PC-Based Control Comes of Age

The 1996 blackouts led to an extensive investigation of the events leading up to the grid collapse. Evaluations of sub-system performances led to engineering design changes to improve system response. As with most complex systems, there was not a single fix that would miraculously correct the problem. Instead, many ideas for improvements were developed, evaluated and implemented.

During the evaluations of the incident in the Pacific Northwest region (where the system initially started to collapse on both occasions), it was determined that control system performance at four hydroelectric power generating stations needed improvement.

These generating stations are located in areas that are strategically important to the electrical transmission system because of proximity to major transmission system interties. Their location allows these stations to be a first line of defense during an electrical disturbance, but only if the units perform as required.

Control System Upgrades Critical

The generating stations' original control systems were antiquated. Although still performing as originally implemented (supported, as all control systems are, by the efforts of a very talented group of technicians), it was apparent that they would not be a good platform for improving system performance. This was especially true with respect to the integration of new technologies.

Faced with the need for vastly improved levels of performance, a decision was made to implement a new plant-wide control system. Automated Control Systems, Inc. was brought in to evaluate needs and develop the new control systems.

Project goals were clear and comprehensive. The facility's management believed that extensive use of COTS (commercial off the shelf) technology would be the way to extend system life, and provide best-of-breed product use. The utility's engineers insisted on a high level of fault tolerance, and a common code base across the system. The challenge was to evaluate a wide variety of products and design a control system that would meet these goals.

Because of the technology's low cost, high performance, high reliability, freedom to mix and match components, and inherent ability to modify the hardware without a huge price penalty, PC-based controls were considered to be an attractive, cost-effective choice. The larger question was whether or not PC-based controls would provide the required reliability and flexibility.

A Dam Fine Start Up

The same assessment criteria applied to proprietary components was used to evaluate the PC-based technology. These criteria included:

• Does the function and design of the device meet the requirements of the application?
• What are the failure states of the solution and how do the failures impact safety and the process?
• What is the track-record of the technology in similar applications?