Research On Noise Reduction For Zero Sequence Current In Compensated Neutral Grounded Systems

Compensated neutral grounding is superior to other types of system grounding. A ground fault that occurs on the compensated distribution system draws a small fault current at the fault point, therefore does not require immediately clearing. So that compensated neutral grounding allows for continuous service to loads after a ground fault. A controlled shutdown for fault repairs at a convenient time provides tremendous value to continuous manufacturing processes by reducing production losses, equipment damage, and outage times.Although the system will operate with one ground fault, it will not operate with two. From the time the first ground fault appears, system reliability is at risk should a second ground fault occur. The second ground fault may create a sufficiently low-impedance path between phases and between two circuit breakers that it causes multiple circuit breakers to trip. The possibility of the second ground fault is increased because the first ground fault increases the phase-to-ground voltage for the unfaulted phases by as much as the square root of three. Timely attention to the first fault is required to minimize this risk.More modern ground-fault location systems use dedicated relays and sensors to identify the feeder circuit that is faulted, and they may allow the use of additional sensors outside of the gear to further pinpoint the location of the fault. The fault current has a zero-sequence component and is detectable using current transformers or sensors that sum the three phase currents. Because a primary source of the fault currents is the distributed grounding capacitance, using current detection for fault locating is impossible. From the capacitance, zero-sequence currents flow from all parts of the system to the fault. Additional currents flow from the grounding resistors and fault detectors. As the compensated distribution system draws a small fault current, noise component in the zero sequence current sampling is too large and makes it difficult to distinguish the real signals. To handle such problem, this paper analyzes background noise in the zero sequence current sampling, points out it consists of random noise and periodic components. Furthermore the paper proves that periodic component is generated by the unbalanced nature of distribution systems. Another result in this paper is the algorithm design of an zero sequence current digital filter with noise reduction effect via discrete random signal processing method.