Deregulation Impacts Control And Communications Systems
In 1992, Argentina restructured its electric industry, separating private generation and long-distance transmission and distribution companies. As a result of this restructuring, government regulation can limit T&D natural monopolies as required, while generation can be controlled by competition in the wholesale power market (by marginal prices). The national government sold the T&D businesses to become public utilities, while setting a price cap concession subject to periodical tariff revisions every five years.
The transmission companies must provide open access to their grid to any users (generator or industry), and are not allowed to get into the business of buying and selling electricity (to avoid conflict of interest issues. Distribution concession contracts include requirements for universal service to all residential and small consumers.
The Secretary of Energy, currently the principal authority in the electricity sector, represents the national government and is responsible for defining the politics for the electricity sector and granting the appreciation of the Wholesale Electricity Market agents.
Compañía Administradora del Mercado Mayorista Eléctrico S.A. (CAMMESA) is a non-profit company that coordinates the dispatch of power plants to ensure supply and demand are constantly balanced, and the plants that bid the lowest price to supply power are dispatched first (for example, merit order dispatch). CAMMESA, which calculates the market-clearing wholesale price hourly, also manages the financial transactions, and the collection from buyer's payments to generators and transmission system operators.
ENRE is an independent electricity regulatory agency responsible for overseeing current procedures and quality of service, setting the tariffs of transmission and national distribution companies with powers to apply fines and resolve disputes. In addition, it monitors the standard regulations designed to protect the customers and the environment, as well as private property and public safety, recommending amendments where required to the Secretary of Energy
Transba S.A.
As a result of the 1993 privatization of Argentina's electricity industry, the Empresa de Transporte de Energía Eléctrica por Distribución Troncal (Transba S.A) initiated the operation of the transmission system for the province of Buenos Aires. This province is the largest in Argentina, with an area of 307,571 sq km (118,750 sq miles) and a population of 12.6 million, whose main economic activities include cattle rearing, agriculture, fishing, manufacturing and tourism.
Transba S.A., one of the largest utilities in Argentina, operates and maintains 82 HV/MV substations at voltage levels of 220 kV, 132 kV and 66 kV, and an overhead transmission system of mostly 132 kV that extends to 5675 km (3527 miles) (Fig. 1.).
Maintenance is regionally based — Atlantic, Northern and Southern — with Transba's technical personnel handling the electrical and electronic maintenance (protections, SCADA and system of commercial energy meter). ANTARES.COM, an independent company that began its activities with personnel from Transba S.A. and Transener S.A. under the supervision of Transba's S.A. regional technical personnel, is responsible for the telecommunication systems maintenance.
The operation of the T&D network is organized in a hierarchical manner, with centralized operations from the main control center (COTDT) at voltage levels of 132 kV and 66 kV, and regional operations at 13.2-kV level. Nevertheless, the regional control centers operate the “feeders” under their jurisdiction at 132 kV and 66 kV.
The Telecontrol System
The selection of the manufacturers given contracts for the Transba S.A. telecontrol system followed an internal market research study supported by advice and operational experience from Transener S.A., whose SCADA and telecommunications system was commissioned in 1995. The telecontrol system (SCADA) installed by Transba S.A. was designed to:
Comply with the requirements of CAMMESA, regarding the transmission of substations data to its control center in Rosario (province of Santa Fé)
Improve the security, quality and operational efficiency of the electrical power network.
Installation of the system started in 1997. The first stage comprised adaptation of the substations to be telecontrolled, and equipping the COTDT and the regional centers (CORs). The telecontrol of the 75-HV/MV substations — the complete network — was completed in 2001. With expansion of the network to satisfy load growth, the SCADA system currently controls 82 substations.
The architecture of the telecontrol system is three-tiered: COTDT, four CORs and 82 telecontrolled HV/MV remote substations.
The second level (regional control centers) was required to accommodate a system in which the substations are geographically dispersed over a wide area (Fig. 1). For this reason, the regional centers, apart from their inherent functions, are also the communication concentrators for all the remote terminal units (RTUs) within their region.
ABB Network Management was awarded the contract for the control centers and GE-Harris (Autotrol S.A.I.C.Y.F. — Argentina) supplied the RTUs.
Main Control Center
The COTDT is located on the site of the HV/MV substation Ezeiza (Marcos Paz), some 50 km (31 miles) from Buenos Aires.
The architecture of Transba's COTDT (Fig. 2) is based on six consoles connected in a duplicated Ethernet LAN topology. The system allows the connection of eight consoles. At present, only six consoles are connected. Four of the six consoles (#2, #3, #4 and #5) are dedicated to the operation of the electric power system the remainder (#1 and #8) to the engineering and maintenance of Transba's SCADA system. During every 8-hour shift, three staff members are responsible for the operation of the system. The senior staff operator has two consoles (#3 of Transba and #8 of Transener) that give him responsibility for the remote control of the Transba S.A. system and a view of the 500-kV systems operated by Transener S.A. from its COT in Rosario.
