A decentralized voltage control is proposed for distributed generation (DG) units to provide short and long-term voltage support in distribution networks. Local controllable zones are used to determine the voltage control boundaries for each DG unit. The number of zones and their size depend on the number, location and size of the DG units, and can be reconfigured in real time in response to network topology changes. The performance and value of the proposed control approach are demonstrated under various operating scenarios. The study is based on the IEEE 33-bus radial distribution network implemented in DIgSILENT PowerFactory.