UPDA Electrical key terms

A computational analysis that determines the voltage magnitude and angle at every bus, plus the real and reactive power flowing on each branch, for a specified network and set of generation and demand conditions.

A method of expressing voltages, currents, impedances and powers as fractions of chosen base values so that transformers and voltage levels drop out of calculations, simplifying multi-voltage network analysis.

A calculation of the maximum prospective currents that would flow at each point of a network under specified fault types, used to select switchgear ratings and protective device settings.

The ability of a system or device to hold terminal voltage close to its nominal value as load changes, usually expressed as the percentage voltage rise from full load to no load.

The ratio of real power to apparent power in an AC circuit, equal to the cosine of the angle between voltage and current; a low value means more current is needed for the same useful power.

The oscillating power exchanged between inductive or capacitive elements and the source, measured in volt-amperes reactive, which does no net work but is needed to sustain magnetic fields.

The addition of capacitors or other devices to supply reactive power locally, reducing the current drawn from the supply and improving the power factor seen by the utility.

An assembly of capacitors connected in parallel or series, switched in steps, used to supply reactive power for voltage support or power factor correction on a distribution or industrial system.

The tendency of alternating current to concentrate near the outer surface of a conductor at higher frequencies, which raises effective resistance and reduces the usable cross-section.

Circulating currents induced in a conducting mass by a changing magnetic flux, which cause resistive heating and energy loss in transformer cores and machine bodies.

Energy lost as heat each time the magnetic domains of a core material are reversed through a magnetization cycle, proportional to frequency and to the area of the material's hysteresis loop.

A device that alters the number of active turns on a transformer winding to adjust its voltage ratio, either while energized (on-load) or only when disconnected (off-circuit).

The ratio of the number of turns in the primary winding to the number in the secondary winding, which sets the relationship between primary and secondary induced voltages.

The small current drawn by a transformer primary at no load to establish the core flux; it lags the applied voltage by almost ninety degrees and is largely reactive.

The difference between the synchronous speed of the rotating magnetic field and the actual rotor speed of an induction motor, usually expressed as a fraction or percentage of synchronous speed.

The rotational speed of the magnetic field produced by a polyphase winding, equal to 120 times the supply frequency divided by the number of poles.

A power electronic converter that adjusts the frequency and voltage applied to an AC motor so its speed can be controlled smoothly while limiting starting current and improving efficiency.

A voltage-controlled power semiconductor that combines the high input impedance of a field-effect transistor with the low conduction loss of a bipolar device, widely used in inverters and drives.

The process by which current is transferred from one conducting path to another in a converter or machine, such as turning off one semiconductor switch and turning on the next.

Waveform deformation caused by currents or voltages at integer multiples of the fundamental frequency, produced by non-linear loads and capable of overheating neutrals and transformers.

The reduction in voltage along a circuit caused by current flowing through conductor impedance, commonly calculated as a percentage of nominal voltage to check that equipment receives adequate voltage.

The maximum current a conductor can carry continuously under stated installation conditions without its insulation exceeding its rated temperature.

The ratio of the sum of individual maximum demands of consumers to the maximum demand of the whole group, reflecting that not all loads peak at the same time.

The deliberate connection together of exposed conductive parts and extraneous conductive parts so they sit at substantially the same potential, removing dangerous touch voltages during a fault.

A conductor or group of conductors buried in contact with the ground to provide a low-impedance path for fault current and to reference the installation to earth potential.

The resistance between an earthing electrode and the general mass of earth, which determines how much the electrode potential rises when fault current flows through it.

The potential difference a person could bridge between a hand touching an accessible conductive part and the feet standing on the ground, which must be limited to safe levels.

The potential difference between two points on the ground surface one pace apart, which can drive current through a person's legs near a faulted earthing point.

The maximum short-circuit current a switching device can safely interrupt at its rated voltage without damage or dangerous arcing.

The current that would flow at a point in an installation if a short circuit of negligible impedance occurred there, used to verify protective device ratings and disconnection times.

A fuse or circuit breaker that automatically interrupts current exceeding a set value, protecting conductors from overload and circuits from short-circuit damage.

The coordination of protective devices so that the device nearest a fault operates first, isolating only the affected circuit and leaving the rest of the installation energized.

A protective switch that trips when the vector sum of currents in the monitored conductors indicates earth leakage above a set threshold, providing additional protection against electric shock.

The ratio of average load over a period to the peak load in that period, indicating how efficiently installed capacity is used and affecting the cost of supply.

Planned utility or customer actions that influence the amount or timing of electricity use, such as load shifting, efficiency incentives and tariff structures, to reduce peak demand.

A systematic survey of energy use in a facility that identifies where energy is consumed, quantifies losses and recommends cost-effective measures to reduce consumption.

The total power dissipated in a magnetic core from hysteresis and eddy currents when it is subjected to alternating flux; it is essentially constant for a given voltage and frequency.

A curve showing the torque an electric motor develops at each speed, which determines starting behaviour, stable operating points and suitability for a given driven load.