CN87202183U

CN87202183U - Bypass type protector for ac electric motor

Info

Publication number: CN87202183U
Application number: CN 87202183
Authority: CN
Inventors: 石玉璞; 王景银; 朱玉林
Original assignee: ELECTROMECHANICAL INST JINZHOU CITY
Current assignee: ELECTROMECHANICAL INST JINZHOU CITY
Priority date: 1987-02-19
Filing date: 1987-02-19
Publication date: 1987-10-14

Abstract

The utility model relates to a bypass type protector for AC electric motors. At present, a plurality of motors are burnt out due to the lack of an accurate and effective protection measures. The utility model is composed of a protector body and a circuit board. When one phase of the three-phase machine is opened or overloaded, the generated overload (electric current) is added to a signal transformer through the signal voltage generated by a current divider. The signal is rectified by a rectifier after the pressure boost, and the DC voltage generated by rectifying is connected with a datum power source. The utility model is provided with the functions of the signal transport comparator, the time delay discriminator and the instruction follower. The protector for AC electric motor has the advantages of advanced circuit, simple structure, etc.

Description

Bypass type protector for AC electric motor

The utility model relates to the protective device of low-voltage alternating-current motor.

Existing device to motor implementation protection is the thermal relay that matches with contactor.This protection device construction is simple, and low price, but this protection way can only just can reach predetermined specification requirement under given conditions, and this specified conditions objectively are non-existent.Because motor is not had accurate and effective safeguard measure, have a large amount of motors to be burnt out under abnormal ruuning situation at present, have domestic according to statistics every year 1000000 left and right sides motors to be burnt out, above-mentioned protection way exists very big shortcoming.

The purpose of this utility model is for the protection motor overload, and the accuracy height is provided when the phase failure and under voltage, and is highly sensitive, the current protection device of good stability.

The utility model is made up of protector main body and protector line; the protector main body is made cuboid or square shape; protector line is by shunt; reference power supply; comparator; the time-delay discriminator; command output device is formed; the overload (electric current) that produces after the arbitrary phase phase failure of three phase electric machine or overload adds to signal transformer through the signal voltage that shunt produces; this signal boosts after rectifier rectification produces a direct current voltage and reference power supply links; this signal send comparator; the time-delay discriminator; command output device, its relay normally-closed contact is connected with the coil of contactor.The two ends of this shunt type AC motor protecter are connected with the signal transformer input, and output is connected with rectifier, and the shunt of monophase machine can adopt one or two, and the shunt of three phase electric machine can adopt two or three.

Shunt is made up of two shunt resistances, respectively with the three phase electric machine control circuit in two-phase be in series, shunt two signal transformers respectively in parallel, its output is through the full-bridge rectifier base stage of exporting to comparator after relatively in parallel with reference power supply.Reference power supply is by power transformer, full-bridge rectifier, and pi type filter and voltage-stabiliser tube are formed.Comparator is formed multiple tube by two triodes; its input pipe base stage is formed protective circuit by a plurality of diodes; efferent duct is connected with the time-delay discriminator by diode-coupled, and the time-delay discriminator is connected with corresponding Resistor-Capacitor Unit by unijunction transistor, and command output device is made up of controllable silicon and relay.

Be described further with regard to composition of the present utility model and principle now; shunt is as the device that extracts current signal; available constantan or copper-manganese material are manufactured; when 40 ℃ of the temperature difference; its error should be less than 4%; when machine operation; operating current produces an an amount of millivolt threshold voltage and falls on shunt; (mustn't above 0.1 volt); this voltage drop is the current signal that will extract, and this signal voltage is sent into the electronic protector circuit again after signal transformer appreciates, and signal transformer is except that the appreciation task of finishing signal voltage; also can keep apart 380 volts of voltages of electrical source of power and electronic device, guarantee the work safety of electronic device.Reference power supply is a full-bridge rectification and the direct current stabilizer that filtering is arranged, voltage-stabiliser tube Dw ₁Rw is in parallel with potentiometer, and its effect is the protection requirement that the various motor of protection classification can adapt to rated current, shifting brush on the potentiometer and the current potential U between the positive pole _aBe reference voltage value, i.e. the protective current selective value of protector, signal negative feedback voltage U _bBe respectively through two full-bridge QL by the alternating voltage after two signal transformers appreciations ₁, QL ₂The signal negative feedback voltage of parallel connection after the rectification, the size of this voltage is the big or small linear variation with motor working current, because its polarity of voltage is opposite with the polarity of reference voltage, therefore signal voltage is compared with reference voltage, the signal voltage increase promptly plays a part to reduce reference voltage, and available this formula is represented:

