preferential trip test

Preferential Trips on Ship : Construction and Working

A preferential trip is a kind of electrical arrangement on the ship which is designed to disconnect the non-essential circuit i.e. non-essential load from the main bus bar in case of partial failure or overload of the main supply

The non-essential circuits or loads on ships are air conditioning, exhaust and ventilation fans, and galley equipment which can be disconnected momentarily and can be connected again after fault finding.

The main advantage of the preferential trip is that it helps in preventing the operation of main circuit breaker trip and loss of power on essential services and thus prevents blackout and overloading of the generator.

Construction and Working

The preferential trip circuit consists of an electromagnetic coil and a dashpot arrangement to provide some delay to disconnect the non-essential circuits.

Along with this, there is also an alarm system provided, which functions as soon as an overload is detected and trips start operating. There are some mechanical linkages also in the circuit which instantaneously operates the circuit and completes the circuit for preferential trips.

The dashpot arrangement consists of a small piston with a small orifice and which is placed inside a small cylinder assembly. This piston moves up against the fluid silicon and the time delay is governed by the orifice in the piston.

Working of Preferential Trip

The current passes through the electromagnetic coil and the linkages are kept from contacting using a spring arrangement. As soon as the current value increases the limit, the electromagnetic coil pulls the linkage up against the spring force and operates the instantaneous circuit and the alarm system. The lower linkage completes the circuit for the preferential trip circuit.

The current passes through the coil in the preferential trip circuit which pulls the piston in the dashpot arrangement. The movement of this piston is governed by the diameter of the orifice and the time delay made by the same.

The preferential trip operates at 5, 10 and 15 seconds and the load is removed accordingly. If the overload still persists, then an audible and visual alarm is sounded.

The preferential trip is one of those important electrical circuit diagrams which help in removing the excessive load from the main bus bar, thus preventing situation like blackout which is a dangerous incident to ship, especially when the ship is sailing in restricted or congested waters.

You may also like to read Starting of Emergency generator .

Marine Electrical Equipment and Practice by H.D McGeorge

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14 comments.

i want to free download some engineering book.please allow me for that.thanking you.

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plz tel me how an e.t.o (electro technical officer ) career now a days .Because i heard that lots of people talking abt this rank is waste, no future and recently imo ban this rank in all ships .

waiting for your reply

@ Chandrashekar: This is an important rank in the ship. You will be joining as an Asst. Electrical officer and then you will be promoted to Electrical officer after giving exam as per STCW 2010 (Highest rank for electrical officer). NO. This rank was never banned by IMO

Can you give me detailed instruction on how to simulate or test preference trip onboard ship. I’m an electrical officer. thanks

Operating character appear on the nameplate in an A/C motor a. Temp. Rise b. Input kW c. Rotor torque d. Type of wibding

sir gooday may I ask how to trouble preference trip,, im an on board electrian

how to test the preferential trip and overload trip while generator running in parrellel

emergency generator not coming into service during blockout situation what was problem over there.

Good morning to eto frnd Im getting trouble in preference tripped in ums ship When im tried to generator safety alarm is working good Problem is when i tried to generator shutdown tripped mean lube oil low pressure shutdown tripped then preference tripped happened without load at acb open condition What could be reason plz advise me

Why nowadays we have only 2 preferential trips 5 and 10 seconds ? Why 15 seconds is trip is eliminated?

@Monzur: because of the local level trips and added safety/ Automation.

Hello mr anish. I would like to use your material in giving lectures in ship electrical. Thank you.

Kindly email with details at [email protected]

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Preferential tripping in a marine electrical distribution system

• 21 May 2016

Preferential tripping in a marine electrical distribution system are designed to disconnect non-essential circuits (e.g. breakers controlling air conditioning, galley power, blowers, refrigeration etc.) in the event of partial overload or partial failure of the supply, with the aim of preventing operation of the main breaker trip and loss of power on essential services.

• A method for operating all the overload type trips from one load current carrying coil uses two instantaneous trip levers.
• The top lever is arranged as an instantaneous short circuit trip and opens the breaker directly through mechanical linkages.
• The bottom lever closes instantly at the lower overload current setting and by doing so, completes the circuit through two (or more) non essential circuit trips and a main breaker trip, all incorporating dashpot time delay.
• These relays will trip out non essentials at 5 and 10 second intervals based on their priority and finally, if the over load persists, the main breaker after 15 sees.
• Warning of overload is given by the alarm. Overload protection is provided on both poles.

Working of preferential trip

• The current passes through the electromagnetic coil and the linkages are kept from contacting using a spring arrangement. As soon as the current value increases the limit, the electromagnetic coil pulls the linkage up against the spring force and operates the instantaneous circuit and the alarm system. The lower linkage completes the circuit for the preferential trip circuit.
• The current passes through the coil in the preferential trip circuit  which pulls the piston in the dashpot arrangement. The movement of this piston is governed by the diameter of the orifice and the time delay made by the same.
• The preferential trip operates at 5, 10 and 15 seconds and the load is removed accordingly. If the overload still persists, then an audible and visual alarm is sounded.

One thought on “ Preferential tripping in a marine electrical distribution system ”

sir, how to test the preferential trip ?

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All about Reverse Power Relay and Preferential Trips on Ship Electrical System

Reverse Power Relay is a directional protective relay that prevents/protect the generator from motoring effect (going to reverse direction). It is used where generator runs in parallel with other utility or generator. The relay monitors the power supply from the generator and in case the generator output falls below a preset value, it quickly activates the trip and disconnects the generator .

Construction of  ship  Reverse Power Relay

The relay is made up of lightweight non-magnetic Aluminium disc between two soft laminated iron core electromagnets. The upper magnet is wound with Voltage Coil (PT) which is supplied from one phase & artificial neutral of generator output. The other output magnet is wound with Current Coil (CT) connected to the same phase as the voltage in the upper electromagnet.

Working of ship Reverse Power Relay

Since Voltage Coil has more number of turns, so it has move inductive value and more induced current that lag in the coil by an angle of 90°. The current coil has less number of turns so less number of turns, so it has less inductive valve & less induced current that lag less.

