Dear All,

What is actually the function of Master Reset, what is really happen to the system and can we done Master Reset online/while unit is running.

Best Regards,
Hazli

 

This description applies ONLY to Speedtronic(tm) heavy-duty gas turbine control panels--NOT to those control panels used for LM (aeroderivative) or steam turbine applications.

When one "initiates" a Master Reset, a logic signal, usually L86MR1 or L86MR1_CPB, temporarily goes to a logic "1". Many N.C. (Normally Closed) Master Reset contacts are used in the "latching" portion of logic- and sequencing elements (rungs, algorithms, macros, function blocks, and BBLs--Big Block Language blocks--depending on the vintage of the Speedtronic turbine control system). When the signal goes to a logic "1", the N.C. contact opens, and if the condition is no longer "active" or in alarm/trip, the condition's logic "drops out" and can be reset, or cleared, from the Alarm Display. [One of the most important of GE's heavy-duty gas turbine control philosophies is: ANY condition which results in a unit trip (emergency shutdown) or a Not-Ready-to-Start indication MUST be accompanied by an alarm. Many trip conditions which are latched with a Master Reset contact maintain the alarm indication until the condition is cleared AND a Master Reset has been initiated.]

One of the original intents of the Master Reset function was to allow a method of "latching" an alarm condition which caused a unit trip (emergency shutdown). For example, if the gas turbine exhaust temperature exceeds the trip setpoint, the unit is tripped (fuel is shut off), and the exhaust temperature immediately decreases below the trip setpoint. If the alarm were not "latched", when the operator woke up, ... er, uh, ... arrived (that's what I meant to say--arrived; operators never snore very loud, ... er, uh, ... sleep, ... er, uh, ... take naps on the job--never!) to investigate the trip there would be no indication because the exhaust temperature would be less than the trip setpoint and the operator would not know what tripped the unit. (Most operators can't even determine from a last in-first out alarm display/printout what tripped a turbine in most cases--whether or not the alarm condition was latched in... But that's another digression!)

Another intent of the Master Reset function was to not permit a re-start of the unit until an operator manually reset (unlatched) the trip condition. Some heavy-duty gas turbines have been successfully operated remotely (without human presence) for decades. When a serious trip condition occurred, the Master Reset function required a person to manually initiate the Master Reset to unlatch the alarm and permit a re-start. Most of these remote sites do NOT allow Master Reset via remote push-button--someone actually has to travel to site and investigate the condition and "issue" a Master Reset to allow the unit to be re-started (locally or remotely).

Over the years, the intent of the Master Reset function has been perverted, ... er, uh, ... modified--that's it, modified! Many conditions which are NOT unit trips, but still deemed "critical" (by someone, anyway), are latched in with the Master Reset Function, and require a Master Reset to unlatch and return to normal operation. Many Water- or Steam Injection system trips (emergency shutdowns) require a Master Reset to unlatch the alarm and allow a re-start of the system.

Because of the "misuse" of the Master Reset function by programmers, operators have become so accustomed to using Master Reset to try to unlatch/clear Process- and Diagnostic Alarms that almost before they take any corrective action (okay, BEFORE they do ANYthing else, really) the first "action" they take when ANY alarm occurs is to initiate a Master Reset. If the alarm clears and the unit continues to run they go back to sleep, ... er, uh, ... return to their other duties/tasks (that's it, their other duties/tasks!). If the alarm doesn't clear, they usually call a technician, whose first action is to tell the operator to initiate a Master Reset.... And so it goes....

Many operators, before checking the Process- and Diagnostic Alarm Displays prior to inititaing a unit START initiate a Master Reset, then check the Alarm Displays (IF they even check the Alarm Displays.!.!.!) and THEN initiate a START. They seem to have determined that initiating a Master Reset is an integral part of the START sequence (which it is NOT!!!!).

On MOST units, initiating a Master Reset when the unit is running will not result in any upset to unit operation. To be certain, however, one MUST review their own control sequencing/logic to be certain if that's true for their unit(s).

There are conditions, which if unlatched with a Master Reset when the unit is running, especially if it's running at Base Load, can result in an upset which can cause a unit to trip. For example, if Water- or Steam Injection trips while the unit is running at Base Load and an operator just initiates a Master Reset, the injection setpoint can be so high that the control valve may (will usually) overtravel, resulting in another trip of the Water- or Steam Injection system, which will usually result in at least an Exhaust Overtemperature Alarm--if not an Exhaust Overtemperature Trip. So, it's not the Master Reset that trips the unit--it's the sudden over-injection and sudden loss of steam flow that does it.

