When turbine is running with normal operation, sudden load throw will taking place during export breaker open and turbine comes to house load and immediately turbine got trip without any alarms in DCS but signal is generated in governor panel what are the possible root causes and how to address the issues......
Events of incident as follows:
@15:47:47 plant is running normal with 6.8 MW (installed capacity 10 MW)
@ 15:47:48 Export breaker open and came to house load 1.0 MW
@ 15:47:49 Turbine trip through governor signal
We checked and found all parameters like control oil pressure / control valve function /turbine speed / vacuum/ frequency found normal but without any DCS alarm turbine got trip.
In first out trip history we found External trip input1....at governor panel

Pl do suggest the specific solution to overcome the issues in future

 

Root cause can be multiple
..
It can be a load rejection.. Load shedding..
What is kind of turbine and manufacturer

What is control system installed on this unit. '

We would need alarm list or trends to provide support to solve this issue in the future

 

What happens to the frequency when the generator load decreases so suddenly just before the trip occurs? (You said there weren't any frequency/speed deviations but we don't know how you determined that and how that data was captured for analysis.)

What happens to the generator terminal voltage/generator exciter (AVR) current when the event occurs?

Did this problem just start happening or has it been happening for some time? Or, is it just that the grid tie-line breaker has started opening and this problem just became apparent?

You need to look at the governor/control system (?) wiring information to determine what External Trip Input 1 is. Or, look at the first out trip history to determine what drives the message External Trip Input 1.

USUALLY when the grid tie-line breaker opens and reduces load suddenly the governor/control system may not react quickly enough to reduce the steam flow to the turbine to prevent the frequency from rising above a trip setpoint (usually from a protective relay in the generator protection scheme). Another thing which can occur is that the control valve closes so fast that an under-frequency condition occurs and a trip is generated for that reason. SOME steam turbines have a limit switch on the control valve that will initiate a trip if the valve closes below a certain point when the generator breaker is closed (to try to prevent a reverse power condition) and this might be the problem.

As ControlsGuy25/James says, we would need some graphs/charts/etc. and probably some kind of simple schematic of the governor/control system to understand what might be happening. MANY DCS systems and even some data archival and retrieval systems (often called historians) DO NOT capture data fast enough to show changes in frequency which might occur during such an event, and can often be very misleading. So, if you have high-speed data that would be most helpful.

But, determining what External Trip Input 1 is would also probably be very helpful. If you can tell us what kind of governor/control system is being used we might be able to tell you which terminal board to look at on your electrical drawings to determine where the input is coming from.

 

Thank you for your input.....
Dear sir
plz find the attached DCS trends along with trend data during sudden load throw off condition just before and after house load and tripping conditions....

 

Thank you for your input.....
Dear sir
plz find the attached DCS trends along with trend data during sudden load throw off condition just before and after house load and tripping conditions....

Looks like provided trends and datas are not enough to solve the issue as we dont know what happened to the "grid/line cirucit breaker 52 L at occurence" to get tripped *
We do not know if it is kind of load rejection /shedding or other event can be a electrical fault ...

 

From the original post:

"We checked and found all parameters like control oil pressure / control valve function /turbine speed / vacuum/ frequency found normal "...

From the data provided:



Speed and frequency are normal? In which time/space continuum? (Certainly not the one we're living in on Plant Earth.) At a minimum, the "acceptable" frequency range is ... pretty wide and also abnormal for most power generation operations. A stable frequency is one of the most important aspects of an AC power system--of any size. Troubleshooting an unstable AC power system is difficult.

First of all, the data is once-per-second, and the resolution is poor, also (that's Number Two).

Third, the frequency prior to the load rejection (load throw-off) was 49 Hz. That's 2% off nominal. Many under-frequency relays operate at higher frequencies, yet the TG-set was STILL running.

Fourth, the frequency after the load rejection was 50.7 Hz (or something very near that but we won't know because of the once-per-second data reporting rate). Many over-frequency relays operate at something near that value--and that would explain why the turbine tripped. Usually with a steam turbine the inlet steam is shut off before the generator breaker opens--that's to try limit the overspeed when the load is fully removed from the turbine. Some steam turbines have a protection scheme that monitors load (current flow) and speed--and trips the generator breaker when the rate of speed increase exceeds a preset level AND the load is dropping at a very fast level.

As was written above: Slow data collection rates and poor resolution are pretty useless for troubleshooting high-speed problems--like the one in this thread. As ControlsGuy25/James wrote, we don't know when the generator breaker tripped or when the tie-line breaker tripped.

Discover what External Trip Input 1 is and you'll probably have your answer.

And that's that.

Over and out.

 

Looks like provided trends and datas are not enough to solve the issue as we dont know what happened to the "grid/line cirucit breaker 52 L at occurence" to get tripped *
We do not know if it is kind of load rejection /shedding or other event can be a electrical fault ...

A reply from OP would be greatly appreciated !