Rated Power Frequency Withstand Voltage 1

[TMB64]

what would be the Rated Power Frequency Withstand Voltage
for a 75MVA 11KV-161KV 50 HZ?. I need to specify this criteria for a manufacturer. Thanks!

 

[sslobodan]

It depends of the sensitivity of device you have. As far as I remember from the college from appropriate subject all electroenergetical equipment ( like transformers) should momentarily withstand 1.9 of nominal values. That is a common testing criteria for voltage, so the currents should go up also 1.9, considering U=ZI law. Of course that is top rated gear (hardest test) but you should generally pass with 1.7 rate because it is something that you can buy cheaper from todays manufacturers (Made IN CHINA and such junk) and for the short time overload (I.E. 1h ) it should be 1.3 ratio, because it is the overload factor to all standard electroenergetical equipment, although it is supposed to withstand 1.3 for more than 48h (permanent overload) It also depends on the area of engagement , and can be related to a country laws. So best check the current standards from the country you live in, in Europe standards are ussualy like above. For the frequency I dont know exsactly, but I think we tested some gear on 43 ~ 58 Hz In 50Hz netvork even such are extreme. So again from the area of engagement you might consider 48 ~ 53 Or such. Bigger failure resistivity range - more cash was always the rule.

 

[ausphil]

Firstly, if you are specifying a transformer of this size, don't ask a forum, you should be looking straight at a standard for the values (either local or international).

Secondly, from the sounds of it, you already have the manufacturer picked out, so they should be able to guide you in the selection of the test voltage.

Thirdly, you need to decide what BIL (or lightning impulse withstand level) you are going to specify, as this will decide the power frequency withstand voltage. There may be up to 4 different BIL levels for a particular system voltage, with 4 PFWV values respectively.

Fourthly, you need to know whether your HV winding is fully insulated, as this will restrict the PFWV test value.

But with no responsibility, the PFWV values in our area are:
11kV - 28kV for 1 minute.
161kV - (extrapolated) around 250 - 300kV for 1 minute (again, depending on BIL)

I re-iterate, don't hesitate to look at the standards, they are wonderful documents, and are a must when purchasing equipment in the cost range of a transformer of this size. I would expect that you have referred to them for numerous other parts of the specification, so you should be able to easily glean off the PFWV values quite easily - and if you haven't used the standard for the rest of it, then I suggest that the PFWV values are going to be the least of your concerns.