Aoyuexin 200 series PLC, what are the protection methods for the motor
The application of electric motors covers almost all areas of our human life. In these application areas, electric motors often operate in harsh environments, causing accidents such as overcurrent, short circuit, open phase, and insulation aging. For the underground garage of the living quarter, the loss caused by the failure is immeasurable.
Common faults of motors can be divided into two categories: symmetrical faults and asymmetrical faults. Symmetrical faults include: overload, locked-rotor and three-phase short circuit, etc. The damage to the motor is mainly the thermal effect, causing the winding to heat up or even damage. Its main feature is a significant change in the current amplitude; asymmetrical faults include: open phase, Reverse phase, short circuit between phases, short circuit between turns, etc. This type of fault is the most common type of fault in motor operation. The damage of asymmetric fault to the motor is not only heat generation, but more importantly, the negative sequence effect caused by the asymmetry can cause serious damage to the motor. Therefore, comprehensive protection of large motors is very important. 2 Comprehensive motor protection based on PLC
2 The protection of motors can be divided into the following categories:When the motor fails, in order to protect the motor and reduce the damage of the fault, the speed and reliability of the relay protection device are very important. Under the condition that the capacity of a single machine is increasing day by day, the rated current of the motor can reach thousands or even tens of thousands of amperes, which puts forward higher requirements for the relay protection of the motor. Traditional relay protection devices can no longer meet the requirements, so microcomputer protection came into being.
PLC is used to replace traditional relay control. Compared with it, PLC has better performance than relay control logic, especially high reliability, short design and construction period, convenient debugging and modification, small size, low power consumption, and use. Easy to maintain. Therefore, this paper studies the method of integrated motor monitoring and protection system based on programmable logic controller (PLC).
3.1 The overall structure of the system
The overall structure of the integrated motor monitoring and protection system based on programmable logic controller (PLC)
3.2 PLC model selection and expansion
Two issues should be considered when choosing a PLC model:
(1) What is the capacity of the PLC?
(2) What company's PLC and peripherals to choose. In this system, the following input and output points are included. See the attached table. The system includes 12 switching quantities and 7 analog quantities.
Aoyuexin 200 series PLC is suitable for the automation of detection, monitoring and control in various industries and various occasions. The most powerful function of Aoyuexin enables it to realize complex control functions regardless of whether it is in independent operation or connected into a network. Therefore, Aoyuexin 200 series has a very high performance/price ratio.
OYES CPU 224C integrates 14 inputs/10 outputs, a total of 24 digital I/O points, 7 expansion modules can be connected, and the maximum expansion is 168 digital I/O points or 35 analog I/O points; 24K bytes Program and data storage space; 6 independent 30KHz high-speed counters, 2 independent 20KHz high-speed pulse outputs, with PID controller; 2 RS485 communication/programming ports, with PPI communication protocol, MPI communication protocol and free way communication capabilities; The I/O terminal block can be easily disassembled as a whole, and it is a controller with strong control capability. According to the actual situation of the system, combined with the above characteristics, OYES CPU224C can be used as the host of this system.
OYES CPU224C can expand 7 modules, and it has 14 inputs/10 outputs, a total of 24 digital quantities, so there is no need for digital expansion modules. However, since there are 7 analog inputs, it is necessary to select an analog input module. Aoyuexin 200 series provides EM231, EM232, EM235 and other analog expansion modules. According to the above technical data, two EM231s are selected as analog input modules, so that a total of 4×2=8 analog inputs can be expanded.
4 System software design4.1 Main program
At the beginning of the program, the input is detected from the input unit. First, it is judged whether the KM is closed. If it is closed, the motor is already running, and the start button should not be pressed at this time. If the KM has not been closed, the motor is in a stopped state and you can press start Button. Then judge whether the start button is pressed, if yes, continue with the following procedure, if not, then re-check. If the button has been pressed, check whether the motor is started, if yes, continue with the following procedure, if not, switch to the undervoltage protection subroutine, if the motor has started, judge whether the starting is successful, if yes, continue with the following procedure , If not, switch to start protection. If the motor has started normally, the green light is on. Then judge whether the stop button is pressed, if not, continue the following procedure, if yes, the procedure will end directly and start the next scan.
If the stop button is not pressed, that is, the motor is still running, the fault judgment during the running process is performed. First, check whether a short-circuit fault occurs. The method is: check the three-phase current, and then judge whether Imax is greater than the set value, and if it is, it will jump. Turn to the protection action subroutine segment, the motor starts short-circuit protection, the alarm sounds, and the short-circuit fault indicator light is on. If not, continue with the following procedure. Then judge whether there is a phase failure, the method is: check the three-phase current, judge whether a certain phase current is zero, or check Umn, judge whether it is not zero, if one of them is satisfied, then jump to the protection action subroutine segment , The motor starts to protect against phase failure, the alarm sounds, and the phase failure indicator light is on. If not, continue with the following procedure. Then judge whether an under-voltage fault occurs. For the method, see the description of the under-voltage protection subroutine. Then judge whether there is a ground fault, the method is: check I0, if it is greater than the set value, jump to the protection action subroutine, the motor starts the ground protection, the alarm sounds, and the ground fault indicator light is on. Then judge whether an overload fault occurs, the method is: check the three-phase current, if the current is still greater than the set value after reaching the set time limit, jump to the protection action subroutine, the motor starts overload protection, the alarm sounds, and overload The fault indicator light is on. If it is judged that there is no overload fault, the program completes one scan, and then starts from the first one and performs the second scan, so the end refers to the end of a cycle, not the end of the entire program.
4.2 Undervoltage protection subroutine
In this program segment, collect the voltages of phase A and phase C, find the average value, and compare it with the setting value. If it is less than the setting value, jump to the protection action sub-program segment, motor starting undervoltage protection, The alarm sounds, and the undervoltage fault indicator light is on. If there is no undervoltage fault, the cycle will be ended directly.
4.3 Subroutine for the protection of too long starting time
In this program segment, collect the three-phase current. If it is found that the current is greater than the setting value during the starting process, or the current is still greater than another setting value after the setting time is reached, it will jump to the protection action sub-program and start If the time is too long, the protection will act, the alarm will sound, and the start failure indicator will light up.
5 concluding remarksThrough the design, test and operation of this system, the following conclusions are obtained:
(1) The use of PLC for comprehensive motor protection hardware is simple and reliable.
(2) Ladder diagram language can be used for programming, which is simple and easy.
(3) The system runs reliably and is convenient for maintenance.
(4) Due to the integrated comprehensive design, the system is small in size, low in power consumption, and easy to use and operate.
(5) OYES CPU 224C integrates 14 inputs/10 outputs, a total of 24 digital I/O points, can be connected to 7 expansion modules, large storage space, supports all wizard functions, and is convenient for customers to program.
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