Project Info

Project Title 
Low Voltage Technology Scoping Study: Impact of Small AC Units on Electrical System Voltage Recover
Project Number 
DR 05.05
Investor Owned Utilities 
Project Year(s) 
2005 - 2006

Project Summary

Occasionally, the utility electric grid systems undergo voltage fluctuations caused by faults. These faults are caused by storms, accidents, debris on lines, and equipment failures. Normally, protective relaying is used to disconnect the problem lines and then voltage automatically returns to normal. There have been a few occurrences over the last several years where this voltage restoration has been delayed for up to 30 seconds. It is thought that air conditioning units are contributing to this delayed voltage restoration due to stalling compressors. When an air conditioning compressor stalls, its real and reactive power tends to increase which drags down system voltage. These stalled compressors do not disconnect from the electrical system until their internal thermal protection device is activated. Most large air conditioning systems have low-voltage protection; however, smaller units used in residential and light commercial buildings do not typically have this protection. In this project, laboratory testing was performed on residential and small commercial air conditioning units common in Southern California Edison (SCE) service territory to provide insights on their electrical behavior under low-voltage conditions. This project is a component of a larger, multi-year research project (Evaluation of the Effects of Stalling Residential and Small Commercial Air Conditioning Units on Electrical System Voltage Recovery), which seeks to evaluate the impact of stalling air conditioning unit compressors on delayed electrical grid system voltage recovery after a system fault and to investigate practical solutions to reduce/eliminate the stalling problem.

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