answer for the problem

[Ingenieur]

I don't need convincing.
Others here have explained better than I.
Accept and move on.

actually both positions have been made
this may help https://www.crcpress.com/Computer-A...sis-Second-Edition/Kusic/p/book/9781420061062
I actually took the course from the author

it is absurd to think a generator can assume 100 mva step load and not slow down
and one on the same grid did not (Albiet at a slower rate, ie lag)
the grid will be drug down, the unloaded will follow, at a slower rate
hence different freqs until stabilized

some grids have dozens of large machines
it is not possible for them all to run identically at the same speed

 

[GoldDigger]

actually both positions have been made
this may help https://www.crcpress.com/Computer-A...sis-Second-Edition/Kusic/p/book/9781420061062
I actually took the course from the author

it is absurd to think a generator can assume 100 mva step load and not slow down
and one on the same grid did not (Albiet at a slower rate, ie lag)
the grid will be drug down, the unloaded will follow, at a slower rate
hence different freqs until stabilized

some grids have dozens of large machines
it is not possible for them all to run identically at the same speed

It may take some time to stabilize, but if the integrated phase shift resulting from the frequency difference exceeds maybe 30 degrees it will open protective equipment instead of stabilizing.

 

[Besoeker]

It may take some time to stabilize, but if the integrated phase shift resulting from the frequency difference exceeds maybe 30 degrees it will open protective equipment instead of stabilizing.

Synchronous machines connected to the same supply run at the same speed which is dictated by the frequency of the system.
iwire explained the manual proceedure for getting them synchronised and on line.
On the last couple I had dealings with, the closing proceedure was automatic.

 

[electrofelon]

At the moment of transition from POCO to internal (generator) power, doesnt the plant/site generator HAVE to be at a slightly higher frequency to 'pick up' the load from the grid? The plant I worked at, we had a synchronizer switch that rotated ever so slightly clockwise, and it had to be thrown at 12 o'clock, as mentioned before. At that point, the plant generator and POCO power are in perfect synchronicity, however, since the genset is running at a very slightly higher frequency, it takes the load vs leaving it on the grid. Is this grossly incorrect? Is it phase angle and not frequency that determines what source supplies ALL the power?

I think maybe you are correct, but not quite saying it right. I think most of the disagreements in this thread center around what exactly is meant by "different frequency", specifically how much of a frequency difference there is and for how long the difference exists. Over a significant period of time, the frequency has to be the same, but brief slight changes in frequency will vary the two frequencies relative to each other and thats how we can synchronize then "pick up" or "shed" a load. Lets do an analogy using an internal combustion engine and a timing light aimed at the crankshaft pulley. Ignore ignition advance. The timing light pulse and when the top dead center mark aligns with the pointer occur at the same frequency. Now say I turn the distributer cap. While I am turning the cap the frequency of one of these changes to a slightly different value. When I stop turning the cap, the values are again exactly the same and the result is I changed the relative position to, say, 2 degrees BTDC. So in the case of the synchronous machine, you can and do have different frequencies, but only for a brief period, and this changes the position of two equal frequencies relative to each other

 

[Bugman1400]

actually both positions have been made
this may help https://www.crcpress.com/Computer-A...sis-Second-Edition/Kusic/p/book/9781420061062
I actually took the course from the author

it is absurd to think a generator can assume 100 mva step load and not slow down
and one on the same grid did not (Albiet at a slower rate, ie lag)
the grid will be drug down, the unloaded will follow, at a slower rate
hence different freqs until stabilized

some grids have dozens of large machines
it is not possible for them all to run identically at the same speed

The impact of a 100MVA load step change depends on how stiff the system is in that area. It can change the phase angle but, may not change the frequency. If the system is weaker in that area, it can change the frequency of all the connected units in that area but, all units will still maintain the same depressed frequency. Any difference in frequency between one unit and another unit 5 miles away will cause the phase angle between them to increase until a pole is slipped and instability occurs. You are correct when you say "mech speed = elec speed". When one is changed the other must change to equalize.....how fast they equalize is the topic of instability. Many use the analogy of a rubber band to visualize this concept.

 

[Besoeker]

some grids have dozens of large machines
it is not possible for them all to run identically at the same speed

Drax, UK has six 660MVA synchronous alternators.
They all operate at the same speed/frequency.
If they didn't, you couldn't/wouldn't call them synchronous.
They'd be asynchronous.

 

[Ingenieur]

Drax, UK has six 660MVA synchronous alternators.
They all operate at the same speed/frequency.
If they didn't, you couldn't/wouldn't call them synchronous.
They'd be asynchronous.

does a generator governor have a deadband? NERC requires 0.036 Hz (by convention) iirc, which means one gen could run at 60.036 and the other at 59.964, before any control action was initiated
and an accuracy rating?

which afaik is not the same frequency?

 

[Besoeker]

does a generator governor have a deadband? NERC requires 0.036 Hz (by convention) iirc, which means one gen could run at 60.036 and the other at 59.964, before any control action was initiated

As I suggested, try drawing the sinewave voltages of two different frequencies on the same axis.

 

[ggunn]

You guys are really splitting hairs. What is the error margin for calling two frequencies the same? .1Hz? .01Hz? .001Hz? The same to how many decimal places? Whatever your error margin, inside it they are the same and outside it they are not, and there is no such animal as a zero error margin. Even in the tightest of phase locked loops there is drift and correction.

 

[Tony S]

UK dynamic demand

 

[Bugman1400]

does a generator governor have a deadband? NERC requires 0.036 Hz (by convention) iirc, which means one gen could run at 60.036 and the other at 59.964, before any control action was initiated
and an accuracy rating?

which afaik is not the same frequency?

Which NERC requirement is that from?

 

[Fnewman]

Perhaps PRC-024?