Glossary

In IEEE 1159-2019 dc offset is the presence of a dc voltage or current in an ac power system, arising from geomagnetic disturbances or half-wave rectification, and harmful because it drives transformer saturation and heating.

In IEEE 1159-2019 a dropout is a loss of equipment operation, such as of discrete data signals, due to noise, a voltage sag or an interruption.

In IEEE 1159-2019 electromagnetic compatibility is the ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable disturbances into that environment, and the practice adopts the IEC electromagnetic compatibility approach to describe power quality phenomena.

In IEEE 1159-2019 flicker is the subjective impression of fluctuating light caused by voltage fluctuations; it is the effect on lighting, not the electrical phenomenon, and the practice discourages the phrase voltage flicker where voltage fluctuation is meant.

In IEEE 1159-2019 the fundamental component is the order-one component of the Fourier series of a periodic quantity, at the frequency at which the supply system is designed to operate.

In IEEE 1159-2019 harmonics are sinusoidal voltages or currents at frequencies that are integer multiples of the fundamental supply frequency; combined with the fundamental they produce waveform distortion, and they arise from the nonlinear characteristics of devices and loads.

In IEEE 1159-2019 an impulsive transient is a sudden change in the steady-state voltage or current at other than the power frequency that is unidirectional in polarity; it is characterized by its peak value, rise and decay times and spectral content, lightning is its most common cause, and it can excite system resonances that produce oscillatory transients.

In IEEE 1159-2019 interharmonics are voltage or current frequency components that are not integer multiples of the supply frequency, appearing as discrete frequencies or as a wideband spectrum; the main sources named are pulse-width modulated inverters, static frequency converters, cycloconverters, induction furnaces and arcing devices, and power line carrier signals also count.

IEEE 519-2022 defines an inverter-based resource as a source of electric power connected to the transmission system through a power electronic interface and made of one or more inverter-based resource units able to export active power from a primary energy source or storage, and defines a unit as one inverter or a group of inverters at a single point of connection.

In IEEE 1159-2019 a long-duration rms variation is a deviation of the rms voltage or current from nominal that outlasts the boundary clause 3 sets between short-duration and long-duration variations, described by a magnitude modifier: undervoltage, overvoltage or voltage interruption.

In IEEE 1159-2019 noise is unwanted electrical signals with broadband spectral content superimposed on the power system voltage or current, or found on neutral conductors and signal lines, covering any unwanted distortion that is neither harmonic distortion nor a transient; power electronic devices, control circuits, arcing equipment and switching supplies cause it, improper grounding worsens it, and filters, isolation transformers and line conditioners mitigate it.

In IEEE 1159-2019 the noise floor is the artifact of the measuring system itself, including transducers, input amplifiers and analog-to-digital converters, stated as a small fraction of nominal, and the reference against which the direction of a transient is judged.

In IEEE 1159-2019 a nonlinear load is one that draws a non-sinusoidal current when supplied from a sinusoidal voltage source.

In IEEE 1159-2019 notching is a periodic voltage disturbance caused by the normal operation of power electronic converters as current commutates from one phase to another, creating a momentary short circuit between two phases; it is steady state yet carries high-frequency content, so it sits between transients and harmonic distortion and may exceed what typical harmonic instruments can characterize.

In IEEE 1159-2019 an oscillatory transient is a sudden change in the steady-state voltage or current at other than the power frequency that includes both polarities, changing polarity rapidly and normally decaying within a fundamental cycle; it is described by magnitude, duration and spectral content and subclassified as low, medium or high frequency.

In IEEE 1159-2019 an overvoltage is a long-duration increase of the rms voltage above the nominal range, caused by load switching, changes in reactive compensation, poor voltage regulation or incorrect transformer tap settings rather than by faults.

IEEE 1159-2019 directs that a harmonics monitor used for an IEEE 519 comparison be placed at the point of common coupling as that standard specifies.

In IEEE 1159-2019 a power frequency variation is the deviation of the fundamental frequency from its nominal value, following the balance between load and available generation; small local variations occur continuously, while large excursions follow bulk system faults, the loss of a large block of load or the loss of a generator.

