Integrating advanced power management

Integrating advanced power management with control system architecture enables continuous power to mission critical facilities

By Jack Faett, GE Intelligent Platforms, Charlottesville, Va. November 21, 2012

Mission critical facilities, such as those that support operations in data centers, healthcare, and emergency response, are under intense pressure to maintain continuous system availability while increasing energy efficiency to reduce costs. These modern demands require a renewed focus on the design of mission critical backup power control systems that play a key role in the ability to maintain continuous operations and increase efficiency. Integrating advanced power management strategies into mission critical backup power control systems enhances the ability to deliver on these metrics by enabling power grid synchronization coupled with measurement of power consumption metrics (see Figure 1).

An advanced power management application strategy is only as good as the power monitoring data the solution can deliver. Effective backup power infrastructure management depends on specific criteria for specification categories that include power-measurement configuration, electric meters, power factor resolution, integrated ANSI standard protective calculations, and control system integration (see Table 1).

With the intelligence gained from the mission critical backup power infrastructure data specification, several key advanced power management strategies can be implemented to deliver the best asset performance and reduced total cost of ownership:

Power grid synchronization

Mission critical facilities typically have multiple on-site backup power generators that must be managed and synchronized in the event of a main utility source power outage. For example, backup generator synchronization to the grid may require that voltage differences be less than 2%, frequency between the buses match within 0.5 Hz, and phase shift between generators be less than 2 deg.

The genset controller or auto-synchronizer commands the engine to go faster or slower to adjust the frequency and also interact with the field voltage of the alternator that adjusts the voltage. When the frequency and phase angle values are within the synchronizing bandwidth, the generator can be switched to the grid as the main power source.

Load sharing, shedding

Reactive power metrics provide the ability to collect and analyze electrical system power consumption over time. This critically important data can be used to avoid peak demand charges and to shed loads during peak operating periods to increase efficiency and reduce costs. This functionality enables:

· Synchronization of multiple buses to split the load requirements based on the relative capacity of each backup power generator

· Speed control of each generator so the load does not deviate from the preset dead band

· Raise and/or reduce power load share adjustment signals based on load share metrics and error conditions.

Power factor correction

UPSs, generators, and utilities have power factor specifications. Utility companies generally impose power factor penalties when the consumer’s power factor is lagging or leading by as little as 0.1. Power factor correction can be as simple as switching additional circuit capacitance such as capacitor banks into the facility’s electrical distribution system. However, it may require significantly more coordination to minimize the operation of lightly loaded motors such as cooling fans, which may require moving loads to other circuits.

Power quality monitoring

Advanced power management data collection can be used to drive a waveform capture function of the backup power electrical infrastructure. Waveform captures can provide detailed fault condition views, harmonic power analysis, and capture transient voltages and currents to verify power quality and validate system configurations (see Figure 2).

Harmonic distortion of voltage and current waveforms is introduced into power systems from nonlinear loads. Distorted waveforms can lead to excessive neutral currents and increased transformer and conductor temperatures, and can cause premature equipment failure.

Visualization, control, and analytics

Effective mission critical facility support strategies can be implemented using data collected from an advanced power management system. Continuous operation and performance improvements of all backup power systems are only as good as the run-time data collected for analysis. Coupling the advanced power management data with key software applications provides facility managers and operations personnel with the ability to make informed decisions based on actionable data. These software applications include:

· Critical alarm response management software that empowers operators to make better decisions by providing information and guidance with the exact responses needed to address critical alarms within the backup power system

· Work process management software that allows HMI/SCADA users to provide operators with specific instructions and the precise information they need to make the correct decisions in critical situations or switchover scenarios

· Advanced analytics software that provides insight into the likely causes of events or issues, performs what-if scenario analysis, identifies opportunities for continuous improvement, and prevents future power system problems. For example, analytics can provide insight into metrics such as power usage effectiveness to better understand the relationships among the factors that impact the metric, providing a means to take action on the extracted knowledge.

Conventional control systems

Advanced power management can be accomplished in conventional control systems with the right upfront system design, development, and start-up commissioning to ensure that all components operate seamlessly. However, implementing these advanced power management strategies in a conventional control system does have some drawbacks:

· In addition to the control system, for each grid in the backup power electrical infrastructure, a variety of synchroscopes, meters, switches, lamps, and relays are required to provide the necessary control components. These additional components result in a more complex system architecture and potential for single points of failure.

· External synchroscopes required to perform waveform capture and display are typically not integrated with the conventional control system.

· Multiple programming environments, which may be required to configure, control, and maintain the control, network, and metering systems, increase the risk of human error during normal operation and/or problem resolution.

· Application code must be developed in the backup power control system to collect, interpret, and calculate the appropriate data values for executing the various advanced power management functions required to perform generator synchronization and load sharing. Optionally, these functions could be implemented via manual input with visual indicators and pushbuttons.

· Collecting, interpreting, and contextualizing power and generator parameters from the external devices for use in the control system’s advanced power management functions creates potential for data accuracy and execution latency issues during run time.

· Detailed work instructions for day-to-day operation, maintenance, and failover for operations, engineering, and maintenance personnel will be required.

· Historical data will have to be memory-mapped, collected, and stored into a separate database system for offline analysis.

Integrating advanced power management

Architecting a control solution that integrates advanced power management into the backplane of the control system provides the most flexibility in design and implementation of backup power electrical systems. Advanced technology control solutions that provide multifunction power synchronization and measurement interfaces are ideal for equipment manufacturers and system integrators providing paralleling switchgear and gensets for use in mission critical facilities.

A single control solution with integrated advanced power management can deliver the functionality to manage the entire backup power infrastructure:

· Automatic genset start/stop

· Engine status monitoring, frequency/voltage control, and fault reporting

· Automatic generator paralleling (synchronizing)

· Power quality monitoring and fault reporting

· Power consumption metric measurements

· Load shedding and load sharing

· Waveform capture of all backup power grids

· Data logging and reporting.

In the end, having to design, develop, integrate, start up, and maintain a single control system for the entire backup power infrastructure provides the best possible performance with the lowest total cost of ownership:

· Use of external manual devices can be reduced or eliminated.

· Waveform capture can be displayed directly on the control system HMI.

· Only one programming environment is needed for the control system, HMI, power synchronization, and measurement interfaces.

· All power parameters are collected and calculated by the integrated advanced power management interfaces.

· All data are available in real time to the control via backplane communications, eliminating latency and integrity issues.

· Historical data are available from one control system for visualization, control, and analytics.

Implementing highly available redundant control solution architecture with integrated advanced power management can help ensure continuous operation of the backup power infrastructure in a mission critical facility. With integrated advanced power management control systems, companies can design and implement highly available backup power infrastructures for maximized uptime, reduced costs, and improved performance and efficiency.

Faett is the industry manager for mission critical power at GE Intelligent Platforms, headquartered in Charlottesville, Va. He works with end users, system integrators, and machine builders in the mission critical industry. He has more than 30 years of experience in the areas of system design, program management, sales, marketing, automation, manufacturing execution systems, and project implementation.