Inrush on large autotransformers

[veritas]

Hi

Anyone tell me what are typical maximum inrush values one can expect on large autotransformers (>200MVA, >=220kV)? I need to set the diff hi-set element on a 375MVA, 275kV unit.

Thanks.

 

[prc]

Anything like 5-8times full load current.But better to get the figure from the manufacturer.

 

[veritas]

prc

This seems to be the general rule of thumb for trfr inrush. But I have also seen that for small units (< 5MVA ) it can be up to 10p.u. and someone said for large autos you can look at 2.5p.u..

Are there perhas more specific rule of thumbs depending on trfr size?

Thanks.

 

[prc]

No thumb rules.Inrush varies due to various factors.Transformer size is a parameter. In a voltage transformer it can be 25 times rated current. In a distribution transformer 10-15 times FLC.Power Transformers 8-12 times and very large units 3-5 times.For the size mentioned by you and for auto transformers the range mentioned by me is normal.