Energy Management/Energy Efficiency

What are the most important electrical parameters to monitor for a better Energy Efficiency?

Monitor for a better Energy Efficiency
Monitoring of electrical parameters is a key element in any Energy Efficiency approach.

Implementation of monitoring equipment is the first step of this kind of approach, as it makes an assessment of the actual situation possible, before determination of the most relevant solutions.

Then, it is possible thanks to monitoring to permanently observe the operation of the installation. And finally, it is possible to quantify the Energy Efficiency improvement actions.

But what are the most relevant parameters to monitor?

As far as Energy Efficiency is concerned, measurement of electrical energy is of course number one. Active energy (in kWh or MWh) is generally the main component of the electricity bill. For an accurate assessment, measurement of active energy is recommended at different places in the installation, preferably at every workshop level. The measurement period should be limited, one week being a reasonable compromise in order to compare periods with similar activity levels.

Any observed increase of energy consumption should be carefully analysed, if it is not the result of a planned increase of activity level.

The ideal situation should be a steady and extended decrease of energy consumption.

Measurement of the supply voltage is also very valuable in terms of Energy Efficiency. Three different aspects should be analysed:

  • Amplitude: for an optimum operation, the supply voltage should be maintained in a range of ±5% around the value declared by the Utility. Lower value means that some equipment like motors operate in deteriorated conditions. Higher value means increased power losses in transformers, motors, lighting equipment.
  • Voltage fluctuations are responsible for light flicker and motor vibrations, even if the voltage amplitude remains within the contractual limits.
  • Voltage sags and interruptions are the most important phenomena in terms of Power Quality. Accurate measurement and dating can help find the origin of the disturbance, and possibly facilitate negotiations with the Utility.

measure1Current and Power absorbed at different points in the installation give the image of the instantaneous activity level. Observation of large fluctuations of current or power can direct actions in order to optimize equipment and smooth energy usage.

Continuously high values of current mean that overload tripping is likely and low values means that equipment may be over-rated or unsuited.

Power Factor and Harmonic distortion are other indicators of the way electrical installations are managed. A poor Power Factor, say, lower than 0.9, means that the supply current is un-necessarily high, for a given power transmitted to the loads, and subject to a special charge by the Utility. Power Factor Correction equipment should be implemented.

High harmonic voltage distortion, say, higher than 6 to 8%, may be the cause of disturbances and increased power losses. This observation should trigger the implementation of harmonic mitigation equipment.

Other parameters which are more difficult to manage

For large interconnected networks, the power frequency is maintained by the Utilities within strict limits around 50 or 60Hz. There is nothing to be done at the Distribution level. The only action to be taken in case of measurement showing out-of-range frequency should be to prepare for interruption or black-out!

Voltage unbalance factor is another parameter which is commonly monitored and displayed without being really under control. Fortunately, this is generally not an issue in most electrical installations.

Is it serious, Doc?

As a conclusion, monitoring of electrical parameters is a key factor for a better Energy Efficiency, but interpretation of measurements is the real value. In other words: it is important to know your cholesterol ratio, but you need a Doctor to tell you if it is serious, and to give you medicine if necessary…

4 Responses
  1. pierre peres

    Mr Schonek
    I don’t know if it is the right place to ask this question (I am not familiar with blogs), I am looking for clarifications regarding harmonics.
    Do you have any explanation why derating factor used for cable sizing calculation (refer IEC 60364 5-52) is used only for cable equipped with neutral (3P+N or 3P+N+G) and not for 3 phases cable, while harmonics (3…) are flowing through phase conductors?

    • Jacques Schonek Jacques Schonek

      Dear Sir,
      Thanks for your interest with the Power Management blog by Schneider Electric.
      Here is the answer to your question.
      For cables without neutral, the current to consider is the rms value, taking account of harmonics. The heat dissipation will depend mainly on the rms current. The additional heat because of the higher frequency of harmonic currents is generally negligible.
      For cables with neutral conductor in sinusoidal conditions, the heat dissipation is only due to the phase currents, as the neutral current is considered to be zero in balanced, full-load situation. However, when harmonic currents are present, particularly 3rd order harmonics, the neutral current is not zero anymore, and the corresponding heat dissipation must be taken into account. The result is that the cable must be oversized (or the phase current must be reduced) so that the maximum temperature is not exceeded.
      You can find a more detailed explanation in “Cahier Technique 212: The neutral: A live and unique conductor”, downloadable from our website.

  2. salami

    would you please , guide me what is appropriate period for measurement of electrical parameters in installed capacitor in distribution substations(study of fixed and switching capacitors and effect of them).
    Also in your view which parameters in this study can be more important?



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