CN113922333A - A PLC-based autotransformer step-down control system - Google Patents

Abstract

The invention relates to the technical field of automatic control, in particular to a voltage reduction control system of an autotransformer based on a PLC. Comprises a main power circuit and a control loop. The invention relates to an autotransformer voltage reduction control system based on a Programmable Logic Controller (PLC), which is based on PLC and touch screen control, improves a control loop of an XJ01 autotransformer, and adds a main loop alternating current contactor KM4 to the main loop. When the star point short circuit alternating current contactor KM1, the step-down operation alternating current contactor KM2 and the contacts are adhered, the timer T38 in the PLC detects abnormality, and the main loop alternating current contactor KM4 sends an immediate tripping command to protect the motor and the autotransformer. The scheme has the advantages that the design concept is advanced, and the PLC and the touch screen are stable in operation, safe and reliable; compared with the original wiring mode, the connection is simple; the maintenance is convenient, and even if the internal data is lost, the data can be recovered in only a few minutes.

Description

A PLC-based autotransformer step-down control system

technical field

The invention relates to the technical field of transformer control, in particular to a PLC-based autotransformer step-down control system.

Background technique

Autotransformer control wiring is not unfamiliar to professionals engaged in the electrical industry, and is mainly used for high-power motor starting. Under normal circumstances, the starting of the motor with the motor power greater than 11kW cannot be directly started.

The autotransformer is used to reduce the voltage applied to the stator windings of the motor when the motor is started by reducing the voltage. After the motor is started, the motor is disconnected from the autotransformer, so that it can move normally under full voltage. This step-down start is divided into two types: manual control and automatic control. The control wiring of the autotransformer has the problem of easy burnout. The easy burnout of the XJ01 series autostep-down transformer is often caused by the welding of the main contact of the contactor. The reasons are analyzed as follows: (1) If the main contact of the contactor KM1 is welded, Then the normally open contact of the contactor KM1 cannot be restored from the closed state to the open state, KM2 will continue to be pulled in, KM3 cannot be pulled in, and the motor has been running in the state of auto-coupling and depressurized and burned. (2) After the motor is started, the autotransformer is not allowed to have current flow. If the main contact of KM2 is welded, when the circuit causes the contactor KM1 to lose power and reset according to the program, the intermediate relay KA and the contactor KM3 are energized and closed. When the current flows to the motor through the contactor KM3 and contactor KM2 main contacts and autotransformer two ways. Although the current flowing to the autotransformer is small, long-term operation and heavy load startup can cause the autotransformer to overheat for a long time and eventually burn the equipment. (3) The normal operation of KM3 must be premised on the long-term charging of the intermediate relay KA coil, which is not good for the intermediate relay and will reduce the reliability at startup. (4) There is a danger of direct start of the control circuit, which is not allowed. When the contactor KM2 coil is disconnected, the contacts are in poor contact, and the mechanical mechanism is blocked and cannot work normally, press the run button SB1, and the time relay KT coil will be delayed after the normally open contact of KM1 is closed, regardless of whether KM2 is closed or not. When the time-delayed normally open contact to KT is closed, the intermediate relay KA pulls in and its normally open and closed, KM3 is energized and closed, and the motor runs directly under full pressure.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the present invention adopts programmable controller PLC and touch screen control for the XJ01 autotransformer control loop, and aims to provide a PLC-based autotransformer step-down control system.

