When changing the winding wiring mode to change the motor, sometimes the speed of the asynchronous motor is not compatible with the mechanical equipment being dragged. If there is no motor with suitable speed, the method of changing the number of poles of the motor can be used to change the speed of the motor to adapt to the needs of the mechanical equipment. When the motor is changed to a pole, it is generally necessary to re-change the windings, re-determine the number of wires per slot and the wire size, etc., which often causes unnecessary waste. If some necessary measures are taken, such as changing the wiring method of the windings, the purpose of the pole change can be achieved. However, in this way, certain conditions should be met.
1. The conditions required to change the winding wiring mode must be met. The stator, the number of rotor slots and the number of poles are adapted to the stator, the number of rotor slots and the number of poles are matched. The following relationship must be met: Z-set-Z-fixed ZZ±1 fixed-Z-turn s--the number of rotor slots; P-pole number.
When changing the motor speed, it is not advisable to make the motor speed difference before and after the change too large. According to the preliminary practice, the wiring is changed to change the pole. It is easier to increase the number of poles than to reduce the number of poles. It is difficult to achieve a good result by multiplying the number of poles. Usually the two poles are changed to four poles, the four poles are changed to six poles, the six poles are changed to eight poles, etc., and it is easy to achieve good results.
c. To change the number of poles, consider the relationship between capacity and speed. When changing the number of poles of the motor, it must be considered that the motor capacity is approximately proportional to the speed. When the motor is changed from a low speed to a high speed, its capacity can be increased, but the capacity of the motor cannot be increased in proportion to the rotational speed due to the limitation of the yoke magnetic flux. When the motor is changed from high speed to low speed, its capacity is reduced. Due to changes in the heat dissipation conditions of the motor, the capacity reduction value is greater than the ratio of the speed reduction. Therefore, when changing the number of poles of the motor, it is necessary to pay attention to whether the capacity after the pole change is suitable for the mechanical equipment to be used.
Practice has proved that the motor can be changed to the pole only if the above three conditions are met, otherwise the number of poles of the motor will be changed. It will also be difficult to achieve the required number of revolutions.
2. Change the winding wiring mode to change the pole. 2.1 Original technical data Harbin Guoyuan Public Facilities Co., Ltd. Li Xiaofeng slot number Z turn = 47 slot, stator core outer diameter D outer = 493mm, stator core inner diameter D = 327111111. Stator core length L=260mm. Stator winding technical data: double-layer winding, coil pitch YF11, number of turns per winding W=7åŒ, wire diameter The number of common three-phase winding common coil group is mx2p=3x4= 12 The number of common coil groups per phase winding is (mx2p) / m = (3x4) / 3 = 4 The number of common coil groups per branch is (mx2p) / (mxa) = (3x4) / (3x4) = l The number of coils connected in series in each coil is Z = / (mx2p) = 60 / (3x4) = 5 windings per phase winding W1: = Wx5 = 7x5 = 35 åŒ 2.3 using the original winding to change 2P = 6 Because the number of stator slots of the motor is Zs=60. The number of rotor slots is Z=47, and the number of pole pairs is 2p=6. It is calculated that: Z-set-Z turn=6047=13 (0.±1, ±6,6±1) After analysis, the 4-pole motor can be changed to a 6-pole motor, and the number of slots per phase for each pole of the 6-pole motor is calculated.
Therefore, it is impossible to arrange them into symmetrical three-phase fractional-slot windings, and it is impossible to use the fractional-slot winding list distribution method. To deal with such fractional-grooves, a method in which vacant partial winding components are not used is generally used. When the number of poles of the motor is 2P=6, the number of coils in the three-phase winding of the motor is mx2p=3x 6=18 groups, and the number of three-phase windings is 12 when the original 2p=4. Therefore, if the original two coil groups (10 coils) are divided into three coil groups, each of the three coils is connected into one group. And vacant one coil is not needed, so the 12 sets of coils are changed into 18 sets of coils, of which 6 coils are vacant. Their serial numbers are 10, 20, 30, 40, 50, 60, respectively, in a symmetrical 6-division space position.
Since the number of coil groups per phase is 6 groups, the motor can be connected into four types of branches: a=l.2.3.6. In the end, the choice of a is appropriate. This should be considered. If the number of branches is too small (for example, "=1", the cross-sectional area of ​​each phase winding is too small, then the current allowed by each phase winding will be reduced, and the motor capacity will be corresponding. Reduced. If the number of branches a is selected too much (for example, ot=6), the number of windings per phase will be too small, which will cause the magnetic density of each part of the motor magnetic circuit to increase, and the no-load current will increase sharply. Large, the power factor is bound to drop a lot. Therefore, when the number of branches a is selected, the number of turns per phase should be equal to or slightly larger than the number of turns per phase of the original (2P4), where a=3, and 2 coils per branch. Counting 6 sets of coils, the number of windings per phase is W: p6x7 = 42 åŒ.
For the long-distance coil, it can be regarded as the short-distance coil of Y. The table shows the effective number of turns Ki of the short-distance coefficient 1=0.988 per phase winding! >
Before changing the pole, the current of each strip is 137/4=34.25A. If the current density is kept the same as before the pole change, the current allowed by each branch is still 3425A. The current per phase winding is 34.25x3= 102.75A, the original current is 102.75/137=0.74 times. Since the output power of the motor is proportional to the magnitude of the current, the output power pte of the motor is correspondingly reduced to 0.74 times the Pd before the change, ie: p=0.74xpel=75x0.74=55kWo. Change the motor wiring by changing the winding wiring. It is an effective method to meet the requirements of the load on the speed and motor output power, and improve the utilization efficiency of the motor.
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