CN114783744A

CN114783744A - Power electronic type change-over switch of on-load tap-changer

Info

Publication number: CN114783744A
Application number: CN202210643589.1A
Authority: CN
Inventors: 杜海江; 刘林辉
Original assignee: China Agricultural University
Current assignee: China Agricultural University
Priority date: 2022-06-09
Filing date: 2022-06-09
Publication date: 2022-07-22

Abstract

The invention discloses a power electronic type change-over switch design of an on-load tap-changer. The switch comprises a singular tap combination switching branch, an even tap combination switching branch and a measurement and control module. Each combined switching branch comprises a through-flow branch, an on-off branch, a transition branch and the like. And each branch can be controlled by the measurement and control module according to the designed working time sequence to realize independent on-off control. The designed change-over switch can realize that the main circuit is not open-circuit and the stage winding is not short-circuit in each step of the change-over process; no arc is generated in the switching process; the change-over switch can not bear system voltage in the whole switching process; and the abnormal switching process can timely find and prevent the expansion of faults. The combined type arcless on-load tap changer formed by matching the change-over switch and the tap selector is a substitute product of the existing oil-immersed and vacuum products.

Description

Power electronic type change-over switch of on-load tap-changer

Technical Field

The invention relates to the field of on-load tap changers, in particular to an electromechanical hybrid on-load tap changer.

Background

An on-load tap changer is a device that regulates the output voltage under load by changing the transformer taps. The method is characterized in that a plurality of taps are led out from the high-voltage side of a transformer and connected with a static tap of an on-load tap-changer, and the change of output voltage is realized by controlling a movable tap to connect different static taps.

The on-load tap-changer can be divided into a split type and a combined type. The split type on-load tap-changer mainly comprises a tap selector and a change-over switch. The arc extinguishing mechanism of the transfer switch adopts an oil immersion type and a vacuum type at present.

The ideal on-load tap-changer switching process should be: firstly, a main loop is not opened in a switching process, and a secondary winding is not short-circuited; secondly, no arc is generated in the switching process; thirdly, the possibility of bearing system voltage cannot exist in the whole switching process; and fourthly, the abnormity in the switching process can be timely found out and the fault expansion can be prevented.

The application of power electronic switches to switch arc extinction is a development direction, and there are also many patent applications.

The patent 'a transformer split type arcless on-load tap changer (201410330722.3)' utilizes a main through-current tap and a bidirectional power electronic switch to design a change-over switch in parallel, and has the problems that the change-over process cannot be stopped even when a fault occurs due to the adoption of a spring driving mechanism, and the fault is easy to expand; secondly, if the electronic switch is triggered to fail in the switching process, the fault is enlarged.

The patent "an arcless on-load automatic voltage regulation distribution transformer device and voltage regulation method (201610685827. X)" proposes that the tap switching of a transformer is realized by a compound switch cascade mode, and the design is equivalent to a compound type and has a large number of switches.

The patent "a hybrid on-load tap-changer with thyristor auxiliary arc quenching (201501967943.6)" proposes a method for triggering a thyristor with a mechanical tap arc voltage and for extinguishing the arc of the on-load tap-changer, but the trigger current is not easy to control accurately and the switching process fails to detect and stop.

The patent "on-load tap-changer and control method thereof, transformer (202010129598. X)" proposes a diverter switch of split type on-load tap-changer, but after the transition branch of the power electronic switch is turned on, the main through-current branch is still subjected to electric arc due to the influence of resistance voltage drop of the transition branch when the main through-current branch is turned off.

The patent ' an on-load tap changer for high-voltage transmission transformer and a control method thereof ' (202010824844.3) ' proposes an arcless switching structure and a control method of a diverter switch, which can realize the arcless switching of tapping under normal conditions, but has the premise that each operation step must be capable of normally switching on and off, and once the operation fails, the switch still can bear the system voltage to enlarge the fault.

