High Voltage System - Reason for having High Voltage System On board ships

As we already know about the voltages used onboard a ship. It is usually a 3phase, 60Hz, 440 Volts supply being generated and distributed onboard ship.

1. Higher power requirement on board ship is the foremost reason for the evolution of HV in ships.
2. Higher power requirement has been necessitated by development of larger vessel required for containers transport particularly reefers containers and cruise vessels.
3. Gas carriers needing extensive cargo cooling electric propulsion.
4. For a ship with large electrical power demand, it is necessary to utilize the benefits of a high voltage installation.

The design benefits relate to the simple ohms laws relationship that current (for a given power) is reduced as the voltage is increased. Working at high voltage onboard ship significantly reduces the relative overall size and weight of electrical power equipment.

When Heavy loads are connected to the Low voltage system the magnitude of current flow becomes too large resulting in overheating due to high iron and copper losses.

P = V * I * COS(Φ)

Copper losses = I^2 * R (KW)

Already High Voltage levels of 3.3 KV, 6.6 KV and 11 KV are regularly employed ashore for regional power distribution and industrial motor drives.

For example, a motor (let us assume a bow thruster), maybe a smaller size if it designed to operate on 6600 Volts. For the same power, the motor would be of a smaller size if is designed for 6600 Volts when compared to 440 Volts.

Thus these are the major reasons why recent ships have shifted towards the high voltage systems. The main disadvantage Highlighted by the owner, when working in an HV installation, is the very necessary adherence to stringent safety procedures.

Advantages:

1. For a given power, higher Voltage means Lower current, resulting in:
2. Reduction in size of generators, motors, cables, etc.
3. Saving of space and weight.
4. Ease of Installation.
5. Reduction in cost of Installation.
6. Lower losses- more efficient utilization of generated power.
7. Reduction in short circuit levels in the system which decides the design and application of the electrical equipment used in the power system.

Disadvantages:

1. Higher Insulation Requirements for cables and equipment used in the system.
2. Higher risk factor and the necessity for strictly adherence to stringent safety procedures.

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Communication System Multiple Choice Questions

 Electronics and Communication Multiple Choice Questions

1. In PCM if the transmission path is very long?

a. repeater stations are used

b. pulse width may be increased

c. pulse amplitude is increased

d. pulse spacing is reduced

2. Frequency shift keying is used mostly in?

a. radio transmission

b. telegraphy

c. telephony

d. none of these

3. Leak type bias is used in a plate modulated class C amplifier to?

a. increase the bandwidth

b. prevent excessive grid current

c. prevent tuned circuit damping

d. prevent overmodulation

4. The frequency of normal sound wave determines its?

a. quantity

b. echo

c. loudness

d. pitch

5. Which of the following is most likely to be found in an SSB transistor?

a. Class A, RF output amplifier

b. Class B, RF amplifier

c. tuned modulator

d. Class C, audio amplifier

6. A longwave AM Broadcast transmitter needs?

a. very small carrier power

b. very large carrier power

c. small carrier power

d. large carrier power

7. The term noise temperature is used for?

a. white noise source only

b. thermal noise source only

c. non-thermal noise source only

d. all of the above

8. The thermal noise is due to random?

a. motion of atoms and molecules

b. motion of free electrons

c. vibrations of atom about their mean position, inside the conducting medium

d. none of these

9. At high frequencies, which of the following types of noise become most important?

a. flicker noise

b. short noise

c. thermal noise

d. transit time noise

10. Which of the following is not uniformly distributed over all frequencies?

a. white noise

b. flicker noise

c. short noise

d.  thermal noise

Answers:

1. a

2. b

3. b

4. d

5. b

6. b

7. d

8. b

9. d

10. b

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Control System Multiple Choice Questions

 Electronics and communication Multiple Choice Questions

1. Poles are the complex frequencies of a transfer function where the response becomes?

a. infinite

b. zero

c. oscillatory

d. decaying

2. Zeros are the complex frequencies of a transfer function where the response becomes?

a. infinite

b. zero

c. oscillatory

d. decaying

3. Which of the following is an open loop system?

a. ward Leonard control

b. Amplidyne

c. Armature controlled d.c. motor

d. Field controlled d.c. motor

4. A driver maintains the speed of a car at 50 Km per hour. Here the feedback element is?

a. steering wheel

b. needle of the speedometer

c. eyes

d. all of these

5. Transient response of a system is basically because of?

a. coupling

b. forces

c. friction

d. stored energy

6. In a critically damped system, the damping factor of the system is?

a. zero

b. unity

c. less than unity

d. greater than unity

7. With feedback, the transient response of the system as compared to that without feedback?

a. decays slowly

b. decays more quickly

c. rises at a faster rate

d. remain unaltered

8. By increasing the gain k of the system, the steady state error of the system?

a. decreases

b. increases

c. remain unchanged

d. may increase or decreases

9. Integral error compensation is also called?

a. proportional minus integral compensation

b. proportional plus integral compensation

 c. proportional plus derivative compensation

d. proportional minus derivative compensation

10. For 2% tolerance band, the settling time the second order linear system is? Where t is the time constant.

a. t/2

b. t

c. 2t

d.  4t

Answers:

