Underground cable system- how many?

[mbrooke]

I am design evaluating an underground transmission system consisting of a 330kv loop. This loop will supply several bulk substations which in turn each will supply 110kv area substations. The load on each bulk substation is about 1000MVA max, and each area substation feeds about 180MVA of network load. Parts of the loop will carry approximately 3000MVA when all is said and done.


The question is, how many cables and of what size would you use? Fewer cables of higher ampacity or many cables of lower ampacity? I am thinking 6 circuits of 2 per phase 2000kcmil copper 362kv solid dielectric cables (grounded at both ends encased in concrete duct banks derated accordingly) from bulk substation to bulk substation and 4 145kv 1000kcmil solid dielectric cables between the bulk and each area substations.

Second- what contingency level should I design this for? I am currently thinking N-2 (2 circuits out) on both 330 and 110kv, as failures of underground cables take much more time to repair.

Third, though not really the scope of my question but still partly relevant- cable charging compensation shunt reactors should be placed on each cable bay or lumped and placed on the bus?

I have no reference to go by... I am open to any suggestions/critique. The substations will be GIS btw.

 

[Ingenieur]

not enough info
need to know:
single line
layout of system: lengths, geometry, etc.
sources supplying the system
ampacity is only 1 factor: fault/transient response, v drop, etc

you are going to duct bank 345 kv over long distances?
5000 A 345 kv lines

this is a very large and complex engineering project
I would envision a team of people working on this
https://www.nexans.com/Corporate/2013/60-500_kV_High_Voltage_full_BD2.pdf

 

[Ingenieur]

6 runs x 3 phase x 2/ph or 36 conductors, 12/ph???
that is an ampacity of roughly 15 ka or more depending on installation method
3 Gva / (345 kv x sqrt3) = 5000 A

 

[mbrooke]

not enough info
need to know:
single line

Picture a giant loop similar to this, 8 substations:


https://www.google.com/search?q=fra...CAEQBg&biw=1440&bih=725#imgrc=IgmViSV5RRjW4M:

layout of system: lengths, geometry, etc.
sources supplying the system
ampacity is only 1 factor: fault/transient response, v drop, etc

Sources are 2,200MW generation directly injected into the loop itself predominately south and 10 330kv lines, 4 into 2 of the 8 subs north of the loop and two into a sub at the south of the loop. The two at the south will probably have a phase angle regulator at first glance (guessing).

you are going to duct bank 345 kv over long distances?
5000 A 345 kv lines

Short to medium, the loop end to end is about 45 miles total. Duct bank for now, but may be in service tunnels if lucky.

645amps calculated in duct banks for 2000kcmil.

330 kv overhead lines feeding into the loop are rated 4000 amps LTE, 3,200 normal.

this is a very large and complex engineering project
I would envision a team of people working on this
https://www.nexans.com/Corporate/2013/60-500_kV_High_Voltage_full_BD2.pdf

More like an army. But any info is food for thought.

 

[mbrooke]

6 runs x 3 phase x 2/ph or 36 conductors, 12/ph???
that is an ampacity of roughly 15 ka or more depending on installation method
3 Gva / (345 kv x sqrt3) = 5000 A

3 phase- but yes- 36 conduits plus spares and fiber... racks in tunnels would be ideal.

 

[mbrooke]

Not to add more to the thread, but one thing that I've been told with a straight face is to seriously consider going to 500kv for the loop for the amount of power being run.

 

[Julius Right]

In our power stations -up to 700 MW units-are in pair connected to 400 kV overhead lines using only 2 feeders but 1.5 breakers per unit. One set of cables withstand both units load.
At 110 kV network the transformers are connected in pairs in a simple H scheme.
See ABB Switchgear Manual-11th revised edition.
vol. 11 chpt.11.1.2 Circuit configurations for high and medium voltage switchgear installations.

 

[Tony S]

A system as you suggest would normally be an “open ring” where the open points can be moved in the event of a fault. More switchgear is involved but it creates a versatile and robust system. The system is used extensively in the UK for 33kV & 11kV. The 33kV ring will normally be fed at several points by primary substations with HV connections, usually 132kV or 275kV.

Sometimes the ring is extended so in effect you have a figure 8. At the centre point of the 8 a switch will be open so the circuit is again a ring.

I’ve worked on them for companies with private MV networks.

 

[mbrooke]

A system as you suggest would normally be an “open ring” where the open points can be moved in the event of a fault. More switchgear is involved but it creates a versatile and robust system. The system is used extensively in the UK for 33kV & 11kV. The 33kV ring will normally be fed at several points by primary substations with HV connections, usually 132kV or 275kV.

Sometimes the ring is extended so in effect you have a figure 8. At the centre point of the 8 a switch will be open so the circuit is again a ring.

I’ve worked on them for companies with private MV networks.

Above 33kv it is customary to run everything normally closed. MHO step distance protection (usually 3 zones) and differential (SEL-311L/SEL-411L) is applied to such a setup making fault discrimination easy despite the closed nature if the circuit and varying generation infeed. However I would still be interested in what you know about ring systems- I remember once you posted a paper about it and it was very eye opening for me.

