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在线测试： Test for seamans about High Voltage, Fundamentals (CBT)
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A 440 Volt AC source supplies 2 loads in parallel. The left load has an impedance of 44 Ohms and the right of 11 Ohms. Which of the following is the current taken from the AC supply?
50 Amps.
8 Amps.
44 Amps.
It cannot be calculated from the information given.
A man accidently receives an electric shock resulting in a current of 2 mA flowing through his hands and chest. Which of the following best describes the likely effect on him?
He will feel nothing.
He will feel tingling or mild pain.
He will feel severe pain from burns.
He will be killed.
An AC circuit delivers an active power of 30 kW when supplied at 400 Volts and 125 Amps. Which of the following is the reactive power?
4 kVAr.
30 kW.
40 kVAr.
It cannot be calculated from the information given.
An AC electrical circuit operates at 110 Volts. Which one of the following is the circuit’s voltage rating according to this module?
Low Voltage.
Medium Voltage.
High Voltage.
Extra Low Voltage.
An overcurrent relay is usually used to open a circuit breaker. Which one of the following is another function it may be used for?
To connect a second power supply.
To sound an alarm.
To trip the generator.
To start a generator.
How do electrical engineers refer to a flow of electricity around a circuit?
It is referred to as a current, represented by I.
It is referred to as a current, represented by C.
It is referred to as a voltage, represented by V.
It is referred to as an electron, represented by E.
In analyzing AC electrical circuits, it is common practice to use impedances. Which one of the following best describes what an “impedance” is?
It expresses the practical effect of inductance for a single or group of components.
It expresses the practical effect of resistance, capacitance and inductance for a single or group of components.
It expresses the practical effect of reactance in a circuit.
It expresses the theoretical effect of reactance in a circuit.
PVC insulated cable is very popular ashore. Which one of the following best describes the reason why it is less frequently used on ships?
It gives off poisonous halogen gas if on fire.
Ambient temperatures on ships trading in the tropics are too high.
It is expensive.
It is only used on high voltage cables.
Sometimes conductors are separated to prevent short circuits, using the insulating effect of the air to contain the electricity. Which 2 of the following are reasons why the gap between conductors may be larger than the minimum necessary for the rated voltage?
To allow space for tools to be used.
Where there is a higher than usual risk of short circuit.
Plastic insulating parts cannot be made smaller.
A sudden increase in voltage is possible.
回答
Sometimes it is possible to see electrical conductors, such as busbars, which have no insulation covering parts of them. Which one of the following best describes why these uninsulated live parts do not normally cause a short circuit?
The surrounding air has been used as the insulation.
Insulation is fitted but it is so thin that it is not noticeable.
High speed overload trips are fitted to disconnect the supply.
Each conductor is surrounded by a magnetic field which contains the electricity.
The basic strategy to stay alive while working with high voltage systems may be summarized as DIE. What does DIE stand for?
Disconnect, Isolate, Evaluate.
Direct Insulation to Earth.
Disconnect, Isolate, Earth.
Direction, Inertia, Evaluation.
The battery in the circuit shown has an output of 1,5 Volts. The resistors are 32,75 Ohms each. What voltage is dropped across the right hand resistor?
1,5 Volts.
0,05 Volts.
0,75 Volts.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 12 Volts. If the resistance of the resistor is 3 Ohms what current should be flowing in the circuit?
4 Amps.
4 Farads.
36 Amperes.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 12 Volts. If the resistance of the upper resistor is 3 Ohms what current should be flowing in the circuit?
4 Amperes.
36 Amps.
4 Amps.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 12 Volts. The resistors are 3 Ohms each. What current should be flowing through the battery connections?
12 Amps.
0,75 Amps.
It cannot be calculated from the information given.
4 Amps.
The battery in the circuit shown has an output of 24 Volts. If the resistance of the upper resistor is 3 Ohms and the lower resistor is 5 Ohms what current should be flowing in the circuit?
3 Amps.
4 Amps.
6 Amperes.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 6 Volts. If the resistance of the resistor is 0,5 Ohms what current should be flowing?
12 Hertz.
12 Amps.
3 Amperes.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 6 Volts. If the resistance of the upper resistor is 3 Ohms and the current flowing in the circuit is 1 Amp, then what voltage is dropped across the upper resistor according to Kirchhoff’s Law?
3 Volts.
2 Volts.
1 Volt.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 6 Volts. The resistance of the upper resistor is 3 Ohms and the lower resistor is 9 Ohms. What voltage is dropped across the upper resistor according to Kirchhoff’s Voltage Law?
1,5 Volts.
2 Volts.
1 Volt.
It cannot be calculated from the information given.
The battery in the circuit shown has an output of 6 Volts. The voltage dropped across the upper resistor is 2 Volts. What voltage is dropped across the lower resistor according to Kirchhoff’s Law?
