined operating mode, only the first module is used to change the transformation ratio, impedance or voltage used for excitation of the electrical equipment.

[0029] According to another embodiment, when the on-load tap changer is in the predetermined operating mode, the second module takes a neutral position in which at least one partial winding is bypassed, that is, it is bypassed with a potential but not energized. In other words, a plurality of semiconductor switching elements of the second module are connected to each other so as to form a bypass for at least one partial winding.

[0030] An advantage of this embodiment is that the electrical equipment can be operated uninterrupted by the first module while the bypass switch continues to conduct current, i.e., bypasses the semiconductor switching elements. This may be necessary, for example, when the second module is serviced or when a fault occurs due to a failure of the power supply for controlling the semiconductor switching elements. Furthermore, by operating the on-load tap changer in a default operating mode, losses due to the semiconductor switching elements of the second module can be avoided.

[0031] According to another embodiment, the on-load tap changer is operated in a defined second operating mode in which the transformation ratio, the impedance or the voltage used for magnetization is changed by a second module.

[0032] An advantage of this embodiment is that when the on-load tap changer is operated in the second operating mode, the mechanical parts and electrical changeover contacts of the first module are protected and the corresponding parts experience little wear, thereby increasing the lifespan of the on-load tap changer.

[0033] According to one embodiment, the first module includes a first control device, the second module includes a second control device (12), and the electrical equipment includes a system controller configured to operate the first control device and the second control device.

[0034] According to one embodiment, the second module, the first controller, the second controller, and the system controller are each disposed within a separate housing.

[0035] According to one embodiment, the second module, the first controller, the second controller, and the system controller are located within a common housing.

[0036] According to one embodiment, the second module and the second control device are disposed within a common housing.

[0037] According to one embodiment, the second module and the first control device are arranged within a common housing.

[0038] According to one embodiment, the second module, the second control device, and the system controller are arranged within a common housing.

[0039] According to one embodiment, the second module, the first control device, and the system controller are arranged within a common housing.

[0040] According to one embodiment, the second module, the first control device, and the second control device are arranged within a common housing.

[0041] According to one embodiment, the first control device and the second control device are arranged within a common housing.

[0042] According to one embodiment, the first control device, the second control device, and the system controller are arranged within a common housing.

[0043] According to one embodiment, the second module is arranged within the housing of the electrical equipment.

[0044] According to one embodiment, the bypass switch is arranged within an individual housing or within a common housing together with the second module.

[0045] According to another embodiment, the first control device includes a motor drive device. Preferably, the motor drive device is configured to operate the selector contacts and the switching contacts of the on-load tap-changer in order to switch the winding taps of the control winding. The motor drive device can be configured as a direct drive device having no intermediate connected gear mechanism.

[0046] The second control device is configured as a microcontroller, for example.

[0047] According to one embodiment, the second control device is configured to operate at least one or a plurality of sub-modules or switching cells attached to the sub-modules such that at least one or a plurality of partial windings are connected or reversely connected to the fast control winding quickly, or the partial winding is bypassed.

[0048] Hereinafter, the present invention will be described in detail with reference to the drawings based on the illustrated embodiments. Components that are the same, functionally the same, or have the same effect are denoted by the same reference numerals. In some cases, the same components or components having the same function are described only with respect to the figure in which they first appear. Such description is not necessarily repeated in subsequent figures.

Brief Description of the Drawings

[0049]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0050] Fig. 1 schematically shows a first embodiment of an electrical device 1 according to an improved concept.

[0051] Here, the electrical device 1 is configured as a single-phase controllable transformer. The controllable transformer 1 includes a main winding 2 on the primary side or the secondary side, a control winding 3 having n winding taps, and two partial windings 4 and 5. The partial winding 5 has a larger number of windings than the partial winding 4, for example, three times as many windings. Further, the number of windings of the partial winding 4 and the number of windings of the subsequent partial winding 5 are more than the existing minimum number of windings between two adjacent winding taps, for example, between n and n + 1 of the control winding 3.

