Chapter 7 Section A FAA Questions (Unit 2)

7-2  AMA041

If a generator is equipped with a vibrator type voltage regulator, the actual time the voltage regulator points remain open

A—is controlled by the reverse current cutout relay point clearance.

B—depends on the load carried by the generator.

C—is increased when the external load is greater than the generator output.

7.2. Answer B. JSAT 7A, FGH

The actual time voltage regulator points in a vibrator type voltage regulator remain open is determined by the amount of load being carried by the generator. When the load is great, the voltage drops and the points remain closed longer to allow the voltage to rise. When the load is light, the voltage is high and the points remain closed a very short time.

7-3  AMA041

What is a cause of generator brush arcing?

A—Low spring tension

B—Carbon dust particles

C—Seating brushes with No. 000 sandpaper

7.3. Answer A. JSAT 7A, FGH

Excessive pressure on generator brushes will cause rapid wear, but too little pressure will cause “bouncing” of the brushes which results in arcing and burned and pitted surfaces.

7-5  AMA041

The only practical method of maintaining a constant voltage output from an aircraft generator under varying conditions of speed and load is to vary the

A—strength of the magnetic field.

B—number of conductors in the armature.

C—speed at which the armature rotates.

7.5. Answer A. JSAT 7A, FGH

Efficient operation of electrical equipment in an aircraft depends on a constant voltage supply from the generator. Among the factors which determine the voltage output of a generator, only one, the strength of the magnetic field, can be conveniently controlled.

7-6  AMA041

The pole pieces or shoes used in a DC generator are a part of the

A—armature assembly.

B—field assembly.

C—brush assembly.

7.6. Answer B. JSAT 7A, FGH

In small generators, the frame is made of one piece of iron, while in large generators it is usually made up of two parts bolted together. The frame has high magnetic properties and, together with the pole pieces, forms the major part of the magnetic circuit. The frame and the pole pieces are part of the field assembly.

7-7  AMA022

How many cycles of AC voltage are produced in a six pole alternator of the revolving field type for each revolution of the rotor?

A—Six

B—Four

C—Three

7.7. Answer C. JSAT 7A, FGH

The frequency of the alternator voltage depends upon the speed of rotation of the rotor and the number of poles. When a rotor has rotated through an angle so that two adjacent rotor poles (a north and a south pole) have passed one winding, the voltage induced in that winding will have varied through one complete cycle. Two poles produce one cycle, so six poles will produce three cycles.

7-8  AMA041

If the reverse current cutout relay contact points fail to open after the generator out-put has dropped below battery potential, current will flow through the generator armature

A—opposite the normal direction and through the shunt field in the normal direction.

B—in the normal direction and through the shunt field opposite the normal direction.

C—and the shunt field opposite the normal direction.

7.8. Answer A. JSAT 7A, FGH

The reverse-current cutout is the relay in the voltage regulator which disconnects the battery from the generator. If the battery is not disconnected, it will discharge through the generator armature when the generator voltage falls below that of the battery, thus driving the generator as a motor. When this happens, the current flows opposite the normal direction through the generator armature and in the normal direction through the shunt field.

7-10  AMA041

The commutator of a generator

A—changes direct current produced in the armature into alternating current as it is taken from the armature.

B—changes alternating current produced in the armature into direct current as it is taken from the armature.

C—reverses the current in the field coils at the proper time in order to produce direct current.

7.10. Answer B. JSAT 7A

As the generator rotates, an alternating current is generated within the coils and is converted into DC as it is picked up by the brushes riding on the copper segments of the commutator.

7-14  AMA041

A voltage regulator controls generator output by

A—introducing a resistance in generator- to-battery lead in the event of overload.

B—shorting out field coil in the event of overload.

C—varying current flow to generator field coil.

7.14. Answer C. JSAT 7A, FGH

Among the factors which determine the voltage output of a generator, only one, the strength of the field current, can be conveniently controlled.

7-17  AMA041

What does a rectifier do?

A—Changes direct current into alternating current

B—Reduces voltage

C—Changes alternating current into direct current

7.17. Answer C. JSAT 7A, FGH

A rectifier is a device which transforms alternating current into direct current by limiting or regulating the direction of current flow.

7-18  AMA043

When a diode is checked for an open circuit or a short circuit, it should be

A—checked with a milliamp ammeter.

B—in the circuit.

C—disconnected from the circuit.

7.18. Answer C. JSAT 7A

A semiconductor diode is an electrical check valve and, as such, it allows electron flow in one direction but not in the other. To check for a shorted or an open diode, disconnect it from the circuit and measure its resistance with an ohmmeter set on the R x 1 scale.

7-19  AMA030

Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?

A—Constant current charging of the battery to more than 100 percent of its capacity

B—A high internal resistance condition

C—Excessive current draw from the battery

7-19. Answer C. JSAT 7A

Excessive rates of current flow in a nickel-cadmium battery can cause high temperatures. These temperatures can cause a breakdown of the cellophane-like material that separates the plates in the battery cell. This breakdown creates a short circuit, and current flow increases. The increased current flow will generate additional heat, and cause further breakdown of the separator material. This process is known as vicious-cycling or thermal runaway.

