Need help with this problem: Power factor

[Phil Corso]

Besoeker...

Apparantly your (collectively) was adequate for the OP's needs!

Regards, Phil

 

[weressl]

Trobbins...

How much of load are induction motors?

Is the transformer a conventional 3-ph, 2-winding, oil-immersed unit?

Regards, Phil Corso

Now you have peaked - or poked at - my curiosity as well.

Care to elucidate on the aspects of relevance of the above information, you're requesting, to the question at hand?

 

[kingpb]

Add a stage of cooling fans and it is no longer over the base rating.

Reminds of an old joke:

2 groups of engineers were given a task to fix the problem of a computer overheating.

The first group took it all apart, analyzed every component, and completely redesigned it
to reduce the heating of components. The overall cost to produce was higher for the redesign.

The second group, took a simpler approach; they simply added another fan.

 

[Smart $]

Now you have peaked - or poked at - my curiosity as well.

...

Perhaps piqued, also!

 

[Phil Corso]

To all the PtPs...

Kingpb is on target.

Have a Happy, Prosperous, and more importantly, Healthy New Year!

 

[Besoeker]

Add a stage of cooling fans and it is no longer over the base rating.

But then it is no longer a 25 MVA transformer and the question is about a 25MVA transformer, not something else.
The type of transformer is an irrelevance.

 

[weressl]

But then it is no longer a 25 MVA transformer and the question is about a 25MVA transformer, not something else.
The type of transformer is an irrelevance.

Let's say that we add some cooling fans or liquid nitrogen spray or any other exotic methods of extending the 'rating' of the transformer. Who is going to certify the 'new' rating of the transformer?

We can also just willy-nilly overload the transformer and have a shorter life of it. Utilities do that all times.

All transformers have a base rating and then various overload ratings are specified. That is true for both liquid cooled and dry type transformers. So if the OP's intent was to 'take' these ratings into consideration, he would have stated the full available ratings.

 

[mivey]

Add a stage of cooling fans and it is no longer over the base rating.

Could have been a 16/20/25 but that is not what the OP stated and is really irrelevant since that is not the question asked.

Reminds of an old joke:

2 groups of engineers were given a task to fix the problem of a computer overheating.

The first group took it all apart, analyzed every component, and completely redesigned it
to reduce the heating of components. The overall cost to produce was higher for the redesign.

The second group, took a simpler approach; they simply added another fan.

Amusing, but the question was about a capacitor application.

 

[mivey]

But then it is no longer a 25 MVA transformer and the question is about a 25MVA transformer, not something else.

Let's say that we add some cooling fans or liquid nitrogen spray or any other exotic methods of extending the 'rating' of the transformer. Who is going to certify the 'new' rating of the transformer?
...
So if the OP's intent was to 'take' these ratings into consideration, he would have stated the full available ratings.

There ya go. :thumbsup:

 

[Besoeker]

Let's say that we add some cooling fans or liquid nitrogen spray or any other exotic methods of extending the 'rating' of the transformer. Who is going to certify the 'new' rating of the transformer?

We can also just willy-nilly overload the transformer and have a shorter life of it. Utilities do that all times.

All transformers have a base rating and then various overload ratings are specified. That is true for both liquid cooled and dry type transformers. So if the OP's intent was to 'take' these ratings into consideration, he would have stated the full available ratings.

THB, old fellow, I think it is another of these cases where people want to complicate the original question far outside what was actually asked. You might wonder why they do that. There again, being a sharp cookie, you might not.

The simple point in the question relates to a 25MVA transformer. It is irrelevant how it achieves that rating. ONAN, forced air, water cooled. But 25MVA is what's given.
The question requires a numerical answer on power factor correction. Mivey sorted that out early on.

Introducing non quantifiable changes to cooling is simply nonsense.

 

[Phil Corso]

Bwesoeker...

Fantastic!!

Phil

 

[kingpb]

Could have been a 16/20/25 but that is not what the OP stated and is really irrelevant since that is not the question asked.

Amusing, but the question was about a capacitor application.

Woulda,shoulda, coulda!!!!

No need to be smarmy with your responses.

To stick to the OP - my answer, based on what limited information was given, and my experience as an engineer, is that it is not practical, or good engineering practice to add that much load to the transformer by adding capacitors with the assumption that you can achieve a system pf of 1.0. Its a good exercise for a textbook problem, but not a real world application. It is not good practice to try for a pf greater than 0.95 lagging.

Just for added value, everybody does realize that this would be a medium voltage electrical system greater than 4160V and the capacitors involved would need to be similar to the EATON MV-AutoVAR.

Carry on!

 

[GoldDigger]

You make a good point that in the real world you have to take ferroresonance seriously, especially if you connect right at the secondary of the transformer. And if the load is intermittent, it is preferable to connect downstream of the contactor or switch.

Sent from my XT1080 using Tapatalk

 

[Besoeker]

Its a good exercise for a textbook problem, but not a real world application.

That's the point. It IS a textbook problem - and nothing more.

 

[mivey]

Woulda,shoulda, coulda!!!!

Exactly. That was the emphasis: we can suppose all kinds of stuff.

No need to be smarmy with your responses.

Sarcasm was what I was going for. I'll try to be clearer next time.

To stick to the OP - my answer, based on what limited information was given, and my experience as an engineer, is that it is not practical, or good engineering practice to add that much load to the transformer by adding capacitors with the assumption that you can achieve a system pf of 1.0.

Then recognize the question for what it was and leave it at that.

I will say that I have seen some capacitor vendors pushing a unity correction but that is not the norm. As you know, unity correction may not be wise from an engineering standpoint or from an economic standpoint.