Power Quality in a Competitive Electricity Market Herivelto de Souza Bronzeado, Member, IEEE Companhia Hidro Elétrica do São Francisco - CHESF
Abstract— Deregulation has revolutionised the electric industry. Electricity has been treated as part of a business instead of being a public service. Traditional monopolies has been deregulated and split up into different business units, and electricity has been offered as a product and subjected to competition. Power quality issues, which were discussed separately from the deregulation process, now need to be discussed together as there is a close connection between them. This paper examines the main aspects of the quality of the electric power supply and raises questions that should be taken into consideration in a competitive electricity market. Index Terms - deregulation; power quality; power system disturbances; voltage disturbances. voltage quality;
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I. INTRODUCTION
he Brazilian electric sector has experienced dramatic changes due to deregulation. Electricity distribution companies belonging the federal and state government were privatised, with traditional integrated utilities being broken-up into separated different business areas and make them subjected to economic judgement as well defined entities. These on-going changes have introduced some competition, allowing the electricity consumer to shop around among different energy-providers to meet his needs for electric power. Electricity has been now considered as input “material” in the business process and therefore the poor quality of this “material” will create cost that can be made visible. The competitiveness in a global market has given emphasis to the industry revitalisation with more automation and more electronically controlled, energy-efficient equipment that are often more sensitive to deviation of the supply voltage than its electromechanical predecessor [1]. System disturbances, which were considered as being “normal” for many years, now may cause disruption to a whole industrial process with a resulting loss of production. As the responsibility for Power Quality (or Voltage Quality) problems is not yet very clearly defined, actions to resolve these problems in a deregulated electricity market has been generally delayed. In this paper, some issues of power quality in a competitive electricity market are raised. Case studies are presented in order bring up questions that need to be discussed among all the players in this competitive environment. H. S. Bronzeado is with Companhia Hidro Elétrica do São Francisco CHESF, Rua Delmiro Gouveia, 333 - Anexo II, sala A-316 (DOEL), 50.761– 901 Recife, Pernambuco, Brazil (e-mail:
[email protected] and
[email protected]).
II:
POWER QUALITY
For many years, the quality of the electric power supply was associated essentially with the reability (continuity) of the service. In those days, customers complained only about the problems associated with the voltage regulation and interruptions. However, in the last decades, the sensitivity characteristic of the loads has been dramatically modified, with electricity consumers becoming less tolerant to related voltage disturbances (voltage quality). In other words, the nature of the “quality” of the electric power supply has also been changed. “Power Quality” has captured considerable attention from electric utilities and their end-user consumers. This term has broadly referred to maintaining the near sinusoidal waveform of power transmission and distribution bus-bar voltages at rated voltage, magnitude, symmetry and frequency. It can be also defined as a relative absence of utility related voltage disturbances - particularly, the absence of voltage interruptions, sags, swell, transients, imbalances, distortions and fluctuations as measured at the point of power delivery. It is important to point out that these disturbances cannot be controlled only by the utilities. The power network is largely vulnerable to natural phenomena such as lighting, strong winds, etc and, also, faults caused by vandalism, equipment failure, etc, which are inherent to system operation. There exist, also, voltage disturbances with of nature “quasipermanent” that are caused by the operation of non-linear loads (arc furnace, converter, etc) that belong to the customer. Fig. 1 shows the main voltages disturbances which are directly associated with Power Quality problems [2]. Power quality or voltage quality problems have a direct economic impact on many commercial and industrial customers. Besides financial impacts, there are numerous indirect and intangible cost (“social cost”) associated to these problems. Typically, residential customers do not suffer direct financial loss, but can be a potent political force against the utility that provides poor service. An important point to consider is that the increasing sensibility of the customer’ equipment is probably one of the most significant parameters to affect the “quality” of the electric power. III. ELECTRIC UTILITY DEREGULATION Electric utility deregulation was a complex, confusing and sometimes a contradictory world. Heralded as the death knell for monopolistic utility companies, deregulation came with the promise of cheaper electricity, better service and more options
