Ketidakseimbangan beban pada suatu sistem distribusi tenaga listrik selalu terjadi dan penyebabnya yaitu penggunaan energi listrik oleh pelanggan yang tidak selalu sama atau tidak merata pemakaiannya. Akibat ketidakseimbangan beban tersebut timbulah arus di netral trafo. Arus yang mengalir di netral trafo ini menyebabkan terjadinya rugi-rugi (losses), yaitu rugi-rugi akibat adanya arus netral pada penghantral netral trafo dan rugi-rugi akibat adanya arus netral yang mengalir ke tanah. Rugi-rugi yang terdapat pada trafo adalah rugi daya, rugi inti, dan rugi tembaga. Dalam menganalisis masalah menggunakan metode matematis meliputi persamaan ketidakseimbangan beban trafo, rugi-rugi daya dan efisiensi trafo. Setelah dianalisis, diperoleh bahwa bila terjadi ketidakseimbangan beban yang besar, maka arus netral yang muncul juga besar, losses akibat arus netral yang mengalir ke tanah juga semakin besar sehingga efisiensi trafo semakin menurun. Pada Gardu JKL ketidakseimbangan beban sebesar 20% (siang hari) dan 40,66% (malam hari) dengan losses sebesar 1,180 kW (siang hari) dan 1,636 kW (malam hari), losses akibat adanya arus netral pada penghantar netral sebesar 5,720 kW (siang hari) dan 6,503 kW (malam hari), losses akibat adanya arus netral yang mengalir ketanah sebesar 2,753 kW (siang hari) dan 4,894 kW (malam hari), dan efisiensi trafonya sebesar 97,16% (siang hari) dan 96,16% (malam hari).

The unbalance of the load on an electric power distribution system always occurs and cause is namely the use of electric energy by customers are not always the same or uneven in use. Due to load unbalance arise the current in the neutral of the transformer. The current flowing in the neutral of the transformer is lead to the occurrence of the loss (losses), namely the loss due to neutral currents on conductor of neutral of the transformer and the loss due to neutral current flowing to the ground. Loss contained in a transformer is a power loss, core loss and loss of copper. In analyzing the problem using a mathematical method includes the equation of imbalance of the load transformer, power losses and efficiency of transformer. After analyzed, it is obtained that when there is an imbalance of the load, then the neutral current, which appears too large, losses due to neutral current flowing to the ground is also greater so that the efficiency of the transformer decreases. At the Substation JKL unbalance load of 20% (during the day) and 40,66% (night) with a loss of 1,180 kW (during the day) and 1,636 kW (night), the losses due to the presence of neutral current in the neutral conductor of 5,720 kW (during the day) and 6,503 kW (night), losses due to neutral current flowing to the ground amounted to 2,753 kW (during the day) and 4,894 kW (night), and efficiency transformer amounted to 97.16 levels% (during the day) and 96,16% (night).