Testing Spark Plugs of Mark-V Control System

8/11/2019 Testing Spark Plugs of Mark-V Control System

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reference/output; this is for DLN primary combustion zone re-ignition during a normal fired shutdown. It is a second set of contacts from another relay output (contact output) in the Mark V wired in parallel with the "primary" relay output used duringstarting. I believe this is the L2TVX1A output, but, again, that's just a guess without being able to see the CSP at your site to becertain.)

The spark plug bodies must be firmly grounded to non-painted metal. (They are bolted to the combustion cans using metal boltswhich serve as the ground during normal operation; usually just laying them on the galvanized metal grating outside the turbinecompartment will suffice.) Personnel working in the area where the spark plugs are laid in the open should be notified and staya couple of meters away from the spark plugs when they are going to be energized.

Many times the safety procedures for an outage require that the AC source for the spark plugs be isolated (by opening ancircuit breaker or lifting a wire somewhere in the low voltage circuit (120 VAC or 220 VAC, depending onlocale/configuration). I've been to several sites where the maintenance technicians forgot that the AC power to the plugs had

been isolated during preparations for the outage and were claiming the Mark V wasn't working correctly when they forced thelogic signal to energize the spark plugs because they weren't sparking.... The Mark V just switches an AC source which isexternal to the Mark V to energize the spark plug transformers. The Mark V does NOT provide the AC sources for the spark

plug transformers; it simply serves to switch the AC source on and off (by closing or opening relay contacts). The AC sourcemust not be isolated during this test.

Hope this helps--wish I could be more specific about the exact logic signal which drives the relay output at your site, but it'salways best to refer to the documentation for your site (including configuration files).

Posted by pascal on 22 December, 2013 - 7:14 am

Shyam

Just check on your wiring list (or interconnecting diagram) where is your ignition transformer connected it will give you thename of the signal to force, but usually forcing L2TVX will do the job all other signals are some "spare" one (at the time therewere two ignition transformers such as with Frame3 GT).

I am just a little worry about you last signal L2TVX1A_REF, is your card the VPRO card connecting the ignition transformer?and in that case it would be useful to also force the signal L4_XTP (also sometime named L4NEG) but usually ignitiontransformer are connected to TRLY card.

Posted by CSA on 22 December, 2013 - 2:31 pm

pascal,

Mark V's don't have TRLY cards; Mark VI's and Mark VIe's do.

The "standard" for discrete outputs for all digital Speedtronic turbine control panels (if adhered to by designers and field people) is to use a separate logic signal name to "drive" an output and NOT to use contacts associated with that logic signalanywhere in logic. That way, when an output is forced the force does only one thing: acts on the output. And does NOTaffect anything else in logic/sequencing/control.

Sometimes, but not always, the separate logic signal is driven, in a separate rung, by the "main" logic signal, but frequently--especially in Mark V--the output logic signal coil is in configured to be in parallel with the logic that drives the "main" logicsignal (L2TVX in this case). So, just forcing L2TVX will likely NOT force L2TVX1.

And, if the original poster looks in the CSP no contacts associated with L2TVX1 (and possible L2TVX1A) should be found anywhere else in the CSP--because they are only driving outputs.


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I, too, was surprised to see the L2TVX1A_REF signal, but I wouldn't be surprised to find the signal in a Mark V that'srecently been "upgraded" to a Mark Ve or whatever they're calling it these days, or as some "artifact" of some unused logicsignal that somehow was mistakenly left in the CSP for that site. But, without being able to see the CSP and know moreabout the "Mark V", it's impossible to say for sure.

In the Mark V, trip solenoid outputs driven by the

core frequently had _REF signals associated with them, but the spark plug transformers were not usually driven by

....

Posted by shyam on 25 December, 2013 - 2:21 am

Thanks for your valuable reply. for a couple of days i am not in the site so i could not check the TC2KREPT.TXT and IO.ASG files. but as per wiring drawings it is showing there is 2 relays named-L2TVX1 and L2TVX1A. the control signals(relay drive) for L2TVX1 connected to the, DTBD - 61&62 and the control signals (relay drive) for L2TVX1Aconnected to the,

PTBA- 65&66.

230V AC taken from the external source and going to the ignition transformer through these relays. ie, phase is goingthrough one relay and neutral is going through another relay. Still i am confusing about the last signal "L2TVXIA_REF".

Expecting your feed back..

In my view i think i will have to force both L2TVX1 & L2TVXIA signals to make spark plug activation. can you givefeedback?

Posted by CSA on 25 December, 2013 - 1:56 pm

shyam,

Okay, so part of the mystery is solved. L2TVX1A is assigned to an output of

core, which explains theL2TVX1A_REF (the Mark V uses the _REF signal as a check to see if the output has, in fact, been energized--or de-energized--when commanded).

I don't have access to a Mark V Application Manual, GEH-6195, at this writing to know exactly which output is beingused from the

core. My concern stems from the fact that AC is necessary for the spark plug transformers, and manyof the

core outputs are hard-wired/configured to pass DC (for trip solenoids). So, I'm a little confused about how the

panel is configured.

I would suggest actually tracing wires in the panel to be certain one wire is actually physically connected to the

core;as was said before, it's extremely common to find documentation that was never updated during installation/commissioningto reflect wiring changes made to the Mark V Panel.

If, in fact, the spark plug transformers are connected to the

core the task of energizing them is going to be quite a bitmore complicated. Presuming one leg of the spark plug transformer supply IS connected to the

core you will need toensure that the emergency trip push-button circuit connected to the

core is complete (no P/Bs are latched in the trip

position; many LOTO procedures require at least one E-Stop P/B to be latched and "locked" in the tripped position.

Next, you will need to force the following signals to the following logic states:

L2TVX1 = " 1"L2TVX1A = " 1"L4_XTP = " 0"


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If you don't force L2TVX1A_REF the output will work, BUT you will get a Diagnostic Alarm output feedback notagreeing with reference or something to that effect. You could also for L2TVX1A_REF to a logic "1" to prevent thatDiagnostic Alarm, but it's an unnecessary step.