for the customers. Full-scale retail competition in USA was expected to push down electric rate by 10 percent to start and by 20 to 30 percent eventually [3]. Behind this promise, however, lies complexes web of legislative and logistical pitfall that still remain to be worked out. Utilities, historically responsible for generating, transmitting, and distributing electricity, were required by law to sell some or all of their plants. They still maintain the regional power grid. But consumers living in a deregulated market can buy power from whomever they choose. These new suppliers will purchase power from generation plants wholesales and then will delivery it to the customer over the existing transmission lines. They may have to contract a supply path through several grid owners to reach the customer. However, this delivery system exists only on the paper. Due to the nature of electricity and the power network, which
follow the law of physics, not the law of lawyers, the actual power path may be entirely different from the route contracted. In addition, the power flow may create or picks up disturbances along the way, affecting neighbouring grids and others consumers. Furthermore, a special aspect is that, as a result of the split up of utilities in different business units, the interest for a local grid company to accept disturbances caused by processes of certain customers can be drastically reduced. They might no longer have the income from a large energy contract for those customers, but are left with all the disturbance problems. This is a big issue of Power Quality, or may be better worded as Transmission Quality, that will be more and more important nowadays [4].
Figure 1 – Voltage disturbances associated to Power Quality a) Normal Voltage b) Impulsive Transient
c) Oscillatory Transient d) Voltage Sag
IV. CASE STUDIES In practice, power quality impairment is often the result of sophisticated electromagnetic phenomena interactions. The case of only one source of voltage disturbance impacts is very infrequently. Separate or simplified considerations do not allow finding sufficient compensation solutions for existent power systems in most cases. Also, the combination of Power Quality and deregulation seems to be an exciting and demanding theme for engineers, economists and lawyers. As far as the research is concern there is limited experience on this topic as a whole. Based in the stimulating work by Hans-Ake Jönsson and Karl Bergan [4], some examples are given in this work in order to stimulate discussions and raise some provoking questions.
e) Interruption f) Voltage Swell
g) Harmonic Distortion h) Notch
A. Example 1 A textile industry connected to the local grid has changed the majority of their weaving machines to others that use variable speed drives. A voltage sag to 60%, 6 cycles, caused by a lightning flashover has tripped out the new machines, causing loss of production. The old machines have rode through the voltage sag. The fault was in the national grid, far away from the industry. The system protection operated correctly. Questions: • Who should invest to avoid the production loss? • Is the local grid company responsible for the voltage sags in its system caused by faults in the national grid? • Should not the customer consider the sensibility of their equipment before buying them?
B. Example 2 Similar voltage sag of example 1 impacted a cement industry. The difference from the later situation is that the network is weaker and the voltage sag was due to a fault occurred in the local grid. The local utility complains about the low short-circuit level at the bus bars in the regional transmission network. A big investment is necessary to increase the short circuit level. Questions: • •
Should the regional grid company be responsible for the voltage sag? Who should pay for the investment to increase the shortcircuit level?
C. Example 3 Two industrial customers are connected onto the same bus bar (Point of Common Coupling - PCC) and they had no power quality problems for long years. One of them (say customer A) has non-linear loads, but they cause very low distortion in the PCC. The other one (customer B) has only linear loads. To meet to new requirements for power factor, the customer B had to connect a capacitor bank. After that they have suffered with failure of numerous equipment and loss of production due to harmonic resonance. Questions: •
In this case who should invest to prevent the harmonic resonance?
D. Example 4 A large steel mill is connected to a local grid. It is supplied from a generation company through the network of the regional grid. The generation and regional grid companies are happy, but the customers connected to the local grid complain about flicker. This problem remains for years.
•
•
How can the local grid company act to solve this problem? Should a contract be also made between the steel mill and the local grid company?
