Bass Link HV DC?

DC has less transmission losses than AC since the capacitive and inductive losses for AC are quite significant at these voltages.

Cheers, Nicholas Sherlock

My understanding was that AC was used in transmission because there were lower % line losses at HV, and that it was of course easier to step up / down.

What sort of rectifiers / inverters are they going to be using at each end??? What sort of efficiency can they expect? What sort of losses will the cable have?

I thought I heard that overall only 25% efficiency. Might be wrong on that one. But even at 50% efficiency one would have to question the viability...

Intrigued.

A 300km long submarine cable would not work at all with 50Hz AC, the charging current would actually exceed the capacity of the cable. So therefore DC is the only way it can work. DC is mainly used for underground lines longer than 50km and AC lines longer than say 500km with no t-offs.

DC is much more efficient in transmission lines, its just more difficult to change voltage levels. HVDC transmission lines themselves are also cheaper to build per km than an equivalent HV AC transmission line. The catch is at the converter stations - these are very expensive.

At the end of the day the determining factor for how and why things are built the way they are is overall cost.

Other advantaes of DC links are: The systems at each end dont need to be synchronised The amount of power transferred through the line is easily controlled A DC link does not increase the fault levels of the system

The converter stations are made of massive series-parralell banks of thyristors, theres a fair bit of information on the net about these.

DC transmission links are in use in Australia connecting SA and VIC - Murry Link and think there is one between QLD and NSW, that may only an assynchronous tie in.

Cheers

An under sea HV, 50 Hz cable has capacitance to the a metal sheath over the conductor and insulation.

Just as a guess, imagine that capacitance were kept to a MERE * 33.3 pF * per meter.

Then, for 300km, the total C = 10 uF.

Now, Xc = 1 / ( 2.pi.50.10 exp-6 ) = 318 ohms.

Say the cable was designed to operate at 300 KVAC and 1000 amps = 300 MW.

The current flow due to C alone would be 300 exp3 / 318 = 943 amps.

Big problem.

........... Phil

AC has higher transmission loss, skin effect, capacitative and inductive losses, it has lower voltage-conversion loss.

yeah for short runs the energy lost converting to HV DC and back to AC isn't compensated for by transmission efficiency gains.

it gives frequency isolation between the power grids which may be an advantage in some circumstances

Bye. Jasen

so it's a characteristic impedance issue?

AC? do you mean Aerial ?

Bye. Jasen

Interesting stuff - thanks for the info.

Cheers for the detail Phil.

OK,

just for the exercise, what would be the typical capacitance / meter for shielded HVDC cable?

And thx to everyone for your answers. Learn a little every day...

Bryan

"Bazil"

......... Phil