You are in the planning stages of setting the instantaneous trip of a ship's service generator circuit breaker. According to 46 CFR, Subchapter J (Electrical Engineering), what statement is true regarding the criteria for the instantaneous trip set point, assuming the generator is capable of being paralleled?
• 46 CFR Subchapter J requirements for generator circuit breaker protection on ships • Meaning of instantaneous trip versus long-time/short-time overcurrent settings • Relationship between available short-circuit current and protective device trip settings
• Think about what instantaneous trip protection is designed to prevent when a generator is paralleled to a system with high fault current levels. • Consider whether you want the breaker to trip during normal inrush or paralleling transients, or only during true fault conditions. • Ask yourself: should the trip setting be chosen so that it reliably operates for a fault that reaches the maximum asymmetrical short-circuit current, or so that it stays just clear of it?
• Verify in 46 CFR Subchapter J that the instantaneous trip must coordinate with the generator’s maximum short-circuit current capability. • Check whether the regulation talks about setting the trip above or below the available asymmetrical short-circuit current. • Confirm that the intent is to protect the generator and system while avoiding nuisance trips during normal operation and paralleling.
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