Basic Circuit Components

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHAPTER NINE

WORKBOOK

902.

ELECTRICAL POWER SUPPLY SYSTEM

The electrical power supply system consists of a nominal 28-VDC system and a 26-volt/115-

VAC inverter system. The DC system is comprised of a battery and an engine-operated

generator. On the ground, the DC system can be powered by an external power unit. The AC

power is provided by two inverters which change DC power to AC power. Control of the

electrical system is provided through various circuit breakers, relays, buses, and switches.

903.

BASIC CIRCUIT COMPONENTS

A circuit breaker protects an electrical circuit from overload. It is constructed of a bi-metallic

strip with each metal having a different expansion rate when exposed to heat. Should a piece of

electrical equipment malfunction causing the circuit to overheat, the bi-metallic strip bends and

causes the circuit breaker to "pop," thereby creating an "open" circuit and interrupting electrical

power to the faulty equipment.

A relay is used to control a large amount of current flow with a small amount of current flow.

Activated by a remotely controlled switch, it allows a small amount of current flow to the relay

electromagnetic coil. The relay "closes" and provides a complete circuit to the system component

requiring high current (for example, the engine starter). Relays, therefore, allow the use of small

switches in the cockpit to control large electrical loads. Interruption of current to the relay

"opens" the relay and current flow to the electrical load ceases.

A bus is an electrical power distribution point. A bus can receive electrical power from the

battery, generator, external power unit, or inverters. It then distributes the electrical power to

various electrical loads (i.e., lights, motors, instruments, etc).

904.

DC POWER SYSTEM

The DC power is supplied by the battery, the generator, or an external power unit. Controls for

the DC system are located on the electrical control panel on the right console in both cockpits.

ELECTRICAL POWER SYSTEMS 9-3