CN100411295C - Excitation method and device for synchronous winding type asynchronous motor - Google Patents

Abstract

The invention relates to a synchronous excitation method and device for a winding type asynchronous motor, belonging to the technical field of electric motors. Its technical solution is: it first starts the motor asynchronously to make it run asynchronously in a sub-synchronous state, and then connects an additional resistor R _f in series with one phase of the rotor, and realizes forward excitation by detecting the rotor voltage waveform. The present invention also provides this synchronous excitation device, which is composed of an excitation power supply, a thyristor SCR, a trigger circuit, a diode D, an additional resistor R _f , an asynchronous starting device, and contactors CJ1 and CJ2. The invention not only can make the winding type motor smoothly lead into synchronization after asynchronous start, but also is economical, practical, simple and easy to operate.

Description

Excitation method and device for synchronous winding type asynchronous motor

technical field

The invention relates to an excitation method and device for synchronous operation of a wound-type asynchronous motor after asynchronous start, belonging to the technical field of electric motors.

Background technique

Wound motors are widely used in industrial production, and their working mode is generally asynchronous operation. The synchronous operation of wound motors will improve their energy consumption performance and benefit the power grid. At present, the method of synchronous operation of large-scale wound motors is to use a frequency conversion device to start the motor. The method is to short any two phases of the three phases of the motor rotor as one end, and add DC power to the third phase, and then the frequency conversion device starts from zero. Hertz started to increase the frequency, and the motor was kept in sync during the start process. Since this starting method adopts a frequency conversion device, the investment is very large and the operation steps are also very cumbersome. If the motor is started asynchronously first, and then brought into synchronism, the investment will be reduced, and the complexity will be simplified, but this will inevitably face the problem of how to smoothly bring the asynchronously running wound motor into synchronism.

Contents of the invention

The object of the present invention is to overcome the deficiencies of the prior art, and provide an economical, practical, simple and easy method and device for synchronizing the excitation of a wound-type asynchronous motor.

The said problem of the present invention is realized with following technical scheme:

A synchronous excitation method for a wound asynchronous motor. It first starts the motor in an asynchronous manner to make it asynchronously start to a sub-synchronous state, and then connects an additional resistor R _f in series with one phase of the rotor. By detecting the rotor voltage Waveform, to achieve forward polarity excitation, the specific steps are as follows:

a. The rotor winding of the wound motor is connected to the asynchronous starting device 11, and the stator is powered on, so that the motor starts and runs asynchronously to a sub-synchronous state;

b. Short-circuit any two phases of the three phases of the motor rotor as one end, and connect an additional resistance R _f between the third phase and the third phase;

c. Detect the voltage waveform at both ends of the additional resistor R _f ;

d. When the voltage across the additional resistor R _f is a negative half cycle, the excitation voltage is added, and at the same time, the additional resistor R _f is disconnected by the negative half wave and the trigger circuit.

In the synchronous excitation method of the above-mentioned wire-wound asynchronous motor, the asynchronous starting device adopts the liquid resistance soft start mode, which uses liquid resistance R1, R2, R3 as the starting resistance, and the liquid resistance is fixed by the electrode plate in the liquid resistance box Electrolyte between the electrode plate and the mobile electrode plate is formed. After starting, the distance between the mobile electrode plate and the fixed electrode plate is gradually reduced, so that the liquid resistance connected in series with the rotor circuit of the motor is gradually reduced to zero, so that the motor operates at the asynchronous rated RPM and above.

In the excitation method for synchronizing a wound asynchronous motor described above, the resistance value of the additional resistor R _f is 5-15 Rz ohms, wherein Rz is the winding impedance of one phase of the motor rotor connected in parallel with the other two phases and then connected in series.

A synchronous excitation device for a wound asynchronous motor, which is composed of an excitation power supply 12, a thyristor SCR, a trigger circuit, a diode D, an additional resistance R _f , an asynchronous starting device, a first contactor CJ1, and a second contactor CJ2 , the thyristor SCR is connected in anti-parallel with the diode D, then connected in series with the additional resistor R _f , connected to the excitation power supply 12, and at the same time connected to the three-phase winding of the motor rotor through the normally open contact of the first contactor CJ1, the second Among the three normally open contacts of a contactor CJ1, one side of two normally open contacts is short-circuited together; the control pole of the thyristor SCR contacts the trigger circuit, and the asynchronous starting device passes through the second contactor CJ2. The normally open contacts connect the three-phase windings of the motor rotor.

