Short circuit forces on end-span droppers

[NoFaultRequired]

Hello there,

I've been working with electrical subestations design for a while and this question has been with me throughout the journey.

Here in Brazil it's quite common to have end-span droppers that look like the picture below.

I've never seen an equation or a method to deal with these kind of situation when calculating short circuit forces, I have already asked various engineers here in Brazil that work with this subject but no answer has satisfied me, most companies utilise some kind of approximation or adaption to do the calculation or just don't do it at all.

I wonder if someone with experience in subestation design has seen some kind of method or equation to calculate the forces, here we use the IEC and CIGRÈ standards, but none of them cover this kind of situation (CIGRÈ Brochure covers one very specific type of dropper, but it's not the case here).

Best regards.

Thiago.

 

[jghrist]

IEEE 605-2008, IEEE Guide for Bus Design in Air Insulated Substations, has methods for calculating forces on bus.

 

[bacon4life]

The 1998 version of IEEE 605 had only covered rigid bus. Good to know the scope of the 2008 revision was changed to include strain bus.

 

[7anoter4]

I cannot find in IEEE 605-2008 any calculation method for your droppers. How ever in chapter Annex G Calculation example of short circuit analysis on strain bus system, is here a reference to CIGRE “The Mechanical Effects of Short-Circuit Currents in Open Air Substations, CIGRE WG 02 of SC 23, 1987”.Here is a calculation on some droppers in chpt.3.3. THE DROPPER BEHAVIOUR.
By the way, I was not involved directly with substation calculation, but my colleagues got calculation method from the equipment manufacturer [Siemens for instance].
Also I collaborate once with design companies [as for instance Seargent &Lundy-20 years ago.

 

[NoFaultRequired]

Hey guys,

@jghrist actually, there's nothing directed towards the calcultaion on droppers per this standard and as it seems, this IEEE standard based most of the short circuit calculations on the CIGRÉ standard (Brochure nº 214).

@bacon4life yeah, it was a great improvement!

@7anoter4 infortunately the chpt 3.3 of the CIGRÉ Brochure covers only a very specific dropper configuration that's not really applicable when it comes to higher voltage substations (over 230 kV), beacuse the equation is only valid for a certain geometric relation within the dropper configuration, as you can see in the image below.
I'll check with SIEMENS personnel if they have some kind of advice on this topic.

Thanks for the kind answers guys!

Best regards.

Thiago

 

[stevenal]

Nothing magic about droppers, use the strain bus calculations. This is current based. Voltage doesn't enter into it except for insulator size and conductor spacing.