Why PV-Produced AC-Power Goes to the Loads before Grid-Provided AC-Power?

[Hv&Lv]

To add to the post above, generating points as mentioned are fuel consumption and load determined. Loads pick up, generator lags, more fuel is added to try to keep it at Caleutches 3600 RPM. Loads decrease rapidly,(especially with large solar and partly cloudy days) fuel has to be decreased.

When we have to make ties between generation points, whether it is at the transmission level of the distribution level, we are required to call the central dispatch and get the angular difference between generation points before we tie.
One generation point can decrease fuel just a bit to slow a generator down to get within a degree or two (synchronize) before we make our tie.
Along with hertz the synchronization of generation plants is also monitored just for tying generation points together for load sharing, maintenance, etc..

Solar has really made the process more involved with the addition of bi-directional power. I’ve looked at substation phasors before on a partly cloudy day when the loads are very close to a solar farms output, and the phasor is constantly flipping back and forth as the energy flows from utility or to the utility.
It’s this type of fluctuation that’s hardest on transmission synchronization.

 

[LATTC Student]

What the utility really uses for feedback on aggregate power demand, is grid frequency. The utility has a standard to maintain grid frequency and voltage within a tolerance of the nominal values.

When it comes to conventional generating sources with rotating machinery, the grid frequency is directly determined by the rate that the turbines and generators rotate. Unlike wind power, where there is an inverter to allow turbine speed to be independent from the grid frequency, conventional generating sources have their rotation rate linked to the frequency they generate. There will be a fixed ratio between the RPM of the generator and the frequency in Hz, based on the geometry of the generator. For simplicity, let's consider an example where this ratio is 1:1. This would mean 3600 rpm corresponds to 60 Hz.

The generation stations take time to adapt fuel consumption to the varying power demand. Some forms are more adaptable than others, such as gas turbine plants and hydroelectric. Steam turbine power plants have their own advantages, but in this regard are better suited to supporting the steady base load. Prior to changing the fuel consumption rate, the generators will speed up when load decreases, and slow down when load increases. This means if it is spinning at 3610 rpm, they need to reduce the fuel, and if it is spinning at 3590 rpm, they need to add fuel, all while aiming for the target of 3600 rpm.

Most interesting. We just started Industrial Motor Controls / Transformers on Wednesday and this information certainly helps me understand power generation better as well as the load/frequency relationship at generation plants. Thanks Carultch!

 

[LATTC Student]

To add to the post above, generating points as mentioned are fuel consumption and load determined. Loads pick up, generator lags, more fuel is added to try to keep it at Caleutches 3600 RPM. Loads decrease rapidly,(especially with large solar and partly cloudy days) fuel has to be decreased.

When we have to make ties between generation points, whether it is at the transmission level of the distribution level, we are required to call the central dispatch and get the angular difference between generation points before we tie.
One generation point can decrease fuel just a bit to slow a generator down to get within a degree or two (synchronize) before we make our tie.
Along with hertz the synchronization of generation plants is also monitored just for tying generation points together for load sharing, maintenance, etc..

Solar has really made the process more involved with the addition of bi-directional power. I’ve looked at substation phasors before on a partly cloudy day when the loads are very close to a solar farms output, and the phasor is constantly flipping back and forth as the energy flows from utility or to the utility.
It’s this type of fluctuation that’s hardest on transmission synchronization.

Amazing. I would love to visit a generation plant, or even a substation, someday. Thanks Hv&Lv for more granularity behind the DG from the Utility perspective! I am sure you guys have detailed learned knowledge from Germany's, and others', painful decade of growth.

 

[ggunn]

... he mentioned "when it comes to current, it doesn't really exist, it isn't 'pushed' and the current isn't doing anything. It doesn't arrive until some need for it exists, generally from a load then it flows". . . . . strong emphasis on paraphrase

Thanks again.

Except that for a current source like a grid tied PV inverter, current is indeed pushed. Current is pushed from a current source and pulled from a voltage source.

 

[electrofelon]

Except that for a current source like a grid tied PV inverter, current is indeed pushed. Current is pushed from a current source and pulled from a voltage source.

Where u been hiding out gunny? IIRC you are in Austin, so what: it's too hot to be outside now so you're stuck inside and bored?

 

[ggunn]

Where u been hiding out gunny? IIRC you are in Austin, so what: it's too hot to be outside now so you're stuck inside and bored?

It's kind of a long boring story, mostly due to the pandemic and becoming insanely busy working from home with some personal issues thrown in. You'll see a bit more from me now.