The synchronous excitation device for the above-mentioned wound asynchronous motor, the asynchronous starting device is composed of a liquid resistance box 1, a fixed electrode plate 2, a moving electrode plate assembly, a moving electrode plate driving device and a conductive liquid 8, and the liquid resistance box 1 is a box body made of insulating material; the moving electrode plate assembly is composed of a moving electrode plate 9 and an isolation plate 4, and the isolation plate 4 is two parallel insulating plates vertically placed inside the liquid resistance box 1, and the isolation plate The upper end protrudes from the parallel gap on the top plate of the liquid resistance box, and the mobile electrode plate 9 is a strip-shaped horizontal conductive metal plate connected to the lower ends of the two isolation plates 4; There are three conductive metal plates, the fixed electrode plates are arranged at intervals, and the studs 3 are also used as the connection terminals of the fixed electrode plates; It is connected with the upper end of the isolation plate 4 and forms a transmission relationship with the servo motor 6 through the gear 7 ; the conductive liquid 8 is filled in the liquid resistance box 1 .

The above-mentioned winding type asynchronous motor assimilation excitation device, the asynchronous starting device is additionally provided with a short-sealed third contactor CJ3, and one end of the three normally-open contacts of the short-sealed third contactor CJ3 is respectively connected to three liquid resistors R1, R2 , R3, and the other ends are shorted together.

In the above-mentioned synchronous excitation device for a wound-type asynchronous motor, the conductive liquid 8 is an electrolytic solution.

When the present invention is in use, first start the motor with an asynchronous starting device, so that the motor runs asynchronously in a sub-synchronous state, and then connect an additional resistance R _f to one phase of the rotor in series, and the additional resistance R _f can maintain the motor rotor flow and keep the motor rotor Torque, and provide the rotor voltage waveform to the excitation power supply, the excitation power supply starts to provide excitation current at the negative half cycle of the voltage across the additional resistance R _f , and at the same time trigger the circuit and the negative half wave of the rotor to cut off the thyristor SCR, and disconnect the additional resistance R _f , thus Realize the synchronous operation of the motor. The invention not only can make the winding type motor smoothly lead into synchronization after asynchronous start, but also is economical, practical, simple and easy to operate.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is the electrical schematic diagram of the present invention.

Fig. 2 is a structural schematic diagram of a liquid resistance soft start device.

The labels in the figure are: 1. Liquid resistance box, 2. Fixed electrode plate, 3. Stud, 4. Isolation plate, 5. Rack, 6. Servo motor, 7. Gear, 8. Conductive liquid, 9. Moving Electrode plate, 10. Reducer, 11. Asynchronous starting device, 12. Excitation power supply, M. Winding motor, D. Diode, SCR, thyristor, first contactor CJ1, second contactor CJ2, third contactor CJ3 .

In Figure 1, A, B, and C are the three phase lines of the power supply. The asynchronous starting device is a liquid resistance starting device, and the logic relationship of the trigger circuit is easily realized by PLC or CPU.

In Fig. 2, the three studs 3 are wire terminals, which are respectively connected to the three-phase windings of the motor rotor. Electrolyte, such as water, salt water, etc., is injected into the liquid resistance box to form a water resistance. The resistance value of the water resistance can be adjusted by adjusting the concentration of the electrolyte, and the resistance value of the water resistance R1, R2, R3 is reasonably designed to match the motor rotor reactance value. After testing, when the resistance value of the water resistance is between 1.2 times the rotor impedance and 1.5 times the rotor impedance, the motor stator is directly connected to the grid to start, and the starting current can be controlled below the rated current. In addition to dragging the mobile electrode plate 9, the separator plate 4 also has the effect of isolating the conductive liquid 8, so that the transverse current between the three fixed electrode plates 2 is as small as possible, so its front and rear direction dimensions should be as large as possible, so that The three water resistors R1, R2, R3 are basically equal, and the isolation effect is better. The three fixed electrode plates are respectively arranged in the middle and both sides of the two isolation plates 4, and the fixed electrode plates 2 are fixed on the top plate of the liquid resistance box by the studs 3, and the studs 3 also serve as connection terminals.

