80.How many types of over speed trips are available for turbine and what are the setting?

Electrical Over speed protection

Mechanical Over speed protection

Trip setting for Electrical is 1.05 times the rated speed and that of Mechanical is 1.1 times the rated speed.

A PID speed control will be provided as over-ride to the load control. A Troop control also will be provided with 0.25 Hz dead band. The normal troop setting will be 4 to 8% . The range will be upto 20%.

Troop control is a proportional control. Example 4% troop will produce a 100% output with a deviation 2 Hz. Assume a Unit is running at full load with GOV demand as 95%. The GOV demand will be 0 at 51.9 Hz.

In addition to avoid a turbine tripping due to over speed, Anticipatory Load Schedule logic will be provided. In such case during a load reduction more than 25%, the electrical and thermal load will be compared and if thermal load high after 2 sec, the GOV will be demanded to close fully for a few second and release to the position required by the electrical load before closing.