Over Speed Trip is a safety feature for the engines of ship (auxiliary engines, main engine). It is used to restrict the uncontrolled acceleration of the engines during emergency.
It prevents the speed of engine exceeding the set speed (desired speed) by cutting off the engine. Speed more than desired value can lead mechanical failures and that’s why it is an essential safeguard for the engines.
- If the load is suddenly changed, speed will be changed randomly.
- Governor is fitted to control the fuel injection accordingly. (i.e according to load)
- But, If governor doesn’t work properly at that time, then what we will do ?
- That’s why, we use over speed trip for safe side.
- It cuts the fuel supply whenever the speed exceeds the desired value.
Basically It is of 2 types :
- Mechanical over speed trip
- Electronic over speed trip
Sometimes, Pneumatic-electronic over speed trip is also used.
Mechanical over speed trip
- A simple device having a weighted spring loaded bolt attached into the rotating shaft of Engine.
- Centrifugal force exerted on the bolt exceeds the set spring force when speed exceeds 15% of rated speed.
- Bolt in its outward position strikes a latch which releases the plunger.
- And cut out the fuel supply to the Engine.
Electronic over speed trip
- Electronic protection system monitors three individual magnetic pickups to provide over speed protection.
- It is best suitable for high speed applications.
- It consists of Flywheel mounted speed sensor, Signal condition unit, Detection and comparison unit and trip signal unit.