tap changers

[questor]

I am interested to get some idea of the proportion of distribution transformers that have tap changers. How many are on load and how many are off load. Sim=ple percentages will do. Exclude pole tops.

 

[electricpete]

I was in a large utility that was comprised of merger of 4 smaller utilities.

Two of the utilities had no tapchangers whatsoever... all regulation was done by stand-alone single-phase regulators.

Two fo the other utilities had tapchangers on most of their substation transformers (90%).

My understanding was this resulted from different preferences of the design engineers within those utilities.

 

[gordonl]

I'm in a large industrial supplied at 115kV. We have virtually 100% off load tapchangers which are used for manual changes for loading and nominal changes.

 

[electricpete]

In my previous post talking about "tapchangers" I was referring to On-load tapchangers. Of course the ones without on-load tapchangers had off-load tapchangers.

 

[prc]

This is an extremely difficult question to answer.Answer will vary from country to country ,region to to region.Even the max size of trf that is called a distribution trf also vary from region to region.
General answer will be
On load tap changers are not provided in distribution trfs when the system voltage is relatively stable.But OLTC is provided when System voltage fluctuate a lot -that too quite often-due to poor strength of the system.In India,in certain regions I have seen distribution trfs with OLTC for trfs of rating as low as 500 KVA. In some cases OLTC size ,and cost may be as much as main trf!

 

[sanvapat]

In cpp connected with grid, Off-LTC are used for distribution trafo's, including generator unit transformers ,,whereas Trasformers meant for grid connection are On-LTC, specifically for voltage regulation. Atleast that is what i have seen.