Electrical Systems Flashcards
To what depth is the mica insulation between the commutator bolts of a dc generator undercut?
Equal to the width of the mica.
The purpose of a rectifier in an electrical system is to change
Alternating current to direct current.
Which of the following copper electrical cable sizes should be selected to replace a No.6 aluminum electrical cable?
No.6
If a generator is equipped with a vibrator-type voltage regulator, the actual time the voltage regulator points remain open
Depends on the load carried by the generator.
Integrated drive generators (IDG) employ a type of high output ac generator that utilizes
A brushless system to produce current.
The voltage in an ac transformer secondary that contains twice as many loops as the primary use will be
Greater and the amperage less than in the primary
Major adjustments on equipment such as regulators, contactors, and inverters are best accomplished outside the airplane on test benches with necessary instruments and equipment. Adjustment procedure should be as outlined by
The equipment manufacturer.
The strength of the core of an electromagnet depends upon the material from which it is constructed and which of the following?
The number of turns of wire in the coil and the amount of current (amperes) passing through the coil.
The poles of a generator are laminated to
Reduce eddy current losses.
The pole pieces or shoes used in a dc generator a part of the
Field assembly.
If any one generator in a 24-volt dc system shows low voltage, the most likely cause is
An out-of-adjustment voltage regulator.
To test generator or motor armature windings for opens,
Place armature in a growler and connect a 110v test light on adjacent segments; light should light.
A battery-generator system provides direct current on installations requiring alternating current from the battery-generator system, it is necessary to have
An inverter
A certain switch is described as a single-pole, double-throw switch (SPDT). The throw of a switch indicates the number of
Circuits each pole can complete through the switch.
How are generators rated?
Amperes at rated voltage
CSD driven generators are usually cooled by
oIl spray
The circuit breaker in the instrument lighting system protects the
Wiring from too much current.
Some electric motors have two sets of field windings wound in opposite directions so that the
Motor can be operated in either direction.
During ground operation, aircraft generator cooling is usually accomplished by
An integral fan.
The primary considerations when selecting electric cable size are
Current-carrying capacity and allowable voltage drop.
What is required when operating two aircraft ac generators in parallel?
Frequency and voltage must both be equal.
The starting current of series-wound dc motor, in passing through both the field and armature windings, produces a
High starting torque.
In installations where the ammeter is in the generator or alternator lead, and the regulator system does not limit the maximum current that the generator or alternator can deliver, the ammeter can be redlined at what percent of the generator or alternator rating?
100
Why are the iron cores of most induction coils laminated?
To reduce the effects of eddy currents.
If it is necessary to use an electrical connector where it may be exposed to moisture, the mechanic should
Use a special moisture-proof type.
What is the color and orientation of the position lights for navigation on civil airplanes?
Left side - red, right side - green, rear aft - white.
Where is the generator rating and performance data located?
Stamped on the generator data plate.
Oil canning of the sides of aluminum or steel electrical junction boxes is considered to be
A shorting hazard.
Circuits that must be operated only in an emergency or whose inadvertent activation could endanger a system frequently employ
Guarded switches.
Electric wiring installed in aircraft without special enclosing means (open wiring) offers the advantages of ease of installation, simple maintenance, and reduced weight. When bundling open wiring, the bundles should
Be limited as to the number of cables to minimize damage from a single electrical fault.
The voltage output of an alternator may be regulated by controlling the
Voltage output of the dc exciter.
Which statement relating to electric wiring is true?
When attaching a terminal to the end of an electric cable, it should be determined that the strength of the cable-to-terminal joint is at least equal to the tensile strength of the cable itself.
What does a rectifier do?
Changes alternating current into direct current.
What protection to wires and cables does conduit provide when used in aircraft installations?
Mechanical
in aircraft electrical systems, automatic reset circuit breakers
Should not be used as circuit-protective devices.
One advantage of using ac electrical power in aircraft is
Greater ease in stepping voltage up or down.
Which type of dc generator is not used an airplane generator?
Series wound
When using an ohmeter to check the continuity of a generator field coil, the coil should
Show very low resistance if it is a series field coil.
What is normally used to bond noncontinuous stainless steel aircraft components?
Copper jumpers.
In an ac circuit with no phase lead or lug, which is true?
Real power equals apparent power.
What is the purpose of the selection of derated switches for known continuous load current applications?
To obtain reasonable switch efficiency and service life.
How many cycles of ac voltage are produced in a six-pole alternator of the revolving-field type for each revolution of the rotor?
Three
The commutator of a generator
Changes alternating current produced in the armature into direct current as it is taken from the armature.
When a diode is checked for an open circuit or a short circuit, it should be
Disconnected from the circuit.
The most common method of attaching a pin or socket to an individual wire in an MS electrical connector is by
Crimping
When necessary during operation, CSD disconnect is usually accomplished by
A switch in the cockpit.
If the reverse current cutout relay contact points fail to open after the generator output has dropped below battery potential, current will flow through the generator armature
Opposite the normal direction and through the shunt field in the normal direction.
One purpose of a growler test is to determine the presence of
A shorted armature.
What is the appropriate method for installing pre-insulated terminal lugs and splices to electric wires?
Using a crimping tool to secure the terminal lug.
What is the ratio of turns between the primary coil winding and the secondary coil winding of a transformer designed to triple its input voltage?
Primary will have one-third as many turns as its secondary.
What should be used to protect wires from chafing when they must pass through bulkheads, fire walls, ribs, etc.?
Suitable grommet.
Electric circuits are protected from overheating by
Fuses
If several long lengths of electrical cable are to be installed in rigid conduit, the possibility of damage to the cable as it is pulled through the conduit will be reduced by
Dusting the cable with powdered soapstone.
When approved, splices may be used to repair manufactured harness or installed wiring. The maximum number of splices permitted between any two connectors is
One
In troubleshooting an electrical circuit, if an ohmeter is properly connected across a circuit component and some value of resistance is read,
The component has continuity and is not open.
The normal rating of electrical switches refers to continuous
Current rating with the contacts closed.
Which of the following are considered circuit-protectuve devices that are used in aircraft-electrical systems?
Circuit breakers, fuses, and current limiters.
When using the voltage drop method of checking circuit resistance, the
Input voltage must be maintained at a constant value.
(Refer to Figure 19.) Upon completion of the landing gear extension cycle, the green light illuminated and the red light remained li. What is the probable cause?
Short in the up limit switch.
Which of the following is most likely to cause thermal runaway in a nickel-cadmium battery?
Excessive current draw from the battery.
A voltage regulator controls generator output by
Varying current flow to generator field coil.
What is a cause of generator brush arcing?
Low spring tension.
A circuit breaker is installed in an aircraft electrical system primarily to protect the
Circuit and should be located as close to the source as possible.
When adding a rheostat to a light circuit to control the light intensity, it should be connected in
Series with the light.
The navigation lights of some aircraft consist of a single circuit controlled by a single switch which has an ON position and an OFF position, with no additional positions possible. This switch is referred to as a
Single-pole, single-throw (SPST), two position switch.
How should a voltmeter be connected?
In parallel with the load
Grounding is electrically connecting a conductive object to the primarily structure. One purpose of grounding is to
Prevent the development of radio frequency potentials.
What is the advantage of a circuit breaker when compared to a fuse?
It is resettable and reusable.
Electrical connectors used in the aircraft assemblies should meet which of the following specifications?
Military specifications (MS)
Which of the following must be accomplished when installing an anticollision light?
Install a switch independent of the position light switch.
The type of electric wire terminals used for most aircraft applications, in addition to providing good current carrying capabilities, are designed primarily
To prevent circuit failure due to terminal disconnection.
A CSD unit drives a generator through the use of
A variable hydraulic pump and hydraulic motor.
A residual voltage is a result of magnetism in the
Field shoes
What is the frequency pf am alternator dependent upon?
RPM
(Refer to Figure 18.) Which of the batteries are connected together incorrectly?
3
The inductor-type inverter output voltage is controlled by the
DC stator field current
Which of the following factors must be taken into consideration when determining the wire size to use for an aircraft installation?
1) Mechanical strength
2) Allowable power loss
3) Ease of installation
4) Resistance of current return path through the aircraft structure.
5) Permissible voltage drop.
6) Current carrying capability of the conductor.
7) Type of load (continuous or intermittent.)
2,5,6,7
Aircraft fuse capacity is rated in
Amperes
A circuit protection device called a current limiter is essentially a slow-blow fuse and is designed to be used in
Heavy power circuits.
What is the minimum bend radius for an electrical wire bundle?
Ten times the outside diameter of the bundle.
The over voltage control automatically protects the generator system when excessive voltage is present by
Opening the shunt filled circuit.
The major advantages of alternating current (AC) over direct current (DC) is the fact that its current and voltage can easily be increased or decreased
By means of transformer.
A series-wound dc electric motor will normally require
More current at low RPM than at high RPM.
The pin section of an AN/MS connector is normally installed on
The ground side of a circuit.
What is the advantage of a current limiter?
It will take overload for a short period.
Bonding connections should be tested for
Resistance value.
An ammeter in a battery charging system is for the purpose of indicating the
Rate of current used to charge the battery.
If one switch is used to control all navigation lights, the lights are most likely connected
Parallel to each other and in series with the switch.
A CSD unit that is disconnected in flight, due to a malfunction such as over temperature, may be reconnected.
Only on the ground by maintenance personnel.
How should the splices be arranged if several are to be located in an electrical wire bundle?
Staggered along the length of the bundle.
A voltage regulator controls generator voltage by changing the
Resistance of the generator field circuit.
