Voltage regulation by means of coordinated voltage control is one of the challenging aspects of distribution system operation. Integration of distributed generation (DG), which can also be operated in voltage control mode, in distribution systems may introduce adverse effects including control interactions, operational conflicts and long term oscillations. The seamless operation of distribution systems embedded with DG for effective voltage control is one of the challenging tasks, mainly because (a) DG may interact with the conventional voltage control devices and (b) prioritised operation of different voltage control devices depends on the network topology and real-time characteristics of the system. Coordinated operation involving multiple voltage control devices (i.e., on-load tap changers and voltage regulators in addition to local capacitor banks) and DG units is one of the feasible technical solutions at medium voltage distribution system level. In most of the methods proposed in the literature, the voltage control devices and DG units are tuned and coordinated online using Volt/VAR optimization strategies in accordance with the time-graded operation. However, there is no mechanism to operationally minimize the interactions between DG units and the voltage control devices in real-time between any two consecutive control states. In such case, more generic approach needs to be developed for examining interactions between the DG units and the voltage control devices. In this paper, interactions among multiple DG units and the voltage control devices are identified using their simultaneous and non-simultaneous responses.