definition of "weak infeed" condition 2

[un421ate1]

came across this term in basler directional overcurrent relay,
what is it, what causes it and if objectionable how do you correct it?
many thanx in advance.

 

[waross]

In reference to a system, it is a description of the impedance of the source. A system with higher than normal impedance would be called "Soft".
A system with lower than normal impedance would be called firm or solid. It has a similar precision to saying that some cars are fast and some cars are slow.
Nevertheless it is usfull in conversation to describe general system impedance.
Now in regards to Basler relays, The answer may be completely different.
David Beach is the resident relay expert. Wait for his comments.
respectfully

 

[rcw retired EE]

A weak infeed is when you don't have enough generation behind your relay to push enough current for the relay see a fault and pickup.

For example, I build power plants. The one I'm building now can deliver about 12000 amps to a fault on the 230 kV transmission line, but only when all the generators are on line.

If the generators are off, and the 230 kV line faults right at my terminal, none of my relays will trip because there will be no current flow from my generators. The relays at the other end will see 18000 amps from their substation and will trip and clear the fault. Our substation has a "weak infeed" and will not disconnect from a faulted line.

This is usually a problem for distance and directional relays so logic is added to sense this condition by looking at voltages, absence of faults elsewhere, signals form the other end and other criteria.

I hope this rudimentary explanation helps. If you don't have a generator somewhere behind you, your relays won't see current during faults.

 

[davidbeach]

Put me on the spot, huh? Weak infeed has to do with the protection of lines with sources are both ends, or even three terminal lines, where one source is considerably weaker (softer) than others and how that presents difficulties with the relaying. I don't have time at the moment to go into a drawn out explanation, but there is a FAQ for this forum with lots of reference sources. Any of the protection books should be able to answer the question in great depth. The Blackburn book is a good starting point for learning the basics of protective relaying.

 

[waross]

Sorry to put you on the spot when you are short of time. But I knew we could count on you. Thanks also to rcwilson. I've learned a little tonight. I hope the OP is satisfied.
Respectfully

 

[un421ate1]

many many thanks to respondents.....had sneaky suspicion it wasn't a baseball term.