[0052] The number of partial windings is not limited to two. Basically, a plurality of partial windings may be provided. The number of windings of each of these partial windings may be an integer multiple of the partial winding 4.

[0053] Furthermore, the transformer 1 has a load tap changer 6 for changing the transformation ratio of this transformer 1. The load tap changer 6 includes a first module 7 for switching the winding taps n, n + 1 of the control winding 3 and a second module 8 connected in series to this first module 7 for connecting, reversely connecting, or bypassing the partial windings 4, 5. The first module 7 is provided for control within the steady-state region, and the second module 8 is provided for control within the dynamic region.

[0054] Preferably, the first module 7 exists as a load tap changer composed of a selector for preselecting the winding taps n, n + 1 in a no-current state and a switch for switching the preselected existing winding tap n to the new winding tap n + 1 during load. Further, the load tap changer may have a preselector that can be configured as a coarse tap selector (Grobstufe) or a switching selector (Wender). However, in FIG. 1, for the sake of clarity, the first module 7 is shown in a very simplified manner.

[0055] Preferably, the second module 8 includes two sub-modules 9 each having four switching cells as an H-bridge circuit. In this case, one switching cell has a pair of thyristors connected in antiparallel. One partial winding 4 or 5 is attached to each sub-module 9, and each sub-module 9 is configured to quickly connect or reverse-connect each partial winding 4 or 5 to the control winding 3, that is, within 10 to 1000 milliseconds, by the switching cell or semiconductor switching element, or the partial windings 4 and 5 are configured to bypass each partial winding 4 or 5 so as to have a predetermined potential but not to be energized.

[0056] Furthermore, the second module 8 has a bypass switch 10 disposed on a connection line 14 parallel to the second module 8 and configured to bypass the second module 8 or the two sub-modules 9. The connection line 14 is connected to a load ground line 15.

[0057] The first module 7 includes a first control device 11 configured as a motor drive device, preferably, for operating a selector and a switching switch, and particularly preferably, as a direct drive device without an intermediate connecting gear mechanism.

[0058] The second module 8 is controlled by a second control device 12. The second control device 12 is configured to appropriately operate the two sub-modules or the switching cells attached to these sub-modules so that the two partial windings 4 or 5 are quickly connected or reverse-connected to the control winding 3, or the two partial windings 4 and 5 are quickly bypassed. Furthermore, the second control device 12 is configured to operate the bypass switch 10.

[0059] The first control device 11 and the second control device 12 are operated by a system controller 13 so as to depend on each other.

[0060] Figure 2 schematically shows a second embodiment of the electrical device according to the improved concept. The electrical device 1 according to Figure 2 is similar to the electrical device according to Figure 1 above, and hereinafter, only the differences from the electrical device 1 according to Figure 1 will be described.

[0061] Figure 2 shows the electrical device 1 configured as a controllable inductance. Such an arrangement is used in the energy supply network to control reactive power. The controllable inductance 1 further has a sparse tap winding 16 and a sparse tap control unit 17 in addition to the main winding 2, a control winding 3 having n winding taps, and two partial windings 4 and 5. The sparse tap control unit 17 takes a first position where the sparse tap control unit 17 contacts the first end A of the sparse tap winding 16 and a second position where the sparse tap control unit 17 contacts the second end B of the sparse tap winding 16. When the sparse tap control unit 17 is in the first position, the sparse tap winding 16 is not energized. In contrast, when the sparse tap control unit 17 is in the second position, current is passed through the sparse tap winding 16 and as a result, is added to the main winding 2 and the control winding 3. Thus, the control range of the inductance 1 is increased.

[0062] The inductance 1 is housed in a tank 18 and has a core 19 in which the windings 2, 3, 16, 4, 5 are arranged. Similarly, the on-load tap changer 7 is also arranged in this tank 18. The wires of the on-load tap changer 7 and the windings 2, 3, 16, 4, 5 are drawn out from the tank 18 through the bushing 20. Outside the tank 18, for example, flexible tubes that are similarly connected to the second module 8 and / or the control devices 11, 12 can be connected to the bushing 20.

