Questions and answers to Seagull CES CBT test for seamans about Electric Propulsion Systems, Power Electronics
Welcome to the website where you can find answers for the Computer Based Test (CBT) also known as Crew Evaluation System (CES) on the subject «Electric Propulsion, Power Electronics». This site will help you as a marine specialist improve your knowledge with the help of open information, where you can find questions as well as answers for them. CES/CBT based on practical information and marine specialists experience.
CES & CBT tests developed for evaluating seaman basic knowledge by Seagull Company (rebranded as «OTG»), is an evaluating online-tool, used for revealing any professional preparation needed in specific fields of knowledge, defined by STCW.
CES tests have proven themselves as good tools for the selection and recruitment process, as well as advancing the level of knowledge of the current officers and crew. Ocean Technologies Group use various subjects for question creation, which includes:
Crowd and Crisis Management;
Integrated Navigation System (INS);
Ballast water management;
Handling and Stowage;
Vessel operation management and safety;
Maintenance and repair, etc.
Current test contains Seagull CES questions on the subject «Electric Propulsion, Power Electronics».
These questions can be used to test the competence of a person capable of performing all the duties of an electrical engineer on a ship. The electric propulsion system with a direct frequency converter makes it possible to realize the mode of natural switching of valves, as well as to significantly improve the harmonic composition of the output voltage and currents of the converter. The absence of a pulse-width modulation carrier improves acoustic performance and electromagnetic compatibility with marine equipment. The mode powered by two independent generators improves vibroacoustic characteristics.
The topic “Electric Propulsion, Power Electronics” includes theoretical and practical information on working with electric motors on a ship. Knowledge of this information directly indicates the competence of the employee holding the relevant position on the ship. The combination of an internal combustion engine and an electric motor has numerous advantages and is particularly attractive for shipping. For example, in addition to a significant reduction in fuel consumption (up to 28%!), noise and vibration levels are also significantly reduced. Quietness and total absence of soot are the main advantages of a fully battery electric drive for ships and boats. The engines operate without diesel engines powered by lithium-ion batteries.
This page contains answers to Seagull CES CBT (Crew Evaluation System/Computer Based Test) test about Ship Propulsion System, Power Electronics, and serve as a database of questions and answers, using which seafarer can prepare to exams for getting certificate of competence, or just to challenge yourself with knowledge in this theme.
Test about Electric Propulsion Systems, Power Electronics
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Amount of questions: 38.
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A diode has 2 electrical terminals. Which of the following are the correct names for these terminals?
Anode and cathode.
Anode and electrode.
Electrode and cathode.
Anyline and catadyne.
An inverter circuit is adjusted to supply a motor with a 3 phase waveform which has a cycle time of 50 milliseconds. What is the effective frequency of this supply?
An inverter circuit is used to supply a fan motor with a 3 phase waveform. What is the main reason for inverting the supply to a motor like this?
The adjustable switching rate can be used to control the speed of the motor.
The adjustable switching rate can be used to control the voltage to the motor.
The adjustable switching rate can be used to improve the power factor.
It is hard to find DC motors with enough power.
If a single phase AC supply is to be full wave rectified to DC from a simple transformer, what is the minimum number of diodes that will be required?
If a single phase AC supply is to be full wave rectified using diodes and thyristors to a DC voltage that can be controlled in value, what is the minimum number of thyristors that will be required?
If a three phase AC supply is full wave rectified to DC how many ripples (peaks) would you expect to see on the DC waveform for each complete cycle of the supply?
If a three phase AC supply is to be full wave rectified to DC what is the minimum number of thyristors (or equivalent) that will be required?
The inverter bridge shown is being used to convert DC to supply a motor with a 3 phase AC. If we want a current to flow from V1 to V2 which of the thyristors must be switched on?
Thyristors 3 and 4.
Thyristors 3 and 6.
Thyristors 1 and 4.
Thyristors 1 and 2.
The inverter bridge shown is being used to supply an electric motor. Which of the following best describes this inverter’s basic principle of operation?
Inversion is achieved by establishing a controlled switching sequence.
Inversion is achieved by amplifying variations in supply.
Inversion is achieved by reversing the polarity of each wave.
Inversion is achieved by converting AC to DC.
When talking about electrical motor control systems the PWM control method is often mentioned. What does PWM stand for?
Pulse Width Modulation.
Pulse Wave Modulation.
Proton Wave Modification.
Power Wave Modulation.
Which of the following are the names given to the terminals of a bipolar transistor?
Collector, emitter and base.
Collector, emitter and gate.
Anode, cathode and base.
Collector and emitter.
Which of the following best describes one of the main benefits of transmitting digital control signals rather analogue ones?
Digital signals are less likely to be changed by external interference.
Digital signals are more accurate than analogue signals.
Higher currents can be used with digital signals.
Higher voltages can be used with digital signals.
Which of the following best describes the average voltage applied across the load if the bipolar transistor in this circuit is sent trigger pulses as the supply voltage goes positive and is switched off after 90° (electrical) of the supply cycle?
1/4 of the supply voltage.
1/2 of the supply voltage.
1/8 of the supply voltage.
The supply voltage.
Which of the following best describes the main advantage of PWM drives using transistors over thyristor based inverter drives to control electric motor speeds?
The PWM output waveform is closer to a sine wave.
The PWM output waveform is closer to a square wave.
Motors with PWM drives can be made to go slower.
Motors with PWM drives can be made to go faster.
Which of the following best describes the main difference between a diode and a thyristor?
Thyristors have an extra terminal called the gate.
Diodes have an extra terminal called the gate.
Thyristors have an extra terminal called the cathode.
