An autotransformer step-down control system based on PLC

Abstract

The present invention relates to the field of automatic control technology, and particularly relates to an autotransformer step-down control system based on a PLC. It includes a main power supply circuit and a control loop. The autotransformer step-down control system based on a PLC of the present invention is controlled based on a programmable logic controller (PLC) and a touch screen, and improves the control loop of the XJ01 autotransformer. A main circuit AC contactor KM4 is added to the main circuit. When the star point short-circuit AC contactor KM1, the step-down operation AC contactor KM2, and the contacts are adhered, the internal timer T38 of the PLC detects an abnormality, and the main circuit AC contactor KM4 issues an immediate trip command to protect the motor and the autotransformer. The design concept of this solution is advanced, and the use of the PLC and the touch screen is stable, safe and reliable; compared with the original wiring method, the connection is simple; it is convenient to maintain, and even if the internal data is lost, the data can be restored in only a few minutes.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer control, and particularly relates to an autotransformer step-down control system based on a PLC. Background Art

[0002] The control wiring of autotransformers is not unfamiliar to professionals in the electrical industry and is mainly used for the starting of high-power motors. Generally, motors with a power greater than 11 kW cannot be started directly.

[0003] When starting a motor with an autotransformer step-down, an autotransformer is used to reduce the voltage applied to the stator winding of the motor. After the motor starts, the motor is then disconnected from the autotransformer so that it can operate normally under full voltage. This step-down starting is divided into two types: manual control and automatic control. There are problems with the control wiring of autotransformers being prone to burning out. The XJ01 series of autotransformer step-down starters are often burned out due to the welding of the main contacts of the contactor. The reasons are analyzed as follows: (1) If the main contacts of contactor KM1 are welded, the normally open contacts of contactor KM1 cannot return from the closed state to the open state, KM2 will continue to be energized, KM3 cannot be energized, and the motor will run in the autotransformer step-down state all the time and burn out. (2) After the motor starts, no current is allowed to flow through the autotransformer. If the main contacts of KM2 are welded, when the circuit causes contactor KM1 to lose power and reset according to the program, and intermediate relay KA and contactor KM3 are energized and closed, at this time, the current flowing to the motor passes through two paths: contactor KM3, the main contacts of contactor KM2, and the autotransformer. Although the current flowing through the autotransformer is small, long-term operation and heavy-load starting will cause the autotransformer to overheat for a long time and eventually burn out the equipment. (3) The normal operation of KM3 must be based on the long-term energization of the coil of intermediate relay KA, which is not good for the intermediate relay and will reduce the reliability during starting. (4) There is a risk of direct starting in the control circuit, which is not allowed. When the coil of contactor KM2 is broken, each contact is in poor contact, and the mechanical mechanism is jammed and cannot work normally, when the start button SB1 is pressed, the coil of time relay KT will be energized after the normally open contacts of KM1 are closed regardless of whether KM2 is closed or not. After a delay, the normally open timed contacts of KT are closed, intermediate relay KA is energized and its normally open contacts are closed, and KM3 is immediately energized and closed, and the motor will run directly under full voltage. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention uses a programmable logic controller (PLC) and a touch screen to control the XJ01 autotransformer control circuit, aiming to provide an autotransformer step-down control system based on a PLC.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An autotransformer step-down control system based on a PLC, the system includes a main power circuit 1 and a control circuit 2; wherein,

