A large power transformer excitation system and method

Abstract

The present invention relates to a large-scale power transformer excitation system and method for a circuit system for power supply and distribution. The excitation system includes an excitation system transformer, a low-voltage side switch and an excitation surge current suppression device, and the excitation surge current suppression device includes a phase-controlled main circuit, a bidirectional current suppression module and an inrush current control unit. The excitation surge current suppression device allows the transformers running in parallel to serve as power sources for each other as backup, thereby ensuring the stability and reliability of the power grid system and reducing the negative impact on the electricity consumption of residents covered by the power grid system. In particular, for enterprises that rely on high-quality power supply, the stability and power supply reliability of the power grid system ensure the electricity demand of the enterprise's production and reduce production losses caused by power outages.

Description

Technical Field

[0001] The present invention relates to a circuit system for power supply and distribution, and in particular to an excitation system and method for a large power transformer. Background Art

[0002] In the power supply network system and the distribution network system, in order to improve the economy of transformer operation, ensure power supply reliability and achieve the goal of energy saving and efficiency improvement, when designing and setting up the circuits of the power supply network system and the distribution network system, the design and setting up scheme of parallel operation transformers is usually adopted in the power grid system. In this scheme, the terminals of the same polarity on the primary and secondary sides of each transformer used for parallel operation are connected to each other through the same busbar.

[0003] In the actual application scenario of the above transformer parallel operation scheme, affected by the connection relationship between the circuits in the power grid system where the transformer is located, when the upper circuit fails, it often affects the lower circuit and constitutes a power grid event. For example, the bus connected to the primary side of the parallel transformer uses a single-line power supply method to supply power to the transformer. When the primary side bus trips due to a fault, the circuit of the power grid system where it is located will constitute a specific power grid event. The power grid events that may be triggered are as follows:

[0004] 1. The primary busbar of the transformer is completely shut down, interrupting the power supply to the transformer and its downstream circuits;

[0005] Second, it will impact the stability of the power grid system, which is not conducive to ensuring the power supply quality of the power grid system;

[0006] 3. Affecting the normal electricity consumption of residents;

[0007] 4. Affecting the normal production of enterprises, especially those that rely on high-quality power supply, will cause a decline in product qualification rate due to the decline in power supply quality, thus causing losses;

[0008] 5. Adverse effects on social and economic activities, resulting in direct or indirect economic losses.

[0009] Therefore, how to reduce the risk level of the above-mentioned power grid events and minimize the negative impact of power grid events has become a technical challenge that the power supply side needs to face. Summary of the invention

[0010] In order to solve the problem of how to reduce the risk level of power grid events caused by power supply bus fault tripping of a power grid system in which transformers are operated in parallel as mentioned in the background art, the present invention provides the following technical solutions:

[0011] The utility model relates to an excitation system of a large power transformer, which is suitable for a power grid system of transformers running in parallel.

[0012] The excitation system includes an excitation system transformer, a low-voltage side switch and an excitation inrush current suppression device. The excitation system transformer refers to the transformer that participates in the excitation system among the transformers running in parallel in the power grid system. The low-voltage side windings of each excitation system transformer are connected to the corresponding low-voltage section bus in the power grid system through their own low-voltage side switches; the low-voltage section bus connected to each excitation system transformer is connected to each other through the excitation inrush current suppression device, so that each excitation system transformer can be mutually excited and connected through the excitation inrush current suppression device.

[0013] Furthermore, the excitation system transformer is a three-winding transformer, and its connection method with the busbars of various voltage levels in the power grid system is that the high-voltage side winding of each excitation system transformer is connected to the corresponding high-voltage section busbar in the power grid system, the medium-voltage side winding of each excitation system transformer is connected to the corresponding medium-voltage section busbar in the power grid system, and the low-voltage side winding of each excitation system transformer is connected to the corresponding low-voltage section busbar in the power grid system.

[0014] Furthermore, the excitation system transformer is a double-winding transformer, and its connection method with the busbars of various voltage levels in the power grid system is that the primary winding of each excitation system transformer is connected to the corresponding high-voltage section busbar in the power grid system, and the secondary winding of each excitation system transformer is connected to the corresponding low-voltage section busbar in the power grid system.

[0015] Furthermore, the excitation inrush current suppression device includes a phase-controlled main circuit, a bidirectional current suppression module and an inrush current control unit. The phase-controlled main circuit is composed of a phase-controlled switch and a bypass switch connected in series, and is used to control each excitation system transformer to perform mutual excitation and switching of the connection. The bidirectional current suppression module is connected in parallel to the bypass switch, and is connected in series with the phase-controlled switch, and is used to clamp the excitation inrush current in both directions and suppress overvoltage. The inrush current control unit includes a mutual inductor for voltage signal acquisition and a sensor for loop current signal acquisition, as well as a phase-controlled controller for processing the acquired signals and issuing corresponding phase-controlled switching commands.

[0016] Furthermore, the phase-controlled switches are divided into two groups and are respectively connected to the input and output sides of the bypass switch.

[0017] Furthermore, each group of phase-controlled switches includes a plurality of phase circuit breakers connected in parallel.

