RU2177671C2 - Method for starting two squirrel-cage induction motors - Google Patents

Abstract

FIELD: mechanisms used for general mechanical engineering. SUBSTANCE: starting two motors involves pre-start connection of windings in pairs, kinematic coupling of rotors at least for the time of starting until motors gain desired speed, change-over of stator windings to independent power supply. Proposed method provides for starting two motors without using any additional starting devices. EFFECT: enhanced reliability of starting two motors. 2 cl, 3 dwg

Description

 The invention relates to the field of electrical engineering, in particular, to methods of starting electric motors and can be used in general engineering mechanisms.

 There is a method of starting asynchronous motors with switching stator windings from a triangle to a star at the time of starting (V. Venikov "Transient electromechanical processes in electrical systems". - M.: Higher School, 1970).

 The disadvantage of this starting method is that it cannot be used for engines with the main inclusion in the "star" scheme.

 Known autotransformer engine starting, in which at the time of starting the engine, the voltage on it is lowered using an autotransformer (V. Venikov "Transient Electromechanical Processes in Electrical Systems". - M.: Higher School, 1970).

 The disadvantage of this starting method is the use of an autotransformer, which reduces reliability and increases the cost of the drive.

 A known method of starting a twin-engine electric drive (see description to the AS of the USSR N 712921, H 02 P 7/74, publ. BI N 4, 1980), in which the engine with a phase rotor and an engine with a squirrel-cage rotor are jointly launched inclusion of starting resistors in the phase rotor circuit at the time of starting.

 The disadvantage of this starting method is the use of an engine with a phase rotor, which complicates the electric drive and reduces its reliability.

 Closest to the claimed is a method of starting groups of asynchronous motors with squirrel-cage rotors (see description to the AS of the USSR N 1396231, H 02 P 1/54, publ. BI N 18, 1988), based on the connection of stator windings to the distribution bus and the connection of the windings of the two auxiliary engines before starting in pairs in series with each other, after which, upon reaching the set speed, they are disconnected from the distribution bus and transferred to independent power.

 The disadvantage of this starting method is that to start a group of engines it is necessary to use two auxiliary engines, which are not used after start-up, which reduces the overall dimensions and increases the cost of the electric drive.

 It should also be noted that the starting process of the auxiliary engines themselves does not have stability and predictability of the result, because due to the unequal mechanical and electrical characteristics of the engines, the run-up time of the rotors to the nominal speed is different. This leads to the fact that as a result of a sharp increase in the electrical resistance of one of the engines as it reaches its nominal operating mode, such a voltage distribution is possible that the start of the other engine will stop.

 The problem to which the invention is directed, is to increase the reliability of the start-up, to improve the overall dimensions of the electric drive.

 The technical result achieved by the implementation of the invention is to reduce the load on the supply network at the time of start-up, in conditions of limited power supply.

 The indicated result is achieved by the fact that the stator windings of the engines are connected in series-pair before starting, the rotors of the motors are accelerated to a predetermined speed and the stator windings of the motors are switched to separate power supply, while the rotors of the motors are kinematically connected to each other, at least for the start-up time. The moment of switching the stator windings is determined by the number of engine revolutions. A pair-serial connection is made according to the "common star" or "common triangle" scheme.

 The method is illustrated by drawings, where in FIG. 1 shows a connection diagram of stator windings for starting two asynchronous motors according to the "common star" scheme; in FIG. 2 - the same, according to the scheme "common triangle"; in FIG. 3 is a circuit diagram of an electric drive for starting two engines according to the "common star" scheme.

Starting the engines according to the claimed method is carried out in the following sequence:
- stator windings of two motors are connected in pairs in series according to the "common star" or "common triangle"scheme;
- the rated voltage is applied to the input of the obtained connection, while the voltage attributable to the stator windings of each electric motor is distributed in proportion to the resistance of their windings;
- after a joint run, the same names and ends of the stator windings of the first motor are connected to each other, while the voltage supplied to the stator windings of the other motor becomes nominal;
- disconnect the stator windings of the first engine from the distribution bus;
- the stator windings of the first motor are connected, regardless of the previous switching on, to the main circuit according to the "star" or "triangle" scheme, the rated voltage is applied to the motor.

 At the time of starting, the rotors of the starting engines are kinematically interconnected, for example, by means of a gear transmission, a rigid coupling, a chain transmission. After start-up, both separation of the rotors and independent operation of the engines, as well as the operation of the engines for a common load are possible.

 The electric drive for implementing the proposed method of starting contains two motors 1, 2, the beginning of the stator windings of which are connected to the distribution bus 3, the first is directly, the second through the switching element 4, the ends of the stator windings are combined into common points: the first motor through the switching element 5, and the second - directly, while the ends of the windings of the first motor are connected to the beginnings of the windings of the second motor through a switching element 6.

 The electric drive operates as follows.

 To start the engines, the switching element 6 is turned on, after the joint acceleration of the engines, the switching element 4 is turned on, the motor 1 is excluded from operation, and the rated voltage is applied to the engine 2, then the switching element 6 is turned off, and the switching element 5 is turned on, as a result, the motor 1 is connected at rated voltage.

 Thus, as a result of the solution of the task, the reliability of the start-up increased, it became possible to start the engines without using any additional starting devices.

Claims (2)

 1. A method of starting two asynchronous motors with squirrel-cage rotors, including connecting the stator windings to the supply network, characterized in that the rotors of the motors, at least for the duration of the start, are kinematically connected, the same beginnings and ends of the stator windings are connected in pairs in series according to the general scheme a star or a common triangle, the rated voltage is applied to the input of the obtained electrical connection, and after the start, the stator windings are switched to separate power.  2. The method according to claim 1, characterized in that the switching moment of the stator windings is determined by the number of engine revolutions.

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