Question 57 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is D ### Why Option D (Vacuum-break) is Correct: Vacuum circuit breakers (VCBs) are the most common and reliable type of circuit breaker used for medium and high-voltage applications aboard modern ships (typically for systems between 3.3 kV and 15 kV, which covers most high-voltage shipboard practices). 1. **Safety and Environment:** VCBs use a vacuum interrupter to extinguish the arc, which is a highly efficient and contained method. They do not rely on flammable liquids (like oil) or pressurized gases (like SF6, which is used in gas-break breakers and is a potent greenhouse gas), making them safer and more environmentally acceptable for the confined, demanding ship environment. 2. **Maintenance and Reliability:** VCBs require minimal maintenance, have extremely long operational lives, and are highly reliable, critical factors for equipment operating at sea. 3. **Size and Weight:** Compared to older technologies like oil-break or bulk air-break breakers, VCBs are significantly more compact and lighter, a major advantage in ship design where space is at a premium. ### Why the Other Options are Incorrect: **A) Oil-break:** * **Incorrect:** Oil circuit breakers (OCBs) are an older technology. While effective, they are hazardous aboard a ship because they use large volumes of insulating oil, which is flammable and presents a significant fire risk in confined spaces. Modern shipbuilding standards generally prohibit the use of OCBs for new high-voltage installations. **B) Air-break:** * **Incorrect:** This term is ambiguous. Simple atmospheric air-break (or air magnetic) breakers are common for low-voltage systems, but their use for true high-voltage (above 3 kV) interruption is limited on modern ships because they are noisy, produce large amounts of hot ionized gas (making them unsafe in confined spaces), and are generally large and slow compared to vacuum technology. (Note: Pressurized air-blast breakers are used in some high-power land applications, but are complex, require dedicated compressor plants, and are not the standard high-voltage choice for ships.) **C) Gas-break:** * **Incorrect:** "Gas-break" usually refers to Sulfur Hexafluoride (SF6) circuit breakers. While SF6 breakers are extremely efficient and widely used in land-based substations, they are less common than vacuum breakers aboard ships because: * SF6 gas is an extremely potent greenhouse gas (23,500 times worse than CO2). * Managing and recovering the gas in the event of a leak or maintenance procedure is complex in a marine environment. * VCBs generally meet the size, safety, and performance requirements more economically for typical shipboard high-voltage levels.