As we all know that current carrying conductor produces the magnetic field. So both upper and lower section produces magnetic fields. But Induced current in PT lags more than CT so magnetic field produced in upper section will be weaker than lower section & both magnetic fields will have a difference of 90°

When both fields pass through the Aluminium disc, it produces eddy current. As a result of the formation of eddy current torque is generated that tries to rotate the disc. Under normal power flow, the trip contact on the disc are open and rotation is restricted by stoppers but if a reverse power starts to flow the disc is rotated in opposite direction, moves away from the stoppers in the direction of trip contact that activates the trip.

Why is Reverse Power Relay required?

When two or more power units are running in parallel and if reverse power flow occurs, the same unit will start drawing power from the main bus bar. it can cause overloading of the other power supply unit and hence leads for the preferential trip or may lead to total power failure(Blackout). At the same time the faulty unit will draw power from main bus bar and go for motoring effect and RPM will soot up which leads to over speed trip or in worst case some mechanical failure to the prime mover.

When does reverse power flow…..?

When the prime mover of a generator is not supplying sufficient torque to keep the generator rotor spinning at the same frequency as the bus goes to which the generator is supposed to be connected, the generator will start behaving like a motor and instead of supplying power it will draw power from bus bar. During synchronization, it might be possible to have the synchroscope rotates slow (anticlockwise direction) and then close the breakup. under this condition. The generator would then be drawing current from the bus for instead of supplying current through the bus (which occurs when the breaker is closed with the synchroscope rotates in the fast anticlockwise direction). Faulty Governer of the prime mover. Loss of excitation in the alternator. How do you test reverse power trip? Reverse power trip can be tested by load shifting with the help of Governor control. when the Load has shifted sufficiently from the generator to be offloaded (Nearly 10% of the max rated ), reverse power relay will open the ACB of the same generator. this relay can be tested by simulation using boost test push button on the relay to see if it gives a trip signal.

PREFERENTIAL TRIPPING ON SHIP ELECTRICAL SYSTEM

What is the use of preferential trip.

The preferential trip is a kind of electrical arrangement on the ship which is designed to disconnect the non-essential circuit .i.e non-essential load from the main bus-bar in case of partial failure or overload of the main supply.

The non-essential circuit or loads on the ship are air conditioning unit, exhaust ventilation fans, & galley equipment which can be disconnected momentarily . The main advantage of the preferential trip is to supply uninterrupted power for propulsion and safe navigation under overloading condition of the power unit.

Construction of  preferential trip on ship system

The preferential trip circuit consists of an Electromagnetic coil and a dashpot arrangement to provide some delay to disconnect the non-essential circuits. Along with this, there is also an alarm system provided, which function as soon as overload is detected and trips start operating. There are some mechanical linkages provided in the circuit which instantaneously operates the circuit for preferential trips.

The dashpot arrangement consists of a small Piston with the small orifice and which is placed inside a small cylinder assembly. The Piston moves up against the viscous fluid silicon and the time delay is governed by the orifice in the Piston

Working of ship safety preferential trip

The current passes through the electromagnetic coil and the linkage are kept from the contacting using a spring arrangement. As soon as the current value increases the limit, the electromagnetic coil pulls the linkage up against the spring force and operates the instantaneous circuit and the alarm system. The lower linkage completes the circuit for the preferential trip circuit.

The current passes through the coil in the preferential trip circuit which pulls the piston in the dash pot arrangement. The movement of the piston is governed by the diameter of the orifice and the time delay made by the same. The preferential trip operates at 5,10, & 15 seconds and the load is isolated accordingly. If the overload still persists, then blackout will occur.

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The use of maritime prefferential tripping

Posted by Ryan Oneill | Aug 3, 2023 | Electrical , Engine Room , Latest Articles | 0 |

In a marine electrical distribution system, “preferential tripping” refers to a protective scheme that selectively trips or disconnects specific electrical circuits or equipment in a predetermined order during fault conditions or abnormal situations. The goal is to prioritize the protection of critical or essential equipment and systems while maintaining the overall stability and safety of the vessel’s electrical system.

Here’s how preferential tripping works in a marine electrical distribution system:

• Electrical Fault Detection: The electrical distribution system is equipped with protective devices such as circuit breakers, fuses, relays, or other protective devices. These devices constantly monitor the current, voltage, and other parameters in the electrical circuits.
• Predefined Priority: The system’s design includes a predetermined priority list of electrical circuits or equipment based on their criticality to the ship’s operation. For example, essential services like propulsion, steering, communication, and safety systems might be assigned a higher priority than non-critical systems.
• Fault Occurrence: When an electrical fault occurs, such as a short circuit or overload in a specific circuit or equipment, the protective devices detect the abnormal condition.
• Tripping Sequence: Instead of indiscriminately tripping all the protective devices simultaneously, the preferential tripping system follows the predefined priority list. It starts by tripping the least critical circuits or non-essential equipment first, gradually moving towards more critical systems.
• System Stability: The preferential tripping scheme aims to maintain the overall stability of the electrical distribution system during fault conditions. By ensuring that critical systems remain operational for as long as possible, the vessel has a better chance of avoiding a complete blackout or loss of essential services.
• Fault Isolation: Once the fault is cleared or isolated in a particular circuit or equipment, the system may automatically or manually restore the power to that circuit, if possible, to resume normal operations.

Preferential tripping is particularly crucial in marine electrical systems, as a complete loss of power or critical systems can pose significant risks to the vessel’s safety and operation. By selectively disconnecting less critical loads first, the ship’s crew can have more time to address the fault and avoid catastrophic consequences.

Working of Preferential Trip

As shown in the diagram, when overload current increases and reaches the lower loads of the system,the bottom lever pulls up and completes the circuit. The completion of the system gives an alarm signal and supplies current to the overload trips which are set for‭ ‬5,‭ ‬10‭ ‬and‭ ‬15‭ ‬seconds delay.

‏If the overload current is extremely high,the upper levers of the system get trip, which instantaneously cuts off the the generator thus preventing it from any kind of damage.

5 second Air – conditioning and ventalation

10 second Refrigerated cargo plant

15 second Deck equipment

It’s important to note that the specific implementation of preferential tripping can vary based on the vessel’s design, the complexity of the electrical system, and the specific requirements of the ship’s classification society and regulations. Proper planning, design, and testing of the preferential tripping scheme are essential to ensure the safety and reliability of the marine electrical distribution system.

