Several power quality issues impact the operation and efficiency of electrical equipment:

• Sags/swells
• Harmonic distortion and inter harmonics
• Micro cuts and outages
• Spikes/transients 
• Undervoltage/overvoltage
• Voltage imbalance (unbalance)
• Voltage fluctuations (flickering)
• Under/over frequency
• Poor power factor

It is generally expected that power systems worldwide will experience an increase in harmonic distortion as the green transition progresses.

At lower voltage levels, an increase in harmonic generation is expected, caused by widespread photovoltaic (PV) generation, usage of energy storage, electric vehicle charging/discharging and increasing converter-interfaced loads at a domestic level.

Larger and more frequent voltage variations are to be expected that can lead to both undervoltages or overvoltages. This effect will be strongest in areas of the power system having low system strength.

In distribution networks, over voltage can lead to excess energy consumption, transformer core saturation and stressing of insulation, leading to premature failure.

Undervoltage can lead to reduced energy consumption, malfunctioning of high-intensity discharge lamps, reduction of torque developed by mains-connected motors as well as overcurrent with associated accelerated aging as a consequence.

The proliferation of converter-interfaced renewable generation connections, with intermittent power output, combined with a reduction in system strength through displacement of conventional plants, results in higher volatility in the system voltage at the transmission level.

Voltage dips, typically caused by system faults, transformer energization, or large motors starting, can become more frequent and severe in distribution networks.

Technologies such as photovoltaic systems at the LV level are taking place as single-phase connections, which introduces unbalances into the system.

They are most likely driven by:

• Asymmetrical three-phase loads or unequal distribution of single-phase loads.
• Intermittent loads at the low-voltage level – such as electric vehicle charging points and heat pumps – will have an increased power capacity and are likely to introduce more imbalance.