In the late 1990s, in keeping with the rest of the world, the Chilean Electricity Industry embarked on a major restructuring program that led to several regulations aimed at improving consumer service. The key issues were to reduce energy costs for the end consumer and to improve all service-quality indices, especially the quality of supply. Furthermore, from 1997 to 1999 Chile suffered its worst drought of the 20th century, resulting in blackouts and scheduled customer disconnections — a situation that brought the whole restructuring effort under government scrutiny and subject to adverse public opinion. This situation framed the start of the Compañía General de Electricidad (CGE) supervisory control and data acquisition (SCADA) project.
CGE's combined asset base made it imperative to install a fully functional SCADA system to increase the quality of service to meet the new and tougher regulations set forth by the Chilean authorities.
Compañía General de Electricidad
By tradition, CGE is a distribution utility operating in the private sector since its creation in 1905. CGE developed and operated a network of 40 unmanned substations and 200 km (125 miles) of 66-kV transmission lines around the existing Sistema Interconectado Central (SIC), a transmission/subtransmission network that covers the center and south of Chile. With about 600,000 customers connected directly to its networks — and another 400,000 customers in other regions of Chile and Argentina through its subsidiaries — CGE is the second-largest distribution utility in the country.
With the purchase of 50 substations and 1000 km (622 miles) of 66-kV transmission lines from SIC in 1996, it was evident that a reorganization would be necessary. So at the end of 1999, CGE created a transmission division to operate, grow and maintain the transmission network. In August 2001, this division separated to form a new wholly owned company, CGE TRANSMISIÓN, and integrated the transmission networks formerly operated by TRANSNET (a CGE-owned transmission company) in the northern part of the country.
While CGE and CGE TRANSMISIÓN had several goals, their main objective was to manage the new extended transmission network and maintain the highest-quality standards while limiting the growth in personnel. One of the greatest challenges to continuous service is the time spent locating, isolating and repairing the faulted network. Based on the latest digital technologies, CGE TRANSMISIÓN's upper management deemed the use of a SCADA system would be vital to increase the efficiency in locating and isolating network faults. The steady flow of real-time data from the network would be valuable for technical and economic studies.
CGE TRANSMISIÓN Policy Guidelines
Following unsatisfactory experience with turnkey projects, in 1998 CGE decided to develop the SCADA system through a closely supervised integration of digital technology with existing substation equipment. CGE decided to go with a set of “best of breed” technologies and to have a small but very skilled group of national contractors to assist in the integration, using automation products that had a strong control/telecommunications reputation in the electric SCADA industry.
CGE tested the integration path while deploying a pilot SCADA project in the city of Concepción in the early 1990s. This project covered five urban substations and a control center with a full telemetry/limited telecontrol system. The system depended heavily on analog transducers, cabling and calibration, and was based on proprietary software, protocols and interfaces with the RTUs designed and manufactured in Chile. After a successful start, CGE considered that the integration concept worked well but that the technology was still not sufficiently mature; therefore, CGE decided to wait a few years before pursuing full deployment.
The decision to integrate was based on a choice for open standards and protocols. CGE TRANSMISIÓN needed a system that was compatible with existing diverse equipment (digital intelligent electronic devices [IEDs] from different manufacturers) and would be able to adapt to future requirements.
The cost of the system was another important factor. With CGE's experience in traditional SCADA systems and knowledge of the costs incurred by other Chilean utilities, CGE TRANSMISIÓN estimated the cost of a local integration scheme would be attractive.
The deployment would be unconventional, so the SCADA project was structured in several stages, including a pilot project that targeted a substation in the city of Rancagua, south of the capital Santiago, located very near to the CGE TRANSMISIÓN facilities. This close distance provided an excellent environment for testing the technology and solving all the small issues brought by the integration process. In three months the pilot project was finished and in service, having proved that the technology was viable, flexible and reliable. The next step was to test it for scalability.
Best of Breed Technologies
CGE TRANSMISIÓN selected “best of breed” technologies and contractors. For the RTU hardware, it selected Opto22 for intra-substation integration with all the existing IEDs (meters, protection relays and control relays), alarm panels and analog “field” signals (coming from the power equipment). Limiting the number of analog field signals to minimize the wiring and calibration costs was a design constraint.
For the supervisory software, CGE TRANSMISIÓN selected Intellution Fix-32 for its proven flexibility, rich library of drivers, allowing it to communicate with different equipment, and intuitive interface that enables the quick training of operational personnel.
Short distances and a small quantity of signals within the substation allowed RS-232 point-to-point connections and RS-485 multidrop serial links, using 232/485 converters. The company mainly used MODBUS protocols, which were already available in many of the IEDs, and implemented proprietary GE, ABB, SEL protocols for the rest using the manufacturer-provided protocol documentation.
To provide the communications link between rural substations and their respective control centers, the utility used different alternatives — from fiber optics in the pilot project, to analog phone lines with modems, TCP/IP over frame relay digital links, and radio links with VHF and UHF radio modems.
To keep its focus on using the best technology and contractors for each stage of the project, CGE TRANSMISIÓN decided to separate the functions of control and telecommunications. The control contractor in charge of the substation SCADA and the control center operated under the assumption that he had a “fully transparent channel” available — usually a serial link of at least 9600 bps in the form of a RS-232 port.