Without being able to look at a Signal Flow Diagram (in GEH-6195) I can't understand how an AC signal can be passed through a DC circuit (I'm assuming the

core has a TCTG card, which most GE-design heavy duty gas turbine Mark V control panels use). So, I'm a little leery of whether or not the documentation actually reflects the currentwiring/configuration of the Mark V--but stranger things have happened!

I would suggest, again, that someone take the time to physically trace the spark plug transformer wiring in the Mark V panel, draw a schematic of the circuit, and use this in the future when wanting to perform this test again. It will likely savea lot of effort--and frustration. This could be part of a procedure that outlined what needed to be forced to what logicstate--again, this could be very helpful in the future.

Please write back to let us know what you find and how the test worked (what you had to force; etc.).

Posted by shyam on 26 December, 2013 - 11:25 am

We successfully tested both the spark plugs simultaneously by forcing L2TVX1, L2TVX1A and L4_XTP. Thanks for your support and feed back.

Posted by CS A on 26 December, 2013 - 1:47 pm

shyam,

You are most welcome!

Thanks for the feedback, also. 'Feedback is the most important contribution!'(c) here at control.com. It is whatdistinguishes control.com from a lot of other Web-based forums. When posters who receive assistance fromresponders on control.com provide feedback it lets other people who read these posts--now, and in the future--if theinformation provided was helpful, or not (as the case may be).

I want to be very clear about this particular post, though. It is NOT typical for either leg of the spark plug power source to be connected through the

core of a GE Speedtronic Mark V turbine control panel, so, it's not generallyrequired to force L4_XTP in order to be able to energize the spark plug transformers/spark plugs.

It's unclear (to me, anyway) why any leg of the spark plug power source would be assigned to the

core, unless itwas something demanded during commissioning or by some local technical code or regulation. Even so, it's not clear how an AC source can be routed through the

core trip solenoid outputs. (I do NOT have access to Mark V SignalFlow Diagrams at this writing, so I'm not clear what function PTBA-65 & -66 are connected to in the

core.)

Again, congratulations on the successful--and safe--test. And, thanks for the feedback!

Posted by G.Rajesh on 30 December, 2013 - 1:13 am

It's new subject for us too, spark plug is connected in

core.

But questioner Mr.Shyam can make sure without L4_XTP=0 spark plug is not energized.


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Take careG.Rajesh

Posted by shyam on 8 January, 2014 - 1:20 pm

sorry i was not in the site at the time of testing. i just given instruction to my colleague for testing the spark plug, so icouldn't check your point. this both relays are mounted separately.

anyway i will try to confirm your point and come back to you.

Posted by shyam on 22 June, 2014 - 10:10 am

Sorry for the late reply. We are using 2 relays to give the supply to ignition transformer, one relay drive signal isconnected to DTBD & another relay connected to PTBA. So without forcing this L4_XTP.

The relay which is connected to

will not energize and cannot perform spark plug test..ie, one relay (NO)contact for phase and another relay (NO)contact for neutral of 230v ac as the input of ignition transformer. Once again sorry for the late reply.

Posted by CS A on 23 June, 2014 - 1:04 pm

shyam, or SHYAM,

The configuration you are describing is not typical, so without being able to see the schematic drawings for thecircuit it's very difficult to say for sure what might be the problem.

And I'm not clear if there is second, physical relay that's connected to

, or if it's a second relay output of (or even if there is a ).

I'm going to venture a guess and say that the second relay (the one connected to

) is actually being used tointerrupt the AC neutral to the ignition transformers--but that's just a guess; it may, in fact, be in series with therelay output of . Again, without being able to see the electrical schematic drawing of the circuit it's verydifficult to say with any degree of certainty. You could try measuring the AC voltage across the contact(s) of thesecond relay (the one that's connected to

). You could also use the multimeter to see if one side of the second relay's contact(s) is connected to neutral (earth; ground).

My other scientific wild-arsed guess is that there is a second relay output of the Mark V that is being used toapply power to the coil of the relay to energize the second relay's coil to close the contacts. This should be veryevident in the CSP because it would have to be a logic "1" at the same time as the L2TVX1 relay (that's thetypical signal name; look at the I/O Report to find the actual name used at your site). So, it should be possible tofind that second relay's name, and then use the I/O Report and/or IO.ASG To find which relay output the coil of the second relay the contacts of which are connected to

is located. But, it's a pretty safe bet that a second relay output from the Mark V has to be used to drive the relay that's connected to

--and this is presuming thatthere is a second physical relay (an "interposing" relay) connected to

.

Have you traced the wires in the ignitor circuit from

to see where they go? That will tell you a lot about howthe relay needs to be energized.


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Please write back to let us know how you fare.

Posted by Batman on 29 July, 2014 - 10:44 am

CSA,

I have a question on ignition excitation logic, but before asking that I will post Mark vie version of the controlsequence. L2TVX is "ignition permissive" & l2tvx1 is "ignition permissive relay", which is energized when theoutput of the block L2TVX is "1". Apart from supplying the AC voltage by external means to ignition exciters95SG-2A,3A which in turn make the spark plugs 95SP-2 & 95SP-3 "on", l2tvx1 is also used in a block, which isused for L30SG1_ALM i.e. "EXCITER CHANNEL FAILED WITH IGNITOR ON alarm" with a time delayof K30SG1_ALM (1sec). I guess L30SG1_ALM is like L2TVX1A_REF in Mark- V, which is a check to see if the output is energized or de-energized when commanded.

l 30sg1 l 2t vx1 L30SG1_ALM | / | - - - - - - - - | | - - - - - - - - - - - ( )

Here comes the confusion. In the device summary, the description of 30SG-1 is"DIAGNOSTIC IGNITION EXCITER SWITCH

NORM=NO; CLOSE ON EXCITER FAILURE;".