VI. FINAL COMMENTS
VII. REFERENCES [1] [2]
[4]
[5]
V. CONCLUSIONS From the examples discussed in this paper, certain conclusions can be drawn: • Customers should know more about the sensitivity of their equipment. • Disturbances can travel far away through the network. • New role and responsibilities need to be defined to all players in the electricity business. • It should be clear who shall pay and who will take the benefit. • It will take time to define responsibilities in a competitive environment. • Power Quality cost needs to be visible in order to justify investment decisions.
Responsibilities for Power Quality needed to be defined. Clear contracts for all electric transaction, including the cost of Power Quality, are needed. As long as the responsibility for Power Quality is not clearly defined, actions will be delayed.
Due to deregulation, the electricity consumer has become a “customer” and therefore he should be treated as a customer. At the beginning, this was a difficult change of mindset for many companies and individuals, but it is very important in this competitive environment. The necessary tools to drive this relationship must be contracts [5-7] with very well defined terms and conditions as in any other business transactions. It should be emphasised that in the contracting phase for electrical supply a trade off should be made between the cost to avoid the disturbances and the cost created by them. This creates new demands on existing players in the electric market and great opportunities for new players to satisfy the customers needs. With electricity being considered a commodity or raw material as input in a business process, the customer is less willing to accept the cost of the disturbances. New considerations must be taken into account for developing a reliable power system, which were not previously considered significant. Power Quality Standards are needed.
[3]
Questions: •
• •
[6]
[7]
Ducan, R. C., McGranaghan, M. F. and Beaty, H. W., Electrical Power System Quality, McGraw-Hill. Bronzeado, H. S., Ramos, A. J. P., de Oliveira, J. C., de Abreu, J. P. G., Arruda, A. A. C., Brandão, C. A., “A Proposal to Brazilian Terms and Definitions Associated to Power Quality” (in Portuguese), II Seminário Brasileiro de Qualidade de Energia Elétrica – SBQEE, São Lourenço, 16 – 19 Nov. 1997. Phillips, W. G., “Power to People”, Popular Science, pp. 62 – 65, April 1998. Jönsson, H-A. and Bergan, K., “Deregulation and its Relation to Power Quality Business Development”, Proceeding of CIGRE Regional Meeting, “Power Quality – Assessment of Impact”, New Delhi, 10-11 Sept. 1997. Gueiros, D. A. C., Bronzeado, H. S. and Cavalcanti, T. H., “Aspects of Energy Supply Contracts with Power Quality Clauses”, VIII Encuentro Regional Latino Americano de la CIGRE – ERLAC, Ciudad del Este, Paraguay, July 1999 (in Portuguese) Koch, R.G. Balgobind, P. Tshwele, E., “New developments in the management of power quality performance in a regulated environment”, 2002 IEEE AFRICON 6th. RTE EDF Transport, “Contrat d´Acces au Resseau Public de Transport d´Electricite – Conditions Particulieres”, March 2006 (http://www.rtefrance.com/htm/an/offre/offre_acces_tarif.jsp#tab).
VIII. BIOGRAPHY Herivelto S. Bronzeado (M´1997) was born in mígio, Paraíba, Brazil, on April 2, 1953. He received his Electrical Engineering Degree from the Universidade Federal da Paraíba (today Universidade Federal de Campina Grande – UFCG), in 1975. Since then he has been working for the Companhia Hidro Elétrica do São Francisco (CHESF), Brazil. At the beginning of his
career, he worked on maintenance of transmission lines and high-voltage equipment. In 1980, he started to work with Power Quality, being responsible for performing power system analysis and measurements associated with disturbances on transmission and industrial power systems. He received his MSc in Power System Engineering, from the University of Aberdeen, Scotland, in 1993. Currently, he is the chairman of the Brazilian SC C4 of CIGRÉ-Brazil (Technical System Performance), and the PresidentElected of the IEEE Joint Chapter PES/IAS/PELS Northeast 1, BahiaSection, Brazil. He is working towards his PhD Degree. His research interests include Power Quality, power system transients and transformer modelling for transient and harmonic studies.
