We have 2 PGs 40MW each one,connected to the grid. If island mode is selected, 52G breaker open (or trip), PG1 goes to speed control, and PG2 goes to droop control (KW).
What happened is that we want to disconnect from grid "due to some planned job of public grid" (normally to open 52G). But by mistake or without knowledge, someone has opened 52L breaker (the 2 PGs didn't see that they are in island mode, still running in parallel mode).
After few seconds (8 sec) of the opening of 52L, under voltages of many levels of voltage have been observed (alarms in DCS).Then 52G tripped out by under voltage protection.
The question is: why this under voltage occurred?
Please let me know if you need other information.
Thanks in advance.
What happened is that we want to disconnect from grid "due to some planned job of public grid" (normally to open 52G). But by mistake or without knowledge, someone has opened 52L breaker (the 2 PGs didn't see that they are in island mode, still running in parallel mode).
After few seconds (8 sec) of the opening of 52L, under voltages of many levels of voltage have been observed (alarms in DCS).Then 52G tripped out by under voltage protection.
The question is: why this under voltage occurred?
Please let me know if you need other information.
Thanks in advance.