13.8kv switch panel (2 in 13.8kv feeders + 1 out 13.8/0.4kv tr)

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m sleem

m sleem

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I have a Switch panel which supplied by #2 feeders from #2 sections of the same 13.8kv switchgear in order to have a redundant power supply n+1, currently i am in the design stage and the proposal to have #3 vacuum circuit breaker inside the switch panel,

The question is, can i replace the #2 VCBs (Vacuum circuit breakers) which are receiving the two supplies by #2 LBSs (load break switches) in order to reduce the cost while keeping the VCB for the outgoing feeder?
 
Tony S said:
Sounds like the ideal situation for a ring main unit.
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Exactly, but most of forum members don’t know the meaning of RMU that’s why I am not using it, perhaps you know because you’re in UK.
 
RMU’s are used all over the UK urban MV distribution systems. In the event of a cable fault by using the flexible nature of the ring system a section can be isolated allowing the rest of the system to carry on regardless.

They are an “open” ring, you never have two primary substation in parallel.
 
Tony S said:
RMU’s are used all over the UK urban MV distribution systems. In the event of a cable fault by using the flexible nature of the ring system a section can be isolated allowing the rest of the system to carry on regardless.

They are an “open” ring, you never have two primary substation in parallel.
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Sometimes also in the US, but refereed to as "loops". Its not uncommon for padmounts to have selector switching and a ring to be run through multiple pads with the "middle" pad being the N.O. point. See page 17 (10 in the viewer)


https://www.google.com/url?sa=t&rct...=TB01909001E&usg=AOvVaw0PsWldpSR5CF8T9fxNBq33


Often the ring is fed from a fused PME or PMH pad which has source selection on it. (two switch ways plus 2 fuse ways)
 
Ingenieur said:
will the lbs's be electrically interlocked with the vcb to prevent opening them under load?
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As I said in an earlier post, the switches are fault make / load break. Because of this they have anti reflex operating handles. You can’t suddenly change you’re mind if you close on to a fault, you leave it to the primary substations protection to clear the fault.
 
mbrooke said:
Sometimes also in the US, but refereed to as "loops". Its not uncommon for padmounts to have selector switching and a ring to be run through multiple pads with the "middle" pad being the N.O. point. See page 17 (10 in the viewer)


https://www.google.com/url?sa=t&rct...=TB01909001E&usg=AOvVaw0PsWldpSR5CF8T9fxNBq33


Often the ring is fed from a fused PME or PMH pad which has source selection on it. (two switch ways plus 2 fuse ways)
Click to expand...
With N.O point in the ring, it becomes a radial system and a consumer may lose power for any upstrem fault until change over is done. In a true ring system, it may not happen.
 
Sahib said:
With N.O point in the ring, it becomes a radial system and a consumer may lose power for any upstrem fault until change over is done. In a true ring system, it may not happen.
Click to expand...



That is 100% correct, however the OP would need breakers instead of switches in addition to more advanced relaying such differential, directional over current or step distance. Also that will increase the fault current, and the POCO may forbid it in that they now will have back feed from another feeder which can mess up their own relaying. Further in some cases it can not be done in that the phase angles are to great or simply out of sync with the other feeder.
 
mbrooke said:
That is 100% correct, however the OP would need breakers instead of switches in addition to more advanced relaying such differential, directional over current or step distance. Also that will increase the fault current, and the POCO may forbid it in that they now will have back feed from another feeder which can mess up their own relaying. Further in some cases it can not be done in that the phase angles are to great or simply out of sync with the other feeder.
Click to expand...
In secondary/ primary loop system also, the tie breaker is sometimes operated closed resulting in a ring. It leads to no power loss to a consumer for faults in the loop.
 
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