In Fig. 2, the three water resistances R1, R2, R3 formed by the conductive liquid 8 between the three fixed electrode plates 2 and the moving electrode plate 9 are starting resistances, and each phase winding of the motor rotor passes through slip rings, water resistance R1, R2 and R3 are connected to the mobile electrode plate 9 . After the motor starts, the servo motor 6 drives the rack 5, so that the distance between the movable electrode plate 9 and the fixed electrode plate 2 gradually decreases, and the water resistance connected in series with the motor rotor also gradually decreases, and the relationship between R1, R2, and R3 is maintained. Strictly consistent, when the motor stator is directly connected to the grid, the motor can be started with a starting current less than the rated current. After the start-up is completed, the short-sealed third contactor CJ3 is closed, and the motor can run asynchronously.

The invention adopts an asynchronous starting method to start the motor, and then smoothly pulls the motor into synchronization. Its working process and principle are:

a. The rotor winding of the wound motor is connected to the asynchronous starting device, the stator is powered on, so that the motor runs asynchronously in a sub-synchronous state; the second contactor CJ2 is closed, and then the stator power is connected, and the motor uses the asynchronous starting device to realize soft start. After the motor starts asynchronously and reaches the asynchronous rated speed, the third contactor CJ3 is closed, so that the three phases in the rotor of the wound motor are short-circuited through the slip ring. At this time, the motor is already running at sub-synchronous speed (the so-called sub-synchronous refers to the motor speed is low but close to the synchronous speed), which is a good time to pull in the synchronous speed.

b. Short-circuit any two phases of the three phases of the motor rotor as one end, and connect an additional resistance R _f between the third phase: in the sub-synchronous state of the motor, first close the first contactor CJ1, and then disconnect the second Contactor CJ2. At this time, the trigger circuit controls the half-wave full-angle conduction of the SCR. Since the anti-parallel circuit of the thyristor SCR and the diode D has bidirectional conductivity, it is equivalent to a short-circuit wire, which can be regarded as a direct connection between the two ends of the additional resistance R _f and the motor rotor winding. In this way, two of the three phases of the rotor are short-circuited and connected to the other phase through _Rf , the motor is in an unbalanced starting state, which has little effect on the rotor current, and the motor can still run in a sub-synchronous state.

c. Detect the voltage waveform at both ends of the additional resistor R _f . The excitation circuit collects the voltage signal from both ends of the additional resistance R _f , and according to the polarity of the signal, the direction of the rotor current can be judged, making preparations for realizing the negative half-cycle forward excitation. The additional resistance R _f is chosen to be a small value. During the excitation detection process, the three-phase force of the rotor will not be severely uneven, and the motor speed will not drop significantly, which is very important for smooth excitation.

d. Add the excitation voltage at the negative half cycle of the voltage across the additional resistor R _{f, and disconnect the additional resistor R f: After the excitation circuit obtains the rotor induced voltage information from the additional resistor R f , it} starts at the negative half cycle of the voltage at both ends of the additional resistor R _f The excitation voltage is added, and at the same time, the trigger circuit and the negative half-wave induced voltage make the thyristor SCR cut off. At this time, the diode D is also in the cut-off state when the reverse voltage is applied, and the additional resistor R _f can be regarded as disconnected, and the forward polarity throwing is completed.

