| 5.25.04 | Wade Troxell, Professor/Director,
Colorado State University Carissa
Dragos, Mechanical Engineering Student, Colorado State University |
| Power
Quality Response: A Case Study
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Power reliability encompasses: the more reliable the energy, the less the probability of a large-scale outage such as the one that occurred on the East Coast on Aug. 14, 2003. If the stress that caused the East Coast blackout could have been relieved, the chances of the problem spinning out of control after the first transmission line loss would be greatly reduced. The only way to reduce the stress on the grid is to infuse new technology into an ever-aging grid system.
Peak shaving refers to reducing or “shaving” the energy usage during the period where the power companies charge higher cost because of an increased demand on the utility. The utility company monitors the draw on their system and can predict when the peak and off-peak periods occur. Peak shaving devices are usually energy storage devices that store energy during off-peak times, and during a peak time, supply that energy for usage, instead of the grid, when the energy cost is the highest. Another way to peak shave is to use the information from the utility company as to when this peak occurs, and use less energy during this time and therefore reduce the overall cost.
In reference to Fort Collins Utilities, each day, there is a point when consumers demand the highest amount of energy. This point is called the coincident demand peak and it usually occurs between 11:00 am and 3:00 pm. Based on many previous years data, energy experts can predict when this peak occurs on any given day. Each day, the University’s kilowatt demand during the highest 60 minutes of the utility’s demand (or one hour of FCU’s coincident demand peak), the University has to pay the highest rate ($11.62/kW) during each billing cycle.
Fort Collins Utilities (FCU) provides the necessary electricity to Colorado State University’s Main Campus. Main Campus receives the electricity at 13,200 volts through feeders from two on-campus substations. The university-owned switching station receives the electricity through three electric feeders and sends the electricity to Main Campus. The University then distributes the electrical energy through a looped system of cables. In fiscal year 2003, the highest demand registered was 16 megawatts (MW). With a 16 MW demand and 31 MVA peak capacity, the University should have plenty of electrical capacity for the expected growth over the next several decades.
In fiscal year 2003, 12% of the total electricity usage was spent on the residence halls and apartments on Main Campus. This is a significant portion of the total electricity usage and ways to conserve this energy usage should be examined.
There are many thermodynamic appliances (an appliance that has a basic thermodynamic process to function) used in residential sectors that can be used as Power Quality Response appliances. These are defined as automatic on/off devices. A refrigerator is an excellent example. Refrigerators automatically turn on and off as needed for temperature control approximately every fifteen minutes. Other appliances include hot water heaters and air conditioning/heating units (HVAC). Usually hot water heaters have a big enough capacity to supply hot water for the short period until electricity is restored to it. HVAC systems also work because there is a small increase/decrease in temperature over a short period of time.
The only other required item is the Power Quality stabilizer. PNNL engineers are designing stabilizers that would fit into household appliances and would continually monitor fluctuations in the power grid. The basic idea of the stabilizer is it reads the frequency of the electricity coming into it and reacts based on that reading. A good indication of the power stability is the frequency (in Hz) of the electricity. Normal fluctuations of the frequency are around 60 Hz plus or minus one mHz. If there is a trip in the power (indicating unstable energy), the fluctuation could be up to 7.5 mHz. The stabilizer constantly reads the frequency of the energy through the wall outlet and if a large fluctuation occurs, it detects it and, within milliseconds, shuts off the appliance. After the appliance is shut off, the frequency sensor continuously checks, and if the frequency becomes stable again, the chip turns the appliance back on. In order to not overload the utility company when the appliances all turn on, the chip randomly chooses a time between 0 and 1 minute to gradually restore electricity to all appliances temporarily shut off. This allowance for re-stabilization creates a more reliable energy system.
With the use of Power Quality Response appliances the return to a more stable energy system is much faster. With these appliances, the frequency stabilizes in 0.7 seconds and without it takes 5.8 seconds. These time differences can be crucial and it could mean the difference between a cascading large-region blackout and a localized small-region blackout.
