Coal

Infusing SCADA Software with Real-Time Power Management Capabilities

Issue 9 and Volume 117.

ETAP Real-Time software
ETAP Real-Time software ensures that power issues that can compromise the integrity of operations are identified long before they can jeopardize the facility.

By Tanuj Khandelwal, Vice President, Product and Industry Strategy, ETAP

Supervisory Control and Data Acquisitions (SCADA) systems have revolutionized the power industry since their inception, giving owner/operators unprecedented visibility into powering their power infrastructure. But to date, SCADA/Human Machine Interfaces (HMIs) have only been able to provide static electrical on-line diagrams and do not contain interconnectivity information. In order to be made functionally dynamic, the user must invest additional hours of engineering effort. Complex scripts are developed to show the status of devices and electrical power flow. This not only increases the cost of implementation, but also makes the maintenance and modification for future expansion more difficult.

Real-Time Power Management (RTPM) software is a model-based solution designed to automatically determine if a component is energizedde‐energized based on the status of switching devices such as breakers, switches and contacts as well as the interconnectivity between components. If information is missing or faulty, the software estimates the parameters even without signals actually coming from hardware in the field. The model-based environment makes it very easy to add equipment (drag, drop, connect). This is extremely useful during plant expansions or revamps.

Utilizing RTPM software will reduce development time by 30 percent over traditional SCADA systems, providing a more comprehensive level of intelligent monitoring and will reduce the long term cost of ownership of the SCADA system as improvements are made to the electrical power system in the future.

A true real-time power management application should provide the following features:

1. Intelligent One-Line Diagram
2. Intelligent Monitoring
3. Online Predictive Simulation
4. Sequence of Events Playback

Intelligent One-Line Diagram

A Real-Time Power Management system operates on an intelligent one-line diagram that provides the following features:

Electrical Network Topology Processor

An electrical Network Topology Processor (NTP) automatically determines if a component is energizedde-energized. It looks at the status of switching devices such as breakers, switches and contacts as well as the interconnectivity between components.

In SCADA software, the HMI’s that are built-in do not contain interconnectivity information. Status of components has to be determined from signals actually coming from hardware in the field and scripts have to be written for making the animation on the HMI screens.

Ratings and settings of every component in the electrical network

Ratings and settings of the electrical components are stored in the (RTPM) database. Accessing this information is as easy as double clicking on the component in the one-line diagram view. This information serves as a base for all simulation capabilities of the software as well as some automatic features such as overload and under/over voltage conditions alarming.

Intelligent Monitoring

Monitoring is the base function for any power management software. In addition, seamless integration with metering devices, data acquisition and archiving systems are essential to monitoring software. Real-time or snapshot data are linked to an online model of the system for proper presentation of actual operating status.

All this information should be accessible to the system operator through advance man-machine interfaces such as an interactive one-line diagram that provides logical system-wide view.

Compensation for absent physical meters

Traditional monitoring is based on visualizing meter information from certain limited parts of the system. It is not cost effective to place meters throughout the entire system. The real-time power management system eliminates this need by processing the telemetry data and determines the missing or faulty meter values using advanced techniques such as State and Load Estimator (SLE). Maintenance responsibility and cost are substantially decreased every time equipment is added to the monitoring network as operations can get immediate visibility of the electrical operating conditions without physically metering the equipment.

The system therefore generates pseudo-measurements such as voltage, losses, power flows, etc. and compensates for absence of physical meters – especially in low voltage regions. By generating pseudo-measurements, it is also possible to alarm the operator regarding unobservable or unmetered equipment that is operating abnormally such as overloads.

RAW Data Checking (RDC)

The Intelligent Monitoring module has the capability of determining whether the data monitored makes sense electrically. It utilizes the Network Topology Processor to determine if the measurements follow the basic electrical rules. Some examples are:

  • Power in and out of nodes
  • Measurements on both sides of feeders and transformers
  • Out of range values

Online Predictive Simulation

In order to design, operate and maintain a power system, one must first understand its behavior. The operator must have firsthand experience with the system under various operating conditions to effectively react to changes. This will avoid the inadvertent plant outage caused by human error and equipment overload. The cost of an unplanned outage can be staggering. The ability to perform system studies and simulate “What If” scenarios using real-time operating data on demand is of the essence.

