Long variation in voltage and supply interruption in a distribution system

Abstract

The paper examines a distribution system field data for the assessment of voltage variation and supply interruption. The under voltage has severe impacts on the consumer loads working conditions causing overloading and high transmission losses. The under-voltage limit has been set for voltage below 0.9p.u. The measurement was conducted in the control room for the duration of one week for logging interval of 1-min using Fluke VR1710 that monitors single-phase voltage quality of power network. Long duration variations are considered to be present when the limits are exceeded for greater than 1 minute time lapse. In this paper, the lowest interruption duration recorded was 20 minutes while the number of under-voltage was 41 occurrences. A simple mathematical analysis of power flow deviation was determined for correlation with the frequency disturbances recorded by the equipment. Both measurements and simulation results show that frequency rapidly changes in the network. The lowest and highest frequency vary between (48.7665 Hz to 51.196 Hz) and (48.843 Hz to 51.263 Hz) respectively. Thus, voltage and frequency disturbance statistics vindicate the voltage variation in the site to be within the ±10% limits but the overall performance of frequency monitored in the site violated the operational limits of ± 0.2 Hz (i.e. 49.8 Hz to 50.2 Hz) and ± 0.5 Hz (i.e. 49.5 Hz to 50.5 Hz) for the statutory regulatory. The paper would provide repository data as point of reference for Electric power sector reform act No.6 2005.