CAPÍTULO I. CONTEXTO DE LAS ADICCIONES Y LOS TRATAMIENTOS DE
1.1 Antecedentes de investigación
Governor Function
♦ To control the engine speed within close limits, from no load speed to full rated speed.
♦ To control either the engine speed or the engine load.
Isochronous G overnor
It is a governor w hich m aintains a ‘constant speed’, irrespective o f load and power changes.
Exam ple: Auxiliary engines.
Variable S p eed Governors
When there is a facility to adjust the set speed on the governor according to the load, then the governor is a variable speed governor. Exam ple: M ain engine governor.
Droop
It is the drop in speed from stable ‘no load condition’ to stable ‘full load’ condition i.e. a fall in speed due to load changes.
Marine Diesel Engines L in e A sh o w s iso c h ro n o u s c h a r a c te r is tic s i.e . sp e e d (frequency) is same, 60H z at 0 % lo a d an d 100% lo a d . L in e B sh o w s d ro o p characteristics i.e. a fall in speed o r freq u en cy fro m 6 0H z to 5 8 H z a t 0% lo a d to 100% load. KW LOAD _ . . . Kg-222 Sen sitivity
It is the measure o f the smallest change needed for which the governor responds with the required output signal. It implies that the governor can control the speed within very narrow limits.
Stability
It is the ability to attain a stable speed fo r varied load conditions.
G overnor E ffo rt
It is the force applied by the governor onto the fuel pum p control, when there is a change in load or speed.
D ea d B a n d
It is a band o r range in speed, o nly after w hich the governor will respond.
H u n tin g
It is the fluctuation in the engine speed due to over o r under control of the governor. Too much sensitivity can cause ‘hunting’.
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Governors and Control
Mechanical Governor
T h e fig u re sh o w s a b a sic m e c h a n ic a l g o v ern o r. T h e engine drive input signal 6 is transmitted via the gearing 4 to the governor mechanism. The governor mechanism consists of flyweights 3 on a bell crank 7 pivoted 8 to act on a spring lo a d e d c o lla r 9 w h ic h is
connected to the fuel pum p Fig-223 linkage 5. The speed setting control can be adjusted by the screw 1 changing the spring tension. W hen the engine speed increases if load is reduced, the flyweights m ove outwards, due to their increased centrifugal force. This causes the bell cranks to push the spring loaded collar to reduce fuel. M echanical governors have the following drawbacks: Increased wear, friction, m echanical damage, bearing failures, instability and a limited governor effect
Hydraulic Governor with Compensation
Marine Diesel Engines
1 Ball head 2 Centering spring
3 Receiving piston 4 Reservoir
5 Transmitting piston 6 To fuel linkage increase or decrease
7 Needle valve 8 Oil drain
9 Oil supply 10 Pilot valve !
11 Conical speeder spring
♦ This governor can be considered as isochronous (constant speed), except during the compensation (transient speed drop) period. ♦ It is a ‘stable’ governor.
♦ Compensation or transient speed drop is included in the form of reset action.
♦ Compensation can be changed by adjusting the needle valve setting. ♦ W hen load increases, the engine speed decreases along with the centrifugal force. T he spring force becom ing greater causes the pilot valve 10 to move down. This allows oil to flow to the servo. The servo causes the increase in the fuel racks 6. ♦ The servo simultaneously acts on the transmitting piston 5 which
applies a force onto the receiving piston 3. This receiving piston pushes the centering spring 2 and causes the closing o f the pilot valve (pilot valve moving up). Thus, equilibrium and stability are achieved at a lower speed. Once the oil in the compensating system leaks past the needle valve, the centering spring causes the speeder spring to return to its original valve, so that equilibrium is brought about at the original speed, inspite of the increased load. ♦ The hydraulic governor has operational problems in case o f low
oil level, dirty oil, incorrect viscosity, air lock, wrong adjustments, excessive oil operating temperatures, and wear at fine clearances.
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Governors and Control
Fig-225 It basically consists o f fo u r components
♦ The load sensing input signal 1 which senses the load 12 after the governor alternator 10 and sends this input signal to the setting control unit 4.
♦ The speed sensing input signal 2 w hich senses the speed at the engine flywheel 11 and sends this input signal to the comparator amplifier unit 5.
♦ The setting control unit 4 w hich has settings fo r droop or isochronous mode 6, speed setting signal 7 and ramp generator 8. ♦ The Comparator / Am plifier C ontrol unit w hich compares the input signals with the reference settings and sends an output signal to the actuator 3 to change the racks position o f the engine fuel pumps 9.
Marine Diesel Engines
The advantages o f the electronic governor
Less mechanical components; quick response; no friction; capable of com plex engine speed control; taking into account the engine load and electrical load; overspeed control; load sharing requirements; easy installation; and easy adjustments.
T he main disadvantages o f the electronic governor is that it can fail in case there is a failure o f input current to the governor from any source. T he rem edy is to com bine the electronic g overnor w ith a mechanical hydraulic governor which will act as the back up in case of electronic governor failure.
Governor Adjustments
C om pensation Range
It can b e adjusted b y changing the fulcrum position on the lever connection between the servo output linkage and the compensation transmitter piston.
C om pensation R ate
♦ It is done only after the compensation range has been set. ♦ It is done only in case o f sluggish response, excessive hunting or
overspeeding during initial start-up.
♦ The needle valve is opened till the control ju st becomes unstable, after which it is shut by 1/4® turn.
L o ca l S peed S ettin g Knob
♦ During norm al operation, the control o f speed setting is d one remotely, via the electric m otor mounted on the governor. ♦ This local speed setting knob is used only in case o f failure o f the
remote control system o r when on local control to test the engine over-speed trip.
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Governors and Control
♦ Turning the knob clockw ise changes the tension o f the speeder spring and increases the speed o f the engine.
♦ The number o f turns that the speed setting knob has turned can be seen on the speed setting indicator, which has a m inim um and maximum fuel setting limit.
L o a d L im iter Knob
♦ It limits the fuel and, therefore the load.
♦ It lim its the stroke o f the pow er piston by altering the position of the droop lever fulcrum point.
♦ It is used only when load on the engine is to be limited, as in cases of running-in after major overhauls.
S p eed Droop Knob
It is used to control the speed droop during load sharing operations between generators. It is not usually adjusted.
L o a d Sh a rin g a n d th e N ecessity o f Droop C o n s id e r tw o d ie s e l g e n e ra to rs c o n n e c te d in parallel.
Fig-226 show s the condition I ju st after synchronization has ® b e e n d o n e to ru n th e g e n e ra to rs in p a ra lle l. A t p o in t X , it is s e e n th a t „ g e n e ra to r/ ta k e s fu ll lo a d 100 kwg«52 (1 0 0 % ), w h ile g e n e r a t o r takes no load (0%). 335
Marine Diesel Engines
Fig-227: G enerator2 speed (frequency) control increases so as to take up part o f the load.
Fig-228 : Once g e n e ra to r has taken up some o f the load, generator? w ill decrease its speed (frequency) as it takes up less load. The frequency o f generator; will now be brought back to 60Hz.
F ig-229: B y comparing Fig-228 and Fig-229, w e can conclude that fo r stable operation, droop is
n e c e s s a ry f o r lo a d s h a rin g G e n t and <3an2 between generators.
N ecessity o f d roop f o r lo a d sh aring
In o rder to a chieve sharing o f lo a d , th e g e n e r a to r l a n d g e n e r a t o r lin e s s h o u ld , in te rse c t, as in th e c ase o f Fig-228. This is only possible
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Governors and Control
in case o f a droop i.e. a change in speed (frequency) o f the generator during transient conditions o f load changes.
In F ig -2 2 9 f o r iso ch ro n o u s o p eratio n , b o th g e n e ra to r; and generator2 share the same line i.e. at constant speed or frequency of 60Hz. There can be no crossing o f generator; and generator2 lines if constant speed (isochronous) is to be maintained. Hence, sharing o f load would not be stable.
Electronic Digital Governor for Bridge Control
Bridge Control using an electronic digital governor consists o f 4 units, namely (1) Digital Governor, (2) Remove Control Unit on Bridge, (3) Engine Telegraph and (4) Engine Protection Devices.
1) D igital Governor
Marine Diesel Engines
The various components are described b e lo w : R P M Command
It is the order from the Bridge requesting a certain speed. This input signal should meet the safety settings i.e. the rpm should not rise too fast causing engine overload or the rpm should not be within the critical speed range.
M easured Command
It is the rpm m easured at the engine by m eans o f tw o inductance pick-ups, fitted at the toothed ring. The higher rpm value is chosen from the tw o pick-ups.
R P M Comparator
It compares the measured rpm with the rpm command desired by the Bridge and sends a resultant signal to the regulator amplifier.
Regulator Gain
It regulates the gain o r sensitivity o f the governor during different engine load conditions.
Example:
♦ With constant fuel setting, die dead band o f the controller output is increased so that an engine speed change o f at least 2 rpm is needed, before the governor responds.
♦ W ith rough sea setting, the governor output varies with the engine speed changes.
Controller Gain ♦ This is a P and I controller.
♦ P-gain is varied between normal and rough sea options. Rough sea has a slightly lower gain since the dead band o f the controller output is reduced.
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Governors and Control
♦ I-gain increases in rough sea conditions w hich slows down the controller response.
♦ The gain also improves with both P and I functions, as the difference between the desired and measured rpm value increases to improve the, controller response and prevent over-speed o f the engine.
