On 2 January 2017 at 05:15, Jeremy Nichols <jn6...@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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.