Тест по High Voltage, Management on Ships (CES v5.0)

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Правильные ответы:
1

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?

Ваш ответ правильный:

22 000 Amps.
2

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?

Ваш ответ правильный:

800 kW.
3

A man with dry hands accidently touches an electrical conductor at 50 Volts. Which of the following is the most likely result of this?

Ваш ответ правильный:

It would hurt, but not kill him.
4

Can HV sub-station (P) be supplied via the Starboard side of the ring main while the Port side is isolated?

Ваш ответ правильный:

Yes, provided the total load on HV sub-station (P) and HV sub-station (S) is reduced below 2 000 kiloWatts.
5

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:

Правильный ответ:

Over current.; Over voltage.; Reverse power.; Low frequency.

Ваш ответ:

Over voltage.; Reverse power.; Low frequency.
6

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:

Ваш ответ правильный:

High frequency.; High temperature.
7

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:

Ваш ответ правильный:

Excess current flow.; High ambient temperature.; Poor ventilation.
8

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:

Ваш ответ правильный:

The location of the work.; The details of the work to be done.; The nature and results of any preliminary tests undertaken.; Any measures undertaken to make the job safe.
9

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:

Ваш ответ правильный:

The safeguards that need to be taken during the operation.; The limited time of validity.
10

In relation to electrical equipment, which one of the following best describes the relationship between current levels and overheating in a conductor?

Ваш ответ правильный:

Current causes a heating effect of I2R Watts.
11

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?

Ваш ответ правильный:

Most blasts occur at joints and these are normally sited within strong enclosures.
12

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?

Ваш ответ правильный:

The safe exposure time falls rapidly from a low threshold voltage.
13

In relation to high voltage electrical equipment, which one of the following best describes the main danger from a conductor which becomes overheated?

Ваш ответ правильный:

It can start a fire.
14

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?

Ваш ответ правильный:

An additional earth within sight of the work area should be used as well.
15

In relation to high voltage electrical equipment, which one of the following best describes the meaning of “dead”?

Ваш ответ правильный:

At or about zero voltage and disconnected from all sources of electrical energy.
16

In relation to high voltage electrical equipment, which one of the following best describes the meaning of “disconnected”?

Ваш ответ правильный:

The power supply to the equipment has been broken.
17

In relation to high voltage electrical equipment, which one of the following best describes the purpose of a “Limitation of Access” Permit?

Ваш ответ правильный:

It allows designated persons to enter a restricted area.
18

In relation to high voltage electrical equipment, which one of the following best describes the purpose of a “Danger Notice”?

Ваш ответ правильный:

It calls attention to the danger of approach or interference with the apparatus to which it is attached.
19

In relation to high voltage electrical equipment, which one of the following best describes the reason for getting a Sanction to Test Permit issued?

Ваш ответ правильный:

It is required when testing operations require removal of an earth.
20

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?

Ваш ответ правильный:

They give off strong ultra violet light.
21

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?

Ваш ответ правильный:

Fuses are used in circuits where overcurrent is the only protection required.
22

In relation to high voltage electrical equipment, which one of the following best describes the most likely place to find a circuit main earth?

Ваш ответ правильный:

At a high voltage circuit breaker or isolator.
23

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?

Ваш ответ правильный:

It would allow both transformers to supply a fault, at currents too high to break.
24

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?

Ваш ответ правильный:

A high resistance earth is used to keep earth currents down.
25

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?

Ваш ответ правильный:

It minimises voltage stresses.
26

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?

Ваш ответ правильный:

When a slow acting fault is detected by the control system.
27

Overcurrent protection devices are normally chosen after comparing two capacity ratings – Rated current capacity and Breaking capacity. Which of these capacities is higher?

Ваш ответ правильный:

Breaking capacity.
28

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?

Ваш ответ правильный:

Authorised Persons.
29

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?

Ваш ответ правильный:

HV fuses are longer than HRC fuses of the same capacity.
30

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?

Ваш ответ правильный:

The Sanction to Test allows equipment to be energised where the Permit to Work does not.
31

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?

Ваш ответ правильный:

13 200 Amps.
32

Which of the following are possible causes of voltage overload in high voltage electrical systems? Tick all those that apply:

Ваш ответ правильный:

Lighting strike.; Connection to the wrong supply.; Equipment failure.; Inductive switching.
33

Which of the following are possible causes of voltage overload in high voltage electrical systems? Tick all those that apply:

Ваш ответ правильный:

A floating neutral.; Lighting strike.
34

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:

Ваш ответ правильный:

HV can jump much larger air gaps.; HV can drive higher, more deadly, currents.; HV can create very powerful arcs and blasts.
35

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?

Ваш ответ правильный:

A pressure alarm is normally fitted to continuously monitor the gas.
36

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?

Ваш ответ правильный:

The breaker should not be operated until it has been checked by specialists.
37

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?

Ваш ответ правильный:

The Component Person will sign the permit to say that it is ready for reconnecting.
38

Which of the following best describes the reason why care must be taken when handling or overhauling gas filled circuit breakers?

Ваш ответ правильный:

Arcing breaks down the quenching gas into various toxic gases.
39

Which of the following best describes why more than one Competent Person may be needed to put a high voltage switching plan into effect?

Ваш ответ правильный:

Physically remote breakers may need to be operated promptly to minimise danger.
40

Which of the following best describes why the prospective fault current levels should not be reached in a real world short circuit situation?

Ваш ответ правильный:

The build-up of current is limited by the impedance of the conductors which are inductive.
41

Which of the following describes how isolated high voltage electrical equipment can be changed from a “charged” to a “discharged” state?

Ваш ответ правильный:

Any charge has to be dissipated.
42

Which of the following describes one of the main reasons for having a switching plan drawn up and approved on high voltage ships?

Ваш ответ правильный:

To ensure no essential equipment is accidently disconnected.
43

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?

Ваш ответ правильный:

Sulphur hexafluoride (SF6).
44

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?

Ваш ответ правильный:

Whether they are HV aware.
45

Which of the following best describes the basic principle for deciding where protective devices should be positioned within an electrical network?

Правильный ответ:

Anywhere where they will prevent damage or harm while maintaining electrical supply to as much of the network as possible.

Ваш ответ:

On the high voltage side of every point where the circuit voltage changes.
46

Which one of the following best describes the difference between an Authorised Person (AP) and a Senior Authorised Person (SAP)?

Ваш ответ правильный:

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.
47

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?

Правильный ответ:

They must have sufficient technical knowledge or experience to enable them to avoid danger.

Ваш ответ:

They must be certified by the company.
48

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?

Правильный ответ:

We can break the HV arc more quickly if there is no air to ionise.

Ваш ответ:

The special material used in HV breaker contacts can corrode in air.
49

Which one of the following best describes the resistance reading of the human body when tested at different voltages?

Правильный ответ:

An increase in test voltage causes a reduction in the body’s resistance.

Ваш ответ:

The body’s resistance is more or less constant at different test voltages.
50

Which one of the following best describes what is defined as “High Voltage” with reference to ship’s electrical system?

Правильный ответ:

AC electricity above 1 000 Volts.

Ваш ответ:

AC electricity above 3 kiloVolts.
51

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?

Правильный ответ:

The Authorised Person.

Ваш ответ:

The Head of the personnel department.
52

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?

Правильный ответ:

The person given overall responsibility for carrying out the work should keep all the keys.

Ваш ответ:

The Authorised Person should keep all the keys.
53

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?

Правильный ответ:

One person must be made responsible for overseeing the work and sign the permit.

Ваш ответ:

All officers should sign the permit, ratings do not need to sign.
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