A voltage sag is a short-duration (<1 minute) reduction in voltage levels. It typically lasts for a few milliseconds to a few seconds and can be caused by faults on the power system, sudden large loads, or starting large motors.

Voltage swells are short-duration (<1 minute) increases in voltage levels. They are less common than sags and can be caused by sudden load reductions or switching off large loads.

Interruptions are a complete loss of voltage typically caused breaker trip in response

Undervoltage occurs when the voltage in an electrical circuit drops below the nominal amount for an extended time. It is often caused by overloaded circuits, long wiring distances, or poor power supply infrastructure and can lead to reduced performance, overheating, equipment damage, and system shutdowns.

Conversely, overvoltage happens when the voltage exceeds the nominal amount for an extended time. Typical causes are lightning strikes, faulty equipment, or switching surges. Overvoltage can cause component damage, insulation breakdown, reduced equipment lifespan, and safety hazards such as electric shocks and fires.

Transients are short bursts of energy due to sudden changes in the power system. They can be caused by lightning strikes, switching operations, or equipment failures. Transients can damage sensitive electronic equipment.

An impulsive transient is a single spike and is typically caused by lightning strikes, arcing and electrostatic discharge. Oscillatory transients exhibit a series of decaying spikes and can be caused by switching capacitors, breakers or loads on or off.

Harmonics are distortions in the electrical waveform caused by non-linear loads such as variable frequency drives, rectifiers, and LED lighting. They can cause overheating in equipment, leading to fires. They also cause losses in the power system as more energy is required to run equipment when harmonics are present.

Voltage unbalance occurs when the voltages in a three-phase system are not equal. This can result from uneven distribution of single-phase loads. Voltage unbalance can cause overheating and reduced efficiency in three-phase motors.

Power factor describes how the current and voltage waveforms interact in an AC circuit, specifically how their peaks and valleys align. With good power factor, the peaks and the valleys of the current and voltage are aligned. With poor power factor, the current and voltage waveforms shift with respect to each other. Poor power factor indicates inefficient power usage, meaning that more power is coming from the grid or generator than is reaching the loads. Improving power factor can reduce energy bills and extend equipment life.

Flicker refers to rapid, repetitive variations in voltage magnitude, causing visible fluctuations in lighting intensity. This can result from load changes, equipment switching, or faults in the power system, leading to eye strain and potential equipment malfunction.