Cross Bonding Surge Arrestor

[carlossteiner]

I would like to know if there is a methot to determinate the kV of a cross bonding surge arrestor.

The standard method as used by NGTS in the UK is to select an arrester with a Ur of 1kV per 10kA RMS through fault current at the point of installation. So if the fault level is 40kA, then the rating of the CPA will be 4kV (Ur).

Does exist a more precise calculation? I can not fin it!

Thanks

 

[cuky2000]

The IEEE Std C.62.1, C62.2 & C62.22 could be a good source for sizing surge arresters.

The coefficient of grounding (COG) or the Earth Fault Factor (EFF), are useful in the determination of an arrester rating for a selected location and different method of grounding.
_{The COG is the ratio ELG/ELL, expressed as a percentage, of the highest root-mean-square line-to-ground power-frequency voltage ELG, on a sound phase, at a selected location, during a fault to ground affecting one or more phases to the line-to-line power-frequency voltage ELL which (that) would be obtained, at the selected location, with the fault removed.}

See if the enclosed guideline could be usefull

http://library.abb.com/GLOBAL/SCOT/...A75099E049A5EC1256D56004AA631/$File/2310E.pdf

 

[magoo2]

carlos,

Although the ABB reference looks OK, I don't think it addresses your concern.

When I think of cross bonding, I think of an underground cable system consisting of 3 single-phase cables. At each splice point, the decision on where to connect the sheath of each cable has to be decided. Do I go A to A', B to B', etc. for the sheaths? I'm talking about the sheaths of each cable, where the incoming cables are A, B & C and the outgoing cables are A', B' and C'.

In cross bonding, normally you roll the sheaths of each cable so the sheath of A goes to the sheath of B', sheath of B goes to C', etc.

Rolling the sheaths is really transposing the sheaths so the induced voltage becomes less than if you didn't. So if you had 2 splice points, you could minimize the total sheath voltage.

Please clarify this since cuky's response is going in a different direction.

 

[carlossteiner]

Magoo2,

What cuky2000 is traing to explain is ok, but I think it is for the selection of surge arresters. I am attaching a a file from my librarie.

About cross bonding, what you are writting is right, but usualy in those points the cable sheath is grounded through a surge arrester. It is this what I need to know, how to determinate this MCOV and In for this surge arrestor.

 

[magoo2]

There is some info in CIGRE WG B1.18, Technical Bulletin TB283. They have a section on surge voltage limiters (SVLs) which is what you're asking about.

Also, IEEE 575 was a 1987 guide for application of sheath bondng methods . . . This has not been revised by IEEE.

 

[carlossteiner]

5.7 Cable sheath protection of high-voltage cables
For thermal reasons and to reduce losses along a cable, the cable sheath or screen of highvoltage
single-core cables is mostly earthed at one end only. The unearthed end must then be
protected with arresters against transient overvoltages.
The critical selection criterion for the arrester is the voltage Ui induced along the cable in the
event of a short circuit. This voltage depends on cable geometry and how it layed in the cable
duct, but it generally does not exceed 0.3 kV per kA short-circuit current and km cable length.

The operating point derived from the magnitude of the induced voltage Ui and the time interval
t before the short-circuit current is switched off, must lie below the temporary overvoltage
characteristic to ensure that the right arrester is being used.
Figure: Induced voltage ui in the cable sheath or screen per kA short-circuit current and km
cable length depending on the geometry
for arresters between sheath or screen and
earth
where Ik is the max. short-circuit current and L the length of the unearthed cable section.

The Complete documentation in:
CIGRE document referred to is WG 21-07 Electra 28 May 1973 so the principles are well established

 

[cuky2000]

Enclosed are examples of an electrical schematic and a picture with a sheath link box with a set of sheat voltage limiter (SVL

 

[carlossteiner]

The Images you post are from a TYCO ELECTRONICS Presentation.
Well Thanks every body for your help!

 

[cuky2000]

The images also are free of charge