HELP with Transformer Calculation

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charlie b

charlie b

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Location
Lockport, IL
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Semi-Retired Electrical Engineer
I think we are (once again) allowing language to get in the way of communication. Let me see if I can summarize the two major sides of this discussion:

  • One of you is saying, “The sky is blue.”
  • The other one of you is saying, “No, you are wrong! The grass is green.”

Does that work for everyone?

If not, try this: From my perspective as an electrical engineer working in the power systems design and analysis side of the electrical industry, the word “power” means nothing, if it is spoken or written in isolation. It can only have meaning if there is an adjective immediately preceding it. There are three commonly used adjectives, and I don’t think you need me to list them.
 
Besoeker

Besoeker

Senior Member
Location
UK
charlie b said:
I think we are (once again) allowing language to get in the way of communication. Let me see if I can summarize the two major sides of this discussion:

  • One of you is saying, “The sky is blue.”
  • The other one of you is saying, “No, you are wrong! The grass is green.”

Does that work for everyone?

If not, try this: From my perspective as an electrical engineer working in the power systems design and analysis side of the electrical industry, the word “power” means nothing, if it is spoken or written in isolation. It can only have meaning if there is an adjective immediately preceding it. There are three commonly used adjectives, and I don’t think you need me to list them.
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I respectfully disagree.
Power is an absolute. Call it W, kW, HP J/s or whatever. A 110kW motor outputs 110kW at full rating. It isn't an imaginary rating or black or blue. It is just 110kW.
 
kingpb

kingpb

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Location
SE USA as far as you can go
Occupation
Engineer, Registered
I think electrical folks inside the US get used to seeing Kw only when a non-motor load is described and thus make the leap that Kw= Kva. However, outside the US, (yes, it does exist) motor ratings are not given in Hp, they are given in Kw thus automatically stating that since it's Kw its equal to Kva doesn't make sense.

People in US with oversees experience, and non-US forum regulars or visitors aren't going to automatically make this leap of faith from Kw to Kva, hence why it is important to know your audience and state things, along with assumptions appropriately. So, in that regard, I can say the discussion is more along the lines of the sky is blue (we agree) but it has clouds or doesn't have clouds (pf not =1, or pf=1).

I will say, that every engineering homework or test problem I did, had to indicate any assumptions. If there were none needed, then we had to write "None" or N/A. Currently, the company required format for calcs done in our office also requires it.
 
Besoeker

Besoeker

Senior Member
Location
UK
Mods, I'm fed up with my valid points being deleted while others are allowed to keep their inaccuracies. It is poor moderation. Yes, this is in a public section. But it merits being made public. It is positive and constructive criticism. You could take it on board and learn from it. But probably won't. Like the others, this will magically disappear into the ether - but hopefully not before some of the very worthy members here have viewed it.
 
I

Ingenieur

Senior Member
Location
Earth
kingpb said:
Zero assumptions? Since by vector math: S(va)=P(w)+jQ(var), then only way to get S(va) = P(w) is to assert that jQ(var) = 0; i.e. pf=1
which means you had to Assume pf=1 since none was given.

I can honestly say, where I went to school, you would have just gotten at least 10pts marked off for not stating the assumption that pf=1 and then gotten a zero for arguing with the professor that there were no assumptions, or he would have laughed and ridiculed you in front of the class. :thumbsup:
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I don't have to assume that
they gave P, not S or Q
had they given S or Q, only then would pf factor in

my school, if multiple choice, you would have gotten 100
a deduct if you brought power factor into the mix since it, S or Q are not in the problem statement
 
I

Ingenieur

Senior Member
Location
Earth
Besoeker said:
To assume or not to assume to paraphrase Willie Wiggledagger.
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catching a typo does not make you point valid
in fact the opposite if that is all you got

they do not mention S, Q or pf, ONLY P
that is the only form of power you can use to solve the problem
you can't assume
 
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