Refrigerant pump drainage non-return structure and refrigerant pump

Abstract

The invention discloses a refrigerant pump liquid discharge non-return structure and a refrigerant pump, the refrigerant pump liquid discharge non-return structure comprises a fixed scroll plate and a movable scroll plate, the fixed scroll plate and the movable scroll plate are engaged to form a pump liquid structure, the fixed scroll plate is provided with an inner liquid discharge port communicated with the pump liquid structure, the inner liquid discharge port is connected to an outer liquid discharge port through a liquid discharge flow channel, and the outer liquid discharge port is communicated with the fixed scroll plate. The liquid discharging flow channel comprises a main flow channel and an auxiliary flow channel, the main flow channel extends from the inner liquid discharging port to the outer liquid discharging port, a first opening and a second opening which are communicated with the main flow channel are formed in the two ends of the auxiliary flow channel, the first opening is closer to the outer liquid discharging port than the second opening, and one end of the auxiliary flow channel is obliquely connected to the main flow channel and forms a reverse inlet through the first opening; the other end of the auxiliary runner is connected to the main runner after being bent in an arc mode and forms a reverse outlet through the second opening. The liquid discharging flow channel can prevent most liquid from flowing back from the liquid discharging opening, when the refrigerant pump works, the liquid discharging non-return structure does not move, faults and damage are not prone to occurring, and the problem that in the prior art, a movable part of a liquid non-return valve is prone to damage is solved.

Description

Technical Field

[0001] The invention is used in the field of refrigerant pumps, and in particular relates to a refrigerant pump discharge check structure and a refrigerant pump. Background Art

[0002] Refrigerant pumps can be used to pump liquid and gas-liquid mixed refrigerants. Due to the complex and diverse states of the pumped refrigerants, higher requirements are placed on the structural design of the refrigerant pumps.

[0003] In the prior art, a vortex pump is generally used as a refrigerant pump, wherein before the compression chamber is connected to the discharge port, the volume of the compression chamber reaches the minimum and the liquid pressure is the maximum. After the compression chamber is connected to the discharge port, the flow area between the two gradually increases, and the liquid pressure becomes smaller than before, and the amount of liquid that needs to be discharged cannot be discharged in time, resulting in liquid reflux. Because the liquid is an incompressible fluid, the liquid pressure will increase when the suction chamber finishes absorbing liquid and when the compression chamber starts to discharge liquid, resulting in pressure pulsation, which will cause vibration and noise of the machine, affecting the stability of the fluorine pump, which is the difficulty in the application of the vortex pump. Summary of the invention

[0004] The object of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a refrigerant pump discharge check structure and a refrigerant pump.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] In a first aspect, a refrigerant pump discharge check structure comprises a fixed scroll and a movable scroll, wherein the fixed scroll and the movable scroll are meshed to form a pump liquid structure, the fixed scroll is provided with an inner discharge port connected to the pump liquid structure, the inner discharge port is connected to an outer discharge port via a discharge channel, the discharge channel comprises a main channel and a secondary channel, the main channel extends from the inner discharge port to the outer discharge port, and two ends of the secondary channel form a first opening and a second opening connected to the main channel, the first opening is closer to the outer discharge port than the second opening, one end of the secondary channel is obliquely connected to the main channel and forms a reverse inlet through the first opening, and the other end of the secondary channel is connected to the main channel after being bent in an arc shape and forms a reverse outlet through the second opening.

[0007] In combination with the first aspect, in some implementations of the first aspect, the drainage channel is provided with a plurality of the secondary channels.

[0008] In combination with the first aspect and the above-mentioned implementations, in some implementations of the first aspect, the secondary flow channel includes a left secondary flow channel and a right secondary flow channel symmetrically arranged on both sides of the main flow channel, and the left secondary flow channel and the right secondary flow channel form a heart-shaped structure.

[0009] In combination with the first aspect and the above-mentioned implementations, in certain implementations of the first aspect, the back end surface of the fixed scroll plate is provided with a groove and a cover plate, the groove connects the inner drainage port and the outer drainage port, and the cover plate covers the groove and defines the drainage channel through the groove.

