CN111048352A

CN111048352A - Special on-load voltage regulating switch for distribution transformer and on-load voltage regulating distribution transformer

Info

Publication number: CN111048352A
Application number: CN201811188811.3A
Authority: CN
Inventors: 吕云洁; 叶传海; 周甫庆
Original assignee: Jinan Aidi Electric Equipment Co ltd
Current assignee: Jinan Aidi Electric Equipment Co ltd
Priority date: 2018-10-12
Filing date: 2018-10-12
Publication date: 2020-04-21

Abstract

The invention discloses a special on-load voltage regulation switch for a distribution transformer and the on-load voltage regulation distribution transformer, wherein the switch comprises an installation mainboard, an insulation back plate, a driving mechanism assembly, a selection switch assembly, a change-over switch assembly and a transition element, the driving mechanism assembly comprises a stepping motor, a gearbox, a bevel gear, a driving gear and a square shaft, the rotating motion of the stepping motor is transmitted to the driving gear by means of the gearbox and the bevel gear, the driving gear drives the square shaft to rotate, and then the selection switch assembly and the change-over switch assembly are driven to act, so that the conversion of voltage regulation gears is completed. The on-load voltage regulating switch is miniaturized, is installed in a distribution transformer without changing the conventional shape and the conventional volume of the on-load voltage regulating switch, realizes frequent voltage regulation of the distribution transformer under the condition of load, stabilizes the power supply voltage, reduces the loss, realizes wide and multi-gear and refined voltage regulation, simultaneously realizes the same service life of the switch as that of the distribution transformer body, does not need maintenance in the service life, and improves the reliability of on-load voltage regulation of the distribution transformer.

Description

Special on-load voltage regulating switch for distribution transformer and on-load voltage regulating distribution transformer

Technical Field

The device relates to the technical field of electric power products, in particular to a special on-load tap changer for a distribution transformer and the on-load tap changing distribution transformer.

Background

The distribution transformer is the last transformer of a power supply network, is applied to various fields of the national civilization, is distributed in various corners of cities and countryside, and is huge in quantity. The existing distribution transformer is in a non-excitation voltage regulation mode, a power supply is cut off firstly during voltage regulation, then a non-excitation voltage regulation switch is manually adjusted, and power transmission is recovered after adjustment is finished. Because the voltage can be regulated only by power failure and timely voltage regulation cannot be realized, the distribution transformer in an actual power supply network is equal to a distribution transformer without voltage regulation measures, the power supply voltage has low qualification rate and poor stability, and the loss of the distribution transformer and the loss of electric equipment are increased due to abnormal operation of the electric equipment. Along with the continuous promotion and development of social economy and power grids, the requirement on the voltage quality is higher and higher, so that the requirement on the reliability of the on-load voltage-regulating distribution transformer is higher and higher, and the requirements on the voltage-regulating gear number and the wide voltage-regulating range of the on-load voltage-regulating distribution transformer are also increased to meet the requirements of different occasions.

In recent years, there are cases where an on-load tap changer of a main transformer is applied to a distribution transformer to realize on-load tap changing, but the on-load tap changer of the main transformer is large in size, needs to be maintained regularly, cannot meet the reliability requirement of the distribution transformer, and is not suitable for the distribution transformer with large quantity. The on-load tap changer adopting a spring energy storage mode and a permanent magnet and electromagnetic driving mode is also applied to a distribution transformer in the market, although vacuum arc extinguishing is also adopted, the driving mode of the type is adopted, the impact force is large during driving transmission, the service life of relevant parts of the on-load tap changer is influenced, the service life cycle of the on-load tap changer cannot meet the design service life cycle of the distribution transformer, and the on-load tap changer is not suitable for being used in a large number of distribution transformers.

DE19743864C1 describes an on-load tap changer using a reactor transition method, in which both a selector switch assembly and a diverter switch assembly are arranged on the same phase plate, the structural design is complex, the overall switch occupies a large space, and the reactor is used for on-load voltage regulation transition, which greatly increases the cost of the on-load voltage regulation switch and is not suitable for a large number of distribution transformers.