7-20  AMA022

The voltage output of an alternator may be regulated by controlling the

A—voltage output of the DC exciter.

B—speed of the alternator.

C—resistance in the rotor windings.

7-20. Answer A. JSAT 7A, FGH

The output voltage of an alternator is best controlled by regulating the voltage output of the DC exciter, which supplies current to the alternator rotor field.

7-23  AMA041

One advantage of using AC electrical power in aircraft is

A—that AC electrical motors can be reversed while DC motors cannot.

B—that the effective voltage is 1.41 times the maximum instantaneous voltage; therefore, less power input is required.

C—greater ease in stepping the voltage up or down.

7-23. Answer C. JSGT 3D, FGH

Alternating current has largely replaced direct current in commercial power systems for a number of reasons. It can be transmitted over long distances more readily and more economically than direct current, and it can be increased or decreased quite easily by the use of transformers.

7-26  AMA041

The major advantages of alternating current (AC) over direct current (DC) is the fact that its current or voltage can easily be increased or decreased

A—by means of a inverter.

B—by means of a transformer.

C—by means of a rectifier.

7-26. Answer B. JSGT 3D, FGH

Transformers are used to step up or step down the voltage in a system. It is advantageous to transmit AC at a high voltage and then step it down to a power voltage by using a transformer.

7-27  AMA043

When using an ohmmeter to check the continuity of a generator field coil, the coil should

A—show very low resistance if it is a series field coil.

B—be removed from the generator housing.

C—show high resistance when the meter prods are connected to the terminals of the coil.

7-27. Answer A. JSAT 7A

To test the field coil of a generator for continuity, the leads of an ohmmeter are connected to the terminals of the coil. The shunt field coil should show low resistance, approximately 2 to 30 ohms. A series field coil should show practically no resistance because it carries the entire load to the generator and the internal resistance of the generator must be as low as possible.

7-29  AMA041

A voltage regulator controls generator voltage by changing the

A—current in the generator output circuit.

B—resistance of the generator field circuit.

C—resistance in the generator output circuit.

7-29. Answer B. JSAT 7A, FGH

If the current supplied to the field circuit is increased, the voltage output of a generator is increased. By varying the resistance in the field circuit, the voltage regulator controls the current flow and consequently the voltage output.

7-30  AMA041

The most common method of regulating the voltage output of a compound DC generator is to vary the

A—current flowing through the shunt field coils.

B—resistance of the series field circuit.

C—total effective field strength by changing the reluctance of the magnetic circuit.

7-30. Answer A. JSAT 7A, FGH

A compound generator is one that has series field coils and shunt field coils. Regardless of the type of generator, voltage output is always regulated by varying the current flowing through the shunt field coils.

7-31  AMA041

If any one generator in a 24-volt DC system shows low voltage, the most likely cause is

A—a defective reverse current cutout relay.

B—shorted or grounded wiring.

C—an out of adjustment voltage regulator.

7-31. Answer C. JSAT 7A, FGH

A defective reverse current relay would allow battery power to flow in the reverse direction into the generator. Shorted wiring would most likely cause a total cessation of generation. An out of adjustment regulator could result in low voltage.

7-32  AMA041

Aircraft which operate only AC generators (alternators) as a primary source of electrical power normally provide current suitable for battery charging through the use of

A—a stepdown transformer and a rectifier.

B—a dynamotor with a half wave DC output.

C—an inverter and a voltage dropping resistor.

7-32. Answer A. JSAT 7B, FGH

Because batteries produce direct current and therefore need direct current to be charged, aircraft which operate with AC producing alternators generally use a stepdown transformer and a rectifier to produce a suitable direct current for charging the batteries.

7-36  AMA041

How is a shunt wound DC generator connected?

A—One field is shunted across the other.

B—The field and armature are shunted with a capacitor.

C—Both fields are shunted across the armature.

7-36. Answer C. JSAT 7A, FGH

In a shunt-wound DC generator the fields are in parallel with (shunted across) the armature.

7-37  AMA041

The poles of a generator are laminated to

A—increase flux concentration.

B—reduce flux losses.

C—reduce eddy current losses.

7-37. Answer C. JSAT 7A, FGH

The field poles of a generator are bolted to the inside of the frame and form a core on which the field coil windings are mounted. The poles are usually laminated to reduce eddy current losses and serve the same purpose as the iron core of an electromagnet; that is, they concentrate the lines of force produced by the field coils.

7-38  AMA022

What is the frequency of an alternator dependent upon?

A—RPM

B—Voltage

C—Current

7-38. Answer A. JSAT 7A, FGH

The frequency of the alternator voltage depends upon the speed of rotation of the rotor and the number of poles. The faster the speed, the higher the frequency will be; the lower the speed, the lower the frequency becomes. The more poles on the rotor, the higher the frequency will be for a given speed.

7-47  AMA041

A Constant Speed Drive (CSD) unit that is disconnected in flight, due to a malfunction such as overtemperature, may be reconnected

A—manually by the flight crew.

B—automatically if the temperature falls

back into the normal operating range.

C—only on the ground by maintenance personnel.

7-47. Answer C. JSAT 7A

CSD units can be disconnected in flight, in the event of a malfunction, but they can be connected only on the ground.