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Thanks everybody for this exhaustive explanation. Here is the thing I was missing. When a transformer size increases, the reactance decreases and the resistance increases. Now, if we have same load but a higher rating transformer as the reactance will decrease but the resistance is still less...

Thanks WAROSS and all those who contributed. I am grateful for such an exhaustive explanation. I have still not read it as I want to take my to go through it. Waross: I have one more question for you.I would appreciate a word. I beleive I am looking for a thumb rule. What criterion should I...

Hi, I guess ur right. May be I am missing some thing bigtime. I did a basic simulation in ETAP. I used 12.77 mw, MVA @0.80 = 16 mva on a 15 mva TR. %z=8.5 vol on sec bus= 88% 2. Same Load- TR rating 22 MVA same%Z voltage in sec. bus Vol on sec bus-92.26% 3.Same Load- TR rating 30 MVA same%Z...

So, Will it be right to say that if a transformer is on a tap position, the %z will change and so will the Short-circuit current. That means, if I buy a transformer with %10 impedance and then I operate it at %5 Tap in primary. My impedance into the system will change and so will my...

Thanks WAREEAGLE, I never noticed this interesting phenomena, that%Z is not a constant quantity rather it is a factor of load. That means, it refers to full load. So, the less the loading , less is the voltage drop. So, It can be infered that if I have to step 220 KV to 6.6 KV and I need only 3...

Hi Wareeagle: Thanks for your comments. "You are going to have almost that drop, 7%, at PF = 1.0." I am a Jr EE, so not much experience. So should I presume that we need to have a regulator. There must be a way out to tackle this situation. For example in case where there are huge transformers...

Thanks for your comments. David Beach: This is a steady state voltage drop. So I think starting issue is not in the picture. What my concern is, how this problem can be sorted out. By capacitor bank compensation ? Waross: You are right, Transformer is over loaded. Could you advise, where I can...

Well Thanks for the comments. I eventually spoke to mechanical engg and he advised me that he has provided us with the electrical load. A 3.7 MW load for a refrigeration unit for cooling is huge but any ways. Now the situation is; A 220 KV line feeding two 15 MVA transformer with % Z of 8.5 and...

Hi, Could you please advise me how to convert 3.7 MW of cooling load in to Electrical load. Please advise me, if you have any questions. Cheers !

David Beach, I dont mean to counteract your statement but "From the standpoint of heating and losses, the lead/lag of the power factor does not matter" Just would like to have more insight. Leading power factor means transfer of reactive power back to utility and lagging means from the utility...

Hi Just out of curosity, after reading this thread, what ceiling height of a substation has to to with fault current. Another thing, I am a jr electrical engg and I also have been involved in short circuit calc. but I dont recall ever considering a role of AVR in that. Could you kindly advise...

Hi, I was reading a calculation done by one of the guys in our office and it reads like this: The ground rods consists of of the steel reinforcing bars in concrete piles. I studied the whole calculation. But it was strange to find that rods were randomly spaced. But as per code, the two rods...

Thanks Everybody for your valuable contribution. I was wondering, if any body who is into simulation could advise me about modeling a hoist for mining application in ETAP. I would appreciate a word. Thanks

Thanks Mapparent. I dont mean to spoil your weekend but when ever you have a moment, you can drop a word. My question still stands what is the relevance of single phase X/R. Could you advise me an example of a delta/Star secondary fault and then Three phase being smaller than Single phase...

Hi, I came across a short circuit study done by engineers of Schd. Electric. It was contracted by our company to them.I read it and came across few things. They assumes 3 Phase X/R ratio of utility to be same as single Phase for X/R ratio. I know three phase ratio is used for calculating the...

One more, I forgot to mention. I have worked in medium voltage distribution(utility) stuff and I have realized that dievrsity factor can be 60 % and that is how transformers are sized. What is the actually thumb rule while sizing a transformer? Should be fully or 75 % or what percentage loaded...

Thank KJ and Waross. This situation is arising because My supervisor is not in and I was asked to do this. We are expanding the distribution underground and at present I am simulating an existing system and after we figure out the voltage drops, we will plan the next stage. The example I gave...

Thanks KJvR, Here is what I did. I am citing an example here of what I did in one of the cases. Transformer TR06 at zone 4700 Z3 entrance is feeding a switchboard which has 8 sections and out of those 5 are in place with 400A, 50 A, 160 A, 150 A and 100 A breakers. 1. The 400A breaker is...

This is my first time response. No answer, I did not know my question is so dumb.Everybody says here no question is stupid, so some body might have a word to drop. Thanks

Hi Guys, It is my first time here and I am here because people with experience can answer these two questions. Q1 I am doing a load flow study with ETAP. The project is for a location in Africa. I have selected the base case as freq=50 Hzs and standard as IEC. Suppose I do it the other way...