To meet the demand for power efficiencies in the manufacturing industry in South Africa Adroit Technologies has developed a maximum demand agent (MaxDemand) as part of its supervisory control and data acquisition (scada) package.
Danie Sadie, electrical engineer and owner of Sadkons, a systems integrator (SI) and power management solutions company, sent his development requirements to Adroit to come up with an agent that would perform maximum demand monitoring and control.
"Previously, we had to apply the function using lots of separate components in the scada system," says Sadie, who reports that the product is a functional agent block that eliminates the need to write more complex functions to perform the same task.
Sadie has recently installed the MaxDemand agent at one of the facilities of a major cement manufacturer and is currently tendering on the implementation of other similar solutions.
This new agent is available free of charge to all Adroit scada users holding a technology maintenance agreement (TMA) with the company.
Principle of operation
The MaxDemand agent monitors maximum demand (MD) over a block period. It is able to forecast the MD at the end of the period and provides a warning to the operator if the calculation predicts that the plant will exceed its MD quota. It also provides an onscreen indication of how much time the plant has available to react to the warning before the MD setpoint is exceeded.
While the primary aim of the agent is for indication only, automatic control can be achieved by using the MaxDemand status slot of the agent to switch in/out electrical machinery. In this way, should plant operators fail to take evasive action, associated PLCs can shut down portions of the plant as MD is reached.
The agent also calculates kVAr, and kilowatts hours. By multiplying cost per unit with kVAr and kWh the agent can determine the end of month bill or the time/cost during the month thus enabling plant managers to plan and budget their production hours for maximum efficiency and cost savings.
Inputs to the agent include instantaneous raw kW, kVA and kVAr readings where required, the MD limit (kVA) from Eskom, day and time of monthly meter reading/reset, external block period pulse or a default to the PC half-hour periods, block period length (eg 15, 30, 60 minutes) and MD control inhibit input for the periods of the day when MD is not applicable.
Available outputs include predicted maximum demand (MD), MD prediction alarm, records of the actual MD for the month-to-date, roll over of current month MD to previous month MD, tallies of the kWh, Power Factor, kVAr and kVArh for the month.
Conclusion
Power management has become a critical issue in the manufacturing industry as a result of its cost impact and the shortage of electrical power. Control of the power usage on a complex plant can no longer be left to operators because of the potential impact of human error on the monthly electricity bill. Implementation of a dynamic MD agent enables plant manufacturers to eliminate unnecessary power spend and achieve a leaner, more cost effective and efficient manufacturing process.
How maximum demand is calculated
A significant component of industrial electrical bills is based on the peak kVA demand (maximum demand) during a block period over the billing month. The duration of block periods is determined by the supply authority is typically 30 minutes. These maximum demand periods are only applicable during certain times of day when electricity consumption is high. The kVA for each of the specified periods is integrated, and the supply authority uses the block with the highest kVA value as the maximum demand for the metering period. Over and above this, if that demand exceeds a predefined, maximum demand limit, surcharges are applied for the whole metering period.
For more information contact Dave Wibberley, Adroit Technologies, +27 (0)11 658 8100, [email protected], www.adroit.co.za
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