CN211350535U

CN211350535U - Neutral pole structure of miniature circuit breaker

Info

Publication number: CN211350535U
Application number: CN201922255365.XU
Authority: CN
Inventors: 黄穗; 周素珍; 陈清槐
Original assignee: Xiamen Shanxiu Sunshine Technology Co ltd
Current assignee: Xiamen Shanxiu Sunshine Technology Co ltd
Priority date: 2019-12-16
Filing date: 2019-12-16
Publication date: 2020-08-25
Anticipated expiration: 2029-12-16

Abstract

The utility model discloses a miniature circuit breaker's neutral pole structure, including casing, divide-shut brake drive module, circuit board, link mechanism and circuit breaker handle, divide-shut brake drive module include: the motor set is axially provided with a driving shaft and is electrically connected with the circuit board; the transmission gear assembly is connected with the driving shaft; a clearance space is arranged between the driving shaft and the transmission gear assembly, and the transmission gear assembly is connected with the breaker handle; still include quick dropout module, quick dropout module includes: the electromagnet is arranged at the side end of the motor set and is electrically connected with the circuit board; and the head end of the push rod is axially connected with the electromagnet, the middle part of the push rod is arranged in the gap space, and the tail end of the push rod is in touch connection with the transmission gear assembly or in touch connection with the connecting rod mechanism. The utility model discloses in mixing into the neutral utmost point with divide-shut brake drive module, quick dropout functional module, realized that the structure in the little space is laid, except deciliter control, still possess the required quick dropout function of earth leakage protection.

Description

Neutral pole structure of miniature circuit breaker

Technical Field

The utility model belongs to the technical field of the circuit breaker technique and specifically relates to a miniature circuit breaker's neutral pole structure.

Background

The miniature circuit breaker, abbreviated as MCB, is a terminal protection electrical appliance which is most widely used in the power distribution device of an electrical terminal. The MCB is generally designed in an analog-to-digital manner, and basically fixed in shape, size, wiring mode and the like, and is often installed on the endmost branch to play a role in protecting and controlling the electric equipment. With the development of market and technology, the function of the MCB is developed to a trend, and a switching driving module, i.e., an electric operating mechanism (a functional module for switching on and off the MCB), is mixed into a neutral pole (or an N pole for short) of the MCB, and can be used for replacing an original common small-sized circuit breaker without increasing the module of the MCB (the module refers to the multiple of the thickness of a product being 18mm, for example, 2 modules refers to the thickness of the product being about 36 mm), so that the MCB not only has an original overcurrent protection function, but also has a switching on and off control function, and the like, and has great market demands.

Patent No. CN206022261U discloses an electric operating mechanism of a circuit breaker, which is added to the N pole of the MCB, and forms a 2-pole product with the L pole of the MCB, but only has the functions of switching control, overload protection and short-circuit protection; however, when rapid tripping and opening are required, for example, when leakage protection is performed, the circuit breaker needs to trip and open the brake within 40 milliseconds at the fastest speed, and the existing products of this kind cannot meet the standard requirements if a motor acceleration and deceleration mechanism is used to trip and open the brake.

Document No. CN108364837A discloses a novel automatic switching-on/off control mechanism for miniature circuit breaker and circuit breaker, leakage protection action drives a tripping deflector rod to impact an idle trip tripper connecting rod through an electromagnet, so that a tripping link shaft on the idle trip tripper connecting rod drives a tripping link structure inside the circuit breaker to trip, and automatic switching-off is realized.

Disclosure of Invention

An object of the utility model is to provide a miniature circuit breaker's neutral pole structure not only has divide-shut brake drive module, still possesses quick dropout module, and quick dropout when can satisfying earth leakage protection action requires, for realizing above-mentioned purpose, the utility model discloses a following technical scheme:

the utility model provides a miniature circuit breaker's neutral pole structure, includes the casing, installs divide-shut brake drive module, circuit board, link mechanism and circuit breaker handle in the casing, divide-shut brake drive module and link mechanism all be connected with the circuit breaker handle, link mechanism and miniature circuit breaker's other utmost point linkages, divide-shut brake drive module include: the motor set is axially provided with a driving shaft and is electrically connected with the circuit board; the transmission gear assembly is connected with the driving shaft; a gap space is arranged between the driving shaft and the transmission gear assembly, and the transmission gear assembly is connected with the handle of the circuit breaker; still include quick trip module, quick trip module include: the electromagnet is arranged at the side end of the motor set and is electrically connected with the circuit board; and the head end of the push rod is axially connected with the electromagnet, the middle part of the push rod is arranged in the gap space, and the tail end of the push rod is in touch connection with the transmission gear assembly or in touch connection with the connecting rod mechanism.