About The Author

Ryan Oneill

Ryan O'Neill is a well-known maritime enthusiast and writer who has dedicated his life to studying and writing about ships and the maritime industry. With a deep passion for the sea and all things nautical, Ryan has spent years exploring the world's oceans and studying the history and culture of seafaring.

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What you need to know about electrical preferential tripping and sequential restarting

Onboard vessels, modern power management systems make it less likely for power to go out for no reason, but engineers must be familiar with the specific procedures, where to find the instructions and procedures, and ready to act in case of automation failure.

Example of Power Management System

In case of a problem with power main diesel generators or in case of overcurrent, non-essential loads are interrupted automatically, in order to prevent the ship’s power failure. Preferential tripping has been fitted to reduce the possibility of the loss of essential vessel supplies if an event as described above will occur. It has been arranged that load reduction will be achieved by an ordered disconnection of non-essential supplies to prevent a blackout that may put the vessel’s safety at risk.

Example of preferential trip alarm

Depending on the vessel electrical layout and design, there are different stages (two or three) of preferential tripping. For example:

• if the current on a running generator exceeds 100% of the generator rating for a period exceeding 5 seconds, the PMS will initiate the release of the 1st stage preferential tripping (PT1), thereby providing protection against the overcurrent which would otherwise trip the circuit-breaker – non critical ship systems.
• if the current on a running generator exceeds 100% of the generator rating for a further 5 seconds, the PMS will initiate the release of the 2nd stage preferential tripping (PT2) – cargo hold vent fans and packaged air conditioning units.
• in some vessels if the current on a running generator exceeds 100% of the generator rating for a further 5 seconds, the PMS will initiate the release of the 3rd stage preferential tripping (PT3).

Example of 1st and 2nd stage preferential trips alarm

on some other systems the preferential trips can be triggered in three ways regardless of the generator being under PMS or manual control:

• an overcurrent condition in a main generator for a preset time will initiate first stage trips – if the current on a running generator reaches 120 % of the rated full load current for a period of 10 s, the breaker overcurrent protection circuit will initiate the release of the first stage of preferential tripping. If the 120% overload condition should continue for 40 seconds the generator VCB itself would trip, initiating the 2nd stage trip.

Example of DG overcurrent alarm leading to preferential trip alarms

When normal conditions resume, the tripped breakers must be manually reset.

• low lubricating oil pressure
• high fresh water cooling temperature
• overspeed of generator engine
• short-circuit current
• nuisance trip

Should such trip occur then the remaining preferential trips will operate simultaneously.

• manual tripping – the bus tie panel carries emergency stop contacts and preferential trips.

To trip the specific consumers, their circuit breakers are fitted with undervoltage (UV) trips. The supply to these UV trips is interrupted by the preferential tripping relays.

Example of UVT trip device

The identifications labels of the consumers configured for preferential tripping are coloured yellow with either PT1, PT2 or PT3 engraved into them.

Preferential tripping stages are accompanied by alarms into the alarm and monitoring system.

The vessel’s automatic control system will automatically restart the required machinery to restore power to the vessel, but to fulfil this requirement, at least one diesel generator must be left in the automatic standby mode. The essential machinery is started automatically according to the example sequence shown below.

Example of sequential restart list

The sequence is started when power is restored to the 440V main switchboard. The restart sequence is usually left enabled, however, the operator may disable the sequence, and if the sequence is disabled, an ‘auto start sequence disabled’ alarm is raised. The sequence is automatically halted in the case of another blackout.

When normal power is restored after a blackout, all essential service machinery in service before the blackout will be started automatically when the main switchboard has regained power. Motors that were selected for duty before the blackout will be automatically returned to duty when power is restored. Similarly, motors selected for standby will automatically return to standby. If the machinery designated for duty does not restore normal system conditions, such as pressure, within a preset time, the standby motor will cut in automatically. If power is only restored to the emergency switchboard, motors whose supply is from the emergency switchboard will start irrespective of any previous selection. In the event of a blackout all transformers in the HVS will switch off. After the first main generator is connected to the HV busbar the transformer outlets will automatically switch in sequentially in two steps, depending upon the part of the switchboard concerned.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries.

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Preferential Trip

• Preferential trip is a kind of electrical arrangement on ship which is designed to disconnect the non essential circuit that is non essential load from the main bus bar in case of partial failure or overload of the main supply the non essential circuit all loads on ship are air conditioning, exhaust and ventilation fans, and galley equipments which can be disconnected mementarily and can be connected again after fault finding.
• The main advantage of preferential trip is that it helps in preventing the operation of main circuit breaker trip and loss of power on essential services and prevents blackout and overloading of generator.

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WHAT IS PREFERENTIAL TRIP AND REVERSE POWER TRIP ?

Preferential trip:.

Preferential trip is a kind of electrical arrangement on ship which is designed to disconnect the non-essential circuit i.e. non-essential load from the main bus bar in case of partial failure or overload of the main supply The non-essential circuits or loads on ships are air conditioning, exhaust and ventilation fans,and galley equipment’s which can be disconnected momentarily and can be connected again after fault finding. The main advantage of preferential trip is that it helps in preventing the operation of main circuit breaker trip and loss of power on essential services and thus prevents blackout and overloading of generator.

Reverse power trip:

There is not much difference between an alternator and electric motors from the engineer’s perspective. They are both based on similar principles. So just imagine what would happen if an alternator suddenly would act as a motor. This is only possible in systems where two or more generators are running in parallel. Hence this type of protection system is used only if there is more than one alternator on board a ship. The system is designed in such a way that it will release the breaker and prevent motoring of alternator if a reversal of power occurs. This protection device is also used to prevent damage to the prime mover, which might be stopped due to some fault. Though it is extremely difficult to detect reverse current with an alternating current system, reverse power can be detected and protection can be provided by reverse power relay

Sanjeev Kumar

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Operate Alternators, Generators. Test 3

• the breaker connecting bars.
• the generator and the consumers.
• the generator and the bus bars.
• the breaker and the consumers.
• The preferential trip.
• The overspeed trip.
• The under voltage trip.
• The low frequency trip.
• All of these.
• It disallows breaker to be put on load by under voltage.
• It trips the alternator by under voltage.
• It prevents breaker operation in the absence of voltage.

