The Reactive Power, Does It Important For Us

[rdpzycho]

'di ko ma-download.

[♪ ♫ ♫ ♪ ♪ ♪ ♫ ♫ ♫]

hindi ko maintindihan e, importante ba o hindi importante...

kung ganon mali pala yun nag-seminar sa amin  

King Fahd University of Petroleum and Minerals.

Dr. Yasre Ahmed Bin Abdul Aziz Ph.D. Degree in Electrical Engineering (EE) from University of Central Florida  

Ano ba yong seminar nyo? bat nagkaganon? baka may mga latest technology na dyan na hindi pa namin alam dito sa atin....?

share mo naman dito bro  

[robbietan]

tama po yun bumabalik lang sa system yung reactive power kasi di sya na didissipate dahil useless sya,di sya maaabsorb ng load.umiikot lang sya sa system.

not so. energy (VA) is composed of both W and VAR. if the load consumes energy, it consumes both W and VAR

[robbietan]

napansin ko lang kasi sa mga power transformer,rating nya lagi nasa apparent 
power(kVA) saka yung capacitor banks naman nasa reactive power(KVAR) naman yung ratings,baka sa stress may effect yung reactive power kaya importante yung reactive power.

power transformers are so rated since it is the amount of energy they can handle. and energy is VA which is the square root of the sums of the squares of W and VAR.
capacitors are rated in Farads as you may well know. the VAR ratings are based on an assumed frequency that the capacitor will be subjected to. and yes, capacitors supply VAR. Inductors dissipate (use) VAR.

[robbietan]

Yup I got the point nung author, regarding sa pagtaas ng current pag bumababa voltage para mamaintain current(item#2).

Bakit nyo po nasabi na mali yun?

a fixed W motor will draw more current to compensate for a lower voltage, so that it will maintain its constant W output, not maintain its constant current

[kinyo]

marami-rami rin nakopya ... kunsabagay dami talagang articles sa analog website na highly educating

http://www.analog.com/static/imported-files/tech_articles/16242282714726reactive_energy_metering_international_edition.pdf

 

[Mayalin22]

i can't say that the author doesn't know the subject being discussed.. the author is a "full professor", having a Masters and Ph.D degree from a reputable school and his researches extends from electrical power, transmission line and transients.. and the author is experienced..

i wonder why the author didn't mentioned the references.. but i guess, the paper is not a "research paper", on reading his paper.. it's an informal discussion in one particular subject..

however, the author is not citing that the reactive power is not important as "opposed" to the title.. upon my understanding his paper, he's even promoting more on reactive power..

reactive power is one of the important issue for AC phenomena and power calculations for motors, generators and transmission and power lines in measuring the amount of energy going back to the source..

tama po sir mas focus sya sa reactive power... dyan daw po ngayon nakafocus ang study ng mga energy distributors sa buong mundo... ito daw po kasi ang madalas na hindi pinagtutuunan ng pansin dahil wala daw ganong silbi. 

[Mayalin22]

hindi ko maintindihan e, importante ba o hindi importante...


Ano ba yong seminar nyo? bat nagkaganon? baka may mga latest technology na dyan na hindi pa namin alam dito sa atin....?

share mo naman dito bro  

Ito sabi ... 

This article aims to explain and compare the three main methods in use, namely the Power Triangle, the Time Delay and Low-pass Filter.

[Mayalin22]

marami-rami rin nakopya ... kunsabagay dami talagang articles sa analog website na highly educating

http://www.analog.com/static/imported-files/tech_articles/16242282714726reactive_energy_metering_international_edition.pdf

 

yup! dyan nga galing yung ni-lecture sa amin... consultant sya ng analog devices

[glutnix_neo]

1) Reactive power is returned to the electric grid as the windings de-energize - generators provide power in kVA. it is composed of true (kW) and reactive (kVAR). if energy is used by a load, (say a motor) no energy is returned to the grid.

kung masyadong malaki ang reactive energy, hindi lahat yun ay magagamit ng motor at a certain time, saan kaya pupunta yun?

