USING IEEE 1668 FOR POWER QUALITY STUDY
Visualization of data allows one to glance quickly at a graph, chart, or display and understand the results based on understood criteria. For years power quality studies and audits have relied on CBEMA curves, SEMI F47 curves and others to identify equipment and facilities susceptibility to sags. In 2017 IEEE finalized the 1668 standard Recommended Practice for Voltage Sag and Short Interruption Ride-Through Testing for End-Use Electrical Equipment Rated Less than 1000 V.
In addition to specifying the equipment to be used and testing methodology, it also helps define magnitudes and durations of sags that should not result in equipment failure. This allows graphical creation of data that, at a glance, will tell the severity of sag history on a facility. For single and two phase sags, equipment should not experience failure at the points listed in the table below, or at lesser points.
| Minimum Test Point No. | Residual voltage in % nominal | Duration in Seconds | Duration at 50Hz | Duration at 60Hz |
| 1 | 50% | 0.2 | 10 cycles | 12 cycles |
| 2 | 70% | 0.5 | 25 cycles | 30 cycles |
| 3 | 80% | 2.0 | 100 cycles | 120 cycles |
In a more visual form, below is a graph showing the areas that equipment should operate in, and areas that they have potential to fail at.
As investigators, how is this relevant? By using software such as PQ Sapphire, data from multiple sources can be input into the database and a graph can be produced to help customers determine if they are having enough voltage sags in the non-shaded region to consider some form of sag mitigation or voltage stabilization equipment. Below is a graph populated with one months’ worth of voltage sag data.
As shown above, Sapphire was able to create this plot based on single phase data and plot the disturbances based on the 1668 test points. In this instance, there are two points inside the non-shaded region, indicating the potential for equipment failure. A graph this simple is easy to understand and at a glance shows the single phase sag environment for a month at this facility.
Communicating data and test results to customers and clients, internal or external, has always been a challenge, as there has never really been a way to see it, outside of some RMS trend plots or using other styles of curves. The publication and adoption of IEEE 1668 has helped to unify the means of viewing results and allows software packages, such as Sapphire, the ability to translate that data to easy to view and understand graphs.
View IEEE1668 Graph in PQSCADA Sapphire: