Rigid bus calculation supported by underhung insulator 1

[Raj Adrika]

I have to design 34.5 kv rigid bus system which would be supported by underhung insulator ( insulator would be mounted at ceiling)and there would be AL pipe bus at other end of the insulator. I am wondering to calculate span length it would be same calculation as per IEEE 605? Since it would be indoor so should I only consider gravitation and short circuit force or ss there any other consideration I should consider?

I have also bus system which is going from ground level to ceiling using wall (vertical bus system). Is there any guideline or standard how to calculate span length in this scenario.

 

[dik]

Can you provide a x-section showing the size and proposed connection? Depending on the environment... I've been involved with some mining operatons and there may be 1' of 'rock powder' on the 'tray'.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[HTURKAK]

If indoor, no wind , no snow and ice loading .. May be seismic should be considered together with gravity and short circuit?
May be better to look Substation Structure Design Guide ASCE Manuals Engineering Practice No. 113 .

 

[dauwerda]

I imagine short circuit would govern for the allowable bus span over wind or seismic anyway as that voltage tends to have close phase-phase bus spacings and large fault currents. Other factors will probably come into play as well, such as simply utilizing the best support locations inside the building for the bus i.e. The supports will be spaced closer than otherwise necessary simply for ease of installation or placement.

 

[Raj Adrika]

Is there any calculations method to determine the span length? Would it be same calculation as per IEEE 605? How to determine span length the bus going up using vertical wall( please see attached photo).

I would appreciate if anyone could give some advise.

 

[desertfox]

Hi Raj Adrika

Well here is a link to a site that might help with your span calculation:-

http://copperalliance.org.uk/uploads/2018/03/section-4-0-short-circuit-effects.pdf

I assume that all the electrical clearance’s to earth etc have already been met.


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[vmjr24]

I've found that the strength of the insulators, rather than the strength of the bus, generally govern span lengths. Find your short circuit force from IEEE 605 as a distributed load and then calculate the force acting laterally at the insulator. Insulator manufacturers provide allowable cantilever strengths which can be compared to the force you calculate. I believe ASCE 113 allows you to use 50 to 60% of the manufacturer's published cantilever strength depending on if it is a porcelain or polymer insulator.