• generated as distributed.
• monitored and supplied via distributors.
• fed into, monitored and supplied to the consumers.
• fed into and distributed to the motors via starting boxes.
• A connection box has been filled with salt water.
• The armature of a switched off AC motor has short circuited.
• The emergency generator which is currently on stand-by has been splashed with salt water.
• The TV aerial in the mess room has short circuited.
• The reverse current trip.
• The overload trip.
• The high/low frequency trip.
• No difference.
• Very much longer.
• 5 - 7 seconds.
• 7 - 8 seconds.
• 3 - 5 seconds.
• 1 - 2 seconds.
• The temperature of the windings due to load distribution.
• The number of pole pairs of each paralleled alternator.
• The excitation current.
• The power throttle of the driving units.
• 254.34 Volt.

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• Refrigeration
• Diesel Engines
• Turbochargers
• Questions and Answers on Diesel Engines 1
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Tag Archives: Preferential Trip

MEO Orals on Marine Electro Technology Function 5- Part 2

What is essential load ?

• Essential services are those required for the safety of personal and for the safe navigation  and propulsion of the ship.
• They include certain supplies to navigation aids, machinery spaces,  control stations and steering gear.

What is non-essential load ?

• It is a load that has no effects on the safe navigation and main propulsion unit when they are  cut off.
• They are a ir conditioning system, some blower fan except E/R blowers, galley power, r efrigerated cargo plant, d eck equipment, purifier, air compressor, cabin power source except lighting

What is dash pot, where fitted ?

• It is a mechanical device which makes time lag of trip with different viscosity of oil.
• It is fitted in overload trip, p referential trip, u nder voltage release / trip

What is dash pot ?

• Dashpots are fitted for overload trip to get time delay action, so that breaker will not be  opened, due to momentary current surge
• When load current is in excess, it attracts plunger of the solenoid
• Plunger or piston moves up against the displacement of viscose oil or silicone fluid, through a  small hole on the piston
• Time lag depends upon hole size, and viscosity of oil
• Load current setting for trip is about 25% above maximum, but should not exceed 50%

What is preferential trip ?

• It is a generator protection device which is designed to disconnect nonessential load from  the main switchboard in the event of generator over load or partial failure of the supply.
• Operate after a fixed time delay, causing non-essential loads to be shed
• Usual setting for overload trip is 150% load (50% overload)
• When generator load reaches 110%, preferential Trip comes into operation as follows

First tripping at 5 sec

• Shut down non-essential loads (air-condition, entertainment, accommodation fans, cargo  hold fans, amplifiers, etc.) to reduce the generator load

Second tripping at 10 sec

• Shut down essential loads (service required for running the ship properly, leaving the loads  of top priority services to maintain propulsion and navigation) if generator load is still high

Third tripping at 15 sec

• Shut down the main generator as last action, if the load is still too high, it may be due to  short circuit or insulation breaking.

What is the purpose of reverse power relay ?

• If prime mover failure occurred, the generator would act as a motor; the reverse power relay  detects this fault and acts to trip the generator circuit breaker.

What is fuse ?

• Fuse is a protecting device in the circuit against damage from excessive current.
• It is fitted in a circuit to protect the circuit from short circuit and over load.
• Once a fuse is blown, it must be replaced.

Difference between Circuit Breaker and Fuse ?

Circuit breaker

• Has switching actions to close the circuit or to open the circuit, and has a trip circuit if load  current exceeds the set value
• After tripping, circuit breaker can be reused without replacing any part
• Have only breaking function, and fitted in the circuit to protect the circuit from damaging effect  of high current flow
• It breaks the circuit by melting the fuse metal itself
• After breaking, the blown fuse must be renewed

 What is an intrinsically safe circuit or equipment ?

• An electrical circuit or part of a circuit is intrinsically safe, if any spark or thermal effect  produced normally (e.g. by breaking or closing the circuit) or accidentally (e.g. by short circuit  or earth fault), is incapable of igniting a prescribed gas mixture, under prescribed test  condition.
• An equipment, which cannot released sufficient electrical or thermal energy, under any  condition to ignite a particular flammable vapour in its vicinity.

  What is primary cell ?

• It is a chemical cell in which it is possible to transform chemical energy into electrical energy.
• It cannot be recharged.
• The internal resistance of a primary cell is usually high
• Capacity of cell low
• Voltage per  cell is also low
• Simple cell consists of copper plate (positive plate) and zinc plate ( negative electrode)  and dilute H2 SO4 acid.

What is secondary cell ?

• It is a chemical cell (accumulator) which store up electric energy converting chemical  substance into another form while charging.
• The stored electric charge in chemical form transforms  back electrical energy.
• It has two types [lead acid and alkaline (Nickel Cadmium battery) type].
• It has low internal  resistance
• Capacity and voltage per cell is high.  

Oral Guide by – MIN ZAR TAR

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Preferential Trip testing

Post by mann84 » Thu Jul 06, 2017 8:10 pm

Re: Preferential Trip testing

Post by JollyJack » Fri Jul 07, 2017 5:57 am

Post by Big Pete » Fri Jul 07, 2017 3:32 pm

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• REGULATIONS
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ETO ORAL QUESTIONS | FREQUENTLY ASKED | FROM 2018-20 | ETO COC | PART 2