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

A PLC-based autotransformer step-down control system, the system includes a main power circuit 1 and a control loop 2; wherein,

The main power circuit 1 is composed of the main power switch QF, the motor M, the fuse FU1, the fuse FU2, the fuse FU3, the main circuit AC contactor KM4, the motor comprehensive protector FR, the current transformer TA, and the full-voltage operation AC. The contactor KM3, the step-down running AC contactor KM2, the star point short-circuiting AC contactor KM1 and the autotransformer coil ZOB are composed; the three terminals of the motor M are respectively connected to the three live wires L1, L2 and L3. The three live wires L1, L2 and L3 between the motor M and the main power switch QF are connected in series with the full-voltage running AC contactor KM3, the current transformer TA, the motor comprehensive protector FR, the main circuit AC contactor KM4, and the fuse. FU1, fuse FU2, fuse FU3; 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 AC contactor KM2, so The other end of the AC contactor KM2 for step-down operation is connected in parallel with the three live wires L1, L2, and L3 between the current transformer TA and the AC contactor KM3 for full-voltage operation; the third end of the autotransformer coil ZOB is connected in parallel. On the three live wires L1, L2, L3 between the three terminals of the full-voltage operation AC contactor KM3 and the motor M; the motor M is grounded;

The control loop 2 is composed 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.

As an optimized technical solution of the present invention, the off-panel signal component includes a start button SB1, a total stop button SB2, a running button SB3, a stop indicator LD, a closing indicator HD1, a closing step-down start indicator HD2, a closing indicator Running indicator HD3, voltmeter V and ammeter A;

One end of the start button SB1, the total stop button SB2, and the running button SB3 are respectively connected to the input ends I0.0, I0.1, and I0.2 of the PLC, and the common end of the other end is connected to the negative pole of the DC power supply; The DC +24v input terminal 1M 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 the power switch QF1;

One end of the stop indicator LD, the closing indicator HD1, the closing step-down start indicator HD2, and the closing running indicator HD3 are respectively connected to the output terminals Q0.3, Q0.4, Q0.5, Q0 of the PLC. 6. The common terminal of the other end is connected to the neutral line LN of the main power circuit 1 through the 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 main circuit AC contactor The other end of the KM4 coil 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 AC contactor KM2 for voltage reduction operation is connected to the output terminal Q0.1 of the PLC, the other end is connected to the normally closed contact of the AC contactor KM3 for full voltage operation, and the other end of the normally closed contact for the AC contactor KM3 for full voltage operation is connected. It is connected with the normally closed contact of the integrated motor protector FR; the other end of the normally closed contact of the integrated motor protector FR is connected to the neutral line LN of the main power circuit 1 through the power switch QF2; the star point is shorted to the coil of the AC contactor KM1 One end is connected with the output end Q0.1 of the PLC, and the other end is connected between the coil of the AC contactor KM2 for step-down operation and the normally closed contact of the AC contactor KM3 for full-voltage operation;

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, and the normally closed contact of the step-down operation AC contactor KM2 is connected to the star. Connect one end of the normally closed contact of the point shorting AC contactor KM1, the other end of the star point shorting AC contactor KM1 normally closed contact is connected to the normally closed contact of the full voltage running AC contactor KM3 and the motor comprehensive protector FR normally closed between the contacts;

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.

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

As an optimized technical solution of the present invention, the delay time for the PLC to detect the closing failure of the full-voltage operation AC contactor KM3 is 2-5s; When the PLC internal timer T38 cannot detect the running signal of the full-voltage running AC contactor KM3, the delay automatically trips the main circuit AC contactor KM4 to protect the autotransformer.

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

The invention is a PLC-based autotransformer step-down control system, based on programmable controller PLC and touch screen control, the XJ01 autotransformer control circuit is improved, and the main circuit is added with a main circuit AC contactor KM4. When the contacts are stuck, the comparison element detects an abnormality and issues an immediate trip command to the main circuit AC contactor KM4 to protect the motor and the autotransformer. The design concept of this scheme is advanced, the PLC and touch screen are stable, safe and reliable; compared with the original wiring method, the connection is simple; the maintenance is convenient, even if the internal data is lost, it only takes a few minutes to restore the data.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the system of the present invention;

Fig. 2 is the main power circuit diagram of the system of the present invention;

Fig. 3 is the ladder diagram of the PLC of the system of the present invention;

4 is an in-pan layout diagram of the control loop of the system of the present invention;

FIG. 5 is a panel layout diagram of off-panel signal components in the control loop of the system of the present invention.

