Power Quality Standards :
Considering that the electrical energy produced can have an effect on the voltage, the majority of the definitions on the power quality concept are on voltage. Since the current drawn from the system will depend on the load, the current waveform cannot be predicted. The main criterion is the voltage, although large changes in current, as in short-circuit events, affect the voltage. For this reason, the standards and definitions are based on voltage waveform and effective value.

As power quality is related to both producer and consumer, quality related standards can be divided into two groups accordingly. Standards in the first group IEC 61000-2-5: 1995 IEC 61000-2-5: 1995: 'Electromagnetic Compatibility (EMC), Part 2: Environment, section 5': Classifications of Electromagnetic EnvironmentsDescriptions of the Environments and EN 50160: 2000 BS EN 50160: 2000: 'Voltage Characteristics of Electricity Distribution', BRITISH STANDARD INSTITUTION, 2000. Gives the compatibility limits that a device or product must have.

The requirements of the low and medium voltage distribution network
In the EN 50160: 2000 standard, the limits of the concepts such as voltage, frequency, amplitude, cut, unbalance are stated. The EN50160 is not an EMC standard but defines the desired voltage quality in Europe. When the standard is examined, it is seen that generally the events are defined, their reasons are shown but the exact limits are not drawn.
The second group is an example of the IEEE 1159: 2009 standard. In this standard, distortions that may occur at a point defined as a common interaction point on the network are limited and power quality events are defined according to their duration and amplitudes.