The german MR company has filed chinese invention patents with the following application numbers in china: 1. application number 201780005054.9 entitled "on-load tap changer"; 2. application No. 201780007088.1 entitled "on-load tap changer, adjustable transformer with on-load tap changer and method for switching on-load tap changer". The two patents only describe the structures and actions of the selection component and the switching component of the on-load tap-changer, and the driving transmission mechanism of the on-load tap-changer is not illustrated. The design life of the distribution transformer is at least 30 years, the requirement on the reliability of the on-load tap changer is higher, and the two inventions realize the function of voltage regulation of the transformer without interruption, but the reliability of the transformer is not explained. The driving part of the on-load tap changer is also one of the core components, and the invention is not explained, if the driving mechanism adopts a spring energy storage or permanent magnet driving mode, the impact force is large in the switching process, the performance of the on-load tap changer is greatly reduced, and the service life of the on-load tap changer is influenced; meanwhile, each phase switching component part of the switch adopts a single vacuum arc-extinguishing chamber and the matching switching of a mechanical mechanism thereof, the switch is switched from an N tap to an N +1 tap, the vacuum arc-extinguishing chamber needs to be disconnected and closed twice, the current is connected and disconnected in the vacuum arc-extinguishing chamber, the requirement on a contact of the vacuum arc-extinguishing chamber is high, and compared with the vacuum arc-extinguishing chamber which is only connected and disconnected once in the gear shifting process, the reliability is low. The invention relates to an on-load tap-changer, an adjustable transformer with the on-load tap-changer and a method for switching the on-load tap-changer, wherein a preselector is arranged on the basis of the on-load tap-changer, a set of maltese wheels are additionally arranged to increase the voltage regulating gear number, the structure design is complex, the length of the switch is increased, two rods or bars adopted for fixing each part are cylindrical in the attached drawing, the integral height of the switch is increased, the specification and the attached drawing show that the invention is not designed for a miniaturized on-load tap-changer suitable for a distribution transformer in the structure design, the volume size of the on-load tap-changer influences the volume size, the production cost and the installation space of the distribution transformer, and the distribution transformer needs the miniaturized and highly reliable on-load tap-changer.

Disclosure of Invention

The invention aims to provide an on-load tap changer special for a distribution transformer, which solves the problem that the on-load tap changer needs to be maintained regularly in the prior art, simultaneously solves the problems that the on-load tap changer is large in size and inconvenient to install in the prior art, realizes the miniaturization of the on-load tap changer, enables the on-load tap changer to be installed without changing the size and the shape of a conventional distribution transformer, realizes the characteristics of long service life and maintenance-free performance of the on-load tap changer, and enables the service life cycle of the on-load tap changer to be equal to the service life of a distribution transformer.

In order to achieve the purpose, the invention adopts the following technical scheme:

the utility model provides a special on-load tap changer of distribution transformer which characterized in that: the device comprises a mounting main board, an insulating back board, a driving mechanism assembly, a selection switch assembly, a change-over switch assembly and a transition element;

the driving mechanism assembly comprises a stepping motor, a gearbox, a bevel gear, a driving gear and a square shaft;

a position sensor is arranged in the gearbox, and the gear signals are directly collected and transmitted in the driving and transmission process;

the selection switch assembly, the change-over switch assembly and the transition element are respectively provided with three groups to respectively complete the selection and the switching of three-phase voltage regulating gears;

each group of the change-over switch components comprises a change-over switch main board, two vacuum arc-extinguishing chambers and two cams;

each group of selection switch components comprises a selection switch main board, two groups of sheave mechanisms, a fine selection contact component, a roughing driving tooth, an incomplete gear mechanism and a roughing contact component, wherein each sheave mechanism comprises a driving plate and a sheave;

the stepping motor is installed on the gear box, and the gear box, the selection switch main board and the change-over switch main board are fixed on the installation main board;

the insulating back plate is fixedly connected with one end of the selection switch main board and one end of the change-over switch main board;

the square shaft penetrates through the selection switch main board and the change-over switch main board;

the driving gear, the cam and the driving plate are sleeved on the square shaft;

the two vacuum arc-extinguishing chambers are fixedly arranged on one side of the switch main board, and the transition element is fixedly arranged on the other side of the switch main board;

the two groups of sheave mechanisms on each group of selector switch assemblies are respectively installed on two sides of the selector switch main board, the roughing driving teeth are installed and fixed on the sheave of one of the sheave mechanisms, the incomplete gear mechanism is installed and fixed on one side of the selector switch main board, and the roughing contact assembly is fixed on one side of the selector switch main board through a fixing column;

the roughing driving gear, the incomplete gear mechanism and the roughing contact assembly are arranged on the same side of the main board of the selector switch;

