Automatic adjustment of THBA intelligent air circuit breaker test bench and thermal tripping mechanism Shen Zuyu (Tianjin Normal University, Tianjin 300202) is the two parts of the air circuit breaker factory rapid inspection and automatic adjustment of the air circuit breaker thermal tripping mechanism, all using the microcomputer The patrol detection and real-time control technology article mainly discusses the method of controlling the stepping motor with a single-chip microcomputer to adjust the thermal trip mechanism of the air circuit breaker.
It is combined with the high-power AC steady current power supply controlled by our previous MCU, and it becomes a smart test bench with high intelligence. It can replace imported equipment: air circuit breaker; thermal tripping; single chip microcomputer; stepper motor air circuit breaker (commonly known as air switch) should be widely used in industrial and mining enterprises, institutions, shops and houses because it has better overload and The short-circuit protection function gradually replaces the knife switch and fuse. In order to ensure the quality of the product, long-term thermal trip test is required for both the factory test and the type test. The purpose of the test is to evaluate the thermal effect of the product, that is, the overload protection performance requires a test current of several times the rated current and a multi-station test to improve the production efficiency. This proposes a new thermal trip mechanism for the air circuit breaker for the test bench. Generally, it consists of a bimetal. When the current passes, the bimetal is bent and deformed due to the thermal effect of the current. If the current passed exceeds the allowable range, the mechanical linkage mechanism is driven to disconnect the contact of the air circuit breaker, that is, the switch. Tripping for overload protection.
The overall function of the test bench is divided into two parts: the air circuit breaker factory quick test and the automatic adjustment air circuit breaker thermal trip mechanism. The system has functions and switches, and the quick test and automatic adjustment of the thermal release second gear system are reset. The positions of the switches enter their respective programs.
Test bench and intelligent steady flow source man-machine dialogue keyboard In addition, if the serial queue module QSM of the single chip microcomputer is connected with the IBM-PC machine, it can communicate with the host computer, and the test machine can be managed by the system machine. This device is fully automatic and highly intelligent.
2 Factory quick inspection Before the factory quick inspection, the thermal release of the air circuit breaker has been coarsely adjusted, and a quick test is performed before the factory packaging to check whether the thermal tripping characteristics meet the requirements. The process is as follows: given a test Current, and the test current must be stable regardless of the external grid voltage change or the load resistance change during the test. This requires the AC steady current source to be used to detect the thermal trip time of the circuit breaker by the above method, so as to determine the trip time. Short, the trip time is normal, or the trip time is too long. The three different signals are displayed respectively. For example, the trip time is too short and the white light is displayed; the trip time is normally displayed by the green light; the trip time is too long. The light is displayed. Because the trip time is too long, it may be that the thermal tripper of the station itself is faulty. Therefore, when the set time is reached, the test current of the station needs to be automatically cut off to avoid damage to the air circuit breaker due to excessive power supply time.
The trip time is normal and can be shipped. If the trip time is abnormal, the thermal tripper adjustment is unqualified or damaged and needs to be re-adjusted or repaired.
The test bench has 4-10 stations, and each station has a corresponding timer to display the trip time. This time can be obtained in a variety of ways.
The method we adopt is: the test starts to give the test current from the steady current source, each station is shorted by the AC contactor, and the resistance of the AC contactor is very small, so the voltage drop at the station is almost zero when the air switch is put into operation. When the AC contactor is disconnected, current flows into the air circuit breaker. However, because the resistance of the air circuit breaker is not large, the voltage drop is still close to zero. When a station air switch trips and the circuit is disconnected; the resistance of the station is infinite, and the output voltage of the steady current source is all applied to the station. This voltage is sufficient for the intermediate relay to pull in, and then the AC contactor is attracted. Short-circuit this station, the series loop-on test continues. In short, when the AC contactor is closed, the timing is stopped; when the AC contactor is released, the timing is started. Use the normally open auxiliary contact of the AC contactor to generate TTL high and low level, for example, to wait for the circuit check of the single chip microcomputer, and determine the composition of the heat 21 hardware of the air circuit breaker. The 4-station test bench is taken as an example to illustrate the input and output interface. The situation is that each station has a corresponding timer, each timer requires 4 digital LEDs to display 4 digits, so only the hardware can be decoded by the static display MC14495. It only needs to input 4 binary digits. That is, you can directly display the BCD code. It can display 0-F. We only need to display 0-9. The time parameter display of each station must be timed. However, it is a time-sharing refresh. Each station needs to drive three indicator lights and a keyboard and display for the intermediate relay MCU that automatically disconnects the air circuit breaker. Man-machine dialogue window, can display various parameters and set various parameters. In addition to the corresponding trip time of each station breaker, there are also: too short normal, too long trip time range; how long the trip unit The test current of the station is automatically cut off when it is not operated.
