Authors

Abstract

This method finds the Under Load Tap Changer (ULTC) position and
capacitor ON/OFF status of each hour for the next day in main or secondary
distribution substations, so the secondary bus voltage improves and the reactive
power flow into the transformer can be restrained at the same time. The only
condition to achieve these goals is the previous knowledge (by forecasting) of
load demand for active and reactive power and the primary bus voltage for each
hour of that day. The practical constraints are involved through the use of
membership concept in fuzzy set theory, where these constraints are bus voltage
limits, the tolerable worst power factor & the maximum allowable number of
switching operations for the Load Tap Changer (LTC) and capacitor in a day. This
method is also considering the variation of load active & reactive power with its
voltage, where the loads are classified into three categories according to their
relationship with voltage, and so there are constant impedance loads, constant
current loads and constant power loads. To demonstrate the usefulness of this
method an example on one of the Iraqi national grid substations (132/33KV
Yarmook substation) was made in MATLAB.

Keywords