Protection of Transformer

http://wiki.answers.com/Q/What_is_biased_differential_protection_realy it took 10 seconds to find

Re: http://wiki.answers.com/Q/What_is_biased_differential_protection_realy it took 10 seconds to find

And here's the answer you found in those 10 seconds:

"

this is additionl of differential realy......"

To be fair, there were pointers to answers to somewhat similar questions on the same page. I am not the OP, I know what differential protection is on a transformer, I still don't know what biased differential protection is.

Actually transformer differential protection is located on that page. I am quite amazed as I do not find wiki.answers to have been accurate in past years.

So, what is "biased differential protection"?

"The differential protection used for transformers is based on the principle of current circulation. This type of protection is mostly used for transformers as this responds not only to inter turn fault but also provides protection against phase-to-phase faults"

A complete description of differential protection of transformers is given in the following link.Please read complete text and see the drawing ,a fairly good explanation of the subject is available.

http://electricalandelectronics.oplanation erg/2009/03/19/differential-protection-in-

transformers/

That link doesn't work for me, even when I paste "transformers/" on the end and replace oplanation with explanation. Also, when I paste electricalandelectronics it shows up with spaces and I tried replacing those with %20.

Hopefully, this one will (from google):

DIFFERENTIAL PROTECTION IN TRANSFORMERS

I did a quick search on that page for the word biased--nothing shows up. Is there something that discusses biased differential protection on that page?

(I am not the OP, just would like to learn.)

There is another thread on this very subject, maybe the answer is there :

http://cr4.globalspec.com/thread/35342/Biased-Differential-Relays

Perhaps biasing implies deliberate skewing to compensate for tiny errors in manufacturing.... i am going to read some more... maybe the Areva link there...

Some reference to biasing on the Transformers UK page....

Biased Relays

The use of a bias feature within a differential relay permits low settings and fast operating times even when a transformer is fitted with an on-load tapchanger (see above). The effect of the bias is to progressively increase the amount of spill current required for operation as the magnitude of through current increases. Biased relays are given a specific characteristic by the manufacturer.