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.
ETO Power Generation & Distribution 1
What is the typical operating voltage for main power distribution on large commercial vessels?