Basics of Electrical Machines Practice Flashcards

A comprehensive set of vocabulary flashcards covering the basics of electrical machines, core materials, magnetic circuits, and fundamental electromagnetic laws.

Hard Drawn Copper

Copper wires used in electrical machines to increase mechanical strength, although this process also increases resistivity.

Temperature Coefficient of Copper

The temperature coefficient of Cu is $0.00393$ per degree.

Aluminum in SCIM

A cheaper material used for the bars of Squirrel Cage Induction Motors (SCIM) because it can be rolled into thin sheets.

Electrical Carbon

Material made of Graphite used to make brushes in Electrical Machines; it has a negative temperature coefficient where resistance decreases as temperature increases.

Diamagnetic Materials

Materials exhibiting a weak form of magnetism where induced magnetization is small and opposite to the applied magnetic field, characterized by $\text{X}_m < 0$ and $\text{M}_r < 1$. Examples include Cu, Au, Ge, Si, and Diamond.

Paramagnetic Materials

Materials where induced magnetization is small and in the same direction as the applied magnetic field, characterized by $\text{X}_m > 0$ and $\text{M}_r > 1$. Examples include K, W, and Al.

Ferromagnetic Materials

Materials characterized by permanent alignment of magnetic dipoles due to the spin of unpaired electrons, such as Fe, Ni, Co, Gd, and Dy.

Residual Flux Density

The value of flux density ($B$) remaining in a material when the magnetizing force ($H$) is reduced to zero.

Coercive Force

The magnetizing force ($H$) that must be applied to a material to make the residual flux density ($B$) zero.

Magnetostriction

The change in material dimensions when exposed to a magnetic field, causing the material to expand and contract in alternate half cycles, which produces humming sounds in Transformers.

Soft Magnetic Material

A material with a small coercive force that is easy to magnetize and demagnetize, commonly used for electromagnets.

Hard Magnetic Material

A material with a large coercive force that is difficult to magnetize and demagnetize, commonly used for permanent magnets.

CRGO Steel

Cold Rolled Grain Oriented steel, which has the highest permeability in the direction of rolling.

Non-Hygroscopic

A property of insulating materials meaning they do not absorb moisture.

Silica in Iron

An additive (up to about $4 \text{\%}$) used in iron for soft magnetic materials to increase electrical resistivity ($\rho$) and thereby reduce eddy current losses ($P_e$).

Magneto Motive Force (MMF)

The source of a magnetic field, calculated as $F = NI$ in units of Ampere-turns.

Reluctance ($S$)

The opposition to the passage of magnetic field lines through a material, calculated using the formula S = \frac{l}{\text{\mu} A}.

Permeance ($P$)

The reciprocal of reluctance ($P = \frac{1}{S}$).

Fringing

The process of divergence of magnetic field lines at the edges of a material when an air gap is encountered, which generally increases the effective cross-sectional area (CSA) by $5 \text{\%}$.

Magnetic Leakage

The small amount of flux that strays away from the intended path due to the finite reluctance of the core.

Faraday's Law

States that when a time-varying flux passes through a coil, an induced emf is produced that is proportional to the time rate change of flux (e = N \frac{d\text{\phi}}{dt}).

Lenz Law

The principle stating that the induced EMF always opposes the cause of induction.

Statically Induced EMF

EMF induced when the coil is stationary but the flux is time-varying ($e = N A \frac{dB}{dt}$), as seen in Transformers.

Dynamically Induced EMF

EMF induced when a conductor moves inside a magnetic field ($e = N B \frac{dA}{dt}$), as seen in rotating machines.

Motional EMF Equation

The induced emf across the ends of a conductor expressed as e = \text{\int} (\text{\mathbf{v}} \times \text{\mathbf{B}}) \text{\cdot} d\text{\mathbf{l}}.

Dot Convention

A standard used to determine relative voltage polarity and current direction in transformer windings, where voltage polarity is the same on both dots.