Transba's consoles #1 and #8 comprise the RANGER Application Servers (RAS). There are two routers or RANGER Network Servers (DECNIS 600), which allow connection to the CORs of Transba S.A., and with the Control Center of Transener (COT). Hence, it provides the link to the corporate WAN (Transener S.A. — Transba S.A.).
To enhance the operational performance and efficiency of the system, Transba S.A. installed a display wall (BARCO), composed of 3 by 2, 67-inch screens of poly-silicon LCD technology, with a resolution of 1024 by 768 pixels. Console #4 is connected with the Video Wall Server, a PC Pentium III 800-MHz with EOS software and Linux operating system. On screen, the operators have a total network overview and up to four video signals, such as a weather channel and news.
The SCADA-EMS software is RANGER (ABB NM), the operative system is UNIX and the database is Oracle.
Standard functions of the system include basic SCADA functions and extended application functions, which are run in the control center of Transener S.A. (COT), such as state estimator, power flows and contingency analysis. In the COTDT, operators are able to access these functions through the remote console connected to the COT. Different application programs have been developed, which help the technical areas to have access to the historical data of the system for electrical studies and fault evaluations.
Regional Control Centers
As a result of communication channel optimization and the maintenance organization, there are four regional control centers: COR San Nicolás, which controls the network northeast of Buenos Aires; COR Bragado, which controls the center and north; COR Tandil, the southeast; and COR Bahia Blanca, the network in the southwest of the province.
As for the COTDT, the telecontrol equipment (Fig. 3) is based on a duplicated Ethernet LAN with two server consoles, both with 17-inch monitors. The servers are DEC AXP 400, which includes 256 MB of memory, 956 GB of disk memory, CD ROM and floppy disk.
There is a communication front-end (BOW TIE) connected to each server and to a modem sharing device (MSD) that controls the modems to each telecontrolled station.
Currently, Transba and Transener are engaged in a program called Evergreen to permanently update the telecontrol system (hardware and software). Initiated in 2001, the update will continue until 2007. This program, within the framework of updating and upgrading the system, will include changing the total number of servers and routers of the main and regional control centers.
Remote Telecontrolled Stations
The telecontrol equipment in the substations is based on an RTU D20M from GE Harris, which is responsible for the acquisition and updating of field information (position of breakers and disconnectors, measurements and alarms) and the enforcement of commands sent from the COTDT or the CORs.
The RTUs are modular and equipped with the following: analog input module, (transducer measurements) or transducerless module, digital input module (position of breakers and disconnectors and alarms), and digital output module (commands). The data transmission protocol used for the RTU's-COR's link is DNP 3.0, developed by GE Harris. This protocol complies with the requirements of the series 60870-5 International Electro- technical Commission (IEC).
Depending on the existing equipment within the framework of stations, some substations adapted to telecontrol currently use conventional measurement transducers to measure voltage, current, active power, reactive power, frequency and position of transformer taps. In other substations, trans-ducerless modules are installed that acquire three-phase current and voltage, as well as calculate the current, voltage, active and reactive power and frequency. The latest telecontrol implementations have used so-called “smart meters,” which work similarly to the transducerless modules.
Approximately 50% of the substations are equipped with transducerless modules. In the remaining substations, transducers are used to acquire the telemeasurements. There is an average of 400 I/O analog and digital points per substation.
Telecommunications
In 2000, Transba S.A. implemented an ambitious plan to upgrade its telecommunication systems, which were mostly based on analog power line carrier (PLC) over transmission lines, a few analog radio and spread-spectrum technology links by shifting to microwave digital technology. The digital microwave system is considered the backbone of Transba S.A.'s communication system and is designed to:
Enhance critical services, such as transmission of operational data between control centers
Duplicate the links between control centers and the most important substations
Improve and extend the Intranet and telephony system of the company. The company Intranet links the regional and district headquarters of Transba S.A. and Transener S.A., as well as the headquarters of Transener Internacional Ltd. (Brasilia, Brazil).
The digital microwave system of Transba S.A., supplied by Alcatel (Alcatel de Argentina), is tied with important SDH microwave and fiberoptic systems that belong to Transener S.A. It starts in the far south of Argentina, crosses the province of Buenos Aires and terminates in Abasto substation near Ezeiza.
Digital Microwave System
The new digital radio system, PDH technology, with an installed capacity of 8 × 2 Mbps and upgraded to 16×2 Mbps, operates in the 8-GHz band, communicating with 31 stations. It is designed with a ring topology to link each regional center with the others and with the COTDT in Ezeiza. It also will tie the most important stations with their CORs (Fig. 4).
