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Maison Tests en ligne CBT Tous types de navires Ch-Eng / 2nd-Eng Test for seamans about High Voltage, Management on Ships (CBT)
Tests en ligne : Test for seamans about High Voltage, Management on Ships (CBT)
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A 3 phase AC generator is supplying a high voltage switchboard at 11 000 Volts, and has a synchronous impedance of 0,5 Ohms. A solid, symmetrical three phase, short circuit occurs at point A. What is the prospective fault current through circuit breaker B1?
22 000 Amps.
11 000 Amps.
5 600 Amps.
2 800 Amps.
A joint between one supply cable conductor and its terminal on a 6,6 kiloVolt electric motor has a resistance of 2 milli-Ohms. If a short circuit current of 20 000 Amps flows through the joint how much heat is generated at the joint?
800 kW.
400 kW.
80 kW.
40 kW.
A man with dry hands accidently touches an electrical conductor at 50 Volts. Which of the following is the most likely result of this?
It would hurt, but not kill him.
It would kill him.
He would not feel it.
He would suffer severe burns to his hand.
Can HV sub-station (P) be supplied via the Starboard side of the ring main while the Port side is isolated?
Yes, provided the total load on HV sub-station (P) and HV sub-station (S) is reduced below 2 000 kiloWatts.
Yes, provided the HV sub-station loads do not increase.
Yes, if Generator G2 is run instead of Generator G1.
No.
Electrical circuit breakers can protect against a number of types of fault. Which of the following are the faults that can be used to operate a circuit breaker? Tick all that apply:
Répondre
Electrical circuit breakers can protect against a number of types of fault. Which of the following are the faults that can be used to operate a circuit breaker? Tick all that apply:
Répondre
Excessive temperatures can lead to insulation damage and even fires. Which of the following can lead to excessive temperatures in electrical equipment? Tick all that apply:
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High voltage Permits to Work vary but all should include key information. Which of the items of key information listed should be on any HV Permit to Work? Tick all those that apply:
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High voltage Permits to Work vary but all should include key information. Which of the items of key information listed should be on any HV Permit to Work? Tick all those that apply:
Répondre
In relation to electrical equipment, which one of the following best describes the relationship between current levels and overheating in a conductor?
Current causes a heating effect of I2R Watts.
Current causes a heating effect of VI Watts.
High currents can cause high magnetic fields and hysteresis heating.
Current levels do not affect heating.
In relation to high voltage electrical equipment, which one of the following best describes how equipment designers try to deal with the effects of blast following short circuits?
Most blasts occur at joints and these are normally sited within strong enclosures.
Most blasts occur within cables and these are not tightly enclosed so the pressure can escape.
Quick response short circuit protection can prevent blasts.
Conductors are spaced further apart than necessary to minimise the chance of short circuits.
In relation to high voltage electrical equipment, which one of the following best describes how the maximum safe exposure time to electricity changes with relation to its voltage level?
The safe exposure time falls rapidly from a low threshold voltage.
The safe exposure time rises gradually with voltage.
The safe exposure time remains the same regardless of voltage.
The safe exposure time remains the same before rising above a threshold voltage.
In relation to high voltage electrical equipment, which one of the following best describes the main danger from a conductor which becomes overheated?
It can start a fire.
The resistance of the conductor can rise leading to power reduction at the load.
The insulation around the conductor can become discoloured.
The smell can be unpleasant for passengers.
In relation to high voltage electrical equipment, which one of the following best describes the main way to ensure workers do not suffer high voltage electric shock while working out of sight of the circuit main earth?
An additional earth within sight of the work area should be used as well.
The incoming cables to the equipment being worked on should be disconnected.
An insulation tester should be left connected between one phase and earth.
A voltage tester fitted with an alarm should be left connected between one phase and earth.
In relation to high voltage electrical equipment, which one of the following best describes the meaning of “dead”?
