SU1647741A1 - Device for thermal protection of motors - Google Patents

Abstract

The invention relates to protection schemes for electric machines that react to deviations from normal temperature, as well as react to excessive temperature increases caused by current overloads and other disturbances. The purpose of the invention is to increase reliability by making it possible to predict insulation overheating to an unacceptable value. The goal is achieved by placing two parallel circuits from thyristor simultaneously on the frontal parts of the winding of two adjacent phases. This makes it possible to obtain information on the thermal state of all windings of an electric motor. 7 il.

Description

The invention relates to protection schemes for electric machines that react to deviations from normal temperature, as well as react to excessive temperature increases caused by current overloads and other disturbances.

The aim of the invention is to increase reliability by making it possible to predict overheating of winding insulation to an unacceptable value.

FIG. 1 shows a block diagram of the proposed device; in fig. 2-5 diagrams of device operation; in fig. 6 is a diagram of a thermal sensor; in fig. 7 - graphs of the temperatures of operation.

The device consists of a thermal sensor 1 made of two series-connected circuits containing parallel-connected posistor 1a and 16, respectively, at lower and higher response temperatures, each consecutive part of the thermal sensor circuit being installed simultaneously on the frontal parts of the winding of two adjacent phases.

Due to this arrangement of two parallel circuits, it is possible to fully obtain information on the thermal state of all windings of an electric motor. In the two phases of the motor windings there are terminals for connecting the primary windings of two current transformers 2 and 3, respectively, the secondary windings of which are connected respectively to the inputs of the first 4 and second 5 filters, the filter outputs are connected to the inputs of the adder 6. The pulse generator 7 is connected to the first controller input 8 of the duty cycle, the second input of which is connected to the output of the adder 6. The outputs of the regulator 8 of the duty cycle are connected to the posistor 1. the first of them

4 V4

connected through the first resistor 9, and the second - directly. In parallel with the thermal sensor terminals of posistors 1, the diode 10 and the capacitor 11 are connected to each other and connected to each other. The input of the amplifier 12 is connected in parallel to the capacitor 11, the output of which is connected in series with the second 13 and third 14 resistors. The second switch 15 is connected by inputs to the input of the second resistor 15, the first switch 16 is connected to the output of the amplifier 12. The output of the first switch 16 is connected to the first actuator 17 and the switching s. arat 18, and the output of the second key 15 is connected with the second executive body 19.

The device works as follows.

Executive generator 7 generates rectangular pulses of positive polarity, stable frequency and duration (Fig. 2). Voltage pulses are fed from the output of the generator 7 to the first input of the duty cycle controller 8, while in a temperature-sensitive circuit consisting of a temperature sensor (posistor) 1 and the first resistor 9 connected to the outputs of the duty cycle controller 8, a pulse current flows (Fig. 3 ), which creates, respectively, the voltage drop across the temperature sensor of posistor 1 and the first resistor 9.

A voltage drop proportional to the electrical resistance of the posistor 1 is supplied to the capacitor 11 through the diode 10. At the same time, the second input of the durability regulator 8 is supplied with voltage from the adder 6 coming from the secondary windings of the first current transformer 2 and the second current transformer 3, respectively, through the first 4 and the second 5 filters, proportional to the sum of the currents in the phase windings of the protected motor, which allows more accurately form a control signal at the second input of the duty cycle controller 8.

The voltage from the adder 6 to the second input of the bore ratio controller 8 is controlling for it and affects the duration of current pulses flowing in a heat-sensitive circuit consisting of posistor 1 and the first resistor 9. With increasing load, the electric motor consumed their current increases and at the same time the control voltage and duration of the current pulses flowing in the temperature-sensitive circuit increase (Figs. 4 and 5).

With a minimum current in the motor windings and small overloads (for example, up to 2 1H), when the rate of increase of the motor windings temperature is low, through a temperature-sensitive circuit - posistor. 1 and the first resistor 9 flows

pulsed current that does not cause self-heating of the posistor 1.

In this case, the dynamic error of posistors is practically absent, and their thermal state, and, accordingly,

electrical resistance is determined by the thermal state of the motor windings.

At high overloads, for example, more than 21 n, when the rate of increase in the temperature of the windings increases markedly and the dynamic error of the posistor 1 also increases, the duration of the current pulses flowing in the heat-sensitive circuit increases proportionally

current load of the electric motor and due to this additional heating of the posistor 1 occurs, which ensures their accelerated response and compensation of the dynamic error (inertia

posistorov). The magnitude of the equivalent current flowing in a temperature-sensitive circuit is determined by the expression

thirty

Ut

1imp Rin + Rg T

where Dun is the voltage of the power source;

total score 2 Ria Rib

K p -

Ria 4-Rib

5 posistors (Fig. 6);

Ria. Rib - parallel-connected resistors of one of the circuits, respectively, for lower and higher response temperatures:

0 Rg is the resistance of the first resistor 9;

timp - the duration of the current pulse flowing in the heat-sensitive circuit; T is the current pulse period.

5 Thus, the heating of the posistor Ria and Ri6 to the response temperature can occur due to their heating from the motor windings (with a small overload of the electric motor up to 21N) or their

0 of the combined heating of the motor windings and due to the current flowing through the posistors Ria and Ria (at large overloads of the electric motor and currents greater than 2 1H). Since Posistors Ria and Rie have different classification response temperatures, smaller and larger (Fig. 7), they are gradually triggered when heated: first, Posistors Ria, triggering the light or sound alarm, and then Posistors, Rie, providing emergency shutdown overheated electric motor.

For high-quality and stable operation of the temperature-sensitive circuit, the resistance values Ria and Rte of the thermal sensor should be approximately the same in the initial cold state.

