Overspeed Trip in ship’s main engine

Overspeed Trip in ship’s main engine

Excessive speeding is a safety feature provided to a ship’s diesel engine to prevent uncontrolled speeding, resulting in mechanical failure or unforeseen accidents. To prevent the speed of the diesel engine from exceeding the speed limit, high-speed travel is used on diesel engines.

Overspeed Trip

Due to sudden changes in the load on the diesel engine, the engine speed may vary. Although the controller is given control over the speed of the diesel engine, the speed may be out of control, damaging the engine. Therefore, for this reason a speed trip is used.

The foremost objective of the overspeed trip is to cut the fuel supply to the engine cylinder in case the engine speed increases above a certain level. Over speed will appear if any :-

  • Sudden loading of a water-like engine from a storm when the weather is bad, clutch failure, breakage at the engine stop.
  • Stuck fuel control shaft trip requires a personal reset. It should not be able to reset automatically after acceleration as the reason for the acceleration may be possible and the engine may not run again. It needs to be checked periodically to ensure its correct operation. Sometimes engines are fitted with two independent motors over speed, an electro-pneumatic device with a travel speed of 15% higher than the nominal speed and a mechanical device with a travel speed of 18% higher than the nominal speed.

Causes of engine overspeed

The diesel engine is designed with mechanical pressure corresponding to the centripetal and centrifugal forces of the moving parts inside it at a specified operating range. Centripetal force is directly proportional to the square of rotation speed, the pressure increases rapidly and the speed increases. The power connection of the equipment can be overcome by excessive pressure due to increased operating speed. This can lead to fractures of the rotating parts or damage to the equipment itself. Such excessive speed is a serious safety hazard and can lead to a fatal situation.

Preventing Overspeed of engine

  • Mechanical over speed trip
  • Electronic over speed trip

Mechanical over speed trip

Mechanical over speed trip

A simple machine tool may have a weight with wires loaded in the engine spring. Centrifugal force applied to the bolt mounted on a rotating shaft exceeds the pre-set power in the spring when the speed exceeds approximately 15% of the estimated speed and the bolt pulls out. The bolt on its outer surface strikes a plug that removes the plunger that shuts off the fuel supply of the engine.

Electronic Over Speed Trip

Electronic Over Speed Trip
  • Fly wheel speed sensor:

Magnetic speed sensor is popular in generator engines. Due to the suspension of the actuator surface (flywheel tooth gear) the voltage is excelled at selecting the sensor coil, producing an analog electric wave. This cyclic wave formed by the flywheel is read by a sensor.

  • Signal condition unit:

This unit acts as a receiver of a sense of speed. The basic function of a signal conditioner is to convert one type of electronic signal into a readable one into an easy-to-read format. This can be achieved by enlargement, attraction and order of the electric signal.

  • Detection and Comparison unit:

There is a set price that is usually 10% above the estimated speed and serves as the basic value of this unit. The output of the signal state unit is obtained continuously and compared to the set value.

  • Trip signal unit:

There is a set price that is usually 10% above the estimated speed and serves as the basic value of this unit. The output of the signal state unit is obtained continuously and compared to the set value.

  • Propeller overspeed

Propeller (rpms across the tachometer line) can cause vibration and a significant increase in noise. Left unmarked high propeller speed can lead to harp or metal failure and subsequent severe vibration resulting from imbalance. Pull the throttle and lower the plane, and usually you can regain propeller speed control, at least temporarily.

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