RU1817181C - Device for thermal protection of electrical plant in starting mode - Google Patents

Abstract

Usage: in electrical engineering, in particular, for the protection of electric motors. SUMMARY OF THE INVENTION: by pressing the Start button 13, the clamp of the power source 1 is a forbidden-resolving thermistor 6 - limiting resistor 14 is a Start-up button 13 - Stop button 12 - zero About the source (second phase 2) current will flow and the forbidden-resolving thermistor The voltage will be sufficient so that) after it is pulled up in the voltage increasing device 15, the starting contactor 7 is activated. In this case, the closing contact 9 is closed, and then the contacts 10 and 11 are opened and the contacts are closed 8. After that, the thermistors start ayut progrevats inrush current and smoothly (exponentially) reduce their resistance. A soft start of the electrical installation (for example, an asynchronous electric motor or a three-phase 4, or a single-phase motor 5) occurs. As the thermistors heat up, their resistance decreases, the voltage drop across them decreases, and at the load terminals increases. At the end of the start-up, the voltage at the load terminals increases so much that the bypass contactor 16 will operate and: close its contacts 17. From this moment, the thermistors 6 begin to cool, ready to be restarted (new). The installation is switched off by pressing the Stop 12 button. 1 ill.

Description

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The invention relates to devices for temperature protection of electrical installations with start-up thermistors, providing a soft start only due to the properties of the thermistors themselves from switching on when the thermistors are not cooled down. The most effective thermistor starting devices can be used to limit the starting currents (ensuring a soft start) of electric motors, glow circuits of powerful generator and searchlight lamps, network rectifiers of secondary power supplies with transformerless input, etc.

An object of the invention is to increase the efficiency and reliability of a device.

The drawing shows a diagram of the proposed device.

The diagram indicates: 0, 1, 2, 3 - respectively, zero, first, second, third of the phase of the power supply, 4 - three-phase load, for example, an asynchronous short-circuit motor, three-phase mains transformer, etc., 5 - single-phase load ( single-phase motor, transformer, filament circuit of a powerful lamp, etc.), 6 - starting thermistors (thermistor rheostats), 7 - winding of the starting contactor, 8 - closing power contacts of the starting contactor, 9 - closing contact of the starting contactor, 10 - first opening contact of the starting contactor, 11 - second opening contact of the starting contactor.

Pin 9 is triggered earlier in relation to other contacts, i.e., contacts 8, 10 and 11 of the contact group of the starting contactor, 12 - Stop button, 13 - Start button (both with self-reset), 14 - limiting resistor, 15-device, increasing voltage (for example, a transformer), 16 - winding of the shunt contactor, 17 - closing power contacts of the shunt contactor (instead of the shunt contactor, a contactless device, for example, a triac, designed to short-circuit the starting thermistors at the end of the process and start).

Starting thermistors b are connected in series with the closing power contacts 8 of the starting contactor 7 and the resistance of the load phases (windings of motors, transformers, etc.). In this case, the first clamp of the first starting thermistor is connected from the power supply side, and the second from the load side. In parallel with the first starting thermistor b, a transformer is connected through the first opening contact 10, to the output of which a winding of the starting contactor 7 is connected through the second opening contact 11. The common point of contact 11 and

the windings of the contactor 7 through the make contact 9 of the starting contactor 7 are connected to the first terminal of the first thermistor. Another terminal of the start contactor winding is connected to the midpoint of the start button 13 and Stop 12, the other terminal of the start button is connected to the second terminal of the first thermistor 6 through the limiting resistor 14, and the other terminal of the stop button is connected to

5 by zero power source .- Note that the indicated connection to zero or the second fa. It also depends on the voltage of the source, on the voltage for which the winding of the starting contactor is designed (127,220 or 380 V).

0 The device operates as follows.

Let thermistors (including the first one) have a temperature equal to the ambient temperature (cooled thermistors). The resistance of the thermistors is significant. Therefore, when you press the Start button 13 through the circuit, the clamp of the power supply 1 - the first thermistor 6 - the limiting resistor 14 0 the Start 13 button - the Stop 12 button - zero About the source (second phase 2) the current will flow and the voltage will be sufficient on the first thermistor to so that after raising it by the transformer 15, the starting contactor 7 is triggered 7. In this case, the closing contact 9 is closed, and then the contacts 10 and 11 are opened and the contacts are closed 8. After that, the thermistors start to heat up with the starting current and

0 smoothly (exponentially) reduce their resistance. A soft start of the electrical installation (for example, an asynchronous electric motor or a three-phase 4, or a single-phase motor 5) occurs. As the thermistors heat up, their resistance gradually decreases, the voltage drop across them decreases, and at the load terminals increases. At the end of start-up, the voltage at the load terminals rises so much that

0, the bypass contactor 16 is activated and closes its contacts 17. From this moment, the thermistors 6 begin to cool, ready to restart (new) start. The installation is switched off by pressing the Stop 12 button.

If the thermistors do not have time to cool by the time they are turned on again, their resistance is small. The voltage on them will be insufficient so that (after increasing this voltage) the trigger starts:

howl contactor. Installation does not turn on when the thermistors are still cold. Pressing the Start button 13 should be short-term (fractions of a second). In this case, the additional heating of the first starting thermistor is insignificant and there will be practically no temperature distortion of the thermistors in all phases.

The technical and economic advantages of the present invention over the known solution to the problem are to eliminate energy losses and to increase reliability in operation by eliminating temperature distortion of thermistors.

The proposed device is ready for industrial use.

Claims (1)

SUMMARY OF THE INVENTION A device for thermal protection of an electrical installation in a start-up mode, containing start-up thermistors connected in series with the power closing contacts of the start-up contactor and intended to be connected to the corresponding phases of the supply network, connected in series to the Start button and the limiting resistor, the first the opening contact of the starting contactor, characterized in that, in order to increase efficiency and reliability. a transformer is connected in parallel with the first thermistor through the first opening contact of the starting contactor, the winding of the starting contactor is connected through the newly introduced second opening contact of the starting contactor, the common point of connection of which through the newly introduced closing contact of the starting contactor is connected to the first terminal of the first starting thermistor, another terminal of the winding the start contactor is connected to the connection point of the newly entered Stop and Start button, limit the free output The first resistor is connected to the second terminal of the first starting thermistor, the other terminal of the Stop button has a terminal for connecting to the other terminal of the power source, the windings of the newly introduced shunt contactor are designed to connect to the corresponding phases of the mains from the load side, and its make contacts are connected in parallel with the corresponding starting thermistors.