Dear Sandeep,

you are right but this is PQ in common sense.

"Good enough if it suits my needs"

But try - just for fun - how many publications about power quality are generated and then

return to the core of my question "How to judge power quality" taking into account, that if you want to judge something, you would need to find a way to measure it.

If you measure it - what is the unit you use?

Power quality means quality and reliability. Supply of power without variation in frequency, waveform distortion(without harmonics) and voltage required , are the main factor for power quality, along with reliability of supply. Better power quality, reduces the, life consuming cost of the power equipment(transformer and switch gear used in supplying), better power quality is very important for consumer side also, as it reduces, equipment damage due to harmonics( over heating), and reduces the life consuming cost, considerably of equipment/machines used in industry and domestic use. With lower power frequency and voltage life consuming cost increased considerably due to raised current (losses) for same load, refer my papers on,' microprocessor/computer based overload time limit computation and control for life consuming cost of power transformers.'   

Dear Desai,

all true - but not the core to the question "How to judge, evaluate or even measure power quality"

Any suggestions on that?

Online Monitoring, of frequency voltage ,waveform and power factor supplied, using microprocessor/computer or microcontroller, based system, like used in load dispatch centers.

Ok - I got all this set up.

So how many [Unit still missing] does PQ change is THD changes from 1% to 5% while the voltage is stable or how many [fictional unit] do I loose if at 3% THD the voltage sags down to 90% once every 5 minutes?

How many [fictional Unit] is a supply with 50Hz +/- 1 Hz and THD=0 better than one with THD=1% but 50Hz +/- 0.1Hz?

If Power has a quality, you should be able to quantify it, right?

Think of me as nitpicker, but I really want to know!

Economy and quality, you have to decide as power engineer. In large system little dropping of frequency saves considerable power units. As I said, modern transformers(CRGO) are working on higher flux density, with flat top, flux wave causing harmonics for better efficiency. I suggest, 50 Hz +/- 1 Hz  with THD=0.

You could define the quality of 100% like sinusoidal waves, perfectly on phase, at the specified frequency and with the requiered voltage stability. That definition allows to you to define several measurements of deviation, for example THD is an statistical deviation, voltage sags is a collection of events with different characteristics, etc. These measurements helps to evaluate the aspect on interest, for example if you are the subway operator, you will be more worry about Sags than the Harmonic distortion. Finally I could give to you a general definition of power quality deviation: "voltage and current wave forms that not match perfectly with a set of pre-defined and standardized voltage and current wave forms"

Then maybe you want to try to develop different measurements to express that deviation.

For example, if you take the instantaneous vectors of voltage and current and make the dyadic product between them (http://en.wikipedia.org/w/index.php?title=Dyadics), you will get an instantaneous power tensor, that is a Matrix, then you'll be able to calculate the Entrywise norm (http://en.wikipedia.org/wiki/Matrix_norm#.22Entrywise.22_norms), now you have a value that involves all the electric phenomena of those wave forms for each sample time, then you just need to make some kind of mean value to get a measurement of the whole power quality state, because you can make comparisons between that value and the ideal value that is obtained from the described waves above.

But It's just an approach, I encourage you to develop others.

Thanks for your interesting question. 

Dear Odair,

wow - that's a neat idea indeed and it would return the Power Quality in in a sort of p.u. which would be a simple way of judging it.

Thanks for introducing this.

If the values were integrated covering a longer time period, it would depend on this period whether it would be sort of a static Power Quality or a rather transient Power Quality if the interval gets shorter.

Given that you could observe this in a continuous manner, one could define a function  PQ(t) and derive PQ_rms even depending on load, load steps or load variations

Intriguing :-)

You may want to start reading this work:

GENERALIZED INSTANTANEOUS REACTIVE POWER THEORY IN POLY-PHASE POWER SYSTEMS

R. S. Herrera

Power Electronics and Applications, 2009, IEEE

Dear Odair,

power quality and reactive power compensation are different "shoes". Power quality descript the additional encumbrance of the electro technical equipment. And with reactive power compensation you can reduce the costs of electro energy transport!

Regards Christan   

I know, some people say that a low power factor may cause power quality issues, for example overcurrent and overvoltage transients in facilities when some apparatus are turned on.

I can't find the original thesis but if you want to give a deep discussion I could find it for you. I just wanted to show you guys the power tensor.

Dear Odair,

"low power factor may cause power quality issues", I think this context is only a marketing gag for sale improved power-supply units.

 Regards Christan   

I agree with you. 

On Internet forums I often see "power quality" being used as part of hand waving arguments by renewable energy opponents. By not being specific they can hide not knowing much about the subject.

The definition of power quality is:

The set of voltage and current parameters, at a certain location and time, capable of satisfying the customer needs and requirements.

Power quality is a subjective concept. Even though there are standards defining the "desirable" power quality conditions, every system has particularities that may lead to adjust PQ parametrs to local conditions.

Ideal PQ conditions are nowadays impossible to have. Isolated systems are not powerfull enough to provide electricity without voltage chages or fluctuations, strong power grids will always have faults, harmonics, dips, transients, etc. The concept of electromagnetic compatibility - EMC can be helpful in this matter: the probability of a system, device or component to operate properly within its electromagnetic environment, without affecting any other device. Most PQ standards and assessment procedures are based on the EMC concepts.

Hopefully this comments help a little bit. Regards!

Dear Mohit,

if "Customer satisfaction" was the answer - then how do you intent to create a specification on "Satisfaction", that all customers agree to?

How do you measure and define "Customer satisfaction".

A private customer in the middle of nowhere may be satisfied with having electricity 70% of the time.

Industrial customers would certainly not be satisfied.

So - try again :-)

Power quality is ultimately a consumer-driven issue, and the end user’s point of reference takes precedence. Therefore, the following definition of a power quality problem is: "Any power problem manifested in voltage, current, or frequency deviations that result in failure or misoperation of customer equipment."

Dear Memon,

assuming that most electronic devices feature a rectifier in first place,

a change of frequency from 50Hz to 25Hz would not lead to misoperation in such equipments.

So back to this, by now five year old question:

What is the parameter or parameter set to be measured to claim a certain quality?

And what "quality" can be defined to be "sufficient"?

Hello Martin,

Very Interesting question. There are as many meanings for PQ as there are PQ consulting engineers. :-) After 35 years of working in the industry, I have defined 2 different terms.

Quality of Supply (QOS) and Power Quality PQ

QOS is the electricity supplier view of PQ. Their concerns are 2 types. 1. The efficiency of their generation/distribution system. Changes in generation technology, changes in system design to meet the DG intergration, changes in the regulations and demands from the regulators for reporting QOS, changing standards

2. Customer satisfaction. ( not perfect power)

PQ is the consumer view of Power Quality and includes a broad range of parameters, factors and variables on the customer side of meter. Including earthing (grounding), electrical system construction, all PQ electrical parameters, load demands, lightning, human factors of operators, continuous technology changes in the loads (and PQ requirements). For example, lighting loads from incandescent , florescent to Led. Major changes due to the continuous search for more efficient production equipment. Continuously changing sensitivity of loads to new PQ issues.

Interested in history and PQ/QOS case studies. Visit our new PQ Blog. HTTP://powerquality.blog. In process of loading 30 years of experience.

My professional title is Power Quality Practitioner (tm) .