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Power-User

Join Date: Oct 2006
Location: Kolkata, India
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### Reactive Power Absorbed By 3wdg Trafo From 69kV Bus

09/17/2012 12:12 PM

I am working on an Electric network model. Two utility Grids 230/69KV,are connected to 69kV bus, where 2 Nos TG 84MW each are connected by 3 Winding transfors having primary/secondary/tertiary (69/13.8/13.8kV) 100/100/50MVA transformers. Third TG of same rating is connected by 69/13.8kV 100MVA transformer. There are loads in 69kV and tertiary 13.8kV buses. While running load flow in ETAP I have ovserved that 3.1MVAR is flowing towards 3winding transformers from 69kV bus, which is not desirable, whereas the two winding trafo is delivering reactive power power to 69kV bus. Can any one please look into and suggest the possible reason. All utility and 3 TGs are operating in parallel.

Thanks

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Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 2371
#1

### Re: Reactive Power Absorbed By 3wdg Trafo From 69kV Bus

09/18/2012 12:40 AM

Sounds like your generators might be turning too slow. Just a guess.

Measure, measure, measure and start turning off/isolating/altering this network's elements till you find where things change in an unanticipated manner(within safe operating constraints naturally).

If you don't know what is broken find out what is working.

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Power-User

Join Date: Dec 2007
Location: Brasov, Romania
Posts: 221
#2

### Re: Reactive Power Absorbed By 3wdg Trafo From 69kV Bus

09/18/2012 3:42 AM

I may firs ask why this topology with two 3 winding transformers having the same voltage for two windings? Did you try to have all 3 TGs connected each just to a 13,8/69 kV two winding transformer?

In general 3 winding transformers need more reactive power to work (they have larger cores) and your TG might not have enough resource for this. You can see this by changing the TG's power factor. Moreover, the load on the tertiary might mess up the things.

Eventually, if it's just a model it means you can still make changes easily.

PS: Next time when you ask for an answer try to give more information (generator power factor/reactive power, loads power, even what you suspect it might be the issue, the reason for the topology...)

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Guru

Join Date: Jun 2011
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#3

### Re: Reactive Power Absorbed By 3wdg Trafo From 69kV Bus

09/18/2012 4:12 AM

...and a sketch is always good.

I had to read the OP 5 times to get a picture in my mind (which may still be flawed) Paragraphs would be good too.

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Power-User

Join Date: Dec 2007
Location: Brasov, Romania
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#4

### Re: Reactive Power Absorbed By 3wdg Trafo From 69kV Bus

09/18/2012 7:49 AM

Yes, you're right. I forgot about it but it's true that for engineers sketches, drawings or any kind of image are appreciated and moreover, offering a hell lot of information. In many cases if you have the "picture" all you have to do is ask the right question.

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