Special purpose motor is a kind of motor, which is designed and used for specific industry characteristics.Special motors areValve electric device(referred to as: electric device).There are two standards for valve motors implemented in China, one is the technical conditions for three-phase asynchronous motors for general JB/T2195-1998 YDF2 series valve electric devices, and the other is the technical conditions for explosion-proof JB/T8670-1997YBDF2 series valve electric devices.Common special motors include household appliances motors, pump motorsVehicle motor, sewing motor, fan motor, air conditioner motor, textile motorMotor for fan, elevator motor, range hood motor, mechanical equipment motor, washing machine motor, etc.
Special motors areValve electric device(referred to as: electric device).There are two standards for valve motors implemented in China, one is the technical conditions for three-phase asynchronous motors for general JB/T2195-1998 YDF2 series valve electric devices, and the other is the technical conditions for explosion-proof JB/T8670-1997YBDF2 series valve electric devices.It can be seen from the year when the standard was issued that the YBDF2 series valve motors with explosion-proof performance are still in compliance with the national mandatory standards GB3836.1-2010 and GB3836.2-2010.The valve motor is the power input component of the electric device. Its performance is the main factor affecting the torque output technical parameters of the electric device. Its structure needs to meet the requirements of the electric device.
The electric device isElectric valveIts main function is to realize the precise control and fault protection of the valve terminal position, realize the signal feedback of the current position and load status of the valve, and complete the program control with related equipment.Valve electric deviceIt is the control unit of industrial pipeline system, widely used in petroleum, chemical industry, natural gas, metallurgy, municipal administration, power and other industrial fields[1]。
Basic characteristics of special motors
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The working characteristics of the electric device determine the basic performance of the valve motorThree phase asynchronous motorDifferent, the valve motor has the following characteristics.
(A) High starting torque;To ensure that the valve disc is seated and sealed when the valve is opened and closed under static pressure.According to the standard, the ratio of the starting torque to the rated torque of the valve motor is 3.2 and 5.0. The former basically continues the dynamic parameters of the YDF motor designed by our country since the 1970s, while the design of the latter refers to the motor parameters for Limitorque electric devices imported from abroad in the early 1980s;
(B) High starting current;Due to the large starting torque, the corresponding starting current is large.The starting current of the above two valve motors is 7 times of the rated current, so full attention should be paid to the selection of electrical control components;
(C) Short-time working system;According to the working characteristics of the valve with limited travel, the valve motor works in a short time.The different load states make the valve motorRated working timeIt is also different. Generally, the travel time of one operation is 15~30min.Cooling structure is not considered in the design of valve motor;
(D) Small moment of inertia;In the design, the rotor diameter tends to be slender as far as possible to reduce the moment of inertia, thus reducing the impact of the valve disc on the valve seat when the valve is seated.The above performance should be considered in the electromagnetic design of valve motor and the structural design of rotor and stator, while the overall structural design of motor is related to the structure of valve electric device, so the following issues should also be considered:;
(E) Explosion proof performance;The structural design of the valve motor should consider the explosion-proof function or facilitate the derivation of explosion-proof function to meet the needs of explosion-proof valve electric device, because someElectric valveIt is required to work in explosive gas environment.
In order to adapt to the explosion-proof structural characteristics of electric devices, all explosion-proof valve motors are not equipped with independent external wiring devices, so they cannot be used in explosion-proof places alone.The explosion-proof valve motor has explosion-proof function only after it is combined with the explosion-proof electric device, and its explosion-proof test and review shall also be carried out together with the explosion-proof electric device after assembly.The enclosure of the motor and the control chamber of the explosion-proof electric device form an explosion-proof main chamber.
Flange structure with front cover
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In general, the connection size specified in the standard is adopted for domestic self-designed valve electric devices, namely the standards given in JB/T2195-1998 and JB/T8670-1997 mentioned aboveFlange connectionType.
The connection type of the valve motor used for the electric device with imported foreign technology is different from the Chinese standard, which is usually the structural dimension given by the electric device manufacturer.