Compared with the patent 202010824844.3, the patent "an on-load tap changer (202011005326.5) using power semiconductor devices for tapping" divides the main through-current switch connected in series with an inter-stage change-over switch into 2 switches and directly connects the switches to the static tap of a tap selector, and other problems still exist.

The patent "a transition circuit (202011138031.5) for non-multiplexing power electronic on-load tap changer switching" also proposes an arc-free implementation of the switch, but the process of cutting the GM1 by the MC1 may suffer from system voltage and propagate failures if the GM1 control fails.

The patent "an on-load tap changer for a high-voltage transmission transformer and a control method (202110304422.8)" also proposes a power electronic implementation method of a diverter switch, but the switching process of the scheme cannot avoid the generation of electric arcs.

Searching other related patents has not found a solution to achieve the ideal handover process.

Disclosure of Invention

Technical problem to be solved

Aiming at the defects of the prior art and achieving an ideal control target, the invention provides a novel change-over switch structure and a control method.

(II) technical scheme

The switch comprises a odd tap combination switching branch, an even tap combination switching branch and a measurement and control module.

And in the two combined switching branches, one branch is connected with a singular tap of the tapping selector, the other branch is connected with an even tap of the tapping selector, and the two combined switching branches are converged together to serve as an output common tap.

Each combined switching branch comprises three branches, namely a through-flow branch, an on-off branch and a transition branch. And each branch can be controlled by a measurement and control module according to a designed working sequence to realize independent on-off control. The through-current branch circuit is composed of a mechanical switch, bears steady-state load current when in conduction and bears stage winding voltage when in off-state. And the on-off branch and the transition branch are only controlled on-off according to the time sequence in the switching process. The on-off branch adopts a bidirectional power electronic switch, and no electric arc is generated in the on-off control process. The transition branch is formed by connecting a bidirectional power electronic switch and a resistor in series, and an electric arc is not generated in the on-off control process.

The measurement and control module comprises a power supply module, a control module, a communication module and a monitoring module. The power supply module is connected between the odd tap and the even tap of the tapping selector to form a control power supply. The monitoring module measures the voltage and the current of the two combined switching branches for the software of the control module to use. The communication module realizes data exchange with a remote master station, receives a host gear shifting instruction and uploads a running state.

The control module runs control software and is the control core of the whole circuit. Data exchange is carried out with the master station through the communication module, on one hand, a gear shifting instruction of the master station is received, and on the other hand, a gear shifting result is uploaded to the master station through the communication module after gear shifting is finished. The control module controls each branch of the change-over switch to execute gear shifting operation according to a designed control time sequence; in the gear shifting process, whether the switching process is normal or not is judged by monitoring voltage and current signals of the two combined switching branches;

the control process from the singular tap conduction state to the tangential odd tap conduction can be divided into 7 steps, which are described below. Conducting a singular on-off branch and an even transition branch; the second step shuts off the odd number current branch; thirdly, switching off the odd on-off branch; fourthly, switching on the even on-off branch; fifthly, conducting the double-number through-current branch; sixthly, switching off the even on-off branch; and step seven, switching off the even number transition branch. In the switching process, comparing the sampling voltage and current with a set limit value in each step, and if the sampling voltage and current are normal, continuing to perform the next switching operation; otherwise, the reverse sequence is followed, and the initial single tap conduction state is returned to, and the fault is reported.

The control process from the even tap conduction state to the odd tap conduction is similar, and is divided into 7 steps, which is described as follows. Conducting an even on-off branch and an odd transition branch in the first step; secondly, shutting off the even number current branch circuits; thirdly, switching off the even on-off branch; fourthly, switching on a singular on-off branch; step five, conducting odd number current branch circuits; sixthly, switching off the odd on-off branch; and step seven, switching off the single transition branch. In the switching process, comparing the sampling voltage and current with a set limit value in each step, and if the sampling voltage and current are normal, continuing to perform the next switching operation; otherwise, the operation is carried out according to the reverse time sequence, the initial even number tap conducting state is returned, and the fault is reported.