In one embodiment, the device further comprises a transmission deflector rod, the middle of the transmission deflector rod is hinged to the shell, one end of the transmission deflector rod is connected with the push rod, and the other end of the transmission deflector rod is in touch connection with the transmission gear assembly.

Furthermore, a connecting hole is formed in the connecting end of the transmission deflector rod and the push rod, the electromagnet is axially arranged perpendicular to the driving shaft, the push rod is L-shaped, one end of the push rod is axially connected with the electromagnet, and the other end of the push rod is inserted into the connecting hole.

The connecting rod mechanism comprises a lock catch, a trip buckle, a tension spring and a U-shaped rod, a static contact component and a moving contact component which are electrically connected with a circuit board are arranged in the shell, the static contact component is installed on the shell, the lock catch, the trip buckle and the moving contact component are hinged on the shell, the side end of the moving contact component is connected with the shell through the tension spring, the lock catch is unlocked by touching and rotating the trip buckle, the trip buckle bounces off, the tension spring enables the moving contact component to be separated, one end of the U-shaped rod is connected with the trip buckle, and one end of the U-shaped rod is connected with a handle of the circuit.

Preferably, circuit breaker handle below be provided with a transmission boss, the transmission boss in the middle of open and to have the through-hole, U type pole one end insert in the through-hole, realize being connected with the circuit breaker handle, transmission gear subassembly top be provided with the connection boss, the connection boss touch with the transmission boss and be connected.

In another embodiment, the end of the push rod is in touch connection with the latch.

Preferably, the drive gear subassembly include bevel gear, face gear, straight-teeth gear and final stage straight-teeth gear, bevel gear and drive shaft axial coupling, bevel gear and face gear mesh mutually, the straight-teeth gear coaxial setting in face gear top, final stage straight-teeth gear mesh mutually with the straight-teeth gear, final stage straight-teeth gear below be provided with the dog, the transmission driving lever the tip with the dog touching be connected.

Wherein, the straight gear and the face gear are designed as a whole or hinged as a whole.

Further, the circuit breaker handle include connecting portion and handle portion, connecting portion coaxial arrangement on the last straight-tooth gear, connecting portion top be provided with the square shaft hole that supplies other utmost point circuit breaker handle coaxial arrangement, handle portion stretch out outside the casing.

Furthermore, a torsion spring for resetting is arranged above the connecting part of the breaker handle; and a spring for pushing the push rod and the movable iron core to reset is arranged in the electromagnet.

Preferably, the casing include underframe, center and the upper cover plate that connects gradually, divide-shut brake drive module, quick-release module, wiring terminal group and circuit breaker handle install between underframe and center, the circuit board install between center and upper cover plate.

Preferably, the underframe on correspond the position of push rod, be provided with the under bracing platform of epirelief in drive shaft both sides, the upper surface of under bracing platform be provided with the corresponding lower arc cavity of push rod diameter, the center on correspond the position of push rod and be provided with the protruding last supporting bench down, the lower surface of going up the supporting bench be provided with the corresponding last arc cavity of push rod diameter, the push rod set up between last arc cavity and the lower arc cavity.

Preferably, the circuit board on be provided with position sensor, the connecting portion of circuit breaker handle on be provided with and be used for touching position sensor and carry out the locating piece that position detected, the locating piece with a pin of torsional spring support and lean on, another pin of torsional spring support and shells inner wall and support and lean on.

Preferably, the zero sequence current transformer is electrically connected with the circuit board, and notch holes for installing the zero sequence current transformer are formed in the bottom frame, the middle frame and the upper cover plate.