The radio equipment of all links of this new system is the ALCATEL 9470 LX/UX model in split configuration. It is comprised of two units linked to a coaxial cable (RG 213):
An external ODU (outdoor unit), installed next to the antenna.
An internal IDU (indoor unit), installed in the equipment room.
The configurations are:
1+0, for less than 50-km (31-mile) links with ring topology
1+1 HSB (hot standby) for less than 50-km links with open topology
1+1 DE (space diversity) for links of greater than 50 km.
For all links, an availability of 99.995% measured in the worst-case conditions was specified. The radio electric link calculation determined the height and diameter of the Andrew solid parabolic antennas with diameters that varied between 0.60 to 3.7 m (2 to 12 ft).
Multiplex Equipment
The multiplex access equipment is the ALCATEL 1511 model, which is installed with standardized chassis and “pluggable cards” as follows:
Power supply
Management controller
154 WE&M audio channels
2-Mbps network with G703 interface
5 FXO two-wire audio channels (office side)
10 FXS two-wire audio channels (subscriber side)
Four low-speed data channels, RS 232 interface
Four data channels Nx64 V.35 interface.
Where substations are in close proximity, multiplex access equipment is linked by fiber-optic cable with optic modems of 2 Mbps output and G.703 interface.
Management System
All radio and multiplex equipment is locally managed with specific software (NOCTAS) loaded on laptop computers. This product permits analysis of the operative condition of the equipment, management of alarms, change of configuration and parameter adjustment.
The microwave system allows for centralized management operations via software called NECTAS, which runs over an NT Windows operative system. The NECTAS allows the integration of radio and multiplex in a unique interface. For the integration of equipment having access from different places and to standardize interfaces, an additional module called 1322 mediation device is used.
Power supply has been standardized at 48 V
For synchronization of PDH multiplex network, it was decided that the synchronic route should follow the main information data flow route. Thus, Ezeiza Station has been chosen the location to synchronize generation with network multiplex equipment and thus avoid ring formation.
In multiplex configurations the following measures have been taken:
High-speed digital channel to link regional control centers or for the implementation of the administrative network (Intranet)
Low-speed digital channels to link control centers with telecontrolled remote stations
Telephonic channels between exchange or subscriber extensions
Data Transmission Protocols
The data transmission protocol inter-centers (COTDT-CORs and COTDT-COT) is the WSCC. Between COT and the Control Center of CAMMESA (COC), ELCOM 90 is used, which is also the protocol used to transmit data from the control centers of the other Argentine utilities and market agents to the control center of CAMMESA in Rosario (Fig. 5). ELCOM 90 complies with the 60870-6 IEC standard.
The protocol between the CORs and the RTUs is DNP 3.0, a three-layer protocol that complies with the 60870-5 standards of IEC. The data transmission between the RTUs and CORs is done at 1200 bps.
International Projection
Since 2000, specialists from different departments of Transener S.A. and Transba S.A. have been working in “Transener Internacional Limitada” on several projects in different countries of Latin America (for example, Brazil, Panamá, Paraguay and Perú). The company is working on constructing substations and transmission lines, operating electrical transmission systems, and coordinating protection systems and field acceptance tests of SCADA-EMS systems.
Transba S.A. has certified the operation and maintenance of the transmission system in accordance with the requirements of the quality and environmental standards ISO 9001 and ISO 14001. Furthermore, it is carrying out a policy program on public safety within a framework of basic and specific plans of risk prevention.
Summary
Although Argentina is currently experiencing severe economic problems, the utility has invested US$15 million on SCADA and another US$8 million on telecommunications (PLC and digital radio system) over the past six years. This Transba S.A. investment in new technology has improved the quality of supply, system reliability and security, as well as the safety of the electrical power system.
Acknowledgments
The authors wish to acknowledge the support and help received from T.P. Alicia Susana Mazza with the translation of this article.
Arturo González Avenente is the operation manager of Transba S.A He has considerable experience in electrical power systems and in the operation of electrical power networks, having held engineering positions with Hidronor and Transener S.A. He holds a degree in electronic engineering from the University of Buenos Aires.
arturo.gonzalez.avenente@transx.com.ar
Rodolfo Pellizzoni was the project leader of the telecontrol system of Transba S.A. and coordinator of the implementation of the microwave system. Presently, he is a member of the maintenance, engineering and projects management team at Transba S.A., holding the position of senior specialist of control and communications systems. He also works as senior consultant in substation automation and telecommunications on some of the foreign projects on behalf of Transener Internacional Ltd. Pellizzoni earned an engineering degree in telecommunications from the University of La Plata, Argentina, and a postgraduate degree in automation from the University of Rome, Italy.
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