Three Major Areas Affect the Information Coming from Substations: supervisory control and data acquisition (SCADA), data integration architecture at the substation and the communications pathway.

Over the last two and a half years, Dominion (Richmond, Virginia, U.S.) has made a concerted effort to significantly upgrade these functions. Dominion brought in consulting firm KEMA to conduct a comprehensive evaluation of its system as a whole, and provide a fresh look at a communications system and architecture that was quickly becoming obsolete.

As a result of this evaluation, Dominion was able to get all the right people into one room, to look at the whole system and to make several key decisions that would shape the face of the utility's communications system for years to come.

SUBSTATION PERFORMANCE

One of the first steps for any utility looking to unlock substation performance should be automating the retrieval of any and all applicable data whenever possible. This not only includes traditional SCADA data, but also any maintenance data, event record data and so forth. Doing this frees up valuable resources and manpower that can be used more efficiently elsewhere. It also limits the number of users who need to access all the way down into the substation, and therefore minimizes exposure to mis-alarms and accidental operations from a communications standpoint.

For its data communications architecture, Dominion employs a star topology. A star topology is one where data is concentrated from the bottom up, sent to a central substation data hub or data concentrator and then packaged for delivery to the SCADA master. The benefits of this topology are numerous. Firstly, it allows the utility to eliminate all unwanted data at the lowest possible level, which reduces traffic on the SCADA line and, in turn, reduces unnecessary data delays. Secondly, this topology offers the SCADA master one-stop shopping, with one device using one protocol to scan at the substation. Lastly, through the use of DNP 3.0 protocol and its Class Polls, all substation data can be retrieved with one request.

Protocol standardization is another important step in unlocking substation performance. Standardizing on a single protocol or small subset of protocols provides data continuity, minimizes the number of interoperability issues that may arise and allows the utility engineering team to focus on the intricacies of a few protocols instead of having to become experts on many. For Dominion's purposes, the utility standardized on three protocols: SEL Fast Messaging for communications to its SEL relays, Modbus for communications to Modicon PLC's and DNP 3.0 for everything else, including communications back to its SCADA master.

The final important step to making the substation more intelligent is to provide local intelligence to utility field personnel. For Dominion, this comes in the form of an intelligent local human-machine interface (HMI). Traditionally, utilities have used “dumb” HMIs or annunciators (this would be a paper drop or lighted tag display), which is used only for local alarm display and is limited at best. Dominion decided to take things a step further and, through the use of Substation Explorer by Subnet Solutions, expanded the functionality to not only include all substation alarms but also analog values and status points. This increases substation intelligence locally by giving field personnel access to all substation information on one screen, enabling hem to perform their duties more efficiently and effectively.

MAXIMIZING INFRASTRUCTURE

There are several reasons for transitioning to a high-speed communications pathway. For Dominion, the most prevalent reason was a desire to maximize its existing infrastructure and make its substations more intelligent by providing faster, more reliable access to all substation information. This migration path improves Dominion's substation communications for the immediate future and ensures the utility will have the flexibility to easily transition into newer methods and protocols, such as IEC 61850, should it choose to move in that direction.

The term “pure IP” communications (used throughout this article and for the purposes of this discussion) is defined as a high-speed, purely digital IP-based communications pathway where traditional analog communications are no longer used. The first step in eliminating analog communications from the substation communications environment is the transition away from the time division multiplexed (TDM) architecture and stepping into the world of pure IP communications. This transition allows for a more intelligent, efficient and dynamic use of resources.

The implementation of a fully dynamic, high-speed pathway has several advantages, the first of which is the full utilization of all available bandwidth. In the traditional TDM architecture, through the use of a channel bank, sections of the communications pathway are partitioned off and allocated for specific uses, a portion for voice communications, a slower (in Dominion's case, 1200 BAUD) analog portion for SCADA communications and a section for some high-speed traffic (telnet, ftp and other IP-based communications). The problem with this architecture is that it leaves almost no flexibility and locks into specifically allocated sections for specific types of communications. In times of high traffic, this can lead to communications delays in one region, while other regions sit with little to no traffic. The implementation of the pure IP architecture eliminates this problem by allowing for dynamic allocation of the entire communications pathway. This dynamic allocation allows all communications processes to acquire and use the bandwidth that is needed without worrying about hitting allocation barriers.

