MDE Unit 7 Q1

An overspeed trip is a safety device fitted to a diesel engine to prevent it from exceeding its maximum allowable speed.

1. Overspeed – Wikipedia

If the engine speed rises above a predetermined safe limit, the overspeed trip mechanism activates, initiating an emergency shutdown of the engine. This prevents catastrophic damage to the engine, such as the failure of critical components like the crankshaft or connecting rods.

Key components of an overspeed trip system:

• Speed sensor: Measures engine speed.
• Trip unit: Compares the measured speed to a preset limit.
• Actuator: Initiates the engine shutdown.

Types of overspeed trips:

• Mechanical: Utilizes a centrifugal governor to detect overspeed.
• Electrical: Employs electronic sensors and controls for speed measurement and trip activation.

By incorporating an overspeed trip, engine manufacturers ensure a critical layer of protection for both the engine and its operators.

A centrifugal overspeed trip is a mechanical device that protects a diesel engine from overspeeding. It operates based on the principle of centrifugal force.  

1. Mechanical overspeed protection or electronic overspeed protection? – Istec International

Components:

• Governor weights: These are weighted components attached to a rotating shaft.
• Springs: Counteract the outward force exerted by the governor weights.
• Trip mechanism: A lever or linkage connected to the governor weights and the fuel supply or engine shutdown system.

Operation:

• Normal operation: At normal engine speeds, the centrifugal force acting on the governor weights is balanced by the spring force, keeping the trip mechanism disengaged.
• Overspeed condition: As engine speed increases, the centrifugal force overcomes the spring force, causing the governor weights to move outward.   1. Overspeed Trip Device fundamental , Mechanical and Electrical Overspeed, Steam Turbine, Gas Turbine – YouTube www.youtube.com
• Trip activation: The outward movement of the governor weights engages the trip mechanism, which initiates an emergency shutdown of the engine.

Advantages of Centrifugal Overspeed Trips:

• Simplicity: Relatively simple design and operation.
• Reliability: Proven technology with a long history of use.

Limitations:

• Response time: Can be slower compared to electronic overspeed trips.
• Sensitivity: Might be less sensitive to minor speed fluctuations.

While centrifugal overspeed trips have been widely used in the past, modern engines often incorporate electronic overspeed protection systems for improved accuracy and response time.