SU1571718A1 - Device for heat protection of electric motor - Google Patents

Abstract

The invention relates to electrical engineering and can be used for thermal protection of an electric motor. The purpose of the invention is to increase the sensitivity, expand the scope and increase the reliability of the device. Thermal sensors 6 are connected to the secondary winding of the transformer 3, threshold element 7 and power supply unit 9. When the temperature limit of the motor to be protected is exceeded, the resistance of thermal sensors 6 increases, causing an increase in the voltage across them, as well as a voltage change between the neutral point and the neutral wire of the network. The sum of the increments of these voltages goes to the threshold element 7, the operation of which causes the switching on of the executive body 8, which turns off the electric motor. 3 il.

Description

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The invention relates to epactrotechnical technology and can be used for thermal protection of an electric motor.

The purpose of the invention is to increase the sensitivity, expand the scope and increase the reliability of the device.

FIG. 1 shows a diagram of the device, FIG. 2 and 3 - vector diagrams. The first 1 and second 2 resistors are connected in series and connected between the first and second phase wires, and their common point is through the primary winding of the transformer 3 and the third 4 resistor connected in series with it connected to the third phase wire of the power supply network. The capacitor 5 is connected to the primary terminals, and the thermal sensors b to the secondary terminals of the transformer 3. One of the secondary terminals of the transformer 3 is connected to a common point of the first 1 and second 2 resistors, and its second terminal is with one of the input terminals of the threshold element 7, the second input terminal of which is connected to the zero wire of the power supply network The executive body 8 is connected to the output of the threshold element 7, and the power supply unit 9 is connected to the power supply terminals by the AC power supply terminals, and the DC power supply terminals are supplied with thresholds m element 7 The device operates as follows.

In the initial state, when the temperature of the windings of the protected electric power is below the allowable one, the resistance of the thermal sensors is low and, accordingly, the voltage Us is low on them. Resistors 1 and 2 are chosen so that in the initial state the voltage Us between the neural point of the above star (point n) and the net zero (point N) is equal to Us, and the polarity of the connection of the secondary winding of the transformer 3 is such that the voltage from would be out of phase with the voltage Us, as shown in the vector diagram of FIG. 2. In this diagram (and in the diagram in Fig. 3), Ui, U2.U4 are the phase voltages of the above-mentioned star. Then on the threshold element 7 the difference between the voltages from and Us will come, which in the initial state will be equal to zero.

When the temperature of the motor winding reaches its limiting value, the resistance of the thermal sensors begins to increase. Accordingly, the voltage of this star phase U increases, and, consequently, the voltage Us on thermal sensors. The voltage from will begin to decrease to zero, and then increase, but already with

opposite phase FIG. 3 shows the vector diagram for this case. As a result, the threshold element 7 begins to receive a voltage equal to first

5 the differences Ua and Us, and then (after changing the phase of) their sum This voltage triggers the threshold element 7 and turns on the actuator 8, which in turn gives the command to turn off the electric motor

In the event of a short circuit of any of the temperature sensors, their resulting resistance decreases accordingly, and the voltage Us on them, and

15 Voltage Ua increases The difference between these voltages ceases to be zero, which causes the threshold element 7 and the actuator to fail. 8 Reducing the creeping of any 20 phases of the supply network or when it is broken (the voltage of the network phase is absent) the voltage changes both in magnitude and phase, the initial state of equilibrium is disturbed, which also leads to

25 voltages at the input of the porg element and the protection operation

Thus, the introduction of a threshold element in combination with a high sensitivity provides the necessary services with a level to increase the accuracy of the device operation relative to the set limit temperature.

At the same time, the conditions are eliminated under which tripping and tripping of the protection device are triggered, and the reliability of its operation increases as a voltage that is obviously greater than its voltage is applied to the executive unit (relay).

40 primary actuation

The increased sensitivity, accuracy and reliability of the protection device, as well as the prohibition of work in the event of a short circuit of temperature sensors and asymmetry of the phase voltage of the supply network prevents unnecessary overheating of the windings of the protected electric motor and contributes to an increase in the duration of its operation without repairs, which reduces

50 operating costs and creates an economic effect in the national economy.

Claims (1)

Invention Formula 55Device for thermal protection of an electric motor, containing a chain of three thermal sensors connected in series, for installation on the stator windings of an electric motor, the first, second and third resistors, the Raman sensor and the executive the body, the first output of the first resistor is the first output of the device and has a terminal for connecting to the C phase of the mains supplying motor; the first output of the second resistor is the second output of the device and has a terminal for connecting to the phase B of the mains supplying electric motor; the second output of the second resistor connected to a common load point p to which the first capacitor lead is connected, characterized in that, in order to increase the sensitivity, expand the field of application and increase the reliability of the device, in it The transformer, the threshold element and the power supply unit are additionally inserted, the first terminal of the third resistor being the third terminal of the device and having a terminal for connecting to phase A of the mains supplying motor; The second terminal of the third resistor is connected to the first terminal of the primary winding of the transformer and the second terminal of the capacitor, the second Phie 2 0 five 0 the output of the transformer primary winding, the first output of the transformer secondary winding, the first output of the chain of three thermo sensors connected in series and the second output of the first resistor are connected to a common load point n, the second output of the transformer secondary winding is connected to the second output of a chain of three series-connected thermal sensors and to the first the input of the threshold element, the second input of which is the fourth output of the device and has a terminal for connection to the neutral wire of the supplying motor network, the third input of the threshold element is connected to the output of the power supply, the three inputs of which are the fifth, sixth and seventh terminals of the device and have terminals for connecting the network supplying motor, phases A, B and C respectively, the first and second actuator inputs are connected respectively to the first and second outputs of the threshold element. BUT BUT