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What is "the national voltage phase angle"? And what is "a non-dynamic voltage"? I've never worked in power distribution but those are terms that I've never heard, even having spent all my working life as an electrical engineer.

Are you trying to say that everyone everywhere (a) knows which phase they are on (if a single phase supply) or which phase is No.1, and what about how many star-delta transformers the supply has been through?

Then how are you going to know the timing to within a few milliseconds and synchronise your current measurements to that?

It is far easier to look at the voltage locally.

I always thought http://www.nationalgrid.com/ngrealtime/realtime/systemdata.aspx provided real-time data, but just noticed the date/time displayed... I'll check with National Grid.

Paul

Paul - that is frequency, not phase. Even if you know the phase with respect to clock time at one defined instant, as frequency drifts, the phase changes too.

If you run MartinR's PLL, you can watch the frequency changing as the system load varies and sets are put on and taken off to meet the demand. And if you plot 'your' frequency and compare it with the published one (http://www2.nationalgrid.com/uk/Industry-information/electricity-transmi...), you can calibrate your crystal (then change the software divider to read the frequency accurately).

Sorry - I was using made up terms and hoping that they were close enough that people would know what I was talking about. I DON'T have a background in electrical engineering so please forgive me!

It was my understanding that with systems that have current and voltage readings you look at the phase-difference between current and voltage in order to calculate the real power (when they're totally in phase real power=apparent power). Maybe I've got this wrong?

I was also under the impression that the national grid frequency is the same across the country (otherwise different regions would drift apart). The "national voltage phase angle" is my attempt at refering to this national voltage frequency. Although you are implying that what phase one is on and what transformers it's been through means it's impossible even in theory to do it - let alone the timing hurdles!

By non-dynamic voltage I mean one would have to hard code a value for voltage magnitude (say 230V although it could be actually measured with a multimeter to take account local wiring losses?)

I know it's easier to do it locally - I was just looking to see if it was possible to get a crude setup for real power with just a current clamp.

Thanks for your comments

"I was just looking to see if it was possible to get a crude setup for real power with just a current clamp."

NO!