Analysis of Loads Effect on Neutral Current of Distribution Transformers

One of distribution transformer’s function is to convert high voltage electrical energy to low voltage levels. This study analyzing 3 phase distribution transformers with 20/400 volts level which directly supplies Talun region in PLN Rayon Wlingi. PLN or known as State Electricity Company in Indonesia is a company which support and maintain the supply of electricity, especially in generation, transmission and distribution. In actual conditions each phase loads are hard to exactly balanced, these unbalanced loads in three phase creates a neutral current to flow. Neutral current as the vector sum of three phase currents in a symmetrical component. Unbalanced loads can also occur under normal and overload conditions. Overload generates heat and losses that occur in transformer, especially on transformer’s core and transformer’s windings. This study also analyzes the effect of the transformer’s load on the loss and heat of transformer. According to PLN’s distribution transformer management regulations, the maximum distribution transformer loading is 80% of the full load current, while for maximum load imbalance is 25%. Result show that the greater the unbalanced load the greater the value of the neutral current. At the morning Talun feeder has 4 transformers which on bad unbalanced load condition, and at the afternoon it has 3 transformers on bad unbalanced load condition (25% and over). The purpose of this research is to know the characteristic loads on Talun feeder, PLN Rayon Wlingi, so the result of this research can be used to planning the distribution system of PLN Rayon Wlingi on the newest loads and to provide an opportunity for other researchers to further analyze the character of the load and its impact on neutral current, loss and temperature of transformer.