IEEE 1250:2011 pdf free download – IEEE Guide for Identifying and Improving Voltage Quality in Power Systems
Each of these two basic categories has indices associated with it. Indices provide the foundation for charactcrizing thesupply system voltage quality levels in a consistent manner. Indices can be used to establish baselines of performanceas a function of system characteristics.The following subclauses describe indices that can be used to describevoltage quality levels in both of these major categories along with example benchmarking results that can provide thebasis for establishing targets and limits.
3.3 Steady-state (continuous) voltage quality characteristics
Steady-state power quality characteristics must meet minimum requirements to assure the proper operation of equipment.The basic concepts of compatibility levels are established in IEC 61000-2-2:2002 [B4j.’ This concept applies to allsteady-state types of power quality. It is not as applicable to disturbances, such as voltage sags (dips). interruptions,. andtransients. The normal variations of steady-state power quality characteristics allow them to be characterized with trendsover time and with statistical distributions.The statistical nature of these characteristics lends them to being representedby specific statistical levels. For instance, the limits in EN 50160-1999[B2] for steady-state power quality are evaluatedat the 95% probability level. Recent discussions have indicated that other probability levels may also be appropriatefor fully characterizing performance,
Figure 4illustrates the concept that applices for steady-state power quality characteristics. The power quality performanceof the supply system is characterized statistically, and this can be compared with the statistical characteristics of thecquipment immunity to determine the likelihood that equipment will be affected by the voltage quality variations. Theobjective is to define a voltage quality level that can be achieved with reasonable investment in the power system andwill also have a low probability of causing equipment problems. This level is called thec“compatibility level.”Ilt isdefined with statistics. As indicated previously,a typical way of defining the compatibility level for performanceevaluations is the level that can be exceeded only 5% of the time (95% probability that the level will not be exceeded).
Equipment damage level—This is the level of quality that may pose a threat to equipment health if it is exceeded. Suchconditions are important to identify when they occur and to prevent if possible Examples may include harmonicresonance,ferroresonance,high neutral currents,conditions that may cause overheating， and so on. There should besome margin between the compatibility level for the supply and the equipment damage level.
Equipment immunity level—This is the level of quality that may affect equipment performance if it is exceeded. lt isalso defined statistically. There should be some margin between the compatibility level for the supply and the equipmentimmunity level.
Alarm level—This is the level of quality at which notification will occur(i.e.. the level at which an investigation or otherresponse may be warranted).The alarm level should be above the planning level but below equipment immunity,equipment damage,and safety levels.
Planning level—This is the level of quality that the clectric utility establishes as its design objective.Usually,theplanning level is defined at some level below the compatibility level to help assure that the actual compatibility level willnot be exceeded.For instance, the compatibility level for harmonic voltage distortion might be 8%, but the planning levelmight be 5% to help make sure that the 8% level is not exceeded.