4 Volts.
2 Volts.
1 Volt.
It cannot be calculated from the information given.
Thermosetting insulation has been used on the cases of 2 circuit breakers, one rated for low voltage and the other for high voltage. Which of the following options best describes the difference that can be seen in the insulation?
The insulation will be color coded red on the high voltage breaker.
The insulation will be more flexible on the high voltage breaker.
The insulation will be thicker on the high voltage breaker.
The insulation will cover the terminal bolts on the high voltage breaker.
Two electrical conductors are circular in cross section and are otherwise the same except that conductor 1 has twice the diameter of conductor 2. If the resistance of conductor 1 is 2 Ohms what is the resistance of conductor 2?
8 Ohms.
4 Ohms.
2 Ohms.
1 Ohms.
Two electrical conductors are the same except that conductor 1 is four times as long as conductor 2. If the resistance of conductor 1 is 2 Ohms what is the resistance of conductor 2?
0,5 Ohms.
8 Ohms.
2 Ohms.
0,2 Ohms.
Two identical coils are connected in separate electrical circuits. One coil is supplied by a 12 Volt DC source and the other by a 12 Volt AC source. Which one of the following describes which circuit will have the higher current flowing and why?
The DC circuit – because the inductance does not restrict current flow.
The DC circuit – because the resistance will get hotter in the AC circuit.
The AC circuit – because the magnetic field around the inductance boosts current flow.
The AC circuit – because both active and reactive powers are being delivered.
When calculating the resistance of an electrical conductor which one of the following is the symbol used to denote the resistivity of the conductor material?
The symbol R.
The symbol L.
The symbol A.
The symbol ρ.
Which of the following allows the heat being produced in a conductor carrying a current to be calculated?
I2×R.
I×R.
I2×Z.
V/R.
Which of the following best describes how a capacitor works?
It stores energy like a fast charging battery.
It converts electricity to magnetism.
It converts electricity to heat.
It converts electricity to higher voltages.
Which of the following best describes how the apparent power of an AC electrical circuit with a single coil as a load can be calculated?
P = V×I.
P = I2×R.
P = I2×X.
P = V×I Cos Φ.
Which of the following best describes one of the ways that might cause an electrical conductor to suffer voltage overload?
Accidental connection to the wrong supply.
Insulation too thin.
Fuse failure.
An earth faults.
Which of the following best describes one reason why people receiving electric shocks from high voltage (HV) systems are more likely to die than those receiving shocks from low voltage (LV) systems?
The safe exposure time to current falls rapidly as the voltage increases.
They are likely to fall further from HV equipment.
They are less well trained than people working on LV.
They are more likely to have sweaty hands than people working on LV.
Which of the following best describes the effect of over voltage when applied to an electrical conductor?
It will cause thermosetting insulation to go hard.
It will cause insulation breakdown.
It will cause build-up of static charge.
It will be indicated by a colour change in the insulation.
Which of the following best describes the meaning of the symbol Ω when found in an electrical calculation?
The quantity is expressed in Ohms.
It is the impedance of the component.
The quantity is expressed in Coulombs.
It is the resistivity of the conductor material.
Which of the following best describes the reason why designers of electrical systems sometimes specify cables with a greater current carrying capacity than the current predicted to flow in service?
The cables are not class society approved.
The cables are to be bent to a tight radius in several places.
The cables are to be installed in a large bundle on the boiler.
The cables are cheaper when lots of the same size is bought.
Which of the following best describes what we mean by “power factor” in an AC electrical system?
It is the proportion of apparent power which is delivered as active power.
It is the ratio of power drawn from the generator to its maximum capacity.
It is ratio of reactive power to active power.
It is the proportion of apparent power which is converted to reactive power.
Which of the following best describes why traditionally ships’ electrical systems have operated with an insulated neutral?
So as to minimise the risk of essential equipment tripping.
So as to minimise the risk of generator damage.
So as to minimise the cost of the electrical network.
So as to minimise the risk of electrocution.
Which of the following is the level at which electricity becomes high voltage, according to the International Electro-Technical Commission standard for ships?
AC electricity above 11 000 Volts.
DC electricity above 1 000 Volts.
AC electricity above 1 000 Volts.
AC electricity above 50 000 Volts.
Which of the following options best explains how we ensure that electricity flows from the power supply to the load without it “leaking” away?
The conductor is surrounded by insulation to prevent leakage.
The conductor is magnetised to contain the electricity.
The conductor is surrounded by wire mesh to prevent leakage.
The conductor material is polarised during cable manufacture.
Which one of the following best describes reactive power in an AC electrical circuit?
Reactive power reacts against the force of gravity.
Reactive power reacts against the rotation of a rotor.
Reactive power is easily converted back to electricity.
The more reactive power in circuit the more efficient it is.
