Research on the Stator 3D Temperature Field of a New Type of Infiltration Evaporative Cooling Motor

Evaporative cooling is a kind of cooling method used for heat dissipation of medium and large-scale power equipments. It is divided into pipes for cooling and immersion. The former is mostly used for vertical structure motors, and the latter is mostly used for horizontal structure motors.

The traditional cooling method (air cooling, hydrogen cooling, water cooling), the motor stator consists of solid insulation materials (mainly mica series) composed of the main insulation structure, and has formed a series of conventional manufacturing standards, but for infiltration evaporative cooling, bring some incompatibility The problem of avoidance m. The main reaction is that the evaporative cooling medium provides a high-quality insulation environment in the gas-liquid two-phase state while achieving normal-temperature, self-circulating evaporation cooling. This conventional stator insulation not only severely blocks the cooling medium. With the heating body - bare conductor direct heat transfer, and the evaporative cooling medium, its thickness is superfluous, it should be greatly reduced, for this purpose, the introduction of gas, liquid, solid three-state insulation material consisting of the new horizontal Motor stator insulation structure. The study of its temperature field distribution and other issues is an academic gap in the field of motors at home and abroad, and it is also an important basis for determining the design principles of this type of motor.

This article takes a 2500kW high power density, high speed rectification asynchronous generator under development as a research target. The stator of this motor is a horizontal structure, rated voltage is 710V, there are two sets of windings, one set for outputting electrical energy and one set for adjusting excitation, so that the thermal load on the stator side is many times higher than the normal asynchronous machine. The heating situation is very serious, and the motor will be installed in the cabin. The project responsible unit's local maximum operating temperature (including the copper wire inside) of the stator does not exceed 75 T: so how to control the stator temperature rise with a limited motor size , Become one of the key to the unit design. After several demonstrations of the technical solution, the design unit decided to use the best cooling immersion cooling to remove the heat from the stator.

2 new insulation structure and standard program Evaporative cooling medium is F-113, its boiling point is suitable (47 °C under normal pressure), non-inflammable, non-explosive, non-toxic, chemically stable, liquid breakdown voltage is slightly higher than the transformer oil, Is a good insulating medium. For this solid, liquid and gas three-phase electrical insulation system, Xiangtan Electrical Machinery Co., Ltd. has developed several new stator insulation structures and specifications based on the preliminary simulation calculation data provided by the Institute of Electrical Engineering of the Chinese Academy of Sciences. Among them, the ideal is: 0.2mm thick slot insulation, cancel the coil insulation, the use of electromagnetic wire insulation itself, the total thickness of the stator insulation. 3125mm, slot insulation in the flowing liquid groove between all Stator Core segments is removed, slot insulation is only arranged in the core slot to enhance the cooling effect of the coil. The magnet wire of the stator coil is a polyimide fluororesin composite film sintered wire, and the film thickness is. 375mm, 2/3 stacking sintering, one-sided insulation thickness of magnet wire is 0.1125mm. 3 Evaporative cooling stator hottest section 3D temperature field simulation 3.1 The necessity of stator temperature field simulation The rated voltage of this motor is low, The power density is large, but the stator temperature distribution is very strict. Therefore, for the feasibility of the above-mentioned stator insulation structure scheme, the temperature distribution of the stator in a local hottest section under a certain thermal load should be mainly examined, and the load capacity of the stator winding, ie, the rated current density of the stator winding, should be determined. Since the temperature distribution at each point in the actual analyzer is not possible (such as the temperature inside the core and the copper wire), it is important to theoretically calculate the stator temperature distribution correctly. In this paper, a special electromagnetic and thermal problem workstation software, EMAS, is used to simulate the three-dimensional temperature field of the stator. The calculation model for the hottest section of the stator 3.2 The immersion evaporative cooling stator seals the entire set of cavities in the cavity and is completely soaked by the liquid evaporative cooling medium charged inside. The end of the stator and the surface of the iron core are in contact with the evaporative cooling medium and the heat is taken away quickly. Therefore, the hottest section of the stator should be located in the winding in the center stator slot of the straight section. Based on this, the symmetry of the stator structure of the motor can be used as the calculation area for the three-dimensional temperature field from the half-block core, half-pitch and half-radial cores, slots, and evaporative cooling medium of the motor stator. As shown.

