HV Substation Bus Dampening Conductors

[patrick7]

Well here we go! I hope that this discussion will spark some interest and benefitial information exchange. I am in the process of writing a new standard for our company. The new standard deals with dampening cable inside horizontal Al. bus in electric substations.

First off here is a list of the current sizes that we have as min. diameter.
bus size min size of acsr
2 266.8
2.5 266.8
3 266.8
3.5 397.5
4 795
5 1431
6 1590


There are several questions that come up. Your professional opinions and career experiences will be of great help.

First, Do we have to use ACSR? Or will AAC work?
What about the newer conductors available ACCC?

Second, Are the above min. sizes ok? and what is the max.
size?

Third, Is the dampening characteristic of the conductor
within the bus a function of the size ie the cross
sectional area, or weight of the conductor or both?

Fourth, How long is the max bus length that does not
require dampening?

Thank you for all your input and help.

 

[jghrist]

I believe that some of your answers can be found in ANSI/IEEE Std 605-1987, IEEE guide for design of substation rigid-bus structures. If you are writing standards for your company about rigid bus, you need to have a copy of this standard in any case.

 

[jtkirb]

First, Do we have to use ACSR? Or will AAC work?
What about the newer conductors available ACCC?

I don't think I would use ACSR. We use AAC

Second, Are the above min. sizes ok? and what is the max.
size?

Those sizes seem very large.

Third, Is the dampening characteristic of the conductor
within the bus a function of the size ie the cross
sectional area, or weight of the conductor or both?

Since it is INSIDE the bus, it has to do with weight and the damping effect. A lot of times the smaller wire will jump inside the bus helping damp the bus. Heavy ACSR that doesn't move may amplify the bus shake.

Fourth, How long is the max bus length that does not
require dampening?

We use it with any span over 10'.

JTK

 

[cuky2000]

1- Do we have to use ACSR, AAC or ACCC? To reduce bus vibration, any material will help to reduce the vibration. However, dissimilar materialhelps. However, to avoid galvanic corrosion disimiles materials should not be used.

2- Are the above min. sizes ok? What is the maximum size? Economics ussually is the limiting factor for the miximum size. In general, the IEEE Std 605 suggests a range as follow:
[blue]10% < conductor/bus weight < 33%. [/blue]
[sub]NOTE: The standard also recognizes that less cable may be sufficient in some cases to reduce the vibration to acceptable levels.[/sub]

3- Is the dampening characteristic of the conductor within the bus a function of the size i.e. the cross sectional area, or weight of the conductor or both? The natural frequency of the bus & cable combined is direct proportional to the moment of inertia of the cross sectional area and inversely proportional to the mass per unit length. There are other factors such as bus span length and type of support (fixed or pinned end).

4- How long is the max bus length that does not require dampening? Two criteria are suggested by the standard to determine the maximum length base in the bus natural frequency, system and aeolian frequencies as follow:

1) f[sub]natural[/sub]> f[sub]system[/sub] ==> Bus span should be changed or detail dynamic analysis is required to determine level of stresses.

2) f[sub]natural[/sub]> f[sub]aeolian[/sub]/2 ==> Bus span should be changed or dampening is required.

 

[patrick7]

Doesn't the standard call for dampening is the natural freq is less than twice the aeolian freq?

 

[cuky2000]

Is the same as note above in answer 4.2:

f[sub]natural[/sub]> f[sub]aeolian[/sub]/2 or
2f[sub]natural[/sub]> f[sub]aeolian[/sub]
==> Bus span should be changed or dampening is required.

 

[jghrist]

standard call for dampening is the natural freq is less than twice the aeolian freq

is not the same as

f[sub]natural[/sub]> f[sub]aeolian[/sub]/2==> Bus span should be changed or dampening is required.

but the latter is correct.