the rotating motion of the stepping motor is transmitted to the driving gear by means of the gearbox and the bevel gear, the driving gear drives the square shaft to rotate so as to drive the cam and the drive plate to rotate, and the cam pushes the vacuum arc extinguish chamber to be switched on and off to complete the live-line switching of the voltage regulating gears; the driving plate pushes the grooved wheel to move, and the grooved wheel drives the fine selection contact assembly and the rough selection driving tooth to act so as to perform uncharged selection of a pressure regulating gear; when corresponding pressure regulating gear changes, the roughing drive tooth drives incomplete gear mechanism action, and then drives the roughing contact subassembly action, with the uncharged selection of carefully selecting the contact subassembly and accomplishing the pressure regulating gear jointly, accomplish the adjustment of voltage.

According to a preferred embodiment of the present invention, the positioning of the voltage-regulating gear is controlled and positioned by using the stepping motor.

According to a preferred embodiment of the present invention, the transmission case includes a case body, a case cover, an electronic circuit board, a position sensor, and a gear set, wherein the position sensor transmits motion information of the gear set to the electronic circuit board, and the electronic circuit board performs analysis processing to output a shift position of the on-load tap changer.

According to a preferred embodiment of the present invention, two cams in the switch assembly respectively control the on and off of two vacuum interrupters.

According to a preferred embodiment of the present invention, the fine selection contact assembly includes two moving contacts and a stationary contact group, the two moving contacts are respectively and fixedly installed on two grooved wheels of the selection switch assembly, the stationary contact of the stationary contact group is fixedly penetrated on the selection switch main board, and the number of the stationary contacts is the same as the number of teeth of the grooved wheels; when the gear is selected, the grooved wheel drives the moving contact to rotate, and a corresponding static contact in the static contact group is selected.

According to a preferred embodiment of the present invention, the rough selection contact assembly includes a moving contact, two fixed contacts, and a contact fixing plate, where the moving contact and the two fixed contacts are both mounted on the contact fixing plate, and when the rough selection driving tooth moves to engage with a corresponding gear on the incomplete gear mechanism during voltage regulation gear shifting, the rough selection driving tooth drives the incomplete gear mechanism to move, and the incomplete gear mechanism drives the moving contact in the rough selection contact assembly to select the fixed contact in the rough selection contact assembly without current.

An on-load tap changing distribution transformer, characterized in that the on-load tap changing distribution transformer of the on-load tap changing switch special for the distribution transformer with the structure of any one of the preceding claims is adopted.

Compared with the prior art, the on-load tap changer special for the distribution transformer has the advantages that the on-load tap changer special for the distribution transformer is arranged in the distribution transformer body, and the shape and the volume of the conventional distribution transformer are not changed; the invention realizes frequent voltage adjustment of the distribution transformer under the condition of load, stabilizes the supply voltage, reduces the loss, realizes the broad-width voltage regulation of the distribution transformer, can realize the broad-width voltage regulation of 17 grades +/-8 multiplied by 2.5 percent, simultaneously realizes the continuous voltage regulation action of no fault and no maintenance for more than 60 ten thousand times, can realize no maintenance in the service life cycle of the distribution transformer, and improves the reliability of the on-load voltage regulation of the distribution transformer.

Drawings

Fig. 1 is a schematic diagram a of the overall structure of an on-load tap changer dedicated for a distribution transformer according to the present invention;

fig. 2 is a schematic diagram B of the overall structure of the on-load tap changer dedicated for the distribution transformer of the present invention;

FIG. 3 is a schematic diagram of the internal mechanism of the transmission case of the on-load tap changer dedicated to the distribution transformer of the present invention;

fig. 4 is a schematic diagram of a diverter switch assembly (one side of a diverter switch main board) of the on-load tap changer dedicated to the distribution transformer of the present invention;

fig. 5 is a schematic diagram of the other side of the main board of the diverter switch of the on-load tap changer dedicated to the distribution transformer according to the present invention;

FIG. 6 is a general schematic diagram of a selector switch assembly of the on-load tap changer specific to the distribution transformer of the present invention;

fig. 7 is a schematic diagram a for disassembling the selective switch assembly of the on-load tap changer dedicated to the distribution transformer according to the present invention;

fig. 8 is a schematic diagram B of the disassembled selective switch assembly of the on-load tap changer dedicated to the distribution transformer of the present invention;

fig. 9 is a schematic structural diagram of a sheave removed from one side of a selector switch assembly of an on-load tap changer dedicated to a distribution transformer according to the present invention;

fig. 10 is a schematic diagram of a fine-selection gear selection switching sequence of the on-load tap changer dedicated for the distribution transformer according to the present invention.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The embodiments described below are merely intended to more clearly illustrate the technical solutions of the present invention, are selected embodiments of the present invention, not all embodiments, and thus the scope of the present invention is not limited thereto. All other embodiments obtained by a person skilled in the art without making any inventive step are within the scope of protection of the present invention.