[0018] Furthermore, the bidirectional current suppression module includes a phase-controlled branch, a voltage-limiting branch and a grounding branch. The phase-controlled branch is composed of two parallel circuits, and each circuit includes a surge suppression unit and a switch connected in series for controlling the on and off of each circuit. The voltage-limiting branch includes a voltage-limiting protection unit and switches connected in series at both poles for controlling the state of the branch, and the input and output sides of the voltage-limiting branch are respectively connected to the input sides of the two parallel circuits in the phase-controlled branch. The grounding branch is used for grounding.

[0019] Furthermore, the inrush current suppression units of the two circuits connected in parallel in the phase-controlled branch are both silicon stacks, and the negative poles of the silicon stacks of the two circuits are in opposite directions.

[0020] Furthermore, of the two circuits connected in parallel in the phase-controlled branch, only one circuit is in operation at the same time, and the negative pole direction of the silicon stack of the circuit in the operation state is opposite to the excitation direction of the excitation system transformer.

[0021] Furthermore, the working state of the switch connected in series with the voltage limiting protection unit in the voltage limiting branch is divided into two states. State 1 is that the switch is closed in the voltage limiting branch and opened in the grounding branch, and the voltage limiting protection unit is connected to the phase-controlled main circuit through the switch. State 2 is that the switch is opened in the voltage limiting branch and closed in the grounding branch, and the voltage limiting protection unit is connected to the grounding branch through the switch.

[0022] Furthermore, when one of the two circuits connected in parallel in the phase-controlled branch is in a path, the switch connected in series with the voltage limiting protection unit in the voltage limiting branch on the same side as the negative pole of the silicon stack in the path circuit is in state one, while the switch connected in series on the other side of the voltage limiting protection unit in the voltage limiting branch is in state two.

[0023] Furthermore, the voltage limiting protection unit in the voltage limiting branch is a varistor.

[0024] A large power transformer excitation method is suitable for the above excitation system.

[0025] In this method, the excitation system transformers operating in parallel are divided into supply transformers and demand transformers. The supply transformer refers to the transformer that supplies power to the excited transformer among the excitation system transformers operating in parallel, and the demand transformer refers to the transformer that is the power supply object of the power supply transformer among the excitation system transformers operating in parallel. Among them, the low-voltage busbars to which the supply transformer and the demand transformer are respectively connected are connected to each other through an excitation surge current suppression device, and the supply transformer is controlled to supply power to the demand transformer through the internal switching action of the excitation surge current suppression device. In this way, the excitation of the demand transformer by the supply transformer is realized, and the supply transformer is connected to the demand transformer.

[0026] Furthermore, the specific method of the supply transformer exciting and connecting the demand transformer is as follows:

[0027] Pre-state: All switches in the voltage-limiting branch are in state 2, and all switches in the phase-controlled main circuit and the phase-controlled branch are in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are in the closed state.

[0028] Excitation condition: The demand transformer exits the power grid system from its high voltage side.

[0029] Excitation action: First, the phase-controlled switch on the demand transformer side in the phase-controlled main circuit is closed, the switch on the circuit in which the negative pole direction of the silicon stack in the phase-controlled branch is opposite to the excitation direction is closed, and the switch in series with the voltage-limiting protection unit in the voltage-limiting branch on the same side as the negative pole direction of the silicon stack in the closed circuit in the phase-controlled branch is switched to state 1. Secondly, the phase-controlled switch on the supply transformer side in the phase-controlled main circuit is closed to enter the excitation state.

[0030] Excitation state: After the excitation action is completed, the supply transformer immediately supplies power to the demand transformer to excite the low-voltage side winding of the demand transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the bypass switch is closed.

[0031] Connected state: After the supply transformer completes the excitation of the demand transformer, the demand transformer enters a stable operation state and is connected to the supply transformer.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. When the primary busbar of a transformer running in parallel in the power grid system stops completely, the excitation inrush current suppression device of the present invention can be used to excite and connect the transformer through other transformers running in parallel with the transformer, so that the lower circuit of the transformer can be powered normally;

[0034] Second, the present invention forms an excitation system by connecting the excitation inrush current suppression device between the transformers running in parallel in the power grid system, so that after the primary side of a transformer in the excitation system is completely powered off, the transformer can be excited by other transformers in the excitation system and enter a stable no-load operation state, so that other transformers can take over the transformer and ensure that the busbars connected to the medium-voltage side and low-voltage side busbars of the transformer continue to operate. That is, the stability of the power grid system is guaranteed and the reliability of power supply is improved.

[0035] 3. The present invention uses an excitation surge current suppression device to enable transformers running in parallel to serve as power sources for each other as backup, thereby ensuring the stability and reliability of the power grid system, thereby reducing the negative impact on residential electricity consumption covered by the power grid system.

[0036] 4. The present invention uses an excitation surge current suppression device to enable transformers running in parallel to serve as backup power sources for each other, thereby ensuring the stability of the power grid system and the reliability of power supply, thereby reducing the negative impact on the electricity consumption of enterprises covered by the power grid system. In particular, for enterprises that rely on high-quality power supply, the stability and reliability of power supply of the power grid system ensure the electricity demand of enterprise production and reduce production losses caused by power outages.

