Design and calculation of 66 kV neutral grounding resistor for main transformers in Bandar Imam petrochemical complex (BIPC) power station located in South West of Iran

Types of grounding system for industrial networks lower than 45 kV and upper than 132 kV voltage levels are clearly recommended in standards, but for some voltage levels in between, such as 66 kV, is not specified. BIPC´s step up transformers have dY connected winding, 13.8/66 kV rating voltage and secondary side of them has been solidly grounded. The high intensity current of frequent earth faults in 66 kV distributed network in BIPC, caused disruptive effects. In order to limit the short circuit current, calculation has been made to change the existing grounding of step up transformers in BIPC power station. Obviously, the insertion of a resistor in transformers neutral grounding system is affected by; short circuit current protection, unbalance voltages, operation of existing protections, charging currents, and etc. This paper introduces important scientific and applicable notes witch has resulted from months of studies and discussions by some power engineers and experts. These results are good references for neutral grounding resistor calculation, in general.