If we go by the logic block l30sg1 is an "NC" (NOT Gate used), but the device summary says it's an "NO"contact, and it closes on exciter failure. It seems to be contradictory & creating confusion.

Note: The info posted above is collected from the O&M manual & device summary, not from the ToolboxST.

1 out of 1 members thought this post was helpful...

Posted by CSA on 29 July, 2014 - 3:19 pm

Batman,

This is an all-too-common alarm and problem, and may involve ... inversion masking.

The high-energy ignitor power source, 95SG (there's usually only one of these ignitor power supplies, whichdrives two (2) ignitors ("spark plugs")) has a discrete (contact) output which changes state under somecondition. I don't recall if it changes state when both ignitor outputs ARE working, or when one of the ignitor outputs is NOT working. Let's say it changes state when BOTH ignitor outputs ARE working, first.

l2tvx1 is the discrete output of the Mark VIe that, when a logic "1", will apply single-phase AC to 95SG,energizing 95SG. So, when l2tvx1 is a logic "1" the input to 95SG should be energized, and the outputs of 95SGshould also be energized.

(There may be two 95SGs, and the discrete outputs may be connected in series or in parallel.... Things dochange over the years.)

For now, lets' say there's only on 95SG with two outputs, and in this case, when the ignitor power source isenergized and BOTH ignitor outputs are working if the NO contact changes state and closes that would be anindication that both ignitor outputs are working (it doesn't say both ignitors are firing--just that the outputs to bothignitors are energized). In this case, if the input was NOT inverted and the contact closed then l30sg1 would go


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to a logic "1" and the normally open contacts of l30sg1 in the rung you provided would OPEN and there would be NO alarm--which would be correct, right? Both ignitor power source outputs are energized when the input to95SG is energized, and when the application code is telling the ignitors to be energized that's what is desired.

Now, let's continue to say that the discrete output of 95SG changes state when BOTH outputs are energized--however, one of them does not get energized when the input to 95SG is energized. In this case, the discreteoutput would NOT change state (the NO contacts would not close) and if the l30sg1 input were NOT inverted then l30sg1 would NOT go to a logic "1" which means the normally closed contacts of l30sg1 in the rung you

provided would remain closed and one second after the input to 95SG was energized the alarm would beannunciated--which would be a true and correct condition.

All good so far--if we presume the NO discrete output of 95SG changes state when BOTH ignitor outputs areenergized AND when the discrete input driving l30sg1 is NOT inverted.

Let's take the other condition: The discrete output of 95SG changes state when ONE of the outputs is NOTenergized. In this case, if both outputs of 95SG are energized when the input of 95SG is energized the discreteoutput will NOT change state, and if the discrete input driving l30sg1 is NOT inverted, the normally closed contacts of l30sg1 will remain closed and after the time delay the alarm will be annunciated. Which would beincorrect.

But, if one of the 95SG outputs did not energize when the input of 95SG was energized then the discrete outputWOULD change state from NO to closed, and if the discrete input driving l30sg1 was NOT inverted thenl30sg1 would go to a logic "1" and the NC contacts of l30sg1 would open and there would be NO alarm. Whichwould be incorrect.

If the inversion mask of the input driving l30sg1 were changed to INVERTED, then the alarm logic would work correctly if the NO discrete output of 95SG changed state when one 95SG output was NOT energized, and when both 95SG outputs were energized.

So, you need to know a couple of things at this point. One, what is the state of the discrete output when 95SG is NOT energized. Two, what is the state of the discrete output when the input of 95SG IS energized AND bothoutputs ARE energized? I don't know how to simulate the condition when only one output of a working 95SG is

not energized, so I can't help with this.

You may have to have both ignitors out and "on the deck" to see if they are both sparking when the input of 95SG is energized. Of course, if one of the ignitors wasn't working even when it was energized that would be a

bad test, so it would be necessary to switch the ignitors and perform the test a second time. (The outputs of 95SG are too high to measure with a normal multi-meter.)

You also need to know if the Mark VIe discrete input driving l30sg1 is inverted or not inverted.

I generally read the information in the Device Summary and the Manual, but I trust only what I personallyobserve. And, then I go from there. Ideally, if it were my call as the responsible design engineer for the system,I'd want a NO discrete output from 95SG that changed state when the input of 95SG was energized and BOTHoutputs were working--as in our first example above. I would then connect that to a NON-INVERTED input of the Speedtronic to drive l30sg1, which would be logic "0" when the input of 95SG was not energized, and would change to a logic "1" when it was energized and BOTH outputs were working. If 95SG was energized and oneoutput did not work, then the discrete output of 95SG would NOT change state, and l30sg1 would NOT changestate and the NC contacts would remain closed and the alarm would be annunciated.

This would be the most correct indication of the state of 95SG's outputs, and would provide an alarm if a wirewere to come loose in the circuit at some point. Using a NO contact to close when there is a fault will preventan alarm from being annunciated when there is a fault.

I hope this is helpful; it's not very easy to describe in writing. And, when it's not properly commissioned it can bea nuisance alarm for years.


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Again, my recollection is that the discrete output of 95SG changes state when BOTH output of 95SG areenergized when the input to 95SG is energized. If that's true, then it should be connected to a NON-INVERTED input of the Mark VIe, that changes state when the NO contacts of 95SG change state. And, thenthe rung you have provided will work correctly because l30sg1 will be a logic "1" when BOTH outputs of 95SGare energized when the input to 95SG is energized.


CSA,

Thank you for the quick reply. I was under the impression that,

a) 30SG-1 & l30sg1 are same, but I was wrong. From your reply I understand that 30SG-1 is a discrete outputof 95SG and l30sg1 is a discrete input to the Mark VIe through an I/O pack, which changes it's state when30SG-1 is closed.

b) "NC" & inversion (using NOT Gate) are same, but now I realize that an NC relay (l30sg1 in this case) can

be inverted again in the logic block.

