Power management: Automation enhances power management applications
Power systems evolve as organizational needs shift, new standards are established, and facilities and equipment are updated and upgraded. Eventually, power systems become a disparate collection of equipment that does not work in harmony to deliver the optimal level of reliability, safety, or operating costs. As enterprise power system change, they can become more complicated, inefficient, unreliable, undersourced, and difficult to manage—even as the bar for performance, efficiency, and reduced operating costs is set higher.
A comprehensive approach to energy management yields dividends over time by helping organizations reduce energy consumption and costs, improving system reliability, and enhancing personnel safety. A key aspect of a holistic power management approach is the control and automation solutions that help industrial, commercial, institutional, and utility organizations drive efficiencies, identify problems before they cause downtime, and provide the data required to support reliable, efficient, and safe power (see Figure 1).
Whether for new or retrofit applications, power system automation can support effective power management in applications that include:
- Emergency and backup generation
- Automatic transfer schemes
- Station automation
- Distributed generation systems
- Mission critical secure power applications.
Determining project scope
Factors that should be considered when upgrading a facility include regulatory compliance, safety, reliability, capacity, cost, and operational constraints. When considering electrical and control equipment, it is important to define system goals and objectives first. Both new and existing system components in a generation facility must be evaluated to ensure that overall system requirements are met. Assessing existing equipment is a key aspect to upgrading facilities.
Categorizing equipment and evaluating each system is helpful, and ensures that new operation requirements will be met. The following is a checklist of major system components to consider.
Major electrical equipment
- Line switches
- Step-up transformers
- Cable and/or bus duct
- Generator windings
- Meters and relays
- Plant switchgear
- Generator controls, power regulation, and synchronization
- Lighting and surge protection
- Grounding systems
- Station service system
- Battery and dc distribution
Plant control systems
- Machine controls
- Supervisory controls
- Excitation systems
- Governor/gate control systems
- Head works/dam controls
- Fire and security systems
- Plant ventilation
- Machine and process instrumentation.
It is imperative that each major piece of equipment is evaluated according to its operational criteria. A power system study is a crucial analysis tool used to evaluate electrical equipment, and should be performed during existing equipment evaluation and before equipment selection. A typical power system study includes short circuit, load flow, and protection studies as well as an arc flash hazard analysis.
Short-circuit study: Short-circuit studies allow system engineers to determine if the power system protection equipment is suitable for the application. They are meant to identify the key design parameters needed in the selection of new components, while ascertaining if existing components are safe and ensuring that they meet applicable electrical codes.
Load-flow study: Load-flow studies are performed to determine if equipment is properly sized for the intended application. Cables, transformers, capacitors, breakers, fuses, and other system components are modeled to ensure that they are applied within their specific current ratings. The load-flow study allows engineers to determine the effects of a generator capacity upgrade on the entire electrical system, ensuring that all components are adequate for service.
Protection study: A protection study is meant to ensure that major electrical system components are protected from system faults. This study should go far beyond a simple relay coordination study, which looks at overcurrent only. The entire protection system must be evaluated according to today’s standards, as practices have evolved. Existing protection may need to be updated. Often owners, interconnected utilities, and/or insurance companies require that protection systems meet current IEEE and ANSI standards.
Arc flash hazard analysis: An arc flash hazard analysis is required, as new additions to the National Electrical Code (NEC) require personnel to be protected from arc flash hazards associated with electrical systems. This analysis should be performed in the planning stages of a project to guide system engineers in the selection of the appropriate protection and power equipment.
Each subsystem in the plant must be evaluated to ensure that it can easily be monitored or controlled by the upgraded control system. Performing a complete start-up and shutdown of the generating units and noting the functions requiring operator intervention is good practice. Create a checklist and document special or contingency operating conditions that may deviate from normal start-up or shutdown. Most actions required to be performed by plant personnel—including inspections—can be duplicated or replaced by the control system. It is imperative that all systems are in good working order prior to implementing an automated control system. Instrumentation should be added to monitor key operating parameters such as temperatures, pressures, levels, and flows.
Control system specification
Control system expectations and requirements must be established before equipment selection and design criteria decisions are made. Well-defined system expectations will likely avert problems down the road. Also, defining system expectations helps simplify system design. System expectation decisions include:
- Manned vs. unmanned
- Automatic vs. manual control
- Hardware and software expandability
- Real-time monitoring
- Remote dispatch and control
- Voltage or power factor control, which can be influenced by changing ISO and RTO requirements
- Governor vs. gate actuator
- Water resource management (pond level control, minimum flow, and bypass)
- Alarm management and maintenance requirements
- Data collection and reporting requirements
- Redundancy and reliability
- Market and regulatory obligations.