Fig. 1 to 9 are schematic diagrams of a preferred on-load tap changer special for a distribution transformer capable of realizing 17-gear tap changing positions according to the present invention, and referring to fig. 1 and 2, the on-load tap changer special for a distribution transformer comprises an installation main board 1, an insulation back board 2, a driving mechanism assembly 3, a selection switch assembly 4, a change-over switch assembly 5, and a transition element 6; the driving mechanism assembly comprises a stepping motor 31, a gearbox 32, a bevel gear 33, a driving gear 34 and a square shaft 35.

Referring to fig. 3, the transmission case 32 includes a case 321, a case cover 322, an electronic circuit board 323, a position sensor 324, and a gear train 325;

the selector switch assembly 4, the selector switch assembly 5 and the transition element 6 are respectively provided with three groups to respectively complete the selection and switching of three-phase voltage regulating gears;

referring to fig. 4 and 5, each set of the diverter switch assemblies 5 includes a diverter switch main board 51, two

vacuum interrupters

52 and 53, and two

cams

54 and 55; the vacuum arc-extinguishing

chambers

52, 53 are fixedly arranged on one side of the main switch board 51 through related fixing devices, the two

cams

54, 55 are sleeved on the square shaft 35, the transition element 6 is fixedly arranged on the other side of the main switch board 51, and the transition element 6 is preferably a transition resistor.

Referring to fig. 6, 7, 8 and 9, each set of selector switch assembly 4 includes a selector switch main plate 41, two sets of sheave mechanisms 42 and 43, a fine selection contact assembly 44, a coarse selection driving tooth 45, an incomplete gear mechanism 46 and a coarse selection contact assembly 47, and the sheave mechanisms 42 and 43 include

dials

421 and 431 and

sheaves

422 and 432; the fine selection contact assembly 44 includes two moving contacts 441, 442 and a stationary contact set 443, the number of stationary contacts in the stationary contact set 443 is the same as the number of teeth of the sheave 422 or the sheave 432, and the stationary contact set shown in fig. 9 includes 9 stationary contacts; the roughing contact assembly 47 includes a moving contact 471, two

stationary contacts

472, 473, and a contact fixing plate 474;

two groups of geneva gear mechanisms 42, 43 are installed on both sides of the selector switch main board 41 respectively, the moving contacts 441, 442 are installed on geneva

gears

422, 432 respectively, the static contact in the static contact group 443 is fixed to penetrate through the selector switch main board 41, the roughing driving gear 45 is installed and fixed on the geneva gear 422 of one geneva gear mechanism 42, the incomplete gear mechanism 46 is installed and fixed on one side of the selector switch main board 41, the roughing contact component 47 is fixed on one side of the selector switch main board 41 through the fixed column; the roughing driving gear 45, the incomplete gear mechanism 46 and the roughing contact assembly 47 are on the same side of the main board 41 of the selector switch.

The stepping motor 31 is installed on the gear box 32, the option switch main board 41 and the change-over switch main board 51 are fixed on the installation main board 1, the insulation back board 2 is fixedly connected with one end of the option switch main board 41 and one end of the change-over switch main board 51, the square shaft 35 penetrates through the option switch main board 41 and the change-over switch main board 51, and the driving gear 34, the

cams

54 and 55, the

dial

421 and 431 are sleeved on the square shaft 35.

