Discussion on Power Quality is synonymous toQ y y yHarmonics.Perhaps at one time in the history of electricity

l th l lt di t ti d bsupply, the supply voltage distortion caused bycustomer equipment was a concern to Utilities.However, today where electricity supply chainy y pp yhas been vertically and horizontally segregatedand Utilities are becoming more customer-centric (customer focussed) the main cause ofcentric (customer focussed), the main cause ofconcern associated with quality of supplyexperienced by customers can be placed inf ll i dfollowing order:

1. Reliability i.e. frequency and duration of outages2. Voltage sags (dips) caused by short circuits in the networkg g ( p ) y

or inside customer's plant3. Voltage fluctuations caused by rapidly changing load such

l t i f f t di t li (DOL)as electric arc furnace, frequent direct-on-line (DOL)induction motor (IM) starts, welding machines. Customerscan see the light (illumination) fluctuating in sync withg ( ) g yvoltage fluctuation. This light fluctuation or light flicker isvery irritable - especially to those who read using lowwattage incandescent bulbs - typically bed side lampswattage incandescent bulbs typically bed side lamps

4. Transient over voltages - destroying customers voltagesensitive equipment

5. Voltage distortion (harmonics) causing power factorcorrection capacitor bank fuses of capacitor bank itselfgetting damage due to harmonic resonancegetting damage due to harmonic resonance

So there are many facts to generic term Power Quality.Complaints of customers:p :- Anger due to voltage sag issues.- Poor quality of supply - mostly associated with tripping of

their voltage sensitive variable speed drivesSolution:

At U i iti h i i l d i bj t- At Universities, harmonics is a popular academic subjectdue to its challenging mathematics and easy access to textbooks and notes. In real life, harmonics is not as seriousPower Quality issue as voltage sags.

- Calculation of voltage sags is also very challenging andinvolves reasonable level of mathematics You can make itinvolves reasonable level of mathematics. You can make itchallenging by associating fault current and voltage dropcalculations with probability of occurrence of differenttypes of faults.

Average PS engineer or an academic generally associatePower Quality to harmonics and appear oblivious to otherissues that diminishes the quality of supply and hinder endusers productivity.

Where it concerns harmonics, many network operators inEurope are actually very much interested in harmonics.p y y

Why so much interest in harmonics as opposed to other PQi ? h fli k l iissues? such as flicker, voltage sags, transients etc.

This is at least partly driven because there are limitationsThis is at least partly driven because there are limitationsset by regulators on harmonic voltage levels.

Once again why regulators latches on to harmonics for limitsand not other PQ issues? Do they find it easy to copy eachother’s regulations? Or is harmonic (voltage distortion) solethal that it will render use of network for delivery ofelectrical power useless? Or is it sufficiently technical andelectrical power useless? Or is it sufficiently technical andbeyond the comprehension of many such that it gives theillusion of all parties in the electricity supply chain includingregulators are being responsible? Or is to do with history andregulators are being responsible? Or is to do with history and“ergonomics” i.e. harmonics was easier and cheaper tomonitor and record compared to voltage sags, transients,flicker and so on?

Phenomenon of harmonic frequency resonance causinginterference to telephone circuits, damage to capacitorbanks, damage to equipment installed in the network andequipment installed in the customer premises.However not to recall addressing any of these problemsHowever, not to recall addressing any of these problemscompared to problems associated with voltage sags andvoltage fluctuations.Perhaps New Zealand networks and customers are clean andgreen without significant penetration of polluting loads thatcauses significant voltage distortioncauses significant voltage distortion.Therefore PQ is not simply a list of individual / separateperformance parameters which measure the deviation froma steady-state, sinusoidal and balanced operation, but areall interwoven. Sags, Harmonics, Unbalance (even atharmonic frequencies) are all mixed together - - - - andharmonic frequencies) are all mixed together andvarying with time.

Interwoven PQ Phenomena Sags, Harmonics, Unbalanceg , ,Currents - During a Sag on an Inverter

Current unbalance for phase to phase short-circuit (sag) on an Inverter Fig-a

Unbalances at 5th harmonic during phase to phase short circuit Fig-bg

Time-Varying Phasors (Including Harmonics) Fig-3

Fundamental + Harmonics - Converter Varying Load Fig-Time i hvarying phasors