The upper and lower coils in the stator slot correspond to the main winding (output power) and the auxiliary winding (regulation excitation) on the stator side of the motor, respectively. There is no electrical connection between the two. According to the actual situation and knowledge of heat transfer, the following assumptions are made. :a) The hottest section of the stator windings and iron core is located in the middle of the entire core. The middle section is an adiabatic surface. The central section of the radial flow groove on both sides of the central part of the stator is an adiabatic surface; the symmetry from the circumferential direction, the groove center Both the surface and the tooth center surface are adiabatic surfaces; since the temperature rise of the stator windings is low, the resistance change due to temperature change may not be taken into account, ie the copper consumption only changes with the change of the electric load.

Note: In the figure, the axial section of the axial teeth and the yoke is the radial section of the central section of the teeth.

The solution field of the stator three-dimensional temperature field According to the theory of heat transfer, the EMAS workstation describes the solution of the temperature field in the solution domain as a vector; it is a thermal load vector corresponding to electrical and magnetic loads, including eddy current losses and copper losses.

This mathematical model takes into account the second term on the left side of the radiation heat transfer process, ie equation (1). However, the immersed evaporative cooling stator in this paper is completely immersed in the liquid evaporative cooling medium. The heat transfer process consists of heat conduction and convection heat transfer on the surface of the heat dissipation surface. There is no radiation heat transfer process. Therefore, the temperature field in this paper is calculated. Ignore this item.

In addition to the above-mentioned adiabatic surface, the surface of the evaporative cooling medium is a boiling heat exchange surface, which is treated according to the third boundary condition in the heat transfer theory. The evaporative cooling medium surface area is based on the isothermal boundary. Conditional processing.

3.3 Calculation of heat source and determination of evaporative cooling medium temperature In the solution area, the heat source is the stator loss, which is mainly composed of iron core loss (ie iron loss including eddy current loss, hysteresis loss) and electrical loss (ie copper consumption). Among them, the hysteresis loss needs to be based on the maximum magnetism in the stator teeth and yoke to check the magnetization characteristic table of the core material to obtain the corresponding loss factor of the unit weight, so as to obtain the hysteresis loss in the stator core to artificially assign the heat flux density. The method is loaded into the external thermal load vector fV in the workstation calculation model; eddy current loss and copper consumption are loaded into the calculation model by the corresponding boundary conditions calculated in the frequency domain electromagnetic field, and are automatically completed by the electromagnetic calculation module of the workstation. The actual operating temperature of the stator of the EMAS workstation using the vector motor is 50'C. Therefore, in this paper, the amount of magnetic flux A is used as the solution for the boundary value equation of the eddy current field. When the temperature field is simulated and calculated, this value will have practical basis.

It is the orthogonal symmetry line of the magnetic field, on which the second class of homogeneous boundary conditions 3/1/3/1=0 is satisfied; the heart 5\ is the parallel symmetry plane of the magnetic field, which is the first type of boundary condition, and A is the fixed value. The excitation is the rated current density in the main winding and the auxiliary winding of the stator. It is loaded axially along the stator in these two winding regions and the frequency is taken at the frequency of 60 Hz. When the AC electromagnetic field is analyzed, a mathematical model is usually established in the form of a complex number, and The parameters of the linear medium material in the field are related to the frequency of the field: D-flow, magnetic flux density, conduction current density, electric field strength, and magnetic field strength; £, /// represents dielectric constant, conductivity, and magnetic permeability, respectively;

According to the general concept of flow, if the current and magnetic current induced in the electromagnetic field are considered as the excitation source in the field, the complex model of the AC electromagnetic field is the complex number of the Poynting vector, and the loss power term is obtained by (3) After being brought into type (5), after finishing, p is obtained as the complex relative dielectric strength tensor; the complex magnetoresistance tensor is said as the angular frequency.