[0037] 5. The present invention reduces the time of downtime of lower circuits caused by the complete shutdown of the primary busbar of a transformer running in parallel in the power grid system through the excitation system, thereby reducing the direct or indirect economic losses to the society and economy caused by the circuit shutdown.

[0038] 6. The present invention realizes mutual excitation and connection between transformers running in parallel in the excitation system through the switching coordination of each switch in the excitation surge current suppression device, thereby ensuring the stability of the power grid system and the reliability of power supply.

[0039] 7. The present invention coordinates the switching of the switches in the bidirectional current suppression module so that the excitation inrush current suppression device can select the corresponding switching scheme according to the different excitation directions to effectively suppress the inrush current and overvoltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A roadmap for the excitation system of the present invention in parallel operation of a three-winding transformer in a power grid system;

[0041] Figure 2 A roadmap for the excitation system of the present invention in a parallel operation dual-winding transformer in a power grid system;

[0042] Figure 3 This is an example diagram of the application of the excitation system of the present invention in a 220KV transformer;

[0043] Figure 4 This is an example diagram of the application of the excitation system of the present invention in a 110KV transformer;

[0044] Figure 5 The internal circuit diagram of the excitation inrush current suppression device of the present invention connected to two sets of transformers;

[0045] Figure 6 The internal circuit diagram of the bidirectional current suppression module of the present invention;

[0046] Figure 7 The working circuit of the phase control branch, the voltage limiting branch and the grounding branch of the present invention Figure 1 ;

[0047] Figure 8 The working circuit of the phase control branch, the voltage limiting branch and the grounding branch of the present invention Figure 2 ;

[0048] Fig. 9 It is a working logic diagram of the surge control unit of the present invention;

[0049] Fig.10 The present invention is an internal circuit diagram of an excitation inrush current suppression device connected to more than two groups of transformers. DETAILED DESCRIPTION

[0050] The preferred specific embodiments for implementing the present invention are described in detail below, and a clear and complete description is made in conjunction with the accompanying drawings.

[0051] See also Figure 1-Figure 4 The present invention provides a large-scale power transformer excitation system, which is suitable for a power grid system with parallel-operated transformers and is used to realize mutual excitation and connection between the parallel-operated transformers in the power grid system.

[0052] Specifically, the excitation system includes an excitation system transformer, a low-voltage side switch and an excitation inrush current suppression device, among which:

[0053] The excitation system transformer is a transformer that participates in the excitation system among the transformers running in parallel in the power grid system. In other words, the excitation system transformer is a component of the excitation system, and when it is applied to the power grid system, it is a component of the transformers running in parallel in the power grid system.

[0054] The low-voltage side switch is the switch installed on the line between the low-voltage side winding of the excitation system transformer and the low-voltage busbar it is connected to. By controlling the opening and closing of the low-voltage side switch, the circuit between the excitation system transformer and the low-voltage busbar it is connected to can be controlled.

[0055] The excitation inrush current suppression device has no fixed distinction between the incoming and outgoing sides, that is, the incoming side can be used as the outgoing side, and the outgoing side can also be used as the incoming side. The low-voltage busbars connected to the excitation system transformers that need to be used for mutual excitation and connection in the power grid system are connected to each other through the excitation inrush current suppression device, and the excitation system transformers used for mutual excitation and connection are arranged on the incoming and outgoing sides of the excitation inrush current suppression device, so that the excitation system transformers on the incoming and outgoing sides can be controlled by the excitation inrush current suppression device for mutual excitation and connection.

[0056] See also Figure 5 The present invention provides a preferred technical solution for the above excitation inrush current suppression device. In the figure, K0 represents a bypass switch, K1 and K2 represent phase-controlled switches connected in series on the inlet and outlet sides of the bypass switch, respectively, and ZK represents an inrush current control unit.

[0057] Specifically, the excitation inrush current suppression device includes a phase-controlled main circuit, a bidirectional current suppression module and an inrush current control unit. Among them:

[0058] The phase-controlled main route is composed of a phase-controlled switch and a bypass switch connected in series, and a group of phase-controlled switches are connected to the incoming and outgoing sides of the bypass switch. By switching the phase-controlled switch and the bypass switch, the mutual excitation and connection control between the excitation system transformers connected to the incoming and outgoing sides of the excitation inrush current suppression device is realized. That is, the excitation system transformer on the incoming side of the excitation inrush current suppression device excites and connects the excitation system transformer on the outgoing side of the excitation inrush current suppression device; or the excitation system transformer on the outgoing side of the excitation inrush current suppression device excites and connects the excitation system transformer on the incoming side of the excitation inrush current suppression device. Here, there is no fixed distinction between the incoming and outgoing sides of the bypass switch, that is, the incoming side can be used as the outgoing side, and the outgoing side can also be used as the incoming side.

