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HV exit exam questions and answers — Set 3

Set 3 of the High Voltage Safety Officer & Switchgear Operations (HV) exit exam bank — 30 of 193 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 3 — 30 HV exit exam questions with answers

1. Which document contains the shipyard's description of operations regarding the vessel's High Voltage (HV) equipment?

  • A. Preliminary operation manual
  • B. High voltage operation manual
  • C. Performance manual
  • D. Equipment manual
Answer: A — Preliminary operation manual
The Preliminary Operation Manual supplied by the shipyard provides the initial operational philosophy, system architecture, and operating parameters for the vessel's high-voltage equipment.

2. A low voltage protection circuit is used in electric motor starting equipment to:

  • A. Trip circuit contactor when the motor over-speeds due to low voltage
  • B. Trip circuit contactor when the motor develops short circuit due to low voltage
  • C. Allow the motor to restart automatically on restoration of voltage without manual resetting
  • D. Prevent motor from restarting automatically upon restoration of supply voltage
Answer: D — Prevent motor from restarting automatically upon restoration of supply voltage
Under-voltage (low voltage) protection prevents unexpected automatic restarting of motors upon voltage restoration, which protects personnel from mechanical injury and the electrical network from excessive starting surges.

3. In air blast circuit breakers, the compressed air pressure used for arc quenching is in the order of:

  • A. 100 mm Hg
  • B. 1 kg/cm²
  • C. 20 to 30 kg/cm²
  • D. 200 to 300 kg/cm²
Answer: C — 20 to 30 kg/cm²
Air blast circuit breakers (ABCB) utilize high-pressure dry air at approximately 20 to 30 kg/cm² (2 to 3 MPa / 20 to 30 bar) directed across the contacts to rapidly cool and deionize the arc.

4. What is the primary means by which an electrical maintenance worker is protected from electrical hazards while performing work on an electrical circuit?

  • A. Shutting down the necessary equipment only
  • B. Using personal protective equipment (PPE) alone
  • C. Posting safety warning signs
  • D. Performing a lockout / tagout (LOTO) and grounding procedure
Answer: D — Performing a lockout / tagout (LOTO) and grounding procedure
Lockout/Tagout (LOTO) coupled with proving dead and applying safety earths provides positive isolation, preventing accidental re-energization of circuits during maintenance.

5. What is the Polarisation Index (PI) in insulation resistance testing?

  • A. Ratio of 10-minute insulation resistance to 1-minute insulation resistance
  • B. Ratio of 1-minute insulation resistance to 10-minute insulation resistance
  • C. Ratio of 5-minute insulation resistance to 25-minute insulation resistance
  • D. Ratio of test voltage to leakage current after 1 minute
Answer: A — Ratio of 10-minute insulation resistance to 1-minute insulation resistance
Polarisation Index (PI) is defined as the ratio of insulation resistance measured at 10 minutes to the insulation resistance measured at 1 minute (R10 / R1). A PI value above 2.0 indicates clean, dry insulation.

6. The direction of mechanical force experienced by a current-carrying conductor placed in a magnetic field is determined by:

  • A. Fleming's left-hand rule
  • B. Fleming's right-hand rule
  • C. Helix rule
  • D. Corkscrew rule
Answer: A — Fleming's left-hand rule
Fleming's left-hand rule is used for electric motors and determining mechanical force on a conductor (Thumb = Force/Motion, Forefinger = Field, Middle finger = Current).

7. Which of the following insulating media can be used in sphere gaps and high-voltage test setups?

  • A. Liquid insulation (e.g., transformer oil)
  • B. Solid insulation (e.g., polyester, resin-bonded paper)
  • C. Gas insulation (e.g., SF6, N2, CO2, CCl2F2)
  • D. Any of the above
Answer: D — Any of the above
High voltage insulation testing and arc gaps can employ gaseous (air, SF6, N2), liquid (dielectric mineral oils), or solid insulating barriers depending on application requirements.

8. Cartridge and rewireable fuse protection in general distribution circuits is typically used for continuous current ratings up to:

  • A. 10 A
  • B. 20 A
  • C. 50 A
  • D. 100 A
Answer: D — 100 A
Standard general-purpose distribution rewireable/cartridge fuse holders are commonly rated up to 100 A, beyond which High Rupturing Capacity (HRC) bolted fuses or circuit breakers are preferred.

9. Which of the following circuit breakers provides high operating reliability and minimal maintenance requirements?

  • A. Air blast circuit breaker
  • B. SF6 gas circuit breaker
  • C. Vacuum circuit breaker
  • D. Bulk oil circuit breaker
Answer: B — SF6 gas circuit breaker
Sulphur Hexafluoride (SF6) circuit breakers operate in a sealed, non-corrosive environment with high dielectric regeneration, resulting in minimal contact erosion and extended maintenance intervals.

10. Which type of work procedure involves electrical installations that are completely de-energized, isolated, proven dead, and earthed?

