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Summary
A major manufacturer initiated a project in to get their five
(5) plants ready for the coming of electric utility
deregulation. The plants are served by three separate electric
utilities and constitute a load of over 200 Megawatts combined
power. A Wide Area Network connected the plants allowing
access to Local Area Networks within each site. The overall
system concept was to web-enabled SCADA software to provide
remote monitoring and control at each site and connect them to
a systems operation center to allow purchasing of de-regulated
electricity when the market allowed. In the meantime the
systems would be used to gather load profile data at each site
and then aggregate it when the time was appropriate. A web
browser would provide the Human Machine Interface at the
system operation center.
The Web based data acquisition
architecture made it easier to integrate the diverse functions
necessary to provide all of the collected data in a - format
easily understood by all of the programs and databases
involved in the system. In addition the large expenditure
necessary for classic HMI software was eliminated through the
use of web browser based graphic pages.
Using an ordinary web
browser, a operators at the system operations center can
remotely monitor and control energy usage at 5 plants .
This was the first full
control solution offered directly from the web based
architecture used for the metering application. Setpoint
modifications, start/stop and override of system control
points had to be made available through the graphic screens.
Security had to be included to limit access to the setpoint
and start/stop controls on the graphic screens.
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Photo
1: Web Browser -
Energy Usage graphic. |
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Electric Power Monitoring Application
A
typical site involves the metering of the 4-100Kv Utility
feeds and submetering of the 12Kv switchgear across four
separate switch houses at the site. Additional submetering of
some 480v loads was included when they could be metered
economically.
The owner had made a major
investment in the metering and protective relay system on
their high voltage (12.47 kV) Switchgear. They wanted to
include the metering data and the system alarming/trending
data available from the meters/relays installed on the
Switchgear. The meters were installed in four separate
Switchouses throughout the site. Almost 50 meters existed and
were already in place. The wide geographic dispersion of the
meters meant that hardwiring was out of the question. The
plant LAN had to be used to gather the data, however a device
to collect the data at each of the Switchouses was also
necessary to allow collection of the data over the LAN to a
database. The meters utilized the Modbus communications
protocol for communications. A data acquisition and control
unit was designed to allow the use of TCP/IP networking
techniques, data polling of the existing electronic meters and
access to real time data from any PC on the LAN using a web
browser with proper authorization.
Benefits
The Web based data acquisition architecture made it easier to
integrate the diverse functions necessary to provide all of
the collected data in a - format easily understood by all of
the programs and databases involved in the system. In addition
the large expenditure necessary for classic HMI software was
eliminated through the use of web browser based graphic pages.
The system as installed was
expended in to include control of the HVAC at the site. The
system architecture allowed easy expansion to control and
monitor over 100 Air handlers and Air washers along with over
15,000 tons of chillers scattered throughout the site.
With the distribution of the
HVAC throughout the site, the use standard Internet style
TCP/IP communications will allow the system technicians to
access data from any PC with a Web browser installed. Since
the graphics are served up directly from the micro web
server/controller a centralized NT based web server and the
accompanying web application is not required.
A browser
"Plug-in" is loaded into the browser when the
first graphic screen is accessed. After that the screens are
loaded quickly as if they are coming off a centralized server
computer. This allows the operators and technicians to view
the same graphics whether they are on the roof or in the
maintenance shop.
An additional benefit is that engineers, technicians and
managers can log on to the system and remotely access the
process controls at the facility using an ordinary web browser
from anywhere and at any time. This enables engineers
and technicians to solve problems as soon as they occur,
rather than waiting hours or days to drive (or fly) to the
facility.
Implementing
Web Access
The most direct way to implement Internet access to automation data
by customers (including business partners) is the same way one would provide it
for remote users within your company. Simply install web server
software right in the plant automation network, which is the source of the
information. This example is based on the latest in open, field-based
architecture. It is a readily available, off-the-shelf solution.
In this
example, an off-the-shelf web server software suite is provided as part of the
open field-based architecture. OPC servers of various kinds are becoming
available for most automation systems. This one runs in a PC station that also
happens to be used as a link between the automation network and the plant's
information-systems (IS) LAN. The web server suite includes Microsoft's Internet
Information Server, which is included in the standard NT Server 4.0
package.
In this example, the plant's
information-systems LAN is equipped with an Internet server that handles all
Internet traffic for the plant. It is linked to the Internet via a high-speed
router that includes a firewall. Customers gain access by logging on to a web
site at a host name within the company's domain.
If the plant did not
already have an Internet connection, one could be arranged with a local Internet
service provider or telephone company. It would use a modem or other interface
device of the desired speed at the control network's web server
station.
This particular web server software connects to the automation
network using the industry standard OPC. Using a web browser such as Microsoft Internet
Explorer 6.0 or Netscape Navigator 6.1, customers or business partners can view process
graphics, process-variable trends updating on a real-time basis, historic
trends, and summaries of events and alarms.
The web server software allows security to grant or deny
access to individual modules, so that customers get only the information needed.
This arrangement also provides a fringe benefit to the company, in that the
plant LAN serves as an intranet for the automation network's web server station.
Personnel at any computer on the plant LAN can use a web browser to access the
automation system, without having to run automation software.
BroadWin
Software Powers eAutomation
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