Due to the adoption of the structure, the utility model discloses following beneficial effect has: the utility model discloses in mixing the installation in the neutral pole of circuit breaker, through the installation of the special position of electro-magnet and push rod, the installation of "setting the gap space between motor and transmission gear assembly with the push rod middle part promptly with divide-shut brake drive module, link mechanism and quick-release module to realized that the structure in the little space is laid, the length and the thickness of product all are close with current product. The utility model discloses a scheme combines with miniature circuit breaker's L utmost point for the modulus of circuit breaker is the same with current product, not only has divide-shut brake control function, still possesses the separating brake function of tripping fast.

Drawings

Fig. 1 is a schematic structural diagram of the present invention.

Fig. 2 is a schematic front view of the present invention.

Fig. 3 is a schematic sectional view B-B of fig. 2.

Fig. 4 is an exploded view of the first embodiment of the present invention.

Fig. 5 is an enlarged schematic view at a of fig. 4.

Fig. 6 is a schematic view of a connection structure of the first trip and disconnect driving module, the quick trip module, and the breaker handle according to the first embodiment.

Fig. 7 is an exploded schematic view of fig. 6.

Fig. 8 is a schematic view of a connection structure of the first disconnecting/closing driving module, the quick trip module, the link mechanism and the handle of the circuit breaker according to the first embodiment.

Fig. 9 is a rear view from a certain angle of fig. 8.

Fig. 10 is a schematic structural view of the transmission lever.

Fig. 11 is a schematic structural view of the electromagnet driving the transmission shift lever to touch the last-stage spur gear to control the rotation of the circuit breaker handle.

Figure 12 is a schematic view of the connection of the breaker handle to the U-bar.

Fig. 13 is a schematic structural view of the present invention with the upper cover plate removed.

Fig. 14 is a schematic structural view of the present invention with the upper cover plate, the circuit board and the middle frame removed.

Fig. 15 is a schematic structural diagram of a second embodiment of the present invention.

Description of the main symbols:

1: a housing, 11: bottom frame, 111: lower support table, 112: lower arc-shaped cavity, 113: pin, 12: middle frame, 121: upper support table, 122: go up arc cavity, 13: upper cover plate, 14: notch hole, 2: switching-on/off drive module, 21: motor group, 211: drive shaft, 22: drive gear assembly, 221: bevel gear, 222: face gear, 223: spur gear, 224: last-stage spur gear, 225: connection boss, 23: gap space, 24: a stopper, 3: link mechanism, 31: jump buckle, 32: latch, 33: u-shaped bar, 34: tension spring, 4: quick trip module, 41: electromagnet, 42: push rod, 43: transmission stick, 431: hinge hole, 432: connection hole, 51: stationary contact assembly, 52: moving contact assembly, 6: breaker handle, 61: a connection portion, 611: drive boss, 612: through hole, 613: square shaft hole, 62: handle portion, 63: a positioning block, 7: wiring board, 8: position sensor, 9: torsion spring, 10: zero sequence current transformer, 20: and (4) a square shaft.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the present invention is further described in detail with reference to the accompanying drawings and specific embodiments.

Example one

As shown in fig. 1 to 4, the present embodiment discloses a neutral pole structure of a miniature circuit breaker, which includes a housing 1, a switching driving module 2, a link mechanism 3, a quick release module 4, a circuit board 7, and a circuit breaker handle 6. The shell is internally provided with a static contact assembly 51 and a moving contact assembly 52, the opening and closing drive module 2 and the link mechanism 3 are both connected with the breaker handle 6, and the link mechanism 3 is linked with other poles (L poles) of the miniature breaker.

The housing 1 includes a bottom frame 11, a middle frame 12 and an upper cover 13 connected in sequence. The switching-on/off driving module 2, the quick release module 4, the link mechanism 3, the fixed contact assembly 51, the movable contact assembly 52 and the breaker handle 6 are arranged between the bottom frame 11 and the middle frame 12, and the circuit board 7 is arranged between the middle frame 12 and the upper cover plate 13. Gap holes 14 for installing the zero sequence current transformer 10 are further formed in the bottom frame 11, the middle frame 12 and the upper cover plate 13, and the zero sequence current transformer 10 is installed in the gap holes 14 and connected with the circuit board 7 so as to detect current in the circuit breaker.