2) When reactive power supply lower voltage, as voltage drops current must increase to maintain power supplied, causing system to consume more reactive power and the voltage drops further   a constand load motor (for example) will draw more current if the load being supplied to it is lower than its rated voltage. lowering the supplied voltage does not in any way cause a motor to consume more kVAR or kW.

Yun na nga yung point ng author master, constant yung kVAR or kW requirement kaya para mamaintain yun sa pagbaba ng Vout eh natural na tataas ang drawn current

3) If voltage reduction continues, these will cause additional elements to trip, leading further reduction in voltage and loss of the load. power grids reduce voltage in times when demand is greater than the load(supply?). a voltage drop of around 5% is common practice - that is called a "brown out". generators trip when the load is greater than their rated capacity so as to protect their generators from overspeeding.

Parang pareho po kayo ng sinabi ng author,

[robbietan]

The items in red are my comments.

The Reactive Power, Does It Important For Us

I. INTRODUCTION
A. DEFINITION OF REACTIVE POWER   

Almost all power transported or consumed in alternating current (AC) networks. AC systems supply or consume two kind of power: real power and reactive power. (Loads, whether AC or DC, consume energy. Energy in AC loads is composed of 2 components, Watt and VAR).  Real power accomplishes useful work while reactive power supports the voltage that must be controlled for system reliability. (If this is true, then how is DC voltage controlled in a DC system, since DC power have no reactive component?)
For AC systems voltage and current pulsate at the system frequency. (This is true if the load is linear. If the load is nonlinear, then this statement is false). Although AC voltage and current pulsate at same frequency, they peak at different time power is the algebraic product of voltage and current. Real power is the average of power over cycle and measured by volt-amperes or watt (Real power is Watts, Apparent Power is volt-amperes). The portion of power with zero average value called reactive power measured in volt-amperes reactive or vars. (What “zero average value”? No such thing exists – if the average is zero, then it is zero.)
The total power is called the apparent power (symbolized by the capital letter S) and measured by volt-amperes or VA. To describe the reactive power , imagine a person on trampoline , The person real power  goes into moving horizontally across  trampoline as it bounces , the effort the person expend to keep standing(represent reactive power Q ) during bouncing result no net forward motion(represent real power P) , but it's necessary to walk on trampoline . The motion from trampoline always perpendicular to the direction the person is walking. So that the direction between P and Q 90 degree Out of phase. (To better describe reactive power, imagine energy as beer inside a bottle. Pour out the beer in the bottle and the glass is filled with beer and beer froth. The liquid portion is W and the froth is Q. Both comprise the total energy beer.)

II. Measuring reactive power
The amount and complexity of household electrical equipment has increased tremendously over the last few years. Electronic ballast lighting, computer monitors and air conditioners are welcome additions to our homes but come with additional burdens. One of these is on the electricity grid, as these appliances generate more signal harmonics. (Harmonics is enough; appliances do not generate “signal” harmonics)
This change in the end-consumer profile is a disadvantage for energy distributors which bill energy based only on active power. With the application of non-linear loads to power lines the active energy no longer represents the total energy delivered.  As a response to improve billing, the measurement of reactive energy is gaining interest. For example, Italy’s leading energy distributor has decided to install more than 20 million household energy meters with active and reactive power measurements. (In the Philippines, the amount of VAR consumed by households is too small to be billed. Looks like the utilities in Italy need more money from billing VAR from their residential users)
This growing interest in measuring reactive energy leads to the question: What method should an energy meter designer implement to accurately measure the reactive energy? (Utilities in the Philippines have long been using meters that measure VAR usage of industrial customers. And those meters are 99.98% accurate)
Although today’s electronic digital signal processing (DSP) enables reactive energy measurements to be closer to the theoretical value, there is no consensus in the field of energy metering on the methods of measurement. This article aims to explain and compare the three main methods in use, namely the Power Triangle, the Time Delay and Low-pass Filter.
 A. System requirements
Electromechanical meters have set a precedent in reactive energy billing. Although they are bandwidth limited and cannot take into account harmonics of the line frequency (Says who? The electromechanical meters in use in the Philippines can accurately measure the VAR consumption even with the presence of harmonics), they are supported by the international standard for alternating current static var-hour meters for reactive energy (IEC-1268). The standard defines reactive energy measurements at the fundamental line frequency, which implies that it is not mandatory to include harmonics. (Which is why measurements are taken using the root-mean-square of values for voltage and current, harmonics are automatically taken into consideration). It also specifies additional testing conditions to check the robustness of the measurements against the third harmonic, the dc offset in the current input, and the line frequency variation. The various reactive power measurement methods presented in this paper are evaluated against these critical tests of the IEC-1268 (Table 1).

