System and procedure for operating a load tap changer

Abstract

System (200) for operating a load tap changer, wherein the system comprises: a plurality of strands (208, 210), at least one of which is caused to switch from a first tap (202) to a second tap (204) of the load tap changer upon receipt of a tap change signal, each strand having at least one mechanical switch (214, 216) and wherein an electrical connection is established between the first tap (202) or the second tap (204) and a supply terminal (212) of the load tap changer when at least one mechanical switch (214, 216) of at least one of the plurality of strands is opened; and a plurality of semiconductor switches (220, 222, 224, 226), wherein each semiconductor switch (220, 222, 224, 226) is arranged in parallel to the mechanical switches (214, 216) and, in the activated state, provides an electrical connection between the first tap (202) or the second tap (204) and a supply terminal (212) of the load tap changer; and a processing unit (228) configured to selectively activate and deactivate the mechanical switches (214, 216) and the semiconductor switches (220, 222, 224, 226) such that the electrical connection between the at least one tap (202, 204) and the supply terminal (212) is maintained during the transition of the at least one strand (208, 210) from the first tap (202) to the second tap (204) without causing a short circuit between the two taps (202, 204). the processing unit (228) is also configured to: Generating the step switching signal to move at least one strand (208, 210) from the first tap (202) to the second tap (204) when a condition for step switching is met; Generating activation signals for the semiconductor switches (220, 222, 224, 226) when the stage switching signal is generated; and Generating a plurality of deactivation signals for the mechanical switches (214, 216) from at least one strand (208, 210) connected to the first tap (202) when a stage switching condition is met.

Description

background

[0001] The present invention relates generally to the field of voltage regulation and in particular to load tap changers that are operated as voltage regulation devices.

[0002] Electricity is typically generated in large-capacity power plants connected to a transmission network. Electrical power is transmitted over long distances at very high voltages via a transmission system. At distribution substations, the voltage is reduced, and the power is made available to various loads within the distribution network. Voltage regulation in the distribution network is usually achieved by voltage regulation devices such as tap-switching transformers or voltage regulators. Capacitor banks are also widely used in many applications to assist with voltage regulation in distribution networks, where voltage variations are primarily caused by slow changes in loads connected to the distribution system.With the increasing penetration of intermittent renewable energy sources connected to the distribution level, voltage fluctuations in distribution networks are becoming more pronounced and frequent. This development necessitates greater flexibility in network voltage control, leading to an increased and more extensive use of voltage regulation equipment in distribution networks.

[0003] Voltage regulating devices, such as tap-switching transformers, are used to provide a regulated voltage at the output terminals. Tap-switching transformers typically contain at least one primary winding and at least one secondary winding. The primary and secondary windings each contain a plurality of turns. The input voltage is provided at the primary winding. The electrical load is connected to the secondary windings. The magnetic interaction between the primary and secondary windings causes energy to be transferred from the primary to the secondary winding. Transformers convert the input voltage (V) ein ) at the primary winding into an output voltage (V aus) at the secondary winding based on a turns ratio (T2 / T1) of the secondary winding turns (T2) to the primary winding turns (T1). The output voltage is calculated based on Equation 1: Vaus=Vein×T2T1

[0004] A load-to-load tap-switching transformer has several connection points, called "taps," along at least one of its windings. Each of these tap positions corresponds to a specific number of turns. Because the output voltage of the load-to-load tap-switching transformer is determined by the turns ratio of the primary winding to the secondary winding, the output voltage can be varied by selecting different taps. Load-to-load tap changers (OLTCs) are used to change the tap position of a load-to-load tap-switching transformer while it is energized, that is, under load.

[0005] Various mechanisms have been developed for OLTCs to change the turns ratio of the primary winding relative to the secondary winding of load-switching transformers. Several types of OLTCs, both mechanical and electronic, are available on the market. Mechanical OLTCs allow operation during operation but have demanding mechanical requirements. Each tap change operation of mechanical load tap changers results in a certain degree of arcing between the tap contacts and the moving finger contacts. Arcing leads to a gradual degradation of the transformer oil and accelerates the wear of the mechanical contacts. The service life of mechanical tap changers is therefore limited by the number of tap changes. However, conventional OLTCs have a relatively long service life of 15 to 20 years.This is primarily due to the comparatively low number of tap switching operations required to regulate slow voltage fluctuations caused by loads. However, more frequent voltage fluctuations can now be observed in distribution networks, driven by the increasing share of distributed generation from renewable energy sources. Therefore, OLTCs need to be operated more frequently than before. This leads to significantly higher maintenance requirements and a shorter service life. Furthermore, mechanical OLTCs require current-limiting inductors or resistors to limit the short-circuit current that occurs during a tap switching operation. Consequently, cooling of the current-limiting devices may be necessary due to frequent tap switching events.

[0006] The main disadvantage of mechanical tap changers is the unavoidable arcing between the tap contacts and the moving finger contacts when a tap is switched. Purely electronic tap changers, on the other hand, have no moving mechanical contacts whatsoever. Each tap contact is connected to the load via an electronic solid-state switch. The tap position is selected by turning on the corresponding electronic switch (i.e., conducting), while all other switches are off (i.e., non-conducting). Switching from one tap position to another is accomplished by commutation from one electronic switch to the next. Current commutation is therefore achieved without arcing due to the typically very fast switching capabilities of solid-state switches.Although electronic OLTCs are very flexible and arc-free, thus significantly reducing maintenance requirements compared to mechanical OLTCs, they also have disadvantages. The main disadvantage is the high cost of electronic switches. Since an electronic switch is required for each tap position, the cost increases further, especially with a higher number of taps. The second disadvantage is the higher conduction losses of electronic switches compared to mechanical contacts.

