Dear Editor
The Stabroek News of October 20, 2021, article entitled, “Four lines tripped and triggered shutdown-GPL, stated inter alia, these trips, GPL said, led to a sudden and significant loss of generation, destabilizing the Demerara-Berbice Interconnected System (DBIS) and resulting in a total shutdown”. This statement by GPL is erroneous, the trips would have caused a sudden and significant loss of load which would have resulted in an excess of power in the system. Since GPL does not have enough units running in isochronous mode, the system was unable to quickly reduce the power being generated to match the load, this resulted in the engines tripping on over frequency and a total shutdown of the system. It should be noted that this was the second total shutdown of the Demerara Berbice Interconnected System (DBIS) in the month of October 2021. It is disappointing that this happened when the new 46.5 MW Wartsila plant is operational at Garden of Eden (GOE). I say this because I am positive that the new plant has the latest Wartsila Unified Control System (UNIC). The capability of this control system is stated in the Product Guide for the Wartsila 34 DF engine as follows: 14.2.5.2 Page 189; Generating sets – The electronic speed control is integrated in the engine automation system. The load sharing can be based on traditional speed droop, or handled independently by the speed control units without speed droop. The later load sharing principle is commonly referred to as isochronous load sharing. With isochronous load sharing there is no need for load balancing, frequency adjustment, or generator loading/unloading control in the external control system.
Two (2) total system shutdowns in one month are reminiscence of when Wartsila (WOGI) was the operator for the Wartsila power plants in Guyana. Their operational policy was to run the new engines at Kingston 2 and Vreed-en-Hoop in fixed Kilowatt mode and they had manually bypassed the isochronous control mode in both plants. It is my contention that Wartsila has a conflict of interest with them being the Operator of the new 46.5 MW plant at GOE and being the OEM responsible for the warranty of this new plant. It is obvious that Wartsila was operating this plant at GOE in fixed Kilowatt mode and when the four lines tripped, it immediately tripped on over frequency instead of switching to isochronous mode to unload the generators and assist in stabilizing the system. Wartsila is basically running the plant in the most protective mode to ensure that it does not fail during the warranty period. The Vreed-en-Hoop plant has the same UNIC system as the new plant at GOE and they can easily be linked via the fibre optic cable between the plants. If this were done, both plants could be operated in isochronous mode or, the Vreed-en-Hoop plant operated in isochronous mode and the GOE plant operated in fixed Kilowatt mode with the UNIC programmed to switch to isochronous mode in the event of a system disturbance. This would prevent a system shutdown in the event of a large loss of power as occurred when the four lines tripped. The engines at Vreed-en-Hoop and GOE would also be capable of providing adequate spinning reserves if they were operated up to a maximum of ninety percent (90%) load.
Since the Wartsila engines are capable of operating at one hundred and ten percent (110%) of rated load for a maximum of one hour in twenty-four hours, the two plants with all engines operational would be capable of providing 15 MW of spinning reserve for a maximum one hour. Even if one of those engines were to trip, the remaining seven operating engines would still be able to provide 12.6MW of spinning reserves. It should also be noted that the largest engine in GPL is less than 10 MW. I have written ad nauseam about the need for GPL to operate enough engines in Isochronous Control Mode to stabilize the DBIS and prevent total shutdowns of the system. It is obvious that the GPL System Control Engineers do not understand the Power Plant control systems and as such they cannot insist that Wartsila configure and program the UNIC System to the benefit of GPL and the Guyanese public. I would expect that they would claim that they were not trained, and my position is that you do not need training to read and understand the Power Plants operations manual.
Sincerely,
Tara Singh
