RU2061288C1 - Phase-failure protective device for trouble-free operation of induction motor - Google Patents

Abstract

FIELD: electronical engineering; phase-failure protection of induction motors. SUBSTANCE: device has capacitors 11 and switching members 4; in addition, it is provided with two diode rectifiers 10, 20, auxiliary relay 12, and second starter 15; coil of auxiliary relay 12 is connected between neutral points of supply mains and stator winding, its closing contact 18, between one of coil leads of second starter 15 and common point of cathodes of three diodes of rectifier 20 whose anodes are connected to phase leads of supply mains after closing contacts of first magnetic starter 3. Coil of second starter 15 is inserted between neutral point of stator winding and one of common points of parallel-connected contacts of auxiliary relay 12 and second starter 15; coil of first starter 3 is connected between neutral wire lead of supply mains and common point of three diodes of rectifier 10 through circuit of series-connected START-STOP button 8, 9 and contacts of thermal relay 7; anodes of three diodes are connected to supply mains phase leads; capacitors 11 are connected to phase terminals of stator winding in delta. EFFECT: improved reliability of protection. 1 dwg

Description

 The present invention relates to electrical engineering and can be used to protect an induction motor when the phases of the supply network are broken.

A device is known in which the zero point of the stator winding of an induction motor is connected to the zero output of the power source [1]
However, the specified device when the phase failure of the network ensures trouble-free operation of the electric motor under loads of not more than 70% of the nominal. In addition, in the normal mode, the third harmonic of the mains voltage flows through the stator windings of the motor and the conductor connecting the motor zero point to the network zero point, caused by the saturation of the motor core. These currents cause additional losses and reduce motor efficiency.

A device is also known in which the motor zero point is connected to the network zero point through the current relay contact system [2]
The disadvantage of this device is that the connection of the zero point of the motor and the zero point of the network is carried out only when the break of two phases of the network and does not take advantage of such switching when the break of one phase.

 The aim of the invention is to preserve the positive properties of the connection of the network zero point with the stator zero point in emergency mode and the elimination of additional losses in the presence of such a connection in normal operation.

 This goal is achieved by the fact that the zero point of the stator winding is connected to the zero wire of the network only when one or two phases of the network break.

 The drawing shows a diagram of the proposed device. The stator winding of electric motor 1 is connected to a three-phase network through an automaton 2 and a magnetic starter having a coil 3, power contacts 4 and block contact 5. Heating elements of the thermal relay 6 are connected to the network through the motor windings, and its contacts 7 are connected in series with the starter winding 3 Turning the engine on and off occurs when you press the "Start" 8 and "Stop" 9 buttons, respectively. In order for the magnetic starter to not turn off when the mains phase is interrupted, its coil 3 is connected according to a three-phase rectification scheme through diodes 10. Capacitors 11 serve to compensate the reactive power of the motor and ensure its trouble-free operation when one of the phases of the power supply is interrupted. Between the zero points of the network 0 and the stator winding 01, an intermediate relay coil 12 is connected in series with the adjustment resistor 13 and the opening contact of the "Start" button 14, the second magnetic starter connecting the zero conclusions of the network and the stator windings of the motor: points 0 and 01, has a coil 15, power contact 16 and block contact 17. Block contact 17 is connected parallel to the contact of the intermediate relay 18. In parallel with the coil 15, the signal lamp 19 is turned on. So that the starter 15 turns on when the phase of the network is interrupted, its coil is connected in parallel with the motor windings The device according to the scheme of three-phase rectification through diodes 20.

 The scheme works as follows.

 Machine 2 is powered from the network. When the button 8 is pressed, the magnetic starter 3 is turned on. The motor 1 and the capacitors 11 are simultaneously connected to the network by contacts 4. For the period of pressing the “Start” button 8, its opening contacts 14 prevent the false relay 12 from tripping, breaking its circuit. Capacitors 11 compensate for the reactive power of the engine. After releasing the "Start" button, the contacts of button 14 are closed. In normal operation, the voltage between points 0 and 01 is not enough for the relay 12 to operate. If one or two phases breaks, the voltage between points 0 and 01 increases. The relay 12 is activated, closes its contact 18. The starter 15 is activated, which connects points 0 and 01 with its power contact 16, and the block contact 17 is connected parallel to contact 18. The signal lamp 19 "phase failure" lights up. Despite the fact that the coil 12 is shorted by the contact 16, as a result of which the contact 18 opens, the coil 15 is supplied with current through the contact 17 and diodes 20. In the event of an overcurrent in any phase, the thermal element 6 is heated and the motor is disconnected from the network by opening the thermal contact relay 7 in the coil 3. The circuit breaker 2 protects the circuit from short circuits.

 Thus, in the normal mode, additional losses in the electric motor are excluded, caused by the flow of triple frequency currents in the stator windings and in the circuit connecting its zero point to the zero output of the network, and stable operation of the electric motor is ensured when one or two phases of the network break.

Claims (1)

 A device for trouble-free operation of an asynchronous electric motor when one of the phases of the supply network is interrupted, containing the first magnetic starter with a thermal relay, the Start and Stop buttons and capacitors, characterized in that two diode rectifiers, an intermediate relay and a second magnetic starter are inserted into it the coil of the intermediate relay is connected between the zero points of the network and the stator winding through a chain of series-connected variable resistor and the opening contact of the "Start" button, the first rectifier is connected by anodes to phases of the network to the closing contacts of the first magnetic starter, and its cathodes are connected to each other, the second rectifier is connected by anodes to the phases of the network after the closing contacts of the first magnetic starter, and its cathodes are connected to each other, the closing contacts of the intermediate relay and the second magnetic starter are connected in parallel and connected by one the end to the common point of the cathodes of the second rectifier, and the other to the clamp of the coil of the second magnetic starter, the second end of this coil is connected to the zero point of the stator winding, the closing contact of the second magnetic starter is connected between the zero points of the network and the stator winding, the coil of the first magnetic starter is connected between the common point of the cathodes of the first rectifier and the zero point of the network through a chain of sequentially connected Start and Stop buttons and the thermal relay opening contact, and the capacitors connected according to the "triangle" circuit are connected to the phases of the network after the make contacts of the first magnetic starter to the heaters of the thermal relay.