Optimal reactive power dispatch (ORPD) problem basically focuses optimally on management of reactive power sources such as distribution generation (DG) units and reactive power compensation (RPC) devices. Its main purpose, especially in distribution grids, is real power loss and reactive power cost minimization subject to satisfying a set of constraints. On the other hand, optimal site of these devices in distribution system and polynomial load model can significantly affect the ORPD problem. In this paper, a new revision of ORPD in distribution grids combined with optimal DG and RPC allocation considering load model-based power flow and a new objective function is introduced. Moreover, improved grey wolf optimizer (IGWO) as a new and powerful optimization technique is proposed to solve this complex problem. The suggested method is implemented on standard IEEE 33-bus distribution system considering various scenarios and load profiles. The obtained results demonstrate the effectiveness of the introduced problem and ability of the proposed algorithm for finding better solutions compared to other presented methods.