SU1534609A1 - Device for protection of three-phase induction motor supplied from frequency converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used in relay protection devices. The purpose of the invention is to increase reliability by eliminating the false positives of protection in the whole range of frequencies and powers of the asynchronous electric drive and when reversing the electric motor. During normal operation of the electric motor, the bit switches 8, 9, 10 do not allow the voltage on the capacitors of the channel integrators 11, 12, 13 to rise until the voltage of the threshold organs 15, 16, 17 triggers, and the automatic switch 2 does not trip. When the motor phase is disconnected, the corresponding channel bit switch is closed due to the absence of voltage drop on the diodes of the corresponding phase of the three-phase full-wave circuit 7. The channel integrator capacitance is charged to the threshold threshold of the corresponding threshold element, the output signal from which through the circuit OR 18, the amplifying element 19 causes circuit breaker 2. Integrator 14 blocks the operation of the protection device against false positives at the time of the absence of a motor current. 2 Il.

Description

zgob

(putt

The invention relates to electrical engineering, in particular, to protection devices of three-phase asynchronous electric motors supplied from frequency converters with an arbitrary shape of alternating current.

The aim of the invention is to increase reliability by eliminating False positives sewn over the entire frequency range and power of the asynchronous electric drive and when reversing the electric motor. FIG. 1 shows a block diagram of a device for protecting a three-phase asynchronous motor against phase loss; in fig. 2 - schematic diagram of the device.

The device (FIGS. 1 and 2) contains a thyristor frequency converter 1 connected to the mains through an automatic switch 2, an asynchronous motor 3 connected to the output of the frequency converter 1. The output phases of the asynchronous motor 3 include current sensors 4-6, the initial outputs of which are connected to the inputs of a three-wave rectifier two-straightening circuit 7, and the final conclusions are connected to a star, the common point of which is connected to the zero output of a three-phase two-wavelength circuit 7. The initial terminals of current sensors 4-6 are connected via bit switches 8-10 to the first inputs of channel integrators 11-13. To the second inputs of which the output of the integrator 14 is connected, the input of which is connected to the potential load output of a three-phase voltage A half-wave rectifier 7. The outputs of channel integrators 11–13 are connected to the corresponding threshold organs 15–17, the outputs of which are connected to the inputs of a three-input OR 18 circuit, the output of which through the amplifying element 19 controls the automatic switch 2. The thyristor frequency converter is generally can be with direct current link and control

Led rectifier or with uncontrolled rectifier and autonomous inverter with pulse-width regulation. Circuit breaker 2 and current sensors 4-6, which are current type transformers of any type, have parameters determined by the power of the frequency converter. Three phase full-time

) 5 0 5 0 5

0

five

PA rectification circuit 7 is made with zero output and is loaded on resistive loads, for example, in the form of a Larionov bridge. Bit switches 8-10 can be made on transistor switches or integrated circuits that control channel integrators, in the simplest case, implemented as integrating RC circuits. The integrator 14 is implemented on an operational amplifier with a conventional circuit, to the non-inverting input of which a small bias current is applied. The threshold organs 15-17 can be implemented either as comparators on operational amplifiers or logic integrated circuits having a specific trigger threshold. An OR circuit may also be implemented on these logic circuits. An amplifying element 19 is typically implemented on a composite transistor for controlling the circuit breaker 2.

The device works as follows.

In the absence of current in the phases of the converter 1, the voltage drop across the diodes of the three-phase two-opto-period circuit 7 of sensors 4-6 is zero, therefore the zero-resistor bit switches 8-10 are closed, but the voltage on the integrating capacitors of channel integrators 11-13 is zero for an invoice by an integrator 14 having a positive offset at the invert input. A zero signal is formed at the input of the threshold organs 15-17, the threshold organs 15-17 do not operate, their zero level through the OR 18 circuit and the amplifying element 19 will not cause the automatic switch 2 to turn off. In the presence of current in the current sensors 4-6 on a three-wave full-wave diode Circuit 7, almost independently of the current flow of the frequency converter, a constant two-voltage voltage (within the slope of the volt-ampere characteristic of the diodes) is formed, which, being applied to the discharge switches, for example positively opens it, without giving opportunity to increase voltage on the capacitors the channel integrators 11-13 to a voltage actuation threshold bodies 15-17 in the action time, for example, a negative voltage,

