Electrical fundamentals — DC/AC, motors, distribution

46 CFR §111.50-1

§ 111.50-1 -1 Protection of equipment. Overcurrent protection of electric equipment must meet the following listed subparts: (a) Appliances, subpart 111.77. (b) Generators, subpart 111.12. (c) Motors, motor circuits, and controllers, subpart 111.70. (d) Transformers, subpart 111.20. [CGD 74-125A, 47 FR 15236, Apr. 8, 1982, as amended by USCG-2020-0075, 88 FR 16362, Mar. 16, 2023]

46 CFR §111.51-2

§ 111.51-2 -2 Short-circuit calculations. (a) The available short-circuit current must be computed— (1) From the aggregate contribution of all generators that can simultaneously operate in parallel; (2) From the largest probable motor load; and (3) With a three-phase fault on the load terminals of the protective device. (b) The calculated currents must be used to select suitably rated equipment and to allow the selection and setting of protective devices.

46 CFR §111.51-3

§ 111.51-3 -3 Short-circuit calculations for systems below 1500 kilowatts. The following short-circuit assumptions must be made for a system with an aggregate generating capacity below 1500 kilowatts, unless detailed computations in accordance with § 111.51-4 are submitted: (a) The maximum short-circuit current of a direct current system must be assumed to be 10 times the aggregate normal rated generator currents plus 6 times the aggregate normal rated currents of all motors that may be in operation. (b) The maximum asymmetrical short-circuit current for an alternating current system must be assumed to be 10 times the aggregate normal rated generator currents plus 4 times the aggregate normal rated currents of all motors that may be in operation. (c) The average asymmetrical short circ…

46 CFR §111.70-1

§ 111.70-1 -1 General. (a) Each motor circuit, controller, and protection must meet the requirements of sections 4-8-2/9.17, 4-8-4/9.5 and 4-8-3/5 of ABS Marine Vessel Rules; sections 6-1-7/9.9 and 6-1-7/9.15 of the ABS MOU Rules; or IEC 60092-301:1980 (all three standards incorporated by reference; see 46 CFR 110.10-1), as appropriate, except for the following circuits: (1) Each steering gear motor circuit and protection must meet part 58, subpart 58.25, of this chapter. (2) Each propulsion motor circuit and protection must meet subpart 111.35 of this part. (b) In ungrounded three-phase alternating current systems, only two motor-running protective devices (overload coil or heater type relay within the motor and controller) need be used in any two ungrounded conductors, except when a …

DOE-HDBK-1011 Vol.4 §15-1

Distribution system layout and components An electrical distribution system carries power from the generators to the loads through switchboards, feeders, panels, and branch circuits. It begins at the generator and main switchboard, runs through feeder breakers to distribution panels and load centers, and finally to branch circuits serving individual motors, lighting, and equipment. Systems are arranged as radial (one path to each load — simple and cheap but a fault or outage upstream kills everything downstream), or as more reliable ring/loop and selective (secondary-network) layouts that feed critical buses from two directions so a single failure need not cause a blackout. Shipboard practice provides a normal and an emergency switchboard, with an emergency generator and automatic bus tra…

NAVEDTRA 14104 Ch. 12 — Ac Generators

AC generators are also called alternators. In an ac generator, the field rotates, and the armature is stationary. To avoid confusion, the rotating members of dc generators are called armatures; in ac generators, they are called rotors. The general construction of ac generators is somewhat simpler than that of dc generators. An ac generator, like a dc generator, has magnetic fields and an armature. In a small ac generator the armature revolves, the field is stationary, and no commutator is required. In a large ac generator, the field revolves and the armature is wound on the stationary member or stator. The principal advantages of the revolving-field generators over the revolving-armature generators are two essential parts of a dc generator: are as follows: The yoke and field windings, whic…