I have info only about 30SG-1 that it's an "NO" relay, but I am not sure if l30sg1 is an "NC" relay.

Hope I am correct this time, will wait for your reply before asking more questions.

1 out of 1 members thought this post was helpful...Posted by CSA on 30 July, 2014 - 12:27 pm

Batman,

30SG-1 "drives" l30sg1. You should think of it like this:

NORMAL ( Non- I nver t ed) Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal |

Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - | | - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( ) - - - | |

It's important to note that we are talking about a NORMAL (Non-Inverted) discrete input to a digitalSpeedtronic turbine control panel. (We'll discuss INVERTED discrete inputs below.)

It's a rung, yes, but the vertical line in the drawing represents a "division" between hardware and software.What I'm trying to represent is that a physical device (a pair of normally open contacts in this case) "drives" or


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in GE-speak "writes to" a software coil, energizing or de-energizing the software coil if the hardware contactsclose or open, respectively. Yes, l30sg1 is a discrete input to the Speedtronic, but it's really a software coil--withassociated normally open and normally closed contacts. The "coil" of l30sg1 never appears in any ToolboxSTrepresentation, or Legacy Toolbox representation, or in any Mark V representation. However, the Mark IVSpeedtronic Elementary--the finest digital Speeedtronic document ever produced by GE-- DID show therepresentation above. It's how I visualize EVERY single discrete input to any digital Speedtronic turbinecontrol panel. Because, it's what is happening--but it's never shown in modern digital GE Speedtronicrepresentations.

Moderator's Note : the sentence below has been corrected at the author's request.

In the rung above, when the physical contact (30SG-1) is open, the software coil (l30sg1) will be a logic "0",false, dropped out. Just like with any coil (software or hardware) there are contacts associated with the coil:normally open contacts and normally closed contacts.


Har dware | Sof t ware

- - - - - - - - | - - - - - - - - | Physi cal | Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - | | - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( ) - - - | | | | | | | - - - | | - - - | | | - - - | / | - - -

| | OR l 30sg1 | - - - | | - - - | l 30sg1 | - - - | / | - - -

In the drawing above, I'm trying to show normally open and normally closed software contacts "driven by" thesoftware coil l30sg1. The vertical line down from the l30sg1 coil is meant to show that when L30sg1 changesstate, the contacts change state. Below that, I'm just trying to show another normally open- and normally closed set of contacts associated with l30sg1--and they also change state when the software coil l30sg1 changes state.These software contacts can be used in any rung or function block in application code--there's no limit to the

number of normally open or normally closed contacts, and the state of the contacts (open or closed) is a functionof the state of l30sg1. Just like with a physical relay, or pressure switch or temperature switch. When the relayor temperature switch or pressure switch is NOT actuated, normally open contacts of the device will be OPEN,and normally closed contacts of the device will be CLOSED. When the relay or temperature switch or pressureIS actuated, normally open contact of the device will be CLOSED and normally closed contacts associated withthe device will be OPEN. (I don't know about NO coils and NC coils; I only know about NO contacts and NCcontacts.)

When the normally open contacts of 30SG-1 are open then l30sg1 will be false, a logic "0". This means thatnormally open contacts associated with l30sg1 will remain open, and normally closed contacts associated withl30sg1 will remain closed. And, when the normally open contacts of 30SG-1 close the software coil l30sg1 will

be a logic "1" (true). When l30sg1 is a logic "1" (true), normally open contacts associated with l30sg1 will close,


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and normally closed contacts associated with l30sg1 will open. Here's a table to describe this:


30SG- 1 NO l 30sg1 Coi l L30sg1 NO l 30sg1 NC Cont act St at e Logi c St at e Cont act St at e Cont act St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - OPEN " 0" ( Fal se) OPEN CLOSED CLOSED " 1" ( Tr ue) CLOSED OPEN

So, to your a) statement, I respond that you are correct--mostly--in that 30SG-1 is a discrete input through anI/O Pack which changes the state of l30sg1 based on the state of 30SG-1. But, I want to be clear: It's asoftware coil (l30sg1) that changes state when the discrete input (30SG-1) changes state. And, normally open-and normally closed software contacts associated with l30sg1 change state when the discrete input (30SG-1) tothe I/O Pack changes state.

I don't know how to respond to your b) statement; I don't know what your experience or frame of reference isfor inverted signals. Yes, a normally closed contact is an "inverted" normally open contact. But, that's not how Ithink of normally open versus normally closed. I prefer only to think of coils as being 'normal' or 'inverted'--I'llexplain below.

Let's talk about inverted inputs, and inversion masking--as done by GE in their digital turbine control panels.Let's presume that discrete input l30sg1 was inverted in the I/O Pack configuration; it's pictorial representationwould look like the drawing below, and it would also have normally open and normally closed software contactsassociated with it:

I NVERTED Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal | Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - | | - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( I ) - - - | | | | | | | - - - | | - - - | | | - - - | / | - - - | | OR l 30sg1 | - - - | | - - - | l 30sg1 | - - - | / | - - -

Note the "I" in the coil of l30sg1; this represents an inverted coil , or, an inverted discrete input. Note also thatthe inverted discrete input has normally open and normally closed software contacts associated with it.


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The table below shows what the states of the various elements of the discrete input will be based on the state of the normally open contacts of 30SG-1:

I NVERTED Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel

30SG- 1 NO l 30sg1 Coi l L30sg1 NO l 30sg1 NC Cont act St at e Logi c St at e Cont act St at e Cont act St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - OPEN " 1" ( Tr ue) CLOSED OPEN CLOSED " 0" ( Fal se) OPEN CLOSED

For an inverted input, the l30sg1 coil will be a logic "1" when 30SG-1 contacts are open (the opposite of whatone would expect!), and normally open l30sg1 contacts would be CLOSED and normally closed l30sg1 contactswould be OPEN. I prefer to think of inversions as only being applied to software coils, not to contacts.

