Generation on radial transmission lines 1

[Mbrooke]

Is there anything that I need to consider in terms of protective relaying when protecting radial lines with very large amounts of generation on the other side, ie in this case a 1,500MW+ plant on a 30 mile radial 345kv? I'm guessing I could have step distance under-reach for faults out on the line, but remain unsure.

 

[crshears]

Thanks, MBrooke; I'll take the intent for the deed.

To answer your question, yes, more or less; if no boiler, turbine, generator or main output transformer trip occurs, and provided the other technical challenges and considerations as met can be caught in time, there is no underlying reason why a unit cannot undergo grid separation without surviving. In the instance quoted, the unit is not actually ever completely unloaded, as it is still carrying its own station services.

Even during unit trips, if the major electrically driven elements such as boiler feed pumps, pulverizers, etc. use maintained position breakers they are frequently able to hang in through the hiccup of station service transfer to the reserve supply and will continue operating.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Mbrooke]

Any idea if a minimum load needs to exists on the station service transformer to keep that turbine stable?

 

[crshears]

I could not possibly say; that would vary from station to station, as there are so many potential factors involved, and it would take someone with more recent operating experience to give an informed answer.

The only thing I believe would apply is that the smaller the percentage of maximum continuous rating the load is the shorter the length of time the unit would survive before tripping it off manually would become necessary to avoid turbine differential expansion and internal rubbing; perhaps some of the mechanical engineers on these fora might have some input on this...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]