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
For more detail: Motor Protection against Single Phasing and Overheating