After solving each field quantity, the EMAS workstation uses equation (6) to calculate the eddy current losses and copper losses in the cores and windings, and loads it into the thermal load vector matrix corresponding to the electrical and magnetic loads in equation (1).

The saturation temperature of the evaporative cooling medium is determined by the heat load of the stator and the pressure inside the sealed chamber. The change in the stator heat load causes a corresponding change in the pressure in the chamber, and the temperature of the medium also changes accordingly. The determination of heat transfer coefficient and equivalent conductivity of 50MW evaporative cooling steam turbine in Xijiao substation of Shanghai The boiling heat transfer is influenced by the material and surface conditions of the heating surface, the superheat of the heating surface, the pressure of the liquid space, and the physical properties of the liquid. The influence of the factor, so the accurate boiling heat transfer coefficient is almost impossible to get. In the study of engineering thermal problems, a large number of solution fields in boiling fluids under various physical conditions often contain a variety of insulating materials, such as slot insulation, magnet wire insulation, winding insulation, etc. Their geometric dimensions are relatively Other media areas are particularly small, so to avoid over-calculation or over-dimensioning of element sizes, we use the equivalent conductivity coefficient to handle their heat transfer calculations. 31. Through heat transfer analysis, we can see that the equivalent heat transfer coefficient Simulation results and results for 3.5 stator temperature field Since the motor will be used in a space-constrained cabin, significantly reducing the generator volume is another key to the design of the unit. In the motor design, to increase the stator line load, that is, to increase the stator current density under a certain copper wire material can reduce the size of the motor, but at the same time to ensure that the motor in the normal operation, the stator local temperature can not exceed 75 degrees C. Therefore, reasonably determining the stator rated current density of this generator is the purpose of this temperature field simulation. After calculation, it is finally determined that the rated current density on the stator side (including the main and auxiliary windings) should not exceed 7 A/mm2 in order to meet the design and operation requirements of the motor. The simulation results of the three-dimensional temperature field of the stator at current densities of 7 A/mm2 and 11 A/min2 are shown in (a) and (b), respectively. A partial enlarged view of the temperature distribution in the coil insulation and inter-layer insulation of the stator winding at a current density of 7 A/mm2 is given.

As can be seen from the above figure, the hottest section of the immersion evaporative cooling stator is located in the main winding below the slot wedge. This is because the entire stator is seated in the sealed cavity. From the enthalpy to the low, the stator core yoke and the teeth are soaked in evaporative cooling. Simulation tests and results analysis of the evaporative cooling stator on the bottom surface of the groove wedge and the cavity wall were carried out to verify the rationality of the insulation design of the stator and the reliability of the operation. In order to verify the correctness of the simulation results of the temperature field presented in this paper. , Xiangtan Electric Co., Ltd. uses two sets of two wire test wire to make stator stator windings, namely the main winding and the auxiliary winding. The test coils that are wound are embedded into the groove of the E-type analog core, and the coil interlayer mat With a 1mm thick layer insulation and then wedges, the groove size of the E-type analog core is made to fit the design dimension of the stator slot in the electromagnetic scheme of the actual unit. A thermocouple, a thermocouple, is embedded between the layers of the coil and between the coil insulation (or magnet wire) and the slot insulation (or wall).