[0010] In a second aspect, a refrigerant pump comprises the refrigerant pump liquid discharge check structure described in any implementation of the first aspect.

[0011] In combination with the second aspect, in certain implementations of the second aspect, the number of meshing turns of the spiral teeth of the fixed scroll and the orbiting scroll is 1 to 1.5 turns.

[0012] In combination with the second aspect and the above-mentioned implementations, in some implementations of the second aspect, a frame is further included, a back pressure chamber is formed between the movable scroll and the frame, the movable scroll can float axially under the pressure of the back pressure chamber, and a floating gap is formed between the movable scroll and the fixed scroll, and the floating gap is 0.02-0.20mm.

[0013] In combination with the second aspect and the above-mentioned implementations, in some implementations of the second aspect, it also includes a crankshaft, which is installed on the frame, the eccentric portion of the crankshaft is connected to the movable scroll, and self-lubricating bearings are provided between the crankshaft and the frame and between the eccentric portion of the crankshaft and the movable scroll, the surface of the self-lubricating bearing is provided with a Teflon coating, and metal particles are provided in the Teflon coating.

[0014] In combination with the second aspect and the above-mentioned implementations, in certain implementations of the second aspect, the fixed scroll disk is provided with a pressure relief hole connected to the compression chamber of the pump liquid structure, and a one-way pressure relief valve is provided at the pressure relief hole. The one-way pressure relief valve includes a pressure relief flange, a spring and a valve plate. The fixed scroll disk is provided with a valve plate mounting groove at the outer end of the pressure relief hole, and the valve plate is arranged in the valve plate mounting groove. The pressure relief flange is connected to the fixed scroll disk through fasteners, and the pressure relief flange is provided with a through hole communicating with the pressure relief hole, and the spring is supported between the valve plate and the pressure relief flange.

[0015] In combination with the second aspect and the above-mentioned implementations, in some implementations of the second aspect, it also includes a stator and a rotor, the stator includes a stator core and a stator coil, the stator coil is wrapped with an insulating layer, and the stator coil is provided with at least two layers of electric field relaxation layers near the stator core.

[0016] One of the above technical solutions has at least one of the following advantages or beneficial effects: during the operation of the refrigerant pump, when the compression chamber of the pump liquid structure is connected to the inner liquid discharge port, the liquid enters the liquid discharge channel through the inner liquid discharge port and is finally discharged from the outer liquid discharge port. After that, as the area of ​​communication between the compression chamber and the inner liquid discharge port increases, the liquid discharge pressure decreases. At this time, part of the liquid has a tendency to reflux, and the discharged liquid enters the inner liquid return port. At this time, the return liquid flows back from the main channel and the secondary channel respectively, wherein the liquid in the secondary channel flows in through the reverse inlet, flows through the arc-shaped curved section, and then merges into the main channel from the reverse outlet. The liquid in the reverse secondary channel forms a barrier to the liquid in the main channel, thereby effectively preventing most of the liquid return of the pump body. The liquid discharge channel in the present invention flows smoothly when discharging liquid, and is subject to resistance in the opposite direction. In the technical solution of the present invention, the liquid discharge channel can prevent most of the liquid from refluxing from the liquid discharge port, and when the refrigerant pump is working, the liquid discharge check structure does not move, and is not prone to failure and damage, thereby solving the problem that the movable parts of the liquid check valve are easily damaged in the prior art.