  • A. Live working
  • B. Dead working
  • C. Working in the vicinity of live parts
  • D. Hot line working
Answer: B — Dead working
Dead working is defined as work carried out on electrical equipment or installations that are isolated from all sources of supply, proven dead, locked out, and earthed.

11. Following the 2010 Manila Amendments, which regulatory body made High Voltage (HV) system training mandatory for senior engineering staff on vessels with installations above 1,000 V?

  • A. SOLAS
  • B. STCW
  • C. MARPOL
  • D. ISPS
Answer: B — STCW
The STCW (Standards of Training, Certification and Watchkeeping) 2010 Manila Amendments introduced mandatory HV training and certification for Electro-Technical Officers (ETO) and Management Level Marine Engineers (A-III/1, A-III/2).

12. Air blast circuit breakers are particularly preferred for applications requiring:

  • A. Short duty only
  • B. Intermittent duty only
  • C. Repeated frequent duty
  • D. DC traction sub-stations only
Answer: C — Repeated frequent duty
Because compressed air is continually replenished and leaves no chemical breakdown residues, air blast circuit breakers are well-suited for repeated duty and fast arc clearing.

13. High-voltage alternating current (AC) arc interruption is primarily achieved through:

  • A. High resistance interruption
  • B. Low resistance / zero-current interruption
  • C. Both A and B
  • D. Magnetic attraction only
Answer: C — Both A and B
Arc extinction can be achieved by either increasing arc resistance (lengthening, cooling, splitting) or exploiting natural AC zero-current crossing (low resistance method) to deionize the contact gap.

14. The desired protective tripping operation of a power circuit breaker under fault conditions is:

  • A. Manually initiated
  • B. Automatically initiated by protective relays
  • C. Warning buzzer alarm only
  • D. Delayed until watchkeeper reset
Answer: B — Automatically initiated by protective relays
Circuit breakers are designed to trip automatically and instantaneously upon receiving a trip command from associated protective relays (e.g., overcurrent, short circuit, differential).

15. Lower voltage systems supplied through step-down transformers from high-voltage systems must be protected against overvoltages. This is achieved by:

  • A. Direct earthing of the lower voltage system neutral
  • B. Appropriate neutral voltage limiters (surge arresters / spark gaps)
  • C. Both A and B
  • D. Increasing cable insulation thickness only
Answer: C — Both A and B
Protection against HV-to-LV breakdown in transformers is achieved by earthing the secondary neutral (solidly or via impedance) or installing neutral voltage limiters (surge arresters/spark gaps).

16. In the arc extinction process using the high resistance method:

  • A. Arc resistance is decreased with time
  • B. Arc resistance is increased with time
  • C. Arc resistance remains strictly constant
  • D. Arc resistance is reduced to zero
Answer: B — Arc resistance is increased with time
The high resistance method progressively increases the arc resistance by lengthening, cooling, and splitting the arc until the system voltage is insufficient to maintain the arc.

17. On high-voltage positive polarity conductors at elevated pressures, corona discharge visually appears as a:

  • A. Uniform bluish-white glowing sheath
  • B. Reddish glowing spot
  • C. Uniform greenish spot
  • D. Yellow pulsating flame
Answer: A — Uniform bluish-white glowing sheath
Positive corona produces a smooth, uniform bluish-violet/white glow around the conductor surface, whereas negative corona forms concentrated reddish or purplish glowing tufts/spots.

18. The heat produced at an electrical contact point owing to current flow is least affected by:

  • A. Temperature of the surrounding medium
  • B. Contact resistance
  • C. Magnitude of electric current flowing
  • D. Duration of current flow
Answer: A — Temperature of the surrounding medium
Heat generated at contact points is determined by Joule's Law (Q = I²·R·t). Surrounding ambient temperature has minimal direct influence on the heat generation rate compared to I, R, and t.

19. When procedures involve the temporary removal of circuit main earths under a Sanction-to-Test, the earths are secured with working locks. The keys to these locks are:

  • A. Retained by the Authorised Person (HV) who removes and replaces the earth as requested
  • B. Retained by the Chief Engineer
  • C. Retained by the Electro-Technical Officer only
  • D. Kept inside the engine control room safety locker
Answer: A — Retained by the Authorised Person (HV) who removes and replaces the earth as requested
Under marine HV safety rules, the Authorised Person (HV) who issued the Sanction-to-Test retains custody of safety lock keys and personally oversees the removal and re-application of earths.

20. What are the primary hazards associated with an Arc Flash event in High Voltage systems?

  • A. Sudden release of intense thermal energy, blinding light, and acoustic shockwaves
  • B. Severe burns and blast injuries that can be fatal even several meters away
  • C. Catastrophic structural equipment destruction and vaporized shrapnel
  • D. All of the above
Answer: D — All of the above
An arc flash generates plasma temperatures up to 20,000°C, explosive pressure waves (arc blast), intense light, molten metal shrapnel, and toxic gases, presenting catastrophic risk to personnel and equipment.

