Power Quality - Rates Structure

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Rates Structure Modification Proposal for Costumer with Nonlinear Loads August0 A. Abreu M.

JosC T. C. Villalobos B.

Energia Elkctrica de Venezuela C A PO BOX 146, Maracaibo - Venezuela Abstract: The scope of this paper is to show a method of applying a different electrical rate to nonlinear load customers in order to recover the impact of this kind of load can cause in the electrical network, in this way the distributors can be prepared and can invest on the network in order to supply it, and it able us to recover technical losses caused by harmonics current and all other harmonics related problems. This is a sturjl case and it was done at Zulia 9 substation that supplies electrical power mainly to electrosumergible pumps used for oil companies at Zulia state, Venezuela.

Key Words: Metering, Harmonics Rates, Energy Losses, Power Quality.

I. INTRODUCTION The massive use of nonlinear loads in the last decade has caused great inconvenient due to the increase of the harmonics pollution on the power system and the related problems that this can cause. it has been focused only to give us a solution, by in the real world our customers don't want or they can't fit this problem cause financial problems.

In order to find an answer to this, let's go back to basis. When the inductive loads started to be common on the network, there was an inconvenient. the power utilities had to supply great amount of reactive power from the source to the customers, so they had the responsibility of carrying out investments in transmission, in order to deliver this power that it was not billed. There are two ways worldwide used to solve it. One of them is regulating the power factor to a desired value and the end user can have a penalty if this value gets below it. The other one is billing the apparent power, it creates an incentive to the customers to install reactive compensation equipments. This last solution has the advantage to penalize in function of the demand, this procedure is used in Venezuela. Like wise, it can be used in a similar way with the harmonics in current. Establishing an electrical rate that reflects the economical impact that such currents multiple from de fundamental can cause to the network, which it'll in the majority of the cases push the costumer to search for devices that minimize the insertion of them.

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2002IEEE

This paper is focused to show the use and simplicity of applying harmonics electrical rate to customers in order to invest and prepare the network and the distributors for it, it'll allow us to recover technical losses caused by the harmonics current inserted by nonlinear loads. And also we'll show you a proposal and a study case where a modification of the electrical rate structure is explained, so the costumer that inserts harmonics currents to the distribution system will be charged with a monthly payment equal to the economical impact that such currents have on our system, with emphasis in the transformation stage. This involves the substitution from the traditional demand charge to harmonics demand charge, it based on the proposed method [ 5 ] . 11. ECONOMICAL IMPACT CAUSED BY HARMONICS CURRENTS

From 30 different measurement within the ENELVEN system, it was found that the voltage harmonics distortion, only the 13% from the sample exceed the limits established by the IEEE 519-92 [l]. So we realized that high levels of harmonic voltage distortion represent high impedances at the distribution network, that this parameter is a responsibility fiom the electric utility [8]. Therefore, it is important to maintain this impedance levels as lower as possible, to a reasonable economic and technical point. Now checking current harmonics distortion, we found that the 43% from the sample exceed the limits established by the 519-92 [l], parameter that is costumer's responsibility. This harmonics current generator type of load, causes losses on the elements on the electrical network, mainly on lines and transformers. From these elements, the transformers represent the equipments where they produce the most important losses from the power system. An energy (kwh) losses estimation can be calculated fiom the method used to estimate the transformers capacity, when supply non sinusoidal loads ANSI/ IEEE C57.110-1998 [7]. Such losses represented a 14,04% fiom the total load. That if we calculate this in term of money, we're talking about US$258.218,00 of technical loss cause by harmonics current on the evaluated sample [6].

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The evaluated sample represent customer's loads, that they are harmonics current generator, which causes losses on the elements at the electrical network, lines and transformers. the transformers produce the most important losses in the power systems, due to it higher impedance. Actually, transformation level losses cannot be adjusted by the meters, cause the majority of today meters are not capable to get voltage and current waves at the fkequency spectra, and, they are not programmed to quantify such type of losses.

In terms of money the losses that harmonics currents cause, we've taken the cost of kwh according to the electrical rate applicable to each point, which represents a low estimate, since a current at 60 Hz doesn't produce the same losses that at 180 Hz (3 harmonic) or 300 Hz (5 harmonic) etc, those kwh at multiples currents produce higher losses than the fundamental (60Hz), due they're proportional to the square of the frequency. To realize an adequate estimate is necessary the elaboration of a study, which specify the cost of the kwh at different frequencies. That will be done in the near future in our company. 111. ALTERNATIVE CHARGES TO CUSTOMERS

HARMONICS CURRENTS CONTAMIZATION

where, EH: RMS voltage of the common point. IH: RMS current at the common point. N: frequency. X: transformer impedance. This procedure comes from the measurement of the electric power, where the demand in volts-amperes is adjusted in such manner that it will reflect the economic effect opposite to the harmonics current. This technique use the acquisition of the frequency spectra from the current an voltage waveforms at the PCC (point common coupling). The inconvenient to apply this method is that, not all of the countries have the power factor regulation. Another problem is to quantify in terms of money, when the power factor is under the regulation. besides, it is not taken in account the size of the load. Other inconvenient is, that this altemative do not take changes in the impedance of the system, considering it fix.

C.Proposed Harmonics Volt-AmperesAdjusted Method. This proposal comes from the original equations of Alexander McEachem and W.Mack Grady [5] and take into account the impendance of the system proposed by Wilsun Xu and Yilu Liu[ 81.