[0007] The main power circuit 1 consists of a main power switch QF, a motor M, a fuse FU1, a fuse FU2, a fuse FU3, a main circuit AC contactor KM4, a motor comprehensive protector FR, a current transformer TA, a full-voltage operation AC contactor KM3, a step-down operation AC contactor KM2, a star-point short-circuit AC contactor KM1, and an autotransformer coil ZOB; The three terminal ends of the motor M are respectively connected to three live wires L1, L2, and L3. On the three live wires L1, L2, and L3 between the motor M and the main power switch QF, a full-voltage operation AC contactor KM3, a current transformer TA, a motor comprehensive protector FR, a main circuit AC contactor KM4, a fuse FU1, a fuse FU2, and a fuse FU3 are connected in series in sequence; The first end of the autotransformer coil ZOB is connected in series with the star-point short-circuit AC contactor KM1, and the second end is connected in series with one end of the step-down operation AC contactor KM2. The other end of the step-down operation AC contactor KM2 is connected to the three live wires L1, L2, and L3 in parallel between the current transformer TA and the full-voltage operation AC contactor KM3; The third end of the autotransformer coil ZOB is connected in parallel to the three live wires L1, L2, and L3 between the full-voltage operation AC contactor KM3 and the three terminal ends of the motor M; The motor M is grounded;

[0008] The control circuit 2 consists of a PLC, a touch screen, and a panel signal component. The PLC cooperates with the panel signal component and the touch screen to control the main power circuit 1 to complete the step-down function of the autotransformer.

[0009] As an optimized technical solution of the present invention, the out-of-panel signal component includes a start button SB1, a total stop button SB2, a run button SB3, a stop indicator light LD, a closing indicator light HD1, a closing step-down start indicator light HD2, a closing operation indicator light HD3, a voltmeter V, and an ammeter A;

[0010] One ends of the start button SB1, the total stop button SB2, and the run button SB3 are respectively connected to the input terminals I0.0, I0.1, and I0.2 of the PLC, and the common end of the other ends is connected to the negative pole of the DC power supply; The +24v input terminal 1M of the DC power supply of the PLC is connected to the positive pole of the DC power supply; The AC terminal of the DC power supply is connected to the live wire L1 and the neutral wire LN of the main power circuit 1 through a power switch QF1;

[0011] One end of the shutdown indicator light LD, closing indicator light HD1, closing step-down start indicator light HD2, and closing operation indicator light HD3 are respectively connected to the output terminals Q0.3, Q0.4, Q0.5, and Q0.6 of the PLC, and the common terminal at the other end is connected to the neutral line LN of the main power circuit 1 through the power switch QF2; One end of the output terminal Q0.0 of the PLC is connected to one end of the coil of the main circuit AC contactor KM4, and the other end of the coil of the main circuit AC contactor KM4 is connected to the neutral line LN of the main power circuit 1 through the power switch QF2;

[0012] One end of the coil of the step-down operation AC contactor KM2 is connected to the output terminal Q0.1 of the PLC, and the other end is connected to the normally closed contact of the full-voltage operation AC contactor KM3. The other end of the normally closed contact of the full-voltage operation AC contactor KM3 is connected to the normally closed contact of the motor comprehensive protector FR; The other end of the normally closed contact of the motor comprehensive protector FR is connected to the neutral line LN of the main power circuit 1 through the power switch QF2; One end of the coil of the star point short-circuit AC contactor KM1 is connected to the output terminal Q0.1 of the PLC, and the other end is connected between the coil of the step-down operation AC contactor KM2 and the normally closed contact of the full-voltage operation AC contactor KM3;

[0013] One end of the coil of the full-voltage operation AC contactor KM3 is connected to the output terminal Q0.2 of the PLC, and the other end is connected to the normally closed contact of the step-down operation AC contactor KM2. The normally closed contact of the step-down operation AC contactor KM2 is connected to one end of the normally closed contact of the star point short-circuit AC contactor KM1. The other end of the normally closed contact of the star point short-circuit AC contactor KM1 is connected between the normally closed contact of the full-voltage operation AC contactor KM3 and the normally closed contact of the motor comprehensive protector FR;

[0014] The output common terminal 1L of the PLC is connected to the live wire L1 of the main power circuit 1 through the power switch QF2.