21. Electrical alternating current (AC) power is generated and transmitted at high voltage primarily to:

  • A. Safeguard against power theft
  • B. Minimise I²R transmission losses and reduce conductor size
  • C. Reduce the capital cost of generator construction
  • D. Eliminate the need for circuit breakers
Answer: B — Minimise I²R transmission losses and reduce conductor size
Transmitting at higher voltage reduces current for a given power level (P = √3·V·I·cosφ). Lower current drastically reduces transmission line I²R heat losses and copper conductor cross-section requirements.

22. When two diesel generator sets are running smoothly in parallel on the main switchboard during an engine room watch, what does this condition fundamentally imply?

  • A. Both generators have identical terminal voltage, system frequency, and phase sequence
  • B. Both diesels carry identical active kW, reactive kVAr, and line amperage at all times
  • C. Both diesels are operating at varying unsynchronized rotational speeds
  • D. Both generators are operating without voltage regulators
Answer: A — Both generators have identical terminal voltage, system frequency, and phase sequence
Parallel operation requires synchronization: identical terminal voltage, identical frequency, correct phase sequence, and identical phase angle at the moment of breaker closure.

23. In a 3-phase induction motor operating in normal motoring mode, the rotor rotates at a speed that is:

  • A. Equal to the synchronous speed of the stator rotating magnetic field
  • B. Slightly lower than the synchronous speed of the stator field
  • C. Higher than the synchronous speed of the stator field
  • D. Completely unrelated to the stator supply frequency
Answer: B — Slightly lower than the synchronous speed of the stator field
An induction motor requires relative motion (slip) between the rotating stator magnetic field and the rotor conductors to induce rotor current and develop torque. Hence, rotor speed is lower than synchronous speed.

24. For liquid-cooled static frequency converters on electric propulsion vessels, which additional monitoring arrangements must be provided?

  • A. Stand-by coolant pump automatic start / alarm
  • B. Coolant conductivity monitoring (de-ionized water)
  • C. Coolant temperature and flow rate alarms
  • D. All of the above
Answer: D — All of the above
Liquid-cooled marine power converters (drives) require monitoring of deionized water conductivity (preventing arcing), coolant flow, temperature levels, and automatic standby circulation pump cut-in.

25. Which of the following metals has the highest electrical conductivity at room temperature?

  • A. Copper
  • B. Aluminium
  • C. Silver
  • D. Iron
Answer: C — Silver
Silver possesses the highest electrical conductivity of all metals (~6.30 × 10⁷ S/m), followed closely by copper (~5.96 × 10⁷ S/m) and gold (~4.10 × 10⁷ S/m).

26. In a high-voltage circuit breaker, ionization of the contact gap medium is facilitated by:

  • A. Increase in electric field strength across the gap
  • B. Increase in mean free path of electrons
  • C. High temperature of the surrounding dielectric medium
  • D. All of the above
Answer: D — All of the above
Ionization between breaker contacts during contact separation is enhanced by high electric field gradients (voltage stress), thermal excitation at high temperatures, and longer electron mean free paths.

27. If two alternators are operating in parallel synchronism and the excitation voltage of one machine is suddenly increased:

  • A. Both machines will trip instantly
  • B. The over-excited machine will motorize
  • C. Circulating reactive current flows and synchronising torque maintains synchronism
  • D. The system frequency increases proportionally
Answer: C — Circulating reactive current flows and synchronising torque maintains synchronism
Increasing excitation on one alternator increases its generated EMF, driving a circulating lagging reactive current that produces demagnetizing armature reaction and synchronizing torque, preserving synchronism.

28. When a vessel suffers an unexpected total electrical blackout, what should be the watch engineer's initial priority action?

  • A. Notify the Chief Engineer and bridge watch officer immediately while emergency power initiates
  • B. Cancel audible alarms and wait for automation reset
  • C. Start stripping the oily water separator
  • D. Open all high-voltage generator isolators manually
Answer: A — Notify the Chief Engineer and bridge watch officer immediately while emergency power initiates
Upon blackout, immediate notification of the Chief Engineer and Bridge is critical while confirming emergency generator starting and busbar connection, followed by systematic power restoration.

29. What safety precautions must be strictly observed when working on marine High Voltage vessels?

  • A. Observing minimum approach distances corresponding to system voltage
  • B. Employing approved Permit to Work (PTW) and switching procedures
  • C. Using certified high-voltage PPE, face shields, and insulated tools
  • D. All of the above
Answer: D — All of the above
Marine HV safety compliance mandates strict adherence to approach boundaries, written PTW / Sanction-to-Test systems, calibrated HV voltage detectors, earthing sticks, and rated arc-flash PPE.

30. Power loss due to corona discharge on an overhead transmission line is directly proportional to:

  • A. Radius of conductor
  • B. Supply frequency (f + 25)
  • C. Spacing between conductors
  • D. Dielectric constant of air
Answer: B — Supply frequency (f + 25)
According to Peek's formula for corona loss, power loss P is proportional to (f + 25), where f is the system supply frequency.

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