Power management: Automation enhances power management applications

04/17/2013


System protection

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.

Automation functions

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.

PLC concepts

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. 

SCADA/HMI concepts

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. 

Operational enhancements

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. 


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