The stator model is placed in the container of the high pressure test apparatus, sealed and evacuated, and then slowly poured into the F-113 cooling medium until the entire stator model is completely soaked. The two analog coils with different wire gauges are led out from the conductive screw to two voltage regulators. The thermocouple is led from the flange seal to a standard meter showing the temperature and is connected to a meter that measures current and voltage. The specific test process is implemented as follows: At the same time, the input currents of the two voltage regulators are adjusted so that the current density input to the stator analog coil reaches 7 A/mm2, the stability is 1 h, and the temperature at each point under the current density is measured. After that, the current density of the stator analog coil reached 9 A/mm2, 11.5 A/mm2, and 13 A/mm2 respectively, and the temperature was stable at 1 h.

When the test current density is 7A/mm2, the measured temperature results in the analog coil are listed in Table 1, and the simulation calculation results of the same position are listed for comparison. As can be seen from the table, the calculated value and the distribution of measured values ​​are consistent, the maximum error between the two is 20%, which is in accordance with the thermal calculation error of the project, and the measured value is less than the calculated value. Therefore, the three-dimensional temperature field used in this paper The calculation method is feasible and the simulation result has great value. For dense contact, the cooling medium cannot enter the space, and the slot wedges listed in Table 2 below show the stator insulation structure scheme in which the over-negative contact with the cooling medium is sufficient and the temperature is lowest. The rated current density is directly contacted by the cooling medium. The maximum temperature difference occurs when the current density is 7A/mm2. The maximum temperature of the stator is 73.57°C, which corresponds to the temperature between the winding layers and the cooling medium at the time of operation of 13A/mm2. It is 9.4°C. Ask for and leave a certain margin. This simulation of the temperature profile shows that the adiabatic equation used for the immersion evaporative cooling stator proposed in the paper is consistent with the expected estimation of the hottest section of the stator. The edge structure and stator rated current density are reasonable and feasible.

The heat generated by the main winding can only be transmitted to the evaporative cooling medium around it through the stator teeth, and the magnetic density in the stator teeth is large and the heat load itself is high, and the skin effect of the current in the stator windings forms a slot. The phenomenon of heat concentration in the main winding under the wedge is close to the auxiliary winding of the stator iron yoke. The heat is transmitted quickly relative to the main winding. However, because the copper loss is nearly 8 times greater than the iron loss, the temperature of the stator tooth is higher than that of the stator. Higher, the heat load of the stator core yoke is relatively small, and the test result of heat under the charge condition. It can be seen that the temperature in the stator insulation of the stator model exceeds the rated load (7A/mm2) of 28.6% (9A/mm2), 64.3% (11.5A/mm2), 85.7% (13A/mm2), etc. No more than 75°C; except for the copper inside the wire, the temperature rises less than 10°C compared with the operating temperature of the cooling medium. The temperature distribution of the coil is relatively uniform, and there is no insulating layer temperature due to no coil insulation. Drop, comparison of the temperature distribution of the insulation structure between the magnet wire and the rated load of Table 1. No. Insulation Temperature Measurement Winding Interlayer Coil Insulation Intrinsic/'c Measured Value/°C Relative Error/% Calculated Value/X: Measured Value/ X: relative error/% calculated value/r measured value/'c relative error/% Table 2 Test result of heat transfer performance when the new stator insulation structure is overloaded Position No. Current density A/mm2 Winding layer temperature/"C magnet wire Insulation outside temperature / 'C liquid temperature rc 5 Conclusion This paper through a three-dimensional temperature field simulation calculations, model experiments, the proposed new type of infiltration evaporative cooling asynchronous generator stator insulation system has systematically studied and successfully solved the gas, Liquid and solid three-phase insulation system default Determining the temperature distribution problem, the following conclusions: Simulation infiltration evaporative cooling within a three-dimensional temperature field arithmetic error from the scope of sound, should be promoted.

For the immersion evaporative cooling stator, a new type of stator insulation scheme is adopted to increase the current density, and the motor can be greatly reduced in size under the premise of reliable operation. The utilization rate of the motor material can be increased to the highest water-cooled motor at present. The level, or higher.

The new stator insulation scheme realizes the expected insulation and heat transfer effects, and can provide some basis for the design of the stator insulation structure of the same type of unit in the future.