DE1488609B2 - - Google Patents

Description

The present invention relates to a three-phase asynchronous machine with a squirrel cage and a slot bevel, which lead to a reduction of the voltage harmonics that close over the network leads.

For some time, network command systems with audio frequencies have been used to an increasing extent. Here, audio-frequency pulses are superimposed on the 50 Hz network, which means that the remote control is different Objects such as street lighting, meters, stoves, hot water storage tanks, etc. leaves. It is also already known that asynchronous machines interfere with such command systems being able to lead. Since the machine windings are distributed in grooves, they arise during rotation of the rotor impedance fluctuations, so that overcurrents are superimposed on the 50 Hz motor current Frequency is approximately between 500 to 2000 Hz. If the motor is now connected to a longer cable, then there is an audio-frequency voltage drop that can amount to a few volts. Is that also true The control frequency of the network command system roughly corresponds to the interference frequency, so incorrect switching occurs, because the response voltage of the relays to be operated is approximately 1.5 V.

In the magazine "Elektrotechnik und Maschinenbau" on March 10, 1936, you can read on page 221, that the moment of two fields decreases with the product of two skew factors, if the Grooves of the stator and rotor are inclined against each other. However, this will be appreciated by those skilled in the art no indication is given of the way in which the voltage harmonics closing over the network should determine.

The same applies to a publication in "Bulletin SEV", 1935. According to p. 313, through a so-called optimal skew factor, which according to the formula

Ψ opt =

40

is determined, certain upper fields are reduced. However, there are two unknowns in the above relationship: g and v. A whole number is designated by g, which can take on the values 1, 2, 3 ..., ν represents the number of pole pairs of the stator upper fields: It is not known which values have to be chosen for g and ν so that disturbances in Network command systems can be avoided or parasitic synchronous torques can be canceled. The prior publication does not show any way how the person skilled in the art should arrive at such a knowledge.

Only the invention eliminates the identified shortcomings and enables the exact prediction of the groove inclination to be observed.

From detailed theoretical and practical investigations it was found that not the groove inclination per se, but only a complete one certain inclination, which in a relatively complicated way depends on the number of stator slots, the number of rotor slots, the number of pole pairs, the winding tendon, etc., can bring decisive remedy.

The invention is therefore based on the object of the exact predetermination of the avoidance of disturbances in network command systems and parasitic torques to enable three-phase asynchronous machines with squirrel cage.

According to the invention, this object is achieved in that the groove bevel is at least approximately is so dimensioned that the greatest comes out of the relationship

. £)> "/ c (sin

v ¹

The resulting voltage harmonics and closing over the network have their minimum values, where b is the ordinal number of the harmonics E _b , Z _{2 is} the number of rotor slots, ρ is the number of pole pairs, ^p k is the winding factor for the main field, ^v / c is the winding factor for the i> -th upper field , ν the number of pole pairs of the Statoroberfelder, ^{ν η} the skew for the v-th top field, ^M fc the winding factor for the μ-th top field, μ the number of pole pairs of the rotor top fields, ^{μ η} the skew for the μ-th top field means and the sizes " k, ^v k and "k from the equations

^v k =

sin π
T π
■ sin -
ν yhp, q sin
sin - π P.
■ sin - q sin
sin - 6q
V Tl
JT 2 ^y ' V 71 π p6q
μ π
J ~ 6 2 ^{} l} μ π

* P6q

and finally the quantities ^v r / and ^μ η from the relationships

η = Sin ν

"η = Sin μ - ^

h '

where q is the number of stator slots per pole and strand, y is the coil width, τ _{ρ is} the pole pitch and h is the value by which the stator circumference is to be divided in order to obtain the slot inclination.

The ordinal number b can assume the values ± 1, ± 2, ± 3 ..., and the sign is also decisive for the phase sequence.

The quantities ν and μ can be determined according to the expressions ν - ρ (6a + 1), μ = b ■ Z ₂ + v. Here a = 0, ± 1, ± 2, ± 3 ...

