<b>Moderator's Note: this message was originally posted to thread http://www.control.com/thread/1399373118. I made it a new thread to eliminate possible confusion about answers.</b>

Hi to all,

I'm having the similar type of basic question.

Can some one explain what actually is Dead bus and why we synchronize to Dead bus?

I asked this question to my superiors but there was never a clear explanation from them.

Thanks

 

SSU,

A "dead bus" is defined to be a bus that has no current/voltage from any source to power the load(s) that is(are) connected to it.

In some plants there is a tie-line breaker downstream of the generator breaker(s) which connects the output of the plant with a larger grid and other generators and their prime movers. If the generator(s) in the plant are not running, or were also tripped at the time the tie-line breaker opened, the plant would be said to be "black". And the bus between the generator breaker(s) and the tie-line breaker is said to be "dead."

If there is an emergency generator which can be started and used to start the other generator prime mover(s), or if one or more of the generator prime movers is capable of what's called "black start" (without AC from any source) the prime mover can be started and the generator accelerated to rated speed. At that time, there is no voltage on the "line/load" side of the generator breaker, a "dead bus"--so there is nothing to synchronize to. If the generator control scheme is capable of what's called 'dead bus breaker closure' then the generator breaker can be closed to energize the bus between the generator breaker and the tie-line breaker, and this will usually supply the plant "house" or "hotel" load until the tie-line breaker can be re-closed.

In some high-voltage distribution switch-yards which feed multiple circuits (buses) it's possible that one or more of the bus breakers tripped for some reason, and the loads supplied by that(those) breaker(s) are now without power. That would also be considered a dead bus--a circuit without power from any source.

Does this help?

 

> Dead bus and why we synchronize to Dead bus?

An application or variation of this could be to energize HV equipment from a LV generator.

Our site synchronizes to a deadbus in conjunction with progressive excitation (ge term). For whatever reason the utility wont energize the HV side of the our unit transformers. This is left for the station to do. Directly closing the breaker when excited will cause a generator trip due to excessive energization inrush. Our sequence is to close the generator breaker first, dead gen - dead bus, and then turn on the exciter. This will excite both the generator and the HV transformer at the same time, over a period of about 20seconds. We have a permissive from the substation to ensure all downstream load breakers are disconnected.

 

>Does this help?

Hello CSA,

Thank you for a quick reply. Your insights of knowledge really help a lot people, especially new engineers or trainees. Now the term dead bus is clear for me, but can you explain why the GSUT and the 132kv line will be back charged before synchronizing. What is the purpose of backcharge?

And also I would say that you are doing a great job of explaining in detail the Gas turbine control systems in the other post. I'm also following it and trying to learn from a expert like you.

 

SSU... the following thread may shed some light on the reason for pre-charging an OHV line:

http://www.control.com/thread/1026245456

Regards,
Phil Corso

 

SSU,

You're welcome, and I'm glad to be of help.

I think Mr. Corso's reference should help to understand backcharging, as well as 309EGuy's response.

As for the other thread, thanks for the feedback. I'm hoping this well get some people started on their journey of understanding. Because there is so little useful information written about GE-design heavy duty gas turbine control and philosophy one mostly has to learn to read the CSP or application code at their site in order to be able to start to understand what's supposed to happen when to be able to determine if what's happening is supposed to be happening. And, without knowing some of the little tips, hints and tricks of how GE chose signal names can make it very difficult to learn to read and understand.

I can't stress enough the importance of either printing rungs or groups of rungs (if one doesn't have access to a printed copy of the CSP or application code) and of making notes on it. There's almost no other way to really start to get a grasp of things without taking a pencil and high-lighter(s) to one's own copy of logic/sequencing/application code and making notes to help understand what's being "said" in each rung. I used to write the value of every Control Constant next to the oval that just listed the names of Control Constants in the Mark IV Speedtronic Elementary, and I would also write the setpoints of various pressure switches, and temperature switches, and limit switches, and the scaling of transmitters. I would even write the names (full name) of every input and output as I was learning. It took a couple of days, long days, to do this on every job--but after a few jobs I began to see the same signals, values, settings, inputs and outputs, and things just really started becoming clearer and clearer.

After doing that one has a much better grasp of where to find information, and of what the logic/sequencing/application code is doing to control and protect the turbine.

The more notes one makes and has, the better one becomes at understanding--and being able to understand more and more--logic/sequencing/application code. There simply is no book or manual which has all the information from all the drawings and documents in one place--so the best thing to do is to gather all of the documents and drawings and to the extent possible to put as much information in one place by making notes. It's a very satisfying task--it's work, but it pays huge dividends over time. And even very quickly, in some cases. Perosnally, I'm glad it's not all in one place--because I believe that if one has to find the information and then write it on their copies of logic/sequencing/application code that one really learns more than if it were all readily available in one document or manual.

Anyway, thanks for the feedback. It's much appreciated. (Also, if you like the posts, use the thumbs-up icon; or if you don't like the post, ask for clarification and we'll do our best to help clarify whatever is causing the confusion.)

It's very encouraging to hear from others who read the posts that they are also learning from the post started by a single person. That's my goal--to help lots of people by answering one question at a time, not just helping one person at a time with their issue. That's why forums like this are so useful--and I'm grateful for the sponsors and moderators of control.com. (We should all be grateful.) When everyone can see the question(s) and the answer(s) I can attest to the fact that it keeps multiple people from asking the same questions over and over and over again. Again, thanks for the feedback!