SU1398016A1 - Device for overload and overcurrent protection of electric motor - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to relay protection of electric machines, and can be used in electric power stations, substations, in regional electric networks, as well as in power supply systems of industrial enterprises. The purpose of the invention is to increase the sensitivity and reliability of the shield, expanding the field of application. The goal is achieved by the fact that the device is additionally introduced in series with a multi-loop CC analogue of the thermal state of the electric motor 8 and shaper 9 of a signal proportional to the sum of the effective value of the periodic stator matching current of the stator and its derivative, the second comparator 10 and the transistor switch 12. The transistor input key 12 is connected to the output of the first element of the latch time 11, and its output is connected to the power supply circuit of the blocking key 14. The input of the block 8 is connected to the outputs of the drivers rectified signals 4 and 5, and the output of block 9 - with the first input of the second comparator 10. 2 Il. - S (L

Description

ABOUT

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The invention relates to electrical engineering, in particular, to relay protection of electric machines, and can be used in electric power stations, substations, in regional electric networks, as well as in power supply systems of industrial enterprises.

The purpose of the invention is to increase the robustness and reliability of protection, expanding the scope.

Fig. 1 shows the circuit diagram of the protection device; Fig. 2 shows diagrams characterizing the operation of the protection device during the start-up of the protected motor.

The device comprises a motor current sensor 1 comprising a current transformer 2 and a current-voltage converter 3 (an intermediate transformer loaded with a quencher). The rectifier drivers are connected to the output of the latter.

signals, made according to the scheme of single-half-period rectifiers 4 and 5 with sl, live capacitors and discharge resistors connected

The tires are connected to the total voltage of the rectifiers, the driver of the signal proportional to the motor current and its derivative, connects separately the inverting input of the second (output) comparator 10 with the output of the negative half-current rectifier, and the non-inverting output to the output current of the positive half-current. The shaper 6 of a signal proportional to the sum of the half-waves of the stator current is connected through the first element 11 of the time to the input circuit of the transistor switch 12, the executive circuit of which is connected to the DC source by the second element 13 of the time delay and the executive circuit of the blocking key (thyristor analogue) 14 The shaper 7 of the signal proportional to the difference of the half-wave current of the stator through the rectifier 15 is connected to the input of the first comparator 16 loaded by the control circuit of the locking key 14. The second comparator 10 p is connected to input 17 of the executive body protection devices recompense

between each other according to and following the ZO of the circuit breaker 18 in the circuit

but the point of their connection is the cxeNJbi common bus.

The outputs of the formers 4 and 5. of the output signals are connected to the driver 6 of the signal proportional to the sum of the half-waves of the stator current and the driver 7 of the signal proportional to the difference of the half-waves of the stator current made; on operational amplifiers, the shaper 6 being configured on an operational amplifier with a non-zero potential. The device also contains a multi-circuit CS-analogue 8 of the thermal state of the engine and a signal shaper 9 connected in series with it, proportional to the sum of the effective value of the periodic component of the machine current and its derivative.

In this case, the operational amplifier of the coder 6 is connected with a non-inverted input to the capacitor of the negative current half-wave rectifier, and the inverter - to the capacitor of the positive half-wave rectifier;

current, the analogue of the thermal state of the machine is connected to the total voltage of the rectifiers, the driver of the signal proportional to the motor current and its derivative connects separately the inverting input of the second (output) comparator 10 with the output of the negative current half-wave rectifier, and the non-inverting output with the output of the rectifier positive half-wave current. A signal generator 6, proportional to the sum of the half-waves of the stator current, is connected to the input circuit of the transistor switch 12 through the first time element 11, through the executive circuit of which a second time delay element 13 and the executive circuit of the blocking key (thyristor analogue) 14 are connected to a direct current source. A shaper 7 of a signal proportional to the difference of the half-wave current of the stator through the rectifier 15 is connected to the input of the first comparator 16 loaded by the control circuit of the locking key 14. The second comparator OR 10 is connected to the input 17 of the executive body protection device vozdey5

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stator motor 19.