As shown in fig. 6 and 7, the switching drive module 2 includes: a motor unit 21 and a transmission gear assembly 22. The motor set 21 is axially provided with a driving shaft 211, and the motor set 21 comprises a motor and a speed reducing mechanism. The motor unit 21 is electrically connected to the circuit board 7. The transmission gear assembly 22 is connected to the drive shaft 211. In order to minimize the use of space, the transmission gear assembly 22 of the present embodiment includes: bevel gear 221, face gear 222, spur gear 223, and final stage spur gear 224. The bevel gear 221 is axially connected with the driving shaft 211, the bevel gear 221 is meshed with the face gear 222, the straight gear 223 is coaxially arranged above the face gear 222, the straight gear 223 and the face gear 222 are integrally designed or hinged into a whole, and the final-stage straight gear 224 is meshed with the straight gear 223.

As shown in fig. 7, a clearance space 23 is provided between the driving shaft 211 and the bevel gear 221.

The quick release module 4 includes an electromagnet 41, a push rod 42, and a transmission lever 43. The electromagnet 41 is disposed at the side end of the motor unit 21, and the electromagnet 41 is electrically connected to the circuit board 7. The electromagnet 41 is arranged to be perpendicular to the driving shaft 211 in the axial direction, and a spring (not shown in the figure) for driving the push rod 42 and the movable iron core to return is installed in the electromagnet 41. The head end of the push rod 42 is axially connected with the electromagnet 41, the middle part of the push rod 42 is arranged in the gap space 23, and the tail end of the push rod 42 is connected with the transmission shift lever 43.

As shown in fig. 10, a hinge hole 431 is provided in the middle of the transmission lever 43, the pin 113 is provided on the bottom frame 11, and the hinge hole 431 is installed in the pin 113 to realize the hinge connection of the transmission lever 43. The connection end of the transmission shift lever 43 and the push rod 42 is provided with a connection hole 432, and the other end of the transmission shift lever 43 is in touching connection with the final stage spur gear 224 of the transmission gear assembly 22. The push rod 42 is L-shaped, one end of the push rod 42 is axially connected with the electromagnet 41, and the other end is inserted into the connecting hole 432 to realize the connection with the transmission shift lever 43. As shown in fig. 9, a stopper 24 is provided below the final spur gear 224, and the end of the transmission lever 43 contacts the stopper 24.

As shown in fig. 3 and 5, two sets of convex lower supporting tables 111 are disposed on two sides of the driving shaft 211 corresponding to the position of the push rod 42 on the bottom frame 11, a lower arc-shaped cavity 112 corresponding to the diameter of the push rod is disposed on the upper surface of the lower supporting table 111, a convex upper supporting table 121 is disposed on the middle frame 12 corresponding to the position of the push rod 42, an upper arc-shaped cavity 122 corresponding to the diameter of the push rod 42 is disposed on the lower surface of the upper supporting table 121, and the push rod 42 is disposed between the upper arc-shaped cavity 122 and the lower arc-shaped cavity 112.

As shown in fig. 7, the circuit breaker handle 6 includes a connecting portion 61 and a handle portion 62, the connecting portion 61 is coaxially mounted on the final stage spur gear 224 and is rotated by the final stage spur gear 224, and the handle portion 62 extends out of the housing. A torsion spring 9 is installed below the connecting portion 61 of the breaker handle 6 so that the breaker handle 6 is elastically restored. As shown in fig. 12, a transmission boss 611 is provided below the connection portion 61 of the breaker handle, and a through hole 612 is formed in the transmission boss 611, and the through hole 612 allows the U-shaped rod 33 of the link mechanism 3 to be inserted and connected. A connecting boss 225 is arranged above the last-stage spur gear 224, and the connecting boss 225 is in touch connection with the transmission boss 611. A square shaft hole 613 for connecting the other pole breaker handle is provided above the connection portion 61 of the breaker handle 6. As shown in fig. 1, one end of a square shaft 20 is inserted into the square shaft hole 613, and the other end is connected to the L-pole breaker handle, thereby realizing linkage of two poles. Other embodiments, the utility model discloses well circuit breaker handle 6 also can only include connecting portion 61, is provided with handle portion on the circuit breaker handle of other utmost points, by the circuit breaker handle drive of other utmost points the utility model discloses circuit breaker handle 6 interlock.

