During commissioning of GT we are encountering problem after firing during warm up time of one minute. The FSR position decreases to 6 % less than its default minimum position of 11% and trips the Gas Turbine on loss of flame. What needs to be checked for this problem?

 

Is this a new unit being commissioned, or is this occurring after a maintenance outage, or is this occurring as a new turbine control system is being commissioned on an older unit? (There's commissioning, and then there's commissioning. Please, when posting provide as much information as possible.)

The most likely cause is that the FSRMIN control constants are not set correctly for that speed range.

And it's also likely that the GCV LCDT feedback may not have been calibrated correctly.

 

> The most likely cause is that the FSRMIN control constants are not set
> correctly for that speed range.

As is the GE way, there is Minimum FSR, and there is Minimum FSR. One is a Control Constant, and the other is a calculated value, based on current speed. You need to look through the sequencing to determine which is used, and when.

The calculated value of Minimum FSR uses a block with two arrays to come up with the value to be passed to whatever function requires it at the time.

I don't have access to any sequencing or application code at this time, and you didn't say which version of Speedtronic turbine control system is in use at the site. But, the two arrays should have names like FSKMINNn and FSKMINDn, where 'n' represents an integer from 0 through as high as 7 (but never usually that high). One of the arrays is the speed side of the equation (the "x" value), and the other is the corresponding FSR value (the "y" value).

DO NOT CHANGE ANY OF THE SPEED ARRAY CONSTANT VALUES! They should remain the same.

The other thing that may be happening is that the acceleration rate, TNHA, at the time the warm-up timer is expiring may be too high. This could be for one of two reasons: either there's too much torque from the starting means or the value of warm-up FSR is too high (check the exhaust median temperature, TTXM, to see if it's come down after the initial spike from firing).

Tuning start-up, and shutdown, FSR Control Constants can be a challenge, but it is a normal part of commissioning for a new unit, or for a unit being retrofitted with a new control system. If the unit has a Mark VI or a Mark VIe, start-up acceleration reference is set by TNHAR, and FSR is adjusted to make TNHA equal to TNHAR, but the calculated value of FSRMIN is an over-riding value. Tricky, but not impossible.

And, again, the calibration of the LVDT feedback can have an impact on all of this. Especially during firing and warm-up.

Please write back to let us know how you fare.