Your question is evolving slowly. What I can interpreet is, there are two transformers fed from single source. Output of these transformers is connected to load feeders independently through two bus sections. A bus coupler can inter-connect these bus sections if one of the transformer is out.
In above case, there should be ideally two UFR relays, connected to PT of each bus section.
OR there may be one UFR relay connected to PT of common source before transformers.
Dear Sushilksk,
I am still unable to understand why to go for bus frequency check..why not line frequency…can u pls elaborate with good example. I have already stated scenario in my case for which u have replied recently
Choose whichever potential source is most likely to remain connected to your supply . . .
If your loads are fed by multiple circuits and you lose whichever circuit has the UFLS connected to it, you have immediately lost any underfrequency tripping functionality for future events.
If on the other hand all loads are fed by only one circuit, it makes little difference which UFLS potential source you choose.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
Ohh.. how difficult it is...
Mayur Bhavsar said, that he has ONE INCOMER, and it's ALL. There are only outgoing feeders without the possibility to generate electricity!
In this case, no matter where is located VT!
beyond86 hits the nail on the head. Use the voltage you have. If the breaker's closed, line and bus are the same. If the breaker's open the load is already shed. Move along, nothing to see here.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
Respectfully, the three feeders may not be the only load on the system and may be shed to prioritize loads out of other subs.
If other loading is pulling the frequency down, you may want to monitor the incoming frequency so as to know when it is safe to go back online.
Whether the frequency PT is located on the incomer or on the bus, may be influenced by the control scheme and the possibility of the incoming breaker going open during a load shedding event.
-------------------- Ohm's law
Not just a good idea; It's the LAW!
Then again, the OP only ekes out the relevant info as the thread unfolds, and in my view, it is preferable to follow the "more information leads to better answers" right out of the gate.
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