The Power Quality stabilizer is solely used to stabilize the energy, but a small change can also make it a peak shaving device. To address the idea of peak shaving: these stabilizers should all be networked to a main computer. This includes all dorm rooms in the ten dorms including the kitchens in the two apartment complexes. This network wire will be directly connected to the relay that switches the power on and off to the load. On the other end, the main computer will be in control of the relay. When the projected monthly coincident is going to occur the computer will automatically shut off all of the refrigerators connected to it for an hour, therefore saving CSU a portion of the $11.62 charge per kW. Once the hour is over, the computer will randomly restore energy to all refrigerators over a minute so as not to cause a power sag.
Refrigerators were chosen for the best Power Quality Response appliance because hot water heaters and heat ventilation are both created utilizing the University-wide district heating. Air conditioning also was not chosen because it is a seasonal commodity along with heating. The number of people in the ten dorms is 5050. Based on the assumption that there is one small refrigerator (approximately 8 cu. ft.) for every dorm room, there is one small refrigerator for every two people. This means that there are 2525 small refrigerators in the dorm residencies of CSU. These are not frostless refrigerators, in that the refrigerator compartment is not separate from the freezer.
There are two apartment complexes on Main Campus. These apartments contain 1100 people. Based on the assumption that there are two people to every refrigerator, as in the dormitories, there are 550 refrigerators in the apartments on Main Campus. The only difference between these 550 refrigerators and the ones in the dormitories is that these are large apartment refrigerators (approximately 18 cu. ft.). These are assumed frostless refrigerators, where the refrigerator is a separate compartment from the freezer.
The average energy usage for an eight cubic foot refrigerator per year is 975 kWh. On average, an eight cubic foot refrigerator uses 111.30 watts in one hour. The average energy usage for an eighteen cubic foot frostless refrigerator in one year is 2425 kWh in one year. A large frostless refrigerator uses 276.83 watts in one hour.
A refrigerator-freezer will generally keep food at a safe temperature for 4 to 6 hours without electricity, including times at which the refrigerator will be opened. With Power Quality Response technology, the refrigerators would be without electricity for at most one hour and one minute (one minute included for the random return of electricity within one minute). With Power Quality technology, almost half a megawatt will be saved each month during the most expensive usage time. The total savings in one month would be $5,034.84 which adds up to be $60,418.03 a year.
This amount accounts for 13% of the total money spent for the residential electricity of Main Campus on CSU. At first, this sixty thousand dollars would not be an immediate profit because the cost of implementation would have to be taken into account. The initial investment will be approximately sixty thousand dollars including network wiring, stabilizers, labor, and maintenance. This is definitely worthwhile because after one year of using the Power Quality Response technology the University will start making a profit.
These Power Quality Response devices create a win-win-win situation, literally. Colorado State University wins because they can count on overall more stable energy, which creates more reliable energy for the end-users. Also, CSU could potentially save $60,000 a year after a mere one-year payback period. It is a win situation for Fort Collins Utilities because not only is CSU’s energy stabilized, but this stability feeds back into the grid and further stabilizes FCU’s energy and returns more stable energy to their consumers. One would intuitively think that FCU would not like this idea because it means less money for them. But, Fort Collins Utilities currently has a contract with the Fort Collins Electric Board that over the next ten years they need to reduce their overall peak by 10%. Grid-Friendly devices help them move closer to their agreement. Finally yet importantly, using less energy means creating less energy, which in turn means fewer emissions into the atmosphere.
This is a huge win for the environment. Just for perspective, this means CSU will prevent 519 pounds of coal from being burned each month (6,239 pounds per year), and prevent 970 pounds of carbon dioxide emissions each month (11,646 pounds each year) with the reduction of 433.29 kW per month. The win-win-win situation is an important factor because not all parties will want to participate if it is not a benefit to them in some