Basic Magnetism, Electromagnetism and Transformers

Comprehensive vocabulary flashcards covering fundamental magnetism, electromagnetism, magnetic circuit quantities, core losses, and transformer principles based on Outcomes 1 and 2 of unit H01T 34.

Magnetism

A fundamental force of nature arising from the motion of electric charges, resulting in attractive and repulsive forces between objects.

Aligned Domains

The structural arrangement in ferromagnetic materials (such as iron, cobalt, and nickel) where atomic magnetic moments align in the same direction to generate a strong collective magnetic field.

Magnetic Circuit

A closed arrangement designed to guide magnetic flux through a defined path, operating analogously to how an electric circuit guides electric current.

Weber ($\text{Wb}$)

The SI unit of magnetic flux ($\Phi$), simplified in the text as being equal to $10^8$ (or $100,000,000$) magnetic lines of force.

Right-Hand Rule

The rule for a straight current-carrying conductor stating that when the conductor is gripped with the right hand, the thumb points in the direction of conventional current flow and the fingers wrap in the direction of the magnetic field.

Solenoid

A coil of wire wound into a helix that produces a unified and much stronger magnetic field than a single straight conductor carrying the same current.

Magnetic Materials

Materials responsive to magnetic forces, identified in the course as cast iron, mu-metal, alnico, low-carbon mild steel, and silicon steel.

Non-Magnetic Materials

Materials that do not exhibit magnetic properties, listed in the text as wood, PVC, glass, mica, rubber, ceramic, water, and oil.

Magnetic Flux ($\Phi$)

The total magnetic field passing through a given area, measured in Webers ($\text{Wb}$).

Magnetic Flux Density ($B$)

The concentration of magnetic flux lines passing perpendicularly through a specific cross-sectional area, calculated as $B = \frac{\Phi}{A}$ and measured in Teslas ($\text{T}$) or $\text{Wb}/\text{m}^2$.

Magnetomotive Force ($\text{MMF}$)

The magnetic driving force that pushes magnetic flux through a magnetic circuit, calculated as $\text{MMF} = N \times I$ and measured in Ampere-turns ($\text{At}$).

Magnetising Force ($H$)

The intensity or field strength of a magnetic field per unit length of the circuit, calculated as $H = \frac{\text{MMF}}{l}$ and measured in Ampere-turns per metre ($\text{At}/\text{m}$).

Permeability of Free Space ($\mu_0$)

A universal physical constant representing the magnetic permeability of a vacuum, defined as $4\pi \times 10^{-7}\,\text{H/m}$.

Relative Permeability ($\mu_r$)

A dimensionless ratio comparing the permeability of a material ($\mu$) to the permeability of free space ($\mu_0$), which also represents the gradient of a material's B-H curve.

Absolute Permeability ($\mu$)

The measure of how much magnetic flux is produced in a material by a given magnetising force, calculated as $\mu = \mu_0 \times \mu_r$ or $\mu = \frac{B}{H}$, expressed in Henries per metre ($\text{H/m}$).

Reluctance ($S$ or $\mathcal{R}$)

The opposition that a material or path presents to the establishment of magnetic flux, calculated as $S = \frac{l}{\mu_0 \mu_r A}$ and measured in reciprocal Henries ($\text{H}^{-1}$) or $\text{At}/\text{Wb}$.

Static Magnetic Field

An unchanging magnetic field produced either by permanent magnets or by a steady direct current (DC) flowing through a stationary coil.

Pulsating Magnetic Field

A magnetic field generated when alternating current (AC) flows through a single-phase conductor or coil, varying in strength and direction in rhythm with current oscillations.

Rotating Magnetic Field

A magnetic field whose resultant vector rotates around a central axis, produced by supplying out-of-phase AC currents (such as $120^\circ$ in three-phase) to symmetrically spaced stationary stator windings.

Air Gap

A non-magnetic gap in a core path that introduces an extremely high reluctance, requiring a large portion of the total circuit MMF to maintain flux.

B-H Curve

A characteristic graph for a magnetic material plotting magnetic flux density ($B$) against magnetising force ($H$) to show its magnetization behavior, permeability, and saturation.

Magnetic Saturation

The region on a B-H curve where further increases in magnetising force ($H$) yield no substantial increase in flux density ($B$) because nearly all internal domains are fully aligned.

Soft Magnetic Material

A material that magnetises and demagnetises easily with a narrow hysteresis loop and low energy losses, such as silicon steel, low-carbon mild steel, cast iron, and mu-metal.

Hard Magnetic Material

A permanent magnetic material that resists demagnetisation and possesses a wide hysteresis loop, such as Alnico and ferrites.

Remanent Flux Density (Remanence)

The residual magnetic flux density ($B$) that remains inside a magnetic material after the external magnetising force ($H$) has dropped to zero.

Coercive Force

The reverse magnetising force ($H$) required to completely reduce the remanent magnetic flux density of a material back to zero.

Hysteresis Loss

The energy dissipated as heat in a magnetic core during each alternating magnetization cycle due to internal domain friction, proportional to the area enclosed by the hysteresis loop.

Eddy Currents

Circulating closed loops of induced electric current set up within a solid conductive core when exposed to a time-varying magnetic field, causing resistive heating ($I^2 R$) losses.

Lamination

The construction technique of splitting a metal core into thin, insulated sheets to interrupt circulating electrical loops and significantly decrease eddy current losses.

Mutual Induction

The electromagnetic process where a time-varying current in a primary winding induces an electromotive force (EMF) across a nearby secondary winding via a shared magnetic field.

Shell Type Transformer

A transformer core construction where the core limbs form an outer frame or 'shell' enclosing the central limb on which the windings are placed.

Core Type Transformer

A transformer construction where the primary and secondary windings are wound on separate outer vertical limbs without an enclosing outer shell.

Ideal Transformer

A theoretical model characterized by infinite core permeability, zero core losses (no eddy currents or hysteresis), zero winding resistance, zero leakage flux, and $100\%$ operating efficiency.

Transformer Voltage Ratio

The fundamental relationship governed by Faraday's Law stating that the voltage ratio equals the turns ratio: $\frac{V_P}{V_S} = \frac{N_P}{N_S} = \frac{I_S}{I_P}$.

Copper Loss

The load-dependent $I^2 R$ power loss caused by the internal electrical resistance of the primary and secondary transformer windings ($P_{\text{Copper}} = I_P^2 R_P + I_S^2 R_S$).

Core Loss (Iron Loss)

The continuous power loss occurring in a transformer's magnetic core independent of load, consisting of the sum of eddy current loss and hysteresis loss.

Leakage Flux

The portion of magnetic flux generated by the primary winding that escapes into the air rather than linking with the secondary winding, causing leakage reactance.

Power Transformer

A large, high-capacity transformer designed for continuous, high-efficiency electrical energy transfer in power transmission and distribution grids.

Voltage Transformer (VT)

An instrument transformer used to step down high voltages to standardized lower levels (e.g., $110\,\text{V}$ or $220\,\text{V}$) for safe metering and protection; its secondary must never be short-circuited.

Current Transformer (CT)

An instrument transformer with few primary turns (or a busbar) and many secondary turns designed to step down large line currents to standard values ($5\,\text{A}$ or $1\,\text{A}$); its secondary must never be open-circuited while energized.

Autotransformer

A transformer having a single continuous winding on a shared core where a tapped section serves both the primary and secondary circuits without electrical isolation.