[0017] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0019] Figure 1 It is a schematic structural diagram of an embodiment of a refrigerant pump of the present invention;

[0020] Figure 2 yes Figure 1 A schematic structural diagram of a liquid discharge check structure in one embodiment shown;

[0021] Figure 3 It is a schematic diagram of the discharge process of an embodiment of the discharge check structure of the present invention;

[0022] Figure 4 It is a schematic diagram of the liquid return process of an embodiment of the liquid discharge check structure of the present invention;

[0023] Figure 5 It is a schematic diagram of the matching structure of a fixed scroll and a movable scroll in one embodiment of a refrigerant pump of the present invention;

[0024] Figure 6 It is a schematic structural diagram of a one-way pressure relief valve in a closed state according to an embodiment of the present invention;

[0025] Figure 7 It is a schematic structural diagram of a one-way pressure relief valve in a fixed open state according to an embodiment of the present invention;

[0026] Figure 8 It is a schematic structural diagram of an embodiment of a stator of the present invention;

[0027] Fig. 9 yes Figure 8 A partial enlarged schematic diagram in the middle. DETAILED DESCRIPTION

[0028] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0029] In the present invention, if directions (up, down, left, right, front and back) are described, it is only for the convenience of describing the technical solution of the present invention, and does not indicate or imply that the technical features referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, it cannot be understood as a limitation of the present invention.

[0030] In the present invention, "several" means one or more, "multiple" means more than two, "greater than", "less than", "exceed" and the like are understood to exclude the number itself; "above", "below", "within" and the like are understood to include the number itself. In the description of the present invention, if there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0031] In the present invention, unless otherwise clearly defined, the words "set", "install", "connect" and the like should be understood in a broad sense, for example, they can be directly connected or indirectly connected through an intermediate medium; they can be fixedly connected or detachably connected or integrally formed; they can be mechanically connected or electrically connected or able to communicate with each other; they can be the internal connection of two elements or the interaction relationship between two elements. Those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0032] See also Figure 1-Figure 4The embodiment of the present invention provides a refrigerant pump discharge check structure, including a fixed scroll 100 and a movable scroll 200, the fixed scroll 100 and the movable scroll 200 meshing to form a pump liquid structure, capable of conveying liquid, gas, or gas-liquid mixed refrigerant, the fixed scroll 100 is provided with an inner discharge port 101 connected to the pump liquid structure, the inner discharge port 101 is connected to an outer discharge port 103 through a discharge flow channel 102, the discharge flow channel 102 includes a main flow channel 104 and a secondary flow channel 105, the main flow channel 104 and the secondary flow channel 105 are connected to each other, and the main flow channel 104 and the secondary flow channel 105 are connected to each other. The channel 104 extends from the inner drainage port 101 to the outer drainage port 103, and the two ends of the secondary channel 105 form a first opening 106 and a second opening 107 that are connected to the main channel 104. The first opening 106 is closer to the outer drainage port 103 than the second opening 107. One end of the secondary channel 105 is obliquely connected to the main channel 104 and forms a reverse inlet through the first opening 106. The other end of the secondary channel 105 is connected to the main channel 104 after being bent in an arc shape and forms a reverse outlet through the second opening 107.

[0033] Combination Figure 1-Figure 4 During the operation of the refrigerant pump, the fixed scroll 100 and the movable scroll 200 mesh with each other to form a pump liquid structure, and the pump liquid structure continuously transports the refrigerant in liquid, gas, and gas-liquid mixed state to the inner discharge port 101. When the compression chamber of the pump liquid structure is connected to the inner discharge port 101, the liquid enters the discharge channel 102 through the inner discharge port 101 and is finally discharged from the outer discharge port 103. After that, as the communication area between the compression chamber and the inner discharge port 101 increases, the discharge pressure decreases. At this time, part of the liquid has a tendency to reflux, and the discharged liquid enters the inner return liquid port. At this time, the return liquid refluxes from the main channel 104 and the secondary channel 105 respectively. Among them, the liquid in the secondary channel 105 flows in through the reverse inlet, flows through the arc-shaped bending section, and then merges into the main channel 104 from the reverse outlet. The liquid in the reverse secondary channel 105 forms a barrier to the liquid in the main channel 104, thereby effectively preventing most of the return liquid of the pump body. The discharge channel 102 of the present invention allows for smooth flow when discharging liquid, but encounters resistance when discharging liquid. In the technical solution of the present invention, the discharge channel 102 can prevent most of the liquid from flowing back from the discharge port, and when the refrigerant pump is working, the discharge check structure does not move, and is not prone to malfunction and damage, thus solving the problem of easy damage to the movable parts of the liquid check valve in the prior art.

