Pancyprian TS Elec. Eng. III ΘΚ key terms

The relationship stating that the current through a linear resistive element equals the voltage across it divided by its resistance, written I = V/R and used to solve almost every DC circuit problem.

The principle that the algebraic sum of currents entering a node is zero, meaning charge does not accumulate at a junction; it underpins nodal analysis of networks.

The principle that the algebraic sum of voltages around any closed loop is zero, expressing conservation of energy in a circuit and forming the basis of mesh analysis.

The complex ratio of phasor voltage to phasor current in an AC network, combining resistance with inductive and capacitive reactance and carrying both magnitude and phase information.

The cosine of the phase angle between sinusoidal voltage and current, equal to real power divided by apparent power; a low value means larger currents for the same useful power.

The condition in an AC circuit containing inductance and capacitance where reactances cancel, making impedance purely resistive and current or voltage reach a sharp maximum or minimum.

A two-terminal network reduced to a single voltage source in series with a single resistance, valid for calculating the response of any load connected to those terminals.

A method for linear circuits with several independent sources in which the response to each source is calculated separately with the others deactivated, then all responses are added algebraically.

A set of three sinusoidal voltages of equal magnitude and frequency displaced by 120 electrical degrees, allowing constant power transfer and efficient transmission with balanced loading.

Two ways of connecting the windings of three-phase equipment: star joins one end of each winding at a neutral point, delta joins them in a closed loop, changing voltage and current ratings.

A designation such as Dyn11 that states the winding connections of a transformer and the phase displacement between primary and secondary line voltages, critical for paralleling units.

The per-unit voltage that must be applied to one winding of a transformer to circulate rated current with the other short-circuited, governing short-circuit current and parallel operation.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a fraction or percentage of synchronous speed and essential to torque production.

The rotational speed of the rotating magnetic field in an AC machine, equal to 120 times frequency divided by pole number, expressed in revolutions per minute.

A curve showing the mechanical torque an electric motor develops at each rotor speed, revealing starting torque, pull-out torque and the stable operating region of the drive.

A segmented cylindrical assembly on a DC machine armature that, with the brushes, reverses winding connections at the correct instants to convert internal alternating quantities to direct current at the terminals.

The voltage induced in a rotating machine winding that opposes the applied voltage and limits armature current, proportional to flux and rotational speed in a DC machine.

An earthing arrangement in which the supply neutral is connected to earth at several points and combined with the protective conductor, giving a low-impedance path for fault current.

Classification of low-voltage supply arrangements by how neutral and exposed conductive parts are earthed, denoted TN-S, TN-C-S, TT or IT, each requiring different protective measures.

The resistance between an earth electrode and the general mass of earth, determining touch voltage and the tripping effectiveness of protective devices in TT systems.

The protective measure in which a fault causes a device to open the circuit within a specified time, removing dangerous touch voltage from exposed conductive parts.

A protective switch that compares currents in live and neutral conductors and trips when their difference, indicating earth leakage, exceeds a set sensitivity.

The selection of protective device ratings and time-current settings so that the device nearest a fault clears it while upstream devices remain closed, limiting supply interruption.

The current flowing when a low-impedance path bypasses the load, determined by source voltage and network impedance, and used to select breaking capacity and withstand ratings.

A technique decomposing an unbalanced three-phase set of phasors into positive, negative and zero sequence sets, enabling analysis of faults and unbalanced loading.

A method expressing voltages, currents, powers and impedances as fractions of chosen base values, simplifying calculations across transformers and voltage levels in power networks.

The tendency of alternating current to concentrate near the surface of a conductor as frequency rises, increasing effective resistance and reducing usable cross-section.

Ionisation of air around high-voltage conductors where surface field strength exceeds breakdown, causing power loss, audible noise and radio interference on transmission lines.

The addition of capacitors, reactors or static converters to supply or absorb reactive power locally, improving power factor and reducing losses and voltage drop.

A switching technique that varies the on-time ratio of semiconductor devices at high frequency to synthesise a controlled average voltage or current waveform.

A four-layer semiconductor device that conducts in one direction once triggered by a gate pulse and turns off only when current falls below a holding level.

A diode connected across an inductive load or switching device to provide a path for stored inductive energy, protecting semiconductors from overvoltage when current is interrupted.

An electronic converter that adjusts the frequency and voltage supplied to an AC motor, controlling speed and torque while limiting starting current.

An instrument transformer whose primary carries the line current and whose secondary supplies a proportional, isolated current to measuring or protective devices.

An instrument transformer that steps high voltage down to a safe, accurately proportional value for meters and relays while isolating them from the primary circuit.

The total load, usually expressed in volt-amperes at rated secondary current or voltage, that a measuring or protection transformer must supply while staying within accuracy limits.

A measurement applying a steady direct voltage to insulation and recording the resulting leakage current or resistance, revealing moisture, contamination or deterioration.

A low-resistance measurement verifying that protective conductors, bonding and circuit paths are electrically continuous, typically performed with a low-voltage high-current source.

A schematic using one line and standard symbols to show the arrangement of generators, transformers, switchgear and feeders in a power system, omitting phase detail.

A drawing showing the electrical function and interconnection of components using standard graphical symbols, without regard to their physical size or position.

A drawing that shows the physical arrangement of conductors, terminals and connections between devices, used for installation and fault tracing on site.