SU1647745A1 - Device for protecting synchronous motor from asynchronous operation - Google Patents

Abstract

This invention relates to electrical engineering, namely, to relay protection of electrical machines. The purpose of the invention is to reduce the number of motor stops in asynchronous modes by forming a time delay for switching off as a function of the square of the current before the load. When an asynchronous synchronous motor occurs, the stator circuit mode control unit 1 is activated, which is characterized by the appearance of logical unit signals at both of its outputs. The signal at the first output of logic block 7 causes the cyclical operation (in accordance with the slip frequency EMF) of the resynchronization relay 8. The signal at the second output of block 7 starts the relay time. The stator current is sensed by the current sensor 12, and the output current of the stator is released at the output of the amplitude detector 11. When the threshold element 14 is triggered, the stator current enters the multiplication unit 15, which exceeds the block setpoint. The square of the stator current is fed to the input of the integrator 16. Which is triggered by a signal from the second output of logic unit 7. When the signal at the output of integrator 16 exceeds the setpoint of the second threshold element 17, a logical unit signal appears at its output, which passes through the open ( the second output of the logic block 7) the AND 18 and OR 10 logic element, causes the motor switch to shut off. 2 Il. (L S about 4 vj 2 cl

Description

This invention relates to electrical engineering, namely, to relay protection of electrical machines.

The purpose of the invention is to reduce the number of motor stops in asynchronous modes by forming a time delay for tripping as a function of the square of the overload current.

FIG. 1 shows a diagram of the device; in fig. 2 - timing charts of the device.

The device contains a unit 1 for monitoring the stator circuit of a synchronous motor 2. The thyristor exciter 3 is connected to the winding of the rotor of the synchronous motor 2 and the voltage sensor of the rotor 4 by its output terminals, and the stator winding of the synchronous motor 2 is connected to the switch 5. The first input of the block 6 for detecting the EMF of the sliding voltage connected to the functional output of the thyristor exciter 3, and the second input of the unit 6 is connected to the output of the rotor 4 voltage sensor. The inputs of the unit 1 of the control of the stator synchronous circuit mode the motors are connected to the corresponding current and voltage circuits of the stator of the synchronous motor, and the outputs of block 1 are connected respectively to the first and second inputs of logic block 7. The third and fourth inputs of logic block 7 are connected respectively to the first and second outputs of block 6 for EMF detection slip. The first output of logic unit 7 through the resynchronization relay 8 is connected to the control input of the thyristor exciter 3, and the second output of the logic unit is connected via time relay 9 to the first input of the logic element OR tO. A current sensor 12 is connected to the input of the amplitude detector 11, and the output is connected to the inputs of the analog switch 13 and the first threshold element 14. The output of the first threshold element 14 is connected to the control input of the analog switch 13. the output of which is connected to the integrator input 15 through the multiplier 15 16, the output of the integrator 16 is connected to the input of the second threshold element 17, the output of which is connected to the first input of the logic element 18 and its second input is connected to the second output of the logic unit 7 and the control input of the integrator 16. Exit of the AND gate 18 is connected to the second input of the OR gate 10 and its output connected to the switch 5 of the synchronous motor 2.

The device works as follows.

When the asynchronous mode of the synchronous motor 2 arises, the stator circuit mode control unit 1 is activated (figure 1). The stator circuit control unit of the synchronous electric motor contains an impedance relay with a response characteristic located in the first square of the complex resistance plane or a reactive power direction relay with the same response characteristic and undercurrent relay. The operation of block 1 in the asynchronous mode is characterized by the appearance of logical 1 signals at both of its outputs. The signal at the first output of logic block 7 causes a cyclical actuation (in accordance with the slip emf frequency allocated by blocks 4 and 6) of the resynchronization relay 8, which cyclically (with the slip frequency) sends a signal to the control input of the thyristor exciter 3. The signal at the second logic output Unit 7 starts the time relay 9. The stator current of the synchronous motor 2 is sensed by the current sensor 12, and the output current of the stator is released at the output of the amplitude detector 11 (Fig. 2a). If the value of the stator current envelope exceeds the setpoint of the first threshold element 14, the analog key 13 is opened, and only the stator current that exceeds the block setpoint (shaded area, Fig. 2a and c) is received at the multiplication unit 15. FIG. 2 a, b shows time diagrams of the device operation in asynchronous mode with a nominal load on the shaft of the synchronous electric motor 2.

FIG. 2c, d shows the time diagrams of the device operation in the asynchronous mode of a synchronous motor with a load on the shaft less than the nominal one.

The signal at the output of multiplication unit 15 is the square value of the stator current of the motor in asynchronous mode. This signal is fed to the input of integrator 16, which, during asynchronous mode, is triggered by a signal from the second output of logical unit 7. When the signal at the output of integrator 16 (Fig. 2b ) exceeds the setting of the second threshold element 17 at its output a logical signal 1 appears, which passage through the open (signal from the second output of logic unit 7) AND 18 and OR 10 causes switching off the switch five.