[0007] WO 2010 / 022 751 A1 discloses a method for the uninterrupted switching between winding taps of a step-down transformer. Each winding tap is connected to a common load path via a mechanical switch and a series connection of two oppositely connected IGBTs. Permanent main contacts are also provided, by means of which the load branches can be bridged.

[0008] The tap changer disclosed in DE 10 2010 008 973 A1 has two strands, each comprising a parallel circuit consisting of a mechanical switch and semiconductor switches.

[0009] A system for switching between taps for regulating transformers is further described in US 3,662,253 A. In one embodiment, the switching device has a mechanical switch connected to each tap. A semiconductor switch can be connected in parallel to this mechanical switch.

[0010] Therefore, there is a need for OLTC facilities that are more economically viable, require less maintenance, cause fewer line losses, and provide the flexibility to meet the changing control requirements due to the increasing share of intermittent renewable energy sources in the distribution network. Brief description

[0011] The invention relates to a system for operating a load tap changer with the features of claim 1. The system comprises a plurality of branches. At least one of the plurality of branches is caused to switch from a first tap to a second tap of the load tap changer upon receiving a tap change signal. Each branch contains a mechanical switch. When at least one mechanical switch of at least one of the plurality of branches is energized, an electrical connection is established between the first tap or the second tap and a supply terminal of the load tap changer. The system also comprises a plurality of semiconductor switches. Each semiconductor switch is arranged in parallel with the mechanical switches and, when energized, provides an electrical connection between the first or second tap and the supply terminal of the load tap changer.Furthermore, the system includes a processing unit configured to selectively activate and deactivate the mechanical switches and the semiconductor switches, such that an electrical contact is maintained between the at least one tap and the supply terminal during the transfer of at least one strand from the first tap to the second tap without causing a short circuit between the two taps.

[0012] The processing unit of the system is also configured to: generate the step-switching signal to move the at least one strand from the first tap to the second tap when a step-switching condition is met; generate activation signals for the semiconductor switches when the step-switching signal is generated; and generate a plurality of deactivation signals for the mechanical switches of the at least one strand connected to the first tap when a step-switching condition is met.

[0013] The system of any of the above-mentioned types may also include a strand drive system configured to receive the stage switching signal from the processing unit and cause at least one strand to move towards the second tap.

[0014] The processing unit of any of the above-mentioned systems may also be configured to: generate a first deactivation signal for the semiconductor switches connected to a first strand of the plurality of strands, which changes its position from the first tap to the second tap before the first strand is disconnected from the first tap; generate a second deactivation signal for one or more of the plurality of semiconductor switches connected to a second strand as soon as the first strand is connected to the second tap; generate a first activation signal for the mechanical switch connecting the first strand to the supply terminal when the first strand is connected to the second tap; generate a second activation signal for the remaining mechanical switches connecting the plurality of strands to the supply terminal;and generating a third deactivation signal for the majority of semiconductor switches.

[0015] The system of any of the above-mentioned types may also include at least one damping device connected in parallel to the majority of semiconductor switches.

[0016] The semiconductor switches of any of the above-mentioned systems can be bidirectional or unidirectional.

[0017] The semiconductor switches of any of the above-mentioned systems may include a MOSFET and / or IGBT and / or IGCT.

[0018] The load tap changer of any of the above-mentioned systems may have a rotary tap selection device.

[0019] The load tap changer of any of the above-mentioned systems may have a linear tap selection device.

[0020] The invention further relates to a method for operating the load tap changer with the features of claim 9. The method includes deactivating one or more mechanical switches connected to at least one of a plurality of strands at one end and a supply terminal at the other end when a tap change condition is met. The at least one strand is electronically connected to a first tap of a plurality of taps of the load tap changer. The method also includes activating a plurality of semiconductor switches arranged in parallel to the mechanical switches and connected to the at least one strand of the plurality of strands and the supply terminal when the tap change condition is met. Furthermore, the method includes moving the at least one strand of the plurality of strands from the first tap to the second tap.The method also includes the selective activation and deactivation of the plurality of semiconductor switches, and the semiconductor switches connected to a moving strand that is electrically connected to at least one tap are in an activated state, while the semiconductor switches connected to a moving strand that is not electrically connected to any tap are in a deactivated state. Furthermore, the method also includes the activation of one or more mechanical switches connected to at least one strand of the plurality of strands that is electrically connected to the second tap.

[0021] The method may also include: generating a plurality of activation signals for the plurality of semiconductor switches when the stage switching condition is met; and generating deactivation signals for the mechanical switches when the stage switching condition is met.

[0022] The method of any of the above-mentioned types may include the selective activation and deactivation further comprising: generating a first deactivation signal for the semiconductor switches connected to a first strand of the plurality of strands, which changes its position from the first tap to the second tap before the first strand is disconnected from the first tap; generating a second deactivation signal for one or more of the plurality of semiconductor switches connected to a second strand as soon as the first strand is connected to the second tap; generating a first activation signal for the mechanical switch connecting the first strand to the supply terminal when the first strand is connected to the second tap; generating a second activation signal for the remaining mechanical switches connecting the plurality of strands to the supply terminal;and generating a third deactivation signal for the majority of semiconductor switches.

[0023] The method of any of the above-mentioned types may include the selective activation and deactivation further comprising: generating a first activation signal for one or more of the plurality of semiconductor switches connected to a first strand of the plurality of strands when the first strand is connected to the second tap; generating a first deactivation signal for one or more of the plurality of semiconductor switches connected to a second strand as soon as the first strand is connected to the second tap, the second strand being connected to the first tap; and generating a second activation signal for the mechanical switch connecting the first strand to the supply terminal.