The telecommunications contractors would install, configure and test the necessary equipment to provide the fully transparent channel. In that way, irrespective of the link being fast or slow, radio or wired, digital or analog, the error rate would be the ultimate quality measure.
Normalizing the Substations
When conducting a SCADA retrofit, one expected to find a diverse set of equipment at the substations. Depending on the age of the facilities, the control room could be fitted with electromechanical relays, analog electronics or digital IEDs. CGE TRANSMISIÓN's goal was to preserve most of the existing equipment. However, to have continuous signals (voltages, currents and power) flowing into the RTU, it had to replace most of the analog meters with modern multifunction digital meters supplied by companies including Electro Industries, Bitronics and PML. The savings in the installation, wiring and calibration of analog transducers and analog input modules at the RTU offset the additional cost of these meters. The use of multifunction meters as “digital transducers” is one of the key factors in the low cost and fast installation of a SCADA system. Multifunction meter prices have dropped by 50% in the last five years.
These IEDs are fitted with a serial port (either RS-232 or RS-485 with 232/485 adapters as needed) and an industry-standard protocol (typically MODBUS), or alternatively a proprietary but free and well-documented protocol. The Opto22 RTU is programmed to talk to the IED in that protocol through a simple two-wire RS-485 multidrop serial link. SCADA-enabled panels replace the alarm panels, saving the wiring costs of dozens of signals.
Talking to Every IED
In the case of existing digital relays, all the necessary protocol documentation was obtained from the manufacturer and developed by the SCADA contractor in the Opto22 language. In the end, the RTU can retrieve data (and operate, if available) any IEDs in the substation, whereby payment for a one-off software development reduces expenditures on additional wiring and subsequent commissioning tests. Currently, the Opto22 RTUs interface to GE, ABB and SEL protection relays.
During the project, one of the important definitions was the functional and operating regimes of the RTU and the digital protection relays. Today, most digital relays come equipped with auxiliary contacts, making possible complex logical interlocks.
To harmonize the flexibility and complexity of the functions of the RTU and relays, CGE TRANSMISIÓN decided to focus digital relay logic to provide protection functions, enabling relays to interface and interact with other relays in more complex protection schemes. The RTU would assume all the rest of the control functions, even replacing some (non-protection) control relays, like capacitor bank and OLTP control relays, using software routines running in the RTU. Even the intruder alarm function has been moved into the RTU by wiring the infrared beam contacts directly to the RTU, eliminating the need for a dedicated alarm processor. Also, as the RTU receives detailed information on every alarm coming from the alarm panel, the operator receives information that is much more precise than with the old system.
Where a substation is located close to the control center, a multimode fiber-optic link is preferred to connect the RTU with the communications processor at the control center. In small remote substations that do not need constant supervision and only require sporadic operations, an analog modem and cellular links have been used, but the most widely used data link is UHF and VHF radio modems. These data links have proved to be the most useful, with uptime not far behind fiber optics.
CGE TRANSMISIÓN also has installed repeaters at some substations to relay the data links to other locations further away from the control center.
The typical radio link has a bandwidth of 9600 bps and can go up to 19,200 bps, which has proved enough for the application. When more sophisticated channels become available in CGE TRANSMISIÓN service areas, they will be used immediately, as all the RTUs are Ethernet-ready and are remotely (and safely) manageable via a Web browser.
SCADA Installed to Date
CGE TRANSMISIÓN now has 35 substations in the SCADA system (five of them are 154/66 kV, the remainder being 66/15-kV substations) operated from four main regional control centers. In the next few months, 14 retrofitted substations will go into service. Additionally, some four new substations go into service each year, with their SCADA systems installed during the substation construction phase, which shortens the installation time.
In those parts of the transmission system where the substations have the SCADA installed, operation times have been reduced drastically. The utility translates this reduction into ever-improving quality indices. For example, a typical 66-kV manual-reclose operation always included about 20 to 30 minutes driving time to get personnel to the substation. With remote operations, that time to operate has been reduced to less than five minutes. The estimated total cost of the project approaches US$2.2 million.
Also, the looming need for deploying human operators in each substation to reduce operation times has been eliminated. CGE TRANSMISIÓN has been filling the SCADA operators vacancies by retraining the employees formerly dedicated to the routine administration of the substations.
SCADA for the Distribution System
A second SCADA project has just started at CGE TRANSMISIÓN, this time centered on the distribution network owned and operated by its mother company, CGE. Based on the experience developed while integrating the transmission SCADA, CGE TRANSMISIÓN helped CGE to deploy remotely operated pole-mounted load-break switches supplied by S&C Electric (Omni-Rupters) and operated via a Series-M moto-operator provided by EnergyLine, a division of S&C. The communication channel consists of UHF point-to-point data links using DataRadio radio modems, linking the switches to the Control Center. The supervisory control of this SCADA was developed using the same tools as the transmission SCADA (Intellution's Fix32), and the selected communications protocol was DNP 3.0. The pilot project started operations with five switches in Rancagua in August 2001. Two similar projects comprising a total of 19 remotely operated points are underway and expected to go into service next year.
Mauricio Dinamarca is the chief of technological development at operations management for CGE TRANSMISIÓN, which he joined in August 2001. He received a degree in civil electric engineering from Pontificia Universidad Católica de Chile in 1991, following which he joined CGE. During his professional career, he has worked on distribution and transmission projects, coordinated internal software development, and specified instrumentation for laboratory and quality service. Since 1998, he has led the development of the CGE SCADA project.