B. Reactive power theory
The reactive power is defined in the IEEE Standard Dictionary 100-1996 under the energy “magner” as:
 (1)
where Vn and In are respectively the voltage and current rms values of the nth harmonics of the line frequency, and jn is the phase difference between the voltage and the current nth harmonics. A convention is also adopted stating that the reactive energy should be positive when the current is leading the voltage (inductive load).
In an electrical system containing purely sinusoidal voltage and current waveforms at a fixed frequency, the measurement of reactive power is easy and can be accomplished using several methods without errors. However, in the presence of non-sinusoidal waveforms, the energy contained in the harmonics causes measurement errors. (Non true rms meters have this errors, true rms meters do not have these errors)
According to the Fourier theorem any periodic waveform can be written as a sum of sin and cosine waves. As energy meters deal with periodic signals at the line frequency both current and voltage inputs of a single phase meter can be described by:
 (2)
 (3)
where Vn, In and jn are defined as in Equation 1.
C. Active power
The average active power is defined as:
 (4)
The implementation of the active power measurement is relatively easy and is done accurately in most energy meters in the field.
D. Apparent power
The apparent power is the maximum real power that can be delivered to a load. As Vrms and Irms are the effective voltage and current delivered to the load,
Apparent power = Vrms • Irms        (5)
The correct implementation of the apparent energy measurement is bound by the accuracy of the rms measurements.
E. Reactive power calculation
As explained above, different methods can be used to calculate the reactive power. The theoretical definition of the reactive power is difficult to implement in an electronic system at a reasonable cost. It requires a dedicated DSP to process the Hilbert transform necessary to get a constant phase shift of 90° at each frequency. Several solutions have been developed to overcome this limitation. They can be categorized in three groups:
1- Method 1: Power triangle
The Power triangle method is based on the assumption that the three energies, apparent, active and reactive, form a right-angle triangle as shown in Figure 1. The reactive power can
 (6)
then be processed by estimating the active and apparent energies and applying:
Although this method gives excellent results with pure sinusoidal waveforms, noticeable errors appear in presence of harmonics (Table 1). (If measurements are taken using accurate rms meters, there will be no errors if you use this formula to get reactive power)
2- Method 2: Time delay
A time delay is introduced to shift one of the waveforms by 90° at the fundamental frequency and multiply the two waveforms:
 (7)
where T is the period of the fundamental. In an electronic DSP system, this method can be implemented by delaying the samples of one input by the number of samples representing a quarter-cycle of the fundamental frequency (Fline) (Figure 2)
This method presents drawbacks if the line frequency changes and the number of samples no longer represents a quarter-cycle of the fundamental frequency. Significant errors are then introduced to the results (Table 1). (Which is why the grid frequency is tightly controlled at 60Hz, allowing only a 0.3 Hz variation)
3- Method 3: Low-pass filter
A constant 90° phase shift over frequency with an attenuation of 20 dB/decade is introduced. This solution, which has been implemented by Analog Devices, can be realized with a single pole low-pass filter on one channel input (Figure 3). If the cut-off frequency of the low-pass filter is much lower than the fundamental frequency, this solution provides a 90° phase shift at any frequency higher than the fundamental frequency. It also attenuates these frequencies by 20 dB/decade (Figure 4).
Similarly to method 2, this solution is susceptible to variations of the line frequency. However, a dynamic compensation of the gain attenuation with the line frequency can be achieved by evaluating the line period of the signal (Table 1).
 
 
 
 
 
 



 Recent advances in technology have increased consumer demand for electrical products that offer convenience and entertainment in the modern home. With these advances have come increased burdens on utilities that transmit electricity and on consumers that pay for its use. A portion of this burden is due to reactive power.
 
