LA in pad mounted distribution transformer 1

[simatic7]

hi
We are intending to replace all pole mounted transformer and over head distribution lines in a town with pad mounted transformer and underground cabling system. It will be done in a phase to phase basis . I mean like we build up underground cabling system and install new pad mounted transformers and uninstall the existing system.

Here my question is

while installing pole mounted distribution transformer, we install lightning arrester in every transformer location , but how frequently do we need to install LA (lightning arrester) in a pad mounted (kiosk type) transformer or we do not need at all except in specific place or we do install in every location of transformer.

I need the suggestion
regards

 

[magoo2]

It depends on the operating voltage. For 15 kV systems (ph-pf), an arrester at the riser pole is mostly used. For 25 and 35 kV systems, because of the voltage doubling at the open end and the BIL used, it is good practice to have an arrester at the open point as well as at the riser pole.

 

[prc]

Magoo2,What is meant by riser pole and open point?The practice you mentioned is in US ?

 

[simatic7]

Our main intention is to replace the pole top transformer and pole so we eliminate poles so we have only underground cables so why we need riser pole .

Dont we need arrester for switching transients ?
regards

 

[magoo2]

You need a surge arrester at the start (riser pole) of the underground cable and you may need another at the end of the cable (open point). From a surge standpoint, the transformer at the end is such a high impedance that you can consider it an open point where surges typically double in magnitude. They provide protection for the cable and for the transformer(s) for lightning and switching surges.

 

[UtilityGy]

Actually, I was involved in some thing similar few years ago, the project never went to construction but design was almost complete.

It was a trailer park where all O/H lines were tapped to new pad mounted transformers. All lateral tap had fusing (fuse cut-out with arrester). We ordered pad mounted transformers with L.A. It was a 8 kV application actually a very old system.

You can call any pad Dist XFMR manufacturer like moloney electric in Canada or Carter international in Winnipeg and they will be able to provide you some typical application input which certainly comes handy at times.

I am not sure where you are located but in Canada, ESA had input in our design and it was mandatory to do this.

 

[prc]

magoo2,This is an issue not clear to me.Let us consider a 11KV cable connecting between cable box of transmission end transformer to distribution panel board of a factory.There is no exposure for lightning surges to enter and transferred surges from Hv to 11 Kv secondary will be reduced by attenuation due to capacitance offered by the cable.In this case is it necessary to put a LA inside the cable box?