As per existing logic, We are having GT tripping on 2 out of 3 switches actuation. Out of these 3 switches, 2 switches are defined in QD core and 1 switch is defined in CD core. Now, as per logic, if communication with C processor fails, GTG will trip on the actuation of single pressure switch which is defined in QD core.

Now, Can any one please confirm regarding usage of single pressure switch in logic if communication with C processor fails in spite of 2 switches are defined in Q core and which are healthy.

 

<p>Your question is not clear. Specifically, what circuit are you referring to? The three below are TYPICAL from STANDARD Mark V sequencing; all are from a REDUN_SENSR_LUBE_HYD sequencing BBL.
<pre>
L26QT1A L26QA L26QT
-----| |--------| |--------------------( )
<Q> | <Q> |
| |
L26QT1B | |
-----| |----- |
<C> |
|
L26QT1A L3COM_B |
-----| |--------|/|------
<Q> <Q>
</pre>
<p>The above rung says: EITHER high L.O. temperature trip switch AND the <Q> high L.O. temperature Alarm switch _OR_ the <Q> high L.O. temperature trip switch and loss of <C> I/O will trip the unit.
<pre>

L63QT2A L63QT2B L63QT
-----| |--------| |--------------------( )
<Q> | <C> |
| |
L63QAL | |
-----| |----- |
<Q> |
|
L63QT2A L3COM_B |
-----| |--------|/|------
<Q> <Q>
</pre>
<p>The above rung says: BOTH low L.O. pressure trip switches _OR_ the <Q> low L.O. pressure alarm switch AND the <C> low L.O. pressure trip switch _OR_ the <Q> low L.O. pressure trip switch AND loss of <C> I/O will trip the unit.
<pre>

L63HG1L L63HG3L L63HGL
-----| |--------| |--------------------( )
<Q> | <C> |
| |
L63HG2L | |
-----| |----- |
<Q> |
|
L63HG1L L3COM_B |
-----| |--------|/|------
<Q> <Q>
</pre>
<p>This rung differs from the other two because there is no low Gas Fuel Trip Oil pressure alarm switch and there are three low Gas Fuel Trip Oil pressure trip switches.

<p>The rung says: EITHER <Q> low Gas Fuel Trip Oil pressure trip switch AND the <C> Gas Fuel low Trip Oil pressure trip switch _OR_ the <Q> Gas Fuel low Trip Oil pressure trip switch AND the loss of <C> I/O will trip the unit.

<p>All three cases show how, under normal operating conditions, a single switch failure will not cause a turbine trip--improving the reliability of the unit.

<p>L3COM_B is a logic "1" when communications between <Q> and <C> are good--in other words, in this case when <Q> can "see" <C>'s I/O. When the coils of any of the rungs are a logic "1" the unit will be tripped (emergency shutdown).

 

My question is with ref. to following circuit. Now, from this logic, what I could infer is that, if communication with C processor fails, i.e L3com_B=0 and L26QT1A=1(malfunction), GT will trip on the single pressure switch actuation in spite of 2 nos. of switches are defined in Q core and Q core is healthy.

Which means due to malfunction of 26QT1A at the time of communication with C proc failure, GT will trip.

So, is it advisable to design logic in such a way that 2 switches which are defined in Q core should be in series with L3COM_B(inv) for the last line?

 

Aren't you really talking about TWO failures--one of the pressure switch and one of <C>? What are the odds that of the two pressure switches connected to <Q> that the one that fails will be the one that is in series with L3COM_B?

Do you regularly operate your turbine without <C>?

Have you ever operated your turbine without <C>? If so, for how long?

Can you start, stop, raise and lower load of your machine using the <BOI> (Back-up Operator Interface) when <C> isn't running? Can all the operators and technicians at your site? (Actually, you can't start most units if <C> isn't running since the starting means I/O is usually connected to <C>. Most technicians, when they learn this, want to!)

Can you manage alarms from the <BOI> when <C> isn't running? Can all the operators and technicians at your site?

Is there a better way than GE's way? In some cases yes. Once the unit is out of warranty, you are free to configure your unit in any manner you see fit--as long as the owner(s) agree. There are owners/technicians who have replaced the three pressure switches monitoring L.O. pressure for alarm/tripping condition with a single pressure transmitter. Possible? Yes. Advisable? No. But, they do it anyway.

If the owner of the machine will allow you to make the change, have at it. Let us know how you fare with your presentation.

markvguy

 

Okay! OKAY!

Several people--many, actually--have written to point out that their CSP (Control Sequencing Program) uses very different L26QT and L63QT rungs, with a rung which has the two <Q> switch inputs in series to actuate the trip logics. (Why they won't write to control.com to point out the omission is not clear.... This is a place where everyone learns--including those posting replies. And where occasionally everyone forgets to think of every possibility or omits something which is or could be fairly germane and important to the discussion.

Most CSPs do have these rungs with the two <Q> contacts in series, but that isn't what the originator of this thread was asking about. He was asking about the L3COM_B rung with one single <Q> switch in series with it. This author was remiss for not including the two <Q> signals in series in his representations of the rungs, and apologizes for any problems or confusion that might have caused.

markvguy