What to check to ensure the power quality of your installation

Circutor | 16 de June de 2022

Problems are very common in electrical installations. These include machinery stoppages, tripped protective devices and wear on electronic devices - such as industrial robots and variable-speed drives - that are sensitive to disturbances in the grid.

Poor power quality voltage in an installation can result from internal or external causes. If your installation is too far from the transformer substation, for example, your voltage may be abnormally low, causing some equipment to stop randomly. If, on the other hand, you are too close to the transformer substation, your voltage could be abnormally high. This condition is termed permanent overvoltage, and it can damage sensitive electronic components.

Measuring the signal quality not only entails evaluating the voltage value, but other electrical parameters as well, such as the frequency, flicker, harmonics, total harmonic distortion (THD) in voltage and current, imbalance between phases, and quality events such as overvoltages, voltage dips and outages.

The problems that may appear in an electrical installation are very different. To assess the power quality, you need to consider a series of variables, not just the amplitude of the voltage.

Applicable regulation

The EN50160 quality standard, based on statistical calculations of values that are generally recorded every 10 minutes, indicates the limits allowed in each of the recorded variables to ensure power quality. This is regardless of whether the power is provided by an electric utility or any other source of energy.

Quality events graph

Depending on the electrical parameter, the limits required by the standard and the analysis period for acceptance may vary.

For example, for 230 VAC and 50 Hz networks:

• The frequency values recorded every 10 seconds must be between 49.5-50.5 Hz 99.5% of the time and between 47-52 Hz 100% of the time.

• 95% of the phase-neutral voltage values recorded every 10 minutes must be between 207-253 V and 100% of the values between 195.5-253 V.

• 95% of the phase-phase voltage values recorded every 10 minutes must be between 358.53-438.21 V and 100% of the values between 338.62-438.21 V.

• As for the reading, the U2 imbalance between phases (between the negative phase component U2 and the positive phase component U1) must be at the most 2% in 95% of the 10-minute weighted RMS values.

• Quality events must be RMS values and last at least 1⁄2 cycle (10 ms in 50 Hz networks and 12 ms in 60 Hz networks). Events are classified as overvoltages, dips or interruptions, based on the maximum or minimum value they reached.

• Quality events can be grouped in tables based on their duration, and displayed in different types of graphs based on their amplitude and duration.