KR890003536B1 - Arrangement for starting electric motor by star/delta switching - Google Patents

Abstract

The method for starting the motor with Y-Δ connection without using a mechanical timer comprises: (a) supplying the digital value covesponding to three phase AC current to a CPU; (b) calculating the rate current of the motor with the detected current; (c) determining the level on the current curve drawn against to the time, which levels consist of 3 stages; (d) releasing the Y starting relay. When the level is at third stage and exciting the

Description

Y- △ starting processing method in electronic motor control sensor (MCC)

1 is a circuit diagram of an electronic motor controller.

2 is a current-time characteristic diagram when starting a motor.

3 is a flowchart showing a Y-Δ start processing method of a motor according to the present invention.

4 is a flowchart for explaining a constant time interrupt routine of a central processing unit by a timer.

* Explanation of symbols for main parts of the drawings

1: central processing unit 2: timer

4: relay driving circuit 5: power circuit

6: Effective value detection circuit 7: A / D converter

88M ', 88 △', 88Y ': Y- △ switching relay contact of motor MCT: Current transformer

The present invention relates to a Y-Δ start processing method of a motor in an electronic motor control center.

One of the starting methods of a large-capacity induction motor that is performed in a conventional motor control center is a Y- △ starting method. This start method starts in Y state to prevent sudden inrush current during starting, drop the line voltage to 1 / of the full voltage, drop the generation lock to 1/3, then change to △ again when the motor starts. It is taking a way to apply.

Conventionally, in this switching, a mechanical timer is used to switch from Y to △ after a certain time has elapsed. However, this method requires a switching time to be adjusted according to a change in motor capacity or a change in load state. Have.

On the other hand, by making the conventional mechanical motor control center more compact, the installation area is reduced, and in recent years, the monitoring control unit is included as a powerful countermeasure for the diversified user's needs such as automatic operation, energy saving, and stability of the plant. Efforts are being made to develop and control a motor control center by computer control as a backbone technology that supports the high efficiency and high productivity of the entire system.

The electronic motor control center is capable of performing various motor protection functions and control functions. It is composed of a main board consisting of a microprocessor unit part and setting switches, an analog of a switching power supply, a signal detector, and an auxiliary relay for driving a magnetic contactor. Intelligent motor controller with board and display board consisting of sequence buttons for forward, reverse, OFF and reset of motors on the unit, emergency and safety test buttons and LED indicators Can be implemented.

Accordingly, an object of the present invention is to improve the Y- △ start method in the conventional motor control center to remove the mechanical timer and to install the electronic motor controller to have flexibility in the load change or capacity change of the motor current flowing through the motor when starting the motor The present invention will be described in detail with reference to the accompanying drawings to provide a method for sensing and distinguishing the state and performing a Y- △ start.

1 is a circuit diagram showing an embodiment of an electronic motor controller (IMC) to which the present invention is applied. That is, three-phase three-wire AC power lines A, B, and C are connected to the motor M through the contacts 88M ', 88 △', 88Y 'of the power supply relay and the Y- △ switching relay. In order to detect the current flowing through the MCT, a molded current transformer (MCT) is installed to penetrate the three-phase power supply line, and the DC output current detected by the MCT is passed through the effective value detection circuit (6) to the A / D converter (7). ) And the detected current converted into a digital value can be read by the central processing unit (CPU) 1. Here, the effective value of the current output from the effective value detecting circuit 6 is A / D converted based on the rated current value of the motor set by the user in the rated setting circuit 8.

In addition, two of the three-phase three wires connected to the motor M are converted into an alternating current 110V through a transformer 9 and supplied to the power supply circuit 5, and the constant DC voltage generated in the power supply circuit 5 is subjected to the central processing. It is supplied to the power supply of the apparatus 1, the effective value detection circuit 6, the A / D converter 7, and the relay drive circuit 4. As shown in FIG. The relay driving circuit 4 selectively excites the power supply relay 88M and the relays 88Δ and 88Y according to the control command of the central processing unit 1 described later to turn on / off the relay contacts 88Δ 'and 88Y'. This makes the Y- △ start of the motor. In addition, a timer 2 is connected to the interrupt terminal of the central processing unit 1 so that the central processing unit 1 performs a timer interrupt routine every predetermined time.

In the electronic motor controller as described above, the Y- △ start processing method of the motor according to the present invention detects the current flowing through the motor in the current transformer (MCT) at all times and shows the current-time characteristics at the time of starting the motor as shown in FIG. The first state, the second state and the third state are distinguished from each other in the curve to perform Y- △ start. In FIG. 2, the state from 1% to 2 states is obtained at 130% of the rated current of the motor. The change is set at a low level of 130% in order to enable no-load starting, and each state shown in the graph describes the first state indicating that the motor M is connected to the power source and started. Is the state and the second state is the state that the motor is actually running. And the third state is a state which is set to the level of 110% or less of the rated current to indicate that the motor is in a normal state after starting.

The operation of the central processing unit 1 which detects the above state and performs the Y-Δ start process will be described with reference to the flow chart of the juroutine shown in FIG.

