In the past, substation integration efforts focused on integrating functional blocks of equipment through various communications media, which required many different types of devices from different manufacturers. The potential incompatibility among the devices frequently complicated system design and presented significant operations and maintenance (O&M) support problems.

Today, a prefabricated control house can leverage the functionality available in microprocessor relays to integrate the various systems involving control, monitoring and automation.

The integrated architecture within the control house provides a level of integration unparalleled in the industry. The entire control house, or just the panels, are pre-engineered, designed, preconstructed and pretested off-site and then installed in the substation. This solution is inexpensive and has a high degree of reliability with the enhanced functionality of microprocessor-based relays and communications processors, which is the basis for the first completely integrated “drop-in” substation control house delivered to Duke Power's (Charlotte, North Carolina, U.S.) Belmont Tie Station.

While the Belmont Tie Station is not the first substation upgraded under Duke's Substation Automation and Relay Upgrade Program, it is the first substation built as a complete control house off-site, and then delivered intact and “dropped in” the substation yard.

The control house solution delivers a wealth of power system information that provides users with an increased understanding of power system asset status and operation. This information permits risk assessment and outage avoidance, reduced labor and outages for maintenance, and creates a more competitive and reliable power system. In addition, it is possible to monitor asset return-on-investment (ROI), identify and replace obsolete equipment, strategize effective use of resources and financial capital, and increase device and system productivity.

Application at Duke Power

Duke Power's Electric Transmission (ET) recently developed an automation strategy for transmission substations to replace separate equipment for supervisory control and data acquisition (SCADA) and protective-relaying functions used in the past. Since this legacy equipment consisted of electromechanical relays and telemetry SCADA systems, it was not possible to combine protection and SCADA functionality. Beneficial functionality involving sequence-of-events (SOE), digital fault recording (DFR), breaker condition monitoring (BCM) and annunciation required the installation of separate equipment. Because additional equipment from multiple vendors usually does not use a common communications pathway, the result would be higher installation and maintenance costs without an increase in reliability.

The existing architecture hampered ET's ability to retrieve operating information to assist in maintenance and engineering analysis. Furthermore, most of the SCADA and protective-relaying equipment was approaching its end of life. To address the problem, Duke organized the Transmission Substation Automation & Relay Team (TSAR-Team) to develop and implement an automation upgrade program to deal with reliability, obsolescence and information management.

The program focused on the replacement of the protection, control and data acquisition functions within existing transmission tie stations. The primary motivations for this upgrade work were reliability issues associated with the aging infrastructure and the need for good economic business decisions where failure to fund present-day programs would result in higher costs in the future. The TSAR-Team considered the options to replace individual aging devices with microprocessor-based technology or to undertake complete station upgrades, which involved the application of new technology in an integrated approach for complete protection, control and data-acquisition functions.

The complete station upgrade solution offered many benefits, which made it the preferred solution. By using advanced digital-relay technology, the utility realized multifunctional capabilities with lower initial costs as compared with purchasing many discrete components to perform the same functions. Multifunction digital protective relays represented a potential 15% to 25% reduction in capital requirements. In addition, the O&M costs were lowered by using more reliable hardware, which reduced the overall complexity of the control designs. The hardware provided advanced apparatus diagnostics that reduced station inspection times, which would lower O&M expenditures due to an integrated approach using automatic data collection for record keeping and asset management.

Through the use of a new protection and control computer interface, operators can take advantage of additional system information to enhance operability. Providing easy-to-use station one-line and control displays to facilitate service restoration minimizes the potential for operator error and lessens total outage duration.

The utility realizes enhanced functionality through the use of modern protective relays that provide all metering, alarming, SOE and status information. The data are automatically retrieved daily and compared with predefined limits for automatic notification to O&M personnel. The notification improved work deployment on these assets. Additional benefits to the system are those functions that are available within the relays, including fault location, fault current magnitude, 0.2% voltage metering accuracy for load profiling, meter validation and power-quality functions. Breaker monitoring, which is built into the relay, aids in determining optimum maintenance cycles.

After selecting the station upgrade option, the TSAR-Team developed a detailed and prioritized station list placing all ET substations on a 20-year cycle, requiring 11 transmission class substations to receive immediate attention. In the spring of 2000, the TSAR-Team requested quotes to provide seven 100/44-kV substation control houses. In May 2000, the team awarded this work to the Systems and Services Division of Schweitzer Engineering Laboratories Inc. (SEL; Pullman, Washington, U.S.). The Belmont Tie Station received the first completely integrated drop-in substation control house in October 2000.

