How does differential protection work in generators? What is the purpose of baising?
How is the scheme implemented in protection schemes. Do numerical relays offer this protection??

 

Responding to Santan’s 13-Jan (14:21) questions:

1) The fundamental operation is based on comparing current-in to current-out of each phase-winding, thus any unbalance or difference operates the protection device!

2) Not all circuit elements are perfect, that is, current transformer curves are not exact over the entire operating range, nor are secondary burdens (impedances) the same. Then, in order to prevent unwarranted operation due to the maximum error current that could exist. This is accomplished by biasing, as well as other methods!

3) Biasing is one way to desensitize the protection system so errors are precluded from from false trips, especially in the higher fault-current range!

4) Presuming you are differentiating (please excuse the pun) between hardware versus soft-ware based systems, the answer is yes!

If you need additional information, contact me on or off-list!

Regards, Phil Corso ([email protected])

 

Dear Mr Phil,

1. i still confuse your statement about how to work differential relay in generator when there is fault in distribution system like is ground fault or phase fault?

2. how to check air terminal in lightning protection? isn't good or bad status condition?

thank you very much for your attention

 

Responding to Rahmad's 08-Nov-09 (03:05) post...

1) Differential Protection.
In this scheme two current measurements in the same phase, say I1 on one side of the protective zone, and I2 on the other, are compared. When a fault occurs within the machine, I1 will increase, while I2 decreases (or reverses if there is another source) and the resultant differential current, I1-I2, will flow thru the relay's operate-coil. If the fault is external to the machine, then I1=I2, and current flow thru the relay's operate-coil is essentially zero.

The above is ideal when CTs are perfect. Unfortunately, CTs will not always develop the same secondary-current for a given primary-current. This occurs because of manufacturing variations or secondary burden differences. Thus, the relay must be set above any error current that could arise. Fortunately, the error problem is overcome with the addition of restraining or biasing coils that desensitize the operate-coil.

2) Ground and Phase-Fault Protection
Unless the ground and phase-fault magnitudes are the same, two differential protective systems are normally provided.

3) Lightning Arrestor.
Please clarify your question.

Regards, Phil Corso

 

Ok thank you very much

for lightning arrestor
Plan, we're repairing lightning arrestor, like is grounding system and air terminal but i don't know to check air terminal technically. how to check air terminal is good or bad condition?

bst rgrds

 

Rahmad... if used solely for gen protection, then:

o Age?

o Type- airgap, horn, electrolytic, MOV. etc?

o Rated voltage?

o Noises emating from arrester?

o Distance between gen and arrester location?

o Evidence of severe arcing?

o If encased, were tey x-rayed?

Phil Corso