The motor is a most crucial electrical device in the current period of automation. These are used in various industrial applications, but can be protected from the various faluts like mechanical, electrical faults to help their purposes. This article discusses an induction motor protection system from emerging faults by employing a microcontroller. This motor experiences different types of electrical faults like over voltage, under voltage, overload, unbalanced voltage, phase reversing earth fault, and single phasing. Due to these electrical faults, the motor’s windings will get heated which lead to decrease the life of the motor. The degree of the induction motor depends on the costs and functions of the motor.
What is an Induction Motor?
Induction motor (asynchronous motor) is the most commonly used motor in various applications. Because, these motors frequently run at a lower speed than synchronous speed (the speed of the magnetic field which is rotating in the stator). The types of Induction motors available in the market are classified based on the kind of input supply like single phase induction motor, 3-phase induction motors, split phase induction motor, capacitor run induction motor, capacitor start induction motor, and shaded pole induction motor. And also based on the rotor type 3-phase induction motors are classified into 2-types namely wound type, squirrel cage motor and slip ring motor.
Working Principle of Induction Motor
In a DC motor, supply is necessary to be given for the windings of rotor well as the stator. But in this motor only an AC supply is fed with the stator winding. Alternating flux is created around the stator winding because of the AC supply. This spins with synchronous speed is named as Rotating Magnetic Field (RMF). An induced e.m.f can be caused by the relative speeds between rotor conductors & stator RMF. According to the law of Faraday’s electromagnetic induction, the rotor conductors are short circuited, and afterward it is produced because of an induced e.m.f. So this is the reason to call these motors as induction motors.
Now the induced current in the rotor will also make an alternating flux around it. According to Lenz’s law, the induced rotor current direction will tend to resist the cause of its production.
Induction Motor Protection System
The basic idea of this project is to give safety to the Induction Motor. If any of the phases, out of the 3-phases is misplaced and also if the motor’s temperature during process surpasses the set value, the supply to the induction motor is cut-off instantly. This project is supplied with a 3-phase power i.e., the 3-transformers are connected to the 3-phases supply.
The hardware requirements of this project include op-amps, resistors, capacitors, diodes, thermistor, transformers, regulator and relays.
At first, a step down transformer is used to convert the 230V AC to 12V then changes to DC using a bridge rectifier. A capacitor is used to filter out the AC ripples and given to the input voltage regulator 7805.At the regulator’s output we get a constant 5V DC which is used for ICs used in this project. A blocking diode is connected to take the pulsating waveform.
A thermistor is a one kind of resistor whose resistance changes radically with temperature. The term thermistor is a portmanteau of thermal and resistor. Thermistors are extensively used as temperature sensors, inrush current limiters, self-regulating heating elements, and self-resetting over current protectors.
- Comparators look much related to operational amplifiers but, it gives a logic output indicating the relative potentials on its two inputs. An op-amp amplifies the differential voltage between its two i/ps and is designed at all times to be used in closed-loop applications.
- Potential dividers are allied to the inputs of the inverting and non inverting terminals of an op-amp to give some voltage. Voltage supply is given to +V & –V is connected to GND terminal.
- The comparator’s output will be logic high if the input of the non-inverting terminal is superior to the inverting terminal i/p of the comparator.
- If the input of the inverting terminal is larger than the input of the non-inverting terminal then the comparator’s output will be logic low.
A relay is an electrically functioned switch, the flow of current through the relay’s coil creates a magnetic field which attracts a switch and alters the switch contacts. The coil current can be on/off so relays have two switch locations and have double throw switch contacts as shown in the diagram.
Relays let one circuit to button a second circuit which can be totally divided from the first. For instance a low voltage battery circuit can employ a relay to switch a 230V AC mains circuit. There is no electrical connection in the relay between the two circuits; the connection is magnetic & mechanical. To make relay through microcontroller, a ULN2003 relay driver IC is used.
The praposed system is intended to protect an induction motor from over temperature and single phasing. A protection system using lot of motors for the production is very significant in industries.
The basic plan for designing of this project is to offer safety to themotor in industries. If the temperature of the motor during process surpasses the threshold value, motor stops without delay.
The system uses a 3-Phase power supply where 3-single phase transformers are linked to it. If any of the phases is not accessible the equivalent transformer ends supplying power to the circuit. This directs to one of the 4-relays getting switched OFF.
The major relay is powered through a set of 4-relays gets detached because of one relay not being power-driven. Thus the main relay delivers 3-phase supply to the motor gets disconnected. A thermistor is connected to the induction motor body to sense the temperature. If the temperature rises then supply to the 4th relay is disconnected.
Further this project can be developed by using current sensors to protect from the over load and phase sequence sensor to protect the motor from applying wrong phase sequence.
Thus, this is all about induction motor protection system. We hope that you have got a better understanding of this concept.Furthermore, any doubts regarding this concept or to implement any electrical projects, please give your valuable suggestions by commenting in the comment section below. What is the function of an induction motor?