This is where, I think, a lot of people get confused. Normally open contacts can be open or closed, and normallyclosed contacts can be open or closed. They're not always open or closed, respectively; they change state based on the state of the device (for real, physical contacts) or software coil (for software contacts) driving them.ALWAYS, normally open contacts associated with a device or software coil are OPEN when the device isNOT actuated or when the software coil is a logic "0" (False). And, ALWAYS normally closed contactsassociated with a device or software coil are CLOSED when the device is NOT actuated or when thesoftware coil is a logic "0" (False). When the device or software coil IS actuated or when it's a logic "1" (True),normally open contacts associated with the device or the software coil are ALWAYS CLOSED, and normallyclosed contacts associated with the device or the software coil are ALWAYS OPEN (when the device ISactuated or when the software coil is a logic "1" (True)).

I hope this helps. Again, I don't know what your experience has been with inverted signals; quite often peoplerefer to "inverting" a contact when they are changing the contact from normally open to normally closed, or viceversa. To my way of thinking, I don't want to get that confused with inverted discrete inputs versus non-inverted discrete inputs. Both can have normally open and normally closed contacts that ALWAYS behave in the sameway with respect to the device or software coil status. It's only the software coil status that changes based onit's inversion mask setting (NORMAL or INVERTED).

If it's not clear, let me know. I'll try a different tack (to use a sailing term). I have read and re-read and re-re-read the above in an effort to try to ensure there are no errors--but, I'm not the best person to proof-read myown writing. If there are errors, I will try to persuade the Kind, Friendly Moderator to correct them for me.


CSA,

I am really amazed by your sheer persistence to offer help to the needy. And after spending lot of time in typing& re-reading, you were even ready to offer more support if it's not clear. OMG!! I would not do that to astranger if I were you (hate to say this, though). Really we are very fortunate to have you here.

I hope It's clear for me now. Inversion is applied to the software coils, not to the contacts associated with it. Sothe inverted discrete input to the TCP, would result in a block like this, as you said in your reply.

30SG- 1 NO l 30sg1 Coi l l 30sg1 NCCont act St at e Logi c St at e Cont act St at e


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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -OPEN " 1" ( Tr ue) OPEN

CLOSED " 0" ( Fal se) CLOSED

I'll put it this way. 30SG-1 closes on ignition exciter fault (sensing one faulty output or both exciters fault is notknown at this moment), and since inversion is applied to the l30sg1 COIL, it's output to the NC contact is "zero"& which in turn gives output "1" and generates the alarm. But how to identify that an inversion is applied to asoftware coil? Is there any other means to know, than to find it out accidentally & hoping that it must have been

inverted? Has it got something to do with "inversion masking", like it's inverted but "masked"? Guess I am askingtoo many questions, but I am not in a hurry to learn, so reply me when you have free time.

And thanks a ton again for your generous reply to my previous post.

1 out of 1 members thought this post was helpful...Posted by CSA on 31 July, 2014 - 10:09 am

Batman,

I don't think we know when 30SG-1 changes state, actually. We don't know if it changes state when the input to95SG is energized and both outputs are energized, or if it changes state when the input to 95SG is energized and at least one of the outputs is NOT energized. My suggestion to you is to use Trend Recorder to monitor l2tvx1and l30sg1 during the next START. We'll presume that both outputs are energized when the input to 95SG isenergized (that's a fair assumption for now, especially if the unit and ignitor power supply are relatively new). If l30sg1 changes state very shortly after l2tvx1 changes state then my presumption would be that 30SG-1changes state whenever the input to 95SG is energized and BOTH outputs are energized. (This seems to bewhat happened on units I've worked on in the past. This is a "positive" indication that the ignitor outputs are bothenergized when the input to 95SG is energized. If one or both outputs were not energized when the input to95SG was energized, then 30SG-1 would NOT change state--indicating a failure of one or more exciter "channels" (I've always hated that description, but no one ever asked me what the alarm text message should

have read). This would also go along with GE's philosophy of using device contacts that open to alarm or trip-- because the normally open 30SG-1 contacts would NOT close if one or both of the outputs were not energized when the input to 95SG-1 is energized.

As for determining if a discrete input is inverted or not, one needs to use ToolboxST and open the configurationof the I/O Pack(s) through which the signal in question is connected, scroll to the signal name, and then check the configuration of the signal in the main window of ToolboxST. It will read either INVERTED or NORMAL(Not Inverted), or, if the input is unused I think I will read NOT USED. I forget the name of this parameter for discrete inputs, but it should be easy to locate.

I'm pretty certain that if you were able to disassemble 95SG you would find a small electro-mechanical relay,and a normally open contact of that relay would be connected to the two terminals which are 30SG-1. (It might

be a solid-state relay, too; who knows. The point is: A normally open contact of a relay of some sort in 95SG isconnected to the two terminals being described as 30SG-1.) So, there is some internal circuitry that energizesand de-energizes the relay I'm going to call 30SG-1, and a normally open contact is wired to the two terminalsthat are ultimately wired to the two discrete input terminals that drive "imaginary" software coil l30sg1.Imaginary software coil l30sg1 may--or may not--be inverted; that's done in the I/O Pack configuration for thatinput using ToolboxST. Software contacts associated with "imaginary" software coil l30sg1 are used in the rungyou provided to generate an alarm when there is a problem with one or both of the high-energy ignitor exciter

power supply outputs.

I have a question for you, Batman. Why did you choose this particular alarm and discrete input and alarm? Doesthis alarm get annunciated every time the unit is started? Or, has this alarm just recently start to be annunciated every time the unit is started?


13/21

I have been to MANY sites that have this alarm every single time the unit is started--and no one ever takes anyaction. Why? Because the commissioning person from the turbine packager did nothing, and just said, "That'snormal; it will happen every time the turbine starts." Which is hooey. So, please tell us why you chose this inputand alarm to inquire about. Thanks!