1. Axial unfixed type of front cover
The casing only restricts the radial position of the front end cover by matching with the explosion-proof joint surface of the front end cover, while the axial direction of the front end cover is not fixed (there is a jackscrew in the actual structure to ensure that it is not loose during transportation).The rear of the casing is not connected, and the rear bearing hole is directly machined on the casing.The characteristics of this structure are:;It is convenient to adjust the position of the outlet sleeve on the flange seam plane.
2. The front end cover is fixed axially and has the rear end cover type
There are two types of this structure, which can be divided into A and B.The outlet sleeve of structure A is located on the plane of flange locating spigot, and the outlet sleeve of structure B is located on the plane outside the flange spigot.
In the structural design, the diameter of the valve motor shaft head is less thanordinaryelectric machinery.In order to avoid the above phenomenon, the cantilever length of the motor shaft head can be relatively reduced so as to reduce the elastic deformation that may occur during its operation.At the same time, it also ensures that the actual flameproof joint surface under the working state of the motor meets the standard requirements[2]。
Flange structure without front cover
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Some electric devices have considered the installation position of the valve motor stator core in the design, that is, the built-in type or the type without front cover flange, which is often seen in foreign electric device products.
Multi turn electric deviceIt is a well-known brand of electric device.Although the intelligent electric device of Rotork Company no longer adopts this structure, it is simply introduced because of its completely different characteristics from other products and still has applications.
The rotor shaft of the motor and the transmission worm of the electric device are designed as a whole, and the supporting points in the main box areneedle bearingThe supporting point on the rear end cover is the ball bearing. This structure is called "coaxial direct connection" in China.The power line of the valve motor can be easily led into the control chamber of the electric device.When the electric device is working, the output torque of the worm gear will make the worm generate axial force and compress the disc spring used for torque control. Therefore, the rotor will have a certain amount of two-way axial displacement when the torque switch of the electric device acts. This feature is not found in other electric devices.
As far as the overall structure of the electric device is concerned, it is a very creative design.It simplifies the transmission structure of the whole machine, facilitates the preloading and adjustment of the butterfly spring, and coordinates the overall appearance of the product.Rotork's later products still maintain this style.Its limitations are:;The motor and worm shaft are too long, the combination precision with the rotor is difficult to control, and the force on the worm shaft isStatically indeterminate structure。When the valve is opened, the fastening screws of the casing, rear end cover and bearing gland must bear the axial force of the worm, so the output torque specification of the electric device of this structure should not be too large.
summary
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Through the analysis and comparison of the above several typical valve motor structures, the following points can be concluded:
(1) The structural design of the valve motor is restricted by the overall structure of the electric device, such as the transmission, manual/electric switching structure, etc., especially the structural design of the connecting flange and incoming line of the motor;
(2) The structural design of the valve motor should give consideration to the explosion-proof performance and protective performance, because most of the valve motors have explosion-proof function only after being combined with the explosion-proof electric device. At this time, the control chamber of the explosion-proof electric device and the shell of the explosion-proof valve motor form an explosion-proof main chamber;
(3) The explosion-proof level of valve motors in China is mostly ExdIIBT4Gb, and many operating conditions require the explosion-proof level of electric devices to be ExdIICT4Gb or ExdIICT6Gb, so the explosion-proof performance of valve motors is one of the factors that restrict the explosion-proof level of electric devices;
(4) Valve motors with different structure types adapt to different output torque specifications of electric devices. Some are only suitable for small torque specifications, so their power ranges are small;
(5) The valve motor with front cover structure shall be convenient for single machine detection, storage and transportation. The valve motor without front cover structure shall take measures to protect the stator coil, flameproof surface and other parts during storage and transportation, and shall provide methods and measures for single machine detection (before assembly with the electric device);
(6) The power range of the valve motor is large, but the amount of each specification is limited, so the valve motor with standard connection size and outlet position can relatively reduce the manufacturing cost of the product when designing the electric device;
(7) The outdoor grade specified in the Chinese valve motor standard is lower than the standard outdoor grade of electric device, which affects the improvement of outdoor performance of electric device to some extent.
To sum up, the structural design of the valve motor and the overall structure of the electric device restrict each other.Therefore, studying and improving the structure of the valve motor to make it more reasonable will play a positive role in improving the overall performance of the electric device[3]。
