Generator Synchronization Procedure

Generator synchronization is the process of the closing circuit breaker after matching the generator frequency, phase angle & voltage magnitude with grid voltage frequency, phase angle & magnitude respectively. Simply it is used to close the circuit breaker after synchronization check.

Conditions:

In order to synchronize a generator to the grid, four conditions must be met:

1. Phase Sequence
2. Voltage Magnitude
3. Frequency
4. Phase angle

Synchronizing procedure

1. Once the engine starts running properly, synchronization is carried out.
2. In the Engine control room, Check the pressure gauges.
3. On the generator control panel, check if all the ground lights are working properly with adequate brightness.
4. Also check the synchronizing relays for open position. Bring the running or the lead generator to the desired optimum parameters: 480 volts and 60 hertz.
5. Bring the generator that is to be synchronized(in-coming) to the desired parameters. Now turn on the synchronizing relay and keep a close look at the needle.
6. The needle in the synchroscope will move at a varying speed initially. Adjust the speed of the generator by obtaining a steady slow motion of the needle in the clock wise direction.
7. Once the needle is moving at a steady speed, depress the breaker close button when the needle has traveled three-fourth of its way. Energize the breakers when the needle reaches a position similar to the 11' o clock position of a clock.
8. After doing this, check the parameters of the on-coming generator. They should be same as those of the leading generator. i.e 480 Volts and 60 hertz

After synchronizing

1. After the main job of synchronizing, the following steps are to be carried out.
2. Change the governor control to the off-going generator.
3. Now the load shown in the gauges by this generator should be removed off the system as soon as possible before it starts acting as load(reverse power). This can be done by quickly pulling the trip breaker as soon as the generator goes off-line.
4. Once the generator is offline, stop the engine using a toggle switch.
5. After turning off the engine, turn on the engine block heater.
6. At the end, take a proper look at the control panel gauges for adequate pressure and even distribution of load.

It must also be noted that load distribution can be adjusted by varying the fuel supply to the generator via its governor but for current sharing to be equal you would need to vary the excitation current which changes the power factor of the generator.

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 Reference:

 brighthubengineering.com

marineengineeringonline.com

Marine Engineers' World (Facebook)

 Bangladesh Marine Academy

Maintenance Of Emergency Generators On Ship

Emergency Generator like any other normal generator on ship is required for the purpose of production of power (Electricity). But as name suggests, it is to be used in case of the emergency like Black Outs, getting ship to live after dead condition. Since the entire generator on a ship lies in the engine room, there has to be a source of supply that is outside this machinery space. Reason, well engine room is highly prone to fires and other factors, and thus there is a need of generator which is outside this space.

Otherwise:

1. It is a small separate generator which supplies the electric power for emergency load in the event of main power supply failure. 
2. It is located outside the main and auxiliary machinery space and not forward of the collusion bulkhead. 
3. It has own switchboard near vicinity. 
4. It is provided with independent means of automatically starting (by air or battery) to ensure immediate run up following a main power failure and repeated starts of at least 3 times, and further attempt can be made within the 30 minutes.
5. Adequate and independent supply of fuel with a flash point of not less than 43 °C
6. Must be able to be started in cold condition up to zero (0 °C)
7. For cold weather, JCW system must be treated with anti-freeze agent, and heating arrangement provided.

Rules and Regulations for Emergency Power Sources

• Emergency generator shall be automatically started and connected within 45 sec
• Emergency power source, Emergency generator must be sufficient to operate certain essential services at least for the period of 18 hours .
1) Emergency lightening (at alley way, stairways and exits, muster and embarkation stations, machinery space, control room, main and emergency switchboard, firemen’s outfits storage positions, steering gear room)2) Fire detecting and alarming system
3) Internal communication equipment
4) Daylight signaling lamp and ship’s whistle
5) Navigation equipment
6) Navigation lights
7) Radio installations, (VHF, MF, MF/HF)
8) One of the fire pumps, emergency bilge pump

Procedure for starting emergency generator when black out occurs ?

