AC DC Machines final

Three-phase voltages are _____ out of phase with each other.

120

In a transformer, even when there is no load connected, there will be some small current flow known as _____ current.

excitation

The higher power output alternators use a revolving _____

field

To control compounding the strength of the series field must be weakened by connecting

low value variable resistor in parallel with the series field

A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta

primary, secondary

Three lines supply power to a three-phase motor. If one of these lines should open, the motor will be connected to single-phase power. This condition is known as _____.

single-phasing

The squirrel-cage rotor code letters indicate the shape (type) of rotor bars. Different types of bars have a large effect on the _____ of a motor

starting torque

In calculating power in a three-phase circuit, the phase values of voltage and current and power-factor are multiplied by _____.

three

The torque of a squirrel-cage induction motor will be maximum when the phase angle between the stator and rotor fields is _____.

zero degrees

In a three-phase circuit, the true power (watts) is found by _____.

multiplying line voltage by line current

A transformer supplying a house with 240/120 V has a secondary which is center tapped. The conductor connected to the center is called the _____ conductor.

neutral

When a load is connected to the output of a series generator, the initial voltage produced by __________________________________ of the pole pieces produce a current flow through the load

residual magnetism

Counter-electromotive force (CEMF) and back-EMF are names for the voltage induced into the armature of a DC motor

true

In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating.

75%

A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

8.66:1

The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer.

control

In a compound DC motor control circuit, the field loss relay will disconnect the _____ if power is lost to the _____.

armature, shunt field

Of the three factors that determined the output voltage of a shunt DC generator which is the most common way to control output voltage

change the strength of the magnetic field

In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.

H,X

If one alternator does not produce sufficient power to supply a load, another alternator can be connected to the circuit. The second alternator is connected in _____.

parallel

The _____ transformer is constructed in a similar manner to the core type, except that it has a metal core piece through the middle of the window.

shell-type

When a compound generator is to be paralleled with another compound generator the series field and shunt field are most commonly connected

none of the above