160MVA Load 3

[Danilo917]

Gents, given this kind of spot load, what system voltage arrangement should be used
to ensure power quality and reliability of the system? The available subtransmission
system in the area is 66kv ..the 230kv is 160km away from the proposed plant.

Appreciate your suggestions..

 

[dpc]

There is no way to answer this without a lot of additional information on the nature of the loads, capacity of the transmission system, power purchase rates, schedule, budget, reliability requirements, etc.

But 160 km of 66 kV line to serve 160 MVA doesn't sound too promising.

Think about bringing aboard a power engineer with experience in the area to assist. You're not going to get this resolved relying on free engineering advice over the Web.

 

[odlanor]

go to utility and get Minimum technical requirements for connection to transmission facilities

 

[wareagle]

Have you calculated the amperage at 66 kv and 220 kv. Looks like you need a generation plant in the back yard. At 220 kv calculate the VD at max load. Then decide what you need to do.

 

[Danilo917]

Thanks for you replies..i might as well get more details first and coordinate with the utility company in the area..

in the meantime,would you know the rule of thumb in designing the system using 66kv,say, max feeder lengths,max MVA load etc..A 66kv/22kv station transformer is the nearest available supply to this proposed load thats why I want to explore the possibilities of utilizing this voltage system if possible.

Any computation to prove that this 66kv is not feasible will be highly appreciated.

Thanks again

 

[FPelec]

Danilo,
160 MVA (which power factor?) is a very high power for 66 kV systems; IMHO it could be very difficult to safely transmit such power for 160 km. A possible approach to prove this is to consider the voltage stability limit; considering a reasonable X'l=0.3 Omh/km reactance of the line, the total reactance is Xl =0.3 x 160 =48 Ohm; the theoretical maximum power is Pmax =0.5 x V^2 / Xl = 45 MVA. Thus you need at least 4 circuits (and/or you should install series compensation, which is never used in 66kV subtransmission systems as far as I know): this seems reasonably unfeasible and anti-economical to me.
In my opinion the major issue is if the 66 kV subtransmission system can provide 160 MVA at the connection point, i.e. at 160 km away from your load.
If so, it is probable that the connection point is actually a trasforming station in which an higher voltage level is available.
Probably a 220 - 245 kV line is the most appropriate voltage level for such power and distance. Anymay I think that the cost of two eventual 160 MVA autotransformers (for instance 220/66kV)should easily be compensated by reduced lines cost.

Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[waross]

Consider the impedance of the transmission line and the voltage drop per mile at the anticipated loading. You may want to limit the maximum length at a given voltage to the amount of voltage drop that your OLTC can compensate.

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

 

[Danilo917]

Wareagle, at 66kv,the load current would be 1400A while at 220kv the load current would be 420A..Im considering also a generating plant to provide emergency power for the plant. this generating plant could be used also to satisfy an N-1 security level..ill see what VD this load current would bring in..

FPElec,thanks for your input... do you think an HVDC transmission would be economical for this project? What do you mean by reduced line cost that can be compensated?

regards

 

[FPelec]

Danilo,
my opinion is that for a 160 km - 160 MVA overhead line an HVDC solution will be not convenient for both investment cost and losses. This is also confirmed by utilities practice (there are no such small and short HVDC overhead line links in operation, as far as I know) Even a single circuit 220 kV line with single "curlew" conductors should have about 2.3% losses at 160 MW at 160 km; these losses are lower than the two converter stations losses only for a modern VSC-HVDC system (and then you have to consider also DC line losses); If you consider a double circuit, for N-1 compliance, losses drop to 1.1%.
As regards investment costs, for 160 km OHL, HVDC converter stations cost is equal or higher than line costs; you could easily find some $/MW and $/km cost estimates on technical literature.


Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[Danilo917]

FPelec,
If I could manage to bring down the distance to 80km by utilizing 220kv located halfway and transform this voltage to 66kv, given the same reactance of 0.3ohm/km,the Pmax would now be 90MVA..can you suggest what sort of transformer rating combination would be suitable to satisfy the 160MVA load and an N-1 security level? Im thinking of banking four (4) 45MVA but felt that this is a bit expensive proposition though. what do you think?

regards

 

[FPelec]

Danilo,
If you need those 160 MVA all in the same area (a factory, an industrial area?) in my opinion the best solution, from both the technical and economic point of view, is to deliver the power you need with 220 kV line(s) and then to install 220 kV transformers nearby the loads, choosing low voltage according to local practice (reasonably something between 33 and 15 kV). This would reduce transmission lines cost and losses and avoids installation of 220/66kV transformers, with their cost and reliability issues.
Even if the distance between the 220 kV network and the load is 80 km you should consider that maximum transmissible power is a theoretical value, corresponding to an unammisbile voltage drop (it is the limit for voltage collapse), so you have to provide a substantial safety margin.
In order to make a proper preliminary hypotesis you shall account for maximum voltage drop along the line (as waross said) and for reactive power absorption at connection point.
Just for a comparison, the practice in the utility I work for is to connect industrial loads and generating plants between 10 and 100 MVA on the 132kV or 150 kV network and those over100 MVA on the 220 or 400 kV network.

Si duri puer ingeni videtur,
preconem facias vel architectum.