Common starter for multiple induction motors

AC machines are desirable over DC machines., Because of their simple and utmost robust structure without any mechanical commutators. Considering the machine efficiency, reliability, durability, power factor, ripples, stable output voltage and torque, three phase induction motor stays on the top. Whe

Project Title

Common starter for multiple induction motors

Project Area of Specialization

Shared Economy

Project Summary

AC machines are desirable over DC machines., Because of their simple and utmost robust structure without any mechanical commutators. Considering the machine efficiency, reliability, durability, power factor, ripples, stable output voltage and torque, three phase induction motor stays on the top. When we start the motor, rotatory magnetic field starts inducing emf on rotor, but initially rotor acts as a short circuited transformer and it takes time to build up voltage   across it, and draws seven to eight times rated current, this continues for some time, which may burn the winding. So we need a starter that limits the starting current and starts the motor soft and smoothly. Throughout previous times, mechanical starters like wye delta, direct online and autotransformer starters were used.  But they could start single motor and   had lack of efficiency. Soft starter is a solid state device that controls the starting current of motor by adjusting the gate pulse of switches like IGBT, thyristor and Mosfet.

In this project  a closed loop soft starting   technique by means of controlling supply voltage using IGBT’s, 8 bit pic18f4431 controller and   hall effect current sensor acs712 is implemented, which starts multiple motors on the basis of their selection. Supply voltage is provided smoothly in the form ramp function to minimize the inrush starting current. This has done by adjusting the pulse width fed by controller  to the gate of IGBT.

Project Objectives

The prominent objective of this project is to design a soft starter that can start multiple 3 phase squirrel cage Induction motors on the basis of selection by user through controller.it is designed to limit the starting current to start motor.

Every Induction motor needs a starter to start because at the time starting due high relative motion between rotor and rotatory magnetic field it draws seven to eight time the rated current which may burns the motor. Conventional starter like wye –delta starts the motor by reducing the voltage for a while until the motor reaches near to its rated speed. When it shifts the connection from wye (reduced voltage) to delta (rated voltage) the motor feels a jerk which reduces the life of motor. It is limited only for s single motor.so if we are dealing with multiple motors we need multiple starters which will increase the cost and complexity of circuit.

Other advantages are

• Improved Efficiency: The efficiency of soft starter system using solid state switches is more owing to the low on state voltage.
• Controlled startup: The starting current can be controlled smoothly by easily altering the starting voltage and this ensures smooth starting current of the motor without any jerks.
• Controlled acceleration: Motor acceleration is controlled smoothly.
• Low Cost and size: This is ensured with the use of solid state switches.
• Minimize complexity: Instead of using multiple starters and increasing complexity, Now a single unit  can start multiple motors without any difficulty.

Project Implementation Method

Three phase rectifier:

Rectification is process in which AC supply is changed to pulsating  DC.

When 3 phase voltage is applied ,diode conducts in his respective cycle and gives the output. Whenever diode gets forward biased it basically provides a path to flow the current through the load. All the 6 diodes conducts in such a way that they give an output having six pulses having the same polarity. But still there is need to have a filter to make the dc pure.

 Capacitor Filter : In rectifiers capacitor  act as an filter  whether  it is  single  phase  or 3 phase .in positive cycle the capacitor gets charge but when supply starts decreasing it act as a voltage  source to load  and discharge its voltage.it  doesn’t allow the voltage to be dropped unless next cycle comes to provide voltage to load .In that period of time capacitor charges and wait for the supply to decrease below the its  voltage level

3 phase inverter:

Inverter  is a  device that converts DC  to AC .the reverse process of rectifier instead of diode Thyristors ,IGBT’s and MOEFET’s are used .In this circuit IGBT's switches are used for switching purpose of inverter.Due to phase shift patteren of gate pulses the ouput of inverter is generated which is nearly similar to sinusoidal .

low pass filter:Combination of Inductor and capacitor is connected with every generated phase to make it almost a sinusoidal. 

Controller: It is the brain of this project. basically it provides the pulses to the gate of IGBT, on the basis of that pulses inverter gives the output.

Output current is directly proportional to torque  and torque is directly proportional to supply voltage .so by varying supply voltage we can control the starting current  and torque of motor

We have programmed the controller in such a way that it gives pulses having 50% duty cycle at the time of starting and increasing to 100 % in the form of ramp function. Time to reach max duty cycle is depending  on the rating of motor and load associated with it .we have used 2hp 3 phase squirrel cage induction motor under no load conditions  which needs 1.5 second to reach its rated speed .so we have set ramp time of 1.5 second  for controller to reach 100% duty cycle.

When the motor reaches to its rated speed the controller isolates itself from motor switches the connection of input directly to motor with the help of relay .this process will repeat for all motors interfaced with it

Opt coupler: they are used as gate drive circuit and for isolation of voltage.

Sensor:

A hall effect  current sensor is used to measure the output current .which is further displayed on LCD, interfaced with controller.

Benefits of the Project

In the present time, in the most of the applications, AC machines are preferable over DC machines due to their simple and most robust construction without any mechanical commutators. Induction motors are the most widely used motors for appliances like industrial control, and automation; hence, they are often called the workhorse of the motion industry. As far as the machine efficiency, robustness, reliability, durability, power factor, ripples, stable output voltage and torque are concerned, three- phase induction motor stands at the a top of the order. Motor control applications span everything from residential washing machines, fans to hand-held power tools, and automotive window lift, traction control systems and various industrial drives.

Industries that are  dealing with multiple 3 phase squirrel cage Induction motors in thier machineries ,can replace their conventional starters with our unit .It will minimize the  complexity of power circuit and reduce the cost to purchase seprate starter for every motor .

Technical Details of Final Deliverable

A single unit that can start multiple motors on the basis of their selection .

The designed circuit can draw  max 36 Ampere  through it so it can start multiple motors of different rating max up to (7hp)  it is independent of speed .no matter what is the rating of speed ,the designed circuit can start any motor within the given rating limit by reducing starting current .  Starting buttons of all the interfaced motors will be displayed.The user can start any motor by pressing button of keypad but only one motor can start at a time.

Final Deliverable of the Project

Hardware System

Type of Industry

Others

Technologies

Others

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

If you need this project, please contact me on contact@adikhanofficial.com