1. Normally emergency generator cut in automatically when main power fails
2. Starting is initiated by start up relay
3. Falling of frequency or voltage of Main power, cause the start up relay to operate generator starting equipment
4. If this system fails, after switching the MODE selector to Manual (Local) position, generator can be started manually by means of Back up starting equipment within 30 minutes of transitional emergency power battery lighting.

Maintenance:

Following are some important maintenance jobs that need to be carried out in emergency generators on ships:

1. Change of Engine Sump Oil: It is important to check the oil level in the sump regularly. Since the emergency generator is kept on auto mode, which ensures the generator starts and comes on load automatically, it is necessary that before starting the engine for operation, oil level is checked on regularly basis. The condition of the oil will be known during this period and if the oil is having carbon or soot particles, change of complete oil system needs to be done. The running hours for changing of engine oil depends on the manufacturer, the engine make and the oil grade in use. Normally it is done between 250-500 hrs.

2. Clean Air Cleaner: The combustion air for the engine is passed through an air filter, which can be of following types:

1. oil bath air cleaner

2. dry type air cleaner (cartridge or dust collector).

It is important to clean the air filter at correct intervals of time as delay will lead to clogging and less air going in the engine. This will reduce the efficiency of the engine and increase the thermal parameters. When using dry cartridge, ensure to replace them at intervals stated by the maker. Normal replacement schedule is one year or after 5-7 cleanings.

3. Check Water Separator: Some emergency generators are provided with water separator to prevent mixing of water with fuel. Check the level of water and make sure it is below the marked level and regularly drained off. This is to be done to avoid rust and corrosion of fuel line devices and to avoid incomplete combustion.

4. Check Electrolyte in the Battery: A battery is used in one of the starting methods of the emergency generator. The electrolyte level in the battery must be checked at regular intervals either by inserting a level stick or by checking the water level in the level tester cap (if provided). Use distilled water to make up for the low level.

5. Check Alarms and Shutdowns: All the safety devices and alarms fitted in the emergency generator must be checked and tested regularly. Generator with V-belts have additional alarm which will be sounded in the event of belt failure and operated by idler pulley.

6. Check V belt Tension: When V belt is fitted, inspect the same for cracks and damages. Renew the belt if damage/ cracking appearance is more. To check the belt tension, press the belt by thumb in midway of the pulleys and check the inward deflection in mm. It should not be more than 10-15 mm depending upon the make of the generator.

7. Clean Oil Filter Cartridge: The emergency generator is provided with various oil filters such as by pass filter, centrifuge filter, lube oil filter, fuel feed pump filter etc. These filters need to be cleaned or renewal of filter cartridge is to be carried out as per the maker’s instruction or oil condition.

8. Check Valve Clearance: The tappet clearance of the inlet and exhaust valve should be checked at running hours stated in the maintenance section of the generator’s manual. Also ensure the engine is cold before taking the tappet clearance.

Loss of emergency generators at times when they are needed the most can lead to unfortunate and disastrous incidents. Followed a proper planned maintenance system along with thorough regular checks is the key to ensure smooth running of emergency generators on board ships.

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Reference:

www.marineinsight.com

Marine Engineers' World (Facebook)

www.marineengineering.org.uk

Bangladesh Marine Academy

Bedplate of a Large Two Stroke Marine Engine

Bedplate:

A bedplate is the lowermost portion of a marine engine (2 and 4 stroke), which supports the engine structure and is also one of the most loaded constructional parts of the engine. For large engines, the bedplate is fabricated in parts with flat bottom type construction having high surface finish.

Construction of Bedplate:

The bedplate acts as the main strength member, maintains correct alignment and supports the weight of the components. it must be capable of withstanding the fluctuating forces created during operation and transmit them to the ships structure. In addition it may also collect lubricating oil.

In slow speed engine design, it consists of a deep longitudinal box section with stiffening in the form of members and webs.
Transverse members are fitted between each throw of the crankshaft. These support the main bearing saddles and Tie -rod connection. They are attached to the structure by substantial butt welds.To reduce the engine height the sump of the bedplate may be sunken allowing it to fitted into a recess in the ships structure.
Plate and weld preparation is required with welds of the double butt type if possible. Regular internal inspection of the parts especially the transverse girder is required for fatigue cracking. Tie bolts should be checked for tightness.

