Old engineer talks about the phase and slot potential star diagram of the motor
Colleagues S and Ms. discuss the winding scheme of a certain type of motor, so as to effectively weaken the electromagnetic noise. When it comes to the phase band problem, the small S is somewhat awkward, saying that he has always had the concept of 60 or 120 degree phase band, but the phase band problem is not as clear as the fractional or sinusoidal winding.
Because the types of motors are numerous and complicated, the motor windings are mostly standard 60-degree phase belts. Even the 120-degree phase-band windings are rarely involved. The non-standard phase belts and related problems are naturally not much concern.
In view of the above situation, Ms. is considered to be necessary to talk about the phase band and its selection. In order to ensure the symmetry of the three-phase winding potential or the magnetic potential synthesis vector and the maximum absolute value and the minimum harmonic content, non-standard phase-band windings are usually used. For the best option.
When talking about the phase band and its selection, it is necessary to study the slot potential star map. When the potentials of the inner conductors of the armatures on the armature are sinusoidally varied, respectively, these vectors form a radiation star diagram called the slot potential star map.
Slot potential star diagram drawing method
Figure 1 shows the circumferential distribution of the inner conductor of a three-phase synchronous generator in the stator slot. The pole number is 2p=4 and the number of slots is Z=36. The step of drawing the slot potential star diagram is as follows:
1) slot electrical angle α1
When the distance between two adjacent slots is expressed by an electrical angle, it is called the slot electrical angle. Since the entire armature circumference is 360° mechanical angle, when calculated by electrical angle, the range of a pair of pole distances is equal to 360° electrical angle. When the motor has p-pair, the armature circumference should be p360° electrical angle, therefore, the slot electrical angle is
11=p360°/Z......(1)
Where p is the pole pair number of the motor and Z is the number of armature slots. For the motor shown in Figure 1, it is α1=p360°/Z=2×360°/36=20°
2) Draw a slot potential star map
Assuming that the magnetic density of the magnetic pole magnetic field is distributed sinusoidally along the circumference of the air gap and the rotor rotates at a constant speed in the counterclockwise direction, the induced potential of the conductors in the slots of the stator will change sinusoidally with time.
Since the grooves are spatially different from each other by an electrical angle of α1, the potentials of the respective conductors also differ from each other by an angle of α1 in time phase. As shown in a) of Fig. 2, assuming that the conductor potential of the No. 1 slot is represented by a vector 1, the conductor potential vector 2 of the No. 2 slot is delayed by 20° from the vector 1 under the steering of the figure. The same vector 3 lags 20° from vector 2. Slot potential star map physical meaning
It can be seen from a) in Fig. 2 that vectors such as 19, 20, 21, etc. coincide with vectors of 1, 2, 3, etc., respectively, because they are respectively at corresponding positions under the magnetic poles, so their induced potentials are the same. Phase.
In general, for each pole of each phase of the integer slot winding, if the motor has p-pair, there are p overlapping slot potential stars. Generally speaking, when p and Z have the greatest common divisor t, there are t coincident slot potential stars. For the synchronous generator shown in Figure 1, the greatest common divisor of p and Z is 2, so there are two coincident slot potential stars.
Non-standard phase band selection and compliance principles
When studying low harmonic windings to reduce electromagnetic noise, the electrical angle occupied by each phase winding in the 360° electrical angular space is not limited to 60° and 120° as shown in Figure 2, and the variable pole multi-speed motor winding is often used. Non-standard phase bands other than the 60° and 120° phase bands.
Regardless of how the winding phase band is selected, the following principles must be followed:
Under a certain number of conductors, a larger fundamental potential and a fundamental magnetic potential are obtained;
1 In the three-phase winding, for the fundamental wave, the three-phase potential and the magnetic potential must be symmetrical, that is, the three phases are equal in size and the phase difference is 120°; and the three-phase impedance is also required to be equal;
2 The potential and the magnetic potential waveform are close to the sine wave, and the harmonic components in the potential and the magnetic potential are required to be as small as possible.
