The Western HVDC Link

interesting figures, 

2.2GW/600kV implies  a circulating current of ~3.7kA and a load impedance of  some 170 ohms.

Also given the length, 385 000 metres under water and another 50km or so on land,  to make voltage drop sensible at a few %, the round loop cable resistance can only be single figure ohms, so not exactly thin.

Certainly considerable potential for a loud bang if it all gets released at once.


I understand the HVDC conversion is line commutated thyristor stacks, so the positive or negative lead of the  DC from the line is connected to each outbound grid phase in turn by turning on the thyristors in that path at a carefully timed moment, and then the state of the mains cycle on the outbound side defines the 'off' as the  part of the cycle when the net current falls to zero - this switch off method is the reason for the description as  "line commutated".  It can only be used to add current at the right times to an already running grid, and cannot be used as an 'islanded' source of power, which also has implication for how easily you can start it. Wave form quality i.e. harmonic content is also  poor as the current waveform is very  non-sinusoidal, and problems with both radiated and conducted  RF interference from such sites can be significant.

In days of old such things could also be done with modified mercury arc devices, though since about 1970 the thyristor/SCR has become dominant.

The whole thing is some quite remarkable feat of engineering, so it is understandable that start-up is cautious.

interesting figures, 

2.2GW/600kV implies  a circulating current of ~3.7kA and a load impedance of  some 170 ohms.

Also given the length, 385 000 metres under water and another 50km or so on land,  to make voltage drop sensible at a few %, the round loop cable resistance can only be single figure ohms, so not exactly thin.

Certainly considerable potential for a loud bang if it all gets released at once.


I understand the HVDC conversion is line commutated thyristor stacks, so the positive or negative lead of the  DC from the line is connected to each outbound grid phase in turn by turning on the thyristors in that path at a carefully timed moment, and then the state of the mains cycle on the outbound side defines the 'off' as the  part of the cycle when the net current falls to zero - this switch off method is the reason for the description as  "line commutated".  It can only be used to add current at the right times to an already running grid, and cannot be used as an 'islanded' source of power, which also has implication for how easily you can start it. Wave form quality i.e. harmonic content is also  poor as the current waveform is very  non-sinusoidal, and problems with both radiated and conducted  RF interference from such sites can be significant.

In days of old such things could also be done with modified mercury arc devices, though since about 1970 the thyristor/SCR has become dominant.

The whole thing is some quite remarkable feat of engineering, so it is understandable that start-up is cautious.