Islanded Generating Station

[mbrooke]

How does an Islanded 600-2000MW generating station behave? What does typical critical clearing time look like? What is the voltage and frequency divergence during and after a fault for various fault scenarios? How is active and reactive power dispatched/controlled? How does generation behave during trip and reclose events? And how do you "block load"?

 

[iceworm]

I work a lot with islanded generation in that range. And I can tell you for certain is the questions are either simplistic, or have multi-page thesis answers.

How does an Islanded 600-2000MW generating station behave?
With in the limits of the original design - As well as the maintenance pulled on it.

What does typical critical clearing time look like?
Don't know what you are looking for here. The CBs are the same ones used in non-islanded distribution. Although generator SCC are typically low.

What is the voltage and frequency divergence during and after a fault for various fault scenarios?
They go down, then they go up. Unless they went too far and tripped on anyone of a dozen things.

How is active and reactive power dispatched/controlled?
This one baffles me. The load is what it is. The generation has to supply the KW and KVAR the load requires. The generation doesn't control any of this.

If the question is about paralleled small generation:
If it is two paralleled

kw share and kva share​

1 Isoc, 1 droop​

If more than two paralleled

1 Isoc, N-1 droop​

1 swing, N-1 base load​

2 KW and Kvar Share, N-2 base load​

Varying amounts of operator intervention required


How does generation behave during trip and reclose events?
Some trips open the gen main and leave the driver running. Some trips open the Gen main and also shut down the driver. Depends on the protective relaying.

As for reclose, the relaying should open enough feeders the Genset can be put on-line smoothly. If not, the operators have to load shed.


And how do you "block load"?
I don't even know what this means.

 

[mbrooke]

Question- where are 2,000 MW isladed stations used?

I know circuit breakers are the same, but I'd think the CCC would be lower on a radial power plant then a grid.

 

[iceworm]

Question- where are 2,000 MW isladed stations used?

Yeah, that was your words - and I did not correct it for my words. Should have.

My experience is 600KVA to 20MVA.
Oh, and a couple of DIY off-grid, 3KW to 20KW

 

[iceworm]

I know circuit breakers are the same, but I'd think the CCC would be lower on a radial power plant then a grid.

Well, as I said:

... Although generator SCC are typically low. ...

For 10MVA generators, Xd" ~ .20, so SCC is ~ FLA/.2 = 5 FLA for 13.8KV, SCC = 2.1KA

For a 10MVA transformer, %IZ ~ 8%, so SCC ~ FLA/.08 = 12.5 FLA (neglecting transmission impedance) for 13.8KV, SCC = 9.1KA

One may have to purchase higher rated equipment, but at 13.8KV, maybe not.

Either way, the protective relays have to be set within the damage curves.

And I'm thinking you knew all this

 

[mbrooke]

Well, as I said:

For 10MVA generators, Xd" ~ .20, so SCC is ~ FLA/.2 = 5 FLA for 13.8KV, SCC = 2.1KA

For a 10MVA transformer, %IZ ~ 8%, so SCC ~ FLA/.08 = 12.5 FLA (neglecting transmission impedance) for 13.8KV, SCC = 9.1KA

One may have to purchase higher rated equipment, but at 13.8KV, maybe not.

Either way, the protective relays have to be set within the damage curves.

And I'm thinking you knew all this

About a 250MVA generator? What about 10-12 of them in parallel?

 

[iceworm]

About a 250MVA generator? What about 10-12 of them in parallel?

What about it? What about them? I can't tell where you are headed.
Anyway, 250MVA would be out of my area of expertise.
Time for you to do some research. Perhaps you could look up some typical values.

 

[mbrooke]

The short circuit current- as you did with the 10MVA generator.

 

[iceworm]

I happened to know typical values for Xd" for alternators in the 10MVA - 20MVA range - because I have worked with some in that size range. I have not worked with anything in the 250MVA range, so:

...Time for you to do some research. Perhaps you could look up some typical values.

 

[mbrooke]

I'll look.

In the mean time this is what I have in mind:

https://imgur.com/a/AAKmgss

Each circuit is half loaded- normally open ties to neighboring system, load break gang operated switches.