The advent of the small bore slow speed has seen the use of single side bedplates. A box section is then created by using a box section crankcase structure rather than the more traditional A-frame.This has the advantages of reducing width as well as weight and increasing the amount of fabrication so reducing assembly times.

Due to the weight penalty, the use of cast iron is generally limited to smaller units where fabrication becomes impractical. However, cast iron has internal resilience allowing it to dampen down vibrations, this has led to its usage on some medium speed installations, especially passenger carriers, where noise and vibration suppression is important.

The most highly loaded pat of a bedplate is the transverse girder. Classification societies require that residual stress is removed after construction.
The transverse girder acts as a simple beam with the forces of combustion acting on the piston passing down through the bearing. The forces acting on the head are passed through the Tie rods.

It can be seen that to reduce the bending moment the tie rods have to be brought closer to the crankshaft. The limit to this is the securing arrangement required for the main bearing keep. One method is to use two instead of one bolts which can be made of smaller diameter. Sulzer use an alternative and very successful method in the form of jacking bolts. These jack against the bottom of the A-frame.

The important functions of bedplate are:

1. To support the static load of stationary engine frame and blocks
2. To support the dynamic load of the running gear
3. To support the crankshaft and hold it in perfect alignment
4. To distribute the static and dynamic load generated by running engine onto the ship structure
5. To collect the crankcase lube oil and transfer it to the sump tank from where the lube oil pump can take suction
6. To fasten the engine to the tank top transmitting propeller thrust to the hull structure
7. To contribute to the hull strength of the ship at engine room bottom structure

Checks to be Carried on the Bedplate:

It is important to keep a regular check on the bedplate as it’s the foundation of the marine engine. The inspection of bedplate is also included in the planned management system of engine.

Following checks to be carried on the bedplate during inspection:

Cracks: Cracks is the most common problem that occurs on the bedplate structure. Following areas to be carefully checked for cracks:
Welding portion which joins the transverse girders to the longitudinal girders
Under the bearing pockets where cracks can emerge to be radial or follow the line of the pocket which holds the bearing
Radially at tie bolt and frame bolt holes
Around lightening holes provided in the bedplates and girders
At the base of main bearing keeps



Faulty welding: It is to be checked on newly delivered engine or if any welding repairs are carried out in the recent past


Faulty casting – It is to be checked on newly delivered engine with casting construction


Corrosion: As the bedplate is the bottom structure fitted in the bilge section of the engine room, it comes in contact with various fluids such as oil, water etc. and therefore is prone to corrosion. A close check should be made for identifying corrosion.


Loose Frames: The bedplate is held together with A frame and entablature of the engine by means of tie rod. Check the tie rod is tightened and there is no loose portion between the frame and bedplate.
Faulty Holding Down Bolts: The holding down bolts keeps the bedplate in position with the bottom structure of the ship. Check for loose holding down bolts and tighten as per the manual if found loose. Also, check for shearing and fretting on the holding down bolts.


Oil leakages: The bedplate is also responsible to collect the lube oil and transfer it to engine sump. Check for any oil leakage from the bedplate or the joint between the bedplate and the frame.


Ship’s engineers are responsible to ensure that marine engine bedplate is inspected at regular intervals of time and all faults are identified and repaired at the earliest. Failing to do so will result in heavy vibrations, misalignment of crankshaft, and reduction in engine efficiency and failure of engine components.

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Reference:

www.marineinsight.com

Marine Engineers' World (Facebook)

www.marineengineering.org.uk

Bangladesh Marine Academy

Boiler Safety Valve

Boiler Safety Valves:

One of the most critical automatic safety devices in a steam system is the safety valve. It protects lives, equipment and property from potentially dangerous levels of temperature and forces caused by excessive steam system pressure.
The main purpose for a safety valve is to prevent the pressure in a system to exceed certification pressure.
Above certification pressure no one can guaranty the systems safety - and especially for a steam system with a very hot gas with a huge amount of latent heat the consequence with a failure can be dramatically.

Design:

The size of a safety valve depends primarily on the maximum boiler output and the operation pressure of the system. The safety valve must as minimum have the evacuation capacity of all the vapor the boiler can produce running at full power at the working (or certification) pressure.

