Answers - Engine Electrical Systems


1. b
By replacing the slip rings of a basic AC generator with two half-cylinders, called a commutator, DC current is obtained. As the generator's armature rotates, the commutator elements act as a switch causing the current to flow in the same direction through the external circuit.

2. c
Because the windings in a series motor have such a low resistance, it is normal for these motors to draw a large amount when started. However, when this starting current passes through both the field and armature windings, a high starting torque is produced.

3. c
The stationary field strength in a direct-current generator is varied according to the load requirements. For example, as the load increases, the voltage regulator automatically increases the field current to allow the generator to provide the required current load.

4. b
A series-wound motor produces the highest torque of any of the motors listed. Furthermore, a typical starter motor is operated by a 12- or 24-volt direct current battery. Therefore, the most common starter found on reciprocating engines is a direct current series-wound motor.

5. c
The output frequency of an alternator depends on the rotational speed of the rotor and the number of poles. The faster the rotor turns, the higher the frequency generated. By the same token, the more poles on a rotor, the higher the frequency for any given speed.


6. c
When an armature in a motor rotates in a magnetic field, a voltage is induced into the windings that opposes the applied voltage. This back, or counter electromotive force (EMF) increases with motor speed and, therefore, reduces the current flowing through the armature.

7. c
Components that utilize alternators (AC generators) as a source for power, require a specific frequency or hertz output to function properly. One way to ensure that an alternator produces a specified frequency is to have the alternator driven by a constant speed drive (CSD) unit.

8. a
A rough or pitted commutator should be smoothed using very fine sandpaper, such as 000, and then cleaned and polished with a clean, dry cloth.

9. b
A generator master switch is provided in most aircraft so that a malfunctioning generator may be disconnected from the aircraft electrical system to prevent damage to the generator or to the rest of the system. Operation of this switch deactivates the voltage coil in the voltage regulator, resulting in generator output being reduced to residual voltage.

10. c
The opening and closing of the points in a vibrating type voltage regulator controls the generator output. When the points are open, generator output decreases and when the points are closed, generator output increases. Therefore, if the points stick closed, the generator's output will increase to its maximum.

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