[0024] The method of any of the above-mentioned types may also feature the generation of a second deactivation signal for the majority of semiconductor switches.

[0025] Other features and advantages of the present disclosure will become apparent from the following more detailed description of the preferred embodiment in conjunction with the accompanying drawings, which exemplify the principles of certain aspects of the disclosure. Drawings: Fig. Figure 1 illustrates a typical voltage control device with a selector switch of the type of a mechanical on-load tap changer (OLTC); Fig. Figure 2 illustrates a rotary OLTC according to an embodiment of the present invention; Fig. Figure 3 illustrates a switching sequence of mechanical switches and semiconductor switches of an OLTC according to an embodiment of the present invention; Fig. Figure 4 illustrates a linear OLTC according to an embodiment of the present invention. Fig. 5a and Fig. Figure 5b illustrates a switching sequence of mechanical switches and semiconductor switches of a linear OLTC according to an embodiment of the present invention; and Fig. Figure 6 illustrates a method for operating an OLTC according to exemplary embodiments of the present invention. Detailed description

[0026] The following section refers in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the reference numerals used throughout the drawings refer to the same or similar parts.

[0027] Exemplary embodiments of the present invention provide a system and a method for operating a load tap changer, such as those used for voltage regulation by switching the connections from one tap to another in voltage regulating devices, such as load tap changers or voltage regulators. The following description focuses on the use of load tap changers in transformers. However, these load tap changers can also be used in any other voltage regulating device with taps. Generally, tap changers are used in transmission and distribution systems to connect networks with different voltage levels. They contain a plurality of primary windings and a plurality of secondary windings and a tap changer.The step switching device allows a selective connection with different transformer taps and therefore makes it possible to vary the turns ratio (T2 / T1) and thereby the output voltage (V. ausThe step-change device contains a plurality of electrically conductive strands that establish an electrical connection between a selected tap and the load terminal of the load-changer. When a change in the system load occurs and the system voltage is outside a permissible voltage range, a controller triggers a step-change operation, and the electrically conductive strands are moved from one tap to another. The system and method for operating load-changer tap changers (OLTCs), according to embodiments of the invention, helps to eliminate arcing during the transition of the strands from one tap to another. The present invention provides a system comprising a plurality of mechanical switches and a plurality of semiconductor switches.When the phases are connected to a tap, the mechanical switches connected to the phases are activated to establish a current path from the tap to the supply terminal. Upon receiving a step-switching signal, the semiconductor switches are activated. In the activated state, the semiconductor switches establish a current path between the taps and the supply terminal of the voltage regulator. Before the phases begin to move from a first tap to a second tap, both the mechanical switches and the semiconductor switches in the phase that first breaks the connection are deactivated. The semiconductor switches are configured to commutate the current from the first tap to the second tap without arcing. Furthermore, the mechanical switches are activated and the semiconductor switches are deactivated when the phases are connected to the second tap.The system and method can be implemented in voltage control devices that have taps and branches for switching between the taps. Devices for switching between taps can be rotary or linear. The system for operating OLTCs according to the embodiments of the present invention has been described with respect to both linear and rotary switching devices. However, the operating system can also be coupled with other known step switching devices.

[0028] Fig. Figure 1 shows a voltage regulator with an OLTC 100 according to the prior art. The device 100 contains at least one primary winding 102 and at least one secondary winding 104. An input source, such as an electrical network or a battery, can be connected to at least one of the primary windings 102 or the secondary windings 104. An electrical load 106 is connected to the secondary winding 104 if the input source is connected to the primary winding 102. The device 100 can also have a plurality of taps 108 and 110. The taps 108 and 110 are configured to establish an electrical connection between one of the secondary windings 104 and the electrical load 106. The taps 108 and 110 are connected to the electrical load via a plurality of electrically conductive strands (A, B, and C) 112.In one embodiment, strands A and C can operate as bridging strands, and strand B as a continuously conducting strand. Furthermore, the device 100 can also have a plurality of bridging elements 114 and 116. The bridging elements 114 and 116 are connected to the strands 112, e.g., to strands A and C, and are arranged parallel to the continuously conducting strand B and in series between the taps 108 and 110 and the electrical load 106. The bridging elements 114 and 116 can be resistive elements, inductors, or a combination of both. In the illustrated embodiment, resistive elements are used as bridging elements 114 and 116.

[0029] The strands 112 can transition from one tap 108 to another tap 110 using manual or automatic transition devices. Automatic transition devices can include rotary or linear transition devices. Rotary transition devices involve selecting taps arranged in a circular pattern by moving strands 112 using electric motors and a drive gear assembly. Linear transition devices include strands 112 connected to sliding contacts coupled to the taps 108 and 110. The sliding contacts are moved using electric motors and drive gears to connect the strands with different taps 108 and 110.

[0030] The bypass strands A and C contain current-limiting elements, and in steady state, negligible or no currents pass through them, while strand B carries the predominant steady-state current. During operation, when a step-change signal is received, strand B and the bypass strands A and C move toward the next selected tap 110. Before the conducting strand B is disconnected from the first tap 108, strand A is connected to the first tap 108. Strand B then breaks the connection to the first tap, resulting in arcing. While strand A is still connected to tap 108, strand C makes a connection to tap 110. In this state, an electrical connection is established between the two taps 108 and 110.However, the short-circuit current is limited by the bridging elements 114 and 116, which are connected to strands A and C. The conductive strand B may then make contact with tap 110, and the strands with the two bridging elements 114 and 116 will be left open, thus completing the step-switching process. The step-switching process leads to significant energy losses in the bridging elements 114 and 116 and to heat generation. The resulting arcing leads to deterioration of the electrical contacts and maintenance problems.