[0063] According to this exemplary embodiment, the second module 8 and the bypass switch 10, which are simply shown here, are arranged together in the first housing 21, and the first control device 11, the second control device 12, and the system controller 13 are arranged together in the second control device 22. In this case, the housings 21 and 22 can be formed as commercially available switchboards or containers and can be arranged directly on the inductor 1 or the tank 18 of the electrical equipment, or can be arranged spatially close, for example, in a substation where the electrical equipment 1 is present. Also, it is possible to arrange the second module 8, the bypass switch 10, the control devices 12 and 13, and the system controller 13 in a common housing, or to provide separate housings for each individual unit.

[0064] Figure 3 schematically shows a third embodiment of the electrical equipment according to an improved concept. The electrical equipment 1 according to Figure 3 is similar to the electrical equipment according to Figures 1 and 2 above. Hereinafter, only the differences from the electrical equipment 1 according to Figures 1 and 2 will be described.

[0065] Figure 3 shows the electrical equipment 1 configured as a phase-shifting transformer. For better understanding, here the phase-shifting transformer 1 is configured as single-phase by way of example. The phase-shifting transformer 1 shown in Figure 3 is configured as an active power component controller (Querregler) for controlling the active power and has a dual-core structure consisting of a series transformer 23 and an excitation transformer 24 arranged in the core respectively. The excitation transformer 24 has a primary side with a main winding 2 and a secondary side with a control winding 3 having n winding taps, two partial windings 4 and 5, and a load tap changer 6. The voltage is taken out at the primary side of this excitation transformer 24 via the excitation transformer 24, and the magnitude of this voltage is controlled as an additional voltage at the secondary side using the load tap changer 6 via the control winding 3 and both partial windings 4 and 5. This additional voltage generated in the excitation transformer 24 is connected in a delta connection in the series transformer 23. As a result, the additional voltage is phase-shifted by 90° with respect to the input voltage of the phase-shifting transformer.

[0066] The electrical device as a phase-shifting transformer shown in FIG. 3 is not limited to the illustrated embodiment. Similarly, the phase-shifting transformer can be configured in a symmetric or asymmetric double-core structure, or in a single-core structure having a control winding connected to the neutral point, or as an active power component controller or a skin-effect power controller (Schraegregler), or as a single-winding transformer having a magnetic circuit and a booster circuit grounded.

[0067] FIG. 4 shows a flowchart of a preferred embodiment of a method for operating the electrical device 1 according to an improved concept, in particular according to one of the embodiments described with respect to FIGS. 1 to 3.

[0068] In the initial state, the circuit breaker attached to the electrical device 1 is open. That is, the electrical circuit between the electrical device 1 and the corresponding power grid to which this electrical device is attached is interrupted. In other words, this electrical device is separated from the associated power grid. Similarly, the bypass switch 10 is in the open state.

[0069] To operate the electrical device, the bypass switch 10 is closed in step a. In step b, the circuit breaker is closed and the electrical device 1 is connected to the power grid. Connecting the electrical device 1 to the power grid can generate a very high inrush current (so-called inrush current effect). However, the inrush current energizes the closed bypass switch 10 of the second module 8. As a result, the sub-module 9 having the semiconductor switching element is not damaged. After this point, the second module is already in an operable state and can be used to change the transformation ratio, impedance or voltage used for excitation of the electrical device 1. In the next step c, the second module 8 is switched to a neutral position in which the partial windings ④ and ⑤ are bypassed, that is, not energized. In the next step d, the bypass switch 10 is opened again. At this time, the second module 8 is also in an operable state and can be used together with the first module 7 to change the transformation ratio, impedance or voltage used for excitation of the electrical device.