2 software design overall composition: the main program function is to complete the initialization scan function switch of the single-chip microcomputer and transfer to the corresponding program, scan the keyboard and complete the display task, wait for the interrupt to break, 10ms is the time reference in the interrupt processing program to patrol the detection of each station The situation, update the detection time of each station, illuminate the corresponding indicator light, and make a decision on the disconnection test is the current or not. Software block diagram such as 3 automatic adjustment of the air circuit breaker thermal trip mechanism implementation of this part of the function is this: Firstly, the fixed test current is given by the steady current source. When the trip time is approaching, the stepping motor starts to pre-action, ready to adjust the trip adjusting screw of the air circuit breaker, and requires the air circuit breaker trip time to be allowed. Adjust the trip adjustment screw so that the air circuit is just tripped. It is not allowed to overshoot. Obviously, the key to this part is to control the stepper motor, so that the stepper motor runs smoothly, high-precision positioning, high step resolution and small step. angle. In short, controlling the quality of the stepper motor determines the success of this function. Stepper electric control circuit block diagram As shown in the stepper motor control circuit schematic diagram In this circuit, the frequency f of the pulse signal is controlled by the main controller. The distributor converts the pulse signal into a pulse sequence applied to the winding, and the driving circuit power-amplifies the pulse sequence signal to provide sufficient power to drive the circuit to absorb the photoelectric coupling, so that the stepping motor and the microcomputer are optically isolated. The CPU of the MC68322 single chip microcomputer is advanced. 32-bit processor. It consists of system integration module SIM serial queue module QSM, static memory RAM (2KB) and time processing unit TPU. These modules are connected by internal bus (IMB). Time processing unit TPU is the most characteristic function module, which can be programmed. Handle various operations related to time. In fact, the TPU module itself is also a 16-bit microcontroller with many functional circuits that can perform multiple functions. The TPU can perform time-related operations semi-independently from the CPU without CPU intervention. Of course, this 16-bit micro The controller is only translucent to the user and cannot be programmed directly. It must be indirectly controlled by the CPU to change the inherent functions. Since the TPU has excellent performance in handling time-related operations, it is used for stepping. Motor control can not only greatly reduce the burden on the CPU, but also many functions can be realized by programming, which is very convenient to use.
3.1 Hardware circuit design Stepper motor circuit schematic In this circuit, the TPU module is connected to other modules of MC68332 through the internal module bus (IMB) to realize two-way communication between modules, the drive circuit realizes optical isolation, and has power amplification and Over current protection. The stepping motor adopts 110BYC404 as the 4-phase motor, and the step angle is 0.75/1.5=We control it to operate in double and four steps, so the step angle is 0.75=the rotation speed, rotation direction and acceleration/deceleration control of the stepping motor are all The TPU is programmed to control the drive pulse. The TPU automatically generates 16 output channels. These channels have independent hardware circuits that can receive the services of the execution unit in a time-sharing manner.
Each four-phase stepper motor requires four TPU channel controls, so each TPU module can control four 4-phase stepper motors.
3.2 software design TPU program box. 2.1 Operation mode control: In the case of controlling the stepper motor with TPU, just change the PIN-CONTROL (pin control) parameter register (corresponding address: FFFF42 FFFF72) and CHANNELCONTROL (channel control) parameter register by programming. The data of the address: FFFF40FFFF50FFFF60FFFF70) can change the operation mode. We use the double four-step full-step operation mode, which corresponds to 4 PINCONTROL parameters are 9999CCCC6666 and 3333 respectively. The corresponding 4 CHANNELCONTOL parameters are 81818282 respectively. It is very convenient. 3.2.2 Step speed and acceleration/deceleration control: stepper motor There must be an acceleration process when starting, and when the stepper motor stops, there must be a deceleration process or it will overshoot due to inertia. The step motor speed is controlled by the TPU, and two parameters of STEPCNTL0 (step speed control 0) and STEPCNTL1 (step speed control 1) can be changed for control.
These two parameters are located in the parameter register of the first slave channel. The address of the system is FFFF54FFFF56. The other way to control the speed of the stepper motor is to change the clock frequency of the MC68332. This system clock can also be changed by programming. The speed of the motor (speed of acceleration and deceleration) is determined by STEP-RATECNT in the main channel, whose address is the last address in the main channel. In this system, the address of STEP-RATE CNT is FFFF4A, and its value range IE can be set according to the situation. 4 Conclusion The two functions of this device are realized under the premise of high precision, small sine wave distortion and fast response time. Source Power Supply The stable current source performance index we developed is: output current stability accuracy is better than ±1%, sine wave total distortion is less than 5% (power supply distortion is less than 2%, plus grid distortion is around, so the total distortion is less than 5%), the response time is less than 40ms. For the factory fast speed test circuit breaker function part, use the single chip microcomputer and LED to form multiple timers. Compared with the general test, each station needs a timer and then use the programmable controller to achieve the above. The function, low cost and high reliability. The detection speed of this kind of equipment is fast, the time display is correct, and the production efficiency is high. The stepping motor controlled by its TPU module has unique advantages: convenient programming and speed rate operation mode can be programmed and controlled. And can be adjusted online as needed, so the application is very convenient. The TPU can control multiple stepping motors at the same time. This system can also use the MC68332 serial queue module QSM to connect with the IBM-PC serial interface to realize communication with the upper computer. Control and management of multiple test equipment by system machine
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