Posted by Batman on 31 July, 2014 - 8:34 pm

CSA,

I have not faced any problem with this alarm, but when I was going through the start up sequence, this particular block confused me. Now I have a better idea, thanks to you & control.com. I worked in thecommissioning, involved in few start ups in which the turbine was loaded to spinning reserve. Now I am on to adifferent assignment, trying to understand Mark Vie control philosophy during free time.From one of your posts in a different forum I understand that the exact purpose of inversion masking is to makethe logic signal associated with a discrete input a logic "1" when the contact or the circuit is open. I am not sureit it's used here. Please shed some light on this.

Posted by CSA on 31 July, 2014 - 11:10 pm

Batman,

Can you provide a link to the comment so I can build on the information for the explanation?

Posted by Batman on 1 August, 2014 - 8:58 am

> Can you provide a link to the comment so I can build on the information for the explanation?

CSA,

It's from the forum "Getting a better understanding of gas turbine control" and the link ishttp://www.control.com/thread/1399292917.Comment Posted on 18 May, 2014 - 12:46 pm.

1 out of 1 members thought this post was helpful...Posted by CSA on 1 August, 2014 - 4:02 pm

Batman,

I have a better thread (not forum--control.com is the forum, which has individual threads (questions)):

http://www.control.com/thread/1026245600#1026245640

Try this and see if it's helpful or not. (I HOPE it is!)

And to your comment about not helping a stranger, we're all strangers until we meet--even if it's in a World Wide Web/Internet forum, AND I'm not just helping you. Hopefully I'm helping many others--not just now, but


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later, as others find and read the thread and responses.

As I've said before, I was extremely fortunate to have had a "stranger" (as he was in the beginning) help memany, many years ago when I didn't know a compressor bleed valve from a purge solenoid from a false startdrain valve from an LVDT (heck--I couldn't even spell LVDT then!), and so I'm just paying it back, and alsotrying to "pay it forward" to some extent in the hopes that others will learn and be able to do the same with other "strangers" in their lives.

I'm not sharing any proprietary information, and none of this stuff is the "rocket science" it's made out to be. A

lot of if is really simple--if people will just take the time to RTFM (Read The Fine Manual) and do a little bit of Internet research. I do realize that in some parts of the work Internet access is restricted, but I find in thosesame parts of the world that there is (UNFORTUNATELY!!!) a LOT of copyrighted material illegally posted to the World Wide Web/Internet so information is available, just not in more easily accessible locations. (I AMNOT encouraging anyone to ever download copy-righted material that has been posted illegally posted somewhere. Not ever. Never. I'm just saying that it's pretty hypocritical to block access to some sites and

permit access--even encourage, as I've seen in some cases--use of sites that have illegally posted copyrighted material available for download. And that's all I'm going to say on this subject--information is out there, if one is

patient and creative and ambitious.)

Anyway, have a read of the thread above--and my upcoming post to this thread--and see if it all begins to makesense. Actually, I recommend you read them several times over a couple of days, maybe longer, before askingfor any clarification. It's a LOT of information, but hopefully presented in a clear and (intended) concise way,while being as literal as possible (considering all the possibilities and detailing them to make everything as clear as possible).

Together, after reading the two threads (more than once), you should be able to understand the reason for inversion masking, even if, technically, it's not really required in today's digital world of automation controllers.It's still a very useful concept to grasp--open to alarm/trip; closed on good/normal. And, I've been to MANY

plants all over the world (industrialized, first-world countries as well as non-industrialized second- and third-world countries) where BAD things have happened when 'open to alarm/trip; closed on good'normal' hasn't

been used/followed consistently in the plant design and commissioning.

One doesn't technically need inversion masking, it's just makes some things simpler (once certain decisions have been made, and continued through the decades even when control automation systems have changed). It's justone way of accomplishing something that could be done another way--but, as in most parts of the capitalisticworld: if it ain't broke, don't fix it. Changing it in the GE world would entail a LOT of changes to a LOT of drawings and application code--and, again, if it ain't broke, why fix it? (But they should be much better atexplaining it, shouldn't they? Because even their field service personnel and in many cases their control design

personnel don't know or understand this stuff. And that means they can't explain it to anyone else, either.)

And, I always encourage everyone to do this when encountering something new or unusual: Draw things in amanner that makes sense to them while trying to work out and understand them. Sometimes, a drawing from amanufacturer can seem very obtuse and confusing, and just re-drawing it in a manner that you're comfortablewith can be very enlightening. Once you see it in a familiar format, it will make sense in it's "native" format, too.

Use logic diagrams and tables as you work through things and issues--they can be very helpful and useful.

Remember: "Learning is finding out what you already knew." (Richard Bach, 'Illusions') And it is, isn't it? Whensomebody explains something so that you (finally) understand it, or when you finally come to know that youunderstand something, doesn't it feel like, "Hey! That makes sense! I knew that!!!" And we all do, it's justfinding the way to, using our experience and points of reference, have it make sense with what we alreadyknow--and then it really is just like we knew this, we just didn't know we knew it.

I really enjoy seeing that "light" come on for people when they finally realize, "Hey! That's it! I knew this, and now I know I know it!" The expression on someone's face when they have that realization is absolutely


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priceless--even if I can't see their face!

As a former colleague was fond of saying, "This ain't rocket science!" And it's really not. But until one takes thetime to research and understand--and to question things they're told and review and analyze them to see if they're logical and true--a lot of this stuff seems like rocket science.

2 out of 2 members thought this post was helpful...Posted by be_anon on 1 August, 2014 - 10:24 am

> I don't think we know when 30SG-1 changes state, actually.

This may help, from the manual. Note the ignitor box has both NO and NC contacts for 30SG-1:

The exciter contains a diagnostic circuit that operates each time the exciter is operated (each time exciter is inthe "ON" condition). The diagnostics circuit has no effect on the operation of the exciter. The diagnostic circuitmonitors the exciter operation for these two things:

1-Output Voltage for a "minimum" value of approximately 15 KV

2-Spark Rate for a "minimum" value of approximately 1.0 sparks/second.