(RTPM) offers the powerful features in (RTPM) Power Simulator with an interface to utilize online data for simulation. With this feature you can simulate the following scenarios and more:

  • Start of a motor or group of motors for determining the impact in the electrical system
  • Energize/De-energize feeders (steady state and dynamic)
  • Check for Short-Circuit and Arc Flash levels under existing operation
  • Check sequence of operation of protective devices under existing configuration of the network

Sequence of Events Playback

The ability to recover from a system disturbance depends on the time it takes to establish the cause of the problem and take remedial action. This requires a fast and complete review and analysis of the sequence of events prior to the disturbance. Power management software should assist operation and engineering staff to quickly identify the cause of operating problems and determine where energy costs can be reduced. The software should also be able to reconstruct exact system conditions to check for operator actions and probe for alternative actions after-the-fact. This important tool serves as an on-going learning process for the operator.

Besides reducing losses and improving data gathering capability, such an application should assist in increase plant reliability and control costs. The event playback feature is especially useful for root cause and effect investigations, improvement of system operations, exploration of alternative actions and replay of “What If” scenarios. Event playback capability translates into savings. These savings for a typical 50-MW plant are illustrated in Figure 1. For example, a conservative estimate of 10 percent reduction in downtime for an outage that lasts an hour yields about $33,000 in savings.

The RTPM Playback module reconstructs exact system conditions to check for electrical system component status, operator actions and telemeter data. The Playback feature has a direct interface to the RTPM Power Simulator modules for operators and engineers to study alternate solutions for the problems at hand.

Supervisory and Advisory Controls

State-of-the-art supervisory and advisory control capabilities should be used to control and optimize in real-time various parameters throughout the system. Using optimization algorithms, the user can program the power management system (i.e., assist energy consumers by automatically operating their system to minimize system losses, reduce peak load consumption or minimize control adjustment). For energy managers, the power management system can be set up to minimize energy fuel costs and optimize system operation.

In a recent study performed for a large industrial facility (150MVA), advanced optimization algorithms, native to the power management system, were utilized to reduce real and reactive power losses. Assuming a conservative power loss reduction of only 0.1 percent at an average electrical energy cost of USD $0.13/kWh, an energy management system would yield savings of more than $135,000 per year and would pay for itself through the immediate realization of savings in operating and maintenance costs.

Online Control

An advanced power management system should provide the options for full remote control to the system elements such as motors, generators, breakers, load tap changers and other protection devices directly or through the existing SCADA system.

In addition, the software should provide user-definable actions that can be added or superimposed on the existing system for automating system control. This is similar to adding PC-based processors/controllers (kV, kW, kvar, PF, etc.) or simple breaker interlocks to any part of the system by means of the software.

Intelligent Load Shedding

A major disturbance in an electrical power system may result in certain areas becoming isolated and experiencing low frequency and voltage, which can result in an unstable operation. The power management system should have the intelligence to initiate load shedding based on a user-defined Load Priority Table (LPT) and a pre-constructed Stability Knowledge Base (SKB) in response to electrical or mechanical disturbances in the system. Load shedding schemes by conventional frequency relays are generally a static control with fixed frequency settings. Based on Neural Networks, a power management system would be able to adapt to all real-time situations and provide a true dynamic load shedding control (Figure 3). This would allow the operator to optimize load preservation, reduce downtime for critical loads and simulate/test the load shedding recommendations.

Another significant cost component of operations is demand charge of the energy bill. The demand charge is 40 to 60 percent of the bill for sites without peak shaving generation. A single unmanaged demand charge can produce a very large hike in the power bill each month and with “ratcheting” demand charges (the Eskom Network Access (NAC) charge applies to the highest recorded demand above the notified demand for 12 consecutive months), the penalty then has a bearing for a whole year. An intelligent combination of smart applications can provide the current and predicted demand for each day thus managing peak demands on a continuous basis. Loads can be shed intelligently and automatically, peak-shaving generators can be started, load startup can be postponed or sequenced or penalty can be paid if certain processes are vital.

Conclusion

A typical SCADA system displays collected electrical power data in a non-electrical system environment without recognizing the interdependencies of equipment. Extending the overall SCADA system functionality by including an intelligent power monitoring application with an appropriate electrical system context, simulation modules and playback routines will provide the system operator and engineer with a powerful new set of tools to increase the overall system effectiveness. Using these tools, the user can accurately predict the behavior of the electrical system in response to a variety of changes. The playback of recorded message logs into the simulator-equipped monitoring system provides the operator with an invaluable means of exploring the effects of alternative actions during historical events. These simulation techniques will provide a revolutionary training tool to effectively prepare the SCADA operators of the future.

With the growing demand to efficiently operate at a lower cost, manage energy usage from a variety of new sources and train the operator of the future, the time has come to enhance SCADA systems with intelligent applications that provide the flexibility and compatibility to meet today’s energy challenges.

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