Gas Turbine compliance to Standard

[2012TECH]

Hi,

I am auditing a gas turbine unit compliance to a standard (API 616), and item 5.4.3.4 states :The governor for mechanical drive applications shall limit speed to 105% of rated speed.

I found that there is a trip setpoint a 110% of rated speed and no other details on the governor control range; Is there other mechanism to limit the speed to 105% other than tripping the unit? How should I interpret the standard?

 

[byrdj]

not too familair with GTs, but with STs. The 105% limit sounds like either the high speed stop for the governor, or this could be the settling no load speed with the steady state regulationset to 5% from a full load rejection

 

[rmw]

I'm not reading the entire standard, but what I read in your post is that the governor is allowed to run to 105% with no action (no trip, etc.) Sounds like the trip is set 5% higher than the upper operating limit.

rmw

 

[RotaryG]

2012tech,

Unlike governing, Trip is a safety function. For turbines, trip function is provided by an independant system.Usually trip speed is set at about 105% of MCS. MCS is the "Maximum Continous Speed". MCS is at least 105% of the rated speed.

Operation above 105% is not menat to be continous. For most applications (power gen as well as mechancial drive) such a high speed operation may not even be meaningful. Operators would know something is wrong. The reason why the turbine is not tripped immediately above 105% is to avoid nuisance trips caused by the governor control overshooting beyond 105%.