CN2169238Y - Protector for three phase asynchronous motor - Google Patents

Abstract

The utility model relates to a thermal overload protective relay, belonging to the field of a low-voltage electrical apparatus. The utility model transmits electric current to a threshold circuit through rectification and delay via the outputted voltage of a mutual inductor which is serially connected with the power circuit of a motor, or the electric current is transmitted to the threshold circuit by high voltage which is used for checking whether a three-phase power supply is balanced or not. When a fault happens, the voltage of a control circuit is bigger than threshold voltage to trigger the conduction of a thyristor, so that a relay works; the motor is disassembled from a power network; under a normal condition, the thyristor is not conducted; the motor runs normally. The utility model has the advantages of high reliability, low cost and convenient manufacture, etc.

Description

Protector for three phase asynchronous motor

The utility model relates to a kind of improvement of thermal overload protection relay, belongs to the low-voltage electrical apparatus field.

The thermal overload protection relay is the big intermediate item of low-voltage electrical apparatus, is widely used in to exchange 380 volt of 50 He Zhi electrical network of three-phase, as the protection threephase asynchronous.Present method is; when operating motor runs into stall; when the phase failure or overload; be serially connected in the thermal element of thermal overload relay in the electrical network; heated up because of flowing through multiple current; the amount of deflection of " bimetal leaf " on its next door is increased; promote " contact mechanism " action; thereby cut off the coil control circuit of contactor; contactor is disconnected and threephase asynchronous is unloaded down from electrical network; reach the purpose of protection asynchronous motor, because the manufacture process requirement height of " bimetal leaf ", domestic manufacturer is in a large number from external import " bimetal leaf "; consume a large amount of foreign exchanges; thermal element is started to walk heavy current impact and is formed of short duration " annealing ", thermal element decreased performance after starting repeatedly in addition; reduce the amount of deflection of bimetal leaf indirectly, reduced the reliability of thermal overload relay.Another kind method is to use controllable silicon, and existing circuit more complicated, parts are a lot of, and product cost is higher, and debug difficulties is impracticable.

The purpose of this utility model provides a kind of function admirable, reliability height, the three-phase asynchronous motor protector that cost is low.

The utility model is (referring to the Fig. 1) that realizes in the following way, the three-phase alternating current incoming transport contactor 2 of electrical network 1, and the three-phase alternating current of A.C. contactor 2 outputs inserts testing circuit 9, rectified three-phase circuit 8 and motor 3 respectively.With get one in the three-phase that motor 3 connects and be connected in series the less instrument transformer of a primary impedance 4 mutually, 4 levels output of instrument transformer connects rectification circuit 5, rectification circuit 5 connects threshold circuit 7 after connecing delay circuit 6 again, threshold circuit 7 outputs are controlled the utmost points with controllable silicon 12 and are connected; Connect controllable silicon 12 anodes, controllable silicon 12 minus earths behind rectified three-phase circuit 8 serial connection current-limiting resistances 13, the relay 11; Threshold circuit 7 is inserted in testing circuit 9 serial connection anti-jamming circuits 10 backs.The action of relay 11 directly acts on A.C. contactor 2, and promptly relay 11 unloads motor 3 once moving the coil current that cuts off A.C. contactor 2 from electrical network.

This utility model is work like this, and under the normal condition, A.C. contactor closes, three-phase alternating current enters motor, and the direct voltage through the rectification delay of instrument transformer output is lower than the threshold voltage of threshold circuit, not conducting of controllable silicon, relay is failure to actuate, and also no-output of testing circuit this moment.When there was a mechanical failure as stall, or transship when taking place, motor can be by big electric current, and the big voltage of instrument transformer output is after rectification postpones, this voltage is greater than the threshold voltage of threshold circuit, make the controllable silicon conducting, relay circuit work, the actuating of relay, disconnect ac contactor coil, motor unloads from electrical network.When open phase fault occurring, testing circuit will be exported big voltage, and this is exported behind anti-jamming circuit, transports to threshold circuit, greater than threshold voltage, trigger the controllable silicon conducting, relay circuit work, the actuating of relay disconnects ac contactor coil, and motor unloads from electrical network.This protector is made easy to assembly, the job stability height, and action accurately has long, characteristics such as reliability is high, and cost is low of life-span.

Under normal circumstances, the user needs " stopping " motor operation, only press the button that has " normally closed " contact, make the power loop that disconnects motor after the ac contactor coil dead electricity, otherwise the user needs " starting " motor, only need press the button that has " often opening " contact, makes the logical back adhesive of coil of A.C. contactor, and the power loop of connection motor, make motor starting.

Below in conjunction with accompanying drawing, the utility model is described further.

Fig. 1 is a schematic diagram of the present utility model.