The control process can achieve the following steps: the electric arc generated in the switching process is avoided, the short circuit of the primary winding is also avoided, and the open circuit of the main loop is avoided. In the switching process, before each next switching, whether the switching operation in the step and before is completed correctly can be judged according to the measured voltage and current of the combined branch circuit. If the switching fails, executing rollback operation, exiting to the original stable state without fault expansion, and reporting the fault.

(III) advantageous effects

The invention achieves the effects that 1, the main loop can be not opened and the secondary winding can not be short-circuited in each step of the switching process; 2. no arc is generated in the switching process; 3. the change-over switch can not bear system voltage in the whole switching process; 4. and when an abnormity occurs in the switching process, the switching device can timely find and return to a stable state before switching, so that the fault is prevented from being enlarged and reported.

Description of the drawings:

FIG. 1: the invention relates to a structural schematic diagram of a power electronic type change-over switch of an on-load tap-changer;

FIG. 2: timing diagram for switching process from odd tap to even tap

FIG. 3: timing diagram for switch failure rollback in switching from odd tap to even tap

FIG. 4: timing diagram for switching process from even number tap to odd number tap

FIG. 5 is a schematic view of: timing diagram for switch failure rollback in switching process from even tap to odd tap

FIG. 6: power electronic bidirectional switch composed of full-control device IGBT

Detailed Description

The following detailed description of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Fig. 1 shows an embodiment of an electronic power diverter switch of an on-load tap changer. The system is composed of a combined switching branch 1, a combined switching branch 2 and a measurement and control module.

The combined switching branch 1 is formed by connecting a transition branch, a through-flow branch, an on-off branch and the like in parallel. The transition branch consists of a bidirectional thyristor VT1 and a resistor R1. The current branch is formed by a mechanical switch K1 and adopts a magnetic latching relay. The on-off branch is constituted by a triac CR 1. One end of the combined switching branch 1 is connected with a singular tap N of the tapping selector through a node J1; and the other end is connected to a common tap through node J2.

The combined switching branch 2 is also composed of a transition branch, a through-flow branch and an on-off branch which are connected in parallel. The transition branch consists of a bidirectional thyristor VT2 and a resistor R2. The current branch is formed by a mechanical switch K2 and adopts a magnetic latching relay. The on-off branch is constituted by a triac CR 2. One end of the combined switching branch 2 is connected with a tap N +1 of the tap selector through a node J3; and the other end is connected to the common tap through node J4.

The measurement and control module consists of a power supply module, a control module, a monitoring module and a communication module. The power supply module is connected between the odd tap N of the tapping selector and the even tap N +1 of the tapping selector to generate a control power supply. The monitoring module measures the voltage u1 and the current i1 of the combined switching branch 1, and the voltage u2 and the current i2 of the combined switching branch 2. And the communication module exchanges data with the master station, acquires a control instruction and uploads the running state of the selector switch. The control module runs control software, which is a control core of the whole circuit, and generates control signals of VT1, K1, CR1, VT2, K2 and CR2 according to the timing sequence set in the figure 2 and the figure 4 by monitoring voltage and current signals of the two combined switching branches in the gear shifting process. If it is judged through the sampled voltage and current signals that an abnormality occurs in the operation process, the back-off timing designed according to fig. 3 and 5 returns to the initial stable state.

Fig. 2 is a timing diagram of the forward switching from odd taps to even taps, i.e., from K1 conducting to K2 conducting. The switching process is divided into 7 steps as indicated by the abscissa step.

A value of Step 0 indicates a steady state where K1 is on when not switching.

After the switching process starts, step 1 is that CR1 and VT2 are turned on and last for a duration of t1, and if i2 is greater than the limit value in this process, VT2 is turned on, that is, step 1 is performed normally.

