What is this circuit ? :O

Thread Starter

akhu

Joined Jan 3, 2021
39
Circuit.png

Does any one know some thing about this circuit ? I must wirte a functional analysis. Therefore I got some question:

Frist what is that ? Is that an engine or something ? Are the 6 elemetens there SCR's ? And why they are used ? Is there a better solution instead of using them ? And what is this cirucit exactly doing ?And how can I describe the function of the wire where V1 is placed ? And what does die wire means which is right one the side ? And is T1 a center tap ?


I hope that some is here you know something about this.
 
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atferrari

Joined Jan 6, 2004
4,321
My limited contribution: the symbol with the "M" belongs to a motor, not to an engine.

I am sure there are "better solutions". Define first to what.
 

Thread Starter

akhu

Joined Jan 3, 2021
39
@atferrari

For a oven. So what could I do to improve the efficiency?

And it seems that T1 is a center tap but I'm not sure, is there some one who can confirm that?
 

bertus

Joined Apr 5, 2008
21,364
Hello,

The used transformer is a 3 phase transformer with a Delta input and Why output going to a controlled bridge rectifier.

Bertus
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
That was how early larger DC motors were driven in many industrial machines, directly off the 3phase supply, very common in the 70's to 90's, even later.
Appears to have a shunt wound field, the controller for this would have a circuit in the event of field loss etc to prevent runaway..
Max.
 

Thread Starter

akhu

Joined Jan 3, 2021
39
Okay thanks a lot now I know what its. Does someone got the manual? Or something?

And what can we do to proof the efficency? What can we replace. (Usage as a oven.)
 

Ian0

Joined Aug 7, 2020
2,189
It's known as a six-pulse fully-controlled rectifier. Still one of the most efficient ways to speed-control a large DC motor.
The main improvements in efficiency would be to use a brushless motor, but the IGBTs in a variable-speed drive have greater losses than the SCRs, higher voltage drop, and higher switching losses because of the higher operating frequency.

How is it used in the oven?
 

schmitt trigger

Joined Jul 12, 2010
438
General Electric’s SCR Manual, 5th edition, will provide you with all the information required to understand a three phase controlled bridge, and how it relates to DC motor speed control.
 

Thread Starter

akhu

Joined Jan 3, 2021
39
Ohh no, this manuel has more than 700 pages.

But what I can't understand know is why a DC motor with series excitation (correct me If I'm wrong) is wiring together with a three phase controlled bridge. As far as I know this takes only senes for ac.

Furthermore I searched in the internet, so now I can't understand just the part with T1, L1, L2, L3. This must be a center tap (I'm not sure about this), and could find something that is similar.

Maybe some can explain this parts in short and easy way.
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
It also shows a shunt field, separately excited
That could be a series compensation winding.
The output of a 3ph bridge is 180 hertz ripple, no problem for a DC motor.
The transformer is a delta primary, star secondary.
As per post #6, motor controllers of this nature have always been common for DC motor control.
Max..
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
A 3ph transformer is simply 3 transformers on the same frame/core, it can just as easily be achieved using three separate single phase versions.
You have a star or delta option of connection.
The one in the OP is Delta-Star connected.
Max.
 

Ian0

Joined Aug 7, 2020
2,189
I suspect the three-phase version might be cheaper than three single-phase transformers. It will certainly be smaller and lighter.
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
I suspect the three-phase version might be cheaper than three single-phase transformers. It will certainly be smaller and lighter.
It is often done in a pinch, where a replacement is not immediately available etc.
I was once faced with a similar option.
Also it was a effort to point out that in principle, it is derived from three separate circuit devices.
Max.
 

Thread Starter

akhu

Joined Jan 3, 2021
39
So far so good. Now I got the knowlegde. But the next huge questions is:

What can we do to improve, the effiency ? The only I can see, is to replace the 6 thyristor to 6 gto's. And add 3ph transformers so that we have in the end 6 of them ? Would this work ? Or you have better ideas ?
 

MaxHeadRoom

Joined Jul 18, 2013
23,092
What would be the point?
Apart from being a bit of a legacy circuit, the method has worked fine and fairly efficiently in the past.
One thing that had to be observed was the use of Rectifier fusing, as power line failures or surges often caused misfiring and destruction of the SCR(s).
Just mainly replaced now with PWM drives and PM.AC motors.
Where does six transformers fit in?
Max.
 

Thread Starter

akhu

Joined Jan 3, 2021
39
@MaxHeadRoom

This is a good point of view. Now I noticed that it doesnt make sense. But who does the Rectifier fusing look like ? Are they common Rectifier fusing ? Or is there a specific rectifier fusing which was developed for fixing misfiring and destruction of the SCR's ?
 
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