POWERFUL COMPUTERS, SOFTWARE CHANGING PIPELINE SCADA SYSTEMS

Warren R. True
Pipeline/Gas Processing Editor

Advances in computing power in recent years are enabling pipeline operators to collect more data at a central location and to transmit such data more rapidly than ever before.

Additionally, more sophisticated, general-purpose scada software is enabling operators to do more with the data retrieved and to manipulate the information more conveniently and efficiently with advances in graphics capabilities and the power of personal computers.

These developments have for many pipeline operating companies led to a merging of formerly distinct functions, especially of measurement and control. Most significantly, dominance by the traditional concept of a central host computer system and backup mainframe is being challenged by what's being called "distributed" systems. These typically rely on several clusters of computers which perform functions formerly residing in large monolithic systems.

Such distributed systems have brought a degree of Credibility and power to newer scada systems only dreamed of in the early 1980s.

A look at some recent projects will illustrate these trends.

EVOLUTION IN SYSTEMS

Computer developments of the last 20 years have changed the face of pipeline scada operations, just as they have changed every other industry that depends on analysis of operating information to guide its operations decisions.

Andy Wike of Stoner Associates, Houston, says that the increased power of computers has facilitated major advances in scada software packages now available and in the applications that they can support.

Similarly, he says, the developments in networking and communications technologies and their associated reduction in bandwidth cost have accelerated growth in the capability and capacity for data transfer.

Operating companies are now looking to their scada systems not just as systems for use by gas control operations.

32-BIT REVOLUTION

Development and widespread use in the 1980s of the powerful 32-bit computers, which replaced the older, slower 8 and 16-bit machines, wrought a revolution in the speed and capabilities of pipeline scada systems.

The additional power of these systems, says Wike, provided the capacity for advanced decision-support applications on which pipeline-control staff quickly came to rely.

General-purpose scada software packages took advantage of this new architecture.

Wike identifies some of the distinguishing characteristics of these new systems:

The increased physical memory size and operating environment of these systems removed the storage-space restrictions imposed by earlier systems. This removed the need for the scada data base structure rigidly to reflect the physical remote terminal unit (RTU) configuration. In turn, this power provided the capability for the storage of non-scada data, such as communications and accounting data, in the traditional scada data base.
Relieving the storage-space restriction with the 32-bit computer architecture allowed a data base (or, point count) increase of an order of magnitude, says Wike.
In related technologies, he says additional developments which characterized the newer scada systems included the following:
High-resolution color graphic displays provided a much more easily understood presentation of data to the control-center staff than the older monochrome displays. (See accompanying article on enhanced graphics.)
Among examples, he says, are the use of color to indicate alarm conditions and the retrieving of trend information from the scada data base and its being drawn on the screen rather than a limited capability hard-copy, strip-chart recorder.
The use of front-end processors (FEPs)-dedicated computers responsible for polling RTUs-relieved central host computers from this task and thus provided more computer resources for advanced applications (for example, linepack estimation on a gas line or contract delivery monitoring).
As the reliance of control operations on these computer systems grew, the need to maximize system availability also increased, says Wike.
Systems had been commonly installed with a redundant, standby computer to take over the scada operations should the on-line scada computer fail. As the decade progressed, Wike says, networking technology advanced, the most popular of these being the Ethernet (IEEE 802.3) standard.

DISTRIBUTED PROCESSING

The most significant effect of this advancement has been to allow multiple computers easily to handle functions previously dedicated to a single monolithic computer system. This change has come to be termed "distributed processing."

Simply stated, distributed processing refers to dividing, or distributing, what previously were tightly coupled computer applications over several smaller computer systems and coupling these systems with a high-speed communications system, such as Ethernet.

The most readily implemented distribution, says Wike, is vertical and is achieved by placement of computing resources along the data highway between the data source (the RTU) and the destination (the so-called "man-machine interface" or MMI).

FEPs were already commonplace by the end of the decade; communication gateways to other computer systems appeared, as did display servers to handle the MMI processing and data base servers to handle the data base access requests, among other developments.

