×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Bus support spacing for high fault duty.

Bus support spacing for high fault duty.

Bus support spacing for high fault duty.

(OP)
I have been doing some initial calculations for the maximum bus support spacing for a 230 kv swithcyard.  the expected 3 phase sym fault duty is 70kA.  my calculations show the max spacing is 12 feet this is too close.  are there any suggestions of how to increase this and still be able to obtain an insulator with sufficient cantilever strength?
thank you

RE: Bus support spacing for high fault duty.

Increase phase spacing.  Use actual max anticipated fault current (if the 70kA is higher).  Use high strength insulators.  Use three-phase bus supports if the problem is with the steel instead of the insulators.

RE: Bus support spacing for high fault duty.

There was a paper trying to standardize practices by the AIEE which tabulated the recommended bus spacing up to 1175 kV BIL (1954). If you want, try searching for it on the Standard Handbook for Electrical Engineers - Substation Design chapter.

RE: Bus support spacing for high fault duty.

Revitup,

Since you have mentioned about cantilever strength of bus support insulators, in your post, I am raising this question.

Appreciate very much if you could explain what is meant by "UNDERHUNG CANTILEVER STRENGTH" for a post type or cap and pin type insualtors?

Thanks in advance

RE: Bus support spacing for high fault duty.

According to IEC 865  Fm3=miuo/2/pi()*sqrt(2)/2*ip3^2*lng/am where:
Fm3 is the maximum force acting on the central main conductor
ip3 is the peak value of the short-circuit current
lng is the maximum center-line distance between supports along the bus.
am is the effective distance between main conductors [between parallel buses]
am=a distance between coplanar main conductors center-line for single circular cross-section
Bending force on the supports:
Fd=Vf*Vr*alpha*Fm3
Vf =ratio of dynamic and static force on supports
Vr=ratio of stress for a main conductor with and without three-phase automatic reclosing
From table 2 maximum Vf*Vr for three-phase short-circuit is 2.7
alpha=factor for force on support -  for simple supports  [see table 3] =0.5
For a certain conductors and supports you may reduce lng [distance between supports along] or increase the am [distance between parallel buses] in order to reduce the bending force on the supports [as pointed out by jghrist]
 

RE: Bus support spacing for high fault duty.

(OP)
Appreciate very much if you could explain what is meant by "UNDERHUNG CANTILEVER STRENGTH" for a post type or cap and pin type insualtors?
this is the rated strength of a particular insulator when installed in the underhung position (the position that is supported from above and not below) typically the normal insstallation is supported from below
 

RE: Bus support spacing for high fault duty.

The cap and pin types [disc type, longrod type and other like these] doesn't have underhung cantilever strength but only post type or pin type has it.
The pin type does not take main transmission line strain (tension), and functions as a jumper line insulator.
So, only post type has underhung cantilever strength.
Line post insulators are cantilever support members, with ratings defined as follows:
Specified Cantilever Load (SCL) is the ultimate cantilever strength rating of the line post insulator. SCL is identical to the minimum average breaking load (ABL) rating in previous catalogs.
Reference Cantilever Load (RCL) represents the maximum recommended load in cantilever that a post insulator is designed to withstand during its life span. RCL equals 50 percent of the SCL, and is identical to the insulator's maximum working load (MWL) and maximum design cantilever load (MDCL).
For more information see:
http://www.pfisterer.com/download_download/d_6710.pdf
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources