Answer EKM Question 58

Q58. (a) Describe, with aid of sketches, either an electronic governor or a hydraulic governor.
(b) Explain how the governor. described in (a), functions in order to increase fuel to the engine in the event of a load increase.
(c) State the defects which can impair the operation of the governor described in (a)
Ans: Electronic Governor:

Main engine speed is detected by a magnetic pickup which is placed next to a gear, the gear is mounted on the propeller shaft and rotating at the same speed as the engine. The Magnetic Pickup Generates an AC Voltage whose frequency is proportional to engine speed. Magnetic pickup provides the measured value signal of the engine speed and is taken to the comparator unit. The desired value signal for the engine RPM is transmitted from either Bridge or ECR telegraph in the form of an AC voltage of required frequency to the comparator unit through a changeover arrangement.
The difference between the two signals is the RPM deviation or the error signal, which is then passed through the limiting system. This allows the maximum acceleration within the safe operating requirement of the engine, while manoeuvring, but prevent overloading.
All the engine parameters are fed through a transducer into the limiting system. so that it can monitor the limiting values and accordingly, control the engine speed. The timing system programs to increase the power when moving from full ahead to full away, guarding against the excessive power demands and propeller cavitation.
The action is achieved by a system of resistors and capacitors, giving a time delay to the signal.
A tunnel amplifier having a combination of inductance and capacitance in parallel is provided to overstep the critical speed range of the engine.
For crash manoeuvring, a switch may be operated which bypass the limiting and timing system.
The P&I controller processes the signal in order to enhance accuracy. (No-Offset) and speed of response and sense a signal to the electrohydraulic actuator. The actuator converts the electronic signal into mechanical output, which positions the engine fuel pump racks. To correct the error in engine speed compared to the desired value.
In case of failure of the control system, manual control is also possible from the control room or engine room. Telegraph position that directly operates the hydraulic actuator and the fuel rack to control the engine speed.
Advantage of electronic governor:
- Extremely fast response
- No friction hance negligible dead-band
- Simple Installation and Adjustment.
- It is much accurate than the Mechanical one.
Disadvantages of electronic governor:
- It requires an external electrical power supply, failure of input current make it inoperative.
- A defective printed circuit board require a complete replacement and thus costly.


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