At or about zero voltage and disconnected from all sources of electrical energy.
Disconnected from all power supplies.
Isolated from its power supply.
Not capable of movement.
In relation to high voltage electrical equipment, which one of the following best describes the meaning of “disconnected”?
The power supply to the equipment has been broken.
The equipment is dead.
The equipment contains no electrical energy.
The power to the equipment is isolated from all power supplies.
In relation to high voltage electrical equipment, which one of the following best describes the purpose of a “Limitation of Access” Permit?
It allows designated persons to enter a restricted area.
It allows designated persons to be kept out of an area where work is going on.
It limits the number of persons who can be in a designated area at any one time.
It restricts access to an area between specified times.
In relation to high voltage electrical equipment, which one of the following best describes the purpose of a “Danger Notice”?
It calls attention to the danger of approach or interference with the apparatus to which it is attached.
It is a warning against interference with the apparatus to which it is attached.
It is a warning that the equipment to which it is attached is live.
It calls attention to the danger of approaching high voltage equipment when rubber matting has been removed.
In relation to high voltage electrical equipment, which one of the following best describes the reason for getting a Sanction to Test Permit issued?
It is required when testing operations require removal of an earth.
It is required when testing operations require the use of test equipment with an output of 500 Volts or higher.
It is required before an insulation tester can be withdrawn from the stores.
It is required before the power supply can be reconnected after a permit to work is cancelled.
In relation to high voltage electrical equipment, which one of the following best describes the reason why arcs are dangerous to people who can see them?
They give off strong ultra violet light.
They can go on for a long time.
They can throw off a lot of heat.
They can set off fire detectors.
In relation to high voltage electrical equipment, which one of the following best describes when fuses may be used to protect circuits rather than circuit breakers?
Fuses are used in circuits where overcurrent is the only protection required.
Fuses are used in circuits where there is no space for circuit breakers.
Fuses are used everywhere except where power supplies leave a switchboard.
Fuses are not used in high voltage circuits.
In relation to high voltage electrical equipment, which one of the following best describes the most likely place to find a circuit main earth?
At a high voltage circuit breaker or isolator.
Where the switchboard is bolted down.
At intervals of no more than 40 m throughout the network.
At every large motor.
It is common on ships which generate at high voltage to supply the low voltage services via 2 transformers which can be interconnected on the low voltage side via a buts-tie circuit breaker. Which of the following best describes why it is not normal practice to operate with the low voltage bus-tie closed?
It would allow both transformers to supply a fault, at currents too high to break.
It is impossible to synchronise the 2 transformer outputs.
The loads on the 2 transformers cannot be balanced.
The loads on the main generators cannot be balanced.
Most high voltage systems on ships will have their neutral permanently connected to earth, unlike low voltage systems. Which of the following best describes how earth fault currents are limited on neutral earthed systems?
A high resistance earth is used to keep earth currents down.
All circuit breakers are set to trip as soon as any earth leakage is detected.
All circuit breakers rated at over 1 000 Amps are set to trip as soon as any earth leakage is detected.
All circuit breakers rated at over 1 000 Volts are set to trip as soon as any earth leakage is detected.
Most high voltage systems on ships will have their neutral permanently connected to earth, unlike low voltage systems. Which of the following best describes the reason for this?
It minimises voltage stresses.
It minimises earth fault currents.
It maximises conductor efficiency.
It maximises safety.
On some high voltage systems circuit breakers may operate automatically to re-route power supplies. Which of the following best describes when this might be programmed to happen?
When a slow acting fault is detected by the control system.
When a short circuit fault is detected by the control system.
When a circuit breaker is due for service.
When a load requires more current.
Overcurrent protection devices are normally chosen after comparing two capacity ratings – Rated current capacity and Breaking capacity. Which of these capacities is higher?
Breaking capacity.
Rated current capacity.
