3.3 Distributed Energy Resources (DER) Impacts on Distribution Systems

3.3.4 Coordination of DER Systems and Voltage Management Equipment

As high penetrations of “smart inverter-based” DER systems are deployed, their settings must be coordinated with existing distribution equipment, such as load tap changers, capacitor banks, and voltage regulators. For instance, the smart inverter DER volt-var function automatically modifies its vars to counteract voltage fluctuations. The settings of this DER volt-var function must be coordinated with the settings of the distribution equipment on the circuit in order to avoid these devices from conflicting or hunting and to dispatch them in a strategic manner that maximizes value.

Since DER systems can cause voltage changes, their voltage actions must be coordinated with the feeder load tap changer (LTC) and voltage regulators, in order to avoid voltage problems or “hunting” by LTCs and voltage regulators.  The lifespan of these mechanical devices can be shortened if they are activated more often than necessary, so uncoordinated voltage actions can impose a system cost by increasing maintenance activities on these devices.  Mitigations include using power electronics-based voltage control devices such as a static var condenser or emerging solid state voltage regulator technology, as well as making sure the advanced DER voltage functions are appropriately coordinated with the distribution devices.

One of the most evident impacts of DER systems are on distribution voltages along feeders. Not only will load profiles change with higher penetrations of DER, but the feeder voltage profiles will change. There are many types of feeders with differing characteristics e.g. short urban vs. long rural, that affect what the settings of distribution equipment are installed with.  In general DER systems can cause new stresses on distribution circuits, but at the same time, some of the advanced capabilities of DER systems could mitigate these effects.