[0031] Fig. Figure 2 illustrates a rotary-type OLTC 200 according to an embodiment of the present invention. The rotary-type OLTC according to Fig. 2 is connected to a transformer. The transformer, as in Fig. As illustrated in Figure 1, the system also includes at least one primary winding (not shown), at least one secondary winding 234, and a plurality of taps 202, 204, and 206. The taps 202, 204, and 206 are connected to a winding of the transformer. The system 200 also includes a plurality of conductive strands 208 and 210. The strands 208 and 210 are arranged parallel to each other and connected at one end to a supply terminal 212 and configured to be connected to one of the taps 202, 204, and 206 at the other end. The strands 208 and 210 can be made of electrically conductive material, such as metals.

[0032] System 200 also includes multiple mechanical zero-load switches 214 and 216. Mechanical zero-load switches 214 and 216 are each connected to the circuits 208 and 210, respectively. Furthermore, mechanical switches 214 and 216 also connect the circuits 208 and 210 to the supply terminal 212. Mechanical switches 214 and 216 are arranged in parallel and share a common connection point 218, which is connected to the supply terminal 212. In a conducting / activated state, mechanical switches 214 and 216 establish a current path between the tap 202, 204, or 206 and the supply terminal 212.When strands 208 and 210 are connected to one of the taps 202 or 204 or 206 and switches 214 and 216 are activated, the current flowing from the connected tap is routed through strands 208 and 210 via two parallel current paths formed by switches 214 and 216 and is supplied to the supply terminal via the common connection point 218.

[0033] The system also includes a plurality of semiconductor switches 220, 222, 224, and 226. According to embodiments of the present invention, pairs of semiconductor switches 220, 222, and 224, 226 form bidirectional controllable semiconductor switches. Examples of fully controllable semiconductor switches 220, 222, 224, and 226 include, but are not limited to, e.g., insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs) or other field-effect transistors (FETs), GTO thyristors, insulated-gate commutation thyristors (IGCTs), or injection-enhanced gate transistors (IEGTs), or combinations thereof. The materials of such switches may include, e.g., silicon, silicon carbide, gallium nitride, gallium arsenide, or combinations thereof. The semiconductor switches 220, 222, 224 and 226 are arranged to form a plurality of branches 236 and 238.Each branch 236 and 238 of the semiconductor switches can have an equal number of semiconductor switches and is connected in parallel to the other branches of the semiconductor switches and to the mechanical switches 214 and 216. The semiconductor switches 220, 222, 224, and 226 are configured to be in a conducting state when activated by gate signals of appropriate magnitude. In the illustrated embodiment, the semiconductor switches 220, 222, 224, and 226 are divided into two branches connected in parallel to each other. Each branch is connected at one end to one of the strands 208 and 210 and at the other end to the common connection point 218. The semiconductor switches 220, 222, 224, and 226 are thus arranged in parallel to the mechanical switches 214 and 216.

[0034] The system includes a processing unit 228. The processing unit 228 is connected to the mechanical switches 214 and 218 and the semiconductor switches 220, 222, 224, and 226 and is configured to provide activation and deactivation signals for the switches 214, 216, 220, 222, 224, and 226. The processing unit 228 can also be configured to generate a step-change signal when the regulated voltage at 212 is outside a permissible bandwidth. The processing unit 228 is configured to transmit the step-change signal to a string drive system 232, which is connected to the majority of strings 208 and 210. The string drive system 232, according to other embodiments, can include switches connected to electric motors and gear assemblies. The step changeover signal generated by the processing unit 228 is made available to the string drive system 232.Electrical energy is then supplied to the electric motors, which begin to drive the gear assembly. The gear assembly can be connected to the majority of strands 208 and 210. Due to the movement of the gear assembly, the majority of strands 208 and 210 begin to move in a predetermined direction to connect to another tap of the voltage regulating device.

[0035] The processing unit 228 is configured to selectively activate and deactivate the semiconductor switches 220, 222, 224, and 226 during the transition of strands 208 and 210 from one tap to another, e.g., from the first tap to the second tap 204. The processing unit 228 activates at least one semiconductor switch 220, 222, 224, or 226 of branch 236 or branch 238 that is connected to any of the taps 202 or 204. The processing unit 228 is also configured to keep the remaining semiconductor switches deactivated. The switching pattern of the semiconductor switches 220, 222, 224, and 226 is determined by the processing unit 228 to prevent arcing during the transition of strands 208 and 210.The processing unit 228 is configured to interrupt the step changeover signal and the mechanical switches 214 and 216 are activated to establish the defined current paths when the transition of the strands 208 and 210 from one tap to another is completed and the majority of the strands 208 and 210 are connected to only one of the taps 202 or 204 or 206.