In the figure: 1. Main power circuit; 2. Control circuit.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below 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, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

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

Example 1

Please refer to accompanying drawings 1-5, the present invention provides a PLC-based autotransformer step-down control system, the system includes a main power circuit 1 and a control loop 2, wherein the main power circuit 1 consists of a main power switch QF, a motor M , fuse FU1, fuse FU2, fuse FU3, main circuit AC contactor KM4, motor comprehensive protector FR, current transformer TA, full-voltage running AC contactor KM3, step-down running AC contactor KM2, short star point It is composed of AC contactor KM1 and autotransformer coil ZOB; the three terminals of motor M are respectively connected to three live wires L1, L2 and L3, and the three live wires L1, L2 and L3 between the motor M and the main power switch QF are connected in sequence. It is connected in series with full-voltage running AC contactor KM3, current transformer TA, motor comprehensive protector FR, main circuit AC contactor KM4, fuse FU1, fuse FU2, fuse FU3; the first end of the autotransformer coil ZOB It is connected in series with the star point shorting AC contactor KM1, the second end is connected in series with one end of the AC contactor KM2 in the step-down operation, and the other end of the AC contactor KM2 in the step-down operation is connected in parallel with the current transformer TA and the full-voltage operation AC. On the three live wires L1, L2, L3 between the contactor KM3; the third end of the autotransformer coil ZOB is connected in parallel with the three live wires L1, L2, L3 between the full voltage operation AC contactor KM3 and the three terminals of the motor M The motor M is grounded; the control circuit 2 is composed of PLC, touch screen and panel signal components. The PLC control system cooperates with the panel signal components and the touch screen to control the main power circuit 1 to complete the step-down function of the autotransformer.

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

Optimized, the closing indicator HD1 is the main circuit AC contactor KM4 closing indicator; the closing step-down start indicator HD2 is the star point shorting AC contactor KM1 and the step-down running AC contactor KM2 closing drop Voltage start indicator light; closing running indicator HD3 is the closing indicator light of AC contactor KM3 in full voltage operation.

Optimized, the delay time for PLC to detect the closing failure of AC contactor KM3 in full voltage operation is 2 to 5s; when the star point AC contactor KM1 and the AC contactor KM2 in reduced voltage operation are electrocuted and adhered, the PLC internal timer T38 detects that the failure occurs. When the signal of full voltage operation of AC contactor KM3 is reached, the delay automatically trips the main circuit AC contactor KM4 to protect the autotransformer.

Example 2

Based on Embodiment 1, as shown in Figures 1-5, the working principle of the system is:

The main circuit AC contactor KM4 is used to provide a running power supply device for the entire circuit, and is used to supply power to the main power circuit 1 in the present invention. That is, close the main circuit AC contactor KM4 before starting, otherwise the main power circuit 1 and control circuit 2 of the whole system will have no electricity.

In addition, the PLC internal relay is used to monitor whether the full-voltage running AC contactor KM3 is closed, to prevent the star point short-circuiting the AC contactor KM1, the step-down running AC contactor KM2 from being stuck or the contact welding, and the auxiliary contact being in poor contact. And the protection measures that cause the autotransformer to run in the starting state all the time. In order to prevent such accidents from happening, there is a time difference in the PLC programming, and the timer with the letter "T" inside the PLC is used to complete the delayed step-down start. There must be a time difference between T37 and T38. The reason is that T37 is responsible for starting the full-voltage running AC contactor KM3 to close and cutting off the star point short-circuit AC contactor KM1 and the voltage-reducing running AC contactor KM2 coil loop, and T38 is responsible for monitoring the full voltage Check whether the AC contactor KM3 is closed. When the star point is short-circuited with AC contactor KM1 and AC contactor KM2 in voltage-reduced operation, contact sticking occurs, or the closing of AC contactor KM3 in full-voltage operation fails due to other reasons. At this time, the delay closing order of PLC timer T37 has been closed. At the same time, it uses its own delay to disconnect the normally closed contact T37 to cut off its own circuit. At the same time, the PLC timer T38 cannot detect the closing signal of the full-voltage running AC contactor KM3, and the normally closed contact disconnected by the delay of T38 disconnects the PLC internal program Q0.0. In the IO allocation table, the main circuit AC contactor KM4 and the PLC output Q0.0 are the same, so when the PLC output Q0.0 loses power, that is, the main circuit AC contactor KM4 loses the same power, and the main circuit AC contacts When the transformer KM4 is disconnected, the primary circuit is completely cut off, so that the whole device is protected and effectively prevents the autotransformer from running with electricity for a long time, and at the same time, a signal is sent to remind the operator to pay attention.

