Turbine fail to fire

O

Thread Starter

OT

'Common I/O communication loss' is the alarm displayed on the HMI. As a results we cannot fire the GE frame 9e turbine using both the HMI and the backup on the MARKV.

Please what are the causes and solutions to this problem.
 
Pretty sure one of the GE experts will be along soon but it sounds to me like C Processor has died or lost comms.
 
OT,

The <C> processor is commonly known as the "Communicator" and is primarily responsible for allowing operator interfaces (HMIs) to view data from the three control processors (<R>, <S> and <T>) and to send commands to the three control processors. All of the "critical" I/O is connected to the control processors.

"Non-critical" I/O is connected to <C>, and is "shared" by the three control processors--which do the bulk of the control and protection and monitoring of the turbine and auxiliaries.

GE's definition of "critical" I/O is that I/O which is necessary for protection of the turbine <b>AND</b> which is necessary for an operating turbine to remain in operation and protected. That definition <b>DOES NOT</b> include starting means I/O, since once it's running a turbine doesn't require starting means I/O to keep running. So, most starting means I/O is connected to <C> and accessed by the control processors via the DENET that links <C> and <R>, <S> and <T>.

<C>'s I/O is called "common" I/O for this particular alarm (GE is very consistently inconsistent with their alarm messages which is very frustrating to many people). So, "Common I/O Communication Loss" would mean that the three control processors were unable to communicate with <C> (via the DENET, Data Exchange Network in the Mark V control panel which connects the three control processors and <C>) and so were unable to determine the states of <C>'s I/O points.

In order to initiate a turbine start it is necessary for all four processors (and the three protective processors in the <P> core) to be communicating and have their outputs enabled (that's indicated by all cards at I/O State A7). That means that <C>'s I/O (common I/O) must be available for the three control processors to use in starting and controlling the turbine during starting.

A "Failure to Ignite" or "Failure to Fire" Process Alarm would not be possible if the "Common I/O Communication Loss" alarm were continually annunciated; it would block a START attempt which would not allow START or fuel to be admitted to a turbine and therefore a "Failure to Ignite" alarm would not be possible.

There were some problems with some of the PROMsets used in some Mark V turbine control panels that commonly resulted in the "Common I/O Communication Loss" alarm. Upgrading PROMsets (as detailed in one or more GE TILs (Technical Information Letters) usually resolved this alarm condition for good.

However, if all of the controls-related TILs have been implemented and this alarm has just started being annunciated then it could be a problem with corrosion on cable connections in the Mark V. The tinned pins and sockets of cables/connectors (of which there are MANY in the Mark V) are susceptible to corrosion. GE began providing tubes of conductive grease in the boxes with spare cards to be used to help prevent the corrosion. A thin film of conductive grease should be applied to the female connector sockets of EVERY cable connector in the Mark V (when there is no power in the Mark V!) and the connector should be inserted in the socket and then removed and re-inserted a couple of times to be sure the grease gets onto the pins. TOO MUCH CONDUCTIVE GREASE is just as bad as too little, so be judicious in the application.

If there are Diagnostic Alarms on <C> (in the Diagnostic Alarm window, and also on the LCC/SLCC keypad display) that would also be helpful to know to try to troubleshoot a recent spate of "Common I/O Communication Loss" alarms.

Intermittent, unresolved and prolonged 125 VDC battery ground alarms are also known to occasionally weaken Mark V card components and lead to "Common I/O Communication Loss" alarms.

Hope this helps. Please write back to let us know what you find.
 
Top