A South African oil company using gas-to-liquid (GTL) technology chose Adroit's supervisory control and data acquisition (scada) system for monitoring its electricity consumption and minimising unnecessary tariffs and peak-time power expenditure.
To highlight the importance of demand control, the Adroit human machine interface (HMI) at the site includes a customised Eskom time-of-use-account directly on the homepage, enabling production personnel to plan the plant's electricity usage and to gauge its effects on the Eskom account before month end.
Scada alarming is done on the main screen using a realtime display of Eskom's three tariff schedules: standard, peak and off-peak. The alarm is displayed on a single screen - regardless of from which of the 17 substations it comes. The screen also carries predictive information and an alarm is set in the plant if maximum demand is met or exceeded.
In this way, the refinery can forecast and disseminate the information needed to predict the month-end account. "The Adroit system does this every 30 minutes. The closer it gets to the end-of-the-month, the truer the reflection of the calculation," says a company representative.
On the maximum demand system, the refinery can predict in 30-minute intervals if production is in line with demand. This also gives the company a 30-minute window in which to cut down if it looks like demand will exceed the parameters.
The representative goes on to say: "With maximum demand control we save a lot of money - millions, in fact - by catching over-use in time."
The scada replaced an outdated ABB system about six years ago. The refinery's technicians were able to design their own graphics, thanks to the simplicity of the Adroit system. The scada also impressed the company with its cost-effectiveness.
The refinery carries out internal distribution from a 132 kV substation via its proprietary distribution network. The plant consists of 17 substations ranging between 132 kV and 525 V. Excess generated power is fed back into the Eskom system. To do this effectively it uses the Adroit system to monitor all substations, plus two generator systems of 140 MW and 10 MW, monitoring all inputs and outputs on the breakers, currents, and other factors required to forecast electrical demand and hence the Eskom account.
Adroit also provides plant personnel with a virtual heads-up on leaking transformers. "We save millions by tending to oil leak alarms that the scada provides," says the company representative. Early detection means that the plant does not have to shut down for repair.
The plant has 10 viewing stations: three in the control room and the balance distributed around the plant. The Adroit agent server runs on two network cards: one for the refinery and one for the substation network. This enables users to view the entire plant and its substations from anywhere on the site.
Events such as breaker operations, trips and faults are saved separately on the plant's PI system with a time stamp for future reference. PI is an archive system for the entire plant operations and data is viewed over the Ethernet.
The Adroit system on site has 5000 tag points with five user interfaces (UIs) per dongle. The refinery is currently using 3000 tags. The plant mainly uses PLC Direct PLCs (Direct Logic 205) with one Koyo PLC per substation. Each substation uses fibre-optic to Ethernet and an Ethernet switch that links them to the Intranet and Adroit systems.
Future plans for the system include the conversion of several existing RS232 links to Ethernet so that the plant's two servers can be run in hot standby mode. The company representative also confirms that he has recently attended an Adroit Visual Basic (VB) course and will be using his new skills to script information from the Adroit system to an MS Access database.
For more information contact Dave Wibberley, Adroit Technologies, +27 (0)11 658 8100, [email protected], www.adroit.co.za
| Tel: | +27 11 658 8100 |
| Fax: | +27 11 658 8101 |
| Email: | [email protected] |
| www: | www.adroit.co.za |
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