[0015] As an optimized technical solution of the present invention, the closing indicator light HD1 is the closing indicator light of the main circuit AC contactor KM4; The closing step-down start indicator light HD2 is the closing step-down start indicator light of the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2; The closing operation indicator light HD3 is the closing indicator light of the full-voltage operation AC contactor KM3.

[0016] As an optimized technical solution of the present invention, the delay time for the PLC to detect the failure of the full-voltage operation AC contactor KM3 to close is 2 to 5 s; When the star point AC contactor KM1 and the step-down operation AC contactor KM2 have contact sticking, and the PLC internal timer T38 cannot detect the signal of the full-voltage operation AC contactor KM3 running, the main circuit AC contactor KM4 is automatically tripped after a delay to protect the autotransformer.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] A self-coupling transformer step-down control system based on PLC according to the present invention is controlled based on a programmable logic controller PLC and a touch screen, and the control circuit of the XJ01 self-coupling transformer is improved. A main circuit AC contactor KM4 is added to the main circuit. When the contacts are stuck, the comparison element detects the abnormality and issues an immediate tripping command to the main circuit AC contactor KM4 to protect the motor and the self-coupling transformer. The design concept of this solution is advanced, and the use of PLC and touch screen is stable, safe and reliable; compared with the original wiring method, the connection is simple; it is convenient to maintain, and even if the internal data is lost, the data can be restored in only a few minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the system of the present invention;

[0020] Figure 2 It is the main power circuit diagram of the system of the present invention;

[0021] Figure 3 It is the ladder diagram of the PLC of the system of the present invention;

[0022] Figure 4 It is the in-panel layout diagram of the control circuit of the system of the present invention;

[0023] Figure 5 It is the panel layout diagram of the out-of-panel signal components in the control circuit of the system of the present invention.

[0024] In the figure: 1. Main power circuit; 2. Control circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0026] In the description of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0027] Embodiment 1

[0028] Please refer to the appendix Figures 1-5 As shown in Figures 1-5 , the present invention provides an autotransformer step-down control system based on a PLC. The system includes a main power circuit 1 and a control circuit 2. Among them, the main power circuit 1 consists of a main power switch QF, a motor M, a fuse FU1, a fuse FU2, a fuse FU3, a main circuit AC contactor KM4, a motor comprehensive protector FR, a current transformer TA, a full-voltage operation AC contactor KM3, a step-down operation AC contactor KM2, a star point short-circuit AC contactor KM1, and an autotransformer coil ZOB. The three connection terminals of the motor M are respectively connected to three live wires L1, L2, and L3. On the three live wires L1, L2, and L3 between the motor M and the main power switch QF, a full-voltage operation AC contactor KM3, a current transformer TA, a motor comprehensive protector FR, a main circuit AC contactor KM4, a fuse FU1, a fuse FU2, and a fuse FU3 are connected in series in sequence. The first end of the autotransformer coil ZOB is connected in series with the star point short-circuit AC contactor KM1, and the second end is connected in series with one end of the step-down operation AC contactor KM2. The other end of the step-down operation AC contactor KM2 is connected to the three live wires L1, L2, and L3 that are connected in parallel between the current transformer TA and the full-voltage operation AC contactor KM3. The third end of the autotransformer coil ZOB is connected in parallel to the three live wires L1, L2, and L3 between the full-voltage operation AC contactor KM3 and the three connection terminals of the motor M. The motor M is grounded. The control circuit 2 consists of a PLC, a touch screen, and a panel signal component. The PLC control system cooperates with the panel signal component and the touch screen to control the main power circuit 1 to complete the step-down function of the autotransformer.

