This paper studies the impact of the dynamic controls and protection schemes of distributed energy resources (DERs) and dynamic motor loads on the bulk power system (BPS). This will help characterize the distribution system aggregate modelling and parameterization practices that can be recommended for use in BPS planning studies and identify any sensitivity of best practice to the varying degrees of DER penetration. The study uses a detailed unbalanced feeder model with 3-phase and 1-phase DER with dynamic voltage and frequency controls and voltage, rate of change of frequency (RoCoF) and frequency protection alongside 3-phase motor loads with undervoltage protection interfaced to a simple, balanced transmission system model simulated in a coupled RMS domain. The results from this detailed model are then compared with appropriate aggregate models including der _ $a$ and a composite load model equivalent.