Analog signals are also highly susceptible to electromagnetic interference (EMI), which can lead to poor signal quality, in turn severely degrading communications and causing significant problems. The pure IP architecture, by virtue of the fact that it is end-to-end digital communications, provides a high-quality signal with error checking and provisions for data retransmission that vastly increase noise immunity.

While the pure IP architecture provides for increased flexibility and allows for the dynamic use of all available resources, as with anything, there are limits to the amount of total available resources. To assure that high-priority processes are always available, quality of service (QoS) is used to determine a pecking order and assure that in times of high-traffic processes, like SCADA traffic and voice service, are always available.

SEPARATED OPERATIONAL, NON-OPERATIONAL DATA

Another important benefit of implementing high-speed communications is the gained ability to fully separate operational and non-operational data. Recent industry trends have shown a strong migration toward the use of intelligent electronic devices (IEDs). A natural byproduct of the increased use of IEDs is an increase in the amount of information that can be retrieved from the substation. In the past, Dominion has been able to use its slow-speed SCADA pathway to retrieve some of this non-operational data with relative ease, but the amount and variety of data available at the substation over the last couple of years has increased exponentially. This increase has fueled Dominion's need to use its high-speed infrastructure and forced the utility to shift its thinking toward the separation of operational and non-operational data at the substation.

THE CHANGE

Now that we've discussed what this transition is all about and what it means, let's look at what Dominion has done to bring this concept to life.

The question of what to do with the SCADA traffic is a very large part of the change and, in fact, was a major driver in the decision to upgrade and overhaul Dominion's communications architecture.

Given the fact that Dominion has all of this bandwidth, putting its SCADA traffic on the high-speed network was the next logical step. The utility explored options for compressing and wrapping the existing CONITEL protocol in a TCP/IP packet or tunnel, but ultimately decided these options were not the most effective use of resources and efforts. After taking all of its options into account, Dominion decided the best course of action was to begin the migration away from CONITEL and the move toward DNP TCP/IP.

To secure this connection, Dominion has locked its substations completely, implementing firewalls at all substations and using encryption technologies to secure its substations and communications pathways.

Now comes the question of what to do with the existing devices in the substation that have traditionally used dial-up methods to provide access in and out of the substation. Given the desire to make all communications in and out of the substation high-speed digital, the utility decided to do one of four things with these devices:

1. Connect them to a substation data concentrator (SEL-3332 or SEL-2032) capable of acting as a terminal server/port switching device.

2. Install a stand-alone terminal server/port switching device (GarrettCom DynaStar 2000).

3. Replace existing equipment with an Ethernet-ready equivalent device.

4. Connect them to a serial-Ethernet converter.

As with most other utilities, Dominion traditionally has employed remote terminal unit (RTU)-centric architecture with an RTU of some sort being the master device at the substation that reports directly to the SCADA master. Because most RTUs do not support an Ethernet protocol, it can no longer function as the master device of the substation and, in essence, has become no more than a hardwired I/O module.

The architecture of substations has been transitioned to data concentrator-centric architecture, and two migration plans were developed to handle the RTU. The first is that smart RTUs (GE D20) are upgraded to support DNP protocol and now report to the substation data concentrator just like any other substation IED. Then legacy RTUs that cannot be converted to support DNP protocol are replaced with a simple I/O module (SEL 2411). And last but not least, traditional dial-up voice communications are replaced with voice-over-Internet protocol.

KEYS TO SUCCESS

Taking a step into the future and completely shifting philosophies is no small feat, but with careful planning, it can be accomplished efficiently and effectively. This is a look at what Dominion has done to address an aging and increasingly obsolete philosophy and infrastructure.

For any utility looking to do the same, it is important to understand that the future of utility communications is going to encompass multiple areas of the utility, most of which are not used to working together. Second, the utility must take the time to evaluate the system as a whole and get a picture of all the pieces that have to work together on the system. Finally, the solution must be tailored to meet the specific needs of the utility to achieve the best solution.

---

Augustus Johnson IV is an engineer II in Transmission Substation Engineering & Data Communications at Dominion, which he joined in January 2005. His expertise primarily lies in the areas of substation communications architecture, data acquisition, concentration and distribution, and communications protocols. Johnson holds a BSEE degree from the University of Delaware and is a registered engineer in training in the state of Virginia. Augustus.Johnson@dom.com