Fig. 2 is a line map of the present utility model.

Referring to Fig. 1, Fig. 2, from the three-phase alternating current L of electrical network _A, L _B, L _CBehind A.C. contactor CJ, insert motor D, testing circuit 9 and rectified three-phase circuit 8 respectively, insert and to get the instrument transformer CT that is in series, the secondary output-parallel capacitor C of instrument transformer in the three-phase of motor D ₁After carry out bridge rectifier, shunt capacitance C after the rectification ₂, its minus earth, its cathode series resistance R ₁After shunt capacitance C over the ground again ₃, capacitor C ₃Cathode series resistance R ₂After more over the ground and connect capacitor C ₅, capacitor C ₅Anodal serial connection diode BG ₆, diode BG ₆Negative pole series resistor R ₃After meet voltage stabilizing didoe W ₁Negative pole, voltage stabilizing didoe W ₁Positive pole shunt capacitance C over the ground ₆, capacitor C ₆But positive pole meets keyholed back plate SCR control utmost point G, and testing circuit 9 is with three equivalent resistance R ₇, R ₈, R ₉One end is connected with three-phase alternating current three respectively, and the other end also meets diode BG ₁Positive pole, diode cathode serial connection neon bulb L _NThe diode BG of threshold circuit 7 is inserted in the back ₆Negative pole, rectified three-phase circuit 8 is with the three-phase of three-phase alternating current three diode BG of forward serial connection respectively ₇, BG ₈, BG ₉After be connected to current-limiting resistance R ₁₀, resistance R ₁₀Insert the anode A of controllable silicon SCR after the other end serial connection relay J, its negative electrode C ground connection, relay J directly acts on A.C. contactor CJ.During protector work, the A.C. contactor CJ that closes, alternating current inserts motor D, motor work, under the normal condition, instrument transformer CT output voltage is lower than threshold voltage after rectification postpones, testing circuit 9 output low voltages, not conducting of controllable silicon SCR; As stall, overload, motor D winding current increases, CT big voltage of level output of instrument transformer, postpone back input threshold circuit 7 through rectification, because of voltage greater than " threshold voltage ", the conducting of triggering controllable silicon SCR, the relay J loop works, the relay J action disconnects A.C. contactor CJ coil, and motor unloads from electrical network; As the phase failure, diode BG in the testing circuit 9 ₁Positive pole will have high voltage to produce, through rectification and neon bulb L _NAfter transport to diode BG ₆Negative pole, this voltage triggers the controllable silicon SCR conducting greater than " threshold voltage ", motor is unloaded in relay J work.At the motor starting initial stage, instrument transformer produces transient high voltage and then overcomes misoperation by delay circuit.

Claims (1)

1, a kind of three-phase asynchronous motor protector; comprise A.C. contactor, instrument transformer, testing circuit, threshold circuit, relay etc.; the three-phase alternating current incoming transport contactor (CJ) that it is characterized in that electrical network, the three-phase alternating current of A.C. contactor (CJ) output meets three equivalent resistance (R of testing circuit (9) respectively ₇), (R ₈), (R ₉), meet three diode (BG of rectified three-phase circuit (8) ₇), (BG ₈), (BG ₉) positive pole, connect motor (D), from three-phase that motor (D) connects get one mutually, serial connection instrument transformer (CT), the secondary shunt capacitance (C of instrument transformer (CT) ₁) after connect by (BG ₅), (BG ₂), (BG ₃) and (BG ₄) bridge rectifier formed, after the rectification and meet electric capacity (C ₂), its cathode series resistance (R ₁) after over the ground and meet electric capacity (C ₃), electric capacity (C ₃) cathode series resistance (R ₂) after more over the ground and meet electric capacity (C ₅), electric capacity (C ₅) anodal serial connection diode (BG ₆), diode (BG ₆) negative pole series resistor (R ₃) after meet voltage stabilizing didoe (W ₁) negative pole, voltage stabilizing didoe (W ₁) positive pole shunt capacitance (C over the ground ₆), electric capacity (C ₆) but positive pole meets the keyholed back plate SCR control utmost point (G), three equivalent resistance (R in the testing circuit (9) ₇), (R ₈), (R ₉) the other end be connected to diode (BG ₁) positive pole, its negative pole series connection neon bulb (L _N) after be connected to diode (BG ₆) negative pole, three diode (BG of rectified three-phase circuit (8) ₇), (BG ₈), (BG ₉) negative pole be connected to current-limiting resistance (R ₁₀), resistance (R ₁₀) connect the anode (A) of controllable silicon (SCR) behind the other end serial connection relay (J), controllable silicon (SCR) negative electrode (C) ground connection, relay (J) directly acts on A.C. contactor (CJ).

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