[0029] Optimized, the off-board signal components include a start button SB1, a total stop button SB2, a run button SB3, a stop indicator light LD, a closing indicator light HD1, a closing step-down start indicator light HD2, a closing running indicator light HD3, a voltmeter V, and an ammeter A; one ends of the start button SB1, the total stop button SB2, and the run button SB3 are respectively connected to the input terminals I0.0, I0.1, and I0.2 of the PLC, and the common terminal at the other ends is connected to the negative pole of the DC power supply; the +24v input terminal 1M of the DC power supply of the PLC is connected to the positive pole of the DC power supply; the AC terminal of the DC power supply is connected to the live wire L1 and the neutral wire LN of the main power circuit 1 through a power switch QF1; one ends of the stop indicator light LD, the closing indicator light HD1, the closing step-down start indicator light HD2, and the closing running indicator light HD3 are respectively connected to the output terminals Q0.3, Q0.4, Q0.5, and Q0.6 of the PLC, and the common terminal at the other ends is connected to the neutral wire LN of the main power circuit 1 through a power switch QF2; the output terminal Q0.0 of the PLC is connected to one end of the coil of the main circuit AC contactor KM4, and the other end of the coil of the main circuit AC contactor KM4 is connected to the neutral wire LN of the main power circuit 1 through a power switch QF2; one end of the coil of the step-down running AC contactor KM2 is connected to the output terminal Q0.1 of the PLC, and the other end is connected to the normally closed contact of the full-voltage running AC contactor KM3, and the other end of the normally closed contact of the full-voltage running AC contactor KM3 is connected to the normally closed contact of the motor comprehensive protector FR; the other end of the normally closed contact of the motor comprehensive protector FR is connected to the neutral wire LN of the main power circuit 1 through a power switch QF2; one end of the coil of the star point short-circuit AC contactor KM1 is connected to the output terminal Q0.1 of the PLC, and the other end is connected between the coil of the step-down running AC contactor KM2 and the normally closed contact of the full-voltage running AC contactor KM3; one end of the coil of the full-voltage running AC contactor KM3 is connected to the output terminal Q0.2 of the PLC, and the other end is connected to the normally closed contact of the step-down running AC contactor KM2. The normally closed contact of the step-down running AC contactor KM2 is connected to one end of the normally closed contact of the star point short-circuit AC contactor KM1, and the other end of the normally closed contact of the star point short-circuit AC contactor KM1 is connected between the normally closed contact of the full-voltage running AC contactor KM3 and the normally closed contact of the motor comprehensive protector FR; the output common terminal 1L of the PLC is connected to the live wire L1 of the main power circuit 1 through a power switch QF2.

[0030] Optimized, the closing indicator light HD1 is the closing indicator light of the main circuit AC contactor KM4; the closing step-down start indicator light HD2 is the closing step-down start indicator light of the star point short-circuit AC contactor KM1 and the step-down running AC contactor KM2; the closing running indicator light HD3 is the closing indicator light of the full-voltage running AC contactor KM3.

[0031] Optimized, the delay time for the PLC to detect the failure of the full-voltage operation AC contactor KM3 to close is 2 to 5 s; when the star-point AC contactor KM1 and the step-down operation AC contactor KM2 have contact sticking, and the PLC internal timer T38 cannot detect the signal of the full-voltage operation AC contactor KM3 running, the main-circuit AC contactor KM4 will be automatically tripped after a delay to protect the autotransformer.

[0032] Embodiment 2

[0033] Based on Embodiment 1, as shown in the appendix Figures 1-5 , the working principle of the system is as follows:

[0034] The main-circuit AC contactor KM4 is a device that provides operating power for the entire circuit, and in the present invention, it is used to supply power to the main power circuit 1. That is, before starting, the main-circuit AC contactor KM4 is closed first, otherwise the main power circuit 1 and the control circuit 2 of the entire system will be without power.