1. a

2. b

3. d

4. b

5. d

6. b

7. b

8. a

9. b

10. d

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Digital Electronics Circuits Multiple Choice Questions

Electronics and Communication Multiple Choice Questions

1. Scratch-pad memory is a?

a. first-in-first-out memory

b. last-in first-out memory

c. local permanent memory

d. local temporary memory

2. In case of bipolar or static MOS memories, the access time is about?

a. 20 to 400 ns

b. 20 to 400 micro sec

c. 20 to 400 ms

d. 20 to 400 s

3. Access in the magnetic drum is?

a. completely random

b. sequential and cyclic

c. cyclic sequential

d. partly random and partly cyclic sequential

4. Dynamic memory cells are constructed using?

a. FETs

b. MOSFETs

c. Transistor

d. Flip-flops

5. ROM consists of?

a. a decoder followed by an encoder

b. an encoder followed by a decoder

c. a multiplexer followed by a decoder

d. none of these

6. Semiconductor ROMs are sometimes preferred to semiconductor RAMs because?

a. ROMs are cheaper than RAMs

b. ROMs are faster

c. ROMs do not require the power supply for their operation

d. a program stored in ROMs cannot be altered

7. Which of the following is a permanent memory?

a. RAM

b. ROM

c. both RAM and ROM

d. None of the above

8. The storage device used to compensate the differences in the ratio of flows of data is known as?

a. auxiliary storage

b. buffer

c. main storage

d. None of the above

9. Desirable characteristics of a memory unit are?

a. compact

b. speed

c. durability

d. all of the above

10. Parallel adders are?

a. Combinational logic circuits

b. sequential logic circuit

c. both of the above

d.  none of the above

Answers:

1. d

2. a

3. d

4. b

5. a

6. d

7. b

8. b

9. d

10. a

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Electronic Analog Circuits Multiple Choice Questions

Electronics and Communication Multiple Choice Questions

1. An Op-Amp clamper?

a. removes part of the output voltage above a given level

b. converts the input voltage into square wave voltage at a given level

c. clamps the output voltage at a given level

d. removes part of output voltage below a given below

2. Positive half wave rectifier using Op-Amp is generally used to rectify signal of the order of?

a. Kilovolts

b. hundreds of volt

c. tens of volts

d. millivolts

3. An Op-Amp Schmitt trigger is basically?

a. An OP-amp comparator with negative feedback

b. An Op-Amp comparator with positive feedback

c. a triangle wave generator

d. a pulse generator

4. An Op-Amp comparator?

a. is always non-inverting type

b. is always inverting type

c. is always a combination of an inverting Op-Amp and a non-inverting Op-Amp

d. may be inverting type or non-inverting type

5. The best circuit used to eliminate power frequency (50 Hz) hum is?

a. a scratch filter

b. a speech filter

c. an octave filter

d. a rumble filter

6. An Op-Amp circuit capable of selecting sound from one out of two speaker or both is known as?

a. a crossover network

b. a tone control

c. a panning control

d. a octave equalizer

7. Which of the following Op-Amp system is non-linear?

a. voltage to current converter

b. voltage follower

c. active filter

d. sample and hold circuit

8. A cascade amplifier uses?

a. two stages of CE amplifier

b. direct coupled CE-CC circuit

c. direct coupled CE-CB circuit

d. direct coupled CC-CB circuit

9. Typical output offset voltage and input offset current of an Op-Amp is?

a. 1 mV, 10 mA

b. 1 mV, 10 nA

c. 10 mV, 10 nA

d. 10 mV, 10 mA

10. An Op-Amp has a gain of 50 and bandwidth of 100KHz. Its unit-gain frequency is?

a. 5 MHz

b. 100 KHz

c. 10 MHz

d.  2.5 MHz

Answers:

1. c

2. d

3. b

4. b

5. d

6. c

7. d

8. c

9. c

10. a

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Power Electronics Multiple Choice Questions

Electronics and Communication Multiple Choice Questions

1. A step up chopper is required to deliver a load voltage of 660V from a DC source of 220V. Let the non-conduction time of thyristor be 100 micros required the requited pulse width, ton:

a. 150 micro sec

b. 200 micro sec

c. 330 micro sec

d. 240 micro sec

2. The thyristor can be turned on by applying?

a. a positive signal to gate

b. a negative signal to gate

c. holding current to the gate

d. none of the above

3. When two SCRs are connected in parallel configuration?

a. the SCR with lower dynamic resistance will carry lesser value of current

b. the SCR with lower dynamic resistance will carry higher value of current

c. both the SCR with carry equal values of current even if their dynamic resistance are different

d. none of the above

4. A class-C chopper (DC to DC converter) is also known as?

a. one-quadrant regulator

b. two-quadrant chopper

c. steady state chopper

d. all of the above

5. The flyback converter topology in a DC to DC switched mode power supply?

a. should be restricted to low power application

b. can be used for high power application

c. would be selected depending upon the DC load of the equipment in question

d. can be selected without considerations of power requirement of the equipment in questions.

