Power Factor Control

What is Power Factor?

Power factor is just one important step in the larger Power Quality story. This “factor” is calculated using two components of the power in any alternating current electrical circuit.   The two components are ‘real power’ (kilowatts) and ‘apparent power’ (kilovolt amps).

Power Factor is the ratio of ‘real power’ to apparent power, or kW divided by kVA (kW/kVA)

Power Factor values can vary from 0 to 1.00, but typically is more likely to be lagging in a range from 0.70 (poor) to 0.98 (very good). A Power Factor below 0.9 is considered low and should be corrected; subject to a cost benefit justification.  Note: When power factor in your electricity network is low, electric motors and transformer loads etc. (those needing magnetising energy) run less efficiently, and operate at higher temperatures. This can reduce their useful/design life.  The overheating is lost energy, therefore, also, adding to higher operating costs.

What can cause low/poor Power Factor?

We look at three important components to address poor Power Factor: Real Power, Apparent Power and Reactive Power

Real Power, the one measured in kilowatts, is the current and voltage actually doing the work such as creating heat, light, and mechanical motion. Pure resistance electrical loads such as bar heaters, electric hot water systems and ovens do not change power factor. However Reactive Power, which does no useful work, does change power factor. “Reactive Power” is needed to sustain electromagnetic fields associated with electric motors, transformers and other magnetised electrical loads. This is the power that takes up additional space in power distribution systems but does not show up on a simple kilowatt power meters, but power distribution companies have to be able to deliver the total “apparent power” demand, not just the “real power” demand, through their power networks.

Measuring Power Factor

Power factor in an alternating current electrical circuit and can be ‘point-in-time’ measured using a range of power meters or clamp testers. However, a business manager needs to know the bigger picture of a whole 24 hour working day or, in fact a whole business cycle. Sophisticated power quality logging over days will show when power factor is low, whether it is low during critical peak demand periods, or otherwise in off peak or ‘shoulder’ periods. This will help to identify which electrical devices in a business contribute most towards poor power factor and higher power costs generally.

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Analysing Power Quality information – Reporting to business managers

Power quality logging is designed to record a vast amount of information to fully understand an array of conditions within a power circuit.  Almost 100 individual points will be recorded every few minutes on a three phase main power board. This will show the power quality professional the following, to name just ten of the main points:

  1. Phase loadings and Balancing – easy to correct
  2. Neutral wire currents
  3. Highest voltages and current loads in real time
  4. Lowest voltages and current loads in real time
  5. Power factor (PF) – Correctable, however, may not be in isolation
  6. Voltage and current harmonics in power circuits that should be addressed before PF correction is installed
  7. Total harmonic disturbances (THD) a combination of individual order harmonics to the 50th
  8. Flicker (a measure of fluctuations in voltage)
  9. Power load/demand profiles over 24 hour periods or longer if required
  10. Power demand profiles matched against the distribution system’s Peak Periods

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The power quality professional will analyse all this data and produce a report for the business manager. The report will focus on power quality issues to be addressed and prioritised, highlighting cost effective solutions for reducing power consumption generally and the overall cost of power to the business. A most important aspect of the power quality professional’s task is to assist the business manager to understanding the data, thereby gain the knowledge and confidence to better manage her/his annual energy budget.

Solutions for low Power Factor

When electrical devices such as electric motors and transformers need “reactive power” the “reactive power” is drawn from the power grid. This creates the need for the “apparent power” consumption to increase. Low power factor may be corrected within a power circuit by installing “Power Factor Correction” equipment; however, “Power Factor Correction” equipment may not be the Silver Bullet to solve all of your power quality problems, so caution should be taken when overall power quality improvement becomes the business objective. Good decisions to bring about reductions in business operating costs do not come from kneejerk decisions, they come instead from an informed, rationalised perspective. If a business has generally run for years in the dark about electricity, it may take a month or two to become completely enlightened before planning a course of action to improve power quality.

Power-factor-correction

Modern, compact intelligent Energy Management Systems using automatic computer controlled capacitor banks are capable of maintaining power factor close to the unity (1.00), at all times, giving substantial financial savings, which are reasonably quantifiable into dollar terms. Therefore, a return on investment (ROI) timeframe can be estimated prior to Installation.

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Additional Information on Power Factor

While the subject of “power factor correction” is not a common subject for discussion by the general public or in the mass media, it is a well understood phenomenon in professional engineering circles and the power industry. The measurements and calculations for solutions are mathematical certainties. As previously stated, power factor correction alone is not necessarily, the “silver bullet” solution for a business with poor power quality. That is why power quality logging (temporary or, preferably permanently installed) to get sound power quality data should be seriously considered before taking action to install a power factor correction in isolation.