Power Transformer Delta Tertiary Insulation
Power Transformer Delta Tertiary Insulation
(OP)
Good day!
For a 115kV/34.5k/13.8 kV 3-wdg power XFs, what should be the minimum insulation level of the 13.8 kV wdg if:
a. Unloaded tertiary, with no leads taken out
b. Tertiary shall be loaded, either via station service or capacitor for system improvement.
Note that tertiary is not corner grounded.
I am assuming that the 15 kV insulation level (110kV BIL) will suffice. However, some transformer manufacturers suggest to have 25kV insulation (which is about 150kV or 170kV BIL insulation). Of course this results to higher transformer costs.
Additionally, if we intend to ground one corner of the delta tertiary in cases we need to load it, what would be the voltage across the different phases?
For a 115kV/34.5k/13.8 kV 3-wdg power XFs, what should be the minimum insulation level of the 13.8 kV wdg if:
a. Unloaded tertiary, with no leads taken out
b. Tertiary shall be loaded, either via station service or capacitor for system improvement.
Note that tertiary is not corner grounded.
I am assuming that the 15 kV insulation level (110kV BIL) will suffice. However, some transformer manufacturers suggest to have 25kV insulation (which is about 150kV or 170kV BIL insulation). Of course this results to higher transformer costs.
Additionally, if we intend to ground one corner of the delta tertiary in cases we need to load it, what would be the voltage across the different phases?






RE: Power Transformer Delta Tertiary Insulation
When one corner of delta is grounded,voltage to ground at other terminals will be 13.8 kV ie line-line voltage.So protective arresters also should of 13.8KV class.
RE: Power Transformer Delta Tertiary Insulation
Good explanation. Star for you.
Could you also please inform in case of unloaded tertiary with corner grounding, do we still need higher insulation / surge arresters!
Thanks.
RE: Power Transformer Delta Tertiary Insulation
RE: Power Transformer Delta Tertiary Insulation
from your last post, I understand that this transferred surge occurs only when the XF is being tested, is that correct? what test produce this transferred surge?
RE: Power Transformer Delta Tertiary Insulation
RE: Power Transformer Delta Tertiary Insulation
Trasferred surges to tertiary occur when LV or Hv is tested for impulse or switching surges.In service due to travelling surges from lightning or from switching surges.So transferred surges are ocurring not only during testing.In fact all tests are done to simulate max service severe conditions!