Respected sirs,
In our CPP there are 6 gas turbine generators( frame 9e ).my first question is "what will happen if anybody by mistake switch off mark-6 power supply , when gas turbine generator running normal?"

My second question is if GT is under shutdown with mark-6 supply isolated & if anybody energize any motor feeder in GT MCC , then will it run or not? In some motor feeder drawing starting command contact shown NC contact , while in some no contact used. What is the logic behind using different contacts in different motor feeder?

 

This post gave me quite a good belly-laugh!

If by "Mark VI power supply" you meant the 125 VDC that is feeding the <PD> core, then the turbine will trip if it's running.

If by "Mark VI power supply" you mean one of the three redundant control processor's power supplies, then it depends on the "condition" of the other two remaining control processors. If we presume they are all "healthy" and think everything on the turbine is fine, and one of the control processor's power supply is switched off, then nothing should happen except a lot of Diagnostic Alarms and maybe an Exhaust Temperature High alarm if the unit is at or near Base Load.

The answer to your second question is part of GE's heavy duty control philosophy. In this case, they are using the knowledge that the primary failure mode for electro-mechanical relays (the type normally used in Speedtronic turbine control panels for GE-design heavy duty gas turbine applications, especially for motor starter circuits) is to fail in the de-energized (or off) state. Failures are usually because of the failure of the electro-mechanical relay's coil or a loss of power to the electro-mechanical relay's coil, etc. Which means that if the electro-mechanical relay were commanded to energize it couldn't be energized if the coil were failed or the power supply for the coil had failed.

Further, they deem certain motors like the Auxiliary L.O. Pump and the Auxiliary Hydraulic Pump and most compartment ventilation fans and the like, to be "critical". They want these critical motors to start and run to protect the turbine and its auxiliaries, even if they shouldn't be running. A "critical" motor running when it shouldn't be could be considered to be an indication of some kind of problem. If the Aux. L.O. Pump starts running with the turbine is running, it doesn't adversely affect turbine operation. But a critical motor running when it shouldn't be running is a condition that should be looked into and resolved (and it should be a Process Alarm to alert the operators to the condition).

So knowing that electro-mechanical relays typically fail in the de-energized state and that they want these motors to start and run to protect the turbine, instead of energizing the coil of the electro-mechanical relay in the Speedtronic turbine control panel to close the normally open contacts to energize the contactor of a motor starter, they de-energize the coil of the electro-mechanical relay to close the normally closed contacts to energize the contactor of the motor starter.

De-energizing a coil is also known as "dropping out" the coil. This is what GE calls "drop-out-to-run": They de-energize (or drop out) the coils of electro-mechanical relays in the Speedtronic turbine control panel used to start and stop "critical" motors. This means normally closed contacts must be used in the AUTO portion of the motor starter control circuit.

So, to start the Aux. L.O. Pump motor, for example, instead of energizing an electro-mechanical relay in the Speedtronic turbine control panel to energize the contactor in the Aux. L.O. pump motor's starter, they de-energize the electro-mechanical relay in the Speedtronic to energize the contactor in the Aux. L.O. Pump's motor starter.

Typically, the name of the logic signal that drives the Aux. L.O. Pump is L4QAZ. The "L" stands for logic, meaning that it is a software logic signal. The "4" means "master protective" signal, or a critical protective element. The "QA" stands for "L.O. Pump-Auxiliary". And the "Z" stands for "zero".

When L4QAZ is a logic "0", the Aux. L.O. Pump is being commanded to run. When L4BTZ1 is a logic "0", the #1 Turbine Compartment Vent Fan is being commanded to run. When L4HQZ is a logic "0", the Aux. Hydraulic Pump is being commanded to run.

The "Z" at the end of the signal name *in this case* means that when the logic signal is a logic "0" (de-energized, false, "dropped out") that the device is being commanded to start and run. (There *REALLY* is a logic to signal naming, if the signal names are or were chosen correctly!)

When L4QAZ is a logic "1", the Aux. L.O. Pump is being commanded to stop. When L4BTZ1 is a logic "1", the #1 Turbine Compartment Vent Fan is being commanded to stop. When L4HQZ is a logic "1", the Aux. Hydraulic Pump is being commanded to stop.

