The Three-Phase Ground-Fault Circuit-Interrupter System—A Novel Approach to Prevent Electrocution

Development and Prototyping of a Ground Fault Circuit Interrupter for 3-Phase 480 Volt Systems

“…Tabulated results comparing EMTP results with V-HARM appear in Appendix A; they are in the same format as that presented in [9]. Other than the exceptions noted below, results between EMTP and V-HARM agree within 5%, or 1mA, whichever is larger.…”

“…However, assuming the capacitance to ground on each phase is equal (using bundled 3-phase cables), and assuming the phase voltages are balanced, line charging currents will sum to a very small net current, necessarily below the 5 mA threshold, if not a milliamp or so. In an interview with the author of [9], field tests at the Chevron Richmond refinery indicated this to be true.…”

“…This thesis is based on the work of Hamer in [9], in which the tripping logic described in US Patent #7301739 [10] is detailed as a solution to implementing a 3-phase 480 V GFCI. In summary, rather than each feeder acting independently on its own CBCT measurements, a digital relay is used to monitor and control tripping on all feeders and the main bus.…”

“…Consequently, the sum of the phase voltages shifts with respect to ground, and line charging currents become imbalanced; thus the exaggerated nuisance currents on HRG or ungrounded systems. Using the results of (2.6), the current sensed in a non-faulted CBCT is the sum of the line charging currents, which is proportional to the sum of the voltages 2.7On the other hand, for a solidly grounded system, the neutral is fixed at ground potential, and the largest current imbalance that can occur on a non-faulted feeder due to a solid bus fault is proportional to (2.8) A difference of a factor of three between (2.7) and (2.8) [9] which highlight the nuisance tripping currents, and later on to validate test system measurements with simulations. This chapter details the successful verification of the solidly grounded and high-resistance grounded (HRG) systems with V-HARM results.…”

“…TACS (Transient Analysis of Control Systems), a sub-program of EMTP, was used to measure the steady-state root-mean-square (RMS) of the sum of phase currents in the feeder and main branches, emulating zero-sequence CBCT current measurements. For more details, refer to Chapter 5 or [9], which both detail the parameters used. In short, solidly grounded, HRG, and ungrounded systems were all simulated for solid, 700 Ω, and 47 kΩ faults on the bus and each feeder.…”