RU2624734C1 - Asynchronous motor start-up method - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method to start an asynchronous motor without breaking the power chain without changing pairs of poles executed by the inclusion of one of the two separate parts of the three-phase stator windings, with the location of parts in the same slots of stator on a scheme Y with subsequent after takeoff an engine connecting another part of the schemeΔ. The simplest device is necessary to switch it. With the same cross section of the winding wire, the starting current is reduced by 33%. Changing the section of wires in parts of the winding can affect the degree of reduction of the starting current.

EFFECT: reduced starting current of asynchronous motor without breaking the power chain and without the negative effects of higher harmonics at the start of the engine.

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Description

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

A known method of starting an induction motor by switching the stator winding from a star to a triangle is Y / Δ (Voldek A. Electric machines. L.: Energy, 1978. S. 570, Fig. 28.1 g). When switching, the starting current and starting torque are reduced three times.

The disadvantage of this method is in breaking the power supply circuit of the motor and the relatively complex circuit for switching the stator winding from star to triangle.

There is a method of starting an induction motor by switching the stator winding from a triangle to two stars - Δ / YY without breaking the power circuit and without changing the pairs of poles (patent RU 2516255, published on November 27, 2013). The inrush current of the motor is reduced by changing the width of the phase zone of the stator winding from 120 ⁰ el. (Δ) at 60 ⁰ email. (YY) without breaking the power circuit. Patent RU 2516255 is taken as a prototype of the invention.

The disadvantage of this method is the significant negative effect of even higher harmonics on starting the engine according to the Δ scheme.

The technical result of the invention is to reduce the starting current of an induction motor without breaking the power circuit and without the negative effect of higher harmonics on starting the motor.

This goal is achieved by the fact that in the method of starting an induction motor by switching the stator winding without breaking the power circuit and without changing the pole pairs to exclude the influence of higher harmonics on the motor start, one of the two separate parts of the three-phase stator winding according to scheme Y is turned on, followed by connecting the other parts according to the scheme Δ. For this, the stator winding is made of two parts with the connection of one part to the star (Y), the other to the triangle (Δ) with the location in the same grooves of the stator.

Figure 1 shows a diagram of a bipolar winding, figure 2 shows a diagram of the connection of coil groups of parts of a winding, figure 3 shows a diagram of the currents and the harmonic structure of the MDC of each of the two parts of a three-phase winding (the sides of the phase U coils are indicated by squares, phase V by triangles, phase W - circles), in figure 4 is a diagram of the inclusion of the parts of the winding in the network, in figure 5 is a view of the currents and moments when starting the motor, in figure 6 is a diagram of a four-pole winding.

According to figures 1-3, the stator winding contains 18 coil groups. Odd reel groups are connected in a triangle, even are connected in a star. The ratio of the turns in the coils of the star and the triangle is 1 / 1.73. Coil groups of both parts are stacked in the same stator slots. The location of the sides of the coils of each part in the grooves is equivalent to the location of the sides of the coils of a single-layer bipolar winding of the maximum distribution, therefore, the magnetomotive force (MDS) of each part and the winding as a whole does not contain noticeable amplitudes of higher harmonics.

According to figure 4, the terminals U1, V1, W1 (Y) are connected to the network with the subsequent connection of the terminals U, V, W (Δ) after running the engine.

According to figure 5, when the winding parts are included in the network according to the Y + Δ scheme from a wire of the same cross section, the ratio of inrush currents is ≈2 / 3 and moments ≈ (2/3) ² . The data in figure 5 correspond to the calculation below.

Calculation of starting currents and moments of the motor with switching Y + Δ based on 4A112M2. There are 31 turns in the coil in the part of the triangle, 18 turns in the coil in the part of the star. Wire diameter 0.95 mm. The active resistance of the parts of the winding R _1Y = 2.3 Ohms and R _1Δ = 4 Ohms. When converting a triangle into an equivalent star, R _1Yе = 1.33 Ohm. The active resistance of the winding when turned on according to the scheme Y + Δ is R _{1Y + 1Yе} = R ₁ = 0.835 Ohm. Other parameters correspond to the serial engine 4A112M2: inductance of the stator winding x ₁ = 1.0 Ohm, reduced inductive resistance of the rotor winding x ₂ = 1.35 Ohm; reduced resistance of the rotor winding R ₂ = 0.42 Ohm (4A series induction motors. Reference / A.E. Kravchik, M.M.Schlaf, V.I. Afonin, E.A. Sobolenskaya - M .: Energoizdat, 1982 . - 504 p.). According to the parameters, when starting the same directory, the active resistance of the rotor winding decreases according to the law (1 + 0.22 s), and the inductive short circuit resistance increases according to the law (1-0.36 s), where s is slip. Currents and moments of the engine during start-up:

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Thus, the method of starting an induction motor by switching the stator winding according to the Y + Δ scheme with the arrangement of the parts in the same grooves is the simplest to implement, it is carried out without breaking the power circuit and without changing the pole pairs. The MDS of the parts of the winding and the winding as a whole does not contain appreciable amplitudes of higher harmonics. With the same cross section of the wire, the inrush current decrease is almost 33%, which is confirmed by the oscillograms of the inrush currents of the motor with the proposed start method.

According to figure 6, a four-pole stator winding of 24 of the same type of coil groups with leads U1, V1, W1 from a part of the star and with leads U, V, W from a part of the triangle when connected to the network according to the Y + Δ scheme will characterize the motor with almost the same ratio of starting currents and the quality of the harmonic composition of the MDS, as the engine with a bipolar winding.

Obviously, by changing the cross-section of the wires in the parts of the winding, it is possible to influence the degree of reduction of the starting current.

Claims (1)

The method of starting an induction motor by switching the stator winding without breaking the power circuit and without changing the pole pair, characterized in that to exclude the influence of higher harmonics on the motor start, one of the two separate parts of the three-phase stator winding according to scheme Y is turned on, followed by the start of the motor by connecting the other part scheme Δ.

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