How do you evaluate your system performance using power quality and reliability indices?

1 Power quality indices

Power quality indices are numerical values that quantify the deviations of the voltage and current waveforms from their ideal sinusoidal shape and magnitude. These indices can provide insight into the level of distortion caused by nonlinear loads and devices, the efficiency of power utilization, the reactive power demand, the degree of asymmetry among the three-phase voltages, the frequency and duration of voltage sags, and the frequency and duration of voltage swells. Common power quality indices include total harmonic distortion (THD), power factor (PF), voltage unbalance factor (VUF), voltage sag index (VSI), and voltage swell index (VSWI).

2 Power reliability indices

Power reliability indices are numerical values that quantify the availability and continuity of the power supply, and reflect the impact of power outages, interruptions, and variations on customers and equipment. For example, the System Average Interruption Frequency Index (SAIFI) indicates the frequency of power outages in the system by measuring the average number of interruptions per customer per year. The System Average Interruption Duration Index (SAIDI) measures the severity of power outages in the system by calculating the average duration of interruptions per customer per year. The Customer Average Interruption Duration Index (CAIDI) indicates the average restoration time for customers by measuring the average duration of interruptions per interrupted customer per year. The Customer Interruption Cost (CIC) provides an estimate of the economic impact of power outages on customers by calculating the cost of interruptions per customer per year. Lastly, Loss of Load Probability (LOLP) indicates how well system resources meet load requirements by determining the probability that system demand exceeds available generation capacity.

3 How to measure power quality and reliability indices

In order to measure power quality and reliability indices, you need to collect and analyze data from different sources, such as power quality meters, fault recorders, event loggers, and customer surveys. Power quality meters measure and record voltage and current waveforms, harmonics, power factor, voltage unbalance, voltage sags and swells, and other parameters. Fault recorders capture and store voltage and current waveforms during faults. Event loggers record the events that occur in the system. Lastly, customer surveys are questionnaires or interviews that collect information from customers about their power quality expectations, experiences, and satisfaction. All of these sources can help identify the location, type, cause of faults, system response to faults, sequence of events in the system, customer perception of the system performance, and customer interruption cost.

4 How to improve power quality and reliability indices

To improve power quality and reliability indices, you need to identify and mitigate the causes of power disturbances, such as harmonics, power factor, voltage unbalance, voltage sags and swells, and power outages. Harmonics can be reduced by using filters, reactors, or active power conditioners; power factor can be improved by using power factor correction devices; voltage unbalance can be corrected by balancing the loads or using phase balancers; voltage sags and swells can be prevented by using protection devices or voltage regulators; and power outages can be minimized by using backup generation or distribution automation.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?