Why do this? Let's say the control system was configured such that the coil of the Speedtronic relay used to start and stop the Aux. L.O. Pump motor had to be energized to start the motor, meaning that normally open contacts of the relay were used in the control circuit of the motor's starter. If the Aux. L.O. Pump had to be started or running and the coil of the electro-mechanical relay in the Speedtronic used to energize the motor's contactor burned out, the Aux. L.O. Pump would stop when the normally open contacts opened when the coil failed. In other words, if normally open contacts of an electro-mechanical relay in the Speedtronic were used to energize the Aux. L.O. Pump motor starter's contactor and the coil of the electro-mechanical relay failed, then the normally open contacts would open when the relay failed and the the Aux. L.O. Pump motor starter's contactor would be de-energized and the Aux. L.O. Pump motor would stop.

Or if the electro-mechanical relay couldn't be energized to close the normally open contacts to energize the Aux. L.O. Pump motor starter's contactor to start the pump motor when it was required, that could be a serious problem.

But, if the relay was being used such that de-energizing the coil caused the normally closed contacts of the Speedtronic's electro-mechanical relay to energize the the Aux. L.O. Pump motor starter's contactor to start the motor and run the pump, and the coil burned out while it was being energized to stop the motor from running, then the motor would start and run and it would be an indication that there was a problem. Or, if the relay were de-energized to start the motor and it was de-energized to run the motor and the sequencing tried to energize the coil to stop the motor, the relay wouldn't pick up and the motor would continue to run. That doesn't hurt the turbine, and it will actually lead an alert and attentive technician to the failed relay coil condition.

As for why there aren't any contacts from a Speedtronic panel in a particular motor starter control circuit, that's not common, but not unheard of. It all depends on the application. Some applications of the Speedtronic use relays in the Speedtronic to start and stop the L.O. Tank Immersion Heater. Some use one or more temperature switches instead of Speedtronic relay contacts to start and stop the L.O. Tank Immersion Heater. It just depends on the criticality of the device and the philosophy in use at the time the unit was built and installed.

The "drop-out-to-run" philosophy will cause the motor starters of "critical" motors to start when the Speedtronic power supply is shut off or failed because when the Speedtronic relay coils are de-energized the outputs that use normally closed contacts will have their contacts closed, and this will send a signal to start/run many motors.

I hope this helps. "Drop-out-to-run" is just one of the control system configurations and philosophies that differentiates Speedtroninc turbine control systems from most other turbine control systems, and from many applications of PLC as turbine control systems.

Many other turbine control system manufacturers, and many control system integrators programming and configuring PLCs for use as turbine control systems, don't analyze device failure modes and try to make use of that knowledge when designing and programming a control system.

Many other OEMs have taken to using solid-state "relays" to drive critical motor starters. Solid-state relays fail as often in the ON condition as they fail in the OFF condition. So, predicting or making use of the predominant failure mode is nearly impossible.

 

Very well explaination by CSA. Up to the mark.
Summarized the whole manual in language that most people would understand in just 1 page

 

CSA...
How about inventing a ON and OFF button for the MKVI panel, just like so many other electrical equipments from Laptops to Coffee machines. Have another belly-laugh...This question has asked to me in the past during commissioning of a MKV panel, believe or not!
To the Originator: beside 125Vdc, there are additional AC lines connected in the PD (AC1 and AC2). This depends on the project configuration. Usually LNG plants use this (both AC lines are separately feeded from two different busbars via transformers).In this particular case, you need to switch off additional two more feeders to get the MKVI on its knees......

Good Luck...Tempus Fugit

 

>At CSA...
>
Very nice explanation by CSA.

But this thread made me to ask another question, that as Mr CSA has told if one processor will go down, Lots of diagnostic alarms will appear and high exhaust temp may be appear but machine will keep to run.

My question is if any controller fails, exhaust TC readings will not be available, and wouldn't that cause "High spread trip"???

 

Thanks CSA, I am impressed. Keep up the good job, very informative. Very good site, and I am addicted to it.

sardar9

 

Aliya,

So many questions!!! And in such a hurry!!!

What I said was:

>and maybe an Exhaust Temperature High alarm if
>the unit is at or near Base Load.

