46 CFR § 111.12-11 - Generator protection.

§ 111.12-11 Generator protection.

(a) Applicability. This section applies to each generator except a propulsion generator.

(b) General. Each ship's service generator and emergency generator must be protected by an individual, tripfree, air circuit breaker whose tripping characteristics can be set or adjusted to closely match the generator capabilities and meet the coordination requirements of Subpart 111.51. Each circuit breaker must contain the trips required by this section.

(c) Type of trips. A circuit breaker for a generator must:

(1) Open upon the shutting down of the prime mover;

(2) Have longtime overcurrent trips or relays set as necessary to coordinate with the trip settings of the feeder circuit breakers; and

(3) Not have an instantaneous trip with the exception that an instantaneous trip is required if:

(i) Three or more alternating-current generators can be paralleled; or

(ii) The circuit breaker is for a direct current generator.

(d) Setting of longtime overcurrent trips. The pickup setting of the longtime overcurrent trip of a generator circuit breaker must not be larger than:

(1) 115 percent of the generator rating for a continuous rated machine; or

(2) 115 percent of the overload rating for a machine with a 2-hour or greater overload rating.

(e) Setting of instantaneous trips. The instantaneous trip of a generator circuit breaker must be set above, but as close as practicable to, the maximum asymmetrical short circuit available from any one of the generators that can be paralleled.

(f) Reverse-power and reverse-current trips. Each generator arranged for parallel operation must have reverse-power or reverse-current trips.

(g) Location. A ship's service generator overcurrent protective device must be on the ship's service generator switchboard. The generator and its switchboard must be in the same space. (For the purposes of this section, the following are not considered separate from the machinery space: (1) A control room that is inside of the machinery casing and (2) a dedicated switch-gear and semiconductor rectifier (SCR) compartment on a mobile offshore drilling unit that is separate from but directly adjacent to and on the same level as the generator room).

(h) Three-wire, single-phase and four-wire, three-phase generators. There must be circuit breaker poles for each generator lead, except in the neutral lead.

(i) Three-wire, direct-current generators. Each three-wire, direct current generator must meet the following requirements:

(1) Circuit breaker poles. There must be separate circuit breaker poles for the positive and negative leads, and, unless the main poles provide protection, for each equalizer lead. If there are equalizer poles for a three-wire generator, each overload trip must be of the “Algebraic” type. If there is a neutral pole in the generator circuit breaker, there must not be an overload trip element for the neutral pole. In this case, there must be a neutral overcurrent relay and alarm system that is set to function at a current value not more than the neutral rating.

(2) Equalizer buses. For each three-wire generator, the circuit breaker must protect against a short circuit on the equalizer bus.

(j) Circuit breaker reclosing. Generator circuit breakers must not automatically close after tripping.

[CGD 74-125A, 47 FR 15236, Apr. 8, 1982, as amended by CGD 81-030, 53 FR 17847, May 18, 1988; CGD 94-108, 61 FR 28277, June 4, 1996; 62 FR 23908, May 1, 1997]