Locomotive DC Bus Ground Fault Detection via Forcing Function
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Solution Overview
Problem
Locomotive electrical propulsion systems face challenges in detecting incipient ground faults due to transitory nature of ground conditions, leading to system shutdowns and difficulty in identifying the source of faults, especially when moisture-related issues cause excessive leakage currents that resolve by the time maintenance is performed.
Innovation Solution
A method involving a forcing function that applies a unique ground fault augmenting signal to electrical devices connected to a DC bus, allowing for rapid identification of incipient ground faults by magnifying the fault without increasing voltage stress, enabling quick detection and localization of the affected device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional leakage current monitoring is used, then ground faults can be detected, but the detection is unreliable due to the transitory nature of ground conditions and moisture-related variations
Solution Approach 1:
The system performs preliminary action by applying a forcing function to magnify incipient ground faults before they become critical failures. The forcing function proactively stresses the insulation system to reveal weaknesses early, allowing detection before the locomotive is shut down and moved to a shop where environmental conditions change and mask the fault.
Solution Approach 2:
The invention changes the parameter being monitored from steady-state leakage current to transient response characteristics under forced stress conditions. By applying a forcing function that creates controlled voltage stress, the system transforms the detection approach to measure how the insulation responds to changing conditions, revealing incipient faults that are invisible under normal operating conditions.
2Reliability
If the locomotive is shut down for repairs when a ground fault occurs, then safety is ensured, but the fault source cannot be identified because moisture has dried out
Solution Approach 1:
The system takes preliminary action by detecting and identifying incipient ground faults while the locomotive is still in service, before shutdown occurs. The forcing function is applied during operation to reveal faults early, allowing the specific faulty component to be identified before the locomotive is moved to the shop where environmental changes would mask the fault.
Solution Approach 2:
The invention replaces the mechanical approach of shutting down and physically inspecting components with an electrical diagnostic system that uses forcing functions and transient response analysis. This substitution allows remote, non-intrusive identification of the faulty component through electrical measurements rather than mechanical inspection after shutdown.
3Reliability
If maintenance personnel inspect all equipment upon arrival at the shop, then no fault is missed, but valuable time and resources are wasted on fault-free equipment
Solution Approach 1:
The system extracts and isolates the specific component with the incipient ground fault from the entire propulsion system using the forcing function diagnostic. By applying the forcing function to individual components or phases and analyzing the transient response, the system identifies the exact location of the fault, allowing maintenance personnel to focus only on the affected component rather than inspecting all equipment.
Solution Approach 2:
The invention creates an electrical signature or pattern of the fault through the forcing function response that serves as a diagnostic copy of the fault condition. This electrical fingerprint allows remote identification of the faulty component's identity and location, enabling maintenance personnel to retrieve this information and focus their physical inspection efforts only on the specific component that exhibits the abnormal response pattern.
Data Source
AI summary
Method, apparatus and computer-readable code are provided for detecting a location of an incipient ground fault in an electrical propulsion system of a relatively large land-based vehicle, such as a locomotive. A method embodying aspects of the present invention allows to simultaneously apply a forcing function to one or more electrical devices connected to a direct current (dc) bus. The forcing function is configured to magnify (without voltage stress to such devices) an incipient ground fault that may be directly associated with a given electrical device. This enables to quickly identify the incipient ground fault and to uniquely identify the electrical device likely to be experiencing the incipient ground fault.