[time-nuts] Line Voltage - USA

Bob Camp kb8tq at n1k.org
Tue Jan 3 14:08:35 EST 2017


Measuring line voltage for “official” purposes straight up with a lab grade device that may
have a bandwidth of many KHz (or even 100’s of KHz) is generally not a good way to go. 
The line voltage is the value of the fundamental (50 or 60 Hz) sine wave. All the other nonsense
that accumulates is more likely load related than line related. If the power company brings
out the right stuff, it looks more like a spectrum analyzer inside than a normal voltmeter. They
sell a lot of 24 bit audio DAC’s into that sort of gear. Team them up with some DSP and you
get all sorts of interesting data. The “one number” that counts is the fundamental ….


> On Jan 3, 2017, at 1:50 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> On 2 January 2017 at 05:15, Jeremy Nichols <jn6wfo at gmail.com> wrote:
>> Thank you for the detailed analysis, Bill. The voltage measurements I made
>> in my garage laboratory were duplicated by the utility with their meter,
>> which was connected at the service entrance.
> I have just been chatting to a friend who was a controller at two power
> stations in the UK - Darlington (coal) and Bradwell (nuclear). He tells me
> that the voltage is likely to be higher in the summer around 2-3 am in the
> morning. Now it might seem obvious that the load is smaller in summer than
> in the middle of winter, but this is NOT the reason the voltage rises more
> in summer. I must admit though, I could still not understand it, and he
> admits he could not explain it, but just tells me it is so. But a few
> things I did get, which are not all obvious - some are.
> 1) The real power consumed by the users + losses must balance the power
> generated. That's pretty obvious.
> 2) The reactive power (V*A) must also balance - perhaps less obvious.
> 3) The voltage generated by a generator when it is not providing any load
> is controlled by the current in the field winding.
> 4) Before connecting a generator to the grid it is necessary to ensure the
> voltage and phases are matched.
> 5) Once the generator is on the grid, there's nothing the generator can do
> that has any practical effect on the voltage. Even with a nuclear power
> station, the output power it is a small fraction of the overall power being
> generated by the all the power stations, so one power station coming on/off
> line does not have any significant effect on the voltage of the grid.
> 6) What the operator can do is
> * Generator more power, by increasing the steam that drivers the generator.
> * Change the reactive power by changing the field current
> 7) As soon as the generator is connector, he would increase the steam to
> provide at least  5 MW at Bradwell (nuclear, 2 MW at Darlington (coal), as
> failing to do so risks the generator going unstable due to disturbances on
> the grid.  This could easily result in the generator becoming a motor,
> which is not good. So there's a minimum power a generator can practically
> provide - in his case 2 or 5 MW.
> 8) If there were no uses on the grid, so nobody using any electricity, the
> capacitance of the cables would make the load capacitive.
> 9) Users are generally inductive, so in practice the current lags the
> voltage, as the reactive power of users is greater than the the grid.
> 10) The higher power usage in winter means that the power factor is further
> from 1.0.
> I get the feeling that the voltage might go up more in summer as the
> generator are running closer to a point of instability, with small changes
> in load causes significantly more change in power factor than in the
> winter.
> As I say, I never really seemed to get to the bottom of fully understanding
> this, but he assures me that voltages will be less stable at light load
> than at heavy load.
> I guess if I do report a problem, I will get them to measure all 3 phases.
> That must increase the chances of at least one phase going outside
> specification. I am rugulary going over 250 V, but not 10% more which would
> be 253 V.
> Dave
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