The Terasaki XS250ss XS Series air circuit breaker is a highly versatile and commonly used component in marine power systems, striking an excellent balance between intelligent protection, serviceability, and cost for a 250A circuit.
Here is a detailed overview of its role and significance in marine environments.
Model Designation Breakdown: XS250ss
• XS250: 250 Ampere frame size.
• First 's': Withdrawable or Slide-out version.
• Second 's': Equipped with the standard S-Type Electronic Trip Relay.
In summary, the XS250ss is a 250A, withdrawable air circuit breaker with an intelligent S-Type trip unit and a standard breaking capacity.
Key Features & Marine Significance
1. Withdrawable Design (The First 's'):
◦ Marine Significance: This is a critical feature for operational readiness and safety.
◦ It allows the breaker to be racked between CONNECTED, TEST, and DISCONNECTEDpositions.
◦ This enables safe functional testing of protection relays without powering the load and allows for quick isolation and replacement of the breaker without de-energizing the entire switchboard section. For a vessel at sea, this minimizes downtime for critical systems.
2. S-Type Electronic Trip Unit (The Second 's'):
◦ This is the core of its intelligent protection, providing fully adjustable and selective settings:
■ Long-Time Delay (L): Protects against cable overload.
■ Short-Time Delay (S): Ensures selective coordination. A fault on a final sub-circuit will trip that local breaker first, without disconnecting this feeder and causing a wider blackout.
■ Instantaneous (I): For high-level short-circuits.
■ Ground-Fault (G): Absolutely essential for marine safety. Provides sensitive protection against earth leakage, crucial for preventing electric shock and fire in the humid, conductive environment of a ship.
3. Standard Breaking Capacity:
◦ The "ss" model has a robust standard breaking capacity (e.g., 50kA-65kA at 440V AC). For a 250A feeder breaker located one level downstream from the main distribution, this capacity is often perfectly sufficient, as the available fault current has already been limited by upstream breakers.
4. Marine Environment Durability:
◦ Terasaki breakers are built with corrosion-resistant materials and coatings to withstand salt, moisture, and vibration, making them exceptionally reliable for marine use.
Typical Applications in Marine Power Systems
The XS250ss is ideally suited for protecting important feeder circuits and large individual loads. Common marine applications include:
• Feeder to Sub-Distribution Boards: Supplying power to secondary switchboards for areas like the accommodation block, galley, or workshop.
• Large Motor Protection: Direct protection for significant pumps and motors, such as:
◦ General service pumps
◦ Cooling water pumps
◦ Air conditioning and ventilation fans
◦ Hydraulic power packs
• Auxiliary System Main Feeders: Powering dedicated systems for winches, cranes, or other deck machinery.
• Shore Power Connection: Often used as the ship-side breaker for the shore power connection panel.