midterm

What is a DC generator that uses permanent magnets as its field?

magneto

What induces a voltage in the secondary for a transformer?

primary current

The ServoDisc motor is also often called a _____ motor.

printed-circuit

When using the right-hand motor rule, what indicates the direction of thrust of the armature?

thumb

A tape-wound core is assembled by _____.

winding a long continuous tape into a spiral

In a parallel circuit, ET = 120 V, R = 30 Ω, and XL = 40 Ω. What is IR?

4 A

The brush leads are generally marked with ________.

A1 and A2

Which is the formula for finding the quality of a capacitor?

Q= 1/ PF

The speed regulation of a DC motor is proportional to the _____.

armature resistance

. A 100 μF capacitor and a 3.6 k Ω resistor are connected in series. How long will it take for the capacitor to change its charge completely?

1.8 s

A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the secondary phase current?

3.2 A

Three capacitors, a 12 μF, a 20 μF, and a 30 μF, are connected in parallel to a 60-Hz source. What is the total XC?

442.09 Ω

A square wave voltage varies between 0 V and 12 V. The positive pulses are 50 μs wide and there is a 50 μs gap between them. What is the DC average of the waveform?

6V

When testing a transformer, what will reveal problems of insulation breakdown that an ohmmeter will not?

MEGGER

Which of these formulas would be used to calculate reactive power?

VARSC = EC x I

Which of these formulas is used to calculate capacitive reactance?

Xc= E2 / VARSC

Variable capacitors normally have a dielectric of _____.

air

What type of standard identification is depicted in the above schematic?

armature

The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.

brushes

What type of DC motor uses a rotor shaped like a hollow cylinder or cup?

brushless

What type of motor does the above schematic depict?

compound

What does the above diagram represent?

inductors connected in series

An inductor ___________ a change of current.

opposes

What type of circuit is shown in the above diagram?

resistive-inductive parallel circuit

What type of generator does the above schematic depict?

series

In an RLC series circuit, the ratio of resistance, inductance, and capacitance determines how much the applied _____ leads or lags the circuit current.

voltage

In a parallel circuit, the supply voltage is 120 V, 60 Hz. The resistance is 30 Ω and the inductive reactance is 40 Ω. What is the value of the inductor?

0.106 H

Two inductors are connected in series to a 120-V, 60-Hz supply. The values of the inductors are 0.175 H and 0.255 H. The total circuit current is _____.

0.74 A

In a parallel circuit, ET = 240 V, R = 30 Ω, and XL = 40 Ω. What is IT?

10 A

An inductor with an inductance of three henrys (H) is to be connected to a 60-Hz circuit. What will the inductive reactance be?

1131 Ω

What is the reactance of a 25 μF capacitor when the applied frequency is 400-Hz?

15.92 Ω

Because inductive reactance and capacitive reactance are _____ out of phase with each other, they subtract from each other in an AC circuit.

180°

When increasing the amount of output voltage when a loop contains 20 turns of the wire, how much was the inducedvoltage increased?

20 times greater than that for a single-loop conductor

A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?

20:1

Two capacitors, a 20 μF and a 30 μF, are connected in series to a 60-Hz source. What is the total capacitive reactance?

221.04 Ω

In an RC parallel circuit, ET = 240 V, R = 10 kΩ, and XC = 8.2 kΩ. What is IC?

29.27 mA

A transformer has a 240 V primary and a 60 V secondary. With a 5 ohm load connected, what is the primary current?

3 A

Two capacitors, a 20 μF and a 30 μF, are connected in series to a 400-Hz source. What is the total capacitive reactance?

33.16 Ω

In a parallel circuit, ET = 277 V, R = 56 kΩ, and XL = 68 kΩ. What is the phase angle (angle theta)?

39.47°

A series RC circuit contains two resistors and two capacitors. The resistors are 27 Ω and 56 Ω. The capacitors have capacitive reactances of 50 Ω and 40 Ω. What is angle theta?

47.31°

In an RC parallel circuit, ET = 120 V, R = 47 kΩ, and XC = 27 kΩ. What is IT?

5.13 mA

Two capacitors, a 20 μF and a 30 μF, are connected in parallel. What is the total capacitance?

50 μF

An RLC parallel circuit has an applied voltage of 240 volts. R = 60 Ω, XL = 20 Ω, and XC = 36 Ω. What is the capacitive current?

6.67A

A transformer has a 2:1 turns ratio. 120 V is applied to the primary. What is the secondary voltage?

60 V

A series RL circuit has two resistors and two inductors. The resistors dissipate 7 W and 12 W. The inductive powers are 15 VARs and 8 VARs. The applied voltage is 240 V. How much is the circuit current?

