RU2516255C2 - Synchronous motor start-up method - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to the sphere of electric equipment and may be used for production of asynchronous motors with low starting current. Technical result is attained due to the connection diagram and increase in inductive reactance of the stator winding at wye-connection of phases. The method of synchronous motor start-up is suggested by means of switching of a three-phase stator winding in the course of which, according to the invention, two standard coil groups, from the first up to the sixth one, are included into phases of the bipolar winding, two pairs of coil groups, from the first up to the sixth one, are included into phases of the four-pole winding, three triples of coil groups, from the first up to the sixth one, are included into phases of the six-pole winding, at that the phase band width is changed from 120 electrical degrees to 60 electrical degrees by switching the winding from the delta-connection to the wye-wye-connection with formation of neutral point from the delta-connection middle without changes in a number of poles and breakage of phase winding connections.

EFFECT: reducing starting current by preliminary delta-connection of the winding to the mains with further switching to the wye-wye connection, at that switching is made without changes in a number of the stator winding poles and breakage of phase winding connections.

7 dwg, 1 tbl

Description

The invention relates to electrical engineering and can be used in the production of induction motors with reduced inrush current.

There is a method of starting an induction motor by switching the stator winding from a star to a triangle. For this purpose, induction motors are released at a voltage of 380 (Δ) / 660 (Y) V. With this method of starting, in comparison with direct starting, the starting current in the network decreases almost three times (see page 570: Fig. 28.1g ; Voldek A.I. Electric machines / Textbook. L .: Energy, 1978. - 832 S. ill.).

The disadvantage of this method is that in proportion to the change in the starting current, the starting torque of the motor is reduced by almost 3 times, as well as in the complex switching circuit of the winding with rupture of the phase windings.

A known method of starting a three-phase AC motor (see US Pat. No. 2415507, publ. 03/27/2011. Bull. No. 9, taken by the authors for the prototype).

In the known method of starting a three-phase AC motor, comprising connecting the stator windings of two electric motors in pairs in series according to the “common star” circuit and supplying the received electrical connection of the rated voltage to the input, after acceleration, the electrical connection of the stator windings of these motors is broken, and into the circuit: “common star "Or" common triangle "connect the stator winding of the starting motor and accelerate it to operating speed.

The disadvantage of this method is that two motors of comparable power are used for starting, while depending on the load of the starting motor, the voltage drop across the windings of the braked motor changes, which leads to different starting currents and starting torques, and switching is accompanied by rupture of the phase windings.

The technical result of the invention is to reduce the starting current of an induction motor and improve its operational characteristics by switching the stator winding without breaking the phase windings.

The problem is achieved in that in the method of starting an induction motor by switching a three-phase stator winding, the phases of the bipolar winding of which include the same two-coil groups from the first to the sixth, the phases of the four-pole winding include two pairs of the coil groups from the first to the sixth, into the phases of the six-pole winding includes three triples of the first to sixth coil groups, change the phase zone width from 120 electrical degrees to 60 electrical degrees by switching the windings from a triangle and the two stars with constant induction in the air gap to form a zero point from the middle of the triangle without changing the number of pairs of poles and phase windings without discontinuity compounds.

The novelty of the claimed technical solution is achieved due to the fact that to reduce the starting current of an induction motor with the same coil groups from the first to the sixth, the phase zone width is changed from 120 electrical degrees to 60 electrical degrees by switching the windings from a triangle to two stars with constant induction in the air gap with the formation of a zero point from the middle of the triangle without changing the number of pairs of poles and without breaking the connections of the phase windings.

According to the scientific, technical and patent literature, the authors are not aware of the claimed combination of features aimed at achieving the task, and this solution does not follow clearly from the prior art, which allows us to conclude that the solution corresponds to the level of the invention.

The proposed technical solution is industrially applicable, since it is workable, and its use in industry is proposed.

In figures 1 and 2 shows the direction of the currents on the sides of the coils of six coil groups of a two-layer bipolar stator winding, the connection diagram of the coil groups and phases in a triangle, the type of magnetomotive force (MDS) of the winding and the Gerges diagram. Figures 3 and 4 show the direction of the currents on the sides of the coils of the coil groups of the winding when connecting the phases into two stars, the connection diagram of the coil groups and phases into two stars, the MDS winding and the Gerges diagram. Figures 5-7 illustrate circuits that implement the method of starting induction motors with a different number of pairs of winding poles.

According to figure 1, a two-layer bipolar stator winding for implementing the method contains 1-6 coil groups (the sides of the phase A coils are indicated by squares, phase B by triangles, phase C by circles, and the direction of currents in the sides of the coils is shown by dots and pluses). The width of the phase zone is 120 ° (winding coefficient k _obΔ = 0.80).

The network includes winding leads 7, 9, 11, and leads 8, 10, 12 are free. According to figure 2, the MDS contains odd and even harmonics (table 1), which increases the differential scattering, therefore, the inductive resistance of the stator winding. MDS is built for the point in time when the current in phase A has a maximum value. The most pronounced first even higher harmonics ν (Table 1) do not have a noticeable negative effect on engine starting.