1. For a higher pressure the steam is compressed and requires less volume and the size of the valve can be reduced
2. for a lower pressure the steam is expanded and requires more volume and the size of the valve is increased
3. Although the principal elements of a conventional safety valve are similar, the design details can vary considerably. 
4. The DIN style valves (commonly used throughout Europe) tend to use a simpler construction with a fixed skirt (or hood) arrangement whereas the ASME style valves have a more complex design that includes one or two adjustable blow down rings. 
5. The position of these rings can be used to fine-tune the over pressure and blow down values of the valve.
6. For a given orifice area, there may be a number of different inlet and outlet connection sizes, as well as body dimensions such as centreline to face dimensions. 
7. Furthermore, many competing products, particularly of European origin have differing dimensions and capacities for the same nominal size.

Safety Valve Operation:

1. When the inlet static pressure rises above the set pressure of the safety valve, the disc will begin to lift off its seat.
2. However, as soon as the spring starts to compress, the spring force will increase.
3. This means that the pressure would have to continue to rise before any further lift can occur, and for there to be any significant flow through the valve.
4. The additional pressure rise required before the safety valve will discharge at its rated capacity is called the over pressure.
5. The allowable over pressure depends on the standards being followed and the particular application.
6. For compressible fluids, this is normally between 3% and 10%, and for liquids between 10% and 25%.
7. In order to achieve full opening from this small over pressure, the disc arrangement has to be specially designed to provide rapid opening.
8. This is usually done by placing a shroud, skirt or hood around the disc.
9. The volume contained within this shroud is known as the control or huddling chamber.
10. As lift begins and fluid enters the chamber, a larger area of the shroud is exposed to the fluid pressure.

Safety Valves Regulation:

1. Each boiler (including exhaust gas boiler) and steam generator is to be fitted with at least one safety valve and where the water-heating surface is more than 46.5 m2 (500 ft2), two or more safety valves are to be provided. The valves are to be of equal size as far as practicable and their aggregate relieving capacity is not to be less than the evaporating capacity of the boiler under maximum operating conditions.
2. In no case,

- The inlet diameter of any safety valve for propulsion boiler and superheaters used to generate steam for main propulsion and other machinery to be less than 38 mm (1.5 in.) nor more than 102 mm (4 in.).

- For auxiliary boilers and exhaust gas economizers, the inlet diameter of the safety valve must not be less than 19 mm (3/4 in.) nor more than 102 mm (4 in.).

3. In all cases, the safety-valve relieving capacity is to be determined on the basis of the boiler heating surface and water-wall heating surface along with the fuel-burning equipment.

SAFETY VALVE   - PRESSURE ACCUMULATION TEST:

1. Safety valves are to be set under steam and tested with pressure accumulation tests in the presence of the Surveyor.
2. The boiler pressure is not to rise more than 6% above the maximum allowable working pressure when the steam stop valve is closed under full firing condition for a duration of 15 minutes for fire tube boilers and 7 minutes for water tube boilers.
3.During this test, no more feed water is to be supplied than that necessary to maintain a safe working water level.
4. The popping point of each safety valve is not to be more than 3% above its set pressure.

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References: 

marineengineeringonline.com

www.marineinsight.com

www.youtube.com

Marine Engineers' World (Facebook)

Understanding Power Card / Indicator Diagrams and Fault Analysis

Power Cards:

A power card is a graph of cylinder pressure against time.

Purpose Of Taking Power Cards:

·         To calculate indicated power of the engine

·         To determine peak pressures and compression pressures

·         To evaluate the process of combustion inside the engine

·         To evaluate scavenging and exhausting conditions

How to Take:

It is originally drawn using a mechanically driven pen onto graph paper mounted on a drum. The drum was rotated by string, via a cam on the camshaft and pushrod. As the drum rotated the pen mounted on the linkages was pressed up to the paper. For clarity the pen is released once a single cycle has passed otherwise slight fluctuations in power demand could lead to several cycles being superimposed on one another blurring the image.