• How will you enter duct keel
• How will you extinguish the fire in a container?
• How will you identify a PCB and what all components are fitted and how will you identify it and working of all semiconductor components
• How will you know that the flame sensor is faulty?
• How will you order cable?
• How will you reset the system after you tried the level alarm?
• How will you work on any high voltage equipment?
• How would you install a new pressure switch in hydrophore?
• How would you test the main LO standby pump in case running p/p failures and what r the condition standby p/p will take over
• How you decide to use DOL, Star delta and auto transformer when installing new equipment.
• How you will connect the synchronous condenser to MSB and how it will help to improve the power factor?
• How you will extinguish the fire in between containers on deck.
• How you will get Vrms equal to Vm/root 2
• How you will increase the insulation of cargo pumps if it’s an emergency and you need to improve the insulation in order to discharge.
• How you will release CO2.
• How Zener diode working what is break down voltage in Zener diode
• Hydric locking alarm
• Hydrophore p/p is cut in cut off what is the reasons
• Hyper mist and co2
• Hyper mist system, how it works, how it extinguishes the fire, how activate, the protection given where
• ICCP draw and explain
• ICCP? (Why we using zinc as ref electrode)
• IF - a narrow amplifier which having very high gain i.e. 60 to 70 MHz
• If 2 gen is running and one v is 440v other is 410v.    What u will check other than AVR?       If 9 terminals in motor what for 9 terminals?
• If any motor comes to ship what is your job on that
• if bow thruster use to take on the load at 3 generators but now we want to take on the load at 2 generators which have sufficient load capacity then will bow thruster come load at 2 generators if yes then how?
• If connected in the Zener diode series what will happen?
• If earth fault in 24 v DC what you will do? Can you use Megger for rectifying the earth's fault?
• If in your motor inside seawater gone, how will rectify?
• If the steering gear system is not working, what could be the possible reason?
• If the Synchro scope is malfunctioning, which instrument is most essential to parallel an alternator with the bus bar?
• If there is a fire in the CO2 room how will you fight?
• If there is no STP on-board can we discharge sewage?
• If we have 300 ton AC and it is not working, the company send 500 ton AC. How you run the compressor?
• If you hear the 220V low insulation alarm what is your action?
• If your synchroscope is not working how you will parallel the Generator?
• IG alarms and trips.
• IG requirements
• IG System detailed explanation.
• IGBT and SCR (VFD and soft starter)
• IGBT symbol and explain, MOSFET feature.
• IGG not firing also no alarm on the control panel, what is your action.
• IMDG codes.
• IMDG purpose, Classes, UN and PSN
• IMDG volumes, UN number, how many books, classes, and some cross questions
• In MOSFET and transistor which is a voltage device which is current device?
• In ODME which data record
• In reefer, high discharge trip again and again why?
• In reefer, what are the causes of air ingress in the system?
• In the RLC circuit when will get maxim current.
• In sea passage, if you get 440v low insulation alarm what will be your action.
• In solenoid coil, D. C. current is there or A. C. current
• In ST. Gear PID sequence.
• In the UMS ship before departure, what will check as an ETO?
• Incinerator and boiler flame eye is there any difference?
• Induction motor principle
• Infrared and UV flame detectors
• Input-Output signals in PLC
• Insulation class and temperature
• Insulation class?
• International Shore coupling dimensions
• Ionization type of fire detector.
• IOPP issued by
• IP and what is it based on?
• IR Flame sensor, in detail.
• Is synchronous motor self-starting?
• ISM DOC and SOC
• ISPS (SOLAS chapter 11-2)
• ISPS drill frequency
• ISPS, procedure, plan, etc.?
• Jacket water control system
• Latest regulation regarding garbage disposal
• Lifeboat launching procedure
• Lifeboat SOLAS regulations. Safeties and how to launch lifeboat and checks to be carried out before launch and so many cross questions till not satisfied.
• Life throwing apparatus
• Lifeboat safeties
• List all the components illustrated in it
• List of MARPOL equipment in your ship
• List of navigational equipment’s
• List the possible causes.
• Lub oil pump running and can't stop the main engine you want to test the other pump working or not? The answer is not the pressure switch.
• M/E after stand by, 2/E says to you check the M/E and everything good or not? And how u know.
• M/E LO cooler block and explain
• Magnetron changing procedure
• Main air compressor diagram, unloader, and safeties
• Main air compressor starter diagram, functions of pressure switches, setting, priority selection pressure switches
• Main engine safeties.
• Main engine starting air system automation and control system.
• Main engine tacho system how it works
• Main engine trips in LOLP how the trip is executed electrically.
• Maintenance on alkaline batteries
• Maintenance on gyro
• Manual testing of Reverse power relay
• MARPOL all annex from 1 to 6
• MARPOL Annex 6 equipment’s
• MARPOL Annex 6? What other pollutants except  SOX, NOX??
• MARPOL how will u pump out bilges and regulations?
• Master-slave control
• ME alarms & trips with value
• ME Governor Controller
• ME piston ring calibration
• Meaning of expansion valve in AC.
• MGPS + cross questions
• MLC CERTIFICATES
• MLC regulation, when it comes in Regulation, and why the need of MLC
• Monthly routine of DCP.
• Motor enclosures
• Motor taking 100A full load current then. Tell the starting current of the motor
• Motor terminal identification
• MSB fire. What u will do?
• MSB safety                         
• MSB safety check in front of the surveyor on board.
• MSW motor is immersed in seawater, what is your action and cross-questions.
• Multi-Gas Detector
• Name Ozone Depleting substance which is having ODP value one.
• Navigation light comes under which SOLAS regulation
• Navigational light circuit and if the main bulb fused, state of standby bulb
• Need of Loadicator
• NER value calculation
• NOX tier 2 and tier 3
• OCM working
• ODMCS principle operation in details. Cross questions.
• ODMCS requirements and discharging criteria.
• OFF delay timer
• Oil record book entries
• Oily water separator is running for 4 hours but oiler came to u and said bilge tank level is rising. What can be the reason!?
• OMD purpose and testing procedure what is flashpoint and y it is important
• ON delay and OFF delay timer symbols
• On the ship, which place you will get more earth faults?
• On UMS ships what all other alarms etc.
• One dark two bright lamp method?
• One of motor man or engineer said one seawater pipeline is leaking and falling on motor .what is your Acton
• One portable co2 extinguisher is placed near MSB to fight the fire on it.
• Operating range of aux. /main S/G & time
• OWS discharge criteria
• OWS purpose and testing procedure
• OWS types and working
• OWS working principle and testing procedure.
• Oxygen analyzer working and how to calibrate
• Parametric movement of the container
• Performance of fire fighting equipment?
• PID working and concerned equipment on-board?
• Piercing applicator for container fire fighting
• Piezoelectric effect
• PLC battery change procedure?
• PLC controller explains in brief.
• Pneumatic control by Flapper and Nozzle method.
• PNP and NPN
• Portable fire extinguishers, weight, SOLAS regulations, maintenance, etc.?
• Power generation
• Precautions while loading IMDG cargo
• Preferential trip explain with diagram?
• Preferential trip method of overcurrent protection?
• Preferential Trip relay explain
• Pressure drop test for compressors?
• Pressure sensor type and calibration.
• PRESSURE SETTING FOR MARVS