From the formula for E _{b it} follows, in agreement with the experiment, that several harmonics arise, but only one or two oscillations in their size are dangerous for the network. If one now searches for the zero point or the minimum of the maximum harmonics by varying h, the most favorable inclination can be determined. It turns out that in some cases straight

Grooves can be better than chamfered ones. With the motors according to the invention, disturbances Avoid in network command systems. Furthermore, parisitarian torques can also be eliminated, which are known to hinder the start-up of the motor. Overall, an advantageous course of the is obtained Torque curve.

The subject matter of the invention will now be explained in more detail using an example. Given a motor with 2 p = 4, Z ₁ = 36, Z ₂ = 28, γ / τ _ρ = 8/9; ίο it follows q = ZJ {lpm ^) = 3, if Z _{1 means} the number of stator slots and Wi ₁ = 3 means the number of phases.

With these values, the upper shaft voltages E _b can now be determined for certain values of b with a change in h , taking into account the given relationships.

The result can be seen in the drawing. There the variable h characterizing the groove inclination is plotted on the abscissa and the harmonic voltage E _{b is} plotted on the ordinate with b as a parameter in percent of the terminal voltage for nominal load.

A certain frequency belongs to the individual values of b , which is derived from the relationship

= ll + bZ ₂ (ls) / p] -f _N

36

27.5

• τ _Ν1 = 1.3 stator slot pitches.

^25th

follows, where f _{N is} the network frequency and s is the slip. If one assumes, for the sake of simplicity, that the machine is idling, i.e. that s = 0, then the frequencies given in the drawing apply.

From the functions E _b = φ (Tt) it can be seen that for b = ± 2 the voltage harmonics remain negligibly small. The harmonic with b = + 1 does not require a groove bevel, because it fulfills the condition bZ-Jip = 7, and it can be shown that whenever the equation

bZ ₂ / 2p = +1, -2, +4, -5, +7 ... = 3g + 1

(with g-positive or negative integer) is fulfilled, the harmonic cancels the machine with a star connection and closes with the winding not via the mains, but via the winding with a delta connection. If there were no further harmonics closing over the network, the groove inclination would have to be selected with b = +1, taking into account the zero crossing of the curve. Now, however, with b = - 1, the quantity _{bZ 2} / 2p = - 7. It is therefore a mains harmonic that must be canceled. At the zero crossing of b = - 1, h = 27.5. This means that the groove inclination must be (l / 27.5) -ths of the circumference, or

It does not matter whether the inclination takes place in the carriage or the stand.

Claims (2)

Patent claims: 1. Three-phase asynchronous machine with squirrel cage and a slot incline that leads to a reduction from closing over the network Voltage harmonics leads, thereby characterized in that the groove bevel is at least approximately dimensioned so that the greatest emerge from the relationship the resulting voltage harmonics and closing via the network are approximately their minimum values. where b is the ordinal number of the harmonics E _b , Z _{2 is} the number of rotor slots, ρ is the number of pole pairs, ^p k is the winding factor for the main field, ^v k is the winding factor for the vth upper field, ν is the number of pole pairs of the stator upper fields, ^ν η is the skew factor for the v-th upper field, * k the winding factor for the μ-th upper field, " μ the number of pole pairs of the rotor upper fields, ^μ η the skew factor for the μ-th upper field and the quantities ^p k, ^v fc and ^ß k from the equations "k = sin - - ■ sm - yjx _f , qsm 6q sm ^v / c = ρ 6 q sin p6q α π sm -—— ", Ρ 6. μ π. "k = gin JiL y _T . μ π pi p6q and finally the quantities ^v ry and ^μ η from the relationships ^v ? 7 = sin ν ~ h ' "I ₇ = sm where q is the number of stator slots per pole and strand, y is the coil width, % _{v is} the pole pitch and h is the value by which the stator circumference is to be divided in order to obtain the slot inclination. 2. Asynchronous machine according to claim 1, characterized in that the groove inclination is dimensioned so that the largest voltage harmonic (E _b ) closing within the machine in a delta connection is at least approximately equal to zero. 1 sheet of drawings