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HV exit exam questions and answers — Set 9 — High Voltage Safety Officer & Switchgear Operations

Set 9 of the High Voltage Safety Officer & Switchgear Operations (HV) exit exam bank — 30 of 428 questions, with the correct option marked and a one-line explanation for every one. Read it end to end, jump to a single set, or search it — then sit the same bank as a timed paper. The real DG Shipping exit exam is 30 marks with 15 to pass.

These are the bank's original groupings. Practising deals the whole bank out again every time you reshuffle, so a practice “Set 3” is a different 30 questions each time — the set numbers below are the source file's, and are only used here so the key stays navigable. Options are listed in their original order with fixed letters; when you practise, those move too.

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Set 9 — 30 HV exit exam questions with answers

1. Corona effect can be identified by

  • A. Bushy sparks
  • B. A faint violet glow
  • C. Red light
  • D. Arcing between conductors and earth
Answer: B — A faint violet glow
When the air around a conductor is ionised by a high electric field, it emits a faint violet glow, most visible at night. This, along with hissing and ozone, identifies corona.

2. Rubber insulating gloves used for electrical protection must be electrically retested every

  • A. 3 months
  • B. 6 months
  • C. 12 months
  • D. Never
Answer: B — 6 months
Rubber insulating gloves must be electrically tested before first issue and at intervals not exceeding 6 months (OSHA 1910.137 / IEC 60903 practice), and air-tested and inspected before each use.

3. One of the generally recognised hazards of electrical work is ____.

  • A. Arc flash
  • B. Cuts
  • C. Falls
  • D. Concussion
Answer: A — Arc flash
Electrical work hazards are electric shock, arc flash and arc blast. An arc flash releases intense heat and light that can cause severe burns, which is why arc-rated PPE and approach boundaries are used.

4. Which is the 'can't let go' range of current flow through the body?

  • A. 3-9 mA
  • B. 9-25 mA
  • C. 25-60 mA
  • D. 1-3 mA
Answer: B — 9-25 mA
Around 9 to 25 mA, muscles contract involuntarily and the person may be unable to release the conductor. Lower currents are perceptible but releasable; higher currents risk respiratory paralysis and ventricular fibrillation.

5. The secondary of a current transformer must never be ____ while energised.

  • A. Earthed
  • B. Opened
  • C. Examined
  • D. Shorted
Answer: B — Opened
With an open secondary, there is no opposing secondary ampere-turns, so the primary current drives the core into saturation, producing dangerously high secondary voltage and overheating. CT secondaries are shorted before removing instruments.

6. The minimum allowable working space in front of electrical equipment is ____ inches deep.

  • A. 36
  • B. 48
  • C. 24
  • D. 30
Answer: A — 36
The US National Electrical Code (NEC 110.26) requires a minimum working space depth of 36 inches (about 0.9 m) in front of equipment likely to be examined or serviced while energised.

7. Crossing the Prohibited Approach Boundary is considered the same as making ____.

  • A. Insulation
  • B. Confluence
  • C. Contact
  • D. Isolation
Answer: C — Contact
Under NFPA 70E, crossing the prohibited approach boundary is treated as making contact with exposed energised parts, requiring the same protection and justification as direct contact.

8. Work performed on an electrical system within reaching distance of energised components is ____ work.

  • A. Energised
  • B. Essential
  • C. Safe
  • D. Unavoidable
Answer: A — Energised
Any work within reach of exposed energised parts is treated as energised work, requiring justification, an energised work permit, appropriate PPE and observance of approach boundaries.

9. A safety electrical one-line diagram should be used to ____ all sources of electrical energy.

  • A. Identify
  • B. Castigate
  • C. Evaluate
  • D. Modify
Answer: A — Identify
An up-to-date single line diagram shows every source of supply, including generators, shore connection and back-feeds, so that all sources can be identified and isolated before work begins.

10. One of the main functions of personal protective grounds is to provide a ____ impedance path for a short circuit.

  • A. High
  • B. Low
  • C. Smooth
  • D. Adequate
Answer: B — Low
Temporary protective earths bond and short the isolated conductors so that any accidental re-energisation produces a low impedance fault path, causing protective devices to operate quickly and limiting voltage at the work site.