After these decisions have been made and system requirements have been defined, it is time to write a functional scope to advance the design process to the next stage: equipment selection. Existing equipment that does not meet the above criteria should be replaced or upgraded.
The equipment selection process should take into consideration the specific design requirements of the project in conjunction with the overall preferences based on experience, teamwork, and local support. To guide in the equipment selection process, several roadmaps must be drawn. These roadmaps include single line, control system network architecture, and process and instrumentation diagrams.
Single-line diagram: A single-line diagram for electrical equipment must be created that defines the overall power distribution architecture and provides an overview of the entire scope of the electrical upgrade including equipment sizes, relaying and logic schemes, metering points, and data requirements (see Figure 2).
Control system network architecture diagram: The control system network architecture diagram should be created early in the process—before the equipment is specified or purchased. This diagram will guide the control and data requirements of the project and determine the communication methods to be used. Modern control and protection systems inherently include a plethora of information that can be critical to the control of the system, and aid in tuning, troubleshooting, and commissioning the plant.
Process and instrumentation diagram (P&ID): The P&ID is a useful tool in defining process-related systems for the facility, which typically include cooling and hydraulic systems, temperature monitoring, process control, batching, and other auxiliary systems that require instrumentation.
After these diagrams are complete, detailed design and equipment selection can begin. The effort put into the scoping phase will go far toward making equipment selection straightforward.
Today’s protective relays are designed to protect critical assets from damage due to electrical faults and adverse operating conditions (see “Machine condition monitoring”). Recommended practices have evolved to include protection schemes that were not available 20 years ago. Modern digital protection systems are designed to monitor and protect generators and turbines, while collecting vast amounts of usable data. IEEE practices are designed to scale the required protections to the size of the machine or the transformer.
Advanced digital relays are capable of communicating with the digital control system. Digital relay communication provides operating data and supports troubleshooting in the event of a system disturbance or fault. Careful planning for the integration of the protection systems with the control and SCADA systems can reduce recovery time and downtime after a system or unit fault by allowing high-speed clearing. Additional benefits include management of arc flash hazards by providing high-speed fault clearing or maintenance-mode settings for use during maintenance and/or switching activities.
Grounding and surge protection are extremely important, yet often overlooked when assessing protection of generation assets. When applicable, high-resistance grounding provides generator grounding to prevent extreme transient overvoltages, while limiting ground current to levels that do not cause damage. Whenever possible, the best practice is to ground the system using high-resistance protection schemes. Properly sized and applied surge capacitors and lightning arresters should also be considered.
For synchronous machines, synchronism check relays should be applied and an auto synchronizer is recommended. The sync-check relay should supervise the generator breaker closing for either manual or automatic synchronizing. Motor starters or contactors should not be used in synchronous machine applications.
Machine condition monitoring
Monitoring systems should be considered and scaled based on the size and the type of equipment to be monitored. The following list includes basic condition monitoring systems for evaluation:
- Stator winding temperature
- Bearing temperature
- Cooling system temperatures
- Bearing vibration or run-out
- Head cover or draft tube vibration
- Rotor gap
- Insulation integrity, partial discharge detection for systems with voltages higher than 8 kV
- Transformer temperature indication and alarms
- Transformer online oil analysis.
Industrial-grade control and automation systems are designed to monitor equipment status, facilitate troubleshooting, and provide remote telemetry and control.
A common solution implemented is the use of PLCs coupled with a graphical HMI. Properly designed and implemented, this powerful combination can provide a full set of features including:
- Automatically starting and stopping generation units
- Equipment condition monitoring
- Regulatory and production reporting
- Alarm annunciation, reporting, and recording
- Remote telemetry and control
- Power source synchronization.
A PLC is typically used as the brain. Modern PLCs provide a range of functions that include Boolean and ASCII programming, timing/counting, mathematical calculations, and communication options. These flexible systems allow system designers to implement tasks such as unit start and stop sequences, speed governing, equipment condition monitoring, alarm logic and response, station water level control, water flow management, and other specialized functions.
Regardless of the PLC brand, a disciplined approach to control system organization, design, programming, and commissioning is essential to a successful implementation.
Functional description: The first step is to define in detail what the system will do and how it will do it.