The indicator is a sensitive piece of equipment which can malfunction and so it must be treated with care. It can only be used effectively on an engine operating below 200 rpm due to the difficulty involved in getting only a single line on the card. In addition the inertia in the drum can lead to delays distorting the shape. For higher speed diesels either peak pressure indicators are used, or sophisticated electronic monitoring equipment is required with oscilloscope type displays. The time base for these is off transducers mounted on the flywheel.

It is important that the indicator is kept well lubricated with a light high quality oil. Prior to mounting the indicator the indicator cock is blown through to ensure it is clear. Compression cards are then first taken to check for errors caused by wear or friction/stiction in the instrument.

§  Check whether the spring fitted on the indicated instrument will meet the peak pressure (maximum combustion pressure) to be expected

§  Stretch diagram paper firmly over the drum.

§  Before taking diagram, open indicator cock, allow two or three firing strokes, to blow out soot and combustion residues in the cock.

§  After drawing atmospheric pressure line, hook the cord to indicator drive, open indicator cock, take power card and shut off the cock.

§  Make sure that the instrument is not exposed to high temperature for long time. This may affect its accuracy.

§  Remove the hook, turn the drum by hand to a place clear from the power diagram, take compression pressure line with the fuel cut off.

§  After taking indicator cards from all the cylinders, open the instrument and clean all the parts, and lubricate the same.

Precautions While Taking Indicator Cards

• Always lubricate indicator instrument parts to prevent seizure at high temperatures.
• Tightness of the indicator piston inside the cylinder to be checked. It should be a free sliding fit.
• The cock to be free from accumulated carbon particles.
• Do not apply much pressure on the stylus while taking the diagram.
• Allow sufficient cooling time for the instrument after taking diagrams from each units

Types of indicator diagrams:

• Power card / Power indicator diagram
• Compression diagram
• Draw card / Out of phase diagram
• Light spring diagram

Purpose of Indicator Diagrams:

§  The indicator diagram is very important to know the combustion in the cylinder and also to adjust the engine.

§  The diagram is taken periodically from the indicator valve equipped on he cylinder head and combustion condition is to be confirmed.

§  The compression pressure and maximum pressure in the cylinder can be presumed from the indicator diagram.

§  Engine indicator is the device used to take the indicator diagram, which can be considered as a ‘stethoscope’ for diesel engines.

§  Indicator diagrams give efficiency of combustion in the cylinder, condition of the running gear, irregularities in fuel pumping and injection and a lot of things.

Pcom – Compression Pressure

Pmax – Maximum Pressure

Power Card

§  Power card is taken with the indicator drum rotating in phase with the piston movement

§  The area within this diagram represents the work done during one complete cycle to scale

§  Mean Indicated Pressure (MIP) is obtained from this diagram to calculate power produced in the cylinder

Power card of 2 stroke Engine:

1.  scavenge port closed
2.  exhaust port shut-commence of compression
3. fuel injection
4. top dead center
5.  7 post combustion expansion
6. exhaust port opens     

  Four stroke cycle

   

   

•          3-4-5 fuel injection and combustion
•              5-6 expansion
•             6-7-8-Exhaust valve open
•       8-9-10 overlap, exhaust remains open whilst air enters
•       10-1 aspiration and exhaust valve closes 
• Power calculation
  The area swept out by the power stroke will give the power developed by the engine. It should be noted on a four stroke most of the non-power stroke occurs below atmospheric on a naturally aspirated engine and so gives a net loss of power.
  Power = p.A.L.n
   p - Mean average pressure in the cylinder
  A-area of piston [m3]
  L-stroke [m]
  n-revolutions per second
  From a power card this is altered to
  Power = area of diagram/length of diagram x Indicator spring constant
  By use of an instrument called a Planimeter the area scribed out by the pen could be measured giving the power generated by the cylinder. In addition, through experience, certain problems could be diagnosed by looking at the shape drawn. 

