Neural grounding transformers

The best way to ground a power system is to obtain the system neutral through a generator or transformer with a wye-connected winding. However, a system neutral may not be available, particularly in many older low voltage systems and a significant number of existing medium voltage systems. To avoid a high cost of replacing a source transformer, an existing delta-connected system can be grounded using a star/ open delta or star/ delta transformer. During a line-to-ground fault condition, the zero sequence currents can flow into the ground at the point of the fault, and back through the neutral of the grounding transformer, hence providing facility to monitor & limit ground fault current. However Neutral Grounding Resistors are used for system grounding through Neutral Grounding Transformer & generators. A neutral grounding resistor limits the fault current, which is sufficient enough to operate protective relays, yet prevent unwanted fault damage.