Power delivery (PD) elements (also sometimes called power delivery devices) consist of two or more multiphase terminals. Their basic function is to transport energy from one point to another. On the power system, the most common power delivery elements are lines and transformers. Thus, they generally have more than one terminal (capacitors and reactors can be an exception when shunt-connected rather than series-connected). Power delivery elements are standard linear electrical elements generally completely defined in the rms steady state by their impedances. Thus, they can be represented fully by the primitive y matrix (Yprim). 

Figure 1: Power Delivery Element Definition 

See PD Elements in the OpenDSS TechNotes and documentation section for further information and application examples