The rotating motion of the stepping motor 31 is transmitted to the driving gear 34 by means of the gearbox 32 and the bevel gear 33, the driving gear 34 drives the square shaft 35 to rotate, further drives the

cams

54 and 55 and the

drive plates

421 and 431 to rotate, and the

cams

54 and 55 push the vacuum arc-extinguishing

chambers

52 and 53 to be switched on and off through the driving rod, so that the live switching of the voltage regulating gears is completed; the

dial

421 and 431 pushes the

grooved wheels

422 and 432 to move, the

grooved wheels

422 and 432 drive the moving contacts 441 and 442 in the fine selection contact assembly 44 and the rough selection driving tooth 45 to move, the moving contacts 441 and 442 select corresponding static contacts in the static contact set 443, when the rough selection driving tooth 45 moves to be engaged with corresponding gears on the incomplete gear mechanism 46 during corresponding gear shifting, the rough selection driving tooth 45 drives the incomplete gear mechanism 46 to move, and then drives the moving contact 471 in the rough selection contact assembly 47 to select the corresponding static contact 472 or the static contact 473, so that the uncharged selection of the voltage regulating gear is completed, and the voltage regulation is completed.

Referring to fig. 10, there are 7 steps of the fine gear selection switching process performed by the on-load tap changer dedicated to the distribution transformer of the present invention, wherein N, N +1 represents two adjacent coil taps of the tap winding, A, B represents two moving contacts 441, 442 in the fine gear selection contact assembly 44 in the selector switch assembly 4, R represents the transition element 6, and D1, D2 represent two

vacuum interrupters

52, 53 in the selector switch assembly 5.

Timing of switching from N +1 tap to N tap of the regulating winding:

step 1: the moving contacts A, B are all connected with the N +1 tap, and the vacuum arc-extinguishing chambers D1 and D2 are all connected. The current flows through the N +1 tap through the moving contact A and the vacuum arc-extinguishing chamber D2.

Step 2: the vacuum arc extinguish chamber D2 is disconnected, the moving contact A is disconnected with the tap N +1, the moving contact B is still connected with the tap N +1, and current flows through the moving contact B, the transition element 6 and the vacuum arc extinguish chamber D1 from the tap N + 1.

And step 3: the moving contact B is still connected with the N +1 tap, the moving contact A is switched to the N tap from the N +1 tap without current, and the current flows through the moving contact B, the transition element 6 and the arc extinguishing chamber D1 from the N +1 tap.

And 4, step 4: the moving contact B is still communicated with the N +1 tap, the vacuum arc extinguish chamber D2 is closed, the moving contact A is communicated with the N tap, current flows through the moving contact B, the transition element 6 and the vacuum arc extinguish chamber D1 from the N +1 tap, the current flows through the moving contact A and the vacuum arc extinguish chamber D2 from the N tap, and at the moment, short-time circulation is generated between the N +1 tap and the N tap.

And 5: the vacuum arc extinguish chamber D1 is disconnected, the moving contact B is disconnected with the tap N +1, the moving contact A is still connected with the tap N, and current flows through the moving contact A and the vacuum arc extinguish chamber D2 from the tap N.

Step 6: the moving contact A is still connected with the N taps, the moving contact B is switched to the N taps from the N +1 taps without current, and the current flows through the moving contact A and the vacuum arc-extinguishing chamber D2 from the N taps.

And 7: the moving contact A is still communicated with the N tap, the vacuum arc extinguish chamber D1 is communicated, the moving contact B is communicated with the N tap, and current flows through the moving contact A and the vacuum arc extinguish chamber D2 from the N tap.

The above description is made for the fine-selection gear shifting process of the on-load tap changer, and the rough selection part in the selection switch assembly is according to the conventional on-load tap changing mode: the thickness and fineness voltage regulation principle and the positive and negative voltage regulation principle are well known to those skilled in the art and will not be described. Above whole selection switching process, electric arc only produces in the vacuum arc extinguishing chamber, can not produce the pollution to transformer oil, does not need regularly to carry out the oil strain maintenance or change the filter core, has saved the operation maintenance cost greatly.