Diodes are made of silicon and thyristors made of germanium.
Which of the following best describes the main weakness of field effect transistors when considering them for control of the main propulsion motors?
They tend to fail when working at high voltages.
They tend to fail when working in extreme electrical environments.
They are good for a limited number of switching operations before failure.
They have high heat losses.
Which of the following best describes the meaning of “self-commutating” when talking about power electronic devices?
The device will stop conducting when the triggering supply is turned off.
The device will continue to conduct when the triggering supply is turned off.
The device does not need a triggering supply to conduct.
The device has no brushes.
Which of the following best describes the method usually used to ensure that water leaks from water cooled electronic devices do not cause short circuits?
The conductivity of the water is kept low and constantly monitored.
The conductivity of the water is kept low by adding chemicals to the water.
The electronic devices are sealed in plastic.
A water leak detection system is installed in the bottom of every cabinet.
Which of the following best describes the possible result of uncontrolled triggering of a transistor in the inverter circuit of a speed controller?
It could cause a short circuit.
It could cause the motor to reverse.
It could cause the motor to speed up.
It could cause the motor to slow down.
Which of the following best describes the properties of analogue signals when talking about control and monitoring functions?
They can have an infinite number of values.
They have a finite number of values set by the sampling rate.
Analysis by a computer is impossible.
They can easily analysed by a computer.
Which of the following best describes the values transmitted by a digital sensor to a monitoring system?
It normally uses only 2 values.
It normally uses 10 values.
It normally uses an infinite number of values.
It normally uses 256 values.
Which of the following best describes what happens when a diode becomes “reverse biased”?
Conduction will stop.
Conduction will start.
The diode will start to conduct if a gate pulse is received.
The diode output will be reversed.
Which of the following best describes what happens when the gate pulse to a thyristor is turned off?
The thyristor will continue to conduct as long as it forward biased.
The thyristor will continue to conduct as long as it reverse biased.
The thyristor will stop conducting as soon as the pulse stops.
The gate of a thyristor is fed a steady signal not a pulse.
Which of the following best describes what may happen if a diode is not efficiently cooled?
Differential rates of expansion may damage the bond between the P-N junction and the external metal terminals.
The resistance of the diode will increase.
The hysteresis losses will be increased.
The inductance of the diode will increase leading to the power factor worsening.
Which of the following best describes why an inductance is often fitted to the DC link between a rectifier circuit and an inverter circuit?
It helps to smooth the supply of current to the inverter.
It reverses the polarity of the DC power.
It is used to tune out harmonics in the supply.
It is used to improve the power factor.
Which of the following best describes why diodes in power circuits need to be cooled while operating?
There is a forward voltage drop which causes heat to be given off.
Heat is caused while the diode is stopping current flow.
The control circuit for the diodes operate at high currents.
High voltages cause high heat generation.
Which of the following is one of the newer types of semiconductor device for power electronic uses?
Insulated gate bipolar transistor.
Conductive gate bipolar transistor.
Insulated glove bipedal motion.
Insulated base polar transformer.
Which of the following is the name given to the piece of metal often found attached to a thyristor?
A heat sink.
The backing strip.
Which of the following best describes a potential cause of damage to power electronic devices while they are being handled?
Static discharge from wearing man-made fabrics.
Conductor etching due to fingerprints.
Excessive heat from hands.
Excessive vibration when stored on board.
Which of the following best describes how a non-conducting material such as silicon can be made into a semiconductor?
The silicon is doped with another material to free up electrons.
The silicon is subjected to radiation to free up electrons.
The silicon has a core of conducting material inserted into it.
The silicon core is surrounded by a conducting material.
Which of the following best describes the atomic structure of a material that is an electrical conductor?
The material will have incomplete outer valence rings.
The material will have completely filled outer valence rings.
The material will have few valence rings.
The material will have no valence rings.
Which of the following best describes the method commonly used to minimise the number of signal cables that need to be run on a ship using digital monitoring and control signals?
The signals are carried along a common conductor known as a data bus.
The signals are multiplied into a carrier wave.
The signals are modulated on a carrier wave.
The signals are converted to optical format.
Which of the following best describes the method usually used to reduce the risk of uncontrolled triggering of thyristors?
An R-C filter is used.
An N-P filter is used.
Analogue signals are used.
Thyristors do not suffer from uncontrolled triggering.
Which of the following best describes what happens when a diode is connected in a circuit with an AC supply as shown?
The resistor will receive a half wave rectified DC voltage.
The resistor will receive a full wave rectified DC voltage.
The diode will prevent a current from flowing in the circuit.
The resistor will receive an AC voltage of half the supply voltage.
Which of the following best describes what is happening at the atomic level when a voltage is applied to an electrical conductor?
An electrical current flows due to the movement of free electrons from atom to atom.
An electrical current flows due to the movement of protons from atom to atom.
An electrical current flows due to the movement of neutrons from atom to atom.
An electrical current flows due to the movement of bosons from atom to atom.
Which of the following is the major advantage of using semiconductor devices as switches in motor control circuits?
A low voltage, low power circuit can control a supply with higher voltage and current.
Semiconductors are cheaper to buy than mechanical switches.
The semiconductor and motor can be controlled by the same voltage supply.
Semiconductors are quieter than mechanical switches.
Which of the following is the other name by which silicon controlled rectifiers are often knows?
Which of the following statements about the construction of a transistor is true?
It can be constructed as a P-N-P or as a N-P-N device.
It can be constructed as a P-N or as a NP device.
It can be constructed as a P-N-P or as a P-N-P-N device.
It is always constructed as a P-N-P-N device.
Test about Electric Propulsion Systems, Power Electronics
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