which closes the bit keys 8-10. At this moment, the negative rectified pulse voltage from the output of the active load of the three-phase full-wave circuit 7, being applied to the inverting input of the integrator 14, transfers it to state 1 without creating a path for the discharge current of the channel integrators 11-13. A constant integration time of channel integrators is chosen sufficiently long (on the order of 3 s), so that short-term dips to zero motor current will not cause voltage buildup on the integrating capacity of channel integrators 11–13 to the threshold of operation of circuits 15–17. The threshold devices 14-17 are not triggered, no false shutdowns of circuit breaker 2 occur.

When the motor phase is broken, for example, in the current sensor 4 circuit, the voltage drop on the diodes of the corresponding phase of the three-phase full-wave circuit 7 is absent, the channel bit switch 8 is closed, the channel integrator 11 is charged to the threshold of the threshold organ 15, the output signal from which through the circuit OR 18, the amplifying element 19 causes the circuit breaker 2 to be turned off. Similarly, the protection is triggered if any other motor phase is broken. The constant integration time of channel integrators is chosen so that over the entire frequency range of the drive during the negative polarity of the voltage drop across the diodes of the rectifier circuit 7, when the bit switches 8-10 are closed, the voltage on the capacitors is 10

15

20

25

thirty

35

40

The further positive impulse of the voltage drop across the diodes by the rectifiers of the bodies 7 zeroes the voltage on the condenser of the drip integrators 11-1 The integrator 14 blocks the operation of the protection device against false alarms at the moment of the absence of the motor current 3, and the capacity of the integrator 1 is selected so that when operating at low frequencies, when rare impulses of considerable amplitude from the output of the multiphase rectifier circuit 7 arrive at integrator 14, in the intervals between these pulses the discharge current does not have time to discharge the capacitor and integrator voltage to a level at which is provided a discharge flow channel dny currents of capacitors integral operators.

Claims (1)

Invention Formula A device for protection of a three-phase asynchronous electric motor powered by a frequency converter against phase failure containing three current sensors connected to the terminals for switching to the phases of the aforementioned electric motor, the outputs of the sensors connected to the rectifier, integrators connected to threshold organs, three the input element OR, the inputs of which are connected to the outputs of the threshold organs, and the output connected to the current amplifier, characterized in that, in order to increase the reliability of the device by eliminating false protection trips, it includes three bit switches, the inputs of which are connected to the outputs of current sensors, the outputs are connected to the first inputs of channel integrators, as well as the integrator whose input is connected to a rectifier made in three 11-13 integrators fail to have a 5-phase full-wave scheme for you five 0 five 0 five 0 A further positive impulse of the voltage drop across the diodes of the rectifier 7 zeroes the voltage on the capacitor of the drop integrators 11–13. The integrator 14 blocks the operation of the protection device against false alarms at the moment when the motor 3 is not present, and the capacity of the integrator 14 is selected so that when operating at low frequencies, when the input of the integrator 14 comes rare pulses of significant amplitude from the output of the multiphase rectifier circuit 7, In the intervals between these pulses, the discharge bias current does not have time to discharge the capacitor 14 of the integrator to a voltage level at which the discharge currents of the capacitors of the channel integrators flow. Invention Formula A device for protection of a three-phase asynchronous electric motor powered by a frequency converter against phase failure, containing three current sensors connected to the terminals for switching the above-mentioned electric motor into phases, sensor outputs connected to a rectifier, integrators connected to threshold units, three-input element OR, the inputs of which are connected to the outputs of the threshold organs, and the output is connected to the current amplifier, characterized in that, in order to increase the reliability of the device by eliminating false positives three protection switches, the inputs of which are connected to the outputs of current sensors, the outputs to the first inputs of channel integrators, as well as the integrator, whose input is connected to a rectifier made in three It does not increase until the trigger voltage of the threshold organs 15-17. Coming, wiring, and outputs to channel integrators. second entrances , P-GE I + W + Figg