A Real-world Implementation of Centralized RAS System

by J. Wen, P. Arons, E. Lee, Southern California Edison , USA

As a result of green initiatives and Renewable Portfolio Standards (RPS) mandates the generation interconnection requests in California from new renewable resources to the power grid have escalated dramatically in recent years. RAS/SPS has been a timely and economic solution to enable the renewable generation interconnection considering the cost of building and difficulty of siting new transmission lines. Consequently, there will be a proliferation of RAS/SPS in order to accommodate many new generation interconnections.
The challenges that Southern California Edison (SCE), one of the three large Investor Owned Utilities in California, faced from its own system was that the standalone nature of the existing RAS/SPS implementations has limitations of operating in an isolated local substation environment, with little communication of RASs from one to the other, along with laborious traditional /non-optimized maintenance and test practices.

These technical limitations in combination with the need for extensive staffing support impede the company’s ability to deploy large numbers of new RASs and meet generator requested operating dates. Both grid operation reliability and business practice optimization called for a breakthrough solution – centralize the existing distributed and standalone RAS to allow for better RAS development, coordination, and maintenance. With enabling technologies such as advanced field Intelligent Electronic Devices (IEDs) and advanced fast computer hardware and software, SCE’s extensive microwave/fiber communication networks, and the continued development of international standard IEC 61850, the opportunity exists to achieve such a breakthrough. (Figure 1)

The Centralized RAS (CRAS) developed by SCE centralizes the entire monitoring and protection functions, including the arming calculation as well as RAS logic, and establish a platform for future RAS optimization and development. From advanced Information and Communications Technology ICT point of view, there are several breakthroughs: An Intel-based modern computer sever-type controller, capable of IEC 61850 communications, will be the first used as RAS controller instead of proprietary Programmable Logic Controllers (PLCs) based solutions. State-of-the-art information technologies in Cyber security, redundancy, historian, etc. are applied to the RAS central controller systems. CRAS will also be the first of its kind that applies IEC 61850 over such a large scale wide area monitoring and protection network (over 100 substations planned).

Business Drivers
SCE transmission network, as depicted in Figure 2, consists mainly of 500 kV and 230 kV transmission systems with multiple long corridors connecting remote generation as well as interconnecting with numerous neighboring utilities in western United States. This network has become increasingly congested as a result of ever-growing customer load and significant additions of generation from new power supply market participants. RAS has become a timely and economic choice considering the cost of building, the difficulty of siting new transmission lines, and the long lead time required for the new transmission construction. Today, SCE has 17 standalone RAS implementations and expects a need for more than 30 new RAS implementations in the next few years, as shown in Figure 1.

A neighboring utility’s comprehensive RAS experience, together with the challenge to manage and maintain an ever increasing volume of distributed, standalone, RAS, has led to the exploration of the concept of a completely centralized RAS for the entire SCE transmission network by leveraging advanced ICT development and SCE’s fiber backbone network.

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