NCEES 103

[kris7o2]

Hi everyone, does anyone know what the drawing would like for this problem? I am not certain I understand if I completely understand how the surge look.

An industrial plant is served by a 12,470-V M480-V grounded-wye transformer. The high voltage side of the transformer is served from a 12,470-V wye-connected distribution line that has a grounded neutral. The best protection of the transformer against lightning strikes on the 12,470-V line will result from surge arrester connections of:
(A) phase to ground on the 12,470-V side of the transformer
(B) phase to phase on the 12,470-V side of the transformer
(C) phase to ground on the 480-V side of the transformer
(D) phase to neutral to ground on the 480-V side of the transformer

 

[akyip]

Attached are my notes about how surge protective devices (SPDs) work, from the Engineer Pro Guides final exam (practice exam) that I previously studied from.

Basically, an SPD is connected in parallel of and in front of the load to be protected. When I say in front of, I mean from the reference of the source. The SPD is connected between the phase line and the ground and/or neutral (depending on the SPD type or mode). The point of the SPD is to divert large currents from transients or surges (e.g. lightning strike) to ground, before these large currents reach the load.

Hope this helps.

 

[kris7o2]

Thank you Aykip. Also, I downloaded the image and can interpolate your message above to the download. The forum, I believe does not give me the ability to download a higher resolution image that I can zoom in and look at. If you are able to re-upload as two images I would appreciate it, but if you don't I can still pretty much read this. Thanks

Oh, and also do you know why the answer makes the assumption "the high side of the transformer is connected delta (ungrounded)"
Do we always assume a delta transformer is ungrounded, and does it make a difference if the delta was grounded?

 

[alex93]

SPDs and surge arresters are actually 2 different "devices". According to the NEC, SPDs are only for applications of 1000V or less. Over 1000V is a surge arrester. (NEC Articles 280 & 285). Since the problem states that it is looking for a device on the high side of the transformer then a surge arrester would have to be used. Surge arresters are connected phase to ground to divert all that current.

 

[kris7o2]

Hi Aykip, would it be possible to repost your image broken up into two images? If you can do this it would be a big help!

 

[akyip]

Hi Aykip, would it be possible to repost your image broken up into two images? If you can do this it would be a big help!

See the attachments.

 

[osh1397]

Hi everyone, does anyone know what the drawing would like for this problem? I am not certain I understand if I completely understand how the surge look.

An industrial plant is served by a 12,470-V M480-V grounded-wye transformer. The high voltage side of the transformer is served from a 12,470-V wye-connected distribution line that has a grounded neutral. The best protection of the transformer against lightning strikes on the 12,470-V line will result from surge arrester connections of:
(A) phase to ground on the 12,470-V side of the transformer
(B) phase to phase on the 12,470-V side of the transformer
(C) phase to ground on the 480-V side of the transformer
(D) phase to neutral to ground on the 480-V side of the transformer

 

[osh1397]

Source:

Practical Grounding, Bonding, Shielding and Surge Protection

G. Vijayaraghavan

Newnes An imprint of Elsevier

2004

ISBN 0 7506 6399 5