April 1, 2009

In Search of Perfect Power

James M. Hylko

Step 4: Identify the Weakest Links

Many organizations fix problems after the fact and thereby incur the cost of failure in their product cost, according to the Juran Center for Quality. Others avoid fixing problems by adding unnecessary costs at the end of a process by, for example, increasing the number of inspectors and production redundancy. In contrast, the IIT PPS team applied Six Sigma quality principles, including failure modes and effects analysis and error proofing quality tools, to identify and define the types of failures that were possible and determine how to minimize or prevent those failures before they occur.

The team determined the severity (major, moderate, and minor), probability (frequent, occasional, uncommon, and remote), and severity factors (severe weather, aging, usage, and human error) for each failure mode. The severity of the impact of a power failure depends upon the severity of the impact of the loss of power on the customer and may vary from customer to customer.

This process identified several weak links in the system that are now part of the planned PPS upgrades:

• ComEd electricity supply. IIT is located in an area subject to severe weather, but it has only one transmission feed, which makes it more vulnerable to outages. In addition, the campus electricity supply is via older direct buried cables that have been experiencing failures. Furthermore, some of the ComEd supply system is still above ground and subject to weather damage. These conditions resulted in an offsite power supply rating of "frequent." In addition, the severity of the impact was rated as "moderate" due to the economic impacts from the loss of productivity. The analysis concluded with the imperative that IIT will need to ensure that the campus can be supplied by a local alternative power source.

• Site distribution cables. IIT supplies a number of the campus buildings via direct buried cables. The buildings are supplied by two feeder cables that must be manually selected. The PPS design requires that these failure modes be eliminated.

• South Substation. The IIT South Substation is more than 30 years old and nearing its supply capacity. The substation should be upgraded and the power feeds reconfigured to move some of the loads to the newer North Substation.

Step 5: Design the Perfect Power System

IIT’s PPS is modeled after the "High Reliability Distribution System" (HRDS) developed and implemented by S&C Electric for the University of California at Santa Barbara. The team divided the IIT campus into logical groups of buildings that will form electricity and thermal loops to maximize reliability and efficiency. The HRDS leverages a continuously energized loop feeder concept, which provides a redundant supply of electricity to designated campus buildings (Figure 5). Both feeds will be energized and will supply electricity to designated buildings. They will also be capable of carrying the entire building load. In addition, feeder redundancy will allow the rerouting of power to buildings in the event of a distribution feed fault.


5. The perfect number. The IIT High Reliability Distribution System divides the campus
into seven independently controlled and redundantly supplied management zones. Siegel Hall
is the far right building in zone 3. Source: Michael Meiners, Galvin Electricity Initiative

This approach was based on the team modeling projected loads on campus based on expected increases in enrollment and planned construction of new and recommissioned campus buildings. Transformers will be upgraded where necessary, and new 15-kV cables will be installed to provide additional flexibility. The result will be a robust feeder network that will give IIT the option of eliminating the existing above-ground ComEd transformers that step down ComEd distribution voltage of 12.46 kV to the switchgear rating of 4,160 V.

The backbone of the PPS is an intelligent trending, detection, and mitigation system that collects thousands of inputs, trends their parameters, determines their potential impact, and changes the system operation to mitigate the consequences of adverse trends. An Intelligent PPS Controller (IPPSC) that monitors and trends critical parameters to determine the system state manages the PPS. The IPPSC then changes system operating conditions to maintain the system within the specified limits of operation. The monitoring and communications system includes the robust deployment of lower-cost mesh sensors and modules that communicate via either a wireless or a wired IP-standardized communications network, including:

• Advanced meters for each building that measure voltage, frequency, current, reactive power, power consumption, and harmonics as well as individual building loads.

• Signals from the IPPSC to dispatch generation based on PJM real-time electricity and natural gas prices.

• Local generation and storage output levels, storage capacity, and fuel supply status.

For example, in the event of a loss of one section of cable or a switch, the design concept provides for the rapid assessment of fault conditions and opens within 1/4 cycle, simultaneously isolating the fault and allowing power to flow along a secondary feeder route without interrupting power to any loads. This approach uses S&C Vista fault-clearing switchgear in a closed-loop system with directional overcurrent protection relays. This combination of high-speed automated breakers, switches, and redundant feeders allows for the instant reconfiguration of the system to keep power flowing to all buildings.

Siegel Hall, a research lab, is a good example of specific infrastructure upgrades that will mesh with the PPS technology. Siegel Hall’s distribution system consisted of two 4,160-V feeds from the North Substation (Figure 6). Feeders 12 (primary) and 11 (secondary) provided feeder redundancy through manual switches 176 and 177, respectively, which fed into a 500-kVA transformer where power was stepped down to 240 V. Typically, two panels on each of the three floors distributed electricity to lights, fans, and computers. A high-pressure campus steam system supplies heating to the building.

Figure 6 also provides an overview of Siegel Hall’s future Building Integrated Energy System. The PPS upgrades include a redundant electricity supply, efficient hot and chilled water supply, uninterruptible power source and/or generation, renewable energy sources, and an advanced building control system.

6. A world of difference. Each building will have a number of energy system retrofits completed. For example, these diagrams show Siegel Hall’s distribution system before (top) and after (bottom) the planned Perfect Power System upgrades. Source: Michael Meiners, Galvin Electricity Initiative