The necessity to take into account environment problems and in parallel a need for more energy, for the development of emerging economies, makes the management of energy sources a very important problem. The electric transmission network is charged with more loads and consumers. The power control is performed today using power electronics installations, in particular the Flexible Alternating Current Transmission Systems (FACTS). The proliferation of power electronic installations is the cause of higher harmonic pollution in the power grid. As the utility of the FACTS for the management of modern power networks is evident, measures must be taken in order to reduce the created harmonics using various methods. The paper will discuss the admissible limits of harmonics in the network, as defined by the EEC norms and will briefly present some methods used to reduce the harmonic content and level.