[0070] Combining a first module, which is a conventional on-load tap changer, with a second module, which is a power electronics-based on-load tap changer, enables a wide control range at high potential while allowing for a low-cost and space-saving arrangement. Furthermore, the second module, which controls faster within a dynamically controlled area that is lower in cost compared to the first module, can be optimally designed for each application. Therefore, the second module can be appropriately designed only for a part of the control where the second module based on power electronics exhibits advantages due to its switching speed. Additionally, the combined solution is much more space-saving than a solution based purely on power electronics. In summary, a relatively small amount of space is required for the management of the power grid and the operation of the furnace, while a high degree of flexibility can be ensured by the solution of the present invention.

Explanation of Signs

[0071] 1 Electrical equipment (electric operating means) 2 Main winding 3 Control winding 4 First partial winding 5 Second partial winding 6 On-load tap changer 7 First module of 6 8 Second module of 6 9 Sub-module of 8 10 Bypass switch 11 First control device 12 Second control device 13 System controller 14 Connection wire 15 Load ground wire 16 Sparsely tapped winding (displaced tap winding) 20 Sparsely tapped control unit (displaced tap control unit) 18 Tank 19 Core 20 Bushing 21 First housing 22 Second housing 23 Series transformer It should be noted that the "??" in the translation is due to the lack of clear content in the original "??

[0071] ". If there is more specific information, a more accurate translation can be provided. 24 Excitation Transformer The First End of A 16 The Second End of B 16 n-1,n,...n+4 Winding Taps

Claims

1. - At least one control winding (3) having a winding tap (n, n + 1) and at least one partial winding (4, 5), - An electrical function (1) including a on-load tap changer (6) for changing the transformation ratio, impedance, or voltage used for excitation of the electrical function (1), - The on-load tap changer (6) includes a first module (7) for switching the winding tap (n, n + 1) of the control winding (3) and a second module (8) for quickly connecting, reverse connecting, or bypassing the at least one partial winding (4, 5), - The second module (8) includes at least one sub-module (9) having a semiconductor switching element and a bypass switch (10) of the electrical device (1).

2. - The electrical device (1) according to claim 1, wherein the at least one partial winding (4, 5) has a dimension at least as large as the portion existing between two adjacent winding taps (n, n + 1) of the control winding (3).

3. - The electrical device (1) according to claim 1 or 2, wherein the bypass switch (10) is configured to bypass the second module (8) including the at least one sub-module (9) having a semiconductor switching element.

4. - The electrical device (1) according to any one of claims 1 to 3, wherein the bypass switch (10) is configured as a circuit breaker or a load switch.

5. - The electrical device (1) according to any one of claims 1 to 4, wherein the on-load tap changer (6) is operable in a predetermined operating mode in which the bypass switch (10) is closed and the at least one sub-module (9) having a semiconductor switching element is bypassed.

6. - The electrical device (1) according to claim 5, wherein when the on-load tap changer (6) is in the predetermined operating mode, only the first module (7) is used to change the transformation ratio, impedance, or voltage used for excitation of the electrical device (1).

7. - The first module (7) includes a first control device (11), - The second module (8) includes a second control device (12), - The electrical device (1) according to any one of claims 1 to 6, comprising a system controller (13) configured to operate the first control device (11) and the second control device (12).

8. - The electrical device (1) according to claim 7, wherein each of the second module (8) and / or the first control device (11) and / or the second control device (12) and / or the system controller (13) is arranged in an individual housing or in a common housing.

9. - The first control device (11) includes a motor drive device. - The motor drive device is configured as a direct drive device having no intermediate connected gear mechanism, according to claim 7 or 8 of the electrical device (1).

10. - The bypass switch (10) is arranged in an individual housing or in a common housing together with the second module (8), according to any one of claims 1 to 9 of the electrical device (1).

11. - The first module (7) is configured as a high-speed resistive load tap changer or a reactor switch, according to any one of claims 1 to 10 of the electrical device (1).

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