When the response temperature of posistors Fi3 is reached, their electrical resistance increases sharply, which leads to an increase in the total resistance R -. n, the voltage drop across it and the voltage across the capacitor 11 according to

R4n RHP

Uc + Rg

If we take into account that in the initial cold state, the resistances of the posistors Hia and Ri6 are approximately equal, then when the positors of Ria are triggered, the total resistance Rgp of the posistor 1 almost doubles and is determined by the total value of the resistance of the posistors Rie. which have not yet reached the response temperature and have little resistance. The voltage drop across the total resistance R n posistor 1 in this case is fed through diode 10 to capacitor 11 and then through amplifier 12 to the second 13 and third 14 resistors connected in series, forming a voltage divider. If the voltage drop across the second resistor 13 reaches the pitch of the second switch 15, then the second actuator 19 operates, acting on the light or sound signaling, which indicates that the motor winding isolation to the unacceptable overheating. If the operator on duty, having received a pre-emptive signal, cannot change the mode of operation of the electric jigger or temporarily disconnect it from work, proceed to work with another mechanism, the heating process of the motor windings continues until the actuators Ri6 are triggered. designed for higher response temperatures. In this case, the voltage drop on the sum of the resistance R –n posistor 1 increases even more, which leads to an increase in the voltage on the voltage divider made of series-connected second 13 and third 14 resistors. If the voltage on the voltage divider 1 (14) reaches the threshold of operation of the first key 16. Then the first actuator 17 operates, acting on the switching

the apparatus 18, and the superheated electric motor is disconnected from the power source. In this case, the response voltage of the keys 15 and 16 is determined only by the total resistance R vn of the position sensor 1 and does not depend on the amount of current in the temperature-sensitive circuit.

In the mode of frequent frequent starts (which is typical for many electric drives), when the electric motor is already sufficiently heated, due to the thermal effect of the equivalent current U flowing in the heat-sensitive circuit, early operation of the posistor 1 may occur, although the windings temperature of the electric motor does not exceed acceptable for this class of resistance isolation To eliminate the advance response of posistor 1, filters 4 and 5 provide an increase in the control signal at the second input of the duty cycle controller 8, coming from the adder 6 depending on the time of the starting current.

The proposed device achieves a relatively high accuracy of the motor protection due to the flow of a pulsed current proportional to the current in the phase windings integrated in the motor winding, thereby compensating for the dynamic error of the posistor at any speed of the winding temperature dependent on the load. motor, and in comparison with the prototype provides the function of predicting the possibility of overheating by introducing signals The situation is about approaching the heating temperature of the insulation of the windings to an unacceptable value in all operating modes of the electric motor.

The economic efficiency of the invention is determined by increasing the service life of the motor between overhauls, reducing the total number of electrical equipment failures by maintaining the integrity of the insulation of the motor windings during overloads and increasing the continuity of technological processes due to greater information about the thermal mode of the electric motors.

The proposed device can be used to protect against overheating of electric motors for both general industrial and special purposes.

Formupa invention

Device for thermal protection of an electric motor containing a thermal sensor, made in the form of posistors, intended for installation in frontal

parts of motor windings, parallel-connected diode and capacitor are connected in parallel to the terminals of the thermal sensor, two current transformers for switching on to the corresponding phases of the motor supply, a pulse generator connected to the first input of the duty ratio controller, the first output of which is through a resistor, and the second is directly below - connected to the terminals of the thermal sensor; the primary windings of the current transformers are connected to the first and second filters, respectively, whose outputs are connected to the inputs with of the mathmator, the output of which is connected to the second input of the duty ratio controller, the first key, the output of which is connected to the actuator's passage, characterized in that, in order to increase reliability by providing the possibility of predicting the insulation overheating

windings to an unacceptable value, amplify additionally, the second and third resistors forming the voltage divider, the second switch, the second actuator, the amplifier input connected in parallel to the capacitor, the output to the serially connected second and third resistors, are connected to the inputs to the second resistor, the first key by the inputs to the output of the amplifier, the output of the second key is connected to the input of the second actuator, and the chip consists of two series-connected circuits, with holding each parallel connected posistors, respectively, at lower and higher response temperatures, each parallel circuit being designed to be installed on the frontal parts of the winding of two adjacent phases.

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Claims (1)

Claim A device for thermal protection of an electric motor, comprising a thermal sensor. made in the form of posistors intended for installation in the frontal parts of the motor windings, in parallel with the terminals of the thermal sensor are connected in series a diode and a capacitor, two current transformers, designed to be included in the corresponding phases of the motor power supply, a pulse generator connected to the first input of the duty cycle controller, the first output of which through a resistor, and the second is directly connected to the terminals of the temperature sensor, respectively, connected to the secondary windings of the current transformers the first and second filters, the outputs of which are connected to the inputs of the adder, the output of which is connected to the second input of the duty cycle controller, the first key, the output of which is connected to the input of the actuator, characterized in that, in order to increase reliability by making it possible to predict the overheating of the winding insulation up to of an invalid value, an amplifier, a third and a third resistors forming a voltage divider, a second switch, a second actuator are additionally introduced into it, while the input of the amplifier is connected to parallel to the capacitor, the output is connected to the second and third resistors in series, the second key is connected by the inputs to the second resistor, the first key is connected to the amplifier output by the inputs, the second key output is connected to the input of the second actuator, and the temperature sensor is made up of two series-connected circuits containing each parallel-connected posistors, respectively, at lower and higher response temperatures, while each parallel circuit is designed for installation on the frontal parts of the winding of adjacent phases. t-uh  T Figure 2  ____ L  t Fig.Z ¹ £ lb t