This bachelor's thesis describes the basic principles of transformer operation in the first part. The following chapters focus on issue of higher harmonic frequencies. Then it describes the basic design and principles of instrument transformers, which are the main subject of this work. At present, higher harmonic frequencies are becoming more and more common in electrical networks. Therefore, this work tries to bring new knowledge in the issue of higher harmonic frequencies in instrument transformers. The last chapters describe the computational design of an instrument transformer that resists higher harmonic frequencies. This transformer must be able to transfer these frequencies to the secondary winding. It was necessary to study the stan...