Multiple induction motor stater using liquid rheostat

In our project we are using liquid starter for controlling the increased amount of current at the start, for more than one induction motors. For this purpose : 1. First of all we have to design a logic in which the starter after starting first motor will be bypassed and connected to the seco

Project Title

Multiple induction motor stater using liquid rheostat

Project Area of Specialization

Electrical/Electronic Engineering

Project Summary

In our project we are using liquid starter for controlling the increased amount of current at the start, for more than one induction motors. For this purpose

: 1. First of all we have to design a logic in which the starter after starting first motor will be bypassed and connected to the second motor and vice versa.

2. Secondly the resistance range of the starter will cover all ratings of all motors. So, there should be a proper mechanism to control the up and down motion of that starter which is used for increasing or decreasing the starting current of motor. For this purpose, we shall use a microcontroller to control the up and down motion of servo motor to set the resistance as per motor requirement.

3. This assembly can be used at stator side as well as at rotor side providing the rotor is wound. In our project as we are using squirrel cage motor so we shall use it at stator side.

Project Objectives

Now a days classical thermo-mechanical heat engines are replaced by an enormously efficient and robust machine of its kind, an induction motor. The mentioned machine has capabilities beyond the reach of heat engine as for as productivity, durability and efficiency is concerned. After late 50s induction motor is being used with rotatory as well as translatory equipment in all types of industries covering a wide range of process industries and textile. The main reason of using induction motor is its easy design, comparatively cheap and sustainment of heavy load in a better way. However, apart from said benefits; an induction motor has few technical hurdles to deal with. One of the major issues is its starting current which is 6 to 8 times of its rated value. This behavior needs to be deal with reliable engineering solution. The reason is, at the start the slip of motor is maximum i.e.as the rotor is stationary at the start the relative velocity between the stators magnetic field and rotor is maximum so is the induced voltage and hence current(ohms law). By minimizing starting current we can: 1. Safe the motor winding from heavy current. 2. Safe the switch gear. 3. Cost effective i.e. as the switch gear is designed for rated current rather than for starting current. So, if the starting current is controlled by some mechanism we can efficiently use induction motor. Since, there are different methods to minimize this starting current (will discuss it in literature review) but the efficient one is to use liquid starter (rheostat). This method is still working on industrial platform but they are using one liquid rheostat with one motor. As when the starting current of the motor is controlled by the starter it is bypassed and we can use it for another motor by some minor changes. In our project we are doing this. We are automating 8 the current controlling procedure as well as we are starting multiple motors from a single liquid starter sequentially. For the sake of demonstration we are using only two motors but by using the same principle that we shall discuss later we can start many motors with the same starter sequentially.

Project Implementation Method

By using one liquid starter for multiple motors the following objectives shall be fulfilled: 1. Design cost effective; as there would be only three tanks for multiple 3 phase motors the number of tanks would be less hence design cost would be less. Similarly running cost effective; as there would be less tanks there would be less maintenance cost. 2. There would be compact design..

STAGE 2: Designing a frame for Liquid Rheostat : We started the project by sketching a frame that is well suitable for the liquid rheostat the figure of that frame is as shown below: This frame consists of aluminum sides and there are two vertical railings that are being used to move contacts in water.

STAGE 3:To Automate the Rheostat : DC motor is attached on the top of the frame with L298N module and a controller is attached to it. There is code being run in the controller that allows the DC motor to work according to the required setting. 

STAGE 4:Setting of Timer Relay : Timer relay has a time set in which the upper contact above water and lower contact below water will come in contact.  

 STAGE 5: Setting of Contactors with timer relay : The setting that is mentioned above is as follows: For Motor 1: The timer relays auxiliary contact (NO) is connected with contactor K3 and the auxiliary contact (NC) of K3 is being used to operate the main coil of contactor K1 and K2.When supply is given to the circuit the timer begin to count time and being NO for that time. At that time K1 and K2 will be closed and the supply will be passed to motor via liquid rheostat. When the time (that is being set on timer relay) is achieved the timer relay give supply to the main contact of K3 and the supply to K1 and K2 will be cutoff which means the rheostat is bypassed. For Motor 2: The timer relays auxiliary contact (NO) is connected with contactor K6 and the auxiliary contact (NC) of K6 is being used to operate the main coil of contactor K4 and K5.When supply is given to the circuit the timer begin to count time and being NO for that time. At that time K4 and K5 will be closed and the supply will be passed to motor via liquid rheostat. When the time (that is being set on timer relay) is achieved the timer relay give supply to the main contact of K6 and the supply to K4 and K5 will be cutoff which means the rheostat is bypassed.

Benefits of the Project

By using one liquid starter for multiple motors the following objectives shall be fulfilled:

1. Design cost effective; as there would be only three tanks for multiple 3 phase motors the number of tanks would be less hence design cost would be less. Similarly running cost effective; as there would be less tanks there would be less maintenance cost.

2. There would be compact design.

Technical Details of Final Deliverable

Unit Testing

 Contactor Logic Testing First of all we were tested the logic design we designed to shift liquid rheostat from one motor to other and bypassing that motor by the other contactor. It was running successfully. 

Timer Relay Testing Then we check timer relay setting and incorporate it with the contactor as per logic design to check its working and response according to the logic. It responded as per design. 

DC motor with Module (L298N) and Arduino testing Then tested whether DC motor move up and down according to the desired time and desired length or not. It was running successfully Note: At the time of testing we noticed that the steady current achieved very rapidly so we have to increase the rpm of stepper motor that were not achieved as per requirement. DC motor has more torque and have good rotation speed so it was suitable for our purpose. As induction motors achieve steady current very rapidly and their rating is too close to one another so approximately the starting current is same and we start the liquid starter from the top of water for both motor but for different motors with different ratings as used in industries the starting .

Setting the resistance of Liquid Rheostat First of all we mathematically calculate the resistance of both motors upto which we limit the current which is done as follows: For Motor 1: Power Rating=0.5W Current Rating=1.8 Starting current if 7 times=1.8 ? 7 = 12.6A Resistance calculated=Z = V I = 220 2 = 110ohm For Motor 2: Power Rating=0.75W Current Rating=1.92 Starting current if 7 times=1.92 ? 7 = 13.44A Resistance calculated=Z = V I = 220 2 = 110ohm

To Set Calculated resistance To set that calculated resistance we have to set the resistance of water by passing current through it this will give the actual resistance of water.For this purpose we make a series connection having single phase supply,bulb,water in a tank and ammeter in series with the circuit.If bulb is of 100 W current would be 0.4 A and drop on water is decreasing with increase of salt in water.We approximately set it to 44 V drop to set resistance to 110 ohm.

 Function Testing After testing and assembling all the units mentioned above we tested whether they functioned exactly as we wanted i.e. when we gave supply via breaker and rheostat to motors and switch on the breaker, timer relay retrain the supply to K3 for an interval in which the motor achieve its steady current and then give a bypass path to supply by K3.Similarly we had done this for motor 2 and we get the required result .

Final Deliverable of the Project

Hardware System

Core Industry

Others

Other Industries

Manufacturing

Core Technology

Others

Other Technologies

Wearables and Implantables

Sustainable Development Goals

Industry, Innovation and Infrastructure

Required Resources

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