G4NSJ – amateur ham radio odds and ends


This has nothing to do with amateur radio but, it’s interesting. I’ve always been fascinated by high voltages. I mean, very high voltages! I believe that, somewhere the world, they are experimenting with over one million volt transmission lines.

I’ve often wondered what the current is in the national grid. I believe the voltage is around 400kV but, at what current? You can see on the plates below how low the primary current is on small 11kV transformers.

Below is an 11kV to 230 Volts transformer manufactured by Ferranti. The primary current is only 2.73 Amps whereas the secondary current is 131 Amps. It’s a 30kVa transformer.

The point of transformers is to allow high voltage low current transmission and distribution. Step-down transformers reduce the voltage to towns where the voltage is finally reduced to 230 volts for local streets. The higher the current, no matter what the voltage, the higher the voltage drop in cables due to resistance. The lower the current, the lower the voltage drop. If overhead power lines carried 230 volts rather than 400kV, the current would probably be millions of amps. Imagine the size of cables necessary to carry such current!

Shown bellow are 33kV lines.  But, at what current? Anyone know?

33kV lines

Telegraph pole

Telegraph pole