SU758350A1 - Device for overload protection of electric motor - Google Patents

Description

The invention relates to the field of electrical engineering and can be used for relay protection of electric motors.

Known devices for protecting the electric motor 5 from overload £ ΐ}, containing a motor current sensor connected to a threshold element and a time delay element. When an overload occurs, the motor current 10 increases, which is fixed by a threshold element. If overload mode is maintained for a longer time. ' time relay settings, the latter trips and disables the protected motor 15. . ‘

A significant drawback of devices £ ΐ | the time delay is independent of the magnitude of the overload current, so that the device is insensitive to frequent, but short-lived. overloads when the protected motor does not have time to cool in the pause between overloads.

A device ru is also known, in which 25 the delay time per _g operation varies depending on the overload current. The device comprises a current sensor connected through a rectifier to a non-linear charging rear circuit, the output of which is connected to a threshold element. ''

- The disadvantages of the device ^ 2] are:

- reset, information about the previous overload when it disappeared, which leads to a device failure with frequent, short overloads:

- neglect of the ambient temperature and, consequently, less use of the overload capacity of the engine at low '' ambient temperatures.

. The closest in technical essence to the proposed device is a device ^ 3), containing a current sensor included in the circuit of the protected motor with an output rectifier, an ambient temperature sensor, a quadrator, two analog-frequency converters, a reversible counter, a controlled frequency divider, and a stop detection unit engine, engine start-up detection unit, engine under-current detection unit, engine overcurrent detection unit, adder ', alarm unit, digital-to-analog converter Tel, amplifier, actuator and switch · h / 58350 circuit protected motor. The magnitude of the overload current * is converted into a sequence of pulses, the number of which is counted by a reversible counter; during the periods of stopping the 'engine, its cooling is modeled' by applying to the subtractive input of the counter “a sequence of pulses from the output of a controlled frequency divider. The counter readings are proportional to the excess of the engine temperature over the ambient temperature, which are summed with each other, are kept at the specified setting, and in the case of an unacceptable over-; ? engine warm last disconnect from the network. '. ' , fifteen

The disadvantage of the prototype device is that the summation of the meter and voltage., Proportional to the ambient temperature, is carried out using an analog 20 adder, the nonlinearity of which is the cause of the additional error of the device.

The aim of the invention is to increase the accuracy of the operation of the device 25 by converting the temperature of the engine in a digital code.

This goal is achieved by the fact that in the known device for protection

....... of an electric motor from overload, which includes a current sensor with an output rectifier, an ambient temperature sensor, a quadrator, an analog-frequency converter, a reversible counter, a controlled frequency divider, a unit that detects engine shutdown, an engine start-up detection unit, an engine undercurrent detection unit, an engine overcurrent detection unit, an adder, an alarm unit 40, an actuator, and a circuit breaker for the protected motor. For this, at the same time, a quadrator, blocks for detecting stop, starting 45 mode, current underload and overcurrent of the motor are connected to the output of the rectifier through its inputs, the output of the quadrator is connected to the summing input of the reverse counter through an ay-frequency converter, the output of the stop detection unit is connected to the main the input of the controlled frequency divider, the temperature sensor is functionally connected, connected to the first input of the adder, the output of the unit for detecting underload of the connection ^; nen with a blocking input of the executive body, the main input of which is connected to the output of the adder and the input of the block sgnalizatsii / 'and the output' together with the output of the detection unit 'overcurrent 60 is connected to the disconnecting circuits you.

^^ Yi ^^ yo ^! DRIGATELAG ^: The ambient temperature sensor is connected, with the input of the 'Adder through an additionally entered analog-to-digital converter- 65

Vatel, the adder is made in the form of an arithmetic-logical unit, the counter input and the control input of the Frequency Healer are connected to the second input, and the output of the start mode detection unit is connected to the input of the setting of the executive body setting.

The functional diagram of the described device is shown in the drawing.

Current sensor 1 with rectifier 2 at the output Is included in the circuit of the protected motor. 3. To the output of the rectifier 2, a quadrator 4, unit 5 for detecting the stop of the motion ^{1 are} connected by their inputs. contactor, motor start-up detection unit 6, motor under-current detection unit 7 and motor overcurrent detection unit 8 The output of the quadrator 4 is connected via an analog-to-frequency converter 9 to the summing input of the reverse counter 10, the output of which is connected to the first input of the adder 11 and the control input controlled divider 'frequency. The output of the latter is connected to the subtracting input of the counter 10.