Certain transport aircraft use ac electrical power for all normal operation and battery furnished dc electrical power for standby emergency use. In aircraft, the batteries are kept charged by
Rectifiers which use the aircraft’s ac generators as a source of power.
How is a shunt-wound dc generator connected?
Both fields are shunted across the armature.
During inspection of an anticollision light installation for condition and proper operation, it should be determined that
The anticollision light can be operated independently of the position lights.
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
Strength of the magnetic field.
Aircraft which operate only ac generators (alternators) as a primary source of electrical power normally provide current suitable for battery charging through use of
A stepdown transformer and rectifier.
1) There are three basic types of dc motors; series; shunt, and compound.
2)In the series motor, the field windings, consisting of relatively few turns of heavy wire, are connected in series with the armature winding.
Regarding the above statements,
Both no.1 and no.2 are true.
The method most often used in overcoming the effect of armature reaction is through the use of
Interpoles
During inspection of the terminal strips of an aircraft electrical system, it should be determined that
The terminal studs are anchored against rotation.
How can the direction of rotation of a dc electric motor be changed?
Reverse the electrical connections to wither the field or armature windings.
In a generator, what eliminates any possible sparking to the brush guides caused by the movement of the brushes within the holder?
The brush pigtail.
If the positive field lead between a generator and a generator control panel breaks and is shorted while the engine is running, a voltmeter connected to generator output would indicate
Residual voltage
If a wire is installed so that it comes in contact with some moving parts, what protecting should be given the wire?
Pass through conduit
The most common method of regulating the voltage output of a compound dc generator is to vary the
Current flowing through the shunt field coils.
Which motor would be most likely to have an armature brake?
Landing light retraction motor.
In the American Wire Gauge (AWG) system of numbers used to designate electrical wire sizes, the number assigned to a size is related to its
Cross-sectional area
If the integrated Drive Generator (IDG) scavenge oil filter is contaminated with metal, you should
Remove and replace the IDG
To help minimize the radio interference a capacitor will largely eliminate and provide a steady direct current if the capacitor is connected to the generator in
Parallel
How does the magnetic brake used to stop rotation of an electric motor armature operate?
A friction brake is applied by a spring and released by a magnet.
Aircraft electrical junction boxes located in a fire zone are usually constructed of
Stainless steel
What is the principal advantage of the series-wound dc motor?
High starting torque
Static inverters are electronic devices that change DC to AC with the
Use of an oscillator
Which of the following should be accomplished in the installation of aircraft wiring?
Locate the bundle above flammable fluid lines and securely clamp the structure.
How should a coaxial cable be routed?
As directly as possible
What is an important factor in selecting aircraft fuses?
Capacity matches the needs of the circuit.
When selecting hardware for attaching bonding connections to an aircraft structure, which of the following should be considered?
1) Mechanical strength.
2) Allowable power loss
3) Ease of installation
4) Permissible voltage drop
5) Amount of current to be carried
6) Type of load (continuous or intermittent)
1,3,5
An aircraft electrical circuit control relay is
An electronically operated switch.
Which of the following is not one of the purposes of interpoles in a generator?
Reduce field strength
What is the voltage drop for a no.18 copper wire 50 feet long to carry 12.5 amperes, continuous operation? Use the formula VD = RLA VD = Voltage drop R = Resistance per ft = .00644 L = Length of wire A = Amperes
4V
What is a method used for restoring generator field residual magnetism
Flush the fields.
What is the maximum amount of time a circuit can be in operation and still be an intermittent duty circuit?
Two minutes
Electric wire terminals for most aircraft applications must be what type?
Ring
What type of instrument is used for measuring very high values of resistance?
Megohmeter
How can it be determined if a transformer winding has some if its turns shortened together?
The transformer will get hot in normal operation.
When handling a high voltage capacitor in an electrical circuit, be sure it
Is fully discharged before removing it from the circuit.
What is the most accurate type of frequency measuring instrument?
Integrated circuit chip having a clock circuit.
Which of the following are the major parts of a DC motor?
1) Armeture assembly
2) Field assembly
3) Brush assembly
4) Commutator
5) Pole piece
6) Rheostat
7) End frame
1,2,3,7
When considering an alteration, the criteria upon which the selection of electric cable size should be based are
Current-carrying capacity and allowable voltage drop.
When dc generators are operated in parallel to supply power for a single load, their controls include an equalizer circuit to assure that all generators share the load equally. The equalizer circuit operates by
Increasing the output of the low generator and decreasing the output of the high generator until they are equal.
What kind of the switch should you install in a single wire circuit that required the switch to be manually held in the ON position?
Single-pole, single-throw (SPST), two-position normally open (NO.)
Aluminum wire must be stripped very carefully because
Individual strands will break easily after being hicked.
If the (t) terminal of a voltmeter is connected to the -ve terminal of the source voltage and the -ve terminal of the meter is connected to the +ve terminal of the source voltage, the voltmeter will read
Backwards