• Primary and secondary winding in the lightning transformer
• Procedure for changing the fire sensor
• Procedure to work on the radar?
• Proportionate valve and IP converter
• Proximity sensor how it works?
• Proximity sensor, working, where it is used. Difference between proximity and limit switch.
• PSC preparedness by ETO
• PT 100 working range and zero calibration? fish room/meat r00m temp sensor calibration.
• Pump room safeties and timing for light after you switch on the fan
• Purpose of Torsion box in a container ship
• Radar and its possible faults and troubleshooting magnetron changing procedure
• Radar block diagram and frequencies of VHF and Doppler’s log
• Radar frequencies. And Working.
• Radar maintenance.
• Read switch testing.
• Read the drawing of a motor which is having sequential starting
• Reefer container alarm/ Trips & operation.
• Reefer containers, working, power ratings, generator capacity of the ship.
• Reefer gas charging procedure & Gas recovery
• Reefer- refrigeration cycle, gas charging, and recovery
• Refer cable of regulation
• Refrigeration charging processor and how it recover?
• Refrigeration plant in detail.
• Regulation for ballast water management
• Regulation for steering gear motor
• Regulation for steering gear?
• Reliquefaction plant
• Return path of current in 3 phase
• Reverse power relay working
• Rudder not responding for autopilot command. Necessary actions
• Safe container conventions, total no of the annexe, and explain (date of enforcement)
• Safeties of co2 system
• Safeties of compressor room and motor room
• Safeties of the deck and engine crane and precautions
• Safety convention follows on the ship.
• Safety devises on-board to detect the presence of h2s?
• Safety inside the boiler furnace?
• Safety Management Certificate
• Safety of IG, type of Radar used for tank gauging and how is the signal transmitted?
• Safety precautions for working on H.V. equipment.
• Saturday routine how to check hyper mist and flame sensor
• SCADA? Difference between SCADA and PLC? Uses?
• SCBA pre-check.
• SCBA, safety checks, Pressure, Whistle timing and at what pressure it starts whistling
• Second Engineer tells you one motor is not starting and what are the reasons and how would you check?
• SEEMP and role of ETO in it.
• Sensors fitted in on-board
• Sequential starting of motor - which motor will start first after blackout?
• Setting of Reverse power relay what and explain why it is this?
• SF6 breaker content
• Shaft earthing and why we need and used to preventing what. And Cross questions.
• Ship's construction
• Short circuit in single-phase how?
• Short circuit Vs earth fault?
• Sine waveform for voltage current and power for one cycle.
• Single phasing-what happens in the delta and star-connected motors.
• Skin effect
• Slip in induction motor
• Smoke detection system and how it works.
• Smoke detection system for cargo hold
• Soft starter (cross-questions) SCR working& its layer
• Soft starter circuit diagram and cross-questions
• SOLAS chapter 11.2 and instruments on board related to it.
• SOLAS chapter 12 in detail & cargo hold safeties in the bulk carrier.
• SOLAS chapter 12 WIDAS, Loadicator, co2, smoke detection system
• SOLAS chapter 14
• SOLAS chapter 9
• SOLAS Chapter name and explain chapter 12
• SOLAS chapter number, the name for the bulk carrier regulations and what the chapter says.
• SOLAS full form, all chapters include Chapter-II -1 Part D in details + Regulation 44
• SOLAS regulations for bulk career
• SOLAS regulations for the sprinkler system and on board where it uses
• SOLAS related to the electrical system.
• SOLAS requirement of the steering system. Type of steering motor. What is the difference in steering motors and other motors? Safety alarms. Hydraulic lock. What is 100% redundancy in the steering?
• SOPEP equipment’s
• Space heater for the motor, where it is fitted in the system
• Special about LPG ship compared to other ships
• Specification of lamps used in cargo clusters
• Speed control of squirrel cage induction motor electrically and mechanically.
• Speed torque curve of induction motor.
• SSAS block diagram and regulations.
• Stability questions: trim, list, draft.
• Staffing valve in co2
• STAR AND DELTA MOTORS
• Star delta and auto transformer starters.
• Star delta starter cross-question
• Starter routine
• Starter type fire pump
• State the regulation for steering gear
• Steering gear alarms
• Steering gear diagram tracing.
• Steering gear hydraulic lock alarm and how will you rectify it?
• Steering gear hydraulic lock alarm not resetting your actions
• Steering gear hydraulic lock reset?
• Steering gear regulation and safeties in that how auto isolation will work.
• Steering gear safematic. Block explains.
• STEL value for h2s
• STP working principle
• Suction discharge pressure relation with AC/Reefer plant starting stopping?
• Suppose CE told you to check star delta motor what all cold checks you will do (without dismantling the motor)
• Tell about pyrotechnics
• Temperature class and insulation class of motors.
• Temperature sensor
• Temperature sensor calibration
• Tender ship
• Testing of emergency lights weekly from the transition source.
• Testing procedures sprinkler system.
• The induction motor has maximum efficiency at which time?
• The relay which is giving starting signal for an emergency generator.
• This rheostat type voltage regulator.   Anyone know why shunt field is connected in series with rheostat
• Thyristor working.
• Time delay in the fire detection system
• Timer circuit explanation
• Torque speed characteristics
• Toxic gases in enclosed space
• Transformer efficiency
• Transformer parallel operation
• Transformer paralleling cross questions
• Transformers secondary is open will current flow in it
• Transistor as an amplifier
• Trigger, IF, Magnetron?
• True North and other north
• Turbocharger rpm sensor working
• Types of fire sensors?
• Types of heat detectors and working
• Types of insulation class
• Types of materials used for insulation
• Types of motors ac and dc and different type of rotors
• Types of packing for IMDG
• Types of RADAR
• Types of reefers on-board
• Types of timers & their use with drawings.
• UMS checklist procedure
• UV level sensor. Block and explain
• Values of PI and DAR
• Various batteries on-board, VRLA batteries, capacity and charging method, maintenance on batteries,
• VCB rack out procedure
• VCB safeties
• VDR working various inputs
• VFD, speed control of the motor,  
• Viscotherm meter diagram and explanation
• Viscotherm why we use and a motor is running continuously on-board to maintain viscosity where it is located
• Voltage or current is danger to the human body? Current and Voltage values that can cause electrical shock/death to human being and cross-questions
• Water ingress alarm system, sensor locations, purpose, indicator the panel, SOLAS chapter 12?
• Welding machine has step up or step down transformer
• Welding transformer 
• What action u take fire in the galley
• What action you will take in case of an OMD alarm?
• What all checks to be done on cables to find cable is good or bad
• What all frequencies we have to remember from Pulse Radar
• What all gas measuring meter provide on board how will u measure it's working principles.
• What all gases measures in the multi-gas detector
• What all information in capacity plan
• What all information in fire fighting plan
• What all works done on reefer without anyone helping
• What and all conventions applied to the container ship
• What and all extinguishing systems in the galley
• What are active devices and passive devices?
• What are the different alarms in the gas detection system?
• What are frame cargo pump interlocks?
• What are markings on portable fire extinguisher?
• What are the alarms provided in the refrigeration system and what safety provided inside the meet room and fish room
• What is the cause of the defect of PLC?
• What are the classes of garbage?
• What are the components of ICCP?