[0059] The bidirectional current suppression module is connected in parallel with the bypass switch and in series with the phase-controlled switch, and can clamp the excitation inrush current and suppress the overvoltage in both directions. That is, when the excitation system transformer on the incoming line side of the excitation inrush current suppression device excites the excitation system transformer on the outgoing line side of the excitation inrush current suppression device, the bidirectional current suppression module can be used to clamp the excitation inrush current and overvoltage in the process; and when the excitation system transformer on the outgoing line side of the excitation inrush current suppression device excites the excitation system transformer on the incoming line side of the excitation inrush current suppression device, the bidirectional current suppression module can also be used to clamp the excitation inrush current and overvoltage in the process.

[0060] The inrush current control unit includes a transformer for collecting voltage signals and a sensor for collecting loop current signals, as well as a phase control controller for processing the collected signals and issuing corresponding phase control switching commands.

[0061] In this technical solution, the bypass switch is open, and the phase-controlled switches on the incoming and outgoing lines are closed, then the phase-controlled main line forms a passage through the bidirectional current suppression module, and the excitation system transformer connected to one side of the incoming and outgoing lines of the phase-controlled main line excites the excitation system transformer connected to the other side of the incoming and outgoing lines of the phase-controlled main line. Among them, since the current in the excitation process passes through the bidirectional current suppression module, and the bidirectional current suppression module suppresses the inrush current and overvoltage generated, the excitation process can be carried out smoothly, avoiding the impact of the excitation inrush current and overvoltage on the power grid system, and ensuring the stability of the power grid system.

[0062] In the present technical solution, after the excitation is completed, the bypass switch is closed, and the phase-controlled switches on the incoming and outgoing lines remain closed, then the bypass switch bypasses the bidirectional current suppression module, so that the current no longer passes through the bidirectional current suppression module, but passes through the overall phase-controlled main line. At this time, the excitation system transformer connected to one side of the incoming and outgoing line sides of the phase-controlled main line supplies power to the excitation system transformer connected to the other side of the incoming and outgoing line sides of the phase-controlled main line to achieve the purpose of connection. Among them, through the switching coordination of the bidirectional current suppression module and the bypass switch, the excitation system can smoothly switch from the excitation state to the connected state, so that the power grid connected to the connected excitation system transformer can operate normally, ensuring the power supply reliability of the power grid system.

[0063] See also Figure 6-Figure 8 The present invention provides a preferred technical solution for the above-mentioned bidirectional current suppression module. In the figure, K01 and K04 respectively represent switches on two parallel circuits in the phase-controlled branch, K02 and K03 respectively represent switches connected to both sides of the voltage limiting protection unit in the voltage limiting branch, TL represents the inrush current suppression unit, and ZGD-B represents the voltage limiting protection unit.

[0064] Specifically, the bidirectional current suppression module includes a phase control branch, a voltage limiting branch and a grounding branch. Among them:

[0065] The phase-controlled branch is composed of two parallel circuits, and each of the two circuits includes a surge suppression unit and a switch connected in series therewith for controlling the on and off of each circuit. Here, for the two parallel circuits of the phase-controlled branch, the incoming line sides of the two are opposite. That is, for the two parallel circuits of the phase-controlled branch, the incoming line side direction of one circuit is the incoming line side direction of the overall circuit of the bidirectional current suppression module, and the incoming line side direction of the other circuit is the outgoing line side direction of the overall circuit of the bidirectional current suppression module. In addition, more preferably, the surge suppression unit is a silicon stack, and the negative pole directions of the silicon stacks on the two parallel circuits of the phase-controlled branch are opposite, and the negative pole direction of the silicon stack is consistent with the incoming line side direction of the circuit in which it is located.

[0066] The voltage-limiting branch includes a voltage-limiting protection unit and a switch connected in series at its two poles for controlling the state of the branch. The input and output sides of the voltage-limiting branch are respectively connected to the input sides of the two parallel circuits of the phase-controlled branch. That is, the input side of the voltage-limiting branch is connected to the input side of one circuit in the phase-controlled branch, and the output side of the voltage-limiting branch is connected to the input side of the other circuit in the phase-controlled branch. In addition, more preferably, the voltage-limiting protection unit in the voltage-limiting branch is a varistor.

[0067] The grounding branch grounds one side of the voltage limiting protection unit by cooperating with the opening and closing of the switches connected in series on the incoming and outgoing line sides of the voltage limiting protection unit in the voltage limiting branch.

[0068] In this technical solution, only one of the two parallel circuits in the phase-controlled branch is in a conducting state and participates in the work at the same time. The negative pole direction of the silicon stack of the conducting circuit is opposite to the excitation direction of the excitation system transformer.

[0069] In the technical solution, the working state of the switch connected in series with the voltage-limiting protection unit in the voltage-limiting branch is divided into two states. State 1, the switch is closed in the voltage-limiting branch and opened in the grounding branch, and the voltage-limiting protection unit is connected to the phase-controlled main circuit through the switch; State 2, the switch is opened in the voltage-limiting branch and closed in the grounding branch, and the voltage-limiting protection unit is connected to the grounding branch through the switch.

