3 replies to this topic

[laplace]

API-670 defines that overspeed detection systems shall rely on three independent magnetic pickup sensors in a voting scheme 2oo3 (two-out-of-three), that is, to shutdown the machine at least 2 sensors shall detect an abnormal speed simultaneously. If one sensor fails an alarm shall be sent out. My question is, if one pickup fails, the voting scheme shall turn to 1oo2 (one-out-of-two) or to 2oo2 (two-out-of-two)?

Laplace

[bhagat]

Hi
Lapalce

Voting of sensor doesn't change if one sensor is failed. if it is like that machine will tripped by failure of one sensor and no body wants macheine to be stopped by any faulty sensor. if it's change to 1001 or 2002, then there is no meaning for the voting, if one fails it will stopped the machine.

thnaks.
bhagat.

[Adriaan]

API-670 defines that overspeed detection systems shall rely on three independent magnetic pickup sensors

Where I work each turbine has a hardware overspeed protection (spring and weight in axle that when the speed exceeds the limit will toggle a switch that causes the regulator oil to drain, in turn cutting off the steam feed).

The turbines are controlled with an electronic system (governor) that limits the speed automatically and has a switch to test overspeed, this overspeed is lower than the hardware overspeed protection (so the turbine going into ACTUAL overspeed is highly unlikely). There is another switch to test ACTUAL overspeed too of course.

Unfortunately I do not know how the electronic protection works on our turbines (number of pickups) though as far as I know the protection is indirect, relying on oil pressure generated by a special oil pump section on the turbine axle (this also gives us the turbine speed, as a function of the oil pressure).

So, question; does your turbine use those sensors only to detect overspeed (and trigger a shutdown) or does it have a hardware overspeed protection too?