Claims (8)

1. A synchronous excitation method for a wound-type asynchronous motor, which is characterized in that it first starts the motor asynchronously to make it run asynchronously in a sub-synchronous state, and then connects an additional resistance [R _f ] into the rotor in series Between one phase of the motor and the other two short-circuit points, by detecting the rotor voltage waveform, the polarity switching excitation is realized. The specific steps are as follows: a. Connect the rotor winding of the wound motor to the asynchronous starting device, and the stator is powered on, so that the electric motor starts and runs asynchronously to a sub-synchronous state; b. Short-circuit any two phases of the three phases of the motor rotor as one end, and connect an additional resistance [R _f ] between the third phase and the third phase; c. Detect the voltage waveform at both ends of the additional resistance [R _f ]; d. When the voltage at both ends of the additional resistance [R _f ] is a negative half cycle, the excitation voltage is added, and the additional resistance [R _f ] is disconnected at the same time. 2. According to claim 1, the synchronous excitation method of the wound asynchronous motor is characterized in that, the asynchronous starting device adopts a liquid resistance soft start mode, which uses a liquid resistance as a starting resistance, and the liquid resistance is composed of a liquid resistance The electrolyte between the fixed electrode plate and the moving electrode plate in the resistance box is formed. After the motor is started, the distance between the moving electrode plate and the fixed electrode plate is gradually reduced, so that the liquid resistance connected to the motor rotor circuit is gradually reduced to zero. , so that the motor runs at the asynchronous rated speed. 3. According to claim 1, the synchronous excitation method of the wound asynchronous motor is characterized in that the resistance value of the additional resistance [R _f ] is 5 to 15 Rz ohms, wherein Rz is a certain value in the rotor of the motor The winding impedance after the two-phase windings are first connected in parallel and then connected in series with the remaining one-phase winding. 4. A synchronous excitation device for a wound asynchronous motor, characterized in that it consists of an excitation power supply [12], a thyristor [SCR], a trigger circuit, a diode [D], an additional resistor [R _f ], an asynchronous start Device and the first contactor [CJ1], the second contactor [CJ2], the thyristor [SCR] is connected in antiparallel with the diode [D], and then connected in series with the additional resistance [R _f ], and then connected to the excitation power supply [12], and at the same time connect the three-phase winding of the motor rotor through the normally open contacts of the first contactor [CJ1], two of the three normally open contacts of the first contactor [CJ1] One side is shorted together; the control pole of the thyristor [SCR] contacts the trigger circuit, and the asynchronous starting device is connected to the three-phase winding of the motor rotor through the normally open contact of the second contactor [CJ2]. 5. The excitation device for synchronizing the wound asynchronous motor according to claim 4, wherein the asynchronous starting device is composed of a liquid resistance box [1], a fixed electrode plate [2], a moving electrode plate assembly, a moving An electrode plate driving device and a conductive liquid [8], the liquid resistance box [1] is a box made of insulating material; the moving electrode plate assembly is composed of a moving electrode plate [9] and a separation plate [4], The isolation plate [4] is two parallel insulating plates placed vertically inside the liquid resistance box [1]. The upper end of the isolation plate protrudes from the parallel gap on the top plate of the liquid resistance box. The strip-shaped horizontal conductive metal plate connected to the lower end of the isolation plate [4]; the fixed electrode plate [2] is a horizontal conductive metal plate separated from the mobile electrode plate [9], and there are three fixed electrode plates arranged at intervals. The stud [3] doubles as the connection terminal of the fixed electrode plate; the driving device of the mobile electrode plate is composed of a rack [5], a gear [7] and a servo motor [6]. ] connected to the upper end, and form a transmission relationship with the servo motor [6] through the gear [7]; the conductive liquid [8] is filled in the liquid resistance box [1]. 6. According to claim 5, the synchronous input and excitation device of the wound asynchronous motor is characterized in that, the asynchronous starting device is additionally provided with a short-sealed third contactor [CJ3], and a short-sealed third contactor [CJ3] One end of the three normally open contacts is respectively connected to three liquid resistors, and the other ends are shorted together. 7. The excitation device for synchronizing a wound asynchronous motor according to claim 5, wherein the conductive liquid [8] is an electrolytic solution. 8. The excitation device for synchronizing a wound asynchronous motor according to claim 4 or 5, characterized in that the resistance value of the additional resistor [R _f ] is 5-15 Rz ohms, where Rz is the The winding impedance after a certain two-phase winding of the winding is firstly connected in parallel and then connected in series with the remaining one-phase winding.

Images