Electrical Power Systems and Fundamentals

Flashcards covering basic electrical concepts including AC/DC, transformer types, power formulas, and grid components like switches and relays.

AC (Alternating Current)

Current that periodically changes direction; U.S. power systems operate at $60\,Hz$.

DC (Direct Current)

Current that flows in one direction; commonly used in batteries and substation control and protection systems.

Single-Phase

A system using one AC voltage waveform, common in residential applications like $120/240\,V$ service.

Three-Phase

A system consisting of three AC voltage waveforms spaced $120^{\circ}$ apart, identified as A, B, and C phases.

Transmission

The process of moving large amounts of electricity over long distances at high voltage.

Distribution

The delivery of power from substations toward homes and businesses at lower voltages than transmission.

I²R losses

Conductor losses reduced by transmitting power at higher voltage, which results in lower current for the same amount of power.

Transformer

A device that changes AC voltage levels through electromagnetic induction.

Step-up Transformer

A transformer designed to increase voltage.

Step-down Transformer

A transformer designed to decrease voltage.

Wye (Y) Connection

A connection where three windings meet at a common point, which can provide a neutral.

Delta (Δ) Connection

A connection where three windings are connected together in a closed loop or triangle; it does not have a neutral point.

Protective Relay

A device that monitors electrical conditions like current and voltage and sends a trip signal to a circuit breaker when a fault is detected.

Circuit Breaker

A device designed to interrupt current, including high fault current within its rating.

Air-Break Switch

A switching device that opens and closes a circuit in air to isolate equipment and provide a visible open point.

CT (Current Transformer)

A device providing a reduced current signal for protective relays, meters, and monitoring equipment.

PT / VT (Voltage Transformer)

A device providing a lower, measurable voltage signal for protective relays, meters, and monitoring equipment.

Substation

A facility where electrical power is transformed to different voltage levels, switched, monitored, and protected.

Fault

An abnormal electrical condition, such as line-to-ground or line-to-line, that can cause very high current.

Grounding

A safety practice that provides a path for fault current and helps maintain safer electrical conditions.

Ohm’s Law

The mathematical relationship where voltage equals current times resistance: $V = I \times R$.

Electrical Power Formula

The formula used to calculate power in watts: $P = V \times I$.

Voltage

The electrical pressure in a system.

Current

The flow of electricity in a system.

Three-Phase Voltage Relationship

In a balanced wye system, $\text{Line-to-line voltage} = \sqrt{3} \times \text{line-to-neutral voltage}$.