Fuel Limiters There are 3 fuel lim iters: a) Maximumfiiellimiter
It is used to limit fuel to avoid mechanical overloading o f the engine (excess firing pressures and excess bearing loads). It can be overridden from the Bridge using the ‘Cancel Limiter’ button, but the engine should never be run more than 110 % load for more than an hour in a 12-hour period.
b) Torque (fuel) limiter
It is used to limit the fuel to avoid excessive torque conditions i.e,high thermal load on cylinders and high torsional loads on crankshaft especially at low speeds.
c) Scavenge air limiter
It is used to lim it the fuel as per the scavenge air pressure available to ensure proper combustion.
A ctuator P ositioner
The actuator gets an input o f the desired fuel com m and signal. It compares it with the actual position o f the actuator and sends a resultant signal to the actuator which is amplified before being fed into the actuator motor.
Marine Diesel Engines
A ctuator Speed Pick-Up
It is a feedback link which prevents excessive actuator m otor speeds. It allows the actuator amplifier to position the actuator at the correct position quickly.
A ctu a to r
It is a brush-less servom otor fitted w ith a digital encoder fo r m otor output position.
2) R em ote C ontrol Unit
Fig-231
T he mimic diagram as shown displays the functioning o f the remote control unit from the bridge. This mimic diagram has indicator lights to show the sequence and changes taking place during maneuvering. The following components in this mimic diagram are described below.
Bridge shows bridge control.
System S im u la tio n : I t is used during testing and sim ulation o f the engine running conditions while the engine is actually stopped. Stop indicates th at the bridge telegraph lever is at ‘stop’ or the emergency stop button is pressed.
Ahead/Astern C om m and: It only indicates the bridge command that has been requested and not the engine o r camshaft position.
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Governors and Control
Start B lo c k : It indicates that the engine starting is blocked in case of turning gear engaged, low start air pressure, both ipm detectors’ failure, engine tripped, automatic start air valve blocked or start air distributor blocked.
A bove Reversing Lim it indicates that the engine speed is m ore than the m aximum level at which brake air can be supplied. Start Set Point indicates that the governor setting is at its preset start level to allow sufficient fuel for starting. This signal is maintained for 6 seconds.
Ahead / A stern S.V. indicates the presence o f the bridge speed setting signal.
Stop governor indicates the presence o f a signal to the governor to stop fuel admission. This is not a cut-out device.
Cancel Lim iter Governor indicates the scavenge a ir lim iter and torque limiter are cancelled. This happens in case the engine fails to start after three automatic starts. A n alarm indicates the repeated- start function activation.
Above Start Level indicates that the start system will be activated to brake the engine before reversing can take place.
Start S. V indicates start air system is activated.
Stop S. V. indicates the starting air has started the engine above the set point for starting.
Set Point Lim iter indicates that the bridge engine speed request has not been allowed due to the load-up programme being activated above full ahead rpm, or due to the critical range speed being blocked by the bridge control system, or a slow down condition has been activated. This can be cancelled at the bridge panel.
Marine Diesel Engines
3) E n g in e Telegraph System
♦ It conveys the speed anddirection command from the bridge to the engine control room personnel.
♦ W hen on bridge control, the engine room telegraph control is disconnected and becomes a transmitter/recei ver for the bridge to engine room com m and communications. I t indicates the following:
• Standard ring o f bell i f the bridge and engine telegraph position do not match.
• W rong way alarm indicates that the engine room telegraph and engine rotation are opposite.
• Failure o f remote system power supply indicates that bridge control is no m ore possible. Emergency control may have to be done in case o f failure from engine room control. • A n internal comm unication failure between the telegraph
panels.
• Indicators fo r the FW E, S tandby and A t Sea modes.
4) E n g in e P rotection
It is provided to safeguard the engine d uring: a) O verspeed i.e. 107 % o f M CR :
It activates the emergency stop solonoid for shutdown o f the engine.
b) Shutdown for: ♦ low lube oil pressure (1 bar) ♦ jacket water .high temperature(96 deg.C) ♦ thrust block high temperature (85 deg.C) ♦ cam shaft oil low pressure (1.5 bar).
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Governors and Control
c) Slow dow n to dead slow speed rpm, due to: ♦ Low lube oil pressure (1.5 bar) ♦ Low cam shaft oil pressure (2 bar) ♦ Thrust block high temperature (75 deg.C)
♦ Piston coolant no-flow.
♦ Scavenge air temperature high (65 deg.C) ♦ Oil mist detection high.
♦ Cylinder exhaust temperature high (450 deg.C) ♦ Lube oil inlet temperature high (60 deg.C) ♦ Piston coolant high temperature (75 deg.C).
T he Em ergency run button on the bridge can over-ride the shutdown function.