In data base technology, says Wike, the increased power of these computers has made the use of genera purpose data base packages attractive for control-system users.

The magnitude of computing demands in these packages had previously restricted their use to mainframe computers.

Through the use of general purpose query languages, other business areas within an operating company are now able to access the control scada information.

Within the gas-transportation segment in particular, Wike says, the regulatory environment and the consequent market pressures in the U.S. will undoubtedly focus the attention of operating companies on more integration and automation.

These pressures will affect scada technology, with the traditional gas-control computers becoming integrated with other, "back office" accounting and management functions.

Further, the software and hardware industries are moving towards open systems, common standards and protocols, and standard interfaces, as noted by W. Gabris in a 1990 Entelec Conference presentation.

Consequently, with a broad acceptance and implementation of such standards, says Wike, the concept of a scada system lifecycle will be replaced by the lifecycle of individual components. And, with industry standards in place, system upgrades can add functionality on a gradual "plug-in" basis, thus preventing the need to commit to a substantial capital investment in a single budget cycle.

Wike notes the growing pervasiveness of AT&T's UNIX operating systems in the industry as well as the growing use of MIT's X-Windows software design for low-cost, high-resolution graphics interfaces for more versatile and powerful workstations.

Application-independent "graphical user interface" (GUT) software packages are available to cover up the seams between diverse scada applications. System operation with a mouse-driven GUT can virtually eliminate the use of a keyboard, Wike says.

The enhanced screen graphics available at a given pipeline-control workstation as a result of the increased power of computers and sophistication of software is discussed in a companion article (p. 45).

In a presentation last year to the Entelec Conference, J. Anderson noted that the future will see a movement towards a more integrated appearance of scada and application systems which use this windowing standard.

FLOW COMPUTERS ARRIVE

In addition to the growth in power, versatility, and flexibility in general computers both large and small, the evolution of the flow computer for electronic flow measurement (EFM) has increased the amount, improved the quality, and accelerated the retrieval speed of data collected at RTUS.

A major effect of efforts by the U.S. Federal Energy Regulatory Commission (FERC) in the mid-1980s to make the gas-transmission industry more open and competitive has been the growing replacement by EFM of paper-strip chart recorders in the gas field, at plants, and elsewhere.

EFM devices permit more accurate measurement and monitoring of flows, temperatures, and pressures; the storage of more data; and the transmission of data over great distances with today's improved telemetry systems.

Wike says that formerly, larger operating companies might process tens of thousands of charts each month, with the flow-delivery information being available within a month or two of the chart being collected.

"This is a labor-intensive, time-consuming procedure that is prone to error," he says.

If processing the charts takes 2 months, the pipeline company is in effect financing the cost of its gas for those 2 months.

A pipeline company can only recover this cost in the pricing of its service. But with the tight competition on gas pricing engendered by the open access system, even a small percentage improvement in operating costs can make a dramatic difference in the success of a pipeline company in selling its services.

With relatively low-cost devices, the delivery information can be measured electronically and then transmitted back to the gas control scada system through the existing communications networks.

Upon receipt at the central site, these data are most commonly passed on to a mainframe computer for processing.

Indeed, in many cases the installation of these electronic measuring deN,ices can have an immediate pay back, says Wike, justified merely by the financing of the flow of cash. The competitive advantage of service pricing is an additional, though potentially critical, benefit of EFM devices.

From the accounting perspective, noted K. J. MacLennan in a 1989 presentation to the Entelec Conference, FERC is placing requirements on pipeline companies related to record keeping, the primary focus of which is custody transfer via EFM.

Scada systems, Wike concludes, are being required to accommodate the changing needs of the accounting function because the primary source of the accounting data will be the scada system itself.

NEW SYSTEMS

An accompanying article (p. 53) to this one presents details of a recently commissioned scada system on a products pipeline in the U.K. Following are some typical scada installations either under way or planned in the U.S.

These projects illustrate the trends already discussed and show how companies are taking advantage of each new development in computer technology not only for system control but also for more traditional business functions.