[0035] In addition, the PLC internal relay is used to monitor whether the full-voltage operation AC contactor KM3 is closed, to prevent the star-point short-circuit AC contactor KM1, the step-down operation AC contactor KM2 from jamming or the contact tips from fusing and the auxiliary contacts from having poor contact, which may cause the autotransformer to keep running in the starting state. To prevent such accidents from occurring, there is a time difference in the PLC programming. The timer starting with the letter "T" inside the PLC is used to complete the delayed step-down starting. There must be a time difference between T37 and T38 because T37 is responsible for starting the full-voltage operation AC contactor KM3 to close and cutting off the coil circuits of the star-point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2, and T38 is responsible for monitoring whether the full-voltage operation AC contactor KM3 is closed. When the star-point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2 have contact sticking, or for other reasons, the full-voltage operation AC contactor KM3 fails to close. At this time, the delayed closing command of the PLC timer T37 has been issued, and at the same time, its own delayed-open normally closed contact T37 is used to cut off its own circuit. At the same time, the PLC timer T38 cannot detect the signal of the full-voltage operation AC contactor KM3 closing, and the normally closed contact of T38 that opens after a delay disconnects the internal program Q0.0 of the PLC. In the IO allocation table, the main-circuit AC contactor KM4 is made the same as the output terminal Q0.0 of the PLC. Therefore, when the output terminal Q0.0 of the PLC loses power, that is, the main-circuit AC contactor KM4 loses power in the same way, the main-circuit AC contactor KM4 disconnects, and the primary circuit is completely de-energized. In this way, the entire device is protected to effectively prevent the autotransformer from being energized for a long time, and at the same time, a signal is sent to remind the operator to pay attention.

[0036] When the main and auxiliary contacts of the step-down operation AC contactor KM2 and the star-point short-circuit AC contactor KM1 are fused, the action process is the same as the above action process, so it will not be repeated here.

[0037] First, press the start button SB1. The main circuit AC contactor KM4 is energized and attracted, and the normally open contact of the main circuit AC contactor KM4 connected in this circuit closes for self-holding. The main contacts connect to the main power supply circuit 1, and the normally open contact of the main circuit AC contactor KM4 connected in series in the motor protector FR and the total stop button SB2 circuit closes to connect the control circuit. Then press the start button SB1 again. The step-down operation AC contactor KM2 is energized and attracted, and its normally open contact closes, connecting the coils of the star point short-circuit AC contactor KM1, the internal timers T37 and T38. At the same time, the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2 start step-down starting. After the delay, the normally open contact of the PLC internal timer T37 closes to connect the closing circuit of the full-voltage operation AC contactor KM3. One pair of normally closed contacts of the step-down operation AC contactor KM2 and the star point short-circuit AC contactor KM1 connected in series in the full-voltage operation AC contactor KM3 coil circuit disconnect, aiming to prevent the full-voltage operation AC contactor KM3 from malfunctioning when the step-down starting is not completed. When the PLC internal timer T37 times out, the normally closed contact T37 with delayed disconnection connected in series in the step-down starting circuit of the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2 disconnects to cut off the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2. The power supply of the step-down operation AC contactor KM2 coil is cut off and reset. At this time, the power supply of the autotransformer is cut off, and the normally closed contacts of the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2 connected in series in the full-voltage operation AC contactor KM3 circuit close. At the same time, the normally closed contact of the full-voltage operation AC contactor KM3 disconnects the circuit of the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2. The whole starting to running process ends, and at this time, the motor runs normally under full voltage.

[0038] When any one of the star point short-circuit AC contactor KM1 and the step-down operation AC contactor KM2 has its main and auxiliary contacts stuck or for other reasons, and the PLC internal timer T38 cannot detect the closing signal of the full-voltage operation AC contactor KM3 within the specified time, after a delay of 2 - 5s, the PLC internal timer T38 sends a signal to immediately trip the control circuit of the main circuit AC contactor KM4. After receiving the instruction, the main circuit AC contactor KM4 immediately trips the main power supply circuit 1, and the main power supply circuit 1 and the control circuit lose power as a whole to protect the autotransformer and the motor. In addition, an alarm is sent to the operating personnel.