IEEE 1159-2019 uses power quality for the wide variety of electromagnetic phenomena that characterize the voltage and current at a given time and location on the power system, and its glossary defines it as the concept of powering and grounding electronic equipment in a manner suited to that equipment and compatible with the premises wiring and other connected equipment.

IEEE 519-2022 defines pulse number as the total number of successive non-simultaneous commutations in a converter circuit per cycle when operating without phase control, equal to the order of the principal harmonic in the dc output voltage, and uses it in clause 5.6 to relate the harmonic limit multiplier to converter design.

In IEEE 1159-2019 an rms variation is a variation of the rms value of a voltage or current from nominal, the umbrella term for interruptions, sags, swells, undervoltages and overvoltages, which Table 2 divides into short-duration and long-duration categories.

IEEE 1159-2019 attributes voltage sags mainly to system faults, and also to the switching of heavy loads and the starting of large motors, whose starting current drops the voltage across the system impedance.

In IEEE 1159-2019 a short-duration rms variation is a deviation of the rms voltage or current from nominal within the duration band stated in clause 3, described by a magnitude modifier, sag, swell or interruption, and by a duration modifier, instantaneous, momentary or temporary.

In IEEE 1159-2019 a sustained interruption is a long-duration rms variation in which the voltage on one or more phase conductors is completely lost for longer than the short-duration category allows; such interruptions are often permanent, require manual restoration, and are distinct from the reliability term outage.

In IEEE 1159-2019 a swell is an increase of the rms voltage or current above the nominal range that lasts within the short-duration band of clause 3; swells are rarer than sags, arise on the unfaulted phases during a single line-to-ground fault, from switching off a large load or from energizing a large capacitor bank, and the term momentary overvoltage is deprecated as a synonym.

IEEE 1159-2019 explains total demand distortion as the measure IEEE 519 introduced because the total harmonic distortion of a current can be misleading at light load: it expresses the harmonic current as a percent of the maximum demand current rather than of the fundamental.

IEEE 1159-2019 cautions that a current total harmonic distortion figure can mislead, since an adjustable speed drive at light load shows a high percentage while the rms harmonic current is low, and that a complete spectrum with magnitudes and phase angles characterizes harmonic distortion more fully.

In IEEE 1159-2019 total interharmonic distortion is the ratio of the rms of the interharmonic content, taken up to the same maximum order used for total harmonic distortion and excluding the harmonics, to the fundamental, expressed as a percent.

IEEE 1159-2019 uses transient for a phenomenon or quantity that varies between two consecutive steady states over a time short compared with the time scale of interest, either a unidirectional impulse of either polarity or a damped oscillatory wave, and deprecates the synonym surge for power quality work.

In IEEE 1159-2019 an undervoltage is a long-duration decrease of the rms voltage below the nominal range, caused by the opposite events to those that cause overvoltage, such as a load switching on, a capacitor bank switching off or an overloaded circuit; the term brownout is deprecated.

In IEEE 1159-2019 a voltage change is a variation of the rms or peak value of a voltage between two consecutive levels sustained for definite but unspecified durations; a series of them is a voltage fluctuation.

In IEEE 1159-2019 a voltage fluctuation is a series of voltage changes or a cyclical variation of the voltage envelope, normally within the ANSI C84.1 voltage range, caused by loads with significant cyclic variation such as arc furnaces, and assessed through the short-term perceptibility index Pst of IEC 61000-4-15 and IEEE 1453-2015.

IEEE 1159-2019 attributes minor voltage imbalance mainly to unbalanced single-phase loads on a three-phase circuit, with capacitor bank fuse failures and single-phase regulators as other causes, and severe imbalance to single-phasing conditions such as an open upstream protective device.

In IEEE 1159-2019 a voltage interruption is the disappearance of the supply voltage on one or more phases, qualified by a duration term, momentary, temporary or sustained; clause 4.4.2.1 measures an interruption by its duration because its magnitude is always below a small fraction of nominal.

In IEEE 1159-2019 waveform distortion is a steady-state deviation from an ideal power-frequency sine wave, characterized principally by its spectral content, and the category contains dc offset, harmonics, interharmonics, notching and noise.