COLONIAL PIPELINE'S UPGRADE

The system Colonial Pipeline Co., Atlanta, is replacing and the one being installed may indicate where the industry has been and where it is going. In a presentation before the 1991 API Pipeline Conference, Colonial's Steve Meller and M. C. Coke described the project.

Colonial Pipeline consists of 2,885 miles of 30-40 in. main lines, 2,111 miles of 6-22 in. stublines, and 192 miles of local delivery lines. Flow rates in the system range from 1.2 million b/d the Houston-Greensboro, N.C., gasoline system to about 14,400 b/d on some of the small stublines.

Controllers at the central control center in Atlanta operate all the main lines and four of the more complex stublines, the latter being divided among four operating consoles.

System 1 is the 36-40 in. gasoline main line from Houston to Greensboro. System 2 is the 36-in. distillate main line from Houston to Greensboro. System 3 is the 30-36 in. mixed products line from Greensboro to Linden, N.J., along with the 32-in. line from Greensboro to Dorsey, Md.

System 4 includes the Atlanta-Bainbridge, Ga., line, the Atlanta-Knoxville line, the Atlanta-Nashville gas line, and the Atlanta-Nashville distillate line. The scada system being replaced, installed in 1978, was custom built in-house and is therefore unique, said Meller and Coke.

It consists of very large consoles with hand wired panels which represent each of the pipeline locations and mechanical strip chart recorders for operating pressures and gravitometers. There are also "button boxes" for sending commands.

The system was built around now-obsolete MAC-16 minicomputers which are of limited capability and have become increasingly difficult to maintain, said Meller and Coke.

After bid proposals were received in August 1990, contracts were awarded to Valmet Automation Ltd., Calgary, for the software and hardware, and to Evans Consoles Inc., Calgary for the console furniture.

The new central control center will have six operating consoles, a shift supervisor's console, and a training simulator console (Fig. 1). The shift supervisor's console as well as the training simulator console can be converted to operating consoles with minor software changes.

According to Meller and Coke, each of the consoles will have six 20-in., high-resolution color monitors. One mouse and one keyboard will be used for each bank of three monitors. Each bank will be connected to one MMI computer which will be connected through a local area network (LAN) to a scada master computer.

There are two such master computers with one running in prime and the other one in the "hot" backup mode in case the prime one fails.

The new backup control center will be a scaled-down version of the main center in that there will be only three 20-in. monitors and a single MMI computer for each console. A training simulator console will not be provided at the backup center.

The design that Valmet and Colonial created for the scada system uses a distributed network. For example, the design calls for a redundant scada Ethernet LAN as the data highway between the scada master host and the control center console.

In the past, said Meller and Coke, the equivalent item in a scada control center design would have been the backplane bus of some large computer. Here, however, components can be added or removed from the network without requiring system shutdown.

This implies that failure of any given component cannot take down the entire system. In fact, the Colonial system design calls for full operability of the pipeline system given any two coincident failures. This includes the design of the power supplies and communications equipment, as well as the computer components.

The primary and standby computers monitor the health of one another with network messages which are an industry standard design for delivery reliability. Two scada masters at the central control center provide primary and hot standby capability, and two additional scada masters are connected via a "T1" line to accommodate the backup standby failure model.

The T1 is a high-speed telephone leased line circuit which offers nearly a transparent interface to the scada LAN. One of the off-site machines can thus drive the controllers' consoles simply by commanding it to take active control of RTU communications.

A device called a "router" provides interconnection between two central control-center scada LANs and the T1 link. The router also provides controlled access to the company accounting data bases.

Meller and Coke believe that what sets Colonial's effort out from many others is the implementation of a scada system based on a UNIX-like operating system. Meller says that UNIX is not naturally a real-time system and is, therefore, ill-suited for scada applications.

Colonial decided, he says, that hardware performance is sufficient to overcome deficiencies inherent in the UNIX design. Colonial's new system will rely on proven, tested, reliable hardware techniques, such as Ethernet, to ensure delivery of messages between components and on high-quality hardware to ensure the integrity of the system components themselves.