The device works as follows.

The current of the protected motor 19 is transformed by the current transformer 2 according to the magnitude and the level of the nominal primary current of the intermediate transformer 3, which, together with the load control resistor of the secondary circuit, forms the current-to-voltage converter. Shaper 4 and 5 of the rectified signals convert an alternating voltage proportional to the primary current, while signals proportional to its amplitudes are negative and positive. The outputs of the formers 4 and 5 are connected in series and according to. The point of their connection is a common bus for the remaining blocks of the circuit.

A splitter resistor slider is connected to the common bus, which ensures accurate balancing of the voltage of the smoothing capacitors of these half-wave rectifiers and, therefore, minimizes the unbalance caused by the inequality of the parameters of the elements of the rectifier circuits 4 and 5. Relative to the common bus on the opposite sides of the capacitors of the formers 4 and 5 therefore, the voltages are proportional to the amplitudes of the negative and positive half-waves of the current, and voltage capacitors have opposite signs.

If the primary current does not contain. aperiodic subharmonic components, the maximum positive and negative values of currents in the period are equal in absolute value, and their difference is zero. The aperiodic current displaces the forced component with a frequency of 50 Hz, and the amplitude values of the half-waves of current in the period, and consequently, the voltages of the capacitors under consideration are not equal to each other in absolute value. The same holds for the action of the subharmonic component in the transient current (Fig. 2).

The voltages of the smoothing capacitors of the drivers 4 and 5 are fed to the input of the driver 7 of the signal proportional to the difference of the half-wave current of the stator. On the non-inverting input of this capacitor, the capacitor voltages have opposite signs. Therefore, when the potential difference of the capacitors is equal, the output voltage of the driver 7 is equal to zero-JBO. In this case, when the amplitudes of the half-waves of current i (Fig. 2) are not equal to each other, the output potential of the driver 7 increases in absolute value (it can have both a positive sign and a negative sign). In the composition of the differential input signal, except. The component proportional to the aperiodic or subharmonic current is acted upon by a voltage of 50 Hz (Ug, Fig.2), which is an unbalance. The use of a driver 7, along with resistive feedback and capacitive feedback, makes it possible to reduce the fraction of a voltage of 50 Hz in its output voltage (Ujh, Fig. 2). The latter is fed through the rectifier 15 to the first comparator 16 and, in the case of exceeding its setpoint, causes the comparator 16 to switch, and a positive signal is generated at its output to the control input of the blocking key 14 (transistor analogue of the thyristor).

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Thus, the considered channel of the protection device 1 creates conditions for unlocking the blocking key 14 when the aperiodic or free periodic component is contained in the primary current. The second condition for the flow of current through the blocking switch 14 is the presence of its anode Q voltage.

In order to determine the operating modes of the protection device in which the second condition for the flow of current through the blocking key 14 is satisfied, consider the operation of blocks 6, 11 and 12.

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The input signals (Fig. 1) of the signal generator 6, proportional to the sum of the half-waves of the stator current, are also the voltages of the smoothing con2Q capacitors of the formers 4 and 5, which have different polarity relative to the common bus. Voltage capacitors are fed to the inputs of the forcing 6: negative - to non-inverting,

25 positive - to the inverting one (the same voltage is applied to the negative voltage of the trimmer slider). Therefore, if the capacitors are not charged, the output

3Q inertial voltage is positive. This is also the case if the sum of the capacitor voltage modules is less than the set point (set by the trimming resistor connecting the inverting input of the amplifier to the minus of the power supply). The setting is selected at 70% of the voltage corresponding to the periodic forcing component of the inrush current. This component is proportional to the sum of the voltage modules of the capacitors of the rectifiers 4 and 5 in the starting mode of the engine.

