IEC TS 62749
Assessment of power quality – Characteristics of electricity supplied by public networks
|Publication Date:||1 April 2015|
|ICS Code (Other standards related to electricity and magnetism):||17.220.99|
This Technical Specification specifies the expected characteristics of electricity at the SUPPLY TERMINALS of public low, medium and high voltage, 50 Hz or 60 Hz, networks.
NOTE 1 The boundaries between the various voltage levels may be different for different countries/regions. In the context of this TS, the following terms for system voltage are used:
- low voltage (LV) refers to UN ≤ 1 kV;
- medium voltage (MV) refers to 1 kV < UN ≤ 35 kV;
- high voltage (HV) refers to 35 kV < UN ≤ 230 kV;
NOTE 2 Because of existing network structures, in some countries/regions, the boundary between medium and high voltage can be different.
Most of the recommendations for power quality at the SUPPLY TERMINALS are expressed as POWER QUALITY INDICES that describe the manner in which the characteristics of electricity vary. Such variations may appear random in time, with reference to any specific supply terminal, and random in location, with reference to any given instant of time. As such, the POWER QUALITY INDICES are based on the occurrence of the applicable electromagnetic phenomena:
- continuous phenomena, i.e. deviations from the nominal value that occur continuously over time. Such phenomena occur mainly due to load pattern, changes of load, non-linear loads or distributed generation, and
- discontinuous phenomena or events, i.e. sudden and significant deviations from normal or desired wave shape which typically occur due to unpredictable events (e.g. faults) or external causes (e.g. weather conditions).
The power quality indices and the recommended values are intended to be used as technical reference for regulatory purposes (e.g. in NETWORK CODES) or for contracts between network operator and network user (e.g. part of a CONNECTION AGREEMENT).
Power quality requirements combine the obligations of NETWORK OPERATORS with the requirements of equipment or installations on the electromagnetic environment. It is worth noting however, that the requirements of equipment or installations on the electromagnetic environment also include emission aspects that are addressed in other IEC standards (see Clause 2 and Annex F).
NOTE 3 Network operators are in charge of developing and operating the electricity supply system taking into account at the same time:
- provision of adequate conditions for equipment, installations or other networks connected to their network;
- avoidance of unnecessary costs.
NOTE 4 In many countries/regions, requirements concerning the essential characteristics of electricity at supply terminals of public networks are set, or controlled, by National/Regional Regulatory Authorities.
In some cases, additional requirements or differences in requirements can be agreed by terms of a contract (usually a CONNECTION AGREEMENT) between an individual NETWORK USER and the network operator. Such a contract is most likely to arise for network users with relatively large electricity demand, supplied from the MV or HV network, or having power quality sensitive load. It may also arise in sparsely populated or difficult terrain, such as mountain regions, where distribution costs are high. In such an area a network user may be willing to accept a connection, at lower cost, which does not entirely comply with the power quality standards.
NOTE 5 The quality indices and the recommended values appropriately cover the vast majority of locations under acceptable economic conditions, despite the differences in situations, provided that:
- for mass-market products, emission requirements in standards such as IEC 61000-3-2, 3-3, 3-11and/or 3-12 are regularly and appropriately updated to take into account the development of markets and changes in technologies;
- for large installations, emission levels are effectively controlled, e.g. through connection agreement (Annex E lists some methods to improve power quality);
- network operators make use of appropriate methodologies and engineering practices, e.g. based on PLANNING LEVELS and IEC TR 61000-3-6, 3-7, 3-13 and/or 3-14.
NOTE 6 Specification of related measurement methods can be found in IEC 61000-4-30, EMC - Testing and measurement techniques - Power Quality measurement methods.
NOTE 7 Specification of the performance of related measuring instruments can be found in IEC 62586, Power quality measurement in power supply systems.
While power quality is related to EMC in a number of ways, especially because compliance with power quality requirements depends on the control of cumulative effect of electromagnetic emission from all/multiple equipment and/or installations, this Technical Specification is not an EMC publication (see also Annex F).