We have Mark V control at our site for a Gas turbine generator. While we were reviewing the islanding settings through the modeling, we stumbled upon one problem. We used the same Mark-V equation for modelling i.e.
FSR = (TNR-TNH)FSKRN2+FSKRN1

The rate of change on TNR is around 0.02 Hz/sec.

I'll take a case when the generators are in parallel with the grid and running in Preselect modes. Now, when the grid frequency is increasing (a disturbance) at a rate greater than 0.03Hz/sec, initially there will be fast droop control followed by the preselect correction whose rate is again limited to 0.02Hz/sec. Because of droop the generation will keep on decreasing as the correction factor is very less. Generally, the Over frequency islanding setting is 52 Hz but before reaching the threshold of 52 the machine will trip on reverse power!!!! Whereas this is undesirable and the plant should island before reverse power condition arises.

This is not possible only if there is a limit on FSR below which it is not allowed to go in normal running conditions, but i don't find anything like that in Mark V control !!!! Is there any other protection in Mark V or is there any other explanation?

Kindly help.

 

Most Mark Vs have a reverse power detection function. If your CSPs use it, it can be found by working backwards from the alarm drop number. In other words, the drop number can be used to find the signal name which generated the alarm (and the breaker opening event) from the Alarm List (ALARM.LST).

As an example, one job used Alarm Drop 217 to generate the alarm "Generator Breaker Tripped - Reverse Power" and that drop could be traced from ALARM.LST to signal name L32DW. L32DW, when a logic "1", will energize L52GT, which will open the generator breaker. (These are typical signal names used on most jobs. Check your CSP to see what's being used for the Mark Vs on your site.)

Sounds like a challenging operating environment.

 

Alrite I'll look into it...but still, is der any lower limit been provided to FSR in MArk V during running operations so that machine never goes below a specific generation whatever be the case ???