High reliability electrical distribution system for industrial facilities

Continuity of service is most essential in data processing facilities. Insulation failure due to line to ground fault is the most prevalent cause of service interruption in such facilities. Solidly grounded systems create fatal and costly Arc Flash hazards that would cause substantial damage at the fault location. Resistance grounding limits the line to ground fault current. This practice has been in use for many years and is widely applied in industry. This paper explores the application of resistance grounding in data processing facilities, where the distribution systems are typically more complex and may involve multiple sources, such as multiple transformers, multiple generators or a combination of both. This paper proposes that the sizing of neutral grounding resistor (NGR) should be exclusively based on charging current. Application examples are presented and the concept of hybrid grounding in low and high voltage (HV) systems is discussed.