If you were to compare the amount of electricity flowing into your home (i.e. apparent power) with that which performs productive work (i.e. real power) you would see that there is a difference. Known as reactive power, this additional energy is needed to energize motor windings and similar type loads in your home. Reactive power is returned to the electric grid as the windings de-energize, but is quickly needed again since motor windings must be re-energized 120 times per second. Reactive power does no real work, (e.g. turning a fan blade) but provides the magnetizing energy so that real work can be done. (This is untrue, energy consumed by a load does not return to the electric grid. How can you return something that is already consumed? Providing magnetizing energy means energy is consumed – even in the electric fan)

[robbietan]

III. NEEDS OF REACTIVE POWER
Voltage control in an electrical power system is important for proper operation for electrical power equipment to prevent damage such as overheating of generators and motors, to reduce transmission losses and to maintain the ability of the system to withstand and prevent voltage collapse. In general terms, decreasing reactive power causing voltage to fall while increasing it causing voltage to rise. A voltage collapse occurs when the system try to serve much more load than the voltage can support. (Generators shut down when their load is greater than their capacity. Total power S is the measure grids use in control, not reactive power)
When reactive power supply lower voltage, as voltage drops current must increase to maintain power supplied, causing system to consume more reactive power and the voltage drops further . (When there are more loads in the grid, voltage decreases due to voltage drop, not reactive power. Total load S, not just the reactive component, influence grid voltage and frequency). If the current increase too much, transmission lines go off line, overloading other lines and potentially causing cascading failures. (This is true for system faults, where a conductor is grounded. This statement is rank impossible since loads are constant energy consumers, current increase due to low voltage supply can never overload the grid). If the voltage drops too low, some generators will disconnect automatically to protect themselves. Voltage collapse occurs when an increase in load or less generation or transmission facilities causes dropping voltage, which causes a further reduction in reactive power from capacitor and line charging, and still there further voltage reductions. If voltage reduction continues, these will cause additional elements to trip, leading further reduction in voltage and loss of the load. The result in these entire progressive and uncontrollable declines in voltage is that the system unable to provide the reactive power required supplying the reactive power demands.(Correction - remove the word "reactive" from the previous sentences to get the correct idea)
Reactive power needs are determined in the planning process, which is a part of engineering, part economics and part judgment. (By specifying energy efficient motors, the planner has virtually completed this task of determining “reactive power needs"). The engineering analysis requires running large, complex mathematical computer models of the electric system. The economical part required putting costs into models to determine how to achieve an efficient, reliable system. The judgment arises due to the large number of modeling choices, expert assumption and approximations that often are necessary.               
A. Reactive power blackouts
Insufficient reactive power leading to voltage collapse has been a causal factor in major blackouts in the worldwide. Voltage collapse occurred in United States in the blackout of July 2, 1996, and August10, 1996 on the West Coast. Voltage collapse also factored in blackouts of December 19, 1978, in France; July 23, 1987, in Tokyo; March 13, 1989, in Québec; August 28, 2003, in London; September 28, 2003, in Sweden and Denmark; and September 28, 2003, in Italy. (This is B.S. The instances mentioned were mostly caused by line faults that were not controlled due to improper coordination of protection systems.)
While August 14, 2003, blackout in the United States and Canada was not due to a voltage collapse as that term has traditionally used by power system engineers, the task force final report said that" Insufficient reactive power was an issue in the blackout" and the report also "overestimation of dynamics reactive output of system generation " as common factor among major outages in the United States. Due to difficulties modeling dynamic generators output, the amount of dynamic reactive output from generators has been less than expected, worsening voltage problems and resultant power outages. (It was due to a system fault and the failure of the coordination between power generators that lead to the blackout. Put simply, the loss of generating capacity due to a line fault, caused the blackout; not this “insufficient reactive power")           

V. PROBLEMS OF REACTIVE POWER
Though reactive power is needed to run many electrical devices, it can cause harmful effects on your appliances and other motorized loads, as well as your electrical infrastructure. (This is why I think that the author does not know what he is talking about. Reactive power is NEVER HARMFUL for an appliance for the simple fact that it is part of the total energy consumed.) Since the current flowing through your electrical system is higher than that necessary to do the required work (WTF? Current will flow to your system as need be, it is impossible for an appliance to consume more energy that it can handle), excess power dissipates in the form of heat as the reactive current flows through resistive components like wires, switches and transformers. Keep in mind that whenever energy is expended, you pay. It makes no difference whether the energy is expended in the form of heat or useful work.
 