The Turnkey Control House

Although the drop-in control house design and implementation strategy is innovative in its own right, the true advancements lay in the integration of the substation control, monitoring and data acquisition functionality provided by the microprocessor relays and communications processors. Using the intelligence and functionality of the relays, ET eliminated the need for RTUs and PLCs but added the ability to perform distributed automation. Distributed automation is more robust and flexible than centralized automation in RTUs and PLCs, and provides advantages previously unavailable. ET implemented communications processors to integrate communications among microprocessor relays and other intelligent electronic devices (IEDs) that included equipment monitors, weather stations and battery chargers to create a powerful substation-wide database. Alarms and reports are sent to operations personnel or software applications via several communications media.

ET recognized that the traditional SCADA approach does not fit the new information management needs of the substation. SCADA protocols pass only a small amount of the intelligent information available within the IEDs. Choosing the truly open communications architecture of the communications processor allows ET to take advantage of all the information in the relays and other IEDs. RTU and PLC solutions restrict the type and amount of information that can be retrieved, used and passed on to operators.

Benefits of Dual-Primary Protection

In the past, many utilities attempted to minimize their risk of failed protection by installing a primary protection system and then installing another protection system, often from a different vendor, as backup. New product capabilities and integration technology have created opportunities for utilities to install redundant primary protection products in an application called “dual primary.”

Early on, ET established its mission for ensuring the health and availability of the power system by maximizing protection security and dependability. It would achieve security by correct operation to protect apparatus from faults and achieve dependability by reducing protection downtime, thus ensuring that equipment was available to operate. To further increase security, ET selected a dual-primary scheme that prevents weaknesses from overlapping. Choosing reliable high-availability products to minimize downtime ensured dependability.

ET chose protection systems to maximize dependability based on a high mean-time-between-failure (MTBF) and high mean-time-between-removals (MTBR). Redundant protection in the drop-in control house solution also provides redundant monitoring and control. Different redundant platforms reduce the possibility that component failure will affect both protection products. However, both platforms must be individually reliable to maximize dependability. Redundant protection products of the same reliable platform are often more dependable than using a second platform with a lower MTBF.

ET selected microprocessor relays and the communications processor to maximize protection reliability and dependability based on these criteria. By selecting products from a single vendor, ET found that, in addition to achieving the highest degree of reliability and dependability, it also realized the following benefits:

• Improved operations, maintenance, documentation and a reduction in inventory of spare parts as a consequence of having fewer product types.

• Simplified network designs for communication technology, information management, remote engineering access and automatic event collection.

• Reduction in operator errors and unwanted outages as a result of using the same interface on each dual primary device.

• Ability to access and use all information within the IEDs via innovative communication technologies.

• High-speed and robust distributed protection, control and automation via reliable communications.

• Realization of a lower total ownership cost.

A Good Solution

By performing a tremendous amount of logic programming inside the microprocessor relays, ET was able to simplify interconnections and minimize the installed assets by combining substation functionality, traditionally performed in separate single-function devices. The integrated microprocessor-based system is a dynamic system that continuously monitors apparatus conditions and interacts with the substation computer, Transmission Control Center (TCC) and ET's corporate database. The new integrated IED system monitors more than 6000 data points in contrast to the traditional system it replaced, which monitored only 96 status points. Alarm criteria for each data point were defined, and new methods for handling this massive amount of data were developed and integrated into a proactive maintenance system.

The drop-in control house strategy using microprocessor relays and communications processors provides a good solution to the problem of obsolescence. As more assets approach “end-of-service life,” designers must explore new and innovative methods. By developing good relay and control standards, integrators and relay vendors can deliver a quality precommissioned control house that meets asset and business requirements far into the future.

Acknowledgment

The author acknowledges the help of David J. Dolezilek in the preparation of this article. Dolezilek is automation technology manager in the research and design of automated systems at SEL.

Brian A. McDermott received the AS degree from Gaston College in 1981 and was employed by Duke Power in its transmission department. Presently, he provides technical direction for transmission automation and integration, is responsible for engineering studies, develops Electric Transmission's automation strategy and is project manager and alliance manager for ET's automation team. He holds a patent for voltage regulator compensation in power distribution circuits.