Power Electronics II - Lecture 3: Transformers and AC/DC Systems

Vocabulary flashcards covering the principles, history, applications, and mathematical formulations of transformers and AC/DC power systems from Power Electronics II, Lecture 3.

Transformer

An electrical device that converts one AC voltage magnitude to another AC voltage magnitude while maintaining a constant frequency.

Diode Rectifier

A power electronic converter used to convert AC voltage into DC voltage.

Inverter

A power electronic converter used to convert DC voltage into AC voltage.

DC to DC Converter

A power electronic converter used to convert one DC voltage level to another DC voltage level.

Electron (Etymology)

Derived from the Greek word for amber, originating from the observation that rubbing amber accumulates static electricity that attracts materials.

Alexandre Volta

An Italian physicist who invented the DC battery in the 1800s, initiating the practical use of electricity.

Michael Faraday

A scientist who, in the mid-1800s, discovered the fundamental relationship between electrical voltage and magnetic flux that underpins electric power generation.

Niagara Falls Project

A late-1800s electrical transmission project transmitting power $25\,\text{miles}$ to Buffalo, which established the dominance of AC over DC due to efficient high-voltage transmission.

$I^2R$ Loss

Resistive power loss in transmission lines; minimized during power transmission by transmitting at very high voltages to reduce current for a given power level.

Step-up Transformer

A transformer utilized at power generating stations to increase voltage from under $25\,\text{kV}$ up to hundreds of kilovolts (such as $765\,\text{kV}$) for long-distance transmission.

Step-down Transformer

A transformer used at substations to decrease high transmission voltages down to tens of kilovolts for industry and eventually to $120\,\text{V}$ or $230\,\text{V}$ for residential use.

Induction Motor

An AC motor developed by Nikola Tesla that serves as the workhorse of industry, consuming an estimated $65\%$ of all generated electricity.

High Voltage DC (HVDC) Transmission

A DC transmission approach enabled by power electronics that is more efficient than AC for distances exceeding $2000\,\text{km}$ and for subsea transmission.

Iron Core

A core structure in a transformer that provides a very low reluctance path for magnetic flux to link between windings.

Faraday's Law of Induction

The governing physical principle of transformers stating that induced voltage equals the number of turns multiplied by the time rate of change of magnetic flux.

Transformer Voltage Ratio

The relationship stating that the primary voltage divided by secondary voltage equals the transformer turns ratio: $\frac{V_p}{V_s} = \frac{N_p}{N_s}$.

Transformer Current Ratio

The relationship stating that the primary current divided by secondary current equals the inverse of the turns ratio: $\frac{I_p}{I_s} = \frac{N_s}{N_p}$.

Ideal Transformer

A theoretical transformer model that is $100\%$ efficient ($V_s I_s = V_p I_p$), produces no voltage drop under load, and draws zero primary current when the secondary is unloaded.

Voltage Regulation

A figure of merit for power supplies expressing output voltage drop under load, defined as $\frac{V_{s,oc} - V_{s,fl}}{V_{s,oc}} \times 100\%$.

$$V_{s,oc}$$

The secondary open-circuit voltage of a transformer measured under no-load conditions when secondary current is zero.

$$V_{s,fl}$$

The secondary output voltage of a transformer measured when the nominal full-load current is flowing.

ZBD Transformer

The original high-efficiency transformer developed in 1885 at the Gant's Works in Budapest, Hungary, named after the surnames of its three inventors.

Induction Motor Variable Speed Drive

A system that controls the operating speed of an induction motor across a wide range by converting the fixed grid AC frequency into a variable AC frequency.

Wind Turbine Electrical Conversion

A generation application where variable-speed turbine rotation produces variable-frequency AC, requiring conversion to match the fixed $50\,\text{Hz}$ frequency of the national grid.