[0036] In the illustrated embodiment, strands 208 and 210 are connected to the first tap 202. According to one embodiment, in steady-state operating modes of the OLTC, the mechanical switches 214 and 216 are in an activated state, and the semiconductor switches 220, 222, 224, and 226 are in a deactivated state. In another embodiment of steady-state operating modes, switches 214 and 216 and the semiconductor switches 220, 222, 224, and 226 can be in an activated state. The mechanical switches provide a current path from the first tap 202 to the supply terminal 212. The voltage at the supply terminal 212 is proportional to the ratio of the primary winding turns to the number of secondary winding turns selected by the first tap 202.According to certain embodiments, the power supplied by the voltage regulator can be used to supply energy to an electrical load connected to the supply terminal 212. If the voltage requirement of the electrical load changes or the required voltage is outside a permissible range, the processing unit 228 is configured to generate a step-switching signal. Upon receipt of the step-switching signal, the mechanical switches 214 and 216 are deactivated, and the semiconductor switches 220, 222, 224, and 226 are activated. After branch 238 with the semiconductor switches 224 and 226 has been deactivated, strands 208 and 210 begin to move toward the second tap, e.g., tap 204.During the transition of strands 208 and 210 from the first tap 202 to the second tap 204, the semiconductor switches 220, 222, 224, and 226 are selectively activated and deactivated so that at least the first tap 202 or the second tap 204 is electrically connected to the supply terminal 212 and arcing is prevented. The selective activation and deactivation of the semiconductor switches 220, 222, 224, and 226 is described in more detail in conjunction with [reference missing]. Fig. 3 explained.

[0037] The processing unit 228 can further be configured to detect when both strands 208 and 210 have reached the second tap 204. The processing unit 228 can also be configured to activate the mechanical switches 214 and 216 and deactivate the semiconductor switches 220, 222, 224, and 226 when the strands 208 and 210 come into contact with the second tap 204. Thus, the mechanical switches 214 and 216 provide the current path from the tap 204 to the supply terminal 212.

[0038] In the illustrated embodiment, the system may also include a damping device 230 for operation. The damping device 230 is configured to protect the semiconductor switches 220, 222, 224, and 226 and the mechanical switches 214 and 216 from overvoltages caused by current interruptions due to the leakage inductance of the tap during a stage change. In the illustrated embodiment, the damping device 230 is a capacitive element. Other examples of damping devices 230 include, but are not limited to, RC dampers and metal oxide varistors. The capacitive element is designed to store energy pulses flowing during the transition of the strands from the tap to the supply terminal 212, and to release the stored energy when the strands 208 and 210 have transitioned from the first tap 202 to the second tap 204.In the illustrated embodiment, the damping device 230 is connected in parallel to the strand sections 236 and 238. In other embodiments, a plurality of damping devices can be used to protect the semiconductor switches 220, 222, 224, and 226. For example, a damping device can be connected in parallel to each of the branches 236 and 238. Furthermore, in other embodiments, one or more damping devices can be connected in parallel to each semiconductor switch 220, 222, 224, and 226.

[0039] Fig. Figure 3 illustrates a switching sequence for the mechanical switches 214 and 216 and the semiconductor switches 220, 222, 224 and 226 in the system according to Fig. 2 according to an embodiment of the present invention. The processing unit, such as processing unit 228, is configured to selectively activate and deactivate the semiconductor switches 220, 222, 224, and 226 as the strands 208 and 210 move from one tap to another. At 302, when the strands 208 and 210 are connected to the first tap 202, the mechanical switches 214 and 216 are in an activated state, and the semiconductor switches 220, 222, 224, and 226 are deactivated. Current paths 328 and 330, formed by mechanical switches 214 and 216, connect tap 202 to supply terminal 212. When a stage switching condition is detected by the processing unit at 304, semiconductor switches 220, 222, 224 and 226 are activated.Semiconductor switches 220, 222, 224, and 226 are activated by providing gate signals for each semiconductor switch 220, 222, 224, and 226. Activating semiconductor switches 220, 222, 224, and 226 generates two additional current paths 332 and 334. At 306, mechanical switches 214 and 216 are deactivated, and current paths 332 and 334 are used to connect tap 202 to supply terminal 212. At 308, a branch of semiconductor switches 224 and 226 is deactivated, which is connected to the branch oriented in the direction of movement, that is, the branch that is disconnected first from the current tap 202.

[0040] The processing unit is also configured to generate a stage-switching signal in response to the stage-switching state. This stage-switching signal is provided to the string drive system of strings 208 and 210. The stage-switching signal causes strings 208 and 210 to initiate a transition from the first tap 202 to the second tap, as illustrated in Figure 308, where strings 208 and 210 begin their transition in the direction indicated by arrow 336. In the illustrated embodiment, strings 208 and 210 begin moving from the first tap 202 to the second tap 204. In this embodiment, the resulting voltage at the supply terminal 212 is higher when the strings are connected to the second tap 204 than when the strings are connected to the first tap 202. At 310, strand 210 is separated from the first tap 202.The current flowing from the first tap 202 is supplied to the power supply via the current path 332, which is formed by the strand 208 and the activated semiconductor switches 220 and 222. At 312, the strand 210 comes into contact with the second tap 204. At 314, after the strand 210 has been connected to the second tap 204, the processing unit activates at least one semiconductor switch connected to the strand 210. In one embodiment, the processing unit activates at least one of the semiconductor switches 224 and 226 immediately after the strand 210 has come into contact with the tap 204. In other embodiments, the processing unit activates one of the semiconductor switches 224 and 226 after a time interval following the connection between the strand 210 and the tap 204.In the illustrated embodiment, the processing unit activates the semiconductor switch 226, which is connected to strand 210. At 316, when strand 208 is still connected to the first tap 202, at least one semiconductor switch connected to strand 208 is deactivated. As shown in . Fig. As illustrated in Figure 3, semiconductor switch 222 is deactivated. At 316, strand 208 is connected to the first tap 202, strand 210 is connected to the second tap 204, and semiconductor switches 220 and 226 are in their activated state.

