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15.3.1. Mechanic-hydraulic governors for main engines

The engines are normally provided with mechanic-hydraulic governors prepared for pneumatic speed set-ting.

The idling speed is set separately for each installation, for CP-propeller installations normally at 60–70% of the nominal speed and for FP-propeller installations at about 35%.

The standard control air pressure for pneumatically con-trolled governor on engines driving CP-propellers is:

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Speed setting pressure [bar]

The standard governor is provided with the following features:

• fuel injection limiter as a function of the charge air pressure

• shut-down solenoid

• lubricating oil pressure shut-down device with auto-reset feature, microswitch for indication

• speed droop

• microswitch for fuel limiter, this contact can be used for external control purposes e.g. to reduce the pro-peller pitch increase or only for indication

Governors are, as standard, equipped with a built-in de-lay of the speed change rate so that the time for speed acceleration from idle to nominal speed is 10–12 sec-onds.

15.3.2. Electronic governors

Electronic governors consist of the separately mounted electronic speed control unit and the actuator built-on the engine.

The main advantage of electronic governors is that they offer efficient tools for filtering of speed and load signals, which is often required in order to achieve good stability without sacrificing the transient response. Further the dynamic response can easily be adjusted and optimized for the particular installation, or even for different operat-ing modes of the same engine.

Electronic governors are also capable of so called isochronous load sharing. In isochronous mode, there is no need for external load sharing, frequency adjust-ment, or engine loading/unloading control in the exter-nal control system. Both isochronous load sharing and traditional speed droop are standard features in all elec-tronic speed controllers and either mode can be easily selected.

Speed droop means that the engine speed decreases automatically as the engine load increases (in steady state conditions). This will cause a parallel engine to take on load in relation to the speed decrease. The speed droop is normally adjusted to about 4%.

Isochronous load sharing means that the engine speed stays the same, regardless of the load level (in steady state conditions).

Propulsion engines

Electronic governors are recommended for more de-manding installations, e.g. main engine installations with

two engines connected to the same reduction gear, in particular if there is a shaft generator on the reduction gear. Isochronous load sharing is recommended for en-gines on the same reduction gear.

The speed setting can be either an increase/decrease signal, or an analog 4–20mA speed reference. The rate at which the speed changes is adjustable in the control unit.

Actuators with mechanical backup are only recom-mended for single main engines one engine per shaft line. The actuator should in this case be reverse acting, so that the change over to the mechanical backup takes place automatically. The selected governor/actuator type should in this case be a PGA-EG and the pneu-matic speed reference from the I/P-converter should be constantly tracking the electric speed reference in order to keep the pneumatic speed reference just slightly above the electric speed reference. Should however mechanical backup be used on any other applications, it should be of the direct acting type.

Start & maximum fuel limiter

The Start fuel limit for limiting over fuelling during engine start-up is active when the engine is started. When the PID takes control, the ‘Start fuel limit’ is switched out, and the ‘Maximum fuel limit’ is switched in, until the next time the engine is started.

An additional starting fuel limiter function is also pro-vided in the electronic governor by Wärtsilä, to achieve an optimum acceleration with a minimum of smoke dur-ing the start. The speed overshoot when reachdur-ing the target speed is also smaller.

Charge air pressure fuel limiter

This function can be used for diesel-mechanical plants to reduce the amount of smoke produced during load applications, by reducing the fuel injection to corre-spond to the amount of air supplied by the turbocharger until it has accelerated to a steady state speed.

This function is always used for FPP installations and mostly also for CPP installations.

Torque fuel limiter

In applications where a high torque can occur at any speed, such as dredgers, tug boats and die-sel-mechanical icebreakers, the torque limiter function should be used to protect the engine.

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Fuel limit indication

A relay output is provided to give an indication when the actuator output is nearing any one of the fuel limiters.

Fuel limit shift

This function can be used to move the fuel limit out of the way in certain situations by activating an input to the speed control unit.

Ready to close/open clutch

This function monitors the engine speed as a part of the clutch-in automation, giving an output signal to the clutch control system. This is an alternative function to the Fuel Limit Indication (both can not be configured si-multaneously).

Fixed speed

Constant speed mode can be selected by activating an input to the speed control unit. The engine speed will au-tomatically ramp to the programmed speed.

This is an alternative function to the Fuel Limit Shift (both can not be configured simultaneously).

Overspeed limiter

This function is independent of the governor settings and therefore faster. In case of a sudden load rejection e.g. due to a clutch automatic disengagement at high load, or the propeller emerging from the water in rough seas, a load rejection algorithm will come into effect, giv-ing reduced speed overshoot characteristics. The actu-ator output will be driven to a certain reduced position for a certain period of time, if a certain speed is ex-ceeded.

This function is useful in propulsion engines, especially in single engine applications, minimizing the risk for ac-cidental stopping of the main engine.

Diesel engines for electric propulsion

Electronic governors and isochronous load sharing are recommended for diesel electric installations.

There is typically a possibility to split the main switch-board into two independent halves. For this pur-pose the load sharing lines between the speed control units for isochronous load sharing must be grouped ac-cordingly.

The running-in of a diesel engine after overhaul can be enhanced by running the engine at constant desired load in the droop mode in parallel with other engines running in the isochronous mode.

Actuators with mechanical backup are not recom-mended for multi engine installations. Should mechani-cal backup be used, however, it should be of the direct acting type. It is not recommended to run an engine which is controlled by the mechanical backup in parallel with engines which are controlled by electronic gover-nors.

Start & maximum fuel limiter See propulsion engines above.

Charge air pressure fuel limiter

This function is available in the governor, but not recom-mended for generator engines operating in parallel, in other words not in typical diesel-electric applications.

To minimize the formation of smoke during load applica-tions a load increase function should be included in the propulsion control system.

Generator breaker load rejection

In the case of a load rejection due to the generator breaker opening, a load rejection algorithm will come into effect, giving reduced speed overshoot character-istics. This will be activated by the generator breaker opening if the load was above a certain level. The actua-tor output will be driven to zero for a period dependent on the amount of load before the breaker was opened.

This function should always be used in diesel generator applications.

Overspeed trip

This function stops the engine if a certain speed is ex-ceeded.

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