[0070] In the present technical solution, when one of the two circuits connected in parallel in the phase-controlled branch is in a path, the switch connected in series with the voltage limiting protection unit in the voltage limiting branch on the same side as the negative pole of the silicon stack in the path circuit is in state one, and the switch connected in series on the other side of the voltage limiting protection unit in the voltage limiting branch is in state two.

[0071] In this technical solution, due to the coordination between the phase-controlled branch, the voltage-limiting branch and the grounding branch, there is no need to distinguish between the incoming and outgoing line sides of the bidirectional current suppression module during the installation of the parallel bypass switch.

[0072] See also Fig. 9 The present invention provides an optimal technical solution for the above-mentioned surge control unit.

[0073] in:

[0074] The voltage transformers included in the inrush current control unit are respectively arranged on the bus side and the high-voltage side of the excitation system transformer to monitor the voltage signal at the location. Among them, the phase-controlled controller receives the collected bus side voltage signal, and determines the closing angle according to the signal. When the bus side voltage reaches the preset closing and opening angle, the phase-controlled controller controls the corresponding phase-controlled switch and bypass switch to make corresponding closing and opening actions; when the excitation system transformer exits, the phase-controlled controller receives the high-voltage side voltage signal of the excitation system transformer and predicts the residual magnetism of its winding according to the change of the signal.

[0075] The current sensor contained in the inrush current control unit is set in the loop to collect the loop current during normal operation. When it is necessary to exit the excitation system transformer, the phase-disconnecting phase-controlled switch is selected, such as by sequentially interrupting the three-phase current to solidify the direction and amplitude of the residual magnetism of the core, thereby realizing active intervention in the residual magnetism of the winding.

[0076] See also Fig.10 The present invention provides a preferred technical solution for the above phase-controlled switch. In the figure, K0 represents a bypass switch, K1 and K2 represent phase-controlled switches connected in series on the input and output sides of the bypass switch, respectively, and ZK represents an inrush current control unit.

[0077] in:

[0078] Each phase-controlled switch group contains several circuit breakers, and these circuit breakers are wired in parallel.

[0079] In this technical solution, each circuit breaker is connected to an excitation system transformer. That is, the same excitation system transformer is only connected to one circuit breaker in the phase-controlled switch; the same circuit breaker in the phase-controlled switch is also only connected to one excitation system transformer. In this way, by controlling the closing and opening operations of the corresponding circuit breaker, any excitation system transformer connected to one side of the excitation inrush current suppression device can be excited and connected to any excitation system transformer connected to the other side of the excitation inrush current suppression device.

[0080] See also Figure 1-Figure 10 The present invention also provides a large-scale power transformer excitation method, which is applicable to a power grid system with parallel-operated transformers, and is used to realize mutual excitation and connection between the parallel-operated transformers in the power grid system.

[0081] Specifically, this method is applicable to the above-mentioned large-scale power transformer excitation system.

[0082] Excitation system transformers are further subdivided into supply transformers and demand transformers.

[0083] In the excitation system transformer, the transformer to be excited is the demand transformer, and the transformer that supplies power to the demand transformer is the supply transformer. The low-voltage busbars to which the supply transformer and the demand transformer are connected are connected to each other through an excitation inrush current suppression device, and the supply transformer is controlled to supply power to the demand transformer through the switching action inside the excitation inrush current suppression device, so as to realize the excitation of the demand transformer by the supply transformer, and the supply transformer is connected to the demand transformer.

[0084] The specific method for the supply transformer to excite and connect the demand transformer is:

[0085] In the pre-state, all switches in the voltage-limiting branch are in state two, and all switches in the phase-controlled main circuit and the phase-controlled branch are in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are in the closed state.

[0086] Excitation condition, requiring the transformer to exit the grid system from its high voltage side.

[0087] Excitation action, first, the phase-controlled switch located on the demand transformer side in the phase-controlled main circuit is closed, and the switch on the circuit in which the negative pole direction of the silicon stack in the phase-controlled branch is opposite to the excitation direction is closed. The switch in series with the voltage-limiting protection unit in the voltage-limiting branch and on the same side of the negative pole direction of the silicon stack on the closed circuit in the phase-controlled branch is switched to state one. Secondly, the phase-controlled switch on the supply transformer side in the phase-controlled main circuit is closed to enter the excitation state.

[0088] In the excitation state, after the excitation action is completed, the supply transformer supplies power to the demand transformer to excite the low-voltage side winding of the demand transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the bypass switch is closed.

[0089] In the connected state, after the supply transformer completes the excitation of the demand transformer, the demand transformer enters a stable no-load operation state and is connected to the supply transformer. Embodiment 1

[0090] See also Figure 1 , Figure 3 ,as well as Figure 5-Figure 9 This embodiment takes the case of two 220KV three-winding transformers running in parallel in a power grid system as an example.

[0091] In this embodiment:

[0092] The two transformers running in parallel in the power grid system are the excitation system transformers in the excitation system. In this embodiment, the two transformers are respectively referred to as transformer No. 1 and transformer No. 2.