6. A UPS is an example of?

a. a DC SMPS

b. an AC SMPS

c. a DC to DC converter

d. a voltage regulation device

7. An n-channel enhancement MOSFET?

a. has a physical channel

b. has no physical channel

c. is similar in construction to a p channel depletion MOSFET

d. none of these

8. The enhancement MOSFETs responds to?

a. positive and negative gate voltages

b. positive gate voltage only

c. negative voltage only

d. none of above is true

9. A DC chopper (DC to DC converter) is turned on for 30 micro sec and turned off for 10 micro sec. What is its duty cycle?

a. 0.62

b. 0.92

c. 0.75

d. 0.85

10. In a three-phase bridge inverter?

a. firing of SCRs can be done for a period of 120 degree only

b. firing of SCRs can be done for a period of 180 degree only

c. firing of SCRs can be done for a period of 120 degree and 180 degree periods

d.  none of the above

Answers:

1.  b

2. a

3. b

4. b

5. a

6. b

7. b

8. b

9. c

10. c

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Different type of Controllers Onboard

1.  Small-scale controller

-These type of controller are mostly of microcontroller type or of based on other active elements like OP-AMP based.

-They are deployed to control and monitor very small task in a system.eg:- oxygen analyzer, pH monitoring, and alarm system.

-Specifically, these type of system give out the Digital alarms but with one more OP-AMP integrated into the system it gives out the analog signals.

-configuring and changing the signal to these devices is very difficult with limited instruments available onboard.

-make sure connection and solder point are not getting loosen due to vibrations.

-Ensure proper shock absorber/cushion is maintained.

-Ensure earthing point is not loosed.

-Ensure Potentiometer setting are not changed due to vibration.

2.   PID Controllers(-ve feedback closed loop controller)

-They are process controllers designed to monitor the analog signals and controls the actuators via analog or digital signals onboard they are used for temperature, flow, level.

They come in standard industrial grade hard plastic package of fix number of screw connecting pins.

-These controllers can be reconfigured but caution must be taken with the parameters. If not done as per process then it can cause damage to the machine as well as to the operator.

      

-Parameters of the PID comes in its operation manual.

This controller can be connected in many configurations as master-slave, +ve feedforward, -ve feed forward system. Not much repairing can be done onboard on PID, they can only be reconfigured and these controllers don't decalibrate on there own.

-Before reconfiguration ensure good input and the output signal from PID because changing parameters mostly takes the expertise level and knowledge.

-Insufficient power.

-I/O terminals damage.

-The controller might be in manual/maintainance mode 

3.    PLC Controllers

These are programmable controllers for digital and analog actuation of actuators. They provide an open architecture and flexibility again PLC comes in size and variety, once they are programmed then only wiring and instrumentaion work resides.

Types of PLC Onboard

a. MICRO PLC-(programmable relays)

-These are programmable relays with less number of I/O terminals with onboard programming facility on them.

eg:-

Schneider electric Zelio

seimens LOGO

b. Compact PLC

-They are relevant to medium scale automation with the limited number of IO terminals, but can be added with I/O modules upto 10 in Nos. They have 2 or 3 communication ports

c. Modular PLC

-These are very varsatile PLC controller for high scale automation with I/O terminals in range of thousands. 

-There I/O module comes in standard addon block with easy installation and 2 or more inbuilt communication ports.

-PLC comes in many brands(Allen Bradely, schneider electric, siemens, ABB, mitshubishi, delta automation, Omron and many more) with their different software  of different version

-Although many of us know the PLC ladder programming but never try to program the PLC onboard as it will void the manufacturer or programmers warranty.

-PLC indications give out the health of it, still, problems in PLC is very limited

   -battery drained or damaged

   -unregulated power supply

   -PLC in error/fault mode due to memory or hardware reason.  

4.    DCS(Distributed Controller system)

-These are very powerful controllers with many controllers connected to it which are distributed throughout the system.

-It has its own SCADA integrated to it which can control and aquize the data on different systems and communicate to one redundant server.

-DCS is a tailor made automation syatem for a specific process. Nowdays many brands started to manufacture DCS.

In marine sector, it is used on fully automated ships like of NYK.

-They are very reduant and expensive controll system that is placed on board, nowadays company started to interface neural logic along with PLC and HLL language.

eg:-

honeywell dcs system 

yokogawa dcs system

ABB DCS system

Now a days companys like siemens are trying to make DCS more compact with the there PCS7 system and more is on the way.

-These controllers no matter which type or brand they work very efficiently without failing.

-There is very less probability of Controller Damage but a very high probability of input failure due to a faulty sensor or faulty input line.Still, in case of any replacement, make sure connection are connected in the same way as they were previously.

ABOUT THE AUTHOR

JOGINDER SINGH is an Automation Engineer and currently working in GE Shipping as an Electro Techno Officer.

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