Over speed protection

M

Thread Starter

mhm

can anybody help me about over speed:
Which over speed comes first mechanical or electrical?????????
 
mhm,

Typically, if a piece of rotating equipment has an electrical or electronic overspeed AND a mechanical overspeed mechanism, the electrical/electronic overspeed is configured to trip the equipment before the mechanical overspeed.

Mechanical overspeed mechanisms ("bolts") are usually not very repeatable (meaning they don't always trip at exactly the same speed), and they are known to also not operate in every instance (some large steam turbines exercise the mechanical overspeed weekly, because such turbines usually operate for months or years between shutdowns and the mechanical overspeed mechanisms can become bound and stick and not work if not regularly exercised (without actually tripping the turbine)).

Electrical/electronic overspeeds are usually much more repeatable, meaning they trip at exactly the same speed each time. This is one reason many mechanical overspeed mechanisms have been removed from some equipment and are no longer supplied on many new equipments, instead using a second, independent electrical/electronic overspeed to back up the first (for redundancy).

Hope this helps!
 
On GE turbines that have both types of overspeed protection, the electrical operates first, typically at 110% speed and the mechanical bolt is usually set at 112% speed.
 
For GE LSTG MI & MII, the mechanical was <b>THE</b> overspeed trip with an electrical backup that primary purpose was to provide overspeed protection during the few minutes per week when the mechanical was locked out for exercising.

the recommended electrical BUOST was set 0.5% above the maximum MOST setting.

For the few GE,C(MSTG design) MII's I have seen, the BOUS only dropped out the lockout 3% below MOST.
 
electrical overseed trip should be 110% of rated speed, and mechanical over speed bolt should be operated at 112.5%, and first electrical over speed should be operate.
 
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