Why do we use MHO type Loss of Excitation Protection for Generators? 1

[rayas91]

Hi,

Why do we use MHO type Loss of Excitation Protection for Generators?
And Why two zones ? , what do zones show us ?

Thanks ,

 

[davidbeach]

Because 50-60+ years ago somebody figured out how to do it that way. I don't know whether the negative or positive offset version was first, but the other followed. Religious wars on the level of of vs. mac ensued. Nobody has come up with anything better. To avoid taking sides, the modern manufacturers include both. A comprehensive protection book, such as Blackburn, could provide much more depth.

 

[waross]

David's 60+ years may be as much as 75 years ago.
This paper from GE dates the introduction of the Single phase Offset mho Relay as 1941.
See:

http://store.gedigitalenergy.com/faq/documents/489/ger-3183.pdf

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Thanks, I knew it was essentially "for ever" but didn't know how far back and wasn't bothered to look. If rayas91 really wanted to know, there's this thing called google...

 

[rayas91]

Much Thanks davidbeach and waross , I had that document ger-3183..But I couldnt understand that.It may be because of my english level.

Thanks again.