Auto-Transformers

Dear plcs.net member,
In the picture below ,about Auto-Transformer circuit use to start
Motor (pump) 41 KW.380 volt 50 Hz.
The condition is:
In manual mode use control relay ,in Automatic mode use PLC.
Manual mode,After press switch Start ,K1+K2 energize (tapped 80% reduce voltage toaround 307 V and get torque about 64 % )after that 12 sec.(timer)
Only K3 energize like direct on line (K1+K2 stop)
Could you please give some suggestion about sizing of Contactors(K1,K2,K3) .
Thank you very much.

K3 would need to be rated at Full Load Current of the motor AC3 rated.
K1 & K2 I would size the same at 80% of Full Load current, by ohms law an 80% reduction in voltage will reduce start current to 80%.

Unless space is a premium I would look at sizing all three contactors the same as it reduces spare part inventories.

You should look at conveting this to a soft starter (danfoss make a good compact unit with internal bypass contacts for around the cost of the contactors and timers).

What corkers said is okay.

Many years ago when I was doing some projects for a major US manufacturer of NEMA and IEC starters. They always used full rating to size everything, plus there was already a safety factor in there, to boot. Overkill? Possibly. (probably, Definitely)

As far as the IEC starters and contactors, it is hard for me to believe that something so much smaller, can have the same duty cycly. I have never noticed any problems with the IEC devices in comparison, but I always wondered. For stuph that I am going to be around, if it is IEC, then I generally upsize it, for an additional safety factor, even though it isn't really neccessary.

I know some people have had trouble withthem, but some of the demands being placed on them probably exceed recommended ratings.

As I said, what corkers said is okay. I just like to over engineer things.

Now, if someone could explain to me why if the yanks invented (stumbled across it by accident) electricity, so to speak, why is it that so much of the world has strange voltages, and 50 cycles.

regards......casey

Well, Casey, the Italians might object to claims of Yank supremacy in utilizing electricity - a couple of fellows by the name of Volta and Ampere come to mind! And of course Tesla, who developed three phase systems, was born in Serbia.

American NEMA rated starters are beefier and can withstand more severe duty cycles than IEC rated starters. As with many things, in the US material was cheap and time wasn't, so it made economic sense to use a little overkill in the design of NEMA contactors. By contrast, the IEC rated starters and contactors require a little more knowledge of the actual loads and duty cycle, and allow less robust desgin to save material cost at the expense of additional engineering.

I have used IEC contactors without problem on applications that don't have frequent starting. Most US manufacturers now have dual rated starters - the same hardware, but you can pick your size based on actual requirements.

Thank you very much for all reply.

Thank you very much for all reply.
Normally,I prefer to use inverter.(Really,never use Auto-Transformer)
In this case better idia from kc9ih to upsize it.
..some more price but better ..

Thanks a lot again
Sawassdee krub

starter

Hi Platootod
If your going to build a starter it wouldn`t hurt
to put a second timer in to make sure your start
timer has worked. Set the time in timer 2 say
3 seconds longer than the start timer if the
start timer works and the Main line contactor
comes in OK. If the MLC doesn`t come in let timer 2
drop everything out. This is common practice on
these starters.

Hi Platootod
Your diagram is for three steps sequence.
1. K2=ON, auto transformer works as a reactor.
2. K2=ON and K1=ON auto transformer mode.
3. K3=ON direct line.
If you don't use the step 1 then you don't need the contactor K1

More pictures

Dear rgua,

Thanks you very much for your's suggestion.
Normally, I use Start Star - Run Delta and Softstart to perform this task.
But in this case use Auto transformer for start Pump (need a good
torgue and reduce ampere during start).
I have no experience with Auto-Tranformer starting method ,so that I really need more suggestion about this circuit.

If you don't use the step 1 then you don't need the contactor K1
That mean K1 in control Circuit 1 ..Or not (use only K2&K3 in power circuit from the first picture that I have post.

