Distribution, dedicated vs tertiary feed?
Distribution, dedicated vs tertiary feed?
(OP)
What are the disadvantages of using the tertiary windings of a 400kv to 132kv 500MVA Grounded wye auto transformer to feed a 22kv distribution system over having a separate 132-22kv transformer?






RE: Distribution, dedicated vs tertiary feed?
RE: Distribution, dedicated vs tertiary feed?
Regards
Marmite
RE: Distribution, dedicated vs tertiary feed?
Could a large power transformer be ordered as to have a similar cumulative fault withstand to a 132-22kv distribution transformer?
The distribution system is low impedance grounded. All loads out on the line are delta so the line itself is delta. To obtain a zero sequence source a fault duty zig-zag grounding transformer will be placed on the distribution bus bonded to the ground mesh via a 5 ohm resistor.
The reason it is being considered is because the cost is substantial reduced from not having separate distribution transformers.
RE: Distribution, dedicated vs tertiary feed?
RE: Distribution, dedicated vs tertiary feed?
RE: Distribution, dedicated vs tertiary feed?
In the current case,also it is bettter to avoid loading distribution system from tertiary. However if it is essential there is no problem. The tertiary impedances will be of the order of 60/45 % ( from HV and MV sides on 500 MVA base) But since the tertairy loading will be at much lower levels, regulation may not be an issue at tertiary terminals.The main point is whether you want disturbance in your 400 kv from faults on DT level.
RE: Distribution, dedicated vs tertiary feed?
RE: Distribution, dedicated vs tertiary feed?
The regulation I was referring to was attempting to keep the 22kV feeder at exactly 22 kV. In my neck of the woods, the 500 kV buses swing as can swing all the up 550 kV (+10%). The system operator uses the 500/230 kV and 230/115 kV transformer LTCs to regulate voltage at the lower levels to only swing a couple of percent. Depending on the exact configuration of the windings and LTC, the voltage variation on tertiary will be driven by the voltage variation on the common winding.
RE: Distribution, dedicated vs tertiary feed?
I did look into it, and you are correct, the available fault current coming from the tertiary windings will be significant to the point air choke reactors will be needed before feeding the distribution buss.
The other option was adding separate 132-22kv transformers right in front of the 132kv buss fed by the power transformers.
RE: Distribution, dedicated vs tertiary feed?
RE: Distribution, dedicated vs tertiary feed?
Just to ask, I could be wrong but in the UK, do any real world situations exist where an auto transformer tertiary feeds 33kv sub transmission? Ive heard if it being done but never found out how it was done, if it all.