We can determine how much reactive power your electrical devices use by measuring their power factor, the ratio between real power and true power. (If you use this method, you can just calculate the ratio, no need for “measuring power factor”). A power factor of 1 (i.e. 100%) ideally means that all electrical power is applied towards real work. Homes typically have overall power factors in the range of 70% to 85%, depending upon which appliances may be running. Newer homes with the latest in energy efficient appliances can have an overall power factor in the nineties.
 

The typical residential power meter only reads real power, i.e. what you would have with a power factor of 100%. (Unity power S is 100%, real power P means it is Watts. Which means meters can read power consumption even if the pf is not unity. Another instance of the author not knowing what he is talking about) While most electric companies do not charge residences directly for reactive power, it’s a common misconception to say that reactive power correction has no economic benefit. To begin with, electric companies correct for power factor around industrial complexes, or they will request the offending customer to do so at his expense, or they will charge more for reactive power. (Correct since more reactive power consumption equals more total energy consumption which means the utility has to supply the customer with bigger wires to carry more energy).  Clearly electric companies benefit from power factor correction, since transmission lines carrying the additional (reactive) current to heavily industrialized areas costs them money. (Correction, to carry more energy, transmission wires have to be bigger.) Many people overlook the benefits that power factor correction can offer the typical home in comparison to the savings and other benefits that businesses with large inductive loads can expect. (Why correct power factor in the home when you are not billed for VAR consumption?)   .

Most importantly, you pay for reactive power in the form of energy losses created by the reactive current flowing in your home. (AC current, not reactive current. An infinitesimal amount. I checked). These losses are in the form of heat and cannot be returned to the grid. Hence you pay. The fewer kilowatts expended in the home, whether from heat dissipation or not, the lower the electric bill. Since power factor correction reduces the energy losses, you save. (A more infinitesimal amount, I checked also).  
As stated earlier, electric companies correct for power factor around industrial complexes, or they will request the offending customer to do so, or they will charge for reactive power. (Utilities here are doing that since Day 1 of the plant’s operation) They’re not worried about residential service because the impact on their distribution grid is not as severe as in heavily industrialized areas. However, it is true that power factor correction assists the electric company by reducing demand for electricity, thereby allowing them to satisfy service needs elsewhere. (No, power factor correction does not reduce total power demand). But who cares? Power factor correction lowers your electric bill by reducing the number of kilowatts expended, and without it your electric bill will be higher, guaranteed. (Power factor correction does NOT reduce the number of kilowatts. Another instance where I think the author does not know what he is talking about.)
 
 
We’ve encountered this with other electric companies and have been successful in getting each of them to issue a retraction. Electric companies do vary greatly and many show no interest in deviating from their standard marketing strategy by acknowledging proven energy saving products. Keep in mind that promoting REAL energy savings to all their customers would devastate their bottom line. (Is this a pitch for them fake “energy savings products”? If so, this author has lost his credibility completely)
Power factor correction will not raise your electric bill or do harm to your electrical devices. (Altho installing too many capacitors would certainly harm your system) The technology has been successfully applied throughout industry for years. When sized properly, power factor correction will enhance the electrical efficiency and longevity of inductive loads. Power factor correction can have adverse side effects (e.g. harmonics) on sensitive industrialized equipment if not handled by knowledgeable, experienced professionals. (Power factor correction capacitors are the VICTIMS of harmonics. Another instance where the author does not know what he is talking about).  Power factor correction on residential dwellings is limited to the capacity of the electrical panel (200 amp max) and does not over compensate household inductive loads. By increasing the efficiency of electrical systems, energy demand and its environmental impact is lessened (Here the author is correct)

