ETO Power Generation & Distribution 1 — Questions and Answers
Question 1: What is the typical operating voltage for main power distribution on large commercial vessels?
- 440V AC (Correct answer)
- 120V AC
- 240V AC
- 690V AC
Correct answer: 440V AC
440V AC is the standard main distribution voltage on large commercial vessels, balancing transmission efficiency with manageable safety risks for shipboard systems.
Question 2: What type of alternator is most commonly used in a ship's power generation system?
- Salient pole synchronous generator (Correct answer)
- Squirrel cage induction generator
- Wound rotor induction generator
- Permanent magnet alternator
Correct answer: Salient pole synchronous generator
Salient pole synchronous generators are used on ships because they provide stable voltage and frequency control through adjustable field excitation, essential for reliable shipboard power.
Question 3: What is the primary purpose of a bus tie breaker in a ship's electrical distribution system?
- To connect two separate busbars enabling parallel generator operation (Correct answer)
- To protect individual circuits from overcurrent faults
- To regulate voltage levels on the main switchboard
- To isolate the shore power connection from the vessel
Correct answer: To connect two separate busbars enabling parallel generator operation
A bus tie breaker connects two busbars so generators can operate in parallel, increasing total power capacity and allowing load sharing between machines.
Question 4: Which protection relay prevents a generator from absorbing power from the busbar when operating in parallel?
- Reverse power relay (Correct answer)
- Overcurrent relay
- Earth fault relay
- Under-voltage relay
Correct answer: Reverse power relay
The reverse power relay detects when a generator is consuming power from the busbar instead of supplying it, preventing motoring of the prime mover which could cause mechanical damage.
Question 5: What is the standard frequency used for electrical power generation on US-flagged commercial vessels?
- 60 Hz (Correct answer)
- 50 Hz
- 400 Hz
- 25 Hz
Correct answer: 60 Hz
US-flagged commercial vessels use 60 Hz, consistent with the US shore power standard, while vessels from many European and Asian countries use 50 Hz.
Question 6: What device automatically maintains constant terminal voltage of a synchronous generator as electrical load varies?
- Automatic Voltage Regulator (AVR) (Correct answer)
- Governor
- Power factor controller
- Synchroscope
Correct answer: Automatic Voltage Regulator (AVR)
The Automatic Voltage Regulator (AVR) senses generator output voltage and adjusts field excitation current to maintain constant voltage under varying load conditions.
Question 7: What is the primary function of the governor on a diesel generator set aboard a ship?
- To maintain constant engine speed regardless of load changes (Correct answer)
- To regulate the output voltage of the alternator
- To protect the generator from overcurrent faults
- To synchronize generators before paralleling
Correct answer: To maintain constant engine speed regardless of load changes
The governor controls fuel injection to maintain constant engine speed, and thus electrical frequency, as the electrical load on the generator changes.