[0041] At 318, the processing unit activates semiconductor switch 224. At 320, the processing unit deactivates semiconductor switch 220, thus interrupting the current path through strand 208. Both semiconductor switches 220 and 222, which are connected to strand 208, are deactivated when strand 208 is disconnected from the first tap 202. At the same time, both semiconductor switches 224 and 226 are activated, and the load current is diverted to flow through current path 334. At 322, strand 208 comes into contact with the second tap 204, and mechanical switch 216 is activated. At 324, when both strands 208 and 210 are connected to the second tap 204, the processing unit stops the stage switching signal. Interrupting the step changeover signal deactivates the string drive system, which in turn prevents strings 208 and 210 from moving.At this moment, semiconductor switches 220 and 222 and mechanical switch 214 are activated. At this point, semiconductor switches 220, 222, 224, and 226, as well as mechanical switches 214 and 216, are in an activated state, and the load current is distributed to current paths 328, 330, 332, and 334. At point 326, semiconductor switches 220, 222, 224, and 226 are deactivated, and the second tap 204 and the supply terminal 212 are connected via current paths 328 and 330, which are formed by mechanical switches 214 and 216.

[0042] The illustrated switching sequence for commutation of the current from current path 332 to 334 is referred to as 4-step current commutation. The 4-step current commutation process comprises sequence steps 312 to 320 in which the semiconductor switches 220, 222, 224, and 226 are selectively activated and deactivated to change the current path from the first tap 202 to the second tap 204. The 4-step current commutation can be based on a comparison of voltage values ​​between the voltages at the two taps or on the direction of the current through the supply terminal 212. The illustrated sequence is based on a comparison between the voltage value at the first tap 202 and the voltage value at the second tap 204.

[0043] According to other embodiments, the switching sequence for the semiconductor switches 220, 222, 224, and 226 can include a two-step current commutation process to commutate the current from the first tap 202 to the second tap 204. The two-step current commutation process is based on knowledge of both the voltage difference between the first tap 202 and the second tap 204, and the current direction at the supply terminal 212. While two methods have been described in the preceding paragraphs, it may be apparent to those skilled in the art that other modifications of the switching sequence can also be implemented to selectively activate and deactivate the semiconductor switches in order to achieve arc-free, short-circuit-free, and continuous current commutation from string 208 to string 210.

[0044] Fig. Figure 4 illustrates a linear OLTC 400 configured to actuate a voltage regulating device according to an embodiment of the present invention. The tap changer 400 includes a plurality of taps, such as taps 402 and 404, a plurality of strands 406 and 408, a plurality of mechanical switches 410 and 412, a supply terminal 414, a plurality of semiconductor switches 416, 418, 420, and 422, a common connection point 424, a processing unit 426, and a damping device 428. The plurality of taps 402 and 404 provide a desired turns ratio between the primary winding and the secondary winding of the transformer (not shown) when connected to the supply terminal 414. The majority of strands 406 and 408 are designed to be connected to one of the majority of taps 402 and 404.Mechanical switches 410 and 412 are connected to the respective strands 406 and 408. The strands with mechanical switches 410 and 412 are connected to a common connection point 424, which is also connected to the supply terminal 414. The processing unit 426 is configured to detect the need for a step switching operation when the regulated voltage is outside a permissible voltage range. Based on the current value of the regulated voltage, the processing unit 426 activates either switch 410 or switch 420 to connect one of the taps 402 or 404 to the supply terminal 414. For example, in the illustrated embodiment, the first tap 402 of the device 400 is selected. In such a case, switch 410, which is connected to the strand 406 that is connected to tap 402, is activated.

[0045] If the regulated voltage is outside a permissible voltage range, the processing unit 426 generates a step-change signal configured to move the strands 406 and 408 to connect a suitable tap to the supply terminal 414. The processing unit 426 is configured to transmit the step-change signal to a strand drive system 430. The strand drive system 430 is mechanically connected to the strands 406 and 408. When the strand drive system 430 receives the step-change signal, electrical devices cause a gear assembly of the drive system 430 to move. The gear assembly, in turn, causes the strands 406 and 408 to move in a specific direction. For example, the step-change signal can indicate to connect the second tap 404 to the supply terminal 414.In such an embodiment, strand 408 leads to the second tap 404 while mechanical switch 412 is still deactivated and the current flows through mechanical switch 410. After a connection is established between strand 408 and tap 404, mechanical switch 412, which is connected to strand 408, is activated. Simultaneously, switch 410, which is connected to strand 406, is deactivated. The processing unit 426 is configured to selectively activate and deactivate semiconductor switches 416, 418, 420, and 422 during the transition of the strands from tap 402 to tap 404, in order to commutate the current from one tap to another without arcing and without interrupting the load current.

[0046] Fig. 5a and Fig. Figure 5b illustrates a switching sequence of the mechanical switches 410 and 412 and the semiconductor switches 416, 418, 420 and 422 in the system according to Fig. 4 according to an embodiment of the present invention. The processing unit, such as processing unit 426, is configured to selectively activate and deactivate the semiconductor switches 416, 418, 420, and 422 during the transition of strands 406 and 408 from one tap to another. In the illustrated embodiment, the mechanical switch 410, which is connected to strand 406, is activated at 502. Strand 406 is connected to the first tap 402, and the current path to the supply terminal 414 is provided by the tap 402, strand 406, and the mechanical switch 410. When a step-change signal is received at 504, strand 408 begins to move to the second tap 404 in the direction indicated by arrow 522. At 506, the semiconductor switches 416 and 418, which are connected to string 406, are activated.An additional current path 524 is established between the first tap 402 and the supply terminal 414 via the semiconductor switches 416 and 418. At 508, the processing unit deactivates the mechanical switch 410, which is connected to the strand 406. Furthermore, at 510, the processing unit activates at least one of the semiconductor switches, such as semiconductor switch 422, which is connected to strand 408, now connected to the second tap 404. Additionally, at 512, the processing unit deactivates at least one of the semiconductor switches connected to strand 408 (e.g., semiconductor switch 418). At 514, the processing unit activates the second semiconductor switch (e.g., 420) connected to strand 408. At 516, the activated semiconductor switch 416, which is connected to strand 406, is deactivated.At this point, the current flowing from the voltage regulator is commutated to tap 404 and routed through current path 526, which connects the second tap 404 to supply terminal 414 via the activated semiconductor switches 420 and 422. At 518, the mechanical switch 412, connected to string 408, is activated. The current flowing from the voltage regulator is supplied to supply terminal 414 via current path 526 and current path 528, formed by mechanical switch 412. At 520, semiconductor switches 420 and 422 are deactivated when the step-change signal is interrupted. The load current now flows only through current path 528, and the step-change operation is complete.

