Theory Test 1

What determines the polarity of magnetism when current flows through a conductor?

The direction of electron current flow through the conductor

What determines the strength of the magnetic field when current flows through a conductor?

1. magnetic lines of flux

2. the amount of current flowing through the wire

Name three factors that determine the amount of induced voltage in a coil.

1. The number of turns of wire in the coil
2. The speed of the cutting action
3. The strength of the magnetic field

How many lines of magnetic flux must be cut in 1 s to induce a voltage of 1 V?

One volt is induced in a conductor when magnetic line of flux are cut at a rate of 1 weber per second.

What is the effect on induced voltage of adding more turns of wire to a coil?

It increases the induced voltage, as more flux lines are cut per second. Since the added turns act like conductors connected in series, the induced voltage adds together.

Into how many time constants is an exponential curve divided?

An exponential curve is divided into 5 times constants

Each time constant of an exponential curve is equal to what percentage of the maximum amount of charge?

Each time constant is equal to 63.2% of some value.

What electronic component is often used to prevent large voltage spikes from being produced when the current flow through an inductor is suddenly terminated?

Two devices used to help prevent large spike voltage are the resistor and the diode.

What is a generator?

A generator is a device that converts mechanical energy into electric energy

What type of voltage is produced in all rotating armatures?

AC voltage is produced in all rotating armatures

What are the three types of armature winding?

Lapwound, Wavewound and Frogleg

What type of armature winding would be used for a machine intended for high-voltage, low-current operation?

Wave-wound armatures

What are interpoles, and what is their purpose?

Interpoles are small pole pieces inserted between the main field poles. Their purpose is to correct armature reaction by restoring the main magnetic field to its normal condition.

How are interpoles connected in relation to the armature?

Interpoles are connected in series with the armature, which allows their strength to increase as armature current increases

What type of field winding is made with many turns of small wire?

The shunt field winding

How is the series field connected in relation to the armature?

The series field is connected in series with the armature

How is the shunt field connected in relation to the armature?

The shunt field is connected in parallel with the armature

What is armature reaction?

Armature reaction is the twisting or bending of the magnetic lines of flux of the pole pieces

What is armature reaction proportional to?

Armature reaction is proportional to armature current

What are eddy currents?

Eddy currents are currents that are induced into the metal core material by the changing magnetic field as the armature spins through the flux lines of the pole pieces

What condition characterizes over compounding?

The output voltage is higher at full load than it is at no load

What is the function of the shunt field rheostat?

The rheostat allows part of the current that would normally flow through the series field to flow through the resistor. Reducing the amount of magnetic flux produced by the series field, which reduces the amount of compounding.

What is used to control the amount of compounding for a generator?

A series field shunt rheostat

Explain the difference between cumulative- and differential compounded connections.

Cumulative-compound generators have their series and shunt field winding connected in such a manner that they aid each other in the production of magnetism.

Differential-compound generators have their series and shunt field winding connected in such a manner that they oppose each other in the production of magnetism

What is the voltage regulation of a DC generator proportional to?

proportional to the resistance of the armature

What is counter torque proportional to?

It is proportional to the output current if the field excitation current remains constant

What is counter torque a measure of?

The measure of the useful electric energy produced by the generator

In your own words, explain how a basic DC generator works. Be sure to include the roles of motion, magnetic lines of flux, the conductor, and electromagnetic induction in your explanation

A basic DC generator converts mechanical energy into electrical energy. When a conductor is moved through a magnetic field, it cuts the magnetic lines of force. This motion causes electromagnetic induction, which induces a voltage (EMF) in the conductor. If the conductor is connected to a complete circuit, current flows. In a DC generator, a commutator changes the alternating voltage produced in the armature into a unidirectional (DC) output.

What is Lenz’s Law?

If it is induced it is opposite to what created it.

- If inducing on South it causes it to have a North magnetic polarity

Self vs Seperately Excited

Self: Only needs generator and mechanical power

Excited: Needs a serperate DC power source

Series:
Shunt:
Brushes

S1, S2
F1, F2
A1, A2

What does a commutator do?

It changes the AC produced in the armature into DC

What are the 3 types of DC generators?

1. Series

2. Shunt

3. Compound

How to make voltage

1. Motion

2. Lines of Flux

3. Conductor

What type of armature winding would be used for a machine intended for low-voltage, high-current operation?

Lap-wound

What type of armature winding would be used for a machine intended for medium-voltage, medium-current operation?

Frogleg

What do series generators do?

Increase output voltage as load is added

When is a Magnetic Field created?

Created around the conductor when current flows

Induced Voltage is?

The opposite polarity to applied voltage

Current:

It rises in an inductor at an exponential rate

Inductors produce?

They produce extremely high voltages when current flow is stopped