Output voltage=reference voltage-signal voltage

U _c＝U _a－U _b

As seen, after protective current selected accent to turn round the some values of aligning, reference voltage was a fixed value.The operating current of motor is during less than its rated value, and signal voltage all is less than reference voltage value, output voltage U _cBe on the occasion of.If motor working current is during greater than its rated value, signal voltage is greater than reference voltage, and output voltage is a negative value, and though output voltage be on the occasion of or negative value, all to deliver to the base stage of switching circuit triode, differentiate that the switching circuit of link is to work as output voltage U _cFor on the occasion of the time, triode T ₂Conducting, current collection is zero potential very, equals door and closes, and output voltage U is worked as in the output of no signal voltage _cDuring for negative value, triode T ₂End, collector electrode has positive tens volts current potential, equals door and opens, and signal voltage output is arranged, and then this voltage signal is passed through diode D ₂Send into the capacitor C of delay circuit ₆Positive pole carries out signal and differentiates.The delay circuit discriminator is a difference of differentiating normal operation of motor and failure operation, the operating current of alternating current machine, except that operation under failure condition and increasing, the phenomenon of electric current also appears increasing in operation under normal circumstances, as starting current, therefore impulse current etc. adopt a kind of way of timing to differentiate one from the other, the delay circuit discriminator is served as above-mentioned task, and delay circuit is by unijunction transistor T ₃, capacitor C ₆And resistance R ₁₃, R ₁₄Deng composition.The signal voltage of input is added in capacitor C ₆Positive pole on, voltage passes through resistance R ₁₃, R ₁₄To capacitor C ₆Charging, delay time are that starting characteristic according to motor is by adjustable resistance R ₁₄Resistance determine, generally about 7 ± 1.5 seconds, every current signal less than 7 seconds, capacitor C ₆The crest voltage of charging is less than unijunction transistor T ₃Conducting voltage, so unijunction transistor still is in blocking, not output signal.Because three-phase pipe T when switching circuit has signal ₂End triode T behind the blackout ₃Conducting immediately, capacitor C at this moment ₆Positive pole by diode D ₂Discharge with triode.Every current signal greater than 7 seconds, capacitor C ₆The crest voltage of charging is greater than the conducting voltage of unijunction transistor, so the unijunction transistor conducting, and signal output is arranged, because the unijunction transistor conducting, electric current is by the first base resistance R ₉Just produce one 3 volts above voltage drops, this voltage signal flows to command output device.Command output device is that the voltage signal of input is delivered to the controllable silicon trigger electrode, trigger thyristor SCR conducting, make relay J work, cut off normally-closed contact, thereby make contactor C outage, contactor C contact disconnects, cut off motor power, reached the effect of assurance motor safety, the utlity model has the circuit advanced person, simple in structure, characteristics such as production cost is low.

Accompanying

drawing

1,2 is a shunt type AC motor protecter structural representation, and 1 is the protector main body among the figure, and 2 is the protector line plate, and 3 is shunt.

Accompanying drawing 3 is shunt type AC motor protecter circuit theory diagrams.3 is shunt among the figure, and 4 is reference power supply, and 5 is comparator, and 6 are the time-delay discriminator, and 7 is command output device, and 8 is signal transformer, and 9 is contactor.

Embodiment:

Shunt adopts outsourcing piece, model is the fixed definite value shunt of FL-2 type, accuracy is 0.5 grade, technical specification be 5A, 10A, 20A, 50A, 75A, 100A, 150A, 200A all can, rated voltage is 75MV, signal transformer, iron core adopts iron-nickel alloy, tongue is wide to be 4mm, and folded thick is 6mm, and primary winding is that φ 0.14,50T, secondary coil are φ 0.07,5500T.Other electric elements all adopt the domestic standard part.

Claims

1; the shunt type AC motor protecter; form by protector main body and protector line; it is characterized in that protector main body [1] makes cuboid or square shape; protector line plate [2] and shunt [3] are fixed on protector main body [1] inside by connector; protector line is by shunt [3]; reference power supply [4]; comparator [5]; time-delay discriminator [6]; command output device [7] is formed; the overload (electric current) that produces after the arbitrary phase phase failure of three phase electric machine or overload adds to signal transformer [8] through the signal voltage that shunt [3] produces; this signal boosts after rectifier rectification produces a direct current voltage and reference power supply [4] links, and this signal send comparator [5], time-delay discriminator [6]; command output device [7], its relay normally-closed contact is connected with the coil of contactor [9].

2, according to the described shunt type AC motor protecter of claim 1; the two ends that it is characterized in that shunt are connected with the signal transformer input; its output is connected with rectifier, and the shunt of monophase machine can adopt one or two, and the shunt of three phase electric machine can adopt two or three.