Neat - submarine cable power system

[electrofelon]

This is how the repeaters in submarine fiber optic cables are powered (From wikipedia):

Repeaters are powered by a constant direct current passed down the conductor near the centre of the cable, so all repeaters in a cable are in series. Power feed equipment is installed at the terminal stations. Typically both ends share the current generation with one end providing a positive voltage and the other a negative voltage. A virtual earth point exists roughly half way along the cable under normal operation. The amplifiers or repeaters derive their power from the potential difference drop across them.


So if I understand this correctly, station A has a dc power source with the positive connected to the cable's power conductor, and the negative connected to a good earth ground. Station B has the negative connected to the cable's power conductor and the positive connected to earth ground. I wonder how much potential they typically use? Think they drive a ground rod in the middle of the atlantic at that neutral point

 

[nakulak]

forget ground, think difference of potential

 

[electrofelon]

I think the earth interconnects the electrical systems from both stations. Otherwise we would have a violation of kirchoffs laws. I believe they are saying that there is only one power conductor in the cable.

 

[steve66]

I think the earth interconnects the electrical systems from both stations. Otherwise we would have a violation of kirchoffs laws. I believe they are saying that there is only one power conductor in the cable.

That's what it looks like to me. Since all the power supplies are in series, they don't have to drive gound rods in the middle of the alantic, just on each end of the run.

Steve

 

[jrannis]

Anybody ever wire airport runway lighting? All of the transformers are in series.

 

[mdshunk]

Anybody ever wire airport runway lighting? All of the transformers are in series.

I did a helicopter landing pad, and it was that way. Constant current arrangement. They do that for "brightness control" to suit the lighting and visibility conditions.

 

[dbuckley]

Yes, with submarine cables all the repeaters are in series, there is a power supply at each end, and the supply stations use a ground network as the return conductor.

The voltage is tens of thousands of volts. All those miles of copper have a serious resistance, theres a lot of ohms involved.

Yes, airport lights are series connected lamps (or transformers), constant current 6.6A, voltage as required, may be up to 10KV (5KV either side of ground). Also used to be used a lot for street lighting, but now consigned to history.

Trivia - if you put in a decent ground system, the resistance between any two points on the planet is about 500 ohms. Thats why a ground return path is a neat idea. Not only is it used for communications systems, but for power systems. The High Voltage DC link that runs by my house on it's 300 mile journey uses ground as the unbalanced return conductor, and with only one of the two poles operating theres about 1000A of ground current, so the grounding electrodes are obviously fairly substantial...