The rise in temperature level of a motor during its operation beyond a permissible limit is known as overheating. The causes of motor overheating are motor overloading, distortion in the supply voltage, impaired cooling capability, unbalanced supply voltages etc. Because of overheating, we can face the problems such as Electrical fire, Insulation failure, Decrease in life time of motor due to earlier wear and tear of the motor windings etc.Hence, for three phase induction motors, it is necessary that all the three phases of supply be present and the Motor Temperature be within the permissible limits. Hence, for the protection of the motors from mechanical damage and to increase its life time, it is very necessary to protect the phase motors from Single Phasing and Overheating.
In this project, We are going to design a hardware circuit to prevent the three phase loads from single phasing or overheating by disconnecting the load from the supply whenever any one of the two occurs, to monitor the current status of the motor by the help of LCD screen showing the current temperature and bulbs showing which phases are currently present, inform the user through alarm and by sending SMS to the user’s mobile whenever any one of the abnormal condition occurs.
The hardware circuit makes the use of AT89C51 microcontroller to sense the abnormal condition i.e. single phasing or overheating and sound a buzzer and send SMS to the user’s mobile by the use of a GSM Modem and de-energize the 4-pole contactor which disconnects the load from the supply. Three single phase transformers are used in star connection whose primary is connected to the 3 phase supply. The secondary ends of 6V are connected in parallel, which produces net output voltage of 0 V whenever all phases are present and nearly 6 V when any one of the phase fails. The LM35 temperature sensor senses the motor temperature. The output of the temperaturesensor is analog signal. Hence, it is converted into Digital signal by using an Analog/Digital converter ADC 0804 and fed to the microcontroller. According to the motor class insulation, the hot spot temperature or the critical temperature of the motor can be set. The current motor temperature can be continuously monitored in the LCD screen. In case, if the motor temperature exceeds the hot spot or the critical temperature, the microcontroller buzzes an alarm, sends SMS and disconnects the supply from the load. Hence, as a real time application, this project finds it best place to be used in the Industries and various sectors to prevent the motor from the damages from Single Phasing and Overheating so as to improve the life expectancy of the motors and save the High cost machines from frequent failure and permanent damages
This project, consist of the above blocks. It mainly consists of two major blocks. Temperature sensor and phase sensor block. The Phase sensor block is generally used to sense the Single Phasing and temperature sensor block is generally used to sense the overheating in the motors. In Phase sensor block, 3 single phase potential transformers are connected in star connection in the primary side and delta connection in the secondary side. The output of the delta connected transformers is again fed to the rectifier and regulator circuit. If all the phases are present, the output of the rectifier and regulator circuit is 5V, if not, it is 0V. Hence this 5V or 0V is fed to the AT89C51 microcontroller to control the relay connected to it. On the other hand, the temperature sensor senses the temperature of the motor. In case, if the temperature of the motor exceeds the set temperature of the motor, the microcontroller trips the relay and hence disconnects the load from the supply. The AT89C51 microcontroller block is interfaced with GSM module, LCD Display and Buzzer. If anyone of the two cases occurs, the GSM modem will send a message to the user’s mobile stating the present status of the motor and also sounds a buzzer. Hence, in this way, this circuit prevents the motor from the effects of overheating and single phasing. The elaborated description of the various blocks used in this project is summarized below.