Power quality is generally measured by the shape of the voltage waveforms supplied at the customer's meter. The voltage waveforms may reduce, increase, fluctuate or distort due to controllable or uncontrollable circumstances.

Any types of electrical equipments can be affected. Standard building systems such as lighting, HVAC and communications equipments are frequently affected. The most costly power quality problems often involve more sensitive high-tech equipments such as computer controlled equipment and data systems.

If you answer YES to any of these questions, you are likely to be experiencing a Power Quality problem:

• Are you experiencing premature failures of electronic equipments or motors and drives?
• Your adjusted speed drives often trip into offline mode.
• Your computer tends to shut down inexplicably.
• Your computer’s screen tends to jitter.
• You are experiencing equipment problems during or shortly after lightning storms.
• Your circuit breakers tend to trip without being overload.
• Your transformers cases are extremely hot to the touch.
• Your power factor capacitor bank fails prematurely.
• Your equipments tend to malfunction at the same time of the day.
• Your automated systems fail for no apparent reason.
• Certain electronic systems tend to function in one location but not in another location.
• Do certain electronic systems work in one location but not in another location.
• Your lights tend to dim or flicker. This incident is then follow by the maloperation of critical equipment

The most common causes of Power Quality problems include lightning strikes, equipment failures, third party encroachment, weather conditions and operation of non-linear & fluctuating loads.

Some of the international standards that explain the power quality phenomenon are:

• IEC 61000-2-1: Definition of Electromagnetic Compatibility (EMC) EMC is concerned with the possible degradation of the performance of electrical and electronic equipments due to the disturbances present in the electromagnetic environment, in which the equipment operates
• IEC 61000-2-4: Compatibility levels in industrial plants for low frequency conducted disturbance
• IEC 61000-2-12: Electromagnetic compatibility (EMC) - Part 2-12: Environment - Compatibility levels for low-frequency conducted disturbances and signalling in public medium-voltage power supply systems
• IEC 61000-3-6: Assessment of emission limits for distorting loads in MV and HV power systems.
• IEC 61000-3-7: Assessment of emission limits for fluctuating loads in MV and HV power systems.
• MS 1760:2004: Guide on voltage dips and short interruptions on Public Power Supply System. The original standard is the IEC/TR 161000-2-8
• IEC 61000-4-11: Immunity test for voltage dips, short interruptions and voltage variation for equipment less than 16 Amp
• IEC 61000-4-34: Immunity test for voltage dips, short interruptions and voltage variation for equipment more than 16 Amp
• Engineering Recommendation P28 : Planning limits for voltage fluctuations caused by industrial, commercial and residential equipment in the United Kingdom.
• Engineering Recommendation G5/4 : Planning levels for harmonic voltage distortion & connection of non-linear equipment to Transmission and Distribution Systems in the United Kingdom.
• SEMI F47: Specification for semiconductor processing equipment voltage sag immunity
• SEMI F49 : Guide for semiconductor factory system voltage sag immunity