Turning to Renewable Energy Sources (RES) is the most logical politics in securing the modern society from critical changes in earth increasing temperature. However, Distributed Generation (DG) sources could lead to new challenges in electricity network, mainly allocation of DG sources in distribution level of power system will set the existing network under stress of power flow parameters. The generated alternation in lines current, voltage profile and power loss will make a mutation in operator optimal decision. This paper will present a detailed survey on DG impact on power flow components violation. Also, some advanced issues such as difficulty in transformers tap changer, capacitors and power quality problems (i.e. intermediate harmonic interference, transient over voltage) will be addressed by the paper. The research shows a necessity to multi-level load consideration in active distribution networks due to DG existence. The study clarifies main problems in DG application from electricity distribution system operator aspect.