Turbine Overspeed Trip Test

Turbine over-speed trip test propose to function test of safety equipment which should work to prevent turbine get damage due to over-speed at more than 10% from nominal value and for measure the check point trigger of work.

Turbine over-speed trip test could be carried out when the Unit after DE-synchronized or after outage. If we do after De-synchronized no need too much planning but if we do after outage we need much more planning.

For this time we describe how to carried out it after outage that we have boiler and turbine cold condition. Toshiba's turbine must have to run the turbine with generator synchronization for warming the turbine at least three hours and then do to DE-synchronization to do over-speed trip test.

Picture below is telling about the scenario of boiler warming by axillary steam to feed-water tank / DE-aerator and then delivery to steam drum. HP Turbine also can be warmed by auxiliary steam (HP Pre-warming).

After Fans started we can do air flow test and ESP (electronic-static precipitation sparking test) but these tests are not mandatory. After light off, we could do boiling out at super-heater area if we did leak test at super-heater area when outage, if not we can direct to firing the boiler the created steam pressure 85barg and steam temperature 380-400 degree of Celsius.



















This picture below is talking about how to minimize the turbine warming by low speed and high speed heat soak with steam temperature set. Too much higher of steam temperature will get longer time of turbine warming.


















Picture below is talking right on turbine over-speed trip test. It needs 336 T/h of main steam flow and 348 T/h of feed-water flow. They are a little bit equal but right on 3313 rpm and turbine trigger to trip by over-speed, the main steam pressure increase from 85 to 88 bar and makes steam drum level drops for a moment. After that steam drum level will be rapid increase due to main steam flow drop to 240 T/h compare to feed-water flow 462 T/h.