When the power is turned on, the current value memory address is initialized in step 100. Then, in step 101, it is determined whether there is an operation command, and if there is no operation command, the operation command is continued. If there is an operation command, the motor proceeds to step 102 and starts Y. Excite relay 88Y. In the next step 103, it is determined whether the current curve of FIG. 2 is in the second state, and when it is in the second state (marked with a logic " 1 "), it immediately goes to step 106 to determine whether it is in the third state, while step 103 If it is not in the second state (logical "0" display), it is determined in step 104 whether the current value A is 130% or more of the rated current, and if it is greater than or equal to 130%, the second state display is made to "1" in step 105. Next, go to step 106, while if smaller, go to step 111 to do some work. If in step 106 it is determined that the three-state indication is "1" and is displayed as "1", go to step 109 and if not, go to the next step 107 to determine whether the current value B is less than or equal to 100% of the rated current. do. In step 107, if the current value B is greater than 100% of the rated current, go to step 111 and let the work be done; if the current value B is less than or equal to 100%, in step 108 the 2 state is set to "0" and the 3 state display is set to "1". After making, release relay 88Y and proceed to step 109. In step 109, it is determined whether the current value is 0 [A]. If the current value is not 0, go to step 111 to process a certain task. If the current value is 0, go to step 110 and excite the relay 88 △ to start △. The process ends. In step 111, if the day C indication to perform a certain day C is "1", go to step 112; if the day C indication is not "1", go to step 113. In step 112, the current value flowing to the motor is read out and stored in the current value storage area, and the C display is made "0" (where information on the current value storage area is dealt with in the constant timer interrupt routine of FIG. 4). Next, in step 113, it is determined which constant work D is to be performed, and if the work D display is "1", the process goes to step 114; if the work D display is not "1", the process goes to step 115.

In step 114, the contents of the address indicated by the current value memory address are reduced to the current value address, and all the contents of the address indicated by the current value memory address -3 are divided by 4, and the average value is stored. Makes "0".

Then, in step 115, it is determined which work is to be performed, and if the work E display is "1", the processing proceeds to the next step 116, and if the work E display is not "1", the process returns to step 103 to perform the processing. Repeat it. In step 116, all the values from the address indicated by the current value memory address to the address indicated by the current value memory address -19 are divided by 20, and the average value B is stored. Make it 0 ". The process then returns to step 103 and repeats the above process.

Here, the operation of the CPU 1 performing the interrupt routine at regular intervals by the timer will be described by exploring the flowchart of FIG. 4 is a service routine performed by the CPU 1 when an interrupt is requested at regular intervals by a timer 2 external to the CPU. In other words, when an interrupt is requested, an instruction to perform the work A is performed in the juroutine of FIG. 3 with the work A indication "1" in step 200, and then the value indicating the current value storage address is increased in step 201. Then, in step 202, it is determined whether the second status display is "1", and if "1", the flow goes to step 203, and if not, to step 206. In step 203 increase the counter value of day C, go to step 204, and multiply this day C counter value by 4, if it is equal then in step 205 give day C indication "1" and instruct it to process day C. Set the one C counter value to zero and go to step 206. Also, in step 204, even if the day C counter value is not equal to 4, go to step 206 to increase the day D counter value, and then go to step 207 to compare whether the day D counter value is equal to 20, and if so, display day D in step 208. Is set to "1", the D counter value is set to 0, and the current value memory address is initialized. Then, in step 207, the process returns to the previous step of the interrupt service routine as if the D counter value is not equal to 20.

According to the Y- △ start processing method of the motor as described above, for example, even if the motor is not connected to the power line in the past, an accident occurs in which a full voltage is applied by changing from Y to △ after a predetermined time, but the method according to the present invention In the present invention, the current flowing through the motor is sensed so that the current value of the motor remains only in the first state. In addition, according to the conventional Y contact excitation release time and △ contact excitation time, the Y contact is opened and after a certain time delay, the △ contact is closed. May occur, but in the method of the present invention, upon detecting the third state of the current curve, the relay 88Y is immediately released to open the Y start relay contact, and then the total current of the motor becomes 0 (the Y contact is completely opened). )) After △ start relay 88 △ and △ contact is attached, there is no risk of such an accident.

As described above, the application of the Y- △ start processing method of the present invention in the electronic MCC can eliminate the conventional mechanical timer and has the special advantage of ensuring the reliability of the start even under load change or capacity change of the motor.

Claims (2)

In the electronic motor control center (MCC), in the Y-start processing method, detecting a current from a three-phase AC power line connected to a motor, converting the detected DC current into a digital value, and supplying the same to a central processing unit (CPU); Calculating, by the central processing unit, the current value converted into a digital value according to the rated current value of the motor, and a first state, a second state, and a third state in a curve of current with respect to the time of the motor when the motor is started. Setting the level of the state, exciting the relay for starting the Y according to the operation command of the motor, judging the second state and the third state of the current curve, and the current curve at the time of starting the motor. Releasing the Y start relay immediately when it detects that it is in the third state, and after confirming that all current flowing through the motor is zero, △ start the start relay. Y- △ start-up processing method in an electronic motor control center of claim. The method of claim 1, wherein the first state of the current curve with respect to the time at which the motor is started is set to a level of 130% of the rated current of the motor, and the second state is set from the 130% level to a level of 110%, And the third state is set to be below the 110% level.

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