The paper proposes an application of a hierarchical automatic voltage regulation scheme for a cluster of hydro power plants connected to HV networks. The topology considered in the paper is a radial network in which the hydro power plants are connected to each other and have a single point of connection at the HV level. The technique proposed in the paper is based on well-assessed control strategies that are used in HV transmission systems, but has not been applied so far to medium voltage networks. A case study based on a cluster of hydro power plants composed of 11 generators and a distribution grid is presented and discussed in detail.