Electric motors are used aboard ship to operate guns, winches, elevators, compressors, pumps, ventilation systems, and other auxiliary machinery and equipment. There are many reasons for using electric motors: they are safe, convenient, easily controlled, and easily supplied with power.

A motor changes electrical energy into mechanical energy. There are important reasons for changing mechanical energy to electrical energy and back again to mechanical energy. One reason is that electric cables can be led through decks and bulkheads with less danger to

Figure 12-10.-Switchboard indicating meters.

watertight integrity than steam pipes or mechanical shafts. Another reason is that damage to a steam line can cause steam to escape, resulting in personnel injury. If an electric cable is used and a fault occurs, the circuit breaker protecting the cable opens automatically. The ac motor is used extensively by the Navy because it is smaller and requires less maintenance than the do motor.

Most ac motors used aboard ship use threephase, 60-Hz, 450-volt power. Although most ac motors operate at a single speed, some motors, such as the prime movers for fuel oil pumps, lube oil pumps, and ventilation fan motors, have two operating speeds.

MOTOR CONTROLLERS

Controlling devices are used to start, stop, speed up, or slow down motors. In general, these controllers are standard equipment aboard ship and are operated either manually, semiautomatically, or automatically. They are dripproof and shock resistant. In some installations, the controllers are operated by remote control, with the switch at a convenient location.

Motor control devices (controllers, master switches, and electric brakes) protect the equipment to which they are connected. Controllers provide protective and governing features for every type of shipboard auxiliary. Various types of master switches are used to govern the controllers. Electric brakes are used to bring a load to rest, or to hold it at rest, when electric power to the motor is cut off. Aboard ship, electric brakes are used primarily on hoisting and lowering equipment such as cranes, winches, and windlasses.

Most controllers function simply to start or to stop auxiliary machinery; but, some controllers also provide for reversal of direction or multispeed operation. Motor controllers, sometimes called starters, have overload protective devices to prevent burning out the motor. Most controllers cut out automatically when the electric power fails, and they have to be restarted manually. This type of motor controller is called a low-voltage protection (LVP) controller. Another type of motor controller, which is used primarily with vital loads, is called a low-voltage release (LVR) controller. The LVR controller disconnects the motor from the supply voltage if the supply voltage drops below a predetermined level. When the supply voltage returns to a normal level, the LVR controller automatically restarts the motor.

BATTERIES

Aboard ship, batteries are one of the sources for emergency and portable power. Storage batteries are used to power emergency equipment, ship's boats, and forklifts. The storage battery is also used as a source of energy for emergency diesel generators, gyrocompasses, and emergency radios.

You should be familiar with safety precautions you must follow when you work around batteries. Batteries must be protected from salt water, which can mix with the electrolyte (the acid solution) and release poisonous gases. Salt water in the electrolyte also sets up a chemical reaction that will ruin the battery. If a battery is exposed to salt water, notify the electric shop immediately.

Storage batteries, when being charged, give off a certain amount of hydrogen gas. Battery compartments should be well ventilated to discharge this gas to the atmosphere.

WARNING

Flames or sparks of any kind, including lighted cigarettes, should never be allowed in the vicinity of any storage battery that is being charged.

When the battery is in a low or discharged state and does not perform properly, you should notify the Electrician's Mate (EM).