Transformer

Hi all

I have a client how wants to regulate the voltage going into a transformer. I have this working with a regulator you turn by hand and it works perfect.
He now wants this dine from a plc based in a ct on the outfeed of the transformer. So now I must get the Amp reading into the plc as well

Any ideas would be great

Donnchadh

Donnchadh said:

Hi all

I have a client how wants to regulate the voltage going into a transformer. I have this working with a regulator you turn by hand and it works perfect.
He now wants this dine from a plc based in a ct on the outfeed of the transformer. So now I must get the Amp reading into the plc as well

Any ideas would be great

Donnchadh

Click to expand...

I know they make CTs with a 4-20mA output. I've used the Kele brand before with good results.

EDIT: Were you asking how to get the signal into the PLC or what regulator to use that can run off an analog output?

Hi brstilson

Thanks for that.
Now that will get me the current reading perfect but any ideas on how to change the voltage from the plc. The voltage is 220 but i may want to change it from anywhere from 180 to 220.

Great quote

Donnchadh

I have this working with a regulator you turn by hand and it works perfect.

Click to expand...

Tell us more about this regulator.

Donnchadh said:

I have a client how wants to regulate the voltage going into a transformer. I have this working with a regulator you turn by hand and it works perfect.

Click to expand...

How are you varying the voltage now? Variac transformer that you operate by hand? If that's the case, a suitably sized stepper could run a variac, but that's a bit of a kludge. This does give you a sine wave output however.

Do you need a sine wave output, or is a variable duty-cycle solid state "dimmer" OK? If it's the latter, have a look at these controllers from Crydom:

http://www.crydom.com/en/Products/Catalog/l_pcv.pdf

They take a 0-5v, 0-10v, or 4-20ma signal in and chop the AC to give you the average voltage you desire. They're for resistive loads only. Select the model for the voltage and amperage you need.

Try a search for "Proportional Control Solid-State Relay." Crydom makes lots of models that may work for you.


-rpoet

I think he's talking about a Variac/ auto transformer / variable transformer or whatever they are called in your neck of the woods, operated with a manual rotating knob.

edit:beat me by seconds!

Need much more information.
What size is the transformer? What power levels? Single or three phase?
For small loads, you can buy/build a triac based power controller.
For large loads, or three phase, I'd slap together a three phase converter with back to back SCR's on each phase.

You can still buy simple closed loop controllers and firing circuits from Contrex.

put a small motor on the variac, what is the process?

What about some kind of damper motor mechanically linked to the voltage regulator? I've used Belimo before and they work fairly well. The ones I used modulated from a 2-10V signal.

I use something like this many years ago to control input of a transformer 460 VAC/13000 3 Phase, 60 Hz, 300 KVA.
The company was called Phasetronics but they seem to be out of businnes, they were localed in Clearwater, Florida, USA.

http://instrumentation-central.com/pages/scr_power_controls.htm

I use SCRs by Control Concepts. They are compact, readily available and work great. 99% of the time the zero and span are right on.
ccipower.com

You will need a phase angle SCR for controlling a transformer.
Just order the correct size with a 4-20 ma control signal.
You will no longer need the "regulator".

If you post the transformer specs and I can point you to the correct SCR.....or just call Control Concepts. You will need KVA, Voltage, and if it is 1 or 3 phase.

NetNathan said:

I use SCRs by Control Concepts. They are compact, readily available and work great. 99% of the time the zero and span are right on.
ccipower.com

You will need a phase angle SCR for controlling a transformer.
Just order the correct size with a 4-20 ma control signal.
You will no longer need the "regulator".

If you post the transformer specs and I can point you to the correct SCR.....or just call Control Concepts. You will need KVA, Voltage, and if it is 1 or 3 phase.

Click to expand...

Phase angle control will work only if the OP doesn't care about a sine wave output. Chopping the waveform like that does terrible things for harmonic content. The OP will need a choke on the output of the controller as a low-pass filter (we do this all the time for lighting dimmers in the entertainment industry). If he needs a sine wave output, than a motor-driven variac is the easiest way to go.


-rpoet

...any ideas on how to change the voltage from the plc? The voltage is 220 but i may want to change it from anywhere from 180 to 220.

Click to expand...

Here are 2 variable transformers with the right voltage range, and controlled by a stepper motor. That might get you close. Now all you need to do is rig up PLC outputs for the stepper motor.

http://www.ebay.com/itm/New-Staco-M...utotransformer-Motor-/171036423486#vi-content

I see that Staco Energy has a motor driven autotransformer with a FRC-20 Controller interface with a voltage or current feedback signal.
http://www.stacoenergy.com/variable_transformers.htm#MotorDriven

In my business (industrial heat treat equipment) we use phase angle SCRs to control transformers for the elements on a normal basis.
This is very common place and we never need to use "chokes" on the output (unless maybe it is already built into the SCR unit). I have never had any issues out of the harmonic disturbance in using phase angle.

You only have 2 firing choices with SCR controllers, phase angle or zero cross.
Using zero cross (on-off) is a no-no on a transformer, because it saturates the transformer, if the on-off is too fast. Phase angle is more linear.

It sounds like presently he is using a variac to control the input to the transformer by varying the ac to the primary. An SCR will do this far better and way faster than a motor driven variac. I have converted several of this type of control system to SCR.
It really depends on the specs on the transformer, it may even be better to control the secondary.