MARK-II system is installed on one of our gas turbine system. We faced a serious incident a couple of years ago when turbine was running on FSNL, 52GX was out and somebody accidental rack in the Earthling Isolator 89E. It was a huge explosion and fire. Afterwards when analyzed it was revealed that electrical contact of 89E (Earth Isolator) and 86X (Main Breaker trip lockout relay) where only taking part in permissive logic (MARK-II DWG Sheet 4A, Customer Contacts). Both contacts were bypassed once the 14HS relay was energized.

Means that turbine would not trip if these contacts actuate in normal operating condition. This situation is very vulnerable for the repetition of such incident.

Why there is no protection or turbine trip in case of 89E is energized when turbine is at its normal operating speed? How this situation could be rectified or resolved so that no further incident such as mentioned should re-occur? Any suggestions??

 

First, and most importantly, hopefully nobody was hurt.

Second, as the owner/operator of a unit which is no longer under warranty, you are free to make any changes to the protective logic, or any other logic, that you see fit to take responsibility for.

If you and your company as owners and/or operators deem that the logic as supplied was faulty, and not the training and procedures in use at the plant, then you are free to change the logic to reflect your requirements and needs.

Finally, it is hoped that the training and procedures in use at the plant have already been modified to preclude such an event from ever occurring again. There are interlocks which can be installed on racking and closing mechanisms to prevent racking in and closing breakers under certain conditions.