 

[mbrooke]

In our power stations -up to 700 MW units-are in pair connected to 400 kV overhead lines using only 2 feeders but 1.5 breakers per unit. One set of cables withstand both units load.
At 110 kV network the transformers are connected in pairs in a simple H scheme.
See ABB Switchgear Manual-11th revised edition.
vol. 11 chpt.11.1.2 Circuit configurations for high and medium voltage switchgear installations.

Thanks. Is this the correct edition?

https://www.scribd.com/doc/118169283/ABB-Switchgear-Manual-11th-Ed-2006

 

[mbrooke]

In our power stations -up to 700 MW units-are in pair connected to 400 kV overhead lines using only 2 feeders but 1.5 breakers per unit. One set of cables withstand both units load.
At 110 kV network the transformers are connected in pairs in a simple H scheme.
See ABB Switchgear Manual-11th revised edition.
vol. 11 chpt.11.1.2 Circuit configurations for high and medium voltage switchgear installations.

I also came across this, which I think is the same as ABB 11.1.2; at least in part:



http://electrical-engineering-portal.com/circuit-configurations-hv-mv-switchgear-installations

http://electrical-engineering-portal.com/outdoor-switchyard-layouts





H scheme bus at 110kv you mean 110 to MV?

 

[Julius Right]

What I have with me it is only 11th edition.
The last edition it is 12th edition.
http://new.abb.com/de/en/ueberuns/geschaeftsfelder/power-grids/switchgear-manual

 

[mbrooke]

What I have with me it is only 11th edition.
The last edition it is 12th edition.
http://new.abb.com/de/en/ueberuns/geschaeftsfelder/power-grids/switchgear-manual

$30? I can handle that

btw, I want to thank you for pointing me to this. Looking at the old version on the net, very informative regarding GIS and AIS.


Also found this too, nice info for its age.

https://translate.googleusercontent...700201&usg=ALkJrhiacIfTjb7PND_ipSTshKYfyZDwYw

 

[Ingenieur]

am I the only one that thinks designing a 345 kv xx GW transmission & distribution system with multiple prim/sec nodes using an internet knowledge base is a risky proposition and counter to good engineering practice?
this is a large undertaking and the system should be computer designed and modelled, not back of the napkin calcs
the SC/fault study alone is quite an undertaking
10's of millions of $'s, possibly more

 

[Julius Right]

I am sorry, Ingenieur. I don't think you need to design the cable run or circuit breakers assembly.
What you need to do is fill in a bid with as much detail as possible, choose bidders and specify what will be appropriate.
For instance, for a Steel Complex of 13 substations 110/10/6.3 kV 25-40 MVA transformer units and 3 steam turbines of 50-200 MVA-as back-up supply- a network of 40 km of 750 sqr.mm copper oil-filled paper insulated cable was required. The entire work was divided in 3 bids : one for Siemens, one for BICC and one for Pirelli. They did the design including structural details.
The substations and the indoor central station of 40 switchgears was local designed but the circuit breakers was 5000 MVA 1.5 kA [ a French company product]. The design company had three different electrical, structural and mechanical departments.

 

[mbrooke]

am I the only one that thinks designing a 345 kv xx GW transmission & distribution system with multiple prim/sec nodes using an internet knowledge base is a risky proposition and counter to good engineering practice?

This thread certainly won't be substitution for anything- rather general opinion/guidance. Everyone has to start somewhere.

this is a large undertaking and the system should be computer designed and modelled, not back of the napkin calcs

PTI PSS among others will be smoking the servers. Hand calcs would take years even in the hands of a skilled mathematicians. Load flows, thermal/voltage studies, transient stability, critical clearing, very fast transients in the GIS... just to name a few require extensive modeling.

the SC/fault study alone is quite an undertaking
10's of millions of $'s, possibly more

Well I'm getting 50.4ka worst case 330kv short circuits But thats where computers come in :thumbsup:

 

[Ingenieur]

I am sorry, Ingenieur. I don't think you need to design the cable run or circuit breakers assembly.
What you need to do is fill in a bid with as much detail as possible, choose bidders and specify what will be appropriate.
For instance, for a Steel Complex of 13 substations 110/10/6.3 kV 25-40 MVA transformer units and 3 steam turbines of 50-200 MVA-as back-up supply- a network of 40 km of 750 sqr.mm copper oil-filled paper insulated cable was required. The entire work was divided in 3 bids : one for Siemens, one for BICC and one for Pirelli. They did the design including structural details.
The substations and the indoor central station of 40 switchgears was local designed but the circuit breakers was 5000 MVA 1.5 kA [ a French company product]. The design company had three different electrical, structural and mechanical departments.

but he is tasked with the design
SOMEONE has to do the design
you can give a performance based spec and bid design/build
but it still needs engineered

he's talking xx GW range
a system like this would likely incorporate FACTS

this is not a one man job

 

[mbrooke]

he's talking xx GW range
a system like this would likely incorporate FACTS

It might, but hoping to avoid that.

 

[Ingenieur]

It might, but hoping to avoid that.

there may be advantages to using that technology
fault/transient suppression
harmonic attenuation
pf control
etc