If the Output Voltage or the Spark Rate becomes less than the "minimum" value, a relay in the diagnostic circuitis energized and will stay energized for the remaining time the exciter is in the "ON" condition - the relay is de-energized when input power is removed from the exciter (when exciter is in the "OFF" condition).The relay is connected to three terminals of the "Diagnostic Output" terminal strip, but does not send anelectrical signal to those terminals. To have an indication that an exciter malfunction has occurred, an externalcircuit (supplied by the operator) must be connected to the "Diagnostic Output" terminal strip. When the relay isenergized, a circuit between a pair of "normally open" terminals is changed to closed, and a circuit between a

pair of "normally closed" terminals is changed to open.

1 out of 1 members thought this post was helpful...Posted by CSA on 1 August, 2014 - 5:43 pm

be_anon,

Thanks for the information!

So, the diagnostic circuit operates each time the exciter (the ignitor power supply) is energized (so when l2tvx1is a logic "1"). And a relay in the diagnostic circuit operates when there is a fault (low output or low spark rate).

Hmmm.... (That brings up more questions about the alarm text message, but that's for another day.)

So, in this case, 30SG-1 changes state when 95SG-1 is energized AND there IS a fault.

As with the other "big" response earlier, I have read and re-read and re-re-read and re-re-re-read the post tofind errors. Again, I hope the Kind, Friendly Moderator would accept a request to fix any errors should theyrear their ugly heads after it is posted. (Thanks in advance!)

Batman,

Let's take the case of the 30SG-1/l30sg1 discrete input circuit being wired to the normally open (NO) contact of the ignitor exciter diagnostic circuit. Here's our drawing of a non-inverted input circuit:


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NORMAL ( Non- I nver t ed) NO 30SG- 1 Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( Cl oses) on a Faul t )

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal | Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - | | - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( ) - - - | | l 30sg1 | - - - | / | - - -

And here's the alarm rung from Batman's post above:

l 30sg1 l 2t vx1 L30SG1_ALM - - - | / | - - - - - - - - | | - - - - - - - - - - - ( )

And here's a table of what happens when l2tvx1 is energized and there is NOT a fault in the ignitor exciter:


l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - " 0" OPEN "0" ( Fal se) CLOSED " 0"

" 1" OPEN "0" ( Fal se) CLOSED " 1" - ALARM!!!

In this case, l30sg1 is a logic "0" when there is not a fault. Because the NC l30sg1 contacts in the alarm rungwould be closed when there is not a fault this would mean that every time the ignitors were energized and therewas NOT a fault that the Mark VIe would annunciate an alarm--erroneously. (Oh no, Mr. Bill!!!)

And here's a table of what happens when l2tvx1 is energized and there IS a fault in the ignitor exciter:


l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - " 0" OPEN "0" ( Fal se) CLOSED " 0"

" 1" CLOSED "1" ( Fal se) OPEN " 1" - NO al ar m

In this case, l30sg1 is a logic "1" when there is a fault. This would also mean that if the ignitors were energized and there WAS an alarm that the alarm would NOT be annunciated (because the NC l30sg1 contact in thealarm rung would be open). Both conditions are BAD --an alarm when there is NOT a fault, and no alarm when


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there IS a fault.

Now, let's see what would happen if someone just inverted the 30SG-1 input (l30sg1) to the Mark VI, whileleaving the circuit connected to the NO contact of 30SG-1:

I NVERTED NO 30SG- 1 Di sc r et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( Cl oses) on a Faul t )

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal | Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - | | - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( I ) - - - | | l 30sg1 | - - - | / | - - -


l 30sg1 l 2t vx1 L30SG1_ALM - - - | / | - - - - - - - - | | - - - - - - - - - - - ( )

And here's a table of what happens when l2tvx1 is energized and there is NOT a fault in the ignitor exciter when the 30SG-1 (l30sg1) discrete input is inverted:

I NVERTED NO 30SG- 1 Di scr et e I nput

t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( Cl oses) on a Faul t )

l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - " 0" OPEN "1" ( Tr ue) OPEN " 0"

" 1" OPEN "1" ( Tr ue) OPEN " 0" - NO Al ar m

In this case, l30sg1 is a logic "1" when there is not a fault--and there would not be an alarm when there was nota fault when the ignitor exciter was energized because the NC l30sg1 contact in the alarm rung would be open--and this is as it should be.

And here's a table of what happens when l2tvx1 is energized and there IS a fault in the ignitor exciter when the30SG-1 (l30sg1) discrete input is inverted:

I NVERTED NO 30SG- 1 Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( Cl oses) on a Faul t )

l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


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" 0" OPEN "1" ( Tr ue) OPEN " 0"" 1" CLOSED "0" ( Fal se) CLOSED " 1" - ALARM!!!

In this case if there was a fault when the ignitor exciter was energized, l30sg1 would be a logic "0" and the NCcontacts of l30sg1 could be closed and there WOULD BE an alarm. (All is good, Mr. Bill!)

NOW, let's consider what would happen if a wire fell off a terminal in the 30SG-1 circuit that was connected toan inverted input, or a wire came out of a crimp terminal lug, or a wire came loose from the Mark VIe input

terminal board for the 30SG-1 discrete input-- AND there was a fault when the ignitor exciter was energized,then even if the NO contact of 30SG-1 closed the Mark VIe would not see the change of state--and therewould be NO alarm when there was a fault. So, this is not a good thing--and is a "violation" of GE's policy of anopen circuit to alarm or trip and a closed circuit when the condition being monitored is good/normal.

All too often, unfortunately, people just simply change the inversion mask to make an input "work"--but it's notreally working properly, meaning that it would not alarm if there was an open in the circuit. Sure, there's noalarm when there's no fault, but what about when there is a fault and there is an open in the circuit and thecontact closure doesn't get to the Mark VIe? Then there is no alarm--and that's not really "working properly." Inthis case, the ignitor exciter, it's not really too much of a problem because this isn't used as turbine trip or shutdown condition. But, it could make troubleshooting difficult if the turbine were having difficulties starting thatwere a result of problems with the ignitor exciter that weren't alarmed because of a open in the input circuit.