When the AC contactor KM2 operating under voltage drop and the star point short-circuiting AC contactor KM1 main and auxiliary contacts are welded, the action process is the same as the above action process, so the description will not be repeated.

First press the start button SB1, the main circuit AC contactor KM4 is energized and closed, and the normally open contact of the main circuit AC contactor KM4 connected in this circuit is closed and self-holding, the main contact is connected to the main power circuit 1, connected in series The main circuit AC contactor KM4 normally open contact in the circuit of the motor protector FR and the total stop button SB2 is closed to connect the control circuit. Press the start button SB1 again, the AC contactor KM2 for step-down operation is energized and closed, its normally open contact is closed, and the star point is connected to short-circuit the AC contactor KM1 and the coils of the internal timers T37 and T38, and the star point is short-circuited at the same time. The AC contactor KM1 and the AC contactor KM2 in the voltage-reduced operation start to perform the step-down start, and the normally open contact of the internal timer T37 of the PLC is delayed to close the closing circuit of the AC contactor KM3 in the full-voltage operation. Each pair of normally closed contacts of the AC contactor KM2 for step-down operation and the star point short-circuit AC contactor KM1 in series in the coil loop of the AC contactor KM3 for full-voltage operation are disconnected, and the purpose is to lock when the step-down start-up is not over. Prevent the misoperation of AC contactor KM3 in full-voltage operation. The PLC internal timer T37 delays as soon as it is connected in series to the star point to short the AC contactor KM1 and the step-down operation AC contactor KM2. The delay in the step-down start circuit disconnects the normally closed contact T37 disconnects and cuts off the star point short circuit AC contactor KM1, AC contactor KM2 for step-down operation. Step-down operation AC contactor KM2 coil power supply and reset, at this time cut off the power supply of the autotransformer, connect in series with the star point in the full-voltage operation AC contactor KM3 circuit short-circuit AC contactor KM1, step-down operation AC contactor KM2 Normally closed contacts are closed. At the same time, the circuit of AC contactor KM3 in full-voltage operation is normally closed, and the star point is shorted in AC contactor KM1, and the circuit of AC contactor KM2 in step-down operation.

When the star point is short-circuited with AC contactor KM1 and AC contactor KM2 under voltage drop operation, the main and auxiliary contacts are stuck together or due to other reasons, the PLC internal timer T38 cannot detect the full-voltage operation AC contactor within the specified time. After the closing signal of KM3, the PLC internal timer T38 will send an immediate trip signal to the control circuit of the main circuit AC contactor KM4 after a delay of 2-5s, and the main circuit AC contactor KM4 will immediately trip the main power circuit 1 after receiving the command. , the main power circuit 1 and the control circuit as a whole lose power to protect the autotransformer and the motor. In addition, an alarm is issued to the operator.

When stopping, just press the main stop button SB2 or PLC internal program I0.1, the main circuit AC contactor KM4 and the full-voltage running AC contactor KM3 will trip at the same time, the stop indicator LD will be on, and the equipment will enter the stop state.

