Substation Insulator Strings 8

[luiscunha1978]

Hello!

My name is Luis. I've not any electrical background. I work in an engineering company (in the drawing area). Not long ago I saw some drawings of a Substation and I was curious to realize the following components:

I someone could explain my questions I'll be very happy.

Luis

 

[itsmoked]

I suspect it would be a spark gap that hopes to provide a path to earth-ground during over voltage events like a lightning strike. That distance between the two bends would be a pretty accurate voltage regulator in that it would arc at a pretty specific over-voltage. The insulator itself is a fairly lousy 'regulator' as its stand off voltage will vary greatly based on age, dirt, and moisture.

Cool drawing, thanks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[luiscunha1978]

Hi Keith! Thanks for the answer and the kindness. But I still have not noticed something ... in this drawing ... in normal operation, without over-voltages, on the substation side the voltage is 400kV?

I'm sorry if the question is stupid, but I do not understand anything about this area.

Thank you,
Luis

 

[waross]

That end of the string is at zero volts.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[luiscunha1978]

Hi Waross! Thank you but I did not understand very well ... I'm sorry ... I must be very stupid

The point A is at 400kV
The point B is at 0 volts

It's that?

 

[Mbrooke]

Point A is 230kv, point B zero volts.

 

[luiscunha1978]

Hi Mbrooke!Thank you for the answer...but why point A is 230kV and not 400kV?

 

[Skogsgurra]

You just complicated things a bit for mr luiscunha1978

It is true, of course. But I think that we need to add that L-GND on a 400 V system is 230 kV.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

kV..

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[luiscunha1978]

Hi Mr. Gunnar. For a layman like me and in order to realize that... at point A will have 400kV and at point B will have 0V. It is that? Thank you in advanced. My best regards.

 

[Skogsgurra]

No, it is 230 kV, actually. Just as Mbrooke said.

You need to understand that the 400 kV are measured between the phases (lines) in a three-phase system while the voltage across the insulator string is 400 kV divided into square root of three. That results in 230 kV across the string. Same as in a houshold system - only at a different level. Usually 400 V and 230 V.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Mbrooke]

230kv line to ground, in most 3 phase systems voltage is higher between phases then it is to everything grounded.

 

[luiscunha1978]

Please. Do not get into a discussion because of my questions and doubts. My intention is try to understand and thank you both. I think this is a fascinating area. From what I realized it is wrong to say that in a three-phase system a conductor has 400kV, because that is the measure between conductors. If you "look" at only one phase, the reference point will be the ground.

 

[Mbrooke]

In terms of insulators the reference point is usually ground- you are only holding back the voltage from one phase to ground. This is the phase to phase value divided by 1.73.


So on a 500kv line, the phase to ground voltage is 288kv.


1.73 comes from the square root of 3. Just how the math works out.

 

[luiscunha1978]

Thank you Mbrooke! I think in getting there thank you for your time and patience.

 

[waross]

It depends:
If by 400 kV you mean 400 kV to ground then the voltage is 400 kV.
If by 400 kV you mean a 400 kV system, then the voltage to ground is 230 kV.
And,
If the transmission system is DC then the voltage to ground for a 400 kV system will be 200 kV.
I can look over either shoulder and see, about a mile away, a 500 kV DC transmission line.
The end of the insulator attached to the tower should always be at zero Volts. If it is more than zero Volts then something has gone very seriously wrong.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Mbrooke]

@luiscunha1978- ask what you need- don't hold back. I'm willing to answer any and all questions you may have. It is a pleasure

 

[itsmoked]

Bill, why would a 400kV DC system result in 200kV to earth?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[xnuke]

Keith, I'm guessing Bill was referring to a bipolar HVDC system since that is the type most in use today, and if so, he's correct.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[itsmoked]

Hi X; Hmmm. Bipolar. So +200kV and -200kV on parallel conductors and they call that 400kV?

Keith Cress
kcress -

http://www.flaminsystems.com