Transformer Elbow Surge Arrester

[EE_Intern_2]

I am having a difficult time in determining how to select an elbow surge arrester for a 12470V Delta to 208V Wye pad mounted transformer.

I have read that you need the MCOV of the arrester to be above the maximum line-to-ground voltage (including the 10% regulation error), so the arrester needs to be over 7.57KV MCOV .

Then I read that the maximum line-to-ground voltage can be increased by a factor of 1.73 in unfaulted phases when there is a phase to ground fault in the system, so the arrester needs to be desgned for 13.1KV MCOV.

When I look at the IEEE MCOV suggested ratings tables, the "delta systems" column for 12470 nominal line to line voltage is blank?
Some soruces recommended a 9KV surge arrester (MCOV was above max line to ground), while others recommended 18KV surge arrester (MCOV was above max line to ground during a fault).

Can someone please tell me which size surge arrester is correct for my setup 12470 delta-to- 208 wye.

why is the delta column blank in the IEEE MCOV suggested ratings tables? Isn't the surge arrester connected to the primary side of the transformer, which is delta configuration?

Thanks in advance for the information.

 

[beanland]

Manufacturer Literature

Manufacturer Literature

I suggest you look at the CooperPower, OhioBrass, or Elastimold arrester literature for guidance on the proper selection of an arrester. For 12470Y7200V solidly grounded system, they recommend a 9kV or 10kV rated (7.65kV MCOV or 8.4kV MCOV) arrester. If the supply is resistance grounded or ungrounded, different values are needed. General rule: manufacturers determine what the correct application of their equipment will be. Use of equipment against manufacturer recommendations is not wise. So, call the local sales rep of visit the manufacturer websites.