Conclusion

Efficient completion is a way to achieve efficiency and reduce costs to consumers. Efficient competition is difficult to achieve. (Not true, by using energy efficient products, consumers can reduce costs).  Due to innovation and technological progress, the optimal industry structure and mode of regulation may not need to change. As regulated markets move from franchised monopolies toward completion, Regulation needs to move from direct price regulation to market rules. Competitive markets required competitive market design.
Put difficulties, efficient market design does not just happen spontaneously. It is the result of a process that includes full discussion, learning and informed judgment by all affective and responsible parties. (I sincerely hope that the author is not part of those “responsible parties”)         
   

[robbietan]

kung masyadong malaki ang reactive energy, hindi lahat yun ay magagamit ng motor at a certain time, saan kaya pupunta yun?

the motor will not consume more energy than it needs. so the VAR supplied by the grid is just ther, waiting to be used. hindi mangyayari na kukuha ng 100 energy si motor tapos isosoli ung 10 na hindi nya nagamit. pag kumuha ng energy si motor, eksakto palagi.

Yun na nga yung point ng author master, constant yung kVAR or kW requirement kaya para mamaintain yun sa pagbaba ng Vout eh natural na tataas ang drawn current

magkaiba ang constant W at constant VAR. wala akong alam na motor na "constant VAR". its always constant W since ito ang equivalent ng work done.


Parang pareho po kayo ng sinabi ng author,

see the long post above

[robbietan]

pacensya na, I have a lot of free time sa bahay last night....erferferf

[danny]

wow ang haba ng explanation ah
cge basahin ko nga
thanks for sharing

[glutnix_neo]

the motor will not consume more energy than it needs. so the VAR supplied by the grid is just ther, waiting to be used. hindi mangyayari na kukuha ng 100 energy si motor tapos isosoli ung 10 na hindi nya nagamit. pag kumuha ng energy si motor, eksakto palagi.

yung nga po yung point ko the motor will not consume more than what it needs, saan pupunta yung sobrang energy kung nakatenga lang yun habang nakakabit sa circuit?

By the way power electronics engineer nga pala ako with graduate diploma sa power electronics now finishing my MSEE thesis, and 5yrs exp.(I think no need na para sa mga grad studies para maipaliwanag yun kasi kahit ordinary Electrical Engineer alam yun).

gamitin natin simple capacitor inductor(inductor na lang kasi baka sabihin inductive ang motors eh) for example.



Habang may voltage nagstore(engineering term for storing of inductance is energizing not charging) and inductor ng energy, kung mawala kuryente(knowing na maraming nakakabit sa circuit other than the motor), sa palagay nyo saan pupunta yung power na yun?

Magstay ba sya sa inductor?tatakbo lahat sa motor?

[glutnix_neo]

magkaiba ang constant W at constant VAR. wala akong alam na motor na "constant VAR". its always constant W since ito ang equivalent ng work done.

kVAR is dependent sa properties ng motor(inductance). kung hindi nagbabago ang motor hindi magbabago kVar, mas malaki pa chance na magbago ang W kasi pag may sumakay sa motor eh lalong tataas ang req W,

Anyway hindi yun ang topic kundi yung relation ng voltage at current kung constant ang power drawn(it doesnt matter kung ano pang power yan ).

[glutnix_neo]

eto na lang master tanong ko sayo mukhang alam na alam mo ang power factor eh. 

pano gumagana ang power factor corrector?(not the cap bank but the modern PFC)

[insomartin]

  panuood lang muna

[glutnix_neo]

Almost all power transported or consumed in alternating current (AC) networks. AC systems supply or consume two kind of power: real power and reactive power. (Loads, whether AC or DC, consume energy. Energy in AC loads is composed of 2 components, Watt and VAR).

Eto parehong tama,

The author is referring to AC Systems (kaya consume at supply)
Robbie is referring to Loads (kaya consume lang)

mas tama ba ang Watt and VAR over real power and reactive power?(actually pareho lang yun)

I think tama naman po mga sinasabi nyo master, ganun din yung author, ang problema lang eh sa pagcomprehend  or interpret ng paper. still wala pa ring basis na mali yung paper ng author.