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Contents MGPS – Marine Growth Prevention System The seawater system…

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MAIN SWITCH BOARD

Survey of MSB

• Proper cleaning to be carried internally as well as externally normally carried out when board is completely dead (all generator stopped and prime mover locked off). Inspect for dirt and dust (electro clean and vacuum cleaner.
• All main bus bar and auxiliary connections to be checked for proper tightness.
• Bus bar supports will be checked for surface cracking and damage to insulating material.
• Proper contacts to ensure no ingress of moisture.
• Feeder isolation and fuse holders contacts should be checked for any mechanical damage due to overheating or arcing at the contacts.
• Reverse power relay and preferential trip setting.
• Check dead front If not able to touch for more than 3 sec then problem switchboard.
• Check condition of fuses damaged fuses to be replaced.
• Only approved rubber mat to be used.
• Check indication lamps for working should be in working condition.
• Check safety interlocks.
• Check overheating of bus bars and should be rectified as soon as  possible.
• Lubricate mechanisms, contacts and other moving parts.

MSB Safeties  

• Minimum 3mm rubber mat (approved and certified) in front as well as back of switchboard.
• Dead front-end switchboard.
• Insulated door handles (Ebonite)
• Panel doors are also earthed.
• Can’t open door, if breaker is closed.
• No pipeline to pass in vicinity.
• Minimum 1m free air surrounding switchboard.
• Short circuit protection (ACB gen.)
• Preferential trip circuit breaker (110%, 115%)
• Reverse power trip circuit breaker (ACB, Gen)
•  UV/OV trip circuit breaker (ACB, Gen – 50%)
• OF/UF trip circuit breaker (ACB, Gen)  
• Single phasing alarm.
• Over speed trip/relay (ACB, Gen)
• Over Current trip/relay (ACB, Gen)
• Over load trip (ACB, Gen)
• No voltage trip (ACB)
• Fuses, meter, synchronoscope
• Earth fault indication.

Sequence of event in case of mains failure

• Control and monitoring equipment of emergency generator on sensing a large drop in voltage or frequency sends a starting signal to emergency generator.
• Tie breaker between the main switchboard and emergency switchboard opens.
• In 45 sec the emergency generator starts and comes on load. During that time the supply for emergency lighting, alarm etc are maintained by the emergency batteries.
• In case emergency generator fails to come on load,  these batteries can give power to selected lighting, communication and alarm circuits for minimum period of half an hour.
• In electrical power distribution system, a busbar is a metallic strip or bar that conducts electricity within a switchboard, distribution board or other electrical apparatus. Its main function is to conduct a substantial current of electricity, and not to be function as a structural member.
• The material composition and cross-sectional size of the busbar decide the maximum amount of current that can be safely carried.
• Busbar are produced in a variety of shapes such as flat strips, solid bars and rods, solid or hollow tubes, and braided wire. Some of these shapes allow heat to dissipate more efficiency due to their high surface area to cross-sectional area ratio.
• The skin effect makes 50-60Hz AC busbars more than about 8mm (0.31inch) thickness inefficient, so hollow or flat shapes are prevalent in high current applications. A hollow part has higher stiffness than a solid rod of equivalent current carrying capacity.
• A busbar should be rigid enough to support its own weight and forces imposed by mechanical vibration as well as accumulated precipitation in outdoor exposure. In addition, thermal expansion from temp. changes induced by ohmic heating and ambient temp. variations and magnetic forces induced by large currents should be considered.

How busbar are bolted

The first step is the surface preparation. Surface is thoroughly cleared, Roughened and grounded finish surface is preferred.

On the cleaned surface a thin petroleum jelly is applied so as to prevent oxidation. Sometimes lining before bolting is done. This gives good joint efficiency as well as reduce oxidation.

Bolting arrangements:-

• No. of bolts
• Size of bolts
• Bolts to be insulated and earthed.
• Distribution of bolts along with electrical and chemical and mechanical considerations should be taken into account. All these points ensure good joint efficiency.

Bolt Material: –

Galvanised steel , brass, bronze and copper alloy.

Bolt size varies from M6 to M12.

Bolt torque for each bolt size depends upon the material of the bolt and operating temp.

Busbar maybe connected to each other and to electrical apparatus by bolted, damped, riveted or welded connections. Conductor joint to be mechanically strong with relatively low resistance at the joint.

Types of joints: 

• Welded Joint – Current carrying capacity being unimpaired as joint itself is a continuous copper conductor.
• Riveted Joint – Simple, Reliable, Versatile, Compact Disadvantages is that holes drilled on conductor with bolt distorts some of line current.
• Clamped Joint – Gives good joint efficiency if properly clamped.

