Power quality: Measuring algorithm of electrical parameters

The regulations defining power quality by the EN, IEEE & IEC Standards are accepted and followed worldwide. Power quality, what exactly does it mean? It’s not just the power quality, rather it is the usage of electricity; effectively and load dependent. Users generally have major issues in having regulations to most commonly named problems under banner ‘power quality’. It is the general and most familiar terms which describe the parameters of electrical power.

Electricity has become one of the basic necessities of day to day life. Here most inevitable is the energy consumed. However, going a step ahead, we find that most of the energy is been wasted by one means or the other. This waste of energy counts in revenue loss and needs extensive attention to get it under control. Based on this many studies have been undertaken.

• Voltage sags
• Voltage variations
• Interruptions
• Voltage swells
• Brownouts & blackouts
• Voltage Imbalance
• Voltage waveform distortion and THD
• Harmonics & Inter-harmonics
• Noise
• Impulse
• Spikes & Transients
• Electric Shocks
• Flicker
• Power frequency
• Grounding issues
• Voltage fluctuations
• Over & under voltage
• Magnitude and many more commonly know issues

The major concern in power quality is due to the modern day equipment’s which generally include variable speed drives and switched mode power supplies, furnaces and varying load conditions. The variety of loads used in process industries, household appliances and other equipment’s produce harmonics, which are one of the key contributors to the loss of energy. Further, resulting in poor power quality and therefore resulting in heavy penalty from electricity board, unexpected maintenance or even damage of equipment.

IEC 61000-4-30 explains the power quality-measuring algorithm of electrical parameters. IEC 61000-4-30 is an IEC standard that defines the correct measuring algorithms for power quality instruments. Moving ahead let’s see what are key issues which mainly address power quality.

Harmonics are generally defined as “a sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency”. Harmonics can be mostly explained using the musical notes which are created by an instrument while playing. These were known to mankind since long back before the electricity came to existence

Another component of harmonics is inter-harmonics, which are like the shredded pieces of mud in a pile of wheat. To explain the inter-harmonics let us take an example of voltage waveform, comprised of 60 Hz and 200 Hz signals. Integral multiples of 60Hz correspond to 120, 180, and 240 and so on. However, if 200Hz is seen then the resultant calculation may result a varied result in the 3rd or 4th Harmonic if considered for 200 Hz. These in-between frequencies are termed as inter-harmonics.
In order to keep track on the harmonics, IEEE has defined the limits shown in below table.

General harmonic generating loads are:

• Electronic lighting ballasts/controls
• Adjustable speed motor-drives
• Electric arc welding equipment
• Solid state industrial rectifiers
• Industrial process control systems
• Uninterruptible power supplies (UPS) systems
• Saturated inductors/transformers
• LAN/computer networks and many more

Harmonics has very much impact on the system and few of the negative impacts seen are:

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Overheating and premature failure of distribution transformers
– Increasing iron and copper losses or eddy currents due to stray flux losses
• Overheating and mechanical oscillations in the motor-load system
  – Producing rotating magnitude field, this is opposite to the fundamental magnitude field.
• Overheating and damage of neutral ground conductors
  – Trouble sustained type harmonics: 3rd, 9th, 15th
  – A 3-phase 4-wire system: Single-phase harmonic will add rather than cancel on the neutral conductor
  – Malfunction/mal-operation of sensitive tele-control and protection relaying
• False or spurious relay operations and trips of circuit breakers
• Failure of the firing/commutation circuits, found in DC motor-drives and AC drives with silicon controlled rectifiers (SCR-Thyristor)
• Mal-operation instability of voltage regulator
• Power factor correction capacitor failure
  – Reactance (impedance)-Zc of a capacitor bank decreases as the frequency increases
  – Capacitor bank acts as a sink for higher harmonic currents
  – The system-series and parallel resonance can cause dielectric failure or rupture the correction capacitor (meant for power factor failure due to over-voltages and over-currents).

Flickers – An unsteady movement of a flame or light that causes rapid variations in brightness OR Flickering is the opposing changes in intensity of luminosity. These are generally caused due to fluctuations in voltages. Flicker is generally caused due to loads, which draw more current during the processes such as;

• Electric arc furnaces
• Induction motors w/high inrush currents (high efficiency AC units)
• Arc-welders, spot-welders
• Wind turbine generators
• Ovens
• Malfunctioning power electronics
• Any large-draw varying load

According to an article by Dr Kurt Schipman and Dr François Delincé, “the best electrical supply would be a constant magnitude and frequency sinusoidal voltage waveform. The power quality of a system expresses to which degree a practical supply system resembles the ideal supply system.

• If the power quality of the network is good, then any loads connected to it will run satisfactory and efficiently. Installation running costs and carbon footprint will be minimal.
• If the power quality of the network is bad, then loads connected to it will fail or will have a reduced lifetime, and the efficiency of the electrical installation will reduce. Installation running costs and carbon footprint will be high and/or operation may not be possible at all.

Poor power quality can be described as any event related to the electrical network that ultimately results in a financial loss. Possible consequences of poor power quality include:

• Unexpected power supply failures (breakers tripping, fuses blowing)
• Equipment failure or malfunctioning
• Equipment overheating (transformers, motors, leading to their lifetime reduction.
• Damage to sensitive equipment (PC, production line control systems)
• Electronic communication interference
• Increase of system losses
• Need to oversize installations to cope with additional electrical stress with consequential increase of installation and running costs and associated higher carbon footprint.
• Penalties imposed by utilities because the site pollutes the supply network too much.
• Connection refusal of new sites because the site would pollute the supply network too much.
• Impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time (flicker)
• Health issues with and reduced efficiency of personnel