# Which voltage and frequency would be selected if there were no legacy issues?

Which voltage and frequency would be selected if there were no legacy issues?

I can easily find how selection of electricity frequency and voltage was based on backward compatibility and quite arbitrary choices. I'm impressed by the Japanese who are able to keep two frequencies in one country. The question relates to an early 21st technology level and what would be the most logical right now.

This is the relevant information that I found:

The US military uses 400 Hz, as it allows smaller rotors, but it would be hard to use that on much bigger scales as transmission losses would go up.

There seem to be quite few electrocution deaths and quite serious transmission losses in low voltage systems, so there might be a tendency to increase voltage to save energy. Would it be worthwhile? Would just converting voltage before delivering it to household be efficient enough?

(Please, no Tesla, no war of currents... I would not like to see Americans having their holy war here...)

• – user
Commented Sep 25, 2016 at 19:10

## 2 Answers

Goals-

Don't kill people

Transfer electricity cheaply and efficiently

The power loss when transferring electricity = P = IV (current * voltage) and V = I*Rwire ( current * resistance of wire) or P = V^2 /R = I^2 *R

So to minimize power loss when we have a high R (miles of wire) we drive V very high

Then we want to maximize power available to the consumer for a smaller R The same equations apply, so if we can convert the high voltage low current flow to a low voltage high current flow we make much more power available.

The conversion from High V low I to low V high I is very easy in AC current we just put a uneven inductor between them.

The conversion in DC is much more inefficient. This is why we would like to use AC.

What part of electricity kills people? Well It has to have enough voltage to get through humans skin ( a few volts). The easiest way for electricity kill a person by triggering nerves thus causing muscles to spasm (including the heart and lungs) giving people heart attacks. The key to doing this is to have electricity pulsed at the same frequency and nerve cells pulse (which is around 60 hz) Which is the frequency of household current in the US.

So you would want 2 voltages 1 high voltages for transition lines and 1 low voltage for home lines, they should be AC and very far from 60hz in frequency)

• Actually, in many places it's three voltages. Very high for long range transport, medium high for closer to home lines, and "low" to apartments. Purely economic reasons, so without legacy, it would be the same. Commented Sep 21, 2016 at 10:55
• Thanks, this info concerning heart rate was new to me. Anyway, it seems even more complicated with really high frequency (data for 10kHz) being much safer: highvoltageconnection.com/articles/ElectricShockQuestions.htm Commented Sep 21, 2016 at 13:51
• @Mołot good point Commented Sep 21, 2016 at 16:44
• Actually, recent technology makes DC more attractive for long-distance transmission. The reason we didn’t do DC at first was that we didn’t have the technology for reasonably efficient AC->DC->AC conversion and most power generation methods have been AC, also you need AC for common loads such as motors. Due to "recent" innovation, High-Voltage Direct Current transmission lines can be significantly more efficient (both w.r.t. power use and conductor material) than AC lines. Read on on wikipedia. Commented Sep 25, 2016 at 17:24

One constraint on the frequency is that you want it high enough not to cause annoying flickering in your lighting. So you probably don't want to drop too much below the UK 50Hz - I know movie frame rates are 24 fps, but trying alternate eye LCD shutters with a low refresh rate definitely flickered noticeably for me.

You also want a voltage high enough that you can deliver enough power (V x A) to your high demand devices - like heaters, cookers, and washing machines - without worrying about I squared R losses in your connecting cable - halve the voltage, and you need to double the current, which gives you four times as much loss if you keep the cable the same. Or you can go to more expensive thicker cable...