Transmission Line power Ratings.

Anyone know why or what the mechanism is that causes large power transmission lines to differant power carrying capacities depending on which way the power is flowing. Was reading some Nemmco reports regarding the power outages of the last few days and discovered that the main power interconnector between Victoria and SA is rated at 500 MW in the direction of SA >

VIC but only 160 MW Vic > SA. Others are similar, VIc > NSW is more than NSW to VIC over the same power line. I would have thought that wires dont care about direction.

Reply to
Mauried
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Is the report referring to the capacity of the networks to supply one another rather than the capacity of the transmission lines themselves perhaps?

Reply to
K Ludger

Obviously you don't know any audiophiles then! :-)

Reply to
Bob Parker

On an AC power system, the power transmitted down a long (several

100kms) transmission line (or series of lines) is limited by system stability, not the thermal rating of the line. The real power transmitted down an AC transmission line depends on the phase difference between each end of the transmission line. It is important to keep the phase angle across the whole network less than 90 degrees, or instability can occur.

The phase angle can be reduced by capacitors / static compensators etc. These might only be present at one end of the line. This is why the line has an unsymmetrical power transfer. Also different generators can cope with higher reactive power.

High voltage DC power transmission is now often used, as this does not have the stability issues AC transmission has (an also allows systems with different frequencies to be connected).

David

Reply to
David

The Basslink cable between Vic and Tas runs at 400kV DC. More figures are at

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Reply to
Bob Parker

The cable itself can physically carry the same in either direction, its whats at the end that counts, or different state laws/standards on what can be sent / received ?

Generator might not be sufficient at one end to supply the local and remote loads, but in the reverse situation the generator is adequate. same with the switchgear at one end to handle the function, compared to the other.

I doubt its likely - but its maybe possible that it depends where it enters the system, it might run directly from a power station at end A and straight TO a substantial LOAD at end B, (meaning full power can be sent straight to the load at B from station A if available) before it can get to the power station at end B The power station at end B. (on the other side of the load - and the load can't be switched out, and the wire through it isnt capable of carrying power to both the load it passes through and the load at end A

IE:

LOAD A

Reply to
kreed

wires don't but if it's a DC line the inverters at each end may differ in capacity (or even presence).

Reply to
Jasen Betts

Thanks for the responses. In this case its AC , and its the actual power line and the sub station equipment at each end of the line thats the problem, not the generating capacity. When the line was first built it was 500 MW in both directions , but has been slowly derated over the years but in only the one direction. Thats what seemed bizzarre.

Reply to
Mauried

These systems are always complex, a lot more than a single transformer at each end and a piece of wire. You're likely to find a number of parallelled feeds/loads at each end, with different abilities to supply or absorb, and different conditions outside that, such as protection settings and load characteristics. If you want to extend that to conspiracy theories, there are plenty of technical factors that a commercial supplier can invoke of they want to constrain the power they deliver for 'other' reasons, such as getting more dough by selling it somewhere else.

Reply to
Bruce Varley

It's probably politics and big-business at play then. Just like the California power crisis

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Dave.

Reply to
David L. Jones

They used Monster cable ?

Graham

Reply to
Eeyore

Another advantage of HV DC transmission is that there's no peak voltage to worry about. I can't find it now (it was on Wikipedia) but for part of the Itaipu dam output, something like 700kV is used. It also generates 50 and 60 Hz via multiple separate turbines.

Interesting economics here.... "The final cost of ITAIPU amounts to US$ 20 billion, 50% of this value are direct investments and balance financial charges.

If whole area of the lake - at nominal level - would be covered by solar modules the power of the would be 135 000 MWp, which would produce 230 TWh a year. For the same yearly output as ITAIPU a solar PV-plant would cost US$

132 billion."

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Also

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Graham

Reply to
Eeyore

It might not be a limit so much as a constraint. One issue is what happens to the system if the line trips out. If 500MW were being supply to SA over the line and it were to trip, that would mean SA suddenly lost 17% of of its power (at peak time today). This may be more than the system could handle. Since Victoria uses much more power, a loss of

500MW would not be so significant.

Sylvia.

Reply to
Sylvia Else

**One huge advantage of HVDC transmission is that there is no loss due to capacitance, inductance nor skin effect. It is brilliant for very long distance transmission, or, in the case of Basslink, undersea use. The usual losses in DC transmission are approximately 3% per 1,000km.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

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