When one controller "goes down" while the unit is running, the other two controllers know that those exhaust T/Cs are "lost" and so, no, there will be high spread trip that will be attributed to the loss of the exhaust T\Cs from the controller that is not functioning.

It would be very remiss of a control system manufacturer to have a TMR system capable of running without one of the three controllers and trip because of the loss of the exhaust T/Cs associated with the lost controller. Considering all of the other things GE does to ensure reliability and availability, it wouldn't make much sense not to plan for such and event, now would it?

 

@ Mr CSA

Lolzzz.....
Thanks for feedback CSA, After posting my question, i got the answer by thinking over a period. as failed thermocouples will not be accepted.

I am sorry if i am putting so many doubts here, but realty is the intellectuals are here and their kind response, which no one can get anywhere else.

But thanks for acknowledging it. I am in hurry as my seniors thinks a girl can not be good plant engineer. (Or might be i am thinking so that they think so anyways). That's why i just want to learn Gas Turbine.

 

The discussion is related to several incidents I saw. Let me post the question here in this valuble thread to me. At the drop-out-run design used in the speedtronic as CSA explained, when the 125V power is complete out (for whatever reason) and the turbine tripped, will the AC lube oil pump be able to automatically pick up? Is this drop-out-run design used in other turbine systems (like those used by ALSTOM or Siemense)?

 

eggplant,

Drop-out-to-run ensures that when DC is lost to the Speedtronic turbine control panel that all motors deemed critical which are controlled by the Speedtronic and which have been configured using the drop-out-to-run philosophy will start and run. That's a LOT of motors to all be starting and running at once if DC is completely lost to the Speedtronic turbine control panel, and sometimes the total inrush current will cause the Aux. Transformer breaker to trip very suddenly.

But, yes--on complete loss of DC the electromechanical relay in the Speedtronic turbine control panel used to start/stop the AC Motor-driven Auxiliary L.O. Pump will drop out (it's coil will be de-energized), which will close the Normally Closed contacts of that electromechanical relay in the Speedtronic turbine control panel which will complete the Aux. L.O. Pump motor starter circuit and start the Aux. L.O. Pump motor.

As for whether other turbine manufacturers use the drop-out-to-run philosophy I don't believe many of them do use the same philosophies as GE. Many also use solid-state relays instead of electromechanical relays. The problem with using solid-state relays is that the failure mode cannot be reliably predicted--solid-state relays will fail as often in the "ON" condition as they will fail in the "OFF" condition.

I believe most turbine manufacturers do employ various types of philosophies and methods to improve reliability and enhance availability, but not always the same as other manufacturers. And, certainly, most manufacturers wouldn't be caught dead imitating others--especially by using the same terms or names! Most, I have seen or heard about, are not as simple as drop-out-to-run and can be quite complicated and very confusing.

Hope this helps!

 

Thanks a lot for the reply, CSA.

How about DC emergency lube oil pump? does it have similar control scheme? If both Aux ac and emergency DC pump have the same drop-out-to-run design, will the accidental start up of both pumps while the turbine is spinning cause any problem?

 

eggplant,

I'm not sure if I understand the question; this is a very old thread.

Yes; most of the GE Speedtronic turbine control systems I have had the pleasure to work on used drop-out-to-run logic for the D.C. Emergency Lube Oil Pump motor starter.

I have trouble envisioning how both pumps would accidentally start when the turbine is running. In any case, if the turbine is running and either (or both) pump(s) start when the turbine is running alarms are annunciated to alert the operator to the condition (because they should not be running when the turbine is at rated speed) but there is no affect on turbine operation.

Each pump (the Auxiliary L.O. Pump and D.C. Emergency L.O. Pump) have their own individual relay output to start/stop the pump motors. It would take a simultaneous failure of two relays for both of them to drop out to cause the two pumps to start and run when the turbine is operating at rated speed. I suppose if the two relays were on the same card and that card failed and all of the relays on that card dropped out at the same time then both pumps would start (as well as any other motor scheme employing drop-out-to-run logic connected to relays on that card).

The concept of drop-out-to-run is mostly about ensuring that critical motors start and run when they should. If they start and run when they shouldn't then turbine operation is not adversely affected--and a Process Alarm is annunciated to alert an operator to the condition.

Does this answer your question?