[0093] Transformer No. 1 and No. 2 are both connected to the corresponding 220KV busbars at their high-voltage side windings. Under normal conditions, both transformers obtain electrical energy from the 220KV busbars they are connected to.

[0094] Transformer No. 1 and No. 2 are connected to the corresponding 110KV busbars on their medium voltage side windings. Under normal conditions, both transformers obtain electrical energy from the 220KV busbars they are connected to, and then transform the obtained electrical energy to 110KV and supply it to the 110KV busbars they are connected to.

[0095] Transformer No. 1 and No. 2 are both connected to the corresponding 35KV busbars on their low-voltage side windings. Under normal conditions, both transformers obtain electrical energy from the 220KV busbars they are connected to, and then transform the obtained electrical energy to 35KV and supply it to the 35KV busbars they are connected to.

[0096] A magnetizing inrush current suppression device is connected between the 35KV busbar connected to the No. 1 transformer and the 35KV busbar connected to the No. 2 transformer.

[0097] When the No. 1 transformer's 220KV side busbar fails, needs to be shut down for maintenance or other reasons, in order to ensure the normal operation of the No. 1 transformer's 110KV side busbar and 35KV side busbar, the No. 2 transformer can be excited and connected to the No. 1 transformer by switching on and off the excitation inrush current suppression device. The method of switching on and off the excitation inrush current suppression device is as follows:

[0098] Pre-state: switch K02 and switch K03 are both in state 2, and switch K0, switch K1, switch K2, switch K01 and switch K04 are all in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are all in the closed state.

[0099] Excitation condition, transformer No. 1 exits the power grid system from its high voltage side.

[0100] In the excitation action, first, switches K1, K2 and K04 are closed, and switch K02 is switched to state 1, entering the excitation state.

[0101] In the excitation state, after the excitation action is completed, the No. 2 transformer supplies power to the No. 1 transformer, and excites the low-voltage side winding of the No. 1 transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the switch K0 is closed.

[0102] In the connected state, after the No. 2 transformer completes the excitation of the No. 1 transformer, the No. 1 transformer enters a stable no-load operation state and is connected to the No. 2 transformer.

[0103] When the No. 2 transformer 220KV side busbar fails, needs to be shut down for maintenance or other reasons, in order to ensure the normal operation of the No. 2 transformer 110KV side busbar and the 35KV side busbar, the No. 1 transformer can be excited and connected to the No. 1 transformer by switching on and off the excitation inrush current suppression device. The method of switching on and off the excitation inrush current suppression device is as follows:

[0104] Pre-state: switch K02 and switch K03 are both in state 2, and switch K0, switch K1, switch K2, switch K01 and switch K04 are all in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are all in the closed state.

[0105] Excitation condition, the No. 2 transformer exits the power grid system from its high voltage side.

[0106] In the excitation action, first, switches K1, K2 and K01 are closed, and switch K03 is switched to state 1, entering the excitation state.

[0107] In the excitation state, after the excitation action is completed, the No. 1 transformer supplies power to the No. 2 transformer, and excites the low-voltage side winding of the No. 2 transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the switch K0 is closed.

[0108] In the connected state, after the No. 1 transformer completes the excitation of the No. 2 transformer, the No. 2 transformer enters a stable no-load operation state and is connected to the No. 1 transformer. Embodiment 2

[0109] See also Figure 2 ,as well as Figure 4-Figure 9 This embodiment takes the case of two 110KV double-winding transformers operating in parallel in a power grid system as an example.

[0110] In this embodiment:

[0111] The two transformers running in parallel in the power grid system are the excitation system transformers in the excitation system. In this embodiment, the two transformers are respectively referred to as transformer No. 1 and transformer No. 2.

[0112] Transformer No. 1 and Transformer No. 2 are both connected to the corresponding 110KV busbars at their primary windings. Under normal conditions, both transformers obtain electrical energy from the 110KV busbars they are connected to.

[0113] Transformer No. 1 and No. 2 are both connected to the corresponding 35KV busbars on their secondary windings. Under normal conditions, both transformers obtain electrical energy from the 110KV busbars they are connected to, and then transform the obtained electrical energy to 35KV and supply it to the 35KV busbars they are connected to.

[0114] A magnetizing inrush current suppression device is connected between the 35KV busbar connected to the No. 1 transformer and the 35KV busbar connected to the No. 2 transformer.

[0115] When the No. 1 transformer 110KV side busbar fails, needs to be shut down for maintenance or other reasons, in order to ensure the normal operation of the No. 1 transformer 35KV side busbar, the excitation inrush current suppression device can be switched on and off to allow the No. 2 transformer to excite and connect the No. 1 transformer. The method of switching on and off the excitation inrush current suppression device is as follows:

[0116] Pre-state: switch K02 and switch K03 are both in state 2, and switch K0, switch K1, switch K2, switch K01 and switch K04 are all in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are all in the closed state.

[0117] Excitation condition, transformer No. 1 exits the power grid system from its high voltage side.

[0118] In the excitation action, first, switches K1, K2 and K04 are closed, and switch K02 is switched to state 1, entering the excitation state.

