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Reliability Analysis - Point to Remember

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gokulkrish2

Electrical
Jun 29, 2008
79
Hello all,

Im a new member to this forum. Im working in a mining company and it has a pretty decent power distribution system. Now i have been given a project on to look at the system and analyse it on how reliable it is. Like checking for breakers in apt positions, way to by pass power if in case of a maintenance and etc.

So i wanted to ask you people that what are the points i should keep in my mind before starting up the projects.

Any comments and suggestions from anyone who have done this early?

All replies are highly appreciated

Thanks

gokul
 
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Hi.
Please see attached thread.
thread238-197540
Hope that help.
Good Luck.
Slava
 
For starters, I would draw a one-line of the system. Then I would list for each bus and breaker/feeder pair, PDC, MCC, and transformer, what equipment will be put out of operation in the event of a failure. Note which equipment may be re-energised by switching existing devices and and restrictions.
An example of this may be a pair of Power Distribution Centers joined by a tie breaker. In the event of a feed failure to one of them, the tie breaker may be closed to restore service. The load may have to be curtailed.
I would then look at the implications of a failure of a system with no ready alternate supply.
This would be a starting place.
This is probably an exercise to familiarize you with the plant. You may gain extra points if you include actual loading of the circuits as well as the design loading.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
Hi slavag and waross, thank you both for your replies. I have a question for waross. What is a tie breaker.

Sorry im just an intern and i dont know much of the equipments. Can you tell me what for is a tie breaker used.

thanks,

gokul
 
A tie breaker may be a breaker connecting two buses or two Power Distribution Centers.
In the event of failure of the normal feed to a bus or PDC, the tie breaker may be closed to feed the load from the other feeder.
In normal operation, tie breakers are open. they are closed only when one feeder is missing either due to a failure or for maintenance. There are often protection and fault current issues if the tie breaker is closed when both feeders are present.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
So, just to make sure, can the usual circuit breakers be used as a tie breaker or a tie breaker has a different construction? What kind of error are expected using these tie breakers. can you please explain that in detail?
 
It is to UNTIE two subsytems. Not a tie as in a race.

Breakers usually don't care what they are applied to as long as their specifications are not exceeded. So there generally aren't specific special 'tie breaker' breakers.

More likely they may be in a strange place but not a strange type. You may see one in a panel between other panels all by itself, etc.

Keith Cress
kcress -
 
Consider a substation. There is typically a transformer feeding a breaker. The breaker feeds a set of bus bars. The bus bars feed outgoing circuits. In the same yard is a second transformer feeding a breaker. The breaker feeds outgoing circuits. In this case, a breaker similar to the breakers feeding the buses may be used as a tie breaker to "TIE" the buses together. In the event of a breaker or transformer failure the tie breaker may be used to feed the bus and loads normally fed from the faulted transformer.
In the event that the tie breaker is closed with both buses already energized, the available fault current will approach double, limited by the source impedance.
The equipment is seldom rated for this level of fault and the tie breaker is not closed with both sides energized, except in special cases for a few seconds to take equipment out of service for maintenance. One example of a "TIE" breaker. There are others, often with PDCs.
Keith, was that word meant to be "UNITE" as in "To Join" or "UNTIE" as in "Dislectics UNTIE".
LOL.

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