Step 2 is to turn off K1 for a duration of t2, and if u1 is less than the limit value in the process, it indicates that CR1 is on, i.e., step 1 is executed normally.

Step 3 is to turn off the CR1 for a time duration of t3, in this process, if u1> limit value, it means that CR1 and K1 are turned off, that is, step 2 and step 3 are executed normally, if i1< limit value, it means that VT1 is turned off normally when the previous switching is finished.

Step 4 is to turn on CR2 for time duration t4, and if u2 is less than the limit value in this process, it means that CR2 is on, i.e. step 4 is performed normally.

Step 5 is to turn on K2 for a duration of t 5.

Step 6 is to turn off the CR2 for a time period of t6, and if u2 is less than the limit value in this process, it means that K2 is turned on, i.e. step 5 is performed normally.

And step 7, turning off the VT2 for a time duration of t7, ending the whole switching process, and entering a stable state of K2 conduction.

The switching process does not open the main loop, does not short the stage winding, and realizes no arc through the bidirectional thyristor switch. And faults can be judged and found in real time in the switching process.

Fig. 3 is a timing diagram illustrating a failed back-off switching process from a single tap to an even tap.

When step 1 is executed in fig. 2, if an abnormality is found, CR1 and VT2 are disconnected and the duration of t1 is prolonged, and then the steady state where the odd tap K1 is conducted is returned.

When step 2 is executed in fig. 2, if an abnormality is found, K1 is turned on again for a time period of t2, the step 1 is entered, CR1 and VT2 are turned off again for a time period of t1, and the steady state where the odd tap K1 is turned on is returned.

When step 3 is executed in fig. 2, if an abnormality is found, the process returns from step 3 to the steady state in step 0 according to the timing shown in fig. 3.

When step 4 is executed in fig. 2, if an abnormality is found, the process returns from step 4 to the steady state in step 0 in accordance with the timing shown in fig. 3.

When step 6 is executed in fig. 2, if an abnormality is found, the process is executed from step 6 back to step 0 in the timing sequence shown in fig. 3.

Fig. 4 is a timing diagram of the forward switching process from even taps to odd taps, i.e., the switching process from K2 conducting to K1 conducting. The switching process is similar to that of fig. 2 and is represented by the abscissa step divided into 7 steps.

A value of Step 0 indicates a steady state where K2 is on when not switching.

After the switching process is started, step 1 is that CR2 and VT1 are turned on and lasts for a time period of t1, and if i1 is greater than a limit value in the process, VT1 is turned on, that is, step 1 is performed normally.

Step 2 is to turn off K2 for a duration of t2, and if u2 is less than the limit value in the process, it indicates that CR2 is on, i.e., step 1 is executed normally.

Step 3 is to turn off the CR2 for a duration of t3, in this process, if u2> the limit value, it means that CR2 and K2 are turned off, that is, steps 2 and 3 are executed normally, and if i2< the limit value, it means that VT2 is turned off normally when the previous handover is finished.

Step 4 is to turn on CR1 for time duration t4, and if u1 is less than the limit value in this process, it means that CR1 is on, i.e. step 4 is performed normally.

Step 5 is to turn on K1 for time period t 5.

Step 6 is to turn off the CR1 and continue for a time period of t6, in this process, if u1 is less than the limit value, it means that K1 is turned on, i.e. step 5 is executed normally.

Step 7 is to turn off VT1 for a time period of t7, and the whole switching process is ended, and a steady state of K1 conduction is entered.

Fig. 5 is a timing diagram illustrating the fallback from switching from even taps to odd taps.

When step 1 is executed in fig. 4, if an abnormality is found, CR2 and VT1 are disconnected and the time duration t1 is continued, and then the steady state where the even tap K2 is turned on is returned.

When step 2 is executed in fig. 4, if an abnormality is found, K2 is turned on again and continues for a time period of t2, step 1 is entered, CR2 and VT1 are turned off again and continues for a time period of t1, and then the steady state where the even tap K2 is turned on is returned.