[0047] Fig. Figure 6 illustrates a method for operating voltage regulating devices according to embodiments of the present invention. The operating method is used to regulate a voltage supplied to an electrical load without causing arcing in the load tap changer. If the measured regulated voltage is outside a permissible range, the turns ratio of the voltage regulating device is changed to provide the required voltage for the load. The tap changer, as shown in the Fig. 2 and Fig. Figure 4 illustrates a system comprising a plurality of taps, a plurality of strands, a plurality of mechanical switches, a plurality of semiconductor switches, and a processing unit. The method involves the selective activation and deactivation of the mechanical switches and the semiconductor switches during the transition of the plurality of strands from one tap to another, ensuring that no arcing occurs and that the load current is not interrupted.

[0048] In 602, the method involves activating a plurality of semiconductor switches connected to at least one of a plurality of strands at one end and the supply terminal at the other end when a stage-switching condition is met. In 406, the method involves deactivating one or more mechanical switches connected in parallel to the semiconductor switches and connected to at least one strand of the plurality of strands at one end and the supply terminal at the other end when a stage-switching condition is met. The mechanical switches connected to a first strand that is connected to a first tap of the voltage-regulating device are deactivated.At 606, after the current path through the first strand is interrupted by deactivating the semiconductor switches connected to the first strand, at least one of the majority of strands is moved to a second tap of the voltage regulator in response to a step-switching signal. The step-switching signal is generated in response to a step-switching condition being met. An exemplary step-switching condition involves a change in generation or load in the network connected to the supply terminal, causing the regulated voltage to deviate from a permissible voltage bandwidth. According to one embodiment, the step-switching signal is generated by a processing unit. The processing unit transmits the step-switching signal to a strand drive system, which initiates the movement of the strands.

[0049] During the movement of the strands from one tap to another, the method described in 608 includes the selective activation and deactivation of the majority of semiconductor switches. The semiconductor switches are activated and deactivated such that at least one of the semiconductor switches associated with a strand that is electrically connected to any tap of the voltage regulating device is kept activated, and that the semiconductor switches associated with any strand that is not in contact with any tap are deactivated. This activation and deactivation of switches ensures that the load current is not interrupted. Furthermore, the semiconductor switches are activated and deactivated so that no arcing occurs.At 610, if at least one of the strands is connected to the second tap, the mechanical switches connected to the strands in contact with the second tap are activated to create a steady current path for the current flowing from the voltage regulating device to the supply terminal.

[0050] In one embodiment, the mechanical switch connected to the first strand is deactivated before the strands begin moving from the first tap to the second tap. Simultaneously, the semiconductor switches in the second strand are activated when the first strand reaches the second tap. After the semiconductor switches are activated, the mechanical switch connected to the second strand is deactivated. Once the semiconductor switches in the second strand have fully taken over the load current, 4-step current commutation can be performed between the semiconductor switches in both strands to achieve smooth current commutation from the first tap to the second tap. Subsequently, the mechanical switch in the first strand can be activated, and the parallel semiconductor switches can be deactivated.

[0051] In another embodiment, the semiconductor switches are activated before the mechanical switches associated with each strand are deactivated, before the strands begin moving from the first tap to the second tap. The method also includes deactivating the semiconductor switches associated with the first strand as it moves away from the first tap to the second tap. In this way, the semiconductor switches associated with the first strand are off when the first strand is disconnected from the first tap, and no active current path is interrupted. The method also incorporates a commutation technique, such as 4-step commutation, as described in the Fig. 3 and Fig.Figure 5 illustrates the process that is executed to commutate the current from the first tap to the second tap. After both strands reach the second tap, the mechanical switch connected to the first strand is activated to create an additional current path for the load current. The semiconductor switches connected to the remaining strands are also activated, as is the mechanical switch connected to the second strand. At this point, all mechanical switches and all semiconductor switches are activated. To complete the step switching operation, the semiconductor switches are turned off, while the mechanical switches remain activated to provide a steady-state current path for the load current.

[0052] The method and system for operating OLTCs described in the preceding paragraphs eliminates arcing between the tap contacts and the conductors when a tap is changed. This reduces wear on the mechanical contacts and degradation of the control device oil. Therefore, system maintenance costs are reduced and the service life of the load tap changer is increased. Furthermore, smaller mechanical switches can be used, reducing the size of the operating system. Moreover, the need for cooling these components is eliminated, as there is no requirement for current limiting devices.

[0053] It should be understood that the foregoing description is intended to be illustrative. For example, the embodiments described above can be used in combination with one another.

[0054] The written description uses examples to disclose several embodiments of the invention, including the preferred embodiment, and also to enable any person skilled in the art to carry out the embodiments of the invention, including the manufacture and use of any devices or systems and the execution of any process included. The patentable scope of the invention is defined by the claims.