[0034] Among them, see Figure 3 , Figure 4 The discharge channel 102 is provided with one or more secondary channels 105 .

[0035] Further, see Figure 2 , Figure 3 , Figure 4The secondary flow channel 105 includes a left secondary flow channel 105 and a right secondary flow channel 105 symmetrically arranged on both sides of the main flow channel 104. The left secondary flow channel 105 and the right secondary flow channel 105 form a heart-shaped structure. A plurality of secondary flow channels 105 are arranged along the extension direction of the main flow channel 104. During operation, when the compression chamber of the pump liquid structure is connected with the inner liquid discharge port 101, the liquid is discharged through the inner liquid discharge port 101, the main flow channel 104 and the secondary flow channel 105. After that, as the communication area between the compression chamber and the liquid discharge port increases, the liquid discharge pressure decreases. At this time, part of the liquid has a tendency to flow back, and the discharged liquid enters the outer liquid discharge port 103. At this time, the return liquid is divided into three paths, one of which flows along the main flow channel 104, and the other two flows along the secondary flow channels 105 on both sides. They meet at point a, and the liquid in the secondary flow channel 105 flows back to the main flow channel 104. The check valve 104 forms a barrier to the liquid in the main channel 104, and then a part of the liquid continues to flow in the main channel 104 to reach point b, and the return liquid is divided into three paths, one flows along the main channel 104, and the other two flow along the secondary channel 105, and meet at point c. The liquid in the secondary channel 105 forms a barrier to the liquid in the main channel 104. It has been verified by experiments that the liquid pressure at the external discharge port 103 is 5-8 times the liquid pressure at point c. The check valve structure effectively prevents most of the return liquid from the pump body.

[0036] In some embodiments, see Figure 2 The back end surface of the fixed scroll plate 100 is provided with a groove and a cover plate 108. The groove connects the inner drainage port 101 and the outer drainage port 103. The cover plate 108 shields the groove and defines a drainage channel 102 through the groove. The drainage channel 102 of this embodiment is directly formed on the back end surface of the fixed scroll plate 100, and the structure is simpler and less prone to failure and damage.

[0037] It is understandable that the discharge channel 102 may also be formed by providing an independent pipeline independent of the fixed scroll 100 .

[0038] See also Figure 1 An embodiment of the present invention further provides a refrigerant pump, comprising the refrigerant pump discharge check structure in any of the above embodiments.

[0039] In some embodiments, the refrigerant pump adopts a vortex structure in which a fixed scroll 100 and a movable scroll 200 cooperate, and the number of meshing turns of the vortex teeth of the fixed scroll 100 and the movable scroll 200 is 1 to 1.5 turns. The structural feature of the meshing of the vortex teeth is that there is a non-contact oil film seal between the movable scroll wall and the fixed scroll wall. Through a reasonable design of the turning radius, the lubricating oil between the movable scroll 200 and the fixed scroll 100 forms an oil film, and countless compression chambers are formed during the movement of the movable scroll 200 and the fixed scroll 100. The oil film formed between the compression chambers plays a role of lubrication and sealing, so that the wear of the vortex wall is very low during operation, and the fluorine pump can achieve high-speed operation. Due to the structural characteristics of the scroll, when the number of meshing turns of the scroll is less than 1, a closed compression chamber cannot be formed; when the number of meshing turns of the scroll is greater than 1.5, due to the presence of liquid and gas-liquid mixture in the conveyed material, the scroll will be broken due to excessive liquid compression force, resulting in scroll plate breakage. When the number of meshing turns is designed between 1 and 1.5, the scroll can achieve the purpose of compressing liquid, gas, and gas-liquid mixed refrigerant, and will not break due to excessive liquid compression force, so that the fluorine pump can work normally.

