RU2030053C1 - Gear to protect three-phase asynchronous electric motor against break of phase - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: gear to protect three-phase asynchronous electric motor against break of phase has two equal parts 1 and 2 of principal winding of magnetic starter. Part 1 is wound in opposition to part 2 put on common magnetic core. Parts 1 and 2 are connected with one ends to one and the same phase with other ends each part of winding is coupled to other individual phase. Contacts 3 of magnetic starter are placed in power supply circuit of motor 4. EFFECT: simplified design and increased reliability of protection. 9 dwg

Description

 The invention relates to electrical engineering and can be used to protect against phase failure of electric motors with windings connected by a triangle.

 A known electric motor with a protection and control unit (2), comprising a magnetic starter with a main winding and an additional winding wound on a common magnetic circuit, meets the main winding of the magnetic starter, a relay with two windings and a signal lamp.

The specified motor with a protection and control unit has the following disadvantages. It can be used only for motors whose windings are connected by a star with power from the network with a zero wire. For the application of this invention, commercially available magnetic starters cannot be used, because it will be necessary to add an additional one to the main winding, which will not fit on the magnetic system of commercially available contactors installed in magnetic starters. The protection operation is not reliable enough when the phases are broken, to which the main winding of the magnetic starter is not connected, because in these cases, the vector of voltages and currents in the primary and secondary windings will be shifted one relative to the other by 120 ^° . The specified device is taken as a prototype of the present invention.

 The aim of the invention is to simplify and improve the reliability of a device for protecting against phase failure of a three-phase asynchronous motor with windings connected by a triangle.

 This goal is achieved by the fact that in a device containing a magnetic starter with two windings wound on a common magnetic circuit opposite to each other, the windings comprise two equal parts of the starter winding. These parts of the winding are connected at one end to the same phase and at the other ends, each part of the winding is connected to another separate phase.

 As a result of the application of the present invention, by replacing one main winding with commercially available magnetic starters with two equal parts, reliable protection against phase failure of three-phase asynchronous motors with windings connected by a triangle will be provided without the use of any additional equipment and protection units, which will give significant economic effect.

 Figure 1 is a circuit diagram of the proposed device; in FIG. 2 is a vector diagram of the voltages on the windings of the motor and the magnetic starter during normal operation; figure 3 is a vector diagram of the magnetic flux in the magnetic circuit of the magnetic starter during normal operation; figure 4 is a vector diagram of the voltages on the windings of the magnetic starter with phase failure "A"; figure 5 is a vector diagram of the magnetic flux in the magnetic circuit of the magnetic starter when the phase break "A"; figure 6 is a vector diagram of the voltage across the windings of the magnetic starter when the phase break "B"; Fig.7 is a vector diagram of the magnetic flux in the magnetic circuit of the magnetic starter when the phase "B"; on Fig is a vector diagram of the voltage across the windings of the magnetic starter when the phase "C"; figure 9 is a vector diagram of the magnetic flux in the magnetic circuit of the magnetic starter when the phase break "C".

 The device contains (figure 1) two equal parts 1 and 2 of the main winding of the magnetic starter. Part 1 of the main winding is wound counter to part 2 of the main winding on a common magnetic circuit. Parts 1 and 2 of the winding at one end are connected to the same phase, and at the other ends, each part 1 and 2 of the winding is connected to another separate phase. The contacts 3 of the magnetic starter are included in the power supply circuit of the motor 4.

 The device operates as follows.

 In normal operation, the voltage across the windings of the motor and the magnetic starter are shown in the vector diagram of figure 2.

The magnetic flux Φ _{CA of} part 2 of the main winding and the magnetic flux Φ _{BC of} part 1 of the main winding wound counter to part 2 create a total magnetic flux ΣΦ, which ensures the operation of the device.

For normal operation of the engine, the total magnetic flux ΣΦ _n shown in the vector diagram of figure 3 and taken as unity.

 When phase "A" is disconnected, the voltage on the motor and magnetic starter windings connected to this phase will be generated by the voltage between phases "B" and "C" (Fig. 4).

In this mode, the magnetic fluxes of part 1 of the winding of the magnetic starter - Φ _AC and part 2 - Φ _CA will create a total magnetic flux ΣΦ (Fig. 5) of less than 0.29ΣΦ _n , which will cause the magnetic starter to trip, open its contacts 3 and turn off the motor 4.

 When phase "B" is disconnected, the voltage on the motor windings and the magnetic starter connected to this phase will be generated by the voltage between phases "A" and "C" (Fig.6).

In this mode, the magnetic fluxes of part 1 of the magnetic starter winding - Φ _BC and part 2 - Φ _CA will create a total magnetic flux ΣΦ (Fig. 7) of less than 0.29ΣΦ _n , which will cause the magnetic starter to trip, open its contacts 3 and turn off the motor 4.

 When phase "C" is disconnected, the voltage on the motor and magnetic starter windings connected to this phase will be generated by the voltage between phases "A" and "B" (Fig. 8).

In this mode, the magnetic fluxes of part 1 of the winding of the magnetic starter - Φ _BC and part 2 - Φ _CA compensate each other. The total magnetic flux ΣΦ (Fig. 9) will be zero, which will cause the magnetic starter to trip, open its contacts 3 and turn off the motor 4.

 The application of the proposed device provides, in comparison with the prototype, a simplification and increased reliability of the device for protecting three-phase asynchronous motors with windings connected by a triangle from phase failure due to the use of two parts of the main winding of the magnetic starter in it instead of the full main and additional windings of the magnetic starter and fuse used in the prototype.

 This allows you to apply for the proposed device modernized, mass-produced by domestic industry magnetic starters, as a result of which a significant economic effect will be obtained.

Claims (1)

 A DEVICE FOR PROTECTING A THREE-PHASE ASYNCHRONOUS MOTOR FROM A PHASE SCRAP, containing a magnetic starter with two windings wound on a common magnetic circuit, facing one another, with a control circuit and contacts for connecting the motor, characterized in that, in order to simplify and increase the reliability of the device, the windings comprise two equal parts of the starter winding, these parts of the winding at one end through the control circuit of the starter are connected to the terminal for connection to the same phase, and with the other ends each part of the winding is connected yuchena to terminals for connection to other separate phases.

Images