A. Energy Quality Regulation. Actuality, just in South America is known the application of an altemative of penalty for currents harmonic contents, which is applied in Argentina. This resolution has an inconvenience, it offers high limits in both current and voltage harmonics distortion, additionally, the costumer it only granted a period of 6 months to resolve the problem, during this period the costumer has a penalty and if he doesn't solve this problem within this period, the Distributor can disconnect it fron the network. That's not possible in our country.

In Venezuela is used the appearance power charge and because of this, it only takes the procedure proposed in [SI up to the point where it estimates EH * IH, which will be the harmonics power adjusted. Once you get volt-amperes at higher fi-equency fkom the fundamentals, it proceeds to under the same rate structure without making any modification to it.

B. Power Factor Method. This is a very good initial altemative to recover in some way the technical losses by harmonics current at the transformers which was explained by Alexander McEachem and W. Mack Grady [ 5 ] . It is based on power factor. It is considered a form of pondering in such a way that the currents on each frequency are incremented in function of the transformer impedance and as higher the frequency higher will be the given factor. This comes from the fact that at higher frequency higher the losses, proportion to the square of the frequency.

Figure 1. Comparing both methods

This way is easy to implement due the meters right now are capable to sample the voltage and current fi-equencies spectra and other point is the calculation in terms of money is simple, just take into account the "normal" electrical rate.

K, = [1+ x(N2- l)]

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IV. CASE STUDY

A.- Costumer’s Characteristics. “Zulia 9” sub station, was chosen due to it feeds a very important oil field in the region (a concession from Petroleum de Venezuela-PDVSA to CHEVRON), that represent a high demand from ENELVEN’s system. This substation is fed by two 138 kV lines and distributes in 23,9 kV. It has two transformers of 25/33/42 MVA, 138123.9kV which feed 12 distribution feeders, 10 of then are exclusive of the oil field (fig 2)

Legal meter

ION8500 meter Zuu4 9

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Figure 3. Implementation. Figure 2. S E Zulia 9.

The oil field load comes from flow stations and oil extraction wells devices with high percentage from electrosumergible pumps. This type of equipment is a AC-AC frequency static controlled device. In Venezuela the oil industry uses this technology because of it good performance, representing the six pulse power converter, the most used which has a typical value of 40% current harmonics distortion from the fundamental.

During the metering period, we obtained an average of 4407kVA between the Harmonics Adjusted Demand and the traditional demand charge at 60 Hz.Applying the actual rate of US%/kVA6.00 this costumer would be paying an increase on its monthly payment of US$26600.

On fig 4, you can see a registration of the kVA to 60 Hz and the adjusted by harmonic current, where it can be appreciated by the constant client’s demand.

B.- Implementation. 4aml~

The test consisted in programming an electronic meter (ION 8500-PML) using the equations from Alexander McEachem[S] and the equations presented by Wilsun Xu and Yilu Liu [SI. It is important to emphasize that this meter is new in the market and it has the capacity to obtain the current and voltage harmonic spectra, with enough memory to perform the required mathematic operation. Such meter was installed in parallel to the legal meter (fig. 3).

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Figure 4. Record from the Test at “Zulia 9” substation.

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V. CONCLUSIONS

It was demonstrated that the methodology is easy to implant, once the meters are available and they’ll not require an approval fiom the Venezuelan Electrical Power National Commission, cause the calculation methodology is technically supported and its application will only affect the costumer that insert harmonics current into the system. Getting a new electrical rate structure, where the power utility can get fiom the costumers a supply nonlinear loads revenue.

VI. BIBLIOGRAPHICS REFERENCES [ 11 IEEE Std. 5 19-1992, “IEEE Recommended Practices and Requirements for Harmonics Control in Electrical Power Systems”, Published by IEEE 1.992. [2] IEC 1000-3-6, “Electromagnetic Compatibility (EMC)”

[3] Marco Regulatorio de Calidad de Servicio de Argentina “Base Metodologica para el Control de Emision de Perturbaciones del Product0 Tecnico”, Resolucion ENRE N” 99. [4] W. M. Grady, Robert J. Gilleskie, “Harmonic and now they Relate Power Factor”. PQA’93, San Diego C. A., Nov. 1.993. [SI A. McEachern, W. M. Grady, W. A. Moncrief, G. T. Heydt, M. Mcgranaghan, “Revenue and Harmonics: An Evaluation of Some Proposed Rate Structures”, IEEE Transaction on Power Delivery , Vol. 10, No. 1, January 1995.

[6] A. Abreu, J. T. Villalobos, “Problemas de Calidad de Potencia Fuente de Perdidas TBcnicas en 10s Sistemas ENELVEN-ENELCO”, I Seminario Intemacional de Reduccion de Perdidas de Electricidad y us0 Eficiente de la Energia ElCctrica, CIER, Venezuela 1.999. [7] ANSI/IEEE C57.1 10-1998, “American National IEEE Recommended Practice for Establishing Transformer Nonsinusoidal Load Capability W h e n Suppliying Currents”.

[8] Wilsun Xu, Yilu Liu, “A Method for the Determine Customer Harmonic Contributions for Incentive-Based Harmonic Control Applications”, Panel on Harmonic Measurements and Allocation, 1999 IEEE PES Summer Meeting.

August0 Alfonso Abreu Morales. Electrical Engineer at Rafael Urdaneta University in 1.997. Right now works as Planner Distribution Engineer at Energia Electrica de Venezuela (ENELVEN). E-mail: [email protected]

Jose Thomas Claret Villalobos Bracho. Electrical Engineer at Zulia University in 1.988. Right now works as a revenue protection and power quality counselor at Energia Electrica de Venezuela (ENELVEN). E-mail: [email protected]