The STCW Code has recommendations for the training of engineering personnel having management responsibilities for the operation and safety of electrical power plant above 1 000 Volts. Which of the following is the commonly used name for persons trained to this level?
Authorised Persons.
Competent Persons.
HV Aware Persons.
Chief Electricians.
The high rupture capacity (HRC) fuses used in low voltage systems look similar to high voltage (HV) fuses. Which one of the following best describes the main difference between them?
HV fuses are longer than HRC fuses of the same capacity.
HV fuses are normally square and HRC fuses are round.
HV fuses have a calibration point.
HV fuses are thicker than HRC fuses of the same capacity.
The processes for issuing a high voltage Permit to Work and a Sanction to Test Permit are similar, as are the form layouts normally. Which of the following best describes the relationship between the two permits?
The Sanction to Test allows equipment to be energised where the Permit to Work does not.
The Sanction to Test allows the supply to be reconnected to equipment where the Permit to Work does not.
The Permit to Work allows the supply to be reconnected to equipment where the Sanction to Test does not.
The Permit to Work allows the equipment to be started up where the Sanction to Test does not.
Two identical generators are supplying a high voltage switchboard at 3 300 Volts, each with a synchronous impedance of 0,5 Ohms, when a solid, symmetrical three phase, short circuit occurs at point A. What is the prospective fault current through circuit breaker B1?
13 200 Amps.
6 600 Amps.
26 400 Amps.
3 300 Amps.
Which of the following are possible causes of voltage overload in high voltage electrical systems? Tick all those that apply:
Répondre
Which of the following are possible causes of voltage overload in high voltage electrical systems? Tick all those that apply:
Répondre
Which of the following are the main sources of increased danger from high voltage (HV) over low voltage (LV) electricity? Tick all the answers that apply:
Répondre
Which of the following best describes how the condition of the inert gas in a circuit breaker is monitored after it is put into service?
A pressure alarm is normally fitted to continuously monitor the gas.
A visual pressure indicator is normally fitted which must be checked every day.
Inert gas breakers must be serviced at least once a year by specialists.
A connection is provided to allow a pressure gauge to be fitted for regular checking.
Which of the following best describes the best action to take after a high voltage circuit breaker has opened under fault conditions and the current broken is suspected to have been in excess of the breaker’s continuous rated current capacity?
The breaker should not be operated until it has been checked by specialists.
The breaker should be wound into the test position and test closed before being put back into service.
The resistance through the breaker contacts should be proved to be less than 1 Ohm before being put back into service.
The breaker should have its vacuum or gas pressure checked.
Which of the following best describes the normal way to ensure that high voltage equipment is ready to be reconnected to the supply following maintenance?
The Component Person will sign the permit to say that it is ready for reconnecting.
The Authorised Person will check the equipment over for problems before reconnecting.
The Chief Engineer will check the equipment over for problems before reconnecting.
The Competent Person will tell the engine room watch keeper that it is ready for reconnecting.
Which of the following best describes the reason why care must be taken when handling or overhauling gas filled circuit breakers?
Arcing breaks down the quenching gas into various toxic gases.
The quenching gas is toxic.
The quenching gas is hard to buy.
The surface of the main contacts is very easy to damage.
Which of the following best describes why more than one Competent Person may be needed to put a high voltage switching plan into effect?
Physically remote breakers may need to be operated promptly to minimise danger.
Switching breakers can take the strength of 2 men.
One is needed to check that the other has operated the correct breaker.
The switching plan may be difficult to hold while operating breakers.
Which of the following best describes why the prospective fault current levels should not be reached in a real world short circuit situation?
The build-up of current is limited by the impedance of the conductors which are inductive.
The build-up of current is limited by the impedance of the conductors which are capacitive.
The build-up of current is limited by the impedance of the conductors which are resistive.
The heat build-up in the conductor’s increases circuit resistance.
Which of the following describes how isolated high voltage electrical equipment can be changed from a “charged” to a “discharged” state?
