Chapter 7 A2

The armature of a dc generator is wrapped with ________ windings.

Field

Conducive materials

Gain resistance while temperature rises while others lose resistance. Can vary resistance directly or inversely with temperature.

The assembled armature core_____________. a. is wrapped with field windings b. has axial slots around its periphery c. contacts the brushes d. is constructed of hard-drawn copper bars e. is connected with the rotor

Has axial slots around it's periphery

When a loop of current carrying conductors is placed in a magnetic field, the wire loop will:

Have a torque produced on it

Electric current flow depends on the number of charges:

In motion

The torque produced by the armature conductors in a generator:

Increases with load Opposes the driving torque Is load torque

A way of overcoming armature reaction is by________________________. a. placing the brushes at the air gaps b. feeding AC current into the brushes c. inserting interpoles between the main poles d. reversing the brushes of the armature conductors e. correcting the positions of the poles

Inserting interpoles between the main poles

Another name for the no load characteristic is the:

Internal characteristic

The air gaps between the poles and the armature are _____________. a. filled with insulation b. subject to sparking c. increased with speed d. kept comparatively small e. to insulate the poles from the armature

Kept comparatively small

With regard to the air gaps between the poles and the armature, such gaps must be:

Kept comparatively small

The separately excited generator has a ____________ load characteristic:

Level

The three-point starter for DC motors has connections for: 1. Line. 2. Positive. 3. Negative. 4. Field. 5. Armature. Select one: A. 1, 2, 3 B. 1, 4, 5 C. 2, 3, 4, 5 D. 1, 2, 3, 4 E. 1, 3, 4, 5

Line Field Armature

In a series generator, the load current and generated voltage increase in inverse ratio to the load resistance until __________. a. the machine reaches maximum speed b. the magnetic saturation of the poles is reached c. the generator stops d. the generator reaches its maximum operating temperature e. the generator reaches its minimum operating temperature

Magnetic saturation of the poles is reached

Free valence electrons flow from___________ when connected to an electrical supply.

Negative to positive

A magnetic field is always considered to travel from:

North to South

The practical unit used to represent electrical load is:

Ohm

The displacement between the centres of adjacent poles in an armature is:

One pole pitch

In a shunt motor, if the field becomes disconnected during operation the motor will: Select one: A. Stop. B. Under speed. C. Slow down. D. Not change. E. Over speed.

Overspeed

The manner in which the terminal voltage varies with a varying load current is called the:

Percent voltage regulation

A DC generator is a DC machine driven by an:

Prime mover

When a current carrying conductor forming a loop is placed inside an external magnetic field, then the external field will cause the loop to:

Produce a torque

Resistance

-limits current flow -depends on material -depends on temperature -depends in dimensions

DC motors are restricted to a starting current of about_________% of full load current.

150%

The displacement between the centres of the adjacent poles in an armature is:

180 electrical degrees

The voltage drop at the armature of a shunt DC motor is a percentage that normally does not exceed ______. a. 0.05% b. 0.5% c. 0.9% d. 5.0% e. 50%

5.0%

Some of the characteristics of the series direct current motor include:

A small current at no load conditions. The danger of overspeed as the load is removed. The load current equals the excitation current.

Interpoles are connected in series with the ___________: a. field coils b. load c. armature d. field poles e. stator

Armature

Interpoles carry _______________ current. a. field b. load c. flux d. armature e. stator

Armature

In a shunt motor torque is proportional to: Select one: A. Armature voltage. B. The diameter of the armature. C. The length of the armature. D. Armature current. E. The square of the armature current.

Armature current

An electrical source could be in the form of a....

Battery Generator

The end shields hold the:

Bearing housings

For DC generators the nearer to zero the percentage voltage regulation is then _______________. a. the poorer the voltage regulation b. the greater the voltage regulation c. the higher the operating temperature possible d. the better the voltage regulation e. the lower the operating temperature possible

Better the voltage regulation

The power source must maintain a potential difference:

Between two points

Neutral axis refers to a position of the: Select one: A. Brushes causing minimum sparking. B. Brushes causing maximum sparking. C. Stator causing maximum sparking. D. Stator causing minimum sparking. E. Rotor causing minimum sparking.

Brushes causing minimum sparking

In a magnetic circuit, the magnetic flux is the equivalent of electric __________in an electric circuit.

Current

Armature reaction _______________ the main field. a. increases b. decreases c. reverses d. distorts e. restores

Distorts

When a current carrying conductor is placed in a magnetic field, the field produced by the conductor ______________ the magnetic field between the poles.

Distorts

If a conductor is moved relative to a magnetic field so as to "cut" the magnetic flux then an ______ will be induced in the conductor.

EMF

As the flux of a shunt motor remains constant its torque is ________________________. a. inversely proportional to armature current b. proportional to armature current c. increased d. decreased e. unchanged

Proportional to armature current

Excitation of the shunt field is controlled by a: Select one: A. Long shunt. B. Mechanical governor. C. Short shunt. D. Converter. E. Regulating rheostat.

Regulating rheostat

The behaviour of the separately excited generator with regard to its load characteristic is that as load increases, it's delivery voltage:

Remains constant

If the current in the conductor is reversed, or if the direction of the main field is reversed, then the force on the conductor will be: Select one: A. Stopped. B. Sinosodial. C. Increased. D. Reversed. E. Decreased.

Reversed

In a generator, the direction of the induced emf can be determined by applying Fleming's ______ Hand Rule. a. Back b. Two c. Inverse d. Left e. Right

Right

The shunt generator has a no-load characteristic similar to that of the _________________ generator. a. series b. parallel c. compound d. separately-excited e. internally-excited

Separately excited

When high starting torque is desired a _____________ DC motor is best. a. Series b. Shunt c. Compound d. Three phase e. Manual start

Series

Where a large starting torque is of prime importance the DC motor to use would be the _________________. a. Series b. Long-shunt c. Short-shunt d. Compound e. Cumulative compound

Series

Where high starting torque is required but the running load may be small the DC motor to use would be the _____ motor. Select one: A. Series. B. Shunt. C. Compound. D. Under compounded. E. Over compounded.

Series

Where an approximate constant speed is to be maintained between no load and full load the dc motor to use would be....

Shunt

The three basic ways in which a self excited generator field can be connected are classified as:

Shunt Compound Series

Speed control is usually restricted to ________ motors: 1) Series 2) Shunt 3) Residual 4) Compounded a. 1, 2 b. 1, 3 c. 1, 4 d. 2, 3 e. 2, 4

Shunt Compounded

The armature core is made of:

Soft iron laminations

The end induced in a moving conductor depends on the:

Speed of the moving conductor

The yoke in a DC machine is usually made of: Select one: A. Steel. B. Copper. C. Insulation. D. Semi-conducting materials. E. Aluminum.

Steel

The free valence electrons of a conductor, when connected to the poles of a battery will move towards: Select one: A. Either or both poles, quite randomly. B. Both poles at the same time. C. The positive pole. D. The negative pole. E. The cathode.

The positive pole

Factors determining the resistance of a conductor are:

Type of material Length Diameter Temperature

The magnetomotive force in a magnetic circuit has its equivalent in an electric circuit which is the: Select one: A. Inductance B. Magnetic flux C. Voltage D. Reluctance E. Electric current

Voltage