There is one more caveat about initiating Master Resets to clear alarms: If a Master Reset is issued BEFORE the alarm condition has been investigated (such as "IGV Control Trouble Trip" or "GCV Fault Trip"), it will likely be IMPOSSIBLE to determine which of two, three, or more possible conditions resulted in the alarm/trip. So, as the admonishment on the Master Reset alarm display says: DO NOT RESET THE UNIT BEFORE THE CONDITION IS UNDERSTOOD.

markvguy

 

<p>Thanks markvguy for reply, FYI our unit is 500MW GE steam turbine so maybe slight different as your write it is only for Gas turbine. my main concern is this 2 logic below, what it really happen to the system if DCC, TCQA, TCQB, TCEA master reset activate when we give master reset command.

<p>Best Regards,<br>
Hazli
<pre> +ADwAPAA8- Rung Number 5 +AD4APgA+-

L86MR1+AF8-
L86MR+AF8-

CPB
TCQA

+JQAlACUAJSQ- +JRwlACUAJQAlACUAJQAlACUAJQAlACUAJQAlACUAJQAlACUAJQAlAA- +JQAlACUAJSwlACUAJQA-( )

+JQI-

+JQI-
L86MR+AF8-

+JQI-
DCC

+JRwlACUAJQA-(
)

+JQI-

+JQI-
L86MR+AF8-

+JQI-
TCQB

+JRQlACUAJQA-(
)


L86MR1+AF8-CPB -- COMMAND PB Master reset
LOGIC

LST+AF8-Q1 12 LST+AF8-Q1 17 LST+AF8-Q1
19 LST+AF8-Q2 5 LST+AF8-Q2 6

LST+AF8-Q3 134 LST+AF8-Q4 34 LST+AF8-Q4
93 LST+AF8-Q4 94 LST+AF8-REQ1 41


L86MR+AF8-DCC -- DCC Master Reset
LOGIC

LST+AF8-Q2 -5


L86MR+AF8-TCQA -- TCQA Master Reset
LOGIC

LST+AF8-Q2 -5



L86MR+AF8-TCQB -- TCQB Master Reset
LOGIC

LST+AF8-Q2 -5


+ADwAPAA8- Rung Number 6 +AD4APgA+-


L86MR1+AF8-
L86MR+AF8-

CPB
TCEA

+JQAlACUAJSQ- +JRwlACUAJSwlACUAJQAlACUAJQAlACUAJQAlACUAJQAlACUAJQAlACUAJQAlACUAJQAlAA-( )

+JQI-

+JQI-

L86RSTX +JQI-

+JQAlACUAJSQ- +JRwlACUAJRg-


L86MR1+AF8-CPB -- COMMAND PB Master reset
LOGIC

LST+AF8-Q1 12 LST+AF8-Q1 17 LST+AF8-Q1
19 LST+AF8-Q2 5 LST+AF8-Q2 6

LST+AF8-Q3 134 LST+AF8-Q4 34 LST+AF8-Q4
93 LST+AF8-Q4 94 LST+AF8-REQ1 41


L86MR+AF8-TCEA -- TCEA Master Reset
LOGIC

LST+AF8-Q2 -6


L86RSTX -- EOS RESET(TCEA), AUTO
LOGIC

LST+AF8-Q2 6 LST+AF8-Q3 -138
</pre>

 

There was a REASON for the qualification....and a hunch that you might really be asking this question for something other than a heavy-duty gas turbine installation! It really is important to state the "details" of your installation and the background for your question(s). Osmosis doesn't work over the Internet, last time this author checked...

The application of the Mk V for different types of turbines is slightly different, but it's the differences that can make life "interesting."

IN GENERAL, and this is made without the ability to examine your unit's CSP (Control Sequence Program) and unit configuration, initiating a Master Reset will not trip the steam turbine. The Master Reset in the example you tried to post primarily serves to unlatch any latched Diagnostic Alarm conditions which might be latched. (Before you ask, there is NO way to tell exactly which Diagnostic Alarms require a Master Reset!)

NOTE that for a steam turbine application, there is a HUGE difference between RESET and Master Reset (and that difference depends on the application, so it's very difficult to comment without being able to examine the CSP). This author has seen steam turbines that would trip (emergency shutdown) if a RESET was initiated while the unit was running (another reason for the qualification in the earlier response). [That was probably an error in the CSP, but to this author's knowledge it was never "fixed."]

markvguy