When the on-load tap changer special for the distribution transformer is designed, the on-load tap changer is developed from the aspects of miniaturization, maintenance-free property and equal service life to the design service life of the transformer. The invention adopts a mounting main board with enough tolerance strength to fixedly mount each component so as to reduce the overall height of the on-load tap changer; meanwhile, related parts of rough selection and fine selection of the on-load voltage regulating switch are arranged on the same selection switch mainboard, compared with switches arranged on different installation mainboards, the structure of the on-load voltage regulating switch is simple and compact in design, the length of the switch is reduced, and the overall design of the switch is miniaturized. The flexible driving and precise positioning characteristics of the stepping motor 31 are adopted to carry out the driving conversion and the control positioning of the voltage regulating gears, so that the impact force on relevant parts (a change-over switch assembly and a selection switch assembly) in the driving and transmission process of the on-load voltage regulating switch is greatly reduced, and the actual service life and the reliability of each part of the switch are improved; the stepping motor 31 drives the gear set 325 in the gearbox 32 to rotate, the position sensor 324 transmits the rotation information of the gear set 325 to the electronic circuit board 323, the electronic circuit board 323 analyzes and processes the gear position of the on-load tap changer to be directly output, the position information of the tap position is directly output in the gearbox 32, a conventional high-fault-rate and unreliable position switch feedback device is omitted, and the service life and the operation reliability of the on-load tap changer are greatly improved; two vacuum arc-extinguishing chambers 52 and 53 are arranged in the change-over switch component 5, when the voltage-regulating gear is switched, the two vacuum arc-extinguishing chambers 52 and 53 only act once, and compared with the other vacuum arc-extinguishing chambers which only need to act twice during gear switching each time and need to be matched by a more complicated mechanical mechanism, if the same type of vacuum arc-extinguishing chamber is selected, the service life of the invention is prolonged by one time compared with the other vacuum arc-extinguishing chambers, and the reliability of the switch is improved; by selecting the scheme, the on-load tap changer has the characteristics of miniaturization and high reliability, and is suitable for a proper amount of large distribution transformers. It is within the scope of the present invention to modify the present invention according to the preferred embodiment, for example, to use a motor mechanism such as a servo motor or a linear motor instead of a stepping motor in conjunction with a control program.

The voltage regulation modes of the on-load voltage regulation switch are mainly three types: the on-load tap changer special for the distribution transformer is suitable for both the linear voltage regulation, the positive and negative voltage regulation and the coarse and fine voltage regulation are only different in winding mode and wiring mode of a voltage regulating winding, and the linear voltage regulation mode is adopted, and only the related components for selecting and switching the fine voltage regulating gear are adopted. In an optimal implementation mode, the on-load tap changer can realize the wide voltage regulation of 17 gears +/-8 multiplied by 2.5% by adopting thickness voltage regulation or positive and negative voltage regulation at most, if the voltage regulation of more gears is still needed, the number of the gears of the grooved wheels and the corresponding static contacts can be increased, and the switch volume can be increased accordingly. Fig. 1 to 9 show a preferred embodiment of the present invention, the number of gears can be increased or decreased according to the user's requirement, and the action principle of the on-load tap changer is not changed.

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

Claims

1. The utility model provides a special on-load tap changer of distribution transformer which characterized in that: the device comprises a mounting main board, an insulating back board, a driving mechanism assembly, a selection switch assembly, a change-over switch assembly and a transition element;

2. The on-load tap changer of claim 1, wherein the positioning of the tap position is controlled by the stepper motor.

3. The on-load tap changer special for the distribution transformer according to claim 1, wherein the gearbox comprises a box body, a box cover, an electronic circuit board, a position sensor and a gear set, the position sensor transmits the motion information of the gear set to the electronic circuit board, and the electronic circuit board performs analysis processing to output the gear position of the on-load tap changer.

4. The on-load tap changer of claim 1, wherein two of the cams of the diverter switch assembly control the opening and closing of two of the vacuum interrupters.

5. The on-load tap changer special for a distribution transformer according to claim 1, wherein the fine selection contact assembly comprises two moving contacts and a static contact group, the two moving contacts are respectively and fixedly installed on two sheaves in the selection switch assembly, the static contact in the static contact group is fixedly penetrated on the main board of the selection switch, and the number of the static contacts is the same as the number of teeth of the sheaves; when the gear is selected, the grooved wheel drives the moving contact to rotate, and a corresponding static contact in the static contact group is selected.

6. The on-load tap changer special for a distribution transformer according to claim 1, wherein the roughing contact assembly comprises a moving contact, two fixed contacts, and a contact fixing plate, wherein the moving contact and the two fixed contacts are both mounted on the contact fixing plate, when the roughing drive teeth move to engage with corresponding gears on the incomplete gear mechanism during voltage regulation gear shifting, the roughing drive teeth drive the incomplete gear mechanism to move, and the incomplete gear mechanism drives the moving contact in the roughing contact assembly to select the fixed contact in the corresponding roughing contact assembly without current.

7. An on-load tap changing distribution transformer, characterized in that the on-load tap changing distribution transformer of the on-load tap changing switch special for the distribution transformer with the structure of any one of the preceding claims is adopted.