As shown in fig. 13, the circuit board 7 is provided with a plurality of position sensors 8, and the connection portion 61 of the breaker handle 6 is provided with a positioning block 63 for detecting the position by touching the position sensors 8. When the breaker handle 6 is operated, the positioning block 63 is rotated to a position where it touches different position sensors 8, and the position sensors 8 convert the position information of the breaker handle 6 into an electric signal. One pin of the torsion spring 9 abuts against the positioning block 63, and the other pin abuts against the inner wall of the shell, so that elastic reset is realized.

As shown in fig. 14, 8 and 9, the link mechanism 3 includes a lock 32, a jumper 31, a U-shaped lever 33 and a tension spring 34. The contact assembly comprises a fixed contact assembly 51 and a movable contact assembly 52 which are electrically connected with the circuit board 7, the fixed contact assembly 51 is a bent terminal, and the movable contact assembly 52 is connected with the circuit board 7 through a flexible connection 53. The fixed contact assembly 51 is mounted on the housing, and the latch 32, the trip 31 and the movable contact assembly 52 are hinged on the bottom frame 11. The side end of the movable contact component 52 is connected with the side wall of the shell 1 through a tension spring 34. The lock catch 32 is touched to rotate to unlock the trip catch 31, the trip catch 31 springs open, and the movable contact component 52 is opened under the action of the tension spring. One end of the U-shaped rod 33 is connected with the jump buckle 31, and the other end is connected with the connecting hole of the breaker handle 6.

The operation principle of the present embodiment is described in detail below.

1. The motor rotates forwards or backwards, so that the transmission gear assembly 22 is driven to rotate, the final-stage straight gear 224 rotates clockwise or anticlockwise, and the circuit breaker handle 6 is driven to rotate to realize the switching-on or switching-off of the circuit breaker.

2. In case of overload and short circuit, the latch 32 rotates to unlock and open the movable contact assembly 52 of the circuit breaker.

2. As shown in fig. 11, when an electric leakage occurs, the zero sequence current transformer senses an abnormal current and transmits a signal to the circuit board, the circuit board 7 receives the signal of the electric leakage state, so that the electromagnet 41 is energized, the electromagnet 41 drives the push rod 42, and the push rod 42 drives the transmission shift lever 43 to rotate, so that the end of the transmission shift lever 43 contacts with the final-stage spur gear 224, thereby achieving rapid automatic opening.

Example two

As shown in fig. 15, the present embodiment is different from the first embodiment in that: the quick trip module 4 includes an electromagnet 41 and a push rod 42. The head end of the push rod 42 is axially connected with the electromagnet 41, the middle part of the push rod 42 is arranged in the gap space 23, and the tail end of the push rod 42 is in contact connection with the lock catch 32 of the link mechanism 3.

The operation principle of the present embodiment is described in detail below.

2. When the leakage protection is performed, the circuit board 7 detects the leakage state (which can be detected by the zero sequence current transformer 10 or by a manganin sampling resistor or other methods), so that the electromagnet 23 is electrified, the electromagnet 23 drives the push rod 42, and the push rod 42 drives the lock catch 32 to rotate, so that the circuit breaker realizes opening.

To sum up, will the utility model discloses constitute 2 utmost point products with MCB's the L utmost point, except deciliter control, still possess the required quick dropout function of earth-leakage protection, the practicality is strong, suitable popularization and application.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention should be covered by the present invention.

Claims

1. The utility model provides a miniature circuit breaker's neutral pole structure, includes the casing, installs divide-shut brake drive module, circuit board, link mechanism and circuit breaker handle in the casing, divide-shut brake drive module and link mechanism all be connected with the circuit breaker handle, link mechanism and miniature circuit breaker's other utmost point linkages, its characterized in that, divide-shut brake drive module include:

the motor set is axially provided with a driving shaft and is electrically connected with the circuit board;

the transmission gear assembly is connected with the driving shaft; a gap space is arranged between the driving shaft and the transmission gear assembly, and the transmission gear assembly is connected with the handle of the circuit breaker;

still include quick trip module, quick trip module include:

the electromagnet is arranged at the side end of the motor set and is electrically connected with the circuit board;

and the head end of the push rod is axially connected with the electromagnet, the middle part of the push rod is arranged in the gap space, and the tail end of the push rod is in touch connection with the transmission gear assembly or in touch connection with the connecting rod mechanism.