[0119] In the excitation state, after the excitation action is completed, the No. 2 transformer supplies power to the No. 1 transformer, and excites the low-voltage side winding of the No. 1 transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the switch K0 is closed.

[0120] In the connected state, after the No. 2 transformer completes the excitation of the No. 1 transformer, the No. 1 transformer enters a stable no-load operation state and is connected to the No. 2 transformer.

[0121] When the No. 2 transformer 110KV side busbar fails, needs to be shut down for maintenance or other reasons, in order to ensure the normal operation of the No. 2 transformer 35KV side busbar, the excitation inrush current suppression device can be switched on and off to allow the No. 1 transformer to excite and connect the No. 1 transformer. The method of switching on and off the excitation inrush current suppression device is as follows:

[0122] Pre-state: switch K02 and switch K03 are both in state 2, and switch K0, switch K1, switch K2, switch K01 and switch K04 are all in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are all in the closed state.

[0123] Excitation condition, the No. 2 transformer exits the power grid system from its high voltage side.

[0124] In the excitation action, first, switches K1, K2 and K01 are closed, and switch K03 is switched to state 1, entering the excitation state.

[0125] In the excitation state, after the excitation action is completed, the No. 1 transformer supplies power to the No. 2 transformer, and excites the low-voltage side winding of the No. 2 transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the switch K0 is closed.

[0126] In the connected state, after the No. 1 transformer completes the excitation of the No. 2 transformer, the No. 2 transformer enters a stable no-load operation state and is connected to the No. 1 transformer. Embodiment 3

[0127] See also Fig.10 Based on the first or second embodiment, this embodiment is that the number of transformers running in parallel in the power grid system increases, that is, the number of transformers in the excitation system increases, and the number of switches K1 and switches K2 in the excitation inrush current suppression device increases adaptively.

[0128] In this embodiment:

[0129] The newly added switch of switch K1 and the original switch are connected in parallel. Similarly, the newly added switch of switch K2 and the original switch are connected in parallel.

[0130] These newly added switches correspond to the newly added transformers. That is, the same newly added transformer is only connected to one newly added switch; and one newly added switch is also only connected to one newly added transformer. In this way, by controlling the closing and opening operations of the corresponding switches K1 and K2, any excitation system transformer connected to one side of the excitation inrush current suppression device can be excited and connected to any excitation system transformer connected to the other side of the excitation inrush current suppression device. Embodiment 4

[0131] See also Figure 1-Figure 4 Based on the first embodiment, the second embodiment or the third embodiment, this embodiment aims to solve the problem of whether to continue to use the original transformer in the power grid system.

[0132] In this embodiment:

[0133] If the original power grid system does not use the parallel operation of transformers, a transformer can be added to the power grid system, and the newly added transformer can be operated in parallel with the original transformer. In this way, the excitation inrush current suppression device is connected between the low-voltage side busbars of the original transformer and the newly added transformer.

[0134] If the original power grid system has adopted the method of parallel operation of transformers, the excitation inrush current suppression device can be connected between the low-voltage side busbars of the transformers originally operating in parallel.

[0135] If the transformers in the original power grid system need to be retired, all newly added transformers can be used, and the newly added transformers can be put into operation in parallel with each other. In this way, the excitation inrush current suppression device can be connected between the low-voltage side busbars of each newly added transformer.

[0136] Based on the above content and the accompanying drawings, those skilled in the art can understand and implement the present invention. In addition, any non-creative modifications made to the present invention by those skilled in the art without creative work still fall within the protection scope of the present invention.

Claims

1. A large-scale power transformer excitation system, suitable for use in a power grid system with parallel transformers, characterized in that: The excitation system includes: Excitation system transformer, that is, each transformer involved in the excitation system in the power grid system; The low-voltage side switch is the switch installed on the connection line between the low-voltage side winding of the excitation system transformer and the low-voltage busbar in the power grid system; Excitation surge current suppression device: the low-voltage busbars to which each excitation system transformer is connected are connected to each other through the excitation surge current suppression device, so that each excitation system transformer can be mutually excited and connected through the excitation surge current suppression device; The excitation inrush current suppression device comprises a phase-controlled branch, a voltage-limiting branch and a grounding branch; the phase-controlled branch is composed of two parallel circuits, and each circuit comprises an inrush current suppression unit and a switch connected in series therewith for controlling the on / off of the respective circuit; the voltage-limiting branch comprises a voltage-limiting protection unit and switches connected in series therewith at both poles thereof for controlling the state of the branch, and the incoming and outgoing line sides of the voltage-limiting branch are respectively connected to the incoming line sides of the two parallel circuits in the phase-controlled branch; the grounding branch is used for grounding.

2. The large power transformer excitation system according to claim 1, characterized in that: The excitation system transformer is a three-winding transformer, and its connection with the busbars of various voltage levels in the power grid system is as follows: The high-voltage side windings of each excitation system transformer are connected to the corresponding high-voltage busbar in the power grid system; The medium voltage side windings of each excitation system transformer are connected to the corresponding medium voltage busbar in the power grid system; The low-voltage side windings of each excitation system transformer are connected to the corresponding low-voltage section bus in the power grid system.