So, how to fix this and ensure that an open in the circuit would not prevent a fault from being recognized by theMark VIe? Change the wire at 30SG-1 from the NO contact to the NC contact AND use a non-inverted input.

So, here's all the requisite drawings and tables for a NC contact from 30SG-1 connected to a non-inverted inputdriving l30sg1:

NORMAL ( Non- I nver t ed) 30SG- 1 NC Di scr et e I nput t o Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( Opens) on a Faul t )

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal | Cont act | 30SG- 1 I nput Scr ew l 30sg1- - - |/| - - - - - - - - - - o- - - - - - - - - - - - - - - - - - ( ) - - - | | l 30sg1 | - - - | / | - - -


l 30sg1 l 2t vx1 L30SG1_ALM - - - | / | - - - - - - - - | | - - - - - - - - - - - ( )

And here's a table of what happens when l2tvx1 is energized and there is NOT a fault in the ignitor exciter:



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l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - " 0" CLOSED " 1" ( Tr ue) OPEN " 0"

" 1" CLOSED " 1" ( Tr ue) OPEN " 0" - NO Al ar m

In this case, l30sg1 is a logic "1" when there is not a fault, and the l30sg1 NC contact in the alarm rung would beopen so there would be no alarm. This is good, right? When the ignitor exciter is energized and there IS NOT afault, there will NOT be an alarm.

And here's a table of what happens when l2tvx1 is energized and there IS a fault in the ignitor exciter:


l 2t vx1 30SG- 1 NO l 30sg1 Coi l L30sg1 NC L30SG1_ALM St at e Cont act St at e Logi c St at e Cont act St at e St at e - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - " 0" CLOSED "1" ( Tr ue) OPEN " 0"

" 1" OPEN "0" ( Fal se) CLOSED " 1" - ALARM!

In this case, l30sg1 would be a logic "0" when there was a fault, and because the l30sg1 contact in the alarmrung would be closed there would be an alarm. This would also mean that if the ignitors were energized and there WAS a fault that the alarm WOULD BE annunciated. This is good! This is what we want.

It would also mean that if a wire came loose (fell off) in the 30SG-1 circuit connected to the NC contact thatwhen the ignitor exciter was energized that an alarm would be annunciated--which may be "false", but it alertsthe operator and technician to a problem with the wiring (see more on this below). And this is good, too.

Right?

Well, almost.... By GE's convention, the discrete input coil is usually a logic "1" when there is an alarm or tripcondition, and in the above scenario with a NC 30SG-1 contact driving a non-inverted discrete input l30sg1, it(l30sg1) is a logic "1" when there is NOT a fault. And, the '30' in the signal name stands for "Alarm Device",which implies that when the signal is a logic "1" it should indicate an alarm (or trip) condition. Right?

Well, to make everything match GE's conventions for 'closed circuit to indicate good/normal conditions; opencircuit to indicate alarm/trip condition' AND the discrete input signal should be a logic "1" to indicate an alarm or trip condition AND match the signal naming convention (in this case, a 30 device is an alarm device--implyingthat when the signal l30sg1 is a logic "1" it's indicating a fault with "spark generator #1" (95SG-1)), we have to

invert the input AND change the sense of the contact in the L30SG1_ALM rung, like below:

NC 30SG- 1 Connect ed t o an I NVERTED Di scr et e I nput of a Di gi t al Speedt r oni c Tur bi ne Cont r ol Panel ( 30SG- 1 Changes St at e ( opens) on a Faul t )

Har dware | Sof t ware - - - - - - - - | - - - - - - - - | Physi cal | Cont act |


20/21


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find it a logic "0"--meaning that there was no fault when the ignitor exciter was de-energized. BUT, he findsl30sg1 a logic "1" when the ignitor exciter was not energized--indicating that either:

1) 30SG-1 is not working properly and the NC contact is "stuck" open

or

2) there is an open wire/termination somewhere in the 30SG-1 discrete input circuit

or

3) there is a problem with the 30SG-1 discrete input circuit of the Mark VIe (either the input terminal board hasa problem, or the I/O pack circuitry for that input has a problem)-- BUT in this case the Mark VIe would mostlikely be (SHOULD BE) annunciating a Diagnostic Alarm for this particular input circuit, so an alert technicianshould be able to quickly diagnose the problem as a Mark VIe problem because of the Diagnostic Alarm.

Using his trusty voltmeter, the technician measures the voltage at the 30SG-1 discrete input terminals and finds~130 VDC, indicating an open circuit. He then uses the drawings provided with the unit to check all theterminations in all the junction boxes out to the ignitor exciter junction box and ultimately he finds a wire hascome loose from a crimp terminal in the ignitor exciter junction box. He repairs the crimp (carefully--because itwill have ~65 VDC on the wire while the turbine is running!) and when he checks l30sg1 again using ToolboxSThe finds it is now a logic "0" when the turbine is running. (I would have gone immediately to the ignitor exciter

junction box to look for a loose termination or crimp; and if I didn't find anything there I would follow the conduitleaving the ignitor exciter junction box with the 30CG-1 wires in it to the next junction box, opened that junction

box and looked for loose wires/crimps, and so on until I found the problem. No need to find drawings--whichmay or may not have been marked-up to reflect changes during installation and commissioning.)

So, I think we've beat this subject to it's (hopeful) conclusion.

Posted by Batman on 2 August, 2014 - 10:11 am

CSA,

Can't ask for more!! Thanks a lot for your help & guidance. I'll go through the link you provided, before askingquestions. I regret what I said about helping strangers and yes, we are not strangers anymore!! I totally agreewith your comment "This ain't rocket science". But sometimes it's very difficult to understand the nuances of an"alien" topic no matter how much effort you put into the subject unless some one guides you. Thank you onceagain & all those who share their knowledge on this forum.

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