Understanding Modern Power Monitoring and Control

Facilities looking to voluntarily reduce power demand may be able to reap additional benefits from load curtailment programs Pitzer College is just one of several commercial, industrial, and institutional facilities that have recently installed power management and control systems to avoid peak kW and/or kWh demand charges now imposed by several utilities. Even with a student body smaller than that

Facilities looking to voluntarily reduce power demand may be able to reap additional benefits from load curtailment programs

Pitzer College is just one of several commercial, industrial, and institutional facilities that have recently installed power management and control systems to avoid peak kW and/or kWh demand charges now imposed by several utilities. Even with a student body smaller than that of a lot of high schools, the private undergraduate institution in Claremont, Calif., is leading by example, meeting the requests of the local utility to shed multiple stages of lighting and other loads in classrooms, labs, offices, dormitories, recreation centers, and a greenhouse.

Electric utilities and independent system operators (ISOs) are increasingly hard pressed to meet the peak load electrical demand during certain times of the year. Exceptionally hot summer days — or specific emergency situations — present the conditions most likely to cause demand problems that ultimately make it difficult for the available supply to satisfy the increased load. Faced with these emergency situations, electric energy providers use several methods to achieve load reductions, such as mandatory interruptions or manual or automated curtailments.

Curtailment is a voluntary reduction of a portion of a facility's load based on a request from the power provider. It was just such a request that encouraged Pitzer College to begin reducing its load demand. Some utilities are creating, or expanding, curtailable rates for those customers able to reduce power demand at certain hours of the day by shutting off designated loads, shifting to an alternate fuel, or by supplying supplemental power from an on-site generator. In addition to California, where several factors have led to ongoing energy supply problems, Iowa, Oregon, Minnesota, and Wisconsin have instituted load curtailment programs. Typical customers include industrial facilities, government buildings, and large institutions, such as hospitals and universities.

Under the tariff agreement, Pitzer College must be able to reduce its circuit load by 15% and respond to the utility's request in less than 15 min. In addition, the reduction has to be maintained for the full duration of each declared emergency period, called an outage declaration. In exchange for meeting these curtailment requirements, the college is excluded from the utility's rolling outage (RO) block progression (first Sidebar below).

On the other hand, facilities that fail to comply with the requirements of the tariff agreement can incur stiff penalties. If Pitzer doesn't comply with a request for load reduction, the load curtailment agreement would be immediately terminated and the college would be prohibited from participating in the program for a 5-yr period. The college would also be placed on the RO block progression and incur severe financial penalties.

Working out the solution.

The project at Pitzer College focuses on providing an automatic ON/OFF control system for specified branch circuits serving lighting and other loads. Essentially, this involved retrofitting the interiors of lighting and appliance panelboards in 13 campus buildings with a lighting control system that consisted of modular components. The three main components of the system are electrically operated circuit breakers, which are connected to both a power interface module and a control module. All three components mount within the panelboard.

Each bolt-on circuit breaker adds the switching function of a contactor, eliminating the need for separate relays, contacts, or the need to install a separate enclosure and additional wiring. The power interface module, which furnishes the control power for the circuit breakers, and the control module, which configures the operation of the breakers, are installed at the top of the panelboard. The microprocessor-based controller responds to external signals from other devices and can provide time-based control according to a daily schedule. Each panel can be monitored to determine the status of an individual breaker (ON/OFF/non-responding) or system operation.

With series connected ratings as high as 200,000A, the circuit breakers can handle high short circuit current requirements. Single-, 2-, and 3-pole versions are available in 15A, 20A, and 30A ratings, with voltage ratings to 480V.

For data gathering and control, the lighting panelboards are networked through the college's existing Ethernet backbone, which serves the campus' local area network (LAN). Carrying the electrical power monitoring and control system's digital messages on the campus-wide network minimized the need to install new cabling between buildings. From a PC at the central workstation, the college's facilities manager can review the status of the electrical power system. From the same PC, the facilities department can issue “load shed” commands, while maintaining all the log shed/restore commands and metering data.

Twisted-pair conductors using the RS-485 protocol to connect the lighting panels to the Ethernet Gateway, and then the data can be routed along the Ethernet backbone to a network server, a client PC, or to a router for connection to a WAN/Internet. Other industry-recognized, standards-based protocols can also be used (second Sidebar below). The software allows easy set-up using intuitive graphic displays for information and system configuration.

In states like California where energy demands are straining the grid, load curtailment programs like the one undertaken at Pitzer College will continue to gain popularity. And power management and control systems will be integral to that conversion.

Sidebar: Why Do Rotating Outages Occur?

In March 1998 California opened its energy markets to competition and the state's investor-owned utilities turned over the responsibility of managing the flow of electricity along the state's wholesale power grid to the California Independent System Operator (Cal-ISO).

Operators in the Cal-ISO control room continuously monitor the supply and demand of electricity throughout California. If reserves begin to drop, they communicate with local utilities and electric generators, asking them to provide more power if possible. Simultaneously, users are asked to cut back usage. In these Stage One Emergency declarations the Cal-ISO can access emergency resources to help maintain operating reserves.

A Stage Two Emergency is declared when reserves drop below 5%. At this level, large customers that have signed up to voluntarily curtail power during high demand days are asked to do so. California had more than 16 such curtailments during the summer of 2000.

If an operating reserve shortfall of less than 1.5% is unavoidable, a Stage Three Emergency is initiated. Involuntary curtailments of service to customers, including rotating blackouts, are possible during this emergency declaration.

The idea is that, in times of electrical shortage, it's better to have controlled rotating power outages than to allow uncontrolled or cascading power outages that could damage key components of the power grid.

Sidebar: Plugging into Power Management

In addition to reducing utility demand charges, a power management and control system can offer numerous other advantages. For example, the system could also monitor the HVAC array, selected lighting loads, and several production processes by monitoring their supply breakers or feeders. Thus an engineering department could schedule the downtime for heavy energy use equipment when peak usage occurs, compare utility rate structures, and recommend predictive maintenance based on trends from recorded information. Integrating a predictive maintenance system with plant control offers a high potential for energy cost and plant operation savings.

How do you go about it? The first step is to find out where the power meters, feeder breakers, local displays, transformer temperature monitors, and generator controls are located. Then determine if you have a common communications bus like Modbus, SEAbus, BACnet or RS-485 twisted-pair cable that can be used to transport system data. You may have to install new network cabling, and here, the implementation of an economical cabling layout can help gain budget approval.

At this point, you may decide that it's practical to install new communications devices like smart breakers or an advanced power quality meter. You may also choose to use remote monitoring, in which case you'll need communications equipment that supports remote data acquisition and selective sharing of data among multiple sites.

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