3. The large power transformer excitation system according to claim 1, characterized in that: The excitation system transformer is a double-winding transformer, and its connection method with the busbars of various voltage levels in the power grid system is as follows: The primary windings of each excitation system transformer are connected to the corresponding high-voltage busbar in the power grid system; The secondary windings of each excitation system transformer are connected to the corresponding low-voltage busbar in the power grid system.

4. The large power transformer excitation system according to claim 1, characterized in that: The excitation inrush current suppression device includes: The phase-controlled main circuit is composed of a phase-controlled switch and a bypass switch in series, and is used to control the mutual excitation and switching of each excitation system transformer; A bidirectional current suppression module is connected in parallel with the bypass switch and in series with the phase-controlled switch, and is used for bidirectional clamping of the excitation surge current and suppression of overvoltage. The phase-controlled branch, the voltage-limiting branch and the grounding branch are included in the bidirectional current suppression module; The inrush current control unit includes a transformer for collecting voltage signals and a sensor for collecting loop current signals, as well as a phase control controller for processing the collected signals and issuing corresponding phase control switching commands.

5. The large power transformer excitation system according to claim 4 is characterized in that: There are two groups of phase-controlled switches, which are respectively connected to the input and output sides of the bypass switch.

6. The large power transformer excitation system according to claim 5, characterized in that: Each group of phase-controlled switches contains several circuit breakers in parallel.

7. The large power transformer excitation system according to any one of claims 1 to 6, characterized in that: The inrush current suppression units of the two circuits connected in parallel in the phase-controlled branch are both silicon stacks, and the negative poles of the silicon stacks of the two circuits are in opposite directions.

8. The large power transformer excitation system according to claim 7, characterized in that: Of the two parallel circuits in the phase-controlled branch, only one circuit is in operation at the same time, and the negative pole direction of the silicon stack of the circuit in the on state is opposite to the excitation direction of the excitation system transformer.

9. The large power transformer excitation system according to claim 8, characterized in that: The working state of the switch connected in series with the voltage limiting protection unit in the voltage limiting branch is divided into two states: In state 1, the switch is closed on the voltage-limiting branch and opened on the grounding branch, and the voltage-limiting protection unit is connected to the phase-controlled main circuit through the switch; In state two, the switch is opened on the voltage-limiting branch and closed on the grounding branch, and the voltage-limiting protection unit is connected to the grounding branch through the switch.

10. The large power transformer excitation system according to claim 9, characterized in that: When one of the two parallel circuits in the phase-controlled branch is in a path, the switch connected in series with the voltage limiting protection unit in the voltage limiting branch on the same side as the negative pole of the silicon stack in the path circuit is in state one, while the switch connected in series on the other side of the voltage limiting protection unit in the voltage limiting branch is in state two.

11. The large power transformer excitation system according to claim 1, characterized in that: The voltage limiting protection unit in the voltage limiting branch is a varistor.

12. A large power transformer excitation method, applicable to the excitation system according to claim 9, characterized in that: The excitation system transformers running in parallel are divided into: Supply transformer, i.e., the transformer that supplies power to the excited transformer in the excitation system transformers operating in parallel; Demand transformer, i.e., the transformer in the parallel-operating excitation system transformer that is the object of power supply from the supply transformer; Among them, the low-voltage bus sections to which the supply transformer and the demand transformer are respectively connected are connected to each other through an excitation surge current suppression device, and the supply transformer is controlled to supply power to the demand transformer through the internal switching action of the excitation surge current suppression device, so as to realize the excitation of the demand transformer by the supply transformer, and the demand transformer is connected by the supply transformer.

13. A large power transformer excitation method according to claim 12, characterized in that: The specific method for the supply transformer to excite and connect the demand transformer is: In the pre-state, all switches in the voltage-limiting branch are in state 2, and all switches in the phase-controlled main circuit and the phase-controlled branch are in the open state, and the low-voltage side switches connected to the low-voltage side windings of the supply transformer and the demand transformer are in the closed state; Excitation conditions, requiring the transformer to exit the grid system from its high voltage side; Excitation action, first, the phase-controlled switch on the demand transformer side in the phase-controlled main circuit is closed, the switch on the circuit in which the negative pole direction of the silicon stack in the phase-controlled branch is opposite to the excitation direction is closed, and the switch in series with the voltage-limiting protection unit in the voltage-limiting branch on the same side as the negative pole direction of the silicon stack in the closed circuit in the phase-controlled branch is switched to state 1, and secondly, the phase-controlled switch on the supply transformer side in the phase-controlled main circuit is closed to enter the excitation state; In the excitation state, after the excitation action is completed, the supply transformer supplies power to the demand transformer to excite the low-voltage side winding of the demand transformer. After the inrush current suppression unit and the voltage limiting protection unit complete the corresponding suppression action, the bypass switch is closed; In the connected state, after the supply transformer completes the excitation of the demand transformer, the demand transformer enters a stable operation state and is connected to the supply transformer.

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