System design: The overall system design should consider the entire system lifecycle including installation, commissioning, and maintenance issues. Important decisions to consider include:
- Centralized vs. distributed processing
- Local vs. distributed I/O
- Unit and station I/O grouping
- Isolation for maintenance and lockout/tagout
- Construction sequence and schedule
- Communication architecture
- Remote communication interfaces
- System security.
Programming: Programming should be performed in a structured and modular fashion. Code should be organized into logical sections or subroutines that parallel the physical plant layout. This will facilitate the design, commissioning, and maintenance of the automation system by presenting the control code in a logical and easy-to-interpret fashion. Structured code also aids in the reuse of code for additional units or for future projects.
Commissioning: The final step is to perform system commissioning to verify that all system components are wired correctly, that field devices are working as desired, and that all PLC/HMI programming is correct. Detailed point-to-point wiring checks from the field devices back to the PLC, HMI, and (if appropriate) SCADA should be performed in a controlled and methodical fashion. This end-to-end test proves that the individual components are working correctly and that the system as a whole is performing as expected.
Visualization of plant status and condition, logging of events and metering, and annunciation of alarm conditions are generally managed by an HMI. SCADA systems are typically used to monitor geographically dispersed assets.
Often HMIs are used to log regulatory, alarm, and performance information. These data are commonly stored in an SQL database or an industrial historian. Data may then be pulled from the archive for reporting to meet regulatory obligations, to monitor performance, and to provide insight into plant operations.
Mobile monitoring and control
The 24/7 nature of today’s organizations requires a constant level of monitoring. But profitability requirements often don’t allow for full-time, on-site staff. The solution is telemetry, which allows remote monitoring and control, particularly at automated, unattended plants. Smartphones have become a mobile telemetry platform, allowing operators to remain informed of plant status and alarm conditions, and even providing access for remote control. This is accomplished using a mixture of technologies including SMS text messaging of alarm conditions generated by the station HMI, automated status and production reporting via e-mail, and remote access and control through smartphones and tablet devices.
After the basic control system is designed and in place, it is imperative that system integration personnel work closely with operations to determine best practices for operating each system and the overall operation. Frequently, the automated system can be used to optimize the performance of the facility by implementing best practices as a control strategy.
Software for system, enterprise monitoring
An energy management system (EMS) incorporates the power distribution architecture as well as the software and reporting systems that provide data and information needed to manage a facility’s or enterprise’s energy costs, system training, and commissioning. A typical EMS relies on metering devices and their communications networks.
Metering devices: Metering, protective relaying devices, and/or sensors measure water, air, natural gas, electric, and steam consumption at trouble spots outlined in the audit. You cannot manage what you do not know, and the meters and protective relays provide real-time and historical data about power consumption, helping to identify inefficiencies.
Communications: Communications hardware and wiring interconnects the metering devices to a local area network, intranet, and/or possibly the Internet. Gateways can serve as data collection and alarm notification delivery points for multiple devices in larger systems.
Energy management software is essential to pull data together into understandable, actionable information. The software provides trend data to help plant personnel manage expenses based on energy information collected by the meters. Software and reporting facilitate easy equipment energy consumption with that of the facility and the enterprise to identify electricity hogs and wasteful practices, and analyze and trend energy anomalies, which may be caused by internal equipment malfunctioning or from the incoming power source.
While power management software functionality is constantly evolving, it is more sophisticated and powerful than ever. Today’s software is able to monitor, track, and analyze data from more devices at faster speeds, and has more extensive analysis and reporting capabilities than ever before.
Automation improves operational efficiency
By strategically approaching plant upgrades and automation projects, operators can extend the serviceable life of their equipment while improving the efficiency, reliability, and safety of their systems.
A comprehensive approach to managing operations and energy requirements is critical and yields dividends over time. These dividends include:
- Maintaining vital operations with steady, high-quality power
- Reduced operating costs with effective energy management and maintenance strategies
- Improved electrical designs that require less equipment and space, services that extend equipment life, and equipment that can be installed faster
- Reduced electrical hazards with safety-conscious design and installation that help people recognize and avoid danger
- Reduced risk of construction delays and cost overruns with a coordinated approach to power system design, procurement, installation, and maintenance.
A holistic approach to energy management can turn energy challenges into opportunities.
Kenneth Kopp is an application engineer for power systems automation with Electrical Engineering Services and Systems at Eaton. He has more than 25 years of industry experience in power distribution automation and control systems, and has been with Eaton for more than six years.