From more pictures that I posted here : May I ask some questions..
1. Auto-Tranformer should upsize 4-5 times of 41 Kw. Motor or not?
2. Shall I use K1,K2,K3 at the same size (around 45 Kw rated)because
we need to use Mechanical interlock between K1M & K3M ).
3.In Control & Power circuit below the condition to start like this
correct or not?

Control Circuit 2
Condition to start :
1.Close Q1 (Manual)
2.Press S1 ..K1M energized(On) and K1T delay for 12 sec
3.K1T reach 12 sec..K2M (On) and (K1M OFF)
4.After(K1M OFF) then K3M (On)
5.When K3M (On) then K1T (Off) then K2M off too
6.Now Only K3M(On)
All conditions above should OK or not?
Also,K1T delays time 12 sec ..enough or not.?.(Auto - Transformer start 15 sec max delay)
What a different between control circuit 1 and 2..Which one better?

Thank a lot in advance.

Control circuit 2

more picture control circuit 2

Power circuit 2

More picture ..Power circuit 2
More question sorry
F2 in control circuit 2 = Overload relay ?
(Thermal delay)
How much rated ampere for Q1 and F2 in Power circuit 2

Thanks a lot again

Oops ....sorry you must use three contactor K1, K2 and K3,
Sometimes this power circuit performs a three steps sequence.
1 Auto-transformer mode K1=ON, K2=ON, K3=OFF
2 Reactance mode K2=ON, K1=OFF, K3=OFF the torque is not zero, small time then...
3 Direct line K3=ON, K1=OFF, K2=OFF

Your control circuit is for two steps as you said and needs three contactors too.

"1. Auto-Tranformer should upsize 4-5 times of 41 Kw. Motor or not?"
Not, Autotransformer works few seconds only you can overload it.

Control circuit 2
Sequence.
1. K1M and K1T coil. K1T immediate contact energizes the K2M contactor. Starting.
2. K1T delayed contact cuts K1M coil. K3M goes ON, K2M off

F2 "coil" should protect auto-transformer against too long time, because these transformer are overloaded. You can use another timer.

Q1 and F2 will rated at motor nominal current, Q1 magnetic relay at 6..12 times the motor current.

(sorry for my bad English)
bye

control

Platootod if you have an Allen Bradley Industrial Controls
catalog this is year 2000 page 7 - 90 I`m looking at
it has a good diagram to go by. Cutler Hammer , Westinghouse
all should have these drawings.

Tom Jenkins said:

Well, Casey, the Italians might object to claims of Yank supremacy in utilizing electricity - a couple of fellows by the name of Volta and Ampere come to mind! And of course Tesla, who developed three phase systems, was born in Serbia.

Click to expand...

Well, Monsieur Ampere was actually French. As a matter of fact, if one looks at the most basic law of electricity, in addition to the Italian and the French, a German guy comes to mind. Georg Ohm.

Not to mention Coulomb, Kirchoff, Faraday, Maxwell, Hertz, Oersted and few others in addition to the well-known Franklin, Edison and Westinghouse. That was an international effort. Let's appreciate it.

Thanks so much for all comments

I feel appreciate and thanks so much for all answers and comments.

Platootod

Seems like the manual mode should do fine....what is the PLC automatic mode for, or how is it different?



TOM

My allegiance must lie with Mr. Framklin, who was lucky to have lived thru his accidential discovery. As a weather spotter, radio experimenter, electrician/technician repairing lightning damage, and engineer trying to avoid damage, THE MAN WAS NUTS. Though I think that has been documented. One of my forefathers was Alexander Hamilton, also present at the Decloration signing and on the $10 bill. Picture on the $10 looks a lot like my grandmother did. Very Scary. My fathers grandfather, grew up down the strret from the Franklin children and grandkids, so his first two names were Benjamin Franklin.

I will concede (gee, I have been doing a lot of that lately) that all the people you and LadderLogic mentioned all did great things too, so we could have some thing to do for a living, and to "talk" about.

We could really get into a good discussion on who invented radio (or at least RF).

regards to all.....casey