ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 20.-22.05.2015. 355 HOUSEHOLD ELECTRIC POWER SUPPLY GRID POWER FACTOR TRENDS Arvids Jakusenoks, Aigars Laizans Latvia University of Agriculture arvids.jakusenoks@gmail.com, aigars.laizans@gmail.com Abstract. The article presented is devoted to the research of seasonal trends in household electric grid power factor changes. The power factor (PF) is changing the value and character due to the household electric energy consumption patterns change and different daily/weakly/annual energy needs. Long-term electric energy consumption data collection from the group of individual private houses was organized, and the research revealed that the power factor there has visually recognizable repeated daily (day/night), weakly (working days/weekend) and annual weather based (all seasons - spring/summer/autumn/winter, in Latvia) changes. Data processing allowed developing the equation which with high probability (> 85 %) can predict the power factor changes in the observed household electricity supply grid. Electricity supply utility company to establish appropriate relay protection levels based on the electric load characteristics and to increase the connected loads to the transformer points, which are used to supply energy to particular regions, can use the revealed trend and equation.Development of the power factor compensation system with substantially higher operation quality will take placeusing the microcontrollers with the built-in seasonality equation. Keywords: power supply grid, seasonality, power factor trend, household energy grid. Introduction Energy consumption in the household sector is increasing, and electricity accounts for a significant part of overall household energy consumption all over Europe. Electrical energy is a very important part of the household energy flow because of recent technological developments in home appliances. According to the state officials, householders in Latvia cover 24.1 % of all energy needs using electricity [1], which is a comparable value for households in Europe. At the same time, electric grid development lags behind, especially in the household electric energy supply side because of historically low demands and industrial consumers as the main payers, which requested attention. In line with tremendous growth of instruments, appliances and technologies, which use electric energy, entering the household market, the electric grid quality is becoming more and more important. People try to change their electrical appliance usages [2] by increasing their comfort of living and appliance technologies, the electricity demand changes, therefore the power factor values in the household sector change. The electrical power demand changes all over the world. It changes by time, by seasons, by appliances used [3]. Utility companies want to increase the power consumption from the household side, but do not want to invest extra money in electricity supply line power increase. One of the solutions, which could require less investment, would be the power factor increase in the electricity supply grid, thus increasing the throughput of electric energy without changing supply wires and transformers. Analytic research [4] proves that the household electric grid power factor has changed dramatically within the last 65 years. Mean value of power factor dropped to 0.79 on 2013 in Latvia[4], with additional change of the power factor character – from resistive/inductive to resistive/capacitive because of new technologies used in household appliances. Low values of power factor explain impossibility to serve increased electric power demand due to overload of the supply grid with reactive component. Relay protection devices used for electric grid protection also are not properly working if the power factor and its character are not taken into account. With electric energy use increase in the household sector, resulting in increased electric grid load and power factor change, electric energy supply companies should take into account the electric power use intensity trends, especially daily and annual seasonality, and organize supply and protection system operations in accordance with them. As no research results devoted to household electricity grid power factor seasonality trends were revealed in the available resources, it was decided to find out the trends in electric energy use and power factor change in household with further theoretical basis development for electric power supply and quality control devices.