[0040] In some embodiments, see Figure 1 , Figure 5 The refrigerant pump also includes a frame 300, a back pressure chamber 400 is formed between the movable scroll 200 and the frame 300, the movable scroll 200 can float axially under the pressure of the back pressure chamber 400, and a floating gap 201 is formed between the movable scroll 200 and the fixed scroll 100, and the floating gap 201 is 0.02-0.20mm. When the compression chamber is mostly gas, the movable scroll 200 can float upward, and when the vortex chamber is mostly liquid, the movable scroll 200 can float downward. The floating gap 201 is set between 0.02-0.20mm, which can ensure that the movable disk can float under the action of back pressure when transmitting liquid, gas, or gas-liquid mixed refrigerant, ensuring reliable compression of the refrigerant. When the floating gap 201 is less than 0.02mm, wear and jamming are likely to occur between the movable and fixed scrolls 100, resulting in increased power of the refrigerant pump or even jamming. When the floating clearance 201 is greater than 0.20 mm, the leakage between the orbiting and fixed scrolls 100 increases, and the efficiency of the refrigerant pump decreases.

[0041] In some embodiments, see Figure 1 The refrigerant pump further comprises a crankshaft 500, which is mounted on the frame 300, the eccentric portion of the crankshaft 500 is connected to the movable scroll 200, and a self-lubricating bearing 501 is provided between the crankshaft 500 and the frame 300 and between the eccentric portion of the crankshaft 500 and the movable scroll 200, and the surface of the self-lubricating bearing 501 is provided with a Teflon coating, and metal particles are provided in the Teflon coating. The self-lubricating effect is achieved, so that the self-lubricating bearing 501 maintains wear resistance while taking into account strength, thereby improving the operating reliability of the refrigerant pump.

[0042] In some embodiments, see Figure 2 , Figure 6 , Figure 7 Because the liquid is an incompressible fluid, the liquid pressure will increase when the suction chamber finishes sucking liquid and the compression chamber starts to discharge liquid, resulting in pressure pulsation, which will cause vibration and noise of the machine. In order to ensure the stability of the refrigerant pump's delivery of liquid refrigerant, the pressure can be released from the compression chamber to the outside when the suction chamber finishes sucking liquid and the compression chamber starts to discharge liquid. One-way pressure relief valves are respectively provided in the inner and outer compression chambers of the fixed scroll 100 to reduce pressure pulsation and ensure the normal operation of the refrigerant pump. Specifically, the fixed scroll 100 is provided with a pressure relief hole 109 connected to the compression chamber of the pump liquid structure, and a one-way pressure relief valve 600 is provided at the pressure relief hole 109. The one-way pressure relief valve 600 includes a pressure relief flange 601, a spring 602 and a valve plate 603. The fixed scroll 100 is provided with a valve plate mounting groove 604 at the outer end of the pressure relief hole 109, and the valve plate 603 is arranged in the valve plate mounting groove 604. The pressure relief flange 601 is connected to the fixed scroll 100 through a fastener, and the pressure relief flange 601 is provided with a through hole 605 communicating with the pressure relief hole 109. The spring 602 is supported between the valve plate 603 and the pressure relief flange 601. The structure of the one-way pressure relief valve 600 adopts a structure of a spring 602 plus a check valve plate 603, which is suitable for liquid pressure relief and is not easy to be damaged, ensuring that the check valve plate 603 will not break under liquid pressure.

[0043] In some embodiments, see Figure 1 , Figure 8 , Fig. 9 The refrigerant pump further includes a stator 701 and a rotor 702. The stator 701 includes a stator core 703 and a stator coil 704. The stator coil 704 is wrapped with an insulating layer 705. The stator coil 704 is provided with at least two layers of electric field relaxation layers 706 near the stator core 703. The electric field relaxation layer 706 is a mixed material of resistance and electrostatic capacitance, including a mixture of conductive materials such as SiC and carbon, and dielectrics such as BaTi3, TiO2, and ZrO2. The electric field relaxation layer 706 can relax the voltage generated on the coil end side when the motor is working through the mixed material of resistance and electrostatic capacitance. At the same time, the superposition application of the double-layer electric field relaxation layer 706 can better improve the insulation of the motor.