In those modes, when the primary current exceeds 0, where K is the multiplicity of the starting current} I "is the rated current of the maschine, the output voltage of the shaper 6 begins to decrease, passes through a zero value and then reaches the limit

 negative value. The time of almost complete change of the voltage of the inertial link with the inrush current is 50-60 ms (from this condition the capacity of the reverse

 link connection) Reducing the output voltage of the driver 6 causes the capacitor to discharge of the first time-delay element 11. His difference

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potentials reach zero, then changes its sign. At a certain value of its negative potential, a break in the Zener diode i of the first time delay element 11 occurs and a current passes through the control transition of transistor switch 12. The use of a setting voltage capacitor for charging, which makes the initial part of its discharge curve more flat, and the final part, which determines the response, makes it steeper and thus improves the accuracy of time delay.

The transition of the transistor switch 12 IB wire} provides a state of charge for the capacitor of the second time-delay element 113 and is a sufficient condition for switching on the locking key 14. The latter is therefore included in cases when the current of the protected motor is the time interval, which is longer, the Ci nejpBoro element of time (0.1–0.3 s) exceeds the value of 0.7 Cr – H ,,,, and contains a low frequency component after a specified time. The conditions listed are indications of a successful motor start. Consequently, the locking key 14 locks the protection device in the starting mode of the electric motor jf and the bodies

If the rotor of the machine remains in the decelerated state, the capacitor of the second time element 13 and the electrode continues to charge and after 0.15 - 0.55 s reaches the switching threshold of the comparator 10; The latter, with its positive output potential, triggers the switching of the transistor and the operation of the executive relay of the output organ 17 acting on the elements of the shutdown - the protected motor. The protection time in this case is 0.25 - 0.585 s (a shorter time delay from E: it is fixed and can be set for general motors with a power up to 200 - 5:50 kW, longer for large plants)

The motor protection device, in addition, is equipped with a body 8, which provides operation with a time dependent inversely dependent on current. The time of the adacnas scheme of such an organ contains a three-circuit RC circuit,

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The charge of each of the capacitors of which eKB valences the heating, respectively, of the stator windings, the steel of the machine, the rotor windings (including the mutual exchange of thermal energy transmitted from one part of the machine to another). The input of this master circuit time is connected to the capacitors of drivers 4 and 5 of rectified signals. The output voltage used is half the voltage of the last capacitor, i.e. the potential of its lining relative to the common bus circuit (division of the voltage of the specified capacitor is carried out by a symmetric resistor chain). At the moment of time when the negative output potential exceeds the comparator set point in terms of the model, protection trips. The dependent time organ is responsible for shutting off the electric motor during delayed starts, as well as in case of overloads with current multiples lower than 0.7.

In addition, signals of positive and negative polarities are supplied to the inputs of the second comparator 10, each of which is proportional to the magnitude of the primary current and its derivative. The comparator acts on the sum of the modules of these signals, and thus ensures its operation when the signal is exceeded.

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impressive coefficients determined by the ratio of the parameters of the resistor and capacitor of the former 9J 1 is the periodic component of the motor stator current) of a given value — the comparator setpoint. The ratio of the signal being formed and the setpoint is chosen so that the operation occurs only at currents greater than the starting one (i.e., short circuits with current multiplicities greater than the starting ones. This signal is fed to the second comparator 10 without a time delay and thus provides activation of protection without time delay.

Thus, the sensitivity of the device to the free periodic components of the transient current of the electric machine is increased, as well as

K 1 + K ,, (where K, and K are de-use devices to protect the engine of various capacities.

Connecting the control circuit of the key 12 only to the output of the first time delay organ provides a high gain of the transistor cascade (in a known device, the control current simultaneously passes through the key load circuit, which creates negative feedback, preventing clear switching of the key executive circuit) In addition, the actuator circuit connects the subsequent elements directly to the positive pole of the power source, as a result of which not only the operational force is discharged spruce, but operating conditions are improved locking key is generated necessary supply its current executive part, providing a reliable securing of the locking key in the open state.

