Phase Sequency Changing Problem

One possibility is to introduce a variable frequency drive into the motor starter. The drive will provide the correct phase rotation on the outlet leads at all times, whatever the inlet power is doing.

From your post, your phase rotation stays the same. RYB=YBR=BRY

Now if it changed to say RBY that would change the rotation.

It sounds like you are getting power interuptions to one or more phases intermittantly which is tripping the Air Conditioning units.

At this point I would suggest you get loggers put on the supplies and watch what is happening with your power.

Regards,
Sapper

DEAR,

EXACTLY THE SAME.

I THINK THERE IS A SINGLE PHASING .

Given on what it would take to swap phases in a grid system, it would be hard for me to believe that this would be happening on a consistent basis. If you compressors are shutting down on a "phase loss" thats probably is what is happening. If thats the case there is not much you can do about it except install a redundant system to run until the grid is repaired and goes back on line.

It is surprising that the utility company changes the phase sequence but it happens, especially in the third world. I worked in a utility company at the very beginning of my engineering career and it was a common practice there to change the phase for balancing the loads in the distribution lines.

To avoid this problem, the only good solution is to use the VFD as suggested by PWSlack. However, you can use a three pole manual transfer switch (see the figure how to connect the transfer switch). This doesn't prevent the Air-con service interruption, but you can do the change very quickly – don't need to change the power cable every time it happens.

Hope it helps,

- MS

Sir, with all do respect I think someone is yanking your crank! Remember, your utility company has motors too and I can't see their electricians swapping cables when they would decide to do this.