[0044] Among them, the connection of the stator 701 is connected to the inner side of the sealed terminal fixed on the shell, and the inner side of the sealed terminal is sealed with glue to ensure good insulation. The stator lead-out terminal is connected to the inner side of the sealed terminal fixed on the shell. In order to ensure that the inner side of the sealed terminal is well insulated from liquid, gas, and gas-liquid mixed refrigerant, the inner side of the sealed terminal is sealed with glue.

[0045] In the description of this specification, the description with reference to the terms "example", "embodiment" or "some embodiments" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0046] Of course, the invention is not limited to the above-mentioned embodiments, and those skilled in the art may make equivalent modifications or substitutions without violating the spirit of the invention, and these equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A refrigerant pump discharge check structure, characterized in that: The invention comprises a fixed scroll and a movable scroll, wherein the fixed scroll and the movable scroll are meshed with each other to form a pumping structure, wherein the fixed scroll is provided with an inner discharge port connected with the pumping structure, wherein the inner discharge port is connected to an outer discharge port through a discharge channel, wherein the discharge channel comprises a main channel and a secondary channel, wherein the main channel extends from the inner discharge port to the outer discharge port, wherein two ends of the secondary channel form a first opening and a second opening connected with the main channel, wherein the first opening is closer to the outer discharge port than the second opening, wherein one end of the secondary channel is obliquely connected to the main channel and forms a reverse inlet through the first opening, and the other end of the secondary channel is connected to the main channel after being bent in an arc shape and forms a reverse outlet through the second opening.

2. The refrigerant pump discharge check structure according to claim 1, characterized in that: The drainage channel is provided with a plurality of the auxiliary channels.

3. The refrigerant pump discharge check structure according to claim 2, characterized in that: The secondary flow channel comprises a left secondary flow channel and a right secondary flow channel symmetrically arranged on both sides of the primary flow channel, and the left secondary flow channel and the right secondary flow channel form a heart-shaped structure.

4. The refrigerant pump discharge check structure according to claim 1, characterized in that: A groove and a cover plate are provided on the back end surface of the fixed scroll plate. The groove communicates with the inner liquid discharge port and the outer liquid discharge port. The cover plate shields the groove and defines the liquid discharge channel through the groove.

5. A refrigerant pump, characterized in that: The invention comprises the refrigerant pump discharge check structure according to any one of claims 1 to 4.

6. The refrigerant pump according to claim 5, characterized in that: The meshing number of the spiral teeth of the fixed scroll and the orbiting scroll is 1 to 1.

5.

7. The refrigerant pump according to claim 5, characterized in that It also includes a frame, a back pressure cavity is formed between the movable scroll and the frame, the movable scroll can float axially under the pressure of the back pressure cavity, a floating gap is formed between the movable scroll and the fixed scroll, and the floating gap is 0.02-0.20mm.

8. The refrigerant pump according to claim 7, characterized in that: It also includes a crankshaft, which is installed on the frame, the eccentric portion of the crankshaft is connected to the movable scroll, and self-lubricating bearings are provided between the crankshaft and the frame and between the eccentric portion of the crankshaft and the movable scroll, the surface of the self-lubricating bearing is provided with a Teflon coating, and metal particles are provided in the Teflon coating.

9. The refrigerant pump according to claim 5, characterized in that: The fixed scroll is provided with a pressure relief hole connected to the compression chamber of the pump liquid structure, and a one-way pressure relief valve is provided at the pressure relief hole. The one-way pressure relief valve includes a pressure relief flange, a spring and a valve plate. The fixed scroll is provided with a valve plate mounting groove at the outer end of the pressure relief hole, and the valve plate is arranged in the valve plate mounting groove. The pressure relief flange is connected to the fixed scroll through a fastener, and the pressure relief flange is provided with a through hole communicating with the pressure relief hole. The spring is supported between the valve plate and the pressure relief flange.

10. The refrigerant pump according to claim 5, characterized in that It also includes a stator and a rotor. The stator includes a stator core and a stator coil. The stator coil is wrapped with an insulating layer. The stator coil is provided with at least two electric field relaxation layers near the stator core.

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