Reducing on-load tap-changer operations through utilization of auto-switch capacitor bank with presence of large solar interconnection

Abstract

Voltage control is necessary on a power system to ensure all consumers are operating their equipment at a proper utilization voltage to avoid damage due to improper voltage supply. The traditional distribution power system is equipped with three primary assets to control voltage. These assets are load tap-changers (LTCs), which are sometimes referred to as on-load tap-changers (OLTCs), step voltage regulators, and capacitor stations. With newer technology these antiquated devices can become more intelligent and serve a more precise purpose with the addition of locally installed controllers. These controllers can be expensive but if used intelligently can pay for themselves over time by optimizing the devices they serve. The addition of distributed generators (DGs) causes voltage control to become much more important. Rapid and dynamic changes in generation from solar, wind, diesel, and other forms of distributed generation can create voltage swings that are not tolerable in a traditional power system. Especially when these DGs have large megawatt generation capability. One downside of these voltage swings is the unnecessary tap changes the LTC or OLTC make to compensate for voltage deviations caused by momentary changes in power generation. The more tap changes an LTC make the less life the LTC has and replacement of an LTC can be one of the largest single unit expenses in a maintenance budget. The research and analysis presented in this report demonstrate the negative impacts DGs have on distribution system voltage control and LTCs. Furthermore, a potential solution to reduce load tap changes is identified through intelligent control of capacitor stations. Analysis regarding placement of DGs and voltage control equipment are also reviewed and compared using IEEE 13 Bus System in OpenDSS. Finally, a cost-benefit analysis is presented utilizing equipment currently used in power systems throughout North America.