When step 3 is executed in fig. 4, if an abnormality is found, the process returns from step 3 to step 0 in the timing shown in fig. 5.

When step 4 is executed in fig. 4, if an abnormality is found, the process goes back from step 4 to step 0 in the timing sequence shown in fig. 5.

When step 6 is executed in fig. 4, if an abnormality is found, the process proceeds from step 6 back to step 0 in the timing shown in fig. 5, and the steady state is returned.

Fig. 6 shows a power electronic switch formed by a fully controlled device IGBT. The IGBT device is formed by reversely connecting two IGBTs T1 and T2 in series. The full-control device power electronic switches shown in fig. 6 can also be adopted as VT1, VT2, CR1 and CR2 in fig. 1. And the K1 and the K1 can adopt faster permanent magnet switches, so that the whole switching process is accelerated.

The above description is only an embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. A diverter switch for an on-load tap changer, comprising: a singular tap combination switching branch, an even tap combination switching branch and a measurement and control module, wherein,

each combined switching branch is formed by connecting a through-flow branch, an on-off branch and a transition branch in parallel;

the through-current branch is composed of a mechanical switch, the on-off branch adopts a bidirectional power electronic switch, and the transition branch is composed of the bidirectional power electronic switch and a resistor in series connection;

the measurement and control module consists of a power supply module, a control module, a communication module and a monitoring module, wherein the power supply module is connected between a singular tap and an even tap of the tapping selector to form a control power supply, the monitoring module measures the voltage and the current of the two combined switching branches, and the communication module realizes data exchange with a remote master station, receives a host gear shifting instruction and uploads a running state;

the control module runs control software, receives a gear shifting operation instruction of the master station on one hand, and uploads a switching result to the master station through the communication module after gear shifting is finished on the other hand;

the gear shifting operation has two modes, namely, the conduction from the odd tap conduction state to the odd tap conduction state, and the conduction from the even tap conduction state to the odd tap conduction state.

2. A bi-directional power electronic switch as claimed in claim 1, formed by two thyristors connected in anti-parallel.

3. A bi-directional power electronic switch as claimed in claim 1 formed by two IGBTs connected in series in opposite directions.

4. The mechanical switch of claim 1, formed from a magnetically held relay.

5. The mechanical switch of claim 1, formed from a fast permanent magnet switch.

6. The tangential odd-numbered tap conduction process according to claim 1, which comprises 7 steps, wherein the first step is to conduct an odd-numbered on-off branch and an even-numbered transition branch; the second step shuts off the odd number current branch; thirdly, switching off the odd on-off branch; fourthly, conducting the even on-off branch; fifthly, conducting the double-number through-current branch; sixthly, switching off the even on-off branch circuits; and step seven, switching off the even number transition branch.

7. The tangential odd tap conduction process from the even tap conduction state as claimed in claim 1 can be divided into 7 steps, the first step is to conduct the even on-off branch and the odd transition branch; secondly, shutting off the even number of through-flow branches; thirdly, switching off the even on-off branch; fourthly, switching on odd on-off branches; conducting odd number current branch circuits; sixthly, switching off the odd on-off branch; and step seven, switching off the single transition branch.

8. The tangential odd tap conduction process from the odd tap conduction state to the even tap conduction state as claimed in claim 6, wherein each step is compared with the set limit value according to the sampled voltage and current, if normal, the next switching operation is continued; otherwise, if the abnormity is detected, the operation is carried out according to the reverse time sequence, the initial odd tap conduction state is returned, and the fault is reported.

9. The tangential odd tap conduction process from the even tap conduction state according to claim 7, wherein each step is compared with the set limit value according to the sampled voltage and current, if normal, the next switching operation is continued; otherwise, if the abnormity is detected, the operation is carried out according to the opposite time sequence, the initial even number tap conduction state is returned, and the fault is reported.