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however, the output of the signal conditioner; the cyMhfe proportional stator current half-wave is connected to the input of the first time delay element, and the output of the signal conditioner proportional to the difference of the stator current half-wave through a series-connected rectifier and the first comparator is connected to the control input of the locking key connected in parallel with the second shutter element time, as well as the executive body, characterized by the fact that, in order to increase the sensitivity and reliability of protection, expand the scope of application, Dena transistor switch, a second comparator and a multi-circuit serially connected RC-analog thermal state of the motor generator and a signal proportional to the sum of the current values of the periodic coc

The means of ensuring reliable extrusion of the stator current and its production of a free periodic component of the transient current ensure, in addition, the elimination of false protection triggers in the absence of damage to the electric motor, i.e. provide increased reliability of its protection.

Formula of invention

A device for protecting an electric motor against overload and overcurrent, which contains a current sensor, the primary winding of which has terminals for connecting a motor to the stator circuit, and the secondary winding through a current converter - on. The voltage is connected to the corresponding inputs of the shapers of positive and negative half-waves of rectified signals, the outputs of the latter are connected to the corresponding inputs of the shaper signals, which are proportional to the sum and difference of the half-waves of the stator current.

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No, the multi-circuit RC analogue of the thermal state of the electric motor is connected to the outputs of the rectified signal shapers, and the output of the signal conditioner proportional to the sum of the current value of the periodic component of the stator current and its derivative to the first input of the second comparator, the input of the transistor switch is connected to the output of the first time delay element, and the output is connected to the power supply circuit of the blocking key, the output of which is connected to the second input of the second comparator, the output of the latter is connected to the input th actuator body, with the righting converters connected between the signal, according to a sequentially zu point and their compounds schinoy is common for all operational amplifiers, as in the circuit of negative feedback transducer signal that is proportional to the sum of half of the stator current, the capacitor is connected.

e stator current supply and its production0

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No, the multi-circuit RC analogue of the thermal state of the electric motor is connected to the outputs of the rectified signal shapers, and the output of the signal conditioner proportional to the sum of the current value of the periodic component of the stator current and its derivative to the first input of the second comparator, the input of the transistor switch is connected to the output of the first time delay element, and the output is connected to the power supply circuit of the blocking key, the output of which is connected to the second input of the second comparator, the output of the latter is connected to the input th actuator body, with the righting converters connected between the signal, according to a sequentially zu point and their compounds schinoy is common for all operational amplifiers, as in the circuit of negative feedback transducer signal that is proportional to the sum of half of the stator current, the capacitor is connected.

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Claims (1)

Claim A device for protecting an electric motor from overload and overcurrents, comprising a current sensor, the primary winding of which has terminals for connection to the stator circuit of the electric motor, and the secondary winding through the current converter is na. the voltage is connected to the corresponding inputs of the drivers of positive and negative half-waves of the rectified signals, the outputs of the latter are connected to the corresponding inputs of the drivers of signals proportional respectively to the sum and difference of the half-waves of the stator current, while the output of the driver of the signal proportional to the sum of half-waves of the stator current is connected to the input of the first exposure element time, and 5, the output of the signal driver, proportional to the difference of the half-waves of the stator current, is connected through a series rectifier and the first comparator to the control input of a blocking key connected in parallel with the second time delay element, as well as an actuator, which is different in order to increase the sensitivity and reliability of protection, expanding the scope of application, a transistor switch, a second comparator and a sequentially connected multi-circuit RC analog heat are additionally introduced into the device the state of the electric motor and the driver of the signal proportional to the sum of the effective value of the periodic component of the stator current and its derivative, the input of the multi-circuit RC analog of the thermal state of the electric motor is connected to the outputs of the drivers of the rectified signals, and the output of the driver of the signal proportional to the sum of the effective value of the periodic component of the stator current and its derivative , - to the first input of the second comparator, the input of the transistor switch is connected to the output of the first 35 shutter element time, and an output coupled to the locking key supply chain, the output of which is connected to the second input of the second comparator, coupled to the output of the last 40 with the input of the executive body, while the converters of the rectified signals are interconnected in series according to and the point of their connection is a common bus for 45 of all operational amplifiers, and a capacitor is connected to the negative feedback circuit of the signal converter, proportional to the sum of the half-waves of the stator current.