The output of the stop detection unit 5 is connected to the main input of the frequency divider 12. The sensor 13 of the ambient temperature through an analog-to-digital Converter 14 is connected to the second input of the adder 11, the output of which is connected to the actuator 15 and the signaling unit 16. The output of the motor undercurrent detection unit 6 is connected to the blocking input of the actuator 15, the output of the start mode detection unit 7 is connected to the input of the change in the setpoint of the organ 15, and the output of the latter, together with the output of the motor overcurrent detection unit 8, is connected to the disconnect circuits of the circuit breaker 17 of the protected motor.

• The device operates as follows. After turning on the motor 3 in operation, the voltage at the output of the rectifier 2, in proportion to the motor current, is supplied to the inputs of the quad 4 and blocks 5,6, 7 and 8. And the voltage at the output of the quad 4, is proportional. the thermal loss of the motor being protected is converted by an analog-to-frequency converter 9 into a sequence of pulses whose repetition rate is proportional to the thermal loss of the engine. The specified sequence of pulses is fed to the summing input of the reversible counter. 10 ‘, The temperature rise of the engine is proportional to the difference between the amount of heat released due to losses in the protected engine and the amount of heat / dissipated in the space surrounding the engine. The last amount of heat is taken into account by the feedback circuit from the output of the counter 10

753,350 b

• -.l through a controlled frequency divider 12 to the subtracting input of the counter; 10. When the engine is running, the signal at the output of the engine stop detecting block 5 has the form of a pulse sequence. owls whose frequency is proportional to the thermal power dissipated by the engine and the surrounding space, taking into account its ventilation. Thus, the readings of the counter 10 are proportional to the excess of the engine temperature over the ambient temperature, which is measured by the sensor 13 and converted into a digital code by an analog-to-digital converter 14. The signal from the output of the latter and the signal from the output '. 'counter 10 are added by the adder. '15 11 and their sum is compared with the set point in the executive body 15.

With unacceptable overheating of the engine 3, the signal from the output of the organ 15 acts on the switch 17 and the engine 20 is de-energized.

When the engine is stopped, the pulse repetition rate at the output of the stop detection unit 5 decreases. This / takes into account the reduction in heat dissipation when the engine is stopped due to lack of ventilation. When starting the engine, an output signal is generated at the output of the starting mode detecting unit 7, which is fed to the input of the organ 15 and increases the operation setpoint 41) by the time the engine starts. In the case of current underloading of the motor, when the current consumed by it is less than the long-term allowable, the actuator 15 is blocked. In case of damage to the protected motor, accompanied by overcurrents, the engine is switched off directly from ^: block 8. detection of overcurrent of the motor.

Thus, the introduction of an additional 40 element and Functional relationships provides an increase in the accuracy of the device by converting the ambient temperature and exceeding the engine temperature into a digital code and thereby eliminating the errors of analog summation.

Claims (3)

Formula of the Invention '50 Device for protecting the motor against overload, containing a current sensor included in the circuit of the motor being protected, with a rectifier at the output, an ambient temperature sensor, 55 quadrator, analog-to-frequency converter, a reversible counter, a controlled frequency divider, a unit for detecting engine shutdown , engine start-up detection unit, engine underload current detection unit, “" (overcurrent detection adder, alarm unit, actuator and circuit breaker of the protected motor, and this is connected to the output of the rectifier by its own inputs; a quadrator, blocks for detecting voltage, starting mode, current underload and overcurrent of the motor, a quad output through an analog-to-frequency converter frequency divider, the ambient temperature sensor is functionally connected to the first input of the adder, the output of the underload detection unit is connected to the blocking input of the executive body, basically the first input of which is connected to the output of the adder and the input of the signaling unit, and the output, together with the output of the overcurrent detection unit, is connected to the circuit breakers of the motor switch, which means that, in order to increase the accuracy of operation of the device by converting the temperature of the protected motor into a digital code, an ambient temperature sensor is connected to the input of the adder through an additionally introduced analog-to-digital converter, the adder is made in the form of an arithmetic-logical unit, to the second input of which The counter output and the control input of the frequency divider are connected, and the output of the start mode detection unit is connected to the input of the change in the setting of the executive body. Sources of information taken into account in the examination 1. Fedoseev A. M. Relay protection of electrical systems. SEI, M.-L., 1952, p. 471. 2. Gelfand I .. S., Perelman B-. C. Maximum current relays with adjustable time-current characteristics. Electricity, No. 8, 1973. 3. Electronic relay of maximum protection 7 K2. Express information. ZINITI, a series of automated electric drive, No. 46, 1976, ref. 226 and 227 (prototype).