When an asynchronous mode of a synchronous motor 2 occurs with a load on the shaft less than the nominal one (fig. 2c, d), the device operates in the same way as described, but the time of the electromotive load. The duration of the motor in an asynchronous mode depends on the actual stator current load and the following circumstances are taken into account: the value of the stator current envelope (Fig. 2a, c) depends on the load on the shaft, while the load varies as the amplitude of the variable component so is constant constituting; the frequency of the variable component of the stator current envelope is equal to the slip frequency, therefore, its value is proportional to the load on the motor shaft,

Determining the permissible duration of the asynchronous mode according to the device algorithm (Fig. 1) implies the implementation of the following concept: the process of heating the motor windings during the asynchronous mode is adiabatic; heating the motor windings to temperatures higher than nominal (i.e. temperatures at nominal load on the shaft) is caused by currents exceeding the nominal value (i.e., exceeding the setpoint of the first threshold element 14).

This solution provides some overheating margin for the electric motor, since in asynchronous mode some of the heat is removed from the machine by the ventilation system. In this case, the longer the asynchronous mode, the more heat is removed by the ventilation system.

Time relay 9 performs backup functions when units 11–18 fail.

The set value of the time relay 9 is selected longer than the response time of the second threshold element 17 in the asynchronous idle mode of the operating motor.

The operation of the device during asynchronous start of a synchronous electric motor is similar to that described. At the same time, protection against a delayed start is ensured, taking into account the degree of gravity of the start (i.e., the start can be carried out with different loads on the shaft, which provides for this device a different time of action of the protection against the start and break of the start and run).

F o rm ula invention

Device for protection against asynchronous operation of a synchronous motor, containing a flea of control of the mode of the stator circuit of a synchronous motor, a logic unit, an EMF detection unit

slip, rotor voltage sensor, resynchronization relay and time relay, with the echo of the stator circuit mode control unit of the synchronous motor, is designed to be connected to the corresponding current and voltage of the synchronous motor, and the outputs are connected respectively to the first and second inputs of the logic unit, the third and fourth inputs of the logic unit are connected respectively to the first and second output of the slip emf detection unit, the first input of which is connected to the functional output thyristor exciters, and the second

the input of the slip emf detection unit is connected to the output of the rotor voltage sensor, the input terminals of which are designed to be connected to the rotor winding of a synchronous motor, the first output of the logic unit is connected to the thyristor exciter control input through a resynchronization relay, and the second output is connected to the input of a time relay, This is due to the fact that, in order to reduce the number of stops in asynchronous modes due to the formation of a shutdown time delay as a function of the square of the overload current, it is equipped shackles sensor amplitude

detector, first and second threshold elements, analog key, multiplication unit, integrator, AND and OR logic elements; the input of the amplitude detector is connected to the current sensor, and the output is connected to the inputs of the analog key and the first threshold element, the output of which is connected to the control the analog key input, the analog key output through the multiplication unit, the integrator, the second threshold element is connected to the first input of the AND logic element, the second input of which is connected to the integrato control input a and input time relay, the output of the AND gate and the time switch are connected to first and second inputs of the OR gate, respectively, whose output is connected with the switch of the synchronous motor.

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Claims (1)

FIELD OF THE INVENTION A device for protection against the asynchronous mode of a synchronous electric motor, comprising a control unit for the stator circuit of the synchronous electric motor, a logic unit, a slip EMF detection unit, a rotor voltage sensor, a resynchronization relay and a time relay, while the inputs of the stator mode control unit the synchronous motor circuit is designed to be connected to the corresponding current and voltage circuits of the stator of the synchronous electric motor, and the outputs are connected respectively to the first and second the input of the logic unit, the third and fourth inputs of the logic unit are connected respectively to the first and second output of the slip EMF detection unit, the first input of which is connected to the functional output of the thyristor exciter, and the second input of the slip EMF detection unit is connected to the output of the rotor voltage sensor, the input terminals of which designed to connect to the rotor winding of a synchronous electric motor, the first output of the logic unit through a resynchronization relay is connected to the control input of the thyristor exciter the second output is connected to the input of the time relay, characterized in that, in order to reduce the number of stops in asynchronous modes due to the formation of the time delay for shutdown as a function of the square of the overload current, it is equipped with a current sensor, an amplitude detector, the first and second threshold elements, an analog key, a multiplication unit, an integrator, AND and OR logic elements, while the input of the amplitude detector is connected to a current sensor, and the output is connected to the inputs of the analog key and the first threshold e an element whose output is connected to the control input of the analog key, the output of the analog key through the multiplication unit, an integrator, the second threshold element is connected to the first input of the logical element And, the second input of which is connected to the control input of the integrator and the input of the time relay, the output of the logical element And and the relay time connected to the first and second inputs of the OR gate, respectively, the output of which is connected to the switch of the synchronous motor.