Gas Turbine Not Accelerating

On gas turbine "mark V" during startup after firing, the fire was blue in color. After 1270 rpm the Accelerating speed is going so slow, and don't reach the synchronize speed, until the exhaust temperature going high, and the turbine goes to temperature control. Turbine tripped, and gives command "Exhaust temperature high, TRIP". Why the gas turbine not accelerate ?

Notes:
gas control valve reading 27% during firing to 44% on 2200 rpm.
SRV reading 4% during firing to 10% on 2200 rpm.
Torque convertor charge pump pressure was 60 psi on 2200 rpm.

thanks and regards,
MAZEN SHANABEASH
[email protected]

mazenshanabeash,

This question must be the second most asked question in the history of control.com, only surpassed by questions about Droop speed control. Seriously.

Unfortunately, each time this question gets asked and answered it's just a little different--just enough to make it difficult to Search for other threads on this same topic. I can find two or three past threads but never a preponderance of the many, Many, MANY times this same question has been asked--and answered.

I'm going to start including a common term in every response I make to this question to make it possible to search for the common responses: Buffalo nickel.

Have you read this very recent thread:

https://control.com/thread/1546939821

So, the gas turbine at your site has a Mark V. What is the Frame size of the gas turbine the Mark V controls and protects?

Was the turbine being started from a "cold iron" condition, or was it being restarted from a warm or hot condition (such as after a recent shutdown or trip)?

If the turbine was tripped on a high exhaust temperature, there must have been an alarm prior to the trip warning the operator the exhaust temperature was high--for example, 'Exhaust Temperature High, ALARM.' Exactly what alarms were present and active in the 90 seconds prior prior to trip? Include ANY and ALL Diagnostic Alarms.

When the average exhaust temperature exceeds the exhaust temperature reference/limit by 25 deg F the high exhaust temperature alarm will be annunciated.

When the average exhaust temperature value exceeds the exhaust temperature reference/limit by more than 40 deg F the turbine will be tripped on exhaust over temperature.

When did this problem begin--after a maintenance outage or a previous turbine trip?

Exactly how do you know the precise color of the flame in the combustors? Are there color cameras in all the combustors, or two of the combustors, or four of the combustors? Or are you estimating the color of the flame based on the flame sensor intensity indication? If it's the latter, where did you get the chart or information about what flame colors correspond to what intensity ranges? From GE, or the flame sensor manufacturer, or from the Internet?

Does the gas turbine have conventional combustors or DLN combustors?

If the gas turbine has DLN combustors, which version of DLN combustors does it have--I or 2.0, or 2.6?

What was the value of the average exhaust temperature, signal name TTXM, in the 20 seconds prior to the trip?

What was the value of the exhaust temperature reference/limit, signal name TTRX, in the 20 seconds prior to the trip?

What were the values of the three exhaust temperature spreads (signal names TTXSP1, TTXSP2 & TTXSP3) in the 20 seconds prior to the trip?

When (at what speed) did the starting means cease to provide torque to the turbine shaft?

What was the gas fuel supply pressure in the 20 seconds prior to the trip?

What was the P2 pressure (usually signal FPG2) in the 20 seconds prior to the trip?

What was the P2 pressure reference (usually signal name FPRG) in the 20 seconds prior to the trip?

What kind of gas fuel was being burned when the turbine tripped? Is it "typical" natural gas, or low-BTU natural gas, or some process gas (from a refinery or steel mill)?

What was the IGV angle (signal name CSGV) prior to the trip?

What was the ambient temperature at the time of the trip?

What was the turbine inlet air filter differential pressure prior to the trip?

When was the last time the axial compressor was water washed prior to the trip?

How many exhaust thermocouples are failed (reading negative temperatures)?

When was the most recent turbine maintenance outage, and what was the outage--a Combustion Inspection, or a Hot Gas Path Inspection or a Major Inspection?

What kind of starting means does the gas turbine have--an induction electric motor or a diesel engine?

What is the normal torque converter charge pressure at 2200 RPM?

Because you have provided so little information in you original post the answers to these questions are VERY important, and you must provide the answers to all the questions (even if you don't believe some or most of the questions are relevant!) in order for us to provide any meaningful answers. The reason the turbine tripped could be any one of a number of reasons and the little information you provided doesn't help narrow down the possible causes.

If one had to make a guess, it's probably because the turbine inlet air filters are dirty and need replacing, <b>AND</b> the axial compressor and IGVs are dirty, <b>AND</b> the starting means (including the torque converter) needs refurbishment, <b>AND</b> the gas fuel supply pressure and/or flow was unstable just prior to the trip, <b>AND/OR</b> the gas fuel has a low BTU content, <b>AND</b> the exhaust temperature spreads were high (indicating EITHER one or two failed exhaust thermocouples AND/OR the absence of flame in one or more combustors).

A low BTU content fuel would cause a poor flame color AND possibly result in the seemingly high gas control valve position, trying to increase the turbine acceleration rate.

High exhaust temperature spreads means there isn't flame in one or more combustors which means the hot gases being sent to the turbine section aren't producing enough energy to keep the turbine accelerating at the desired rate--and the Mark V may be increasing the fuel flow-rate to try to maintain the desired acceleration rate so much that the exhaust temperature is hitting the exhaust temperature reference/limt. The Mark V--if the gas fuel supply pressure and flow-rate are stable--would prevent a high exhaust temperature alarm, or high exhaust temperature trip. Unless the pressure and/or flow-rate were unstable, in which case the exhaust temperature could spike resulting in an alarm or trip. But, without a record of alarms prior to the trip and data it's very difficult to be certain what actually happened.

The decreasing acceleration rate is probably the result of dirty inlet air filters and dirty IGVs and dirty axial compressor, requiring excessive fuel to maintain the normal acceleration rate. The excessive fuel combined with the low air flow, and weak starting means (cranking motor and torque converter need refurbishment, replacement or adjustment) contribute to the high exhaust temperature which caused the Mark V to limit fuel flow to protect against exhaust over temperature.

If the problem started after a maintenance outage, it's probably because the GCV and IGV LVDTs were not properly calibrated, and/or the torque converter guide vanes were not properly adjusted or need adjustment, or the torque converter is not transmitting the same torque as when it was newer, or if the starting means is a diesel engine it needs refurbishment or the air filter is excessively dirty or the diesel engine control needs adjustment or is not working properly or the diesel engine fuel filter is dirty and needs replacement.

The gas fuel supply pressure and/or flow was probably unstable just prior to the trip, resulting in the exhaust temperature to spike to more than 40 deg F above the exhaust temperature reference/limit (if, indeed, the turbine actually tripped on excessive exhaust temperature--because it's extremely likely there is no record of alarms when the trip occurred and no one saved a copy of the Trip History Display immediately after the trip occurred). A person without actual data (called actionable data) is just another person with an opinion--and there are lots of people with opinions but that doesn't make them correct.

That's a pretty comprehensive list of what might have caused the problem of sluggish acceleration and possible high average exhaust temperature. You see, it could be any of a number of things--and it's likely that multiple things contributed to the problem. But without the list of alarms prior to the trip AND without knowing a lot about the conditions prior to the trip it's impossible to say anything with any degree of certainty.

Give us more information and we can be more precise.

Buffalo nickel.