How and Why to Monitor Power

Power meters at substations have changed, too. Now they are called intelligent electronic devices, or IEDs. Modern IEDs measure phase currents, voltages, power factor, frequency, harmonics, and other data, according to Mike Coleman, North American manager for GE Multilin, a division of GE Industrial Systems. He says the cost has dropped dramatically, too. "Ten years ago, a fully loaded system with metering equipment, oscillography, and protective relays for a feeder would have cost $20,000 to $30,000. Today, a state-of-the-art IED will do all these functions for a fraction of that money," says Coleman.

Not only that, an IED can communicate all this information over an Ethernet connection. "Data from an IED connected to the corporate network can be accessed to see the energy consumption of a particular feeder, or an engineer can access the IED to check currents and voltages or analyze an event," explains Coleman.

Soft Switching Technologies says its I-Grid power monitoring system can be installed for less than $300 per monitor. A web-based monitor plugs into a 120 or 240 VAC outlet and a phone line. It monitors the power line and records voltage profiles for sags, swells, brownouts, overvoltages, and outages, and sends power quality information through the Internet to the monitor owner and to a central server for display on the I-Grid web site.

"I-Sense

Power equipment manufacturers have been embedding power monitoring functions and communications capabilities into panelboards, transformers, and circuit breakers for several years. Such smart power distribution equipment can monitor its own health and communicate with any device that wants the data.

Rick Grove, staff project engineer at IMC Phosphates, Mulberry, Fla., uses such equipment to monitor total incoming power. "GE Multilin 750 relays, which are used to trip incoming breakers, are connected by Modbus to Allen-Bradley PLCs, and then to MSSQL via RSSQL, and then to web servers," says Grove. This means that Grove is getting the data he needs from circuit breakers, then passing it through the system all the way to a web server for display and analysis. "Metering potential transformers and current transformers are mounted within the metal-clad switchgear, and are the inputs to the Multilin 750 relays."

(Power Plant Takes 10-Year AMS Odyssey)

If you have a DCS in your plant, you might be able to hook directly into such equipment. Honeywell, for example, can plug right into third-party multifunction power meters, relays, and motor monitors. "We make nodes such as the Communications Link Module that interface to these meters via Modbus," says Mark Converti, manager of power generation marketing at Honeywell. The link feeds directly into Honeywell's Power Monitoring and Control, Power Emergency Load Shed, and Tie Line Control software packages. "Power system faults are initially detected at the power meters. Later, the cause of the fault and any harmful effects can be determined by uploading the waveform data captured by the meters to our Plant History database."

It might be a good idea to check with your control system vendor to see what type of similar power monitoring packages they offer. You may be able to tie directly into your existing switchgear and panelboards to get the power quality information you need.

If you can't get a free ride from existing power monitors or smart switchgear, you may have to install the necessary equipment yourself. "Most of the time, the measurement is done at the switchgear or distribution center," advises Jay Park, Power Rich System group product manager at ABB. "Each feeder supplies power to different sections or operations of a plant."

Power quality meters and/or IEDs from companies such as Siemens, Square D, Landis+Gyr, General Electric, and other companies are reasonably easy to install at key distribution points. In almost all cases, they have communications capabilities and software support. "All markets use the same devices for data-gathering," says Park, implying that integration is easy.

Portable tools, such as the Square D analyzer shown in Figure 1, can be used to perform power system surveys, track down problems, or monitor units temporarily. They also can be installed permanently. Like the IEDs, the portable units come with software support and communications capabilities.

Analyzing the Situation

The goal of monitoring power is to find places where you can reduce power consumption and save money. Sometimes, the answer is obvious: Replace a motor with a more efficient one. Other times, the situation requires much more analysis.

Fortunately, power analysis software is available from several vendors, including:

• Siemens: WinPM.Net web-enabled software manages intelligent metering and protective devices, analyzes data, and shares energy usage and power quality data across an entire enterprise.
• ABB: Power Rich monitors and controls power in substations and distribution networks. It fits in applications ranging from $7,000 to $3 million, says Park.
• eLutions: AEM/EP Web is a web-based energy information package that measures, manages, and controls energy usage.
• DOE: MotorMaster+, available free from the Dept. of Energy, helps determine when efficient motors will help.
• Honeywell: PMC power monitoring and control software runs on Honeywell control systems. It has three parts: power control; analysis and predictions of energy usage; and load shedding.
• GE Industrial Systems: Envision, to be announced soon, analyzes the costs of electricity and other plant utilities, and generates real-time and historical views of utility costs.
• Pavilion: Energy Center Optimization Solution is a neural-network energy optimization package that analyzes a plant's energy consumption and devises ways to change plant operations to minimize energy use.

Power monitoring can help find all the "low-hanging fruit," as Frank Hein of Abbott puts it. To get huge energy savings, it may be necessary to install an energy optimization system. "Abbott recognized that to get to the next level of savings, we would have to stop concentrating on improvements in individual pieces of equipment and focus on entire systems," he explains. "Multi-unit optimization allows us to focus on the entire utility system and exploit the complexities of our large equipment set to find the optimal operating scenarios."

Nevertheless, you have to start somewhere. Monitoring power is the first step.