[0055] As used herein, the term "processing unit" refers to software, hardware or firmware, or any combination thereof, or any system, process or functionality that performs or enables the procedures described herein.

[0056] As used herein, an element or step specified in the singular and preceded by the word "a" or "an" should not be understood as excluding the plurality of such elements or steps unless such exclusion is explicitly stated. Furthermore, references to "an embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also have the specified features. Moreover, unless expressly stated otherwise, embodiments "having," "containing," or "with" an element or plurality of elements that has or have a certain property may contain additional such elements that do not have that property.

[0057] A system for operating an on-load tap changer (OLTC) contains multiple branches, each containing a mechanical switch. At least one branch switches from a first tap to a second tap of the OLTC upon receiving a tap change signal. At least one mechanical switch is activated to establish an electrical connection between the first or second tap and a supply terminal of the OLTC. The system also includes semiconductor switches connected in parallel to the mechanical switches, which, when activated, electrically connect the first or second tap to the supply terminal.The system includes a processing unit that selectively activates and deactivates the mechanical switches and the semiconductor switches in such a way that the electrical connection between at least one of the taps and the supply terminal is maintained during the transition of at least one strand from the first tap to the second tap.

Claims

[1] System (200) for operating a load tap changer, wherein the system comprises: a plurality of strands (208, 210), at least one of which is caused to switch from a first tap (202) to a second tap (204) of the load tap changer upon receipt of a tap change signal, each strand having at least one mechanical switch (214, 216) and wherein an electrical connection is established between the first tap (202) or the second tap (204) and a supply terminal (212) of the load tap changer when at least one mechanical switch (214, 216) of at least one of the plurality of strands is opened; and a plurality of semiconductor switches (220, 222, 224, 226), wherein each semiconductor switch (220, 222, 224, 226) is arranged in parallel to the mechanical switches (214, 216) and, in the activated state, provides an electrical connection between the first tap (202) or the second tap (204) and a supply terminal (212) of the load tap changer; and a processing unit (228) configured to selectively activate and deactivate the mechanical switches (214, 216) and the semiconductor switches (220, 222, 224, 226) such that the electrical connection between the at least one tap (202, 204) and the supply terminal (212) is maintained during the transition of the at least one strand (208, 210) from the first tap (202) to the second tap (204) without causing a short circuit between the two taps (202, 204). the processing unit (228) is also configured to: Generating the step switching signal to move at least one strand (208, 210) from the first tap (202) to the second tap (204) when a condition for step switching is met; Generating activation signals for the semiconductor switches (220, 222, 224, 226) when the stage switching signal is generated; and Generating a plurality of deactivation signals for the mechanical switches (214, 216) from at least one strand (208, 210) connected to the first tap (202) when a stage switching condition is met. [2] System according to claim 1, further comprising a strand drive system (232, 430) which is configured to receive the step switching signal from the processing unit (228) and to cause the at least one strand (208, 210) to move in the direction of the second tap (204). [3] System according to claim 1, wherein the processing unit (228) is further configured to: Generating a first deactivation signal for the semiconductor switches (220, 222, 224, 226) connected to a first strand (208) of the plurality of strands (208, 210) that changes the position from the first tap (202) to the second tap (204) before the first strand (208) is disconnected from the first tap (202); Generating a second deactivation signal for one or more of the plurality of semiconductor switches (220, 222, 224, 226) connected to the second strand (210) as soon as the first strand (208) is connected to the second tap (204); Generating an initial activation signal for the mechanical switch (214) that connects the first strand (208) to the supply terminal (212) when the first strand (208) is connected to the second tap (204); Generating a second activation signal for the remaining mechanical switches (216) that connect the majority of strands (208, 210) to the supply terminal (212); and Generating a third deactivation signal for the majority of semiconductor switches (220, 222, 224, 226). [4] System according to one of the preceding claims, further comprising at least one damping device (428) connected in parallel to the plurality of semiconductor switches (220, 222, 224, 226). [5] System according to any of the preceding claims, wherein the semiconductor switches (220, 222, 224, 226) are bidirectional or unidirectional. [6] System according to any of the preceding claims, wherein the semiconductor switches (220, 222, 224, 226) comprise a MOSFET and / or an IGBT and / or an IGCT. [7] System according to one of the preceding claims, wherein the load tap changer has a rotary tap selection device. [8] System according to one of the preceding claims, wherein the load tap changer has a linear tap selection device. [9] Method for operating a load tap changer, wherein the method comprises: Activating a plurality of semiconductor tap changers (220, 222, 224, 226) connected to at least one of a plurality of strands (208, 210) at one end and a supply terminal (212) at the other end when a tap changer condition is met, wherein the at least one strand (208, 210) is electrically connected to a first tap (202) of a plurality of taps (202, 204) of the load tap changer; Deactivating one or more mechanical switches (214, 216) connected in parallel to the plurality of semiconductor switches (220, 222, 224, 226) and connected to at least one of the plurality of strands (208, 210) at one end and to the supply terminal (212) at the other end; Moving at least one of the plurality of strands (208, 210) from a first tap (202) to a second tap (204); selectively activating and deactivating the plurality of semiconductor switches (220, 222, 224, 226) such that the semiconductor switches (220, 222, 224, 226) connected to a moving strand (208, 210) that is in electrical connection with at least one tap (202, 204) are in an activated state and the semiconductor switches (220, 222, 224, 226) connected to a moving strand (208, 210) that is not in electrical connection with any tap (202, 204) are in a deactivated state; and Activating one or more mechanical switches (214, 216) which are connected to at least one of the plurality of strands (208, 210) which is in electrical connection with the second tap (204).

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