11. For voltage measurement, the gap which gives the highest accuracy is the

  • A. Sphere gap
  • B. Field gap
  • C. Rod gap
  • D. None of these
Answer: A — Sphere gap
Sphere gaps give a nearly uniform field and consistent breakdown values, with standard calibration tables, so they are the accepted reference for peak voltage measurement with about ±3% accuracy.

12. The most commonly used insulating material for low and medium voltage cables is

  • A. Polyethylene
  • B. Porcelain
  • C. PVC
  • D. Vulcanised rubber
Answer: C — PVC
PVC is cheap, flexible, flame-retardant and durable, making it the most widely used insulation and sheathing for low and medium voltage cables. Porcelain is used for rigid insulators, not cables.

13. In an alternator, when the load power factor is unity, the armature reaction flux is

  • A. Demagnetising
  • B. Cross-magnetising
  • C. Reduced to zero
  • D. Of square wave form
Answer: B — Cross-magnetising
At unity power factor the armature current is in phase with the EMF, so the armature flux acts at right angles to the main field. This cross-magnetising effect distorts the field rather than weakening or strengthening it.

14. ____ are used for resilient flooring and walkways in front of high voltage panels.

  • A. Insulation gloves
  • B. Insulation mats
  • C. Insulation tapes
  • D. Insulation helmets
Answer: B — Insulation mats
Rubber insulating mats are laid in front of switchboards and HV panels to provide an insulated, resilient standing surface, reducing shock risk to personnel operating or working on the equipment.

15. The electric field strength at which breakdown occurs in a material is called its

  • A. Breakdown voltage
  • B. Dielectric strength
  • C. Tri-electric strength
  • D. Permittivity
Answer: B — Dielectric strength
Dielectric strength is the maximum electric field, usually expressed in kV/mm, that an insulating material can withstand before breakdown. Breakdown voltage depends on thickness, whereas dielectric strength is a material property.

16. Arc interruption in an AC circuit breaker takes place at

  • A. Zero voltage
  • B. Zero current
  • C. High current
  • D. High voltage
Answer: B — Zero current
In AC breakers the arc is extinguished at a natural current zero, when energy input to the arc is minimal. The breaker must then build dielectric strength faster than the restriking voltage rises.

17. An MCB protects a circuit from

  • A. Short circuit
  • B. Overload only
  • C. Both short circuit and overload
  • D. None of the above
Answer: C — Both short circuit and overload
A miniature circuit breaker has a thermal bimetal element for overload protection and a magnetic trip coil for instantaneous short-circuit protection.

18. Surge voltages originate in power systems due to

  • A. Lightning
  • B. Switching operations
  • C. Faults
  • D. Any of the above
Answer: D — Any of the above
Transient overvoltages arise from external causes such as lightning and internal causes such as switching operations, arcing faults and resonance. All must be considered in insulation coordination.

19. In an actual transformer, the iron loss remains practically constant from no load to full load because

  • A. The transformation ratio remains constant
  • B. The permeability of the core remains constant
  • C. The core flux remains practically constant
  • D. The primary voltage remains constant
Answer: C — The core flux remains practically constant
Iron losses (hysteresis and eddy current) depend on core flux density and frequency. Since supply voltage and frequency are constant, the mutual flux stays practically constant at all loads, so iron loss is constant.

20. An alternator is said to be over-excited when it is operating at

  • A. Unity power factor
  • B. Leading power factor
  • C. Lagging power factor
  • D. Zero power factor only
Answer: C — Lagging power factor
An over-excited alternator generates EMF greater than terminal voltage and supplies lagging reactive power to the system, i.e. it operates at a lagging power factor. An under-excited alternator works at a leading power factor.

21. Electrical injuries are commonly caused by

  • A. Unsafe equipment or installations
  • B. An unsafe environment
  • C. Unsafe work practices
  • D. All of the above
Answer: D — All of the above
Electrical accidents typically result from defective equipment or installations, unsafe environments such as wet or confined spaces, and unsafe work practices like working live without isolation. Controls must address all three.