Can be made in complete cross-section being unimpaired.

More mass at joints gives more efficiency cooling area.

Easy Installation

Disadvantages –  Costly clamps and associated fittings.

• Soldered or brayed Joints – Hardly used unless reinforced with clamps or bolts as they weakened mechanically as well as electrically due to short circuit fault current.

Riveted joints are good if properly made, but difficult installation and difficult to remove or tighten in service.

Open or Dead front Switchboard

• Open Switchboard

Open switchboard are those in which all the essential components or equipment’s like circuit breaker, fuses, links and terminals are exposed on outside of an insulated base. For a.c. installation open switchboard is not permitted except for voltage of to earth

• Dead front Switchboard

All modern switchboard are dead front type in which all essential components are enclosed inside steel casing. The steel walls are incorporated within the switchboard is separate the section so that molten metal and arc from short circuit fault do not enter the neighboring sections. Only operating handles and indicator lamps are exposed outside.    

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QnA: MSBD (MAIN SWITCHBOARD)

Q. What is the IP(Ingress Protection) degree provided for MSBD ?

Q. What are the safeties protection provided by ACB?

A. In above list, Some are optional It may have or may not

• Adjustable Long Time Delay Trip -LTD (Normally 105 to 120% of Full Load Current, Trip time from 20 to 120 seconds)
• Adjustable Short Time Delay Trip -STD (Normally 200 to 600% of Full Load Current, Trip time from 0.1 to 1 seconds)
• Adjustable Instantaneous Trip -INST (1000% of Full Load Current, Instant Trip)
• Adjustable Pre Trip Alarm -PTA
• Adjustable Ground Fault Trip -GFT
• Under Voltage Trip -UVT (set at 50% of rated voltage)
• Arc Contacts, Arc Runner, Arc Chutes

Q. What are the safeties provided for MSBD?

A. Following safeties are provided

• Overload protection
• Under frequency protection(58Hz trip,59Hz alarm)
• Over frequency(62Hz trip,61Hz alarm)
• Under Voltage protection(80% of rated voltage,120% of rated voltage)
• Over Voltage Protection
• Reverse Power protection
• Preferential trip protection.
• Continuos Insulation Monitoring is also provided.
• No liquid line over MSB
• Ebonite Handrail
• Approved insulation rubber and Gloves ( It should sustain 15KVA for at least 1 minutes)
• 0.6 meter clearance area all around MSB(For High Voltage its 1 meter)
• Danger, High Voltage, Precaution against electric shock, Burn Playcards
• Circuit diagram of MSB should be near MSB
• MSB is installed in less vibration area of ship
• 1 portable CO2 extinguisher near MSB

Q. How the reverse power is detected?

A. It is difficult to determine the direction of AC to make tripping of generator during motoring. For this purpose the reverse power relay utilizes technique of monitoring current lagging direction to voltage. During sourcing (Generating)the current will lag the voltage by some angle positive way. During motoring of generator this positive lagging to voltage will change to negative lagging to voltage. This change in phasor angle will cause the aluminium disc inside the relay to rotate in opposite direction causing to trip the ACB

Q. What are setting values for reverse power relay?

A. 15% of KW for 4 stroke engine, 25% for 2 stroke engine at synchronous speed. For steam turbine 3% of KW.

Q. What is preferential tripping?

A. When Generator load reaches 110% trip operates after a fixed time delay causing non-essential loads to be shed in order to avoid overload on generators. The tripping sequence is as follows:

First tripping at 5 sec: Shut down non-essential loads [air condition, entertainment, accommodation fans, cargo hold fans, amplifiers, etc.] to reduce the generator load. Second tripping at 10 sec: Shut down essential loads [services required for running the ship properly, leaving the loads of top priority services to maintain Propulsion and Navigation. if generator load is still high. Third tripping at 15 sec: Shut down the main generator as last action, if the load is still too high, it may be due to short circuit or insulation breaking.

Q. What is mechanism of Preferential tripping?

A. Now PLC or Embedded system based PMS(Power Management System). Earlier Dashpot & Timers was used.

Q. What are the methods of synchronization?

A. Synchroscope, Bright Lamp Method, Dark lamp method, Voltmeter method.

SYNCHROSCOPE METHOD: When the incoming generator frequency is same as bus bar frequency say 60Hz and indicator in synchroscope rotates slowly clockwise(about 5 to 7 seconds per revolution). The incoming generator breaker is closed when indicater indicates 12 o clock position in Synchroscope Usually at 11 o clock closing action is taken by personnel because of human response time.

DARK LAMP METHOD: Two lamps are connected to same phase of incoming generator and busbar. Flickering of lamps are monitored. Flickering must be slow and when both lamps are dark ACB is closed.

BRIGHT LAMP METHOD: Two lamps are connected to different phase of incoming generator and bus bar. In phase condition is shown when both lamps are equally bright.

VOLTMETER METHOD: Connect Analog voltmeter(except up to 500V on a 440V system). This procedure is done safely behind synchroscope terminals. Check circuit diagram of synchroscope before doing it. Adjust generator speed until voltmeter move very slowly from zero to maximum and close the breaker when the voltmeter indication passes through zero.

Q. What is Dead-Front Switchboard & Dead Switchboard?

A. Dead-Front switchboard is one with insulated switches and no exposed terminals on front.

Dead-SwitchBoard is one in which there is no supply available

Q. What is Sequential starting?

A. The Automatic starting of Essential machineries after power is restored from Blackout condition. Following is the general sequence starting of machineries.

Immediate starting machineries after power restored without any delay: 1)Steering gear 2)Fuel Oil Feed & Booster pump 3)Radio & Navigation Equipment 4)Engine Room & Accommodation Lighting 05 Secs after main power is restored: 1) Stern Tube Lube oil pump 2) Main LO Pump 10 Secs after main power is restored: 1) MCSW P/P 2) LT CW P/P 3) M/E JCW p/p 15 Secs after main power is restored: 1) Deck seal water p/p 2) Aux.Boiler & Comp.Boiler Feed p/p 20 Secs after main power is restored: 1) All E/R fans 2) Fire & GS Pump

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