# Article

**Keywords:**

numerical examples; box method; heat conduction problem; elliptic equation; local discretization error; finite volume method

**Summary:**

This article focuses its attention on practical use of the box method for solving certain type of partial differential equations. The heat conduction problem of the oil transformer under stationary load is described by this equation. The knowledge of the transformer operating temperature is important for ensuring correct functionality and lifespan of transformer. We consider an elliptic partial differential equation of second order with the Newton boundary condition on a rectangular domain. The paper contains description of a numerical solution procedure of the heat problem and an estimation of local discretization error. The box method is often called the finite volume method, too. The solution of practical examples are presented as well.