22. What safety measures are to be followed while working on high voltage systems on ships?

  • A. Observing clearance distances for the voltage at which the qualified person will work
  • B. Proper precautionary work techniques
  • C. Proper use of PPE
  • D. All of the above
Answer: D — All of the above
Safe HV work on board requires observing minimum approach distances, following a permit-to-work with isolation, proving dead and earthing, and wearing appropriate PPE, as required by company SMS and STCW HV training.

23. In a circuit breaker, ionisation is facilitated by

  • A. Increase in field strength
  • B. Increase in mean free path
  • C. High temperature of the surrounding medium
  • D. All of the above
Answer: D — All of the above
Higher field strength and longer mean free path let electrons gain enough energy to ionise gas molecules on collision, while high temperature causes thermal ionisation. All three promote ionisation and sustain the arc.

24. Which of the following is the best conductor of electricity?

  • A. Copper
  • B. Aluminium
  • C. Silver
  • D. Iron
Answer: C — Silver
Silver has the lowest resistivity of all metals, slightly lower than copper. Copper is used more widely only because silver is far more expensive.

25. For liquid-cooled static converters, which monitoring arrangements shall be provided?

  • A. Stand-by start alarm of coolant pumps
  • B. Coolant conductivity
  • C. Coolant temperature
  • D. All of the above
Answer: D — All of the above
Classification rules require liquid-cooled converters to have monitoring of coolant flow and pump changeover, coolant temperature and coolant conductivity, since high conductivity could cause leakage currents and flashover.

26. In an induction motor, the rotor runs at a speed

  • A. Equal to the speed of the stator field
  • B. Lower than the speed of the stator field
  • C. Higher than the speed of the stator field
  • D. Having no relation with the speed of the stator field
Answer: B — Lower than the speed of the stator field
Torque in an induction motor depends on relative motion between the rotating field and rotor conductors to induce rotor current. The rotor therefore always runs slightly below synchronous speed; the difference is called slip.

27. When two diesel generator sets are running in parallel during your engine room watch, what does it simply mean?

  • A. That both generators have the same voltage and the same frequency
  • B. That both generators have the same kW load, the same kVAR load and the same current
  • C. That both diesels are running at the same speed
  • D. That both generators share exactly 50% of the active load in kW
Answer: A — That both generators have the same voltage and the same frequency
Generators connected in parallel to the same busbar must have the same terminal voltage and frequency. Load sharing in kW and kVAR depends on governor and AVR settings and need not be equal, and engines may differ in speed if pole numbers differ.

28. Alternating current power is transmitted at high voltage

  • A. To safeguard against pilferage
  • B. To minimise transmission losses
  • C. To reduce cost of generation
  • D. To make the system more reliable
Answer: B — To minimise transmission losses
For a given power, raising the voltage reduces the current, and since copper loss is proportional to current squared, losses and conductor size are greatly reduced. This is also why large ships adopt HV distribution.

29. What are the hazards of arc flash?

  • A. Sudden release of large amounts of heat and light energy at the point of the arc
  • B. Serious, even fatal, injuries to workers ten feet or more from the arc
  • C. Permanent damage to equipment
  • D. All of the above
Answer: D — All of the above
An arc flash releases intense heat, light, pressure and molten metal. It can cause fatal burns at considerable distance, blast injuries and permanent equipment damage, which is why arc flash boundaries and arc-rated PPE are specified.

30. Where procedures involve removal of circuit main earths for testing under a sanction-for-test, the earths are secured with working locks. The keys to these locks will be

  • A. Retained by the duty authorised person (HV), who will remove and replace the earths as required
  • B. Retained by the chief engineer
  • C. Retained by the electro-technical officer
  • D. Kept in the safety locker
Answer: A — Retained by the duty authorised person (HV), who will remove and replace the earths as required
Under HV safety rules, earthing devices locked under a permit or sanction-for-test remain under the control of the authorised person, who personally removes and replaces earths as testing requires, ensuring no one else can alter the safety arrangements.

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