friends.
become
Could be. AFAIK the spinning disc meters measure kVAh at some presumed=20 power factor (usually 0.8 i think). Modern electronic meters are likely=20 to do the same for the same reasons. The is due to cost dynamics of kVA = vs=20 kW to the utility company. In 20 to 50 years most everything will be PF=20 compensated and harmonics controlled (and much stuff forcibly = retrofitted).
Disk meters measure true power, not KVAs. They are accurate over a huge range of power, watts to kilowatts, and do the power factor correction very well. It's non-trivial to design an electronic meter that good.
Modern electronic meters are likely
No, they measure true power too. At least all the ones I've seen or designed.
John
I agree. (Except they don't do power factor correction - they directly measure true watt-hours. That is probably what you meant anyway.)
Details are in a thread on alt.engineer.electrical starting 11-21-09 and titled "Balancing the Breaker Box". Much of the thread is forgettable, but look at posts by snipped-for-privacy@shawcross.ca and daestrom , particularly starting 11-30.
Apparently, a small magnet can cause them to read low. They are flux devices, and the external magnet interferes with this. Feynman pointed this out in one of his undergraduate lectures.
According to wikipedia, they work by having two coils generate a magnetic flux that causes the disk to torque in proportion to the product of the current and voltage. There is a permanent magnet that counteracts this torque. An external magnet can affect the fine balance, I suppose.
Bob
This is a well known trick. AFAIK modern meters are shielded.
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