generators

Flashcards covering the principles of magnetism, magnetic materials, electromagnetism, and generator construction/operation based on lecture notes.

What is a magnet?

An object with the ability to attract magnetic materials.

What are the three basic classifications of magnetic materials?

Ferromagnetic, paramagnetic, and diamagnetic.

Which materials are categorized as ferromagnetic?

Metals that are magnetized easily, such as iron, nickel, cobalt, and manganese.

What characterizes diamagnetic materials?

They are metals or non-metals that cannot be magnetized, and magnetic lines of force tend to go around them rather than through them.

What is a magnetic domain?

A group of atoms with their magnetic moments all aligned in the same direction within a material.

What is the difference between temporary and permanent magnets?

Temporary magnets align their domains only while subjected to a magnetizing force, whereas permanent magnets retain their magnetic effect without a nearby magnetizing force.

What materials are added to high-carbon steel to create permanent magnets?

Cobalt, molybdenum, chrome-tungsten, and Alnico 5.

In what direction do magnetic lines of force flow outside and inside a magnet?

By convention, they flow from the north pole to the south pole outside the magnet, and from the south pole to the north pole inside the magnet.

How is the attraction force of a magnet related to the distance between poles?

The attraction force is inversely proportional to the external distance between the magnetic poles.

What is magnetic flux and what is its symbol?

Magnetic flux refers to the lines of force around a magnet collectively, represented by the Greek capital letter $\Phi$ (phi).

Define flux density and identify its symbol.

Flux density ($B$) is the concentration of lines of force at any place within or around a magnet, described as the magnetic flux per unit area.

What is permeability?

Permeability ($\mu$) is a property that determines the ease with which magnetic flux magnetizes a material; materials like soft iron have high permeability.

How is reluctance defined?

Reluctance ($R_m$) is the opposition offered by a material to the establishment of a magnetic path.

What is the relationship between permeability and reluctance?

They are inversely proportional; a material with high permeability provides a path of lower reluctance.

What is saturation in a magnetic material?

The state reached when all magnetic domains have been aligned, and any further increase in magnetizing force produces no increase in magnetism.

What does the left-hand rule for conductors determine?

The direction of the magnetic field surrounding a current-carrying conductor.

In the left-hand rule for conductors, what do the thumb and fingers represent?

The thumb points in the direction of electron flow, and the curved fingers point in the direction of the lines of force.

What three factors affect the strength of an electromagnet?

1. The amount of current in the coil. 2. The number of turns on the coil. 3. The type of core material.

What are eddy currents?

Currents induced within the core material of an electromagnetic device when it is subjected to a changing magnetic field.

How are eddy current losses reduced in electromagnetic cores?

By constructing the core out of thin insulated steel sheets called laminations.

What is hysteresis loss?

Energy lost as heat due to the friction caused by the constant flip-flopping of magnetic domains in an ac circuit.

What is a generator according to Faraday's law of induction?

A device that converts mechanical energy into electrical energy by moving a conductor across magnetic lines of force.

List the four components of a generator's magnetic circuit.

Field yoke (frame), pole cores (stator), armature (rotor), and air gap.

Identify the three primary components of a generator's electric circuit.

Field coils (windings), armature coils (windings), and brushes.

According to Fleming's left-hand rule for generators, what do the thumb, first finger, and second finger indicate?

The thumb points to the direction of conductor movement (thrust), the first finger points to the magnetic field (North to South), and the second finger points to the direction of induced current flow.

What is the formula for the magnitude of generated voltage ($E_{Gen}$)?

$E_{Gen} = k \times \Phi \times n$, where $k$ is the machine constant, $\Phi$ is the flux, and $n$ is the rotational speed.

At what angles is the induced voltage in a basic generator at its peak?

At $90^{\circ}$ (maximum positive) and $270^{\circ}$ (maximum negative).

What device allows a generator to supply alternating current (AC) to a load?

Slip rings.

What device provides the rectifying action to supply direct current (DC) in a generator?

A commutator (split ring).

What type of voltage is always produced within the armature of both AC and DC generators?

Alternating current (AC) voltage.