[0039] When stopping, just press the total stop button SB2 or the PLC internal program I0.1. The main circuit AC contactor KM4 and the full-voltage operation AC contactor KM3 trip simultaneously, and the stop indicator light LD lights up, and the equipment enters the stop state.

[0040] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A self - coupling transformer step - down control system based on PLC, the system includes a main power circuit (1) and a control loop (2); characterized in that: The main power circuit (1) consists of a main power switch QF, a motor M, a fuse FU1, a fuse FU2, a fuse FU3, a main circuit AC contactor KM4, a motor comprehensive protector FR, a current transformer TA, a full - voltage operation AC contactor KM3, a step - down operation AC contactor KM2, a star - point short - circuit AC contactor KM1 and a self - coupling transformer coil ZOB; Three terminal leads of the motor M are respectively connected to three live wires L1, L2, L3. On the three live wires L1, L2, L3 between the motor M and the main power switch QF, there are successively connected in series a full - voltage operation AC contactor KM3, a current transformer TA, a motor comprehensive protector FR, a main circuit AC contactor KM4, a fuse FU1, a fuse FU2, and a fuse FU3; The first end of the self - coupling transformer coil ZOB is connected in series with the star - point short - circuit AC contactor KM1, and the second end is connected to one end of the step - down operation AC contactor KM2. The other end of the step - down operation AC contactor KM2 is connected to the three live wires L1, L2, L3 in parallel between the current transformer TA and the full - voltage operation AC contactor KM3; The third end of the self - coupling transformer coil ZOB is connected in parallel to the three live wires L1, L2, L3 between the full - voltage operation AC contactor KM3 and the three terminal leads of the motor M; The control loop (2) consists of a PLC, a touch screen and a panel signal component. The PLC cooperates with the panel signal component and the touch screen to control the main power circuit (1) to complete the step - down function of the self - coupling transformer. The PLC includes a timer; The output terminal Q0.0 of the PLC is connected to one end of the coil of the main circuit AC contactor KM4. The other end of the coil of the main circuit AC contactor KM4 is connected to the neutral line LN of the main power circuit (1) through a power switch QF2; One end of the coil of the step - down operation AC contactor KM2 is connected to the output terminal Q0.1 of the PLC, and the other end is connected to the normally - closed contact of the full - voltage operation AC contactor KM3. The other end of the normally - closed contact of the full - voltage operation AC contactor KM3 is connected to the normally - closed contact of the motor comprehensive protector FR; The other end of the normally - closed contact of the motor comprehensive protector FR is connected to the neutral line LN of the main power circuit (1) through a power switch QF2; One end of the coil of the star - point short - circuit AC contactor KM1 is connected to the output terminal Q0.1 of the PLC, and the other end is connected between the coil of the step - down operation AC contactor KM2 and the normally - closed contact of the full - voltage operation AC contactor KM3; One end of the coil of the full-voltage operation AC contactor KM3 is connected to the output terminal Q0.2 of the PLC, and the other end is connected to the normally-closed contact of the reduced-voltage operation AC contactor KM2. The normally-closed contact of the reduced-voltage operation AC contactor KM2 is connected to one end of the normally-closed contact of the star-point shorting AC contactor KM1, and the other end of the normally-closed contact of the star-point shorting AC contactor KM1 is connected between the normally-closed contact of the full-voltage operation AC contactor KM3 and the normally-closed contact of the motor comprehensive protector FR. The output common terminal 1L of the PLC is connected to the live wire L1 of the main power circuit (1) through the power switch QF2; when the star-point shorting AC contactor KM1 and the reduced-voltage operation AC contactor KM2 have contact sticking, and the PLC timer cannot detect the signal of the full-voltage operation AC contactor KM3 running, the main circuit AC contactor KM4 is automatically tripped after a delay to protect the autotransformer.

2. The autotransformer step-down control system based on PLC according to claim 1, characterized in that: The delay time is 2 to 5 s.

Images