Testing 3 phase motor with single phase supply

By Yuktix Technologies - August 26, 2014

Testing 3 Phase motor with single phase supply

When we are in office job or in corporate job, our life is full of comfort, weekends, holidays, CL, Medical leaves, others perks, office vehicle etc etc and life seems to be cool and happening. Things start changing when we start thinking and doing something of our own or you can say that when you want to be a entrepreneur. The basic difference between the both is that while being in corporate you are running a engine whom some one else had build and in later case, you are trying to build your engine by yourself and in that case you have to take care of everything, everything means everything starting from idea stage, development stage and when you are in embedded domain, you might even have to do plumbing, painting, electric work etc just like my boss in Yuktix has did and no wonder many other's have done, because there is no other way in the early stage of a start-up.

So the basic aim behind writing down this post was to share the experience of testing a 3 phase motor panel with single phase supply and playing with daemons as stated in this facebook post. So first of all i would like to give some basic information with respect to the single phase supply, 3 phase supply, single phase motor and 3-phase motor.

Single phase supply : In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors.
Three phase supply : Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads.
Single phase AC motors : Single phase induction motors require just one power phase for their operation. They are commonly used in low power rating applications, in domestic as well as industrial use. This article is aimed at giving you a conceptual overview of the working of single phase motors. For more information have a look at this link
3-phase AC motors: Three-phase squirrel-cage induction motors are widely used in industrial drives because they are rugged, reliable and economical. For more information on 3-phase motors have a look at this link.

So i hope that above information and links might have helped you to have some basic knowledge of stated topics. When we talk about embedded, we generally deal in range of 0V to 5V and if required maximum of 12 volts for supply. We never deal with 220V 50 Hz single phase supply or 3-phase supply. So when it came to test the motor panel that we are using to drive a 3-Hp motor, we raise our hands in the air and gave up. At this time, our all time embedded hero, Ashok sir, came into scene and share the way to test the motor panel with single phase supply. The idea was simple. Short the 3 phases of 3-phase supply using MCB, get a single wire out of it, get a neutral line from the panel, plug them into the AC single phase supply, prepare s set-up of 3 bulbs and we are done. wow...for some one, it might be gone over the head, just like happened with me for the first time, but with time, i got that. I will explain each step with pictures and that will make everything clear.

Step 1 : MCB which we were using was 3-phase 16 Amp MCB. So we need to short all the 3 ports of MCB and get a single wire out from the last port as shown in below figure. Also from the panel, we can take out neutral from the panel(every motor panel will have that - named as terminal block ).

MCB with shorted ports and connection to mains

Step-2 : OLR(over load relay). Every motor panel will have thermal overload relay, out of which 3 wires will be coming out(keeping in mind that we are dealing with 3-phase induction motor). So in order to test that, we have 3 options with us.

Test with Multimeter
Test with 3 Red, Yellow and Blue Bulbs
Test with the real 3 -phase motor (If you have...)

Test with Bulbs : Connect the wires as per shown in below pictures with bulbs and neutral and if everything is fine in your motor panel, after giving single phase supply, you 3 bulbs i.e Red, Yellow and Blue will glow showing that you are getting 3 phase output from single phase supply.

Connecting 3 bulbs to 3-phase output

Test with Multimeter : You can test the voltage of 3 R,Y, B terminal blocks coming out of OLR and you will see voltage readings of 240V on these terminal blocks.

Test with 3-phase motor : You can also test the same setting with a real 3-phase motor as we did with 5-hp motor(god, i hadn't even dreamed of running that big monstrous motor. )

3-HP 3-phase motor we are running in our automatic humidifier

5 HP 3-phase motor testing

So this was all what we had done for testing our panel with a 3-Hp/5-Hp motor. And below is the picture of chamber with automatic humidifier and real time readings on the data-logger and on our cloud app which greenhouse/polyhouse owner can access.