Which one of the following best describes the meaning of “voltage stress” when applied to ship’s electrical cables?
It is the voltage per millimetre of insulation.
It is the voltage drop per metre of cable length.
It is the voltage drop caused by a right angle bend with a radius of 5 times the cable diameter.
It is the damage done to insulation following a voltage being applied across it.
Which one of the following best describes the primary method of protecting against overloading of an electrical conductor?
The conductors must be adequately rated for maximum load current under the worst environmental conditions expected.
The best quality voltage overload trip must be fitted.
The best quality current overload trip must be fitted.
The conductors must be placed as far apart as possible.
Which one of the following best describes what the difference is between the thermosetting and the thermoplastic insulations used on ship’s electrical equipment?
Thermoplastic insulations are grey and thermosetting insulations are black.
Thermoplastic insulations soften as they get warmer and thermosetting insulations do not.
Thermoplastic insulations are rigid and thermosetting insulations are not.
Thermosetting insulations soften as they get warmer and thermoplastic insulations do not.
Which one of the following best describes why a length of 10 Amp cable bought from a shop ashore may not be suitable for a circuit carrying 10 Amps on a ship?
Temperatures on ships are often higher than ashore so that the conductor may not be cooled as effectively as assumed by the seller.
Cables on ships often have to be bent around tight corners.
A 10 Amp overload trip on a ship operates at a difference current to those used ashore.
Cables on ships are not allowed to carry more than 60 % of their rated current.
Which one of the following best describes why arc and blast are more of a problem with high voltage (HV) electrical systems?
Arcs cannot form in air at less than 800 Volts.
The amount of energy available in a HV circuit tends to be much higher.
Blasts only happen when faults occur in a confined space like an HV cabinet.
HV circuit breakers are big and slow to operate.
Which one of the following best describes why most circuits on ships are supplied by AC electricity rather than DC?
The voltage level of AC is easily changed.
The waveform of AC makes electric motors run more smoothly.
100 Volts of AC is safer than 100 Volts of DC.
DC generators are not available for ships.
Which one of the following describes the best way of protecting the conductors deep inside electrical machines from the effects of excessive temperature?
Bi-metallic thermal cut outs can be fitted.
Clean ventilation filters on a regular basis.
The current overload trip can be used.
Thermistors can be built into them to sense the temperature.
Which one of the following describes the best way to protect an electrical cable from mechanical damage where it passes through an area on deck where cargo is loaded and unloaded?
Run the cable through steel conduit.
Use cable with a steel centre core.
Run the cable through plastic pipe to keep the water out.
Use multicore cable.
Which one of the following formulas agrees with Ohms Law?
R = V/I.
R = V×I.
R = ρL/A.
I = V×R.
Which one of the following is the most common reason for a rapid rise in the current flowing through an electrical circuit, to a level many times its rated value?
A short circuit.
Bearing failure.
Excessive ambient temperature.
Weakened conductors.
Which one of the following options best describes a possible cause for the softening and weakening of the insulation around an electrical cable?
Tight bends in the cable.
Not enough current flow.
An unexpected rise in conductor resistance.
Unexpectedly high ambient temperature.
Which one of the following options best describes a possible reason for someone being seriously hurt following an electric shock of 10 mA, even though the current passed through the body for only a fraction of a second?
They were thrown backwards and fractured their head.
They suffered circulatory failure leading to brain damage.
Their gloves caught fire.
They trapped their fingers in the cabinet.
Which one of the following options best describes a significant problem with thermosetting types of insulation on ships?
Thermosetting insulation is too flexible and needs excessive support.
Thermosetting insulation is not flexible and can become damaged by impacts.
Thermosetting insulation is too expensive.
Thermosetting insulation is black and hides burn marks.
Which one of the following options best describes the effect on an electrical cable on a ship if the cable is hit by a lightning strike?
A voltage overload and damage to cable insulation.
No effect to a cable rated at over 600 Volts.
No effect to a cable rated at over 6 kiloVolts.
An unexpected rise in conductor resistance.
Which one of the following options best describes what happens when a charged capacitor is connected to a load in an electrical circuit?
Nothing will happen.
A DC current will flow in the opposite direction to the one that charged it.
A DC current will flow in the same direction as the one that charged it.
An altering current will flow in the circuit.
Which one of the following options best describes why connecting cables are usually fitted with flexible insulation?
Flexible insulation is necessary so connections can be made.
Flexible insulation is cheaper than hard insulation.
Flexible insulation is necessary so that cables can be pushed through conduit.
Flexible insulation is thinner and lighter than hard insulation.
Which one of the following options is the way we refer to the restriction to current flow through an inductor in an AC electrical circuit? Refer to the blackboard on the right side of the screen:
4.
3.
2.
1.
Which one of the following would be a typical power factor for a 440 Volt galley stove?
2.
1.
0,8.
0,5.
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