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

Claims (4)

1. a PLC-based autotransformer step-down control system, the system comprises a main power circuit (1) and a control loop (2); it is characterized in that: The main power circuit (1) is composed of the main power switch QF, the motor M, the fuse FU1, the fuse FU2, the fuse FU3, the main circuit AC contactor KM4, the motor comprehensive protector FR, the current transformer TA, the full voltage It is composed of running AC contactor KM3, step-down running AC contactor KM2, star point short-circuiting AC contactor KM1 and autotransformer coil ZOB; the three terminals of the motor M are respectively connected to three live wires L1, L2, L3, The three live wires L1, L2 and L3 between the motor M and the main power switch QF are sequentially connected in series with a full-voltage running AC contactor KM3, a current transformer TA, a motor comprehensive protector FR, a main circuit AC contactor KM4, Fuse FU1, fuse FU2, fuse FU3; 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 AC contactor KM2 for step-down operation is connected in parallel with the three live wires L1, L2, and L3 between the current transformer TA and the AC contactor KM3 for full-voltage operation; the third end of the autotransformer coil ZOB Connected in parallel on the three live wires L1, L2, L3 between the full-voltage running AC contactor KM3 and the three terminals of the motor M; the motor M is grounded; The control loop (2) is composed of a PLC, a touch screen and a panel signal component, and 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. 2. A PLC-based autotransformer step-down control system according to claim 1, characterized in that: the off-panel signal assembly comprises a start button SB1, a total stop button SB2, a run button SB3, a stop indicator light LD , closing indicator HD1, closing step-down start indicator HD2, closing running indicator HD3, voltmeter V and ammeter A; One end of the start button SB1, the total stop button SB2, and the running button SB3 are respectively connected to the input ends I0.0, I0.1, and I0.2 of the PLC, and the common end of the other end is connected to the negative pole of the DC power supply; The DC +24v input terminal 1M 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 the power switch QF1; One end of the stop indicator LD, the closing indicator HD1, the closing step-down start indicator HD2, and the closing running indicator HD3 are respectively connected to the output terminals Q0.3, Q0.4, Q0.5, Q0 of the PLC. 6. The common end of the other end is connected to the neutral line LN of the main power circuit (1) through the power switch QF2; the output end Q0.0 of the PLC is connected to one end of the coil of the main circuit AC contactor KM4, and the main circuit AC The other end of the contactor KM4 coil 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 AC contactor KM2 for voltage reduction operation is connected to the output terminal Q0.1 of the PLC, the other end is connected to the normally closed contact of the AC contactor KM3 for full voltage operation, and the other end of the normally closed contact for the AC contactor KM3 for full voltage operation is connected. It is connected with the normally closed contact of the integrated motor protector FR; the other end of the normally closed contact of the integrated motor protector FR is connected to the neutral line LN of the main power circuit (1) through the power switch QF2; the star point is short-circuited with the AC contactor One end of the KM1 coil is connected to the output end Q0.1 of the PLC, and the other end is connected between the KM2 coil of the AC contactor KM2 operating at reduced voltage and the normally closed contact point of AC contactor KM3 operating at full voltage; 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, and the normally closed contact of the step-down operation AC contactor KM2 is connected to the star. Connect one end of the normally closed contact of the point shorting AC contactor KM1, the other end of the star point shorting AC contactor KM1 normally closed contact is connected to the normally closed contact of the full voltage running AC contactor KM3 and the motor comprehensive protector FR normally closed between the contacts; 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. 3. A PLC-based autotransformer step-down control system according to claim 2, characterized in that: the closing indicator light HD1 is the main circuit AC contactor KM4 closing indicator light; The voltage start indicator HD2 is the star point shorting AC contactor KM1 and the voltage-reducing operation AC contactor KM2 closing and voltage-reducing start indicator; the closing operation indicator HD3 is the full-voltage operation AC contactor KM3 closing indicator . 4. A PLC-based autotransformer step-down control system according to any one of claims 1-3, characterized in that: the PLC control system detects the time delay of the closing failure of the AC contactor KM3 in full-voltage operation The time is 2 to 5s.

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