Compression Diagram

• Compression diagram is taken in similar manner to the power card but the fuel shut off in the cylinder
• The height of this curve shows maximum compression pressure
• If the compression and expansion line coincide, it indicates that indicator is correctly synchronized with the engine
• Reduction in height of this diagram shows low compression which may be due to worn cylinder liner, faulty piston rings, insufficient scavenge air or leaky exhaust valve

Draw Card / Out of Phase Diagram

• Draw card is taken in a similar manner to power card with fuel pump engaged but with the indicator drum 90 degree out of phase with the piston stroke
• This diagram illustrates more clearly the pressure changes during fuel combustion. Fuel timings or injector faults may be detected from its shape

Light Spring Diagram

• Light spring diagram is taken similar to the power card and in phase with the engine and with a light compression spring fitted to the indicator
• This diagram shows pressure changes during exhaust and scavenge to an enlarged scale
• It can be used to detect faults in these operations

Irregularities in Indicator Diagram

Early Ignition

Indications and Effects

• Abnormally high peak pressure of the unit is recorded at the top of the piston stroke.
• Knocking sound comes out of the engine due to heavy loads passed to bearings via running gear.
• Early ignition causes increased thermal efficiency of the engine. Also exhaust temperature reduces since combustion starts long before it is supposed to. But the shock loads and vibrations results in damage of the engine.

Causes

• Incorrectly adjusted or accidentally changed fuel pump timing
• Damaged or incorrectly set fuel valve or fuel injector
• Undesired fuel quality
• Parts inside the cylinder are overheated.

Late Ignition 

Indications and Effects

• Low peak pressure is indicated for the unit after top dead center.
• Combustion continue during expansion stroke, give rise to incomplete combustion of fuel, loss of energy, elevated exhaust gas temperature for the unit, and black smoke at the engine exhaust.
• Reduced power of the engine due to incomplete combustion of the fuel and energy lost in the exhaust.

Causes

• Faulty fuel injector or injector spring tension tighten beyond setting.
• Poor fuel quality
• Wrongly timed or leaking fuel pump
• Engine parts inside cylinder are under cooled
• Incorrect atomization
• Compression pressure low
• Combustion air supply is low

After Burning:

Indication and Effects

• A rise in expansions line is recorded in the later part of piston stroke
• Since burning of fuel continues, exhaust gas temperature and pressure increases, causing black smoke at engine exhaust.
• Unburnt carbon deposits fouls exhaust system, cause damage to exhaust valve and seat, turbocharger surges and there are chances of uptake fires in exhaust gas economizer.
• Elevated temperatures inside cylinders cause breaking up of lubrication and increased wear of liners, piston rings, burning of piston crown, etc.

Causes

• Slow fuel combustion
• Quality of fuel is less
• Low temperature of fuel (Means high viscosity)

Leaky Fuel Injector

Indications and Effects

• Reduced power in the affected unit, high exhaust temperature and presence of black smoke in exhaust.
• Possible knocking sounds or pressure waves in fuel injection system.
• Sudden up and downs in indicated diagram in the fuel injection and expansion side.
• After burning due to incomplete combustion of fuel.

Causes

• Leaking fuel injector.
• Chocking of fuel injector spray holes, which leads to improper atomization and dripping of fuel.

Partly Choked Fuel Valve

Indications and Effects

• Low exhaust gas temperature of the unit
• Power card and draw card indications
• Loss of engine power

Causes

• Fuel oil contamination and improper purification
• Carbon formation at injector tip
• Carbon deposits on fuel valve due to over heating

Low Compression

Indications and Effects

• Low pressure in the indicator card
• Reduced power of engine

Causes

• Improper combustion
• Insufficient air for combustion
• Leakage of air in between piston rings and liner while compression stroke due to worn out liner or piston rings.

Exhaust Valve Opening

Light spring diagram gives indications on faulty exhaust valve and intake port operations.

Early Opening

• Elevated exhaust gas temperature and fouling of exhaust system
• Loss of engine power

Late Opening

• Reduced blow down effect and hence reduced scavenging efficiency
• Low quality of exhaust gas delivered to the turbocharger inversely affect its operation

Choked Exhaust

Indications and Effects

• Power loss in the unit
• Increased exhaust temperature
• Turbocharger surging
• adversely affect scavenging efficiency

Causes

• Improper combustion
• Increased cylinder lube oil

Watch This Video for Better Understanding:

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References: 

marineengineeringonline.com

www.marineinsight.com

www.youtube.com

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