An Analysis of Practical Distribution System Voltages with High Penetration DERs Participating in Bulk System Fast Frequency Response

This paper presents an analysis of voltages on distribution networks that have high penetration distributed energy resources (DERs) participating in bulk system fast frequency response (FFR). Existing system and operating conditions effects with rapid DER injection on distribution system voltages for ancillary service participation is discussed. Two networks are analyzed based on actual networks with DERs participating in FFR. Results show that there is a correlation between the peak transient and settling steady state voltage with the pre-injection operating voltage following rapid DER ramping. The voltage effects can result in rapid voltage rises or sinks following injection. Further investigation is conducted by varying the load of the distribution network. Results show that the load effects the peak transient and settling steady state voltage however, it is minor when compared to varying the substation system voltage. An analysis is conducted comparing DER operating modes of constant power factor and Volt-Var. Results demonstrate that Volt-Var is generally more stable in operation. Lastly, comments are made on how system characteristics may affect distribution voltages following rapid injection from a DER for FFR. Factors include X/R ratio, system strength and operating power factor. All results are conducted in the EMTP-RV software.