8.045 A

A series RC circuit contains two resistors and two capacitors. The resistors are 68 Ω and 56 Ω. The capacitors have capacitive reactances of 66 Ω and 33 Ω. The applied voltage is 240 V. What is the voltage drop on the 56 Ω resistor?

84.70 V

An RLC parallel circuit has an applied voltage of 277 volts. R = 82 Ω, XL = 50 Ω, and XC = 124 Ω. What is the true power?

935.72 W

What type of core is often found on high-voltage distribution transformers?

H-type

Which of these formulas is used to calculate capacitive current?

IC= E/ XC

Which of these formulas is used to calculate total circuit current?

IT= IR2+ IC2

Which of these formulas is used to calculate total circuit current?

IT= IR2+(IL- IC)2

Which nameplate requires the name of manufacturer and related kilovolt-ampere?

NEC® 450.11

What is used to convert three-phase power into two-phase power using two single-phase transformers?

Scott connection

The servomotor featuring a fiberglass and copper rotor is the _____ motor.

ServoDisc

What is the symbol for capacitive reactance?

XC

Which of these formulas would be used to calculate impedance?

Z= E/ IT

What is a device that converts mechanical energy into DC electrical energy?

a generator

Resistance and capacitive reactance are 90° out of phase with each other. What do they form?

a right triangle

What is a magnetically operated machine that can change values of voltage, current, and impedance without changing frequency?

a transformer

In a series circuit, the current-limiting elements must be _____________.

added

The rotating part of a generator is called the _____.

armature

In a parallel LC circuit, the difference in frequencies above and below resonance at which impedance is 0.707 of the maximum is called the _____ of the circuit.

bandwidth

. Nonpolarized capacitors _____.

can be used with either AC or DC

. In the formula Q = C x V, what does Q stand for?

charge in coulombs

The relationship of the strengths of the two fields in a generator determines the amount of _____.

compounding

The current of the secondary induces a ___________ in the secondary windings that is in opposition to the countervoltage induced in the primary.

countervoltage

The material between a capacitor's plates is rated by a value called the _____.

dielectric constant

The compound motor connection that should generally be avoided is the _____.

differential

A compound generator has both series and shunt field windings. When those windings are connected so their fields oppose each other in the production of magnetism, that connection is called _____.

differential-compound

How have the three loads been connected in the above image?

directly with a delta

The transformer that converts a high voltage from the power company down to 240/120 V for homes and businesses is called a(n) _____ transformer.

distribution

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

excitation

Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire.

few; large

I= VA/ E What would be calculated by using the above formula?

full-load current rating of the secondary winding

When determining bandwidth, what components result in a sharp increase and decrease of current?

high-Q components

During the period of time that voltage and current have the same polarity in a pure capacitive circuit, where is energy being stored?

in the capacitor

When a magnetic field continually changes magnitude and direction, a voltage is continually being induced in the coil. This voltage is called _____ voltage.

induced

What is caused by the induced voltage and is therefore proportional to the number of wire turns, strength of the magnetic field, and speed of the cutting action?

inductive reactance

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a(n) _____ transformer.

isolation

In a pure capacitive circuit, the current _____ the applied voltage by _____.

leads; 90°

In some capacitors, there is a small amount of current that flows from one plate, through the dielectric material to the other plate. This current is called _____ current.

leakage

Moving coils farther apart increases the amount of _____________.

magnetic flux leakage

What is the unit for capacitive reactance?

ohm

The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.

one-line

For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides a(n) _____ three-phase transformer.

open delta with one transformer center tapped

It is sometimes necessary to connect the secondary windings of transformers in _________ to increase the current capacity.

parallel

What king of magnets does the armature or rotor of a brushless DC motor contain?

permanent

A temperature coefficient that is __________ indicates the capacitor will increase its capacitance with an increase in temperature.

positive

When making the T connection, the main transformer is connected directly across the _____________.

power line

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

primary; secondary

The speed of the disc servomotor can be varied by changing the amount of voltage supplied to the armature. The voltage is generally varied using _____.

pulse-width

When determining bandwidth, what does Q represent?

quality of bandwidth

The current-limiting property of an inductor is called _____.

reactance

During a 360° rotation of the loop, the polarity of voltage remained the same in both halves and waveform.What is this called?

rectified DC voltage

Which type of generator must be self-excited?

series

The voltage rating of a capacitor _____.

should never be exceeded

What type of motor does the above schematic depict?

shunt

When the field winding of a DC motor is connected in parallel with the armature, the motor is called a _____ motor.

shunt

1. If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a _____.

three-phase bank

When a transformer is shown on a schematic diagram, what is the common practice to indicate polarity of the transformer windings?

using dots