Fault levels

[jan63]

I am working in power station where the switchyard was built in 1977.
Due to expanding network the new fault level calculated over the next few years is 63 kA(old 30 kA).
We have started replacement of equipment like breakers,disconnect,lightning arrestors etc.
The question is do we need to replace the concrete foundations for these equipment.
The old one in my opinion(since Air blast circuit breakers were installed) will with stand the new equipment(SF6 breakers being much lighter).
Does fault levels have direct affect on foundations.

 

[GroovyGuy]

Hey Jan,
You are likely correct, the new SF6 CBs are lighter than the older air-blast CBs. My biggest concern would be what about seismic requirements? Codes have changed a lot over the last 40 years. I would recommend that you need to consider this, more so if the substation is located in a high seismic area.
GG
ps Fault levels do not directly affect foundations

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[jan63]

Ok thanks.That is what I thought

 

[davidbeach]

The foundation for a breaker is unlikely to be affected by fault current levels, but the foundations of the bus supports could be affected. The increased fault level increases the forces on the bus bars during a fault. Depending on where you are, the seismic forces may exceed the fault forces, but in 1977 the design might not have adequately addressed the seismic forces.

 

[cuky2000]

Jan 63, If the existing substation bus support structures is designed with three insulators in the same bus structure, the increase in SC will not significant impact the existing foundation. However, the cantilever strength of post insulators need to be revisited and most likely need to be upgraded.

There is a good chance to reuse the old air blast breaker foundation if there is opportunity to use dead-tank circuit breakers with the three poles mounted on a steel beam anchored on the existing foundations.

I am not sure if the surge arresters and PT's (or CVTs) will be impacted by increase of the SC. CT's ratio for 63kA application need to be revisited to avoid core saturation.

Beware that the existing substation ground grid will heavily impacted by increasing SC.

Will be helpful to know the system voltage and the detail of the bus layout to provide better suggestions in this matter.

 

[jan63]

Ok thank you all.
As fas as bus bar arrangement is concerned we have 220kV and 500kV bus bar interconnected through auto transformers.Breakers are in breaker and a half scheme.
We are replacing the 220kV breakers,CT's,Disconnecctors and bus bar but the foundations have been checked and will be reused. For500kV lightning arrestors and CCVT are also being replaced.The problem is only the 500kV civil foundations..My opinion is it need not be replaced

 

[bacon4life]

We always have a civil engineer run calculations to see if the old foundations can be reused under modern seismic codes. In many cases the breaker foundations were OK, but few have had to be replaced.