Table 1 The relative amplitudes of the harmonics of the MDS ν one 2 four 5 7 8 10 eleven 13 F _mν / F _m one 0.133 0,0571 0.011 0.0058 0.0152 0.006 0.01 0.008

The quality of the MDS is estimated by the value of the differential scattering coefficient, and its value is determined by the Gerges diagram. When connecting the phases into a triangle (figure 2), the radius R _{p of the} main harmonic of the MDS with conditional Z = 72 sides of the coils (p is the number of pairs of poles)

$$R_p=\frac{Z{k}_{\mathrm{about}\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="00000011.png,00000014.png"\; state="\{\{state\}\}">b</figure-callout>}}}{2\pi p}=\frac{72\cdot 0.80}{2\cdot 3.1416\cdot \mathrm{one}}=\mathrm{9,1648}$$

polar moment of inertia of the slot points of the Gerges diagram

$$\begin{array}{l}{R}_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="00000011.png,00000014.png"\; state="\{\{state\}\}">d</figure-callout>}}^2=[2({10}^2+{\mathrm{one}}^2-2\cdot 10\cdot \mathrm{one}\cdot \cos 120°)+2(7^2+{\mathrm{one}}^2-2\cdot 7\cdot \mathrm{one}\cdot \cos 120°)+\\ +2(5^2+5^2-2\cdot 5\cdot 5\cdot \cos 120°)+2(7^2+{\mathrm{four}}^2-2\cdot 7\cdot \mathrm{four}\cdot \cos 120°)+\\ +2(9^2+3^2-2\cdot 9\cdot 3\cdot \cos 120°)+2(3^2+6^2-2\cdot 3\cdot 6\cdot \cos 120°)]/12=\\ =(222+114+150+186+234+126)/12=86\end{array}$$

and the value of the differential scattering coefficient

. $${\tau }_{\partial }=\frac{R_{\partial }^2}{R_R^2}-\mathrm{one}=\frac{86}{{\mathrm{9,1648}}^{{}_2}}-\mathrm{one}=0.024$$

.

According to figure 3, the width of the phase zone is equal to 60 ° (k _obYY = 0.924). The pins 7, 9, 11 are still included in the network, and pins 8, 10, 12 form a zero point. According to figure 4, the MDS does not contain noticeable amplitudes of higher harmonics, which will determine the small inductive resistance of the winding. For this circuit:

; $$R_p=\frac{Z{k}_{\mathrm{about}\mathrm{<figure-callout\; id="2"\; label="b"\; filenames="00000011.png,00000014.png"\; state="\{\{state\}\}">b</figure-callout>}}}{2\pi p}=\frac{72\cdot 0.924}{2\cdot 3.1416\cdot \mathrm{one}}=\mathrm{10,5832}$$

;

; $$\begin{array}{l}{R}_{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="00000011.png,00000014.png"\; state="\{\{state\}\}">d</figure-callout>}}^2=[2(7^2+5^2-2\cdot 7\cdot 5\cdot \cos 120°)+2(9^2+3^2-2\cdot 9\cdot 3\cdot \cos 120°)+\\ +2({10}^2+{\mathrm{one}}^2-2\cdot 10\cdot \mathrm{one}\cdot \cos 120°)]/6=112.3333\end{array}$$

;

. $${\tau }_{\partial 0}=\frac{R_{\partial }^2}{R_R^2}-\mathrm{one}=\frac{112.3333}{{\mathrm{10,5832}}^2}-\mathrm{one}=\mathrm{0,00294}$$

.

The implementation of the proposed method is illustrated by windings in figures 5-7. According to figures 5-7, two coil groups 1 to 2 enter the phases of a bipolar winding; 5-6; 3-4, the phases of the four-pole winding include two pairs of coil groups 1, 1 ′ - 2, 2 ′; 5, 5 ′ - 6, 6 ′; 3, 3 ′ - 4, 4 ′, the phases of the six-pole winding include three triples of coil groups 1, 1 ′, 1 ″ - 2, 2 ′, 2 ″; 5, 5 ′, 5 ″ - 6, 6 ′, 6 ″; 3, 3 ′, 3 ″ - 4, 4 ′, 4 ″.

The method of starting an induction motor is implemented as follows: when the terminals 7, 9, 11 are connected to the network, the phase windings are connected in a triangle, and after the engine starts and the terminals 8, 10, 12 are closed, the phase windings form two stars. When you turn on the motor in a 380 V network, the ratio of turns per phase w, flux Ф and induction in the air gap B _δ (U is the phase voltage) when switching the winding from a triangle to two stars is determined:

; $$\frac{w_{\Delta }}{w_{YY}}=\frac{U_{\Delta }{k}_{\mathrm{about}bYY}{F}_{YY}}{U_{YY}{k}_{\mathrm{about}b\Delta }{F}_{\Delta }}=\frac{380\cdot 0.924\cdot F_{YY}}{220\cdot 0.80\cdot F_{\Delta }}=2$$

;

; $$\frac{F_{\Delta }}{F_{YY}}=\mathrm{one}$$

;

. $$\frac{B_{\delta \Delta }}{B_{\delta YY}}=\mathrm{one}$$

.

When switching, the starting current decreases by 1.73 / 2 times due to the Δ / YY circuit itself and to an even greater extent due to a change in the inductance of the stator winding. According to calculations, at the same winding step as standard motors of medium and high power, the starting current decreases by 1/3, and the constant induction determines the change in the starting torque of the motor in proportion to the change in the starting current.

Thus, the method of starting an induction motor by switching the stator winding according to the Δ / YY scheme is the simplest to implement, it is carried out without changing the number of pole pairs of the stator winding and without breaking the phase windings.

Claims (1)

A method of starting an induction motor by switching a three-phase stator winding, characterized in that the phases of the bipolar winding include the same two-coil groups from the first to the sixth, the phases of the four-pole winding include two pairs of the coil groups from the first to the sixth, the three-coil phases include the three triples of the coil groups from the first to the sixth, the phase zone width is changed from 120 electrical degrees to 60 electrical degrees by switching windings from a triangle to two stars with a constant induction ii in the air gap to form a zero point from the middle of the triangle without changing the number of pairs of poles and phase windings without discontinuity compounds.

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