Any charge has to be dissipated.
The tension of all springs in the equipment must be released.
The power supply must be disconnected.
The power supply must be earthed.
Which of the following describes one of the main reasons for having a switching plan drawn up and approved on high voltage ships?
To ensure no essential equipment is accidently disconnected.
To ensure the bridge know what machinery is available.
To ensure that network circuit diagram is up to date.
To allow the correct caution and danger notices to be removed.
Which of the following is the name of the gas most commonly used in the inert gas filled circuit breakers used on ships high voltage systems?
Sulphur hexafluoride (SF6).
Sulphur dioxide (SO2).
Halon (CBrF3).
Carbon tetrachloride (CCl4).
Which of the following best describes one of the main criteria to be used when an Authorised Person decides whether to issue someone with a Limitation of Access Permit to enter a high voltage switchboard room?
Whether they are HV aware.
Whether they have ever been inside the room before.
Whether they are officers or ratings.
Whether they have been on the ship before.
Which of the following best describes the basic principle for deciding where protective devices should be positioned within an electrical network?
Anywhere where they will prevent damage or harm while maintaining electrical supply to as much of the network as possible.
On the high voltage side of every point where the circuit voltage changes.
On the supply side of every point where the circuit voltage changes.
Near the input to every load in the network.
Which one of the following best describes the difference between an Authorised Person (AP) and a Senior Authorised Person (SAP)?
A SAP must be competent to control all work on high voltage systems and the AP need only be competent for work on part of the system.
An AP must have 3 years sea service before being made SAP.
The SAP must be a qualified electrician but the AP can be a suitably trained engineer officer.
The SAP must be a qualified engineer officer but the AP can be a suitably trained electrician.
Which one of the following best describes the main criteria to be used when an Authorised Person chooses a Competent Person to carry out maintenance on, or switching of, high voltage equipment?
They must have sufficient technical knowledge or experience to enable them to avoid danger.
They must be certified as a STCW III/2 second engineer.
They must be certified as a STCW III/6 electrical engineer.
They must be certified by the company.
Which one of the following best describes the reason for using vacuum circuit breakers in high voltage (HV) networks instead of the air circuit breakers normally used for low voltage (LV) networks?
We can break the HV arc more quickly if there is no air to ionise.
The special material used in HV breaker contacts can corrode in air.
We can break the LV arc more easily using the resistance of the air between the contacts.
We can break the LV arc more easily using air movement to blow away the arc.
Which one of the following best describes the resistance reading of the human body when tested at different voltages?
An increase in test voltage causes a reduction in the body’s resistance.
A reduction in test voltage causes a reduction in the body’s resistance.
The body’s resistance is more or less constant at different test voltages.
The body’s resistance is steady until test voltages rise above 1 000 V when it starts to fall.
Which one of the following best describes what is defined as “High Voltage” with reference to ship’s electrical system?
AC electricity above 1 000 Volts.
AC electricity above 3 kiloVolts.
AC electricity above 3 000 Volts.
DC electricity above 1 000 Volts.
Which one of the following best describes who decides whether a person is a “Competent Person” for the purposes of high voltage electrical work, according to this module?
The Authorised Person.
The Head of the personnel department.
The Technical Superintendent.
The Master.
Which one of the following best describes who should hold the keys for the circuit breaker locks while maintenance is carried out on high voltage equipment if 4 people are to carry out the work?
The person given overall responsibility for carrying out the work should keep all the keys.
Whoever locks the breaker should keep the key for it.
The Authorised Person should keep all the keys.
The engine room watch keeper should keep all the keys.
Which one of the following best describes who should sign to accept the high voltage Permit to Work from the Authorised Person if 3 people are to carry out the work?
One person must be made responsible for overseeing the work and sign the permit.
All 3 should sign the permit.
All officers should sign the permit, ratings do not need to sign.
The permit does not normally need to be signed by the workers.
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