variac control

[diribarren]

Hey ---has anyone controlled a 3 phase variac? I haven't used one before and it is pretty confusing on what all the PLC has control or what inputs need to be sent? The project I was assigned doesn't even have documentation for the variac so for someone who hasn't dealt with one before it is just a black hole.
Any sample work would be GREAT!

Thanks!
Denise

 

[Skogsgurra]

Do you mean a Variac? A variable transformer? If so, are you going to control its primary voltage or what? Does it have a motor for turning voltage up/down? If so, is it the motor you are going to control?

Could you describe a little more, please?

 

[diribarren]

Thats the problem I haven't used a variac and would just like to find an overview of how they work or how to use them---I know it is a Staco and it has 3 internal motors that are controled to produce the power to 5 motors we are using. I know I need to check the voltage to make sure all three phases are good if not set a fault flag and disable the staco. There is an increase and decrease to phase a, b, c of the variac. I know this is confusing cause I got this project after someone else setup all the i/o cards etc. for AB PLC5 now I have to figure out all these i/o and send it to the variac.

I can tell you I have been given an output & input bit from each motor we are sending power to via variac, and an increase/decrease bit for each phase of the variac (phase a,b,c). I also have blk transfers from 1771 nt1 cards sending me amps from phase a,b,c & volts from a,b,c & a watt reading---from each of the motors we are powering.

Does any of this make sense to you??

 

[diribarren]

OH and I have voltage readings from the variac via a blk tx from another 1771 nt1 (variac n-a, variac n-b, variac n-c)

 

[AFab]

I have delt with 3 phase variac's
The concept is quite simple. The variacs for the 3 phase are ajusted my a small gearmotor, usually D.C. The output of the Variacs is either increaced or decreased by controling the direction of the gearmotor. I adapted this old system to PLC control by controling the gearmotor from the PLC and using analog feedback to the PLC. Limit switches should be used on the gearmotor for safty.