2. The neutral pole structure of a small size circuit breaker as claimed in claim 1, further comprising a driving lever, a middle portion of the driving lever being hinged to the housing, one end of the driving lever being connected to the push rod, and the other end thereof being in contact with the driving gear assembly.

3. The neutral pole structure of a small size circuit breaker as claimed in claim 2, wherein a connection hole is formed at a connection end of the driving lever and the push rod, the electromagnet is axially arranged perpendicular to the driving shaft, the push rod is L-shaped, one end of the push rod is axially connected to the electromagnet, and the other end thereof is inserted into the connection hole.

4. The neutral pole structure of a miniature circuit breaker as claimed in claim 1, wherein said linkage mechanism comprises a latch, a trip, a tension spring and a U-shaped rod, a stationary contact assembly and a movable contact assembly electrically connected to the circuit board are provided in the housing, said stationary contact assembly is mounted on the housing, said latch, trip and movable contact assembly are hinged on the housing, the side end of the movable contact assembly is connected to the housing through said tension spring, one end of said U-shaped rod is connected to the trip, and the other end is connected to the handle of the circuit breaker;

the lock catch is touched to rotate so as to unlock the jump buckle, the jump buckle bounces off, and the moving contact component is separated by the tension spring.

5. The neutral pole structure of a miniature circuit breaker as claimed in claim 4, wherein a transmission boss is provided below said circuit breaker handle, a through hole is provided in the middle of said transmission boss, one end of said U-shaped rod is inserted into said through hole to realize the connection with said circuit breaker handle, a connection boss is provided above said transmission gear assembly, said connection boss is in touch connection with said transmission boss.

6. The neutral pole structure of a small size circuit breaker according to claim 4, wherein the end of the push bar is touch-coupled with the latch.

7. The neutral pole structure of a small size circuit breaker according to claim 2, wherein the driving gear assembly includes a bevel gear, a face gear, a spur gear and a final spur gear, the bevel gear is axially coupled to the driving shaft, the bevel gear is engaged with the face gear, the spur gear is coaxially disposed above the face gear, the final spur gear is engaged with the spur gear, a stopper is disposed below the final spur gear, and an end of the driving lever is in contact with the stopper.

8. The neutral pole structure of a small size circuit breaker according to claim 7, wherein the spur gear is integrally designed with the face gear or is integrally hinged.

9. The neutral pole structure of a small size circuit breaker as claimed in claim 7, wherein the breaker handle includes a connecting portion coaxially installed on the last stage spur gear and a handle portion extending outside the case, and a square shaft hole is provided above the connecting portion for coaxially connecting the other pole breaker handles.

10. The neutral pole structure of a small size circuit breaker according to claim 9, wherein a return torsion spring is installed above the connection portion of the breaker handle; and a spring for pushing the push rod and the movable iron core to reset is arranged in the electromagnet.

11. The neutral pole structure of a miniature circuit breaker according to any one of claims 1 to 10, wherein said housing comprises a bottom frame, a middle frame and an upper cover plate connected in sequence, said opening/closing driving module, said quick release module, said terminal set and said circuit breaker handle are mounted between said bottom frame and said middle frame, and said circuit board is mounted between said middle frame and said upper cover plate.

12. The neutral pole structure of a miniature circuit breaker as claimed in claim 11, wherein the bottom frame is provided with a lower support platform protruding upward at both sides of the driving shaft corresponding to the position of the push rod, the upper surface of the lower support platform is provided with a lower arc-shaped cavity corresponding to the diameter of the push rod, the middle frame is provided with an upper support platform protruding downward at the position corresponding to the position of the push rod, the lower surface of the upper support platform is provided with an upper arc-shaped cavity corresponding to the diameter of the push rod, and the push rod is disposed between the upper arc-shaped cavity and the lower arc-shaped cavity.

13. The neutral pole structure of claim 10, wherein a position sensor is disposed on the circuit board, a positioning block for touching the position sensor to detect the position is disposed on the connecting portion of the handle of the circuit breaker, the positioning block abuts against one pin of the torsion spring, and the other pin of the torsion spring abuts against the inner wall of the housing.

14. The neutral pole structure of a miniature circuit breaker as recited in claim 11, further comprising a zero sequence current transformer electrically connected to the circuit board, wherein the bottom frame, the middle frame and the upper cover plate are provided with notch holes for mounting the zero sequence current transformer.