Basic Electrical Railway Power Systems and Electronics

Vocabulary flashcards covering the concepts of basic railway electrical systems, single and three-phase power, transformers, rectifiers, filters, power supplies, voltage regulation, and power electronic converters.

Conventional Energy Sources

Non-renewable sources such as coal, natural gas, and nuclear energy that produce electricity through combustion or nuclear reactions.

Renewable Energy Sources

Energy sources derived from naturally replenished resources including solar, wind, hydroelectric, geothermal, and biomass.

Alternating Current (AC)

An electric current that periodically reverses direction, featuring time-varying voltage and current with standard power system frequencies of $50\,\text{Hz}$ or $60\,\text{Hz}$.

Direct Current (DC)

An electric current that flows in a single direction with constant voltage, constant current, and a frequency of $0\,\text{Hz}$.

Overhead Catenary Line (OCL)

An electric railway distribution system supplying $25\,\text{kV}$ single-phase AC traction power to trains via an overhead contact wire.

Third Rail System

An urban railway traction power supply system delivering $750\,\text{V}$ DC power to electric trains through a conductor rail running along the track.

Single-Phase Power Supply

An AC system using one sinusoidal voltage waveform delivered via one live ($\text{L}$) conductor and one neutral ($\text{N}$) conductor.

Three-Phase Power Supply

An AC system utilizing three sinusoidal voltages of equal magnitude and frequency, each phase displaced by $120^\circ$ electrical degrees from the others.

Phase Relationship

The relative angular position between AC voltages or currents that determines how their respective waveforms align in time.

Transformer

A static electrical device operating on mutual induction that transfers AC electrical energy between circuits at the same frequency while changing voltage and current levels.

Step-up Transformer

A transformer where secondary turns exceed primary turns ($N_2 > N_1$), increasing secondary voltage ($V_2 > V_1$) to minimize $I^2R$ transmission losses.

Step-down Transformer

A transformer where primary turns exceed secondary turns ($N_2 < N_1$), reducing secondary voltage ($V_2 < V_1$) to safe distribution levels.

Railway Traction Transformer

A specialized power transformer located at traction substations that converts high grid voltages into suitable AC or DC traction supply levels for trains.

Rectifier

A power electronic circuit using semiconductor diodes to convert alternating current (AC) into pulsating direct current (DC).

Half-Wave Rectifier

A rectifier circuit using a single diode that conducts during positive AC half-cycles only, producing an average DC voltage of $V_{DC} = \frac{V_m}{\pi}$.

Full-Wave Bridge Rectifier

A rectifier topology using four diodes in a bridge arrangement to process both AC half-cycles, delivering an average DC voltage of $V_{DC} = \frac{2V_m}{\pi}$ and a maximum efficiency of $81.2\%$.

Capacitor

A passive electrical component that stores energy in an electric field, opposes changes in voltage ($C = \frac{Q}{V}$), blocks DC at steady state, and allows AC to pass.

Inductor

A passive component that stores energy in a magnetic field, opposes changes in current ($v = L \frac{di}{dt}$), allows DC to pass, and opposes AC.

Capacitor Filter

A shunt-connected filtering circuit that charges to the peak rectified voltage and slowly discharges into the load to reduce DC voltage ripple.

Inductor Filter

A series-connected filter component that resists abrupt current changes, passing DC while smoothing out AC ripple currents in high-load applications.

Voltage Regulation

The measure or ability of a power circuit to maintain a stable output voltage across load terminals despite variations in input voltage, load demand, or temperature.

Linear Power Supply

A power regulation system that maintains constant output voltage by dissipating excess energy as heat through linear control elements.

Switching Power Supply

A power conversion circuit that regulates output voltage using high-frequency switching components and energy storage elements, achieving high efficiency ($80\% - 95\%$).

Uninterruptible Power Supply (UPS)

An electrical backup system comprising a rectifier, energy storage battery, and inverter to deliver continuous, regulated power to critical loads during mains failures.

AC-AC Converter

A power electronic system that alters the voltage amplitude, frequency, or phase of an AC input directly without utilizing an intermediate DC link.

DC-DC Converter (Chopper)

A power electronic circuit that converts a fixed input DC voltage into a controlled variable DC output voltage by varying the switching duty cycle ($D$).

Buck Chopper

A step-down DC-DC converter topology whose average output voltage is less than the input voltage ($V_{out(avg)} = D \times V_{in}$).

Boost Chopper

A step-up DC-DC converter topology whose average output voltage exceeds the input voltage ($V_{out(avg)} = \frac{V_{in}}{1 - D}$).

Inverter (DC-AC Converter)

A power electronic device that converts direct current (DC) input power into alternating current (AC) output power at required voltage levels and frequencies.

Regenerative Braking

An energy recovery process in electric trains where traction motors act as generators during deceleration, returning power back to the grid or line via inverters.