We are designing a new 600 MVA 240 kV/138 kV substation. The AC station service is 208Y/120 V, 3 phase, 4 wire. The primary source is a 75 kVA padmount transformer fed from a local 25 kV distribution line. The client wants a full-capacity alternate source for the station service. The...
I had mentioned in a previous post that I have a client who has several 63 kV - 13.8 kV delta-wye ANSI Group 2 transformers. Some of these transformers have A-B-C sequence on the primary, some have A-C-B. The client is attempting to parallel secondaries. Obviously, there is a problem with...
Is anyone aware of any standards for, or have references for or experience in, constructing system voltage phasing diagrams?
Our client has several systems that were originally designed as radials. They now wish to tie together the secondary side of these systems to allow parallel operation if...
A client has standardized on using a crushed limestone backfill, sieve passing 100% 6mm (1/4 inch) particles, to obtain a better heat dissipation in the vicinity of buried 15 kV cables. Unfortunately, no one seems to know the actual thermal resistivity of the limestone.
Does anyone have any...
ANSI C37.91 and C57.109 provide through-fault current duration guides for liquid-immersed transformers. Does anyone know of similar guides for dry-type transformers? In particular, I am trying to construct a damage curve for a dry-type 950 kVA autotransformer.
Equation 68, zero sequence current for line-to-line-to-ground fault, of IEEE Std 80-2000 contains the following error:
Numerator currently reads "X1 x (X0 + X2) + (X2 + X0)"
Numerator should read "X1 x (X0 + X2) + (X2 x X0)"
Anybody know of any references for estimating or calculating transformer inrush current for purposes of protective device coordination? Rule of thumb I have seen is 12 times full-load current for 0.1 s. I have also seen other recommendations of 3 times FLC for 10 s and 25 times FLC for 0.01s...
I want to include cost of losses in a transformer specification I am preparing, and have determined my annual load and no-load loss costs. I am having trouble determining the worth of these losses, however.
I have the 1986 version of the Red Book, which uses the present worth of an annuity to...
