Tuesday, October 25
Power Factor, Flicker
1:30 pm-3:30 pm
This sessionís three papers deal with the well known electrical power supply problems: Voltage sag/dip with causation of flicker affecting residential customers and creating other power quality problems for commercial and industrial users, and low power factor. The authors correctly attribute the voltage flicker to starting large motors, and voltage regulation. These three papers make one aware of the problem, shows practical solution with application of available technology, and finally the economic benefit of the solution.
Things You Need to Ask Your Power Supplier Before Running a Large Motor
Ricky Evans, Power Monitors, Inc.
If your business is rock crushing or a similar operation that is a known flicker producing activity; you have certain things you need to ask the power producer before you purchase the equipment. if equipment gets installed and a flicker problem appears on the power suppliers system, the economic impact of resolving this power quality problem my be significant.
Since some customers do not know what they need to ask the power supplier and some power suppliers do not know what they need to ask customers, a condition exists that can allow known power quality problem producing equipment to get purchased and installed in a customer facility.
If all the questions would have been asked up front (either by the supplier or the customer) most power quality problems for the customer and power supplier could have been avoided.
Power Quality Problems: Causes, Impacts, and Solution Part III: Voltage Regulator, Design and Testing (Case Study)
Abdullatif Bagegni, Merrimack College
Voltage regulation devices are often applied to utility and industrial power systems in order to maintain the voltage within Ī5 percent of nominal. As has been well documented, adding switching capacitor banks to a power system can significantly improve the power system voltage regulation. However, switching capacitor banks can cause resonances, as well as voltage and current transients that may have significant negative impacts on equipment. Utilizing harmonic filters instead of capacitor-only banks can maintain a constant voltage, improve power factor, reduce transients to allowable levels, and also reduce harmonics and avoid resonance issues in the power system.
The science building distribution system of Merrimack College was the case study for this project. The study focused on improving voltage regulation. The following results are a brief synopsis of the said study. The measurements taken indicated the line voltage was 478.22V. It was calculated that a total of 77-kVAR would be required to improve the voltage to 482.06V. A series LC circuit meeting this requirement was designed, installed, and tested. Measurements of voltage, current, real power, reactive power, and power factor were made before and after regulator application.
The implemented design resulted in improved voltage regulation, improved power factor and in savings of over 10 kW-hr. Based on local rates of $0.06 per kW-hr, this application conservatively gives a yearly savings in excess of $5,000.
Switched Capacitor Scheme for Reducing Flicker Due to Starting Large Motors
Ernst Camm, S&C Electric Company
Dennis Hansen, PacifiCorp
Steve Larson, PacifiCorp
The direct on-line starting of 1800 and 2000 hp pump motors at a pump station in Wyoming was causing significant voltage sag problems on PacifiCorpís 34.5 kV distribution feeder, resulting in complaints about flicker from residents in a nearby town. Voltage sags associated with the starting of the two motors at the pump station were partially mitigated by the application of a switched capacitor bank installed on the 34.5 kV side of three single-phase 833 kVA, 34.4/2.4 kV transformers serving the pump station, but the time delays associated with the switching of the bank were too long to reduce flicker sufficiently. The existing capacitor bank was also unreliable.
PaciCorp initiated a detailed study to investigate various solutions for mitigating the flicker problem due to the pump motor starts. The solutions evaluated in the study included modifications to the existing capacitor controls and adding an additional capacitor bank, installing a power-electronically-switched VAR compensator, and installing adjustable-speed drives for the pump motors. A switched capacitor scheme, utilizing two capacitor banks with advanced controls, provided an effective and least-cost solution. This paper describes the details of the flicker-mitigation study and presents field measurements of voltage sags before and after the implementation of the switched capacitor scheme at the pump station.
Sunday, March 9, 2014