Practically all Navy ships are equipped with diesel-driven emergency generators. Diesel engines are particularly suited for this application because of their quick starting ability. Emergency generators furnish power directly to the radio, radar, gunnery, and vital machinery equipment through an emergency switchboard and automatic bus transfer equipment.

The typical shipboard plant consists of two diesel emergency generators, one forward and one aft, in spaces outside engine rooms and firerooms. Each emergency generator has its own switchboard and switching arrangement. This controls the generator and distributes power to certain vital auxiliaries and a minimum number of lighting fixtures in vital spaces.

The capacity of the emergency units varies with the size of the ship. Regardless of the size of the installation, the principle of operation is the same.

You may obtain detailed information concerning the operation of diesel-driven generators from appropriate manufacturers' technical manuals.

MOTOR GENERATORS

Aboard Navy ships, certain weapons, interior communications, and other electronics systems require closely regulated electrical power for proper operation. Special, closely regulated motor generator (MG) sets supply this power (usually 400 Hz). Any given ship has several MGs to provide power to specific loads. These MGs are often of different ratings. The rating of an MG set can be less than 1 kW or as large as 300 kW. MGs can also be used to provide electrical isolation. Isolation is required when certain loads cause distortion of the power and adversely affect the operation of other equipment.

The MG set (fig 12-5) is generally a twobearing unit. (Older units often consist of a separate motor and generator connected together and mounted on a bedplate.) The frame is of onepiece construction. The stationary component parts of the motor and generator are press fit into a welded steel frame. The rotating elements are mounted on a single one-piece shaft. The MG is usually deck mounted horizontally on its own integral feet; however, some specially designed, vertically mounted units are also provided. MGs with 100-kW power and larger are usually cooled by a water-air cooler mounted on top of the MG.

Solid-state voltage and, often, frequency regulating systems are provided on MGs. They are mounted either in a control box, which is directly mounted on the MG for forced-air cooling, or in bulkhead-mounted control panels. The voltage

Figure 12-5.-Motor generator.

Figure 12-6.-30-kW motor generator.

regulator fig. 12-6 controls the voltage output of the generator portion of the MG. This voltage may be either 450 volts or 120 volts, depending on the application. The frequency regulator controls the speed of the MG motor, and therefore the output frequency of the MG. Voltage- and frequency-sensing circuits continuously sample the output of the MG and provide feedback to their respective regulators. By doing this, they maintain the output voltage and frequency at the required level (usually to plus or minus one-half percent of the rated value). A magnetic controller is provided to start and stop the unit. It also protects the MG from operating at continuous overload and removes power to the MG if there is an undervoltage condition.