As of Mar. 1, the new control center has taken control of all four systems previously operated in the old control center, says Meller. The off site system has yet to be shipped; when completed early next month, Colonial expects to abandon the old center.

The N-SAT system is being installed in phases, of which Phase I is nearing completion this week. Meller says that the two new consoles for which central control is being applied for the first time are expected to be on-line in the fall.

AMOCO GAS' SOUTH TEXAS SYSTEM

Amoco Gas Co. is in the final stages of installing a new scada system located at its Texas City, Tex., operations headquarters.

Andrew Richmond, Amoco Gas senior engineer, says that the company's scada system provides real-time monitoring and collection of custody-transfer data used for billing customers. In that combined duty, Amoco Gas' new system reflects the merging of functions previously mentioned as a trend for modern scada systems.

Supplied by Amocoams/Modular Inc., Aurora, Ill. (AMI), the system (Fig. 2) includes a new master station, several new operator stations, a 900-Mhz radio system with two repeaters, and 58 new RTUs at various metering and process facilities (Fig. 3).

Richmond also says that while the radio system is the primary means of communication with field RTUs, Amoco Gas also uses a 1200-baud telephone system primarily for sites beyond the radio system as well as direct hard-wire connections.

An equipment console in the system administrator's office contains all required master station equipment for this system. It is from this console that communications with the RTUS, operator stations, and various host site peripheral devices are maintained.

AMI's standard Adacs software package runs on redundant DEC VAX 3100 computers. Both computers communicate over an Ethernet thin-wire (coaxial) cable.

Included in the network are three 8-line terminal servers. These DEC servers provide modem support and connections to a synchronous I/O lines. DECserver 1 provides communications with the RTUs, DECserver 2 with the master station printers (alarm and report loggers), and DECserver 3 with operator stations.

To provide operator station backup in the event of failure of one of the DECservers, the critical operator displays are split between DECserver 2 and DECserver 3.

Operator stations allow access to the centralized master station from various locations. Two operator stations are in Amoco Gas' Texas City offices, one in the Westlake (Houston) corporate offices, one each in the offices of the dispatcher, the operations foreman, the scada foremen, and a portable version for maintenance personnel.

Each operator station consists of an 80386-based personal computer with 2 mb RAM memory, a 40-mb hard drive, and a 19-in. VGA monitor. At each operator station, AMI's "WinTerm" software runs under MS-DOS in an MS-Windows environment. (Amoco Gas' use of enhanced graphics is discussed more full), in a companion article, p. 45.)

WinTerm allows for the simultaneous use of other DOS-based software packages for, among other capabilities, generating graphics, word processing, and integrating, spreadsheets.

On the 900-Mhz radio system, a standard continuous polling system has been installed to ensure periodic verification of the health of each RTU.

Amoco Gas measures and controls the flow with AMI's EFM-700 RTUS--electronic flow measurement devices. AMI says that the consolidation of measurement and control functions has reduced equipment costs, increased efficiency, and eliminated "cross claims" of multiple vendors.

Each RTU accepts process signals from high resolution flow, pressure, and temperature transducers to perform standard AGA-3 (with NX-19) and AGA-7 flow calculations on up to four flow-meter (orifice or turbine) tubes.

Provisions have been made for manual or automatic downloading (from the master station to the applicable RTUS) of the gas chromatograph-derived data for custody-transfer quality flow calculations.

Each RTU stores 35 days of hourly and daily flow data, an audit trail log, event log, and alarm log.

The Amoco Gas system uses the EFM-700's PID-type control capabilities to maintain optimum flow profiles and to sequence multiple gas streams through centralized meter runs. Control may be based on flow rates with pressure overrides, or vice versa, says AMI.

RTU setpoints are modified locally with a built-in membrane keypad or laptop computer, or remotely over the radio link from the master station computer. At several RTU sites, online gas chromatographs have been plugged into a secondary RS-232 port on the EFM-700 RTU communications in an Ascii format.

Both at the master station and the RTUS, provision has been made for the future implementation of a new AGA-3 which incorporates an AGA-8 supercompressibility factor that takes into account a fuller range of hydrocarbon components.