Single-Phase Ground Fault Detection in Low Current Networks
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Solution Overview
Problem
Current methods are ineffective for detecting and locating single-phase ground faults in low current grounded power-distribution networks, particularly those with neutral points grounded via an arc suppression coil, due to low fault currents and high resistance grounding, leading to reliability and safety issues.
Innovation Solution
A method and device that detect and locate single-phase ground faults by monitoring transient voltage and current signals at multiple feeder locations, using band-pass processing to extract characteristic values, and synchronously picking up signals across phases to determine zero-sequence voltages and currents, with a feeder monitoring device equipped with capacitive sensors and Rogowski coils to accurately identify fault points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power-distribution network uses low current grounding to improve reliability during single-phase ground faults, then the system can continue operating for 1-2 hours, but the fault detection becomes extremely difficult due to low fault currents and high resistance grounding
Solution Approach 1:
The patent introduces an intermediary signal injection mechanism where a detection signal is injected into the power distribution network during single-phase ground faults. This intermediary signal acts as a mediator between the fault condition and the detection system, enabling the detection of ground faults even when the natural fault current is too low to be detected by conventional methods. The injected signal creates a measurable response that reveals the fault location without disrupting the low-current grounding operation.
2Device complexity
If conventional detection methods are used, then the system structure remains simple, but they fail to detect single-phase ground faults in low current grounded networks due to CT saturation and low signal levels
Solution Approach 1:
The patent applies preliminary action by injecting a detection signal before the actual fault current flows through the system. This preliminary signal is introduced through the neutral point of the transformer, allowing the detection system to establish a reference measurement state before the low-current fault condition develops. By performing this preliminary signal injection, the system can detect ground faults with high precision without requiring complex additional hardware during the actual fault event.
3Duration of action of stationary object
If the fault is not cleared quickly after occurrence, then the system can maintain operation temporarily, but overvoltage caused by the ground fault may lead to power system accidents such as cable explosion, PT burnout and bus burnout
Solution Approach 1:
The patent implements a feedback mechanism where the detection system continuously monitors the power distribution network for single-phase ground faults and provides immediate feedback when a fault is detected. The system measures the response to the injected signal and compares it against threshold values, providing real-time feedback about the fault condition. This feedback enables rapid fault identification and location, allowing the protection system to clear the fault before overvoltage damage can occur, thus resolving the contradiction between maintaining operation and preventing damage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables timely and accurate detection and location of single-phase ground faults, improving power supply reliability and safety by capturing low-level transient signals without CT saturation, and providing precise fault indication on a GIS map.
Implementation Method 1
picking up a voltage signal on the power distribution line through a capacitive voltage sensor
Implementation Method 2
picking up a current signal through a Rogowski coil
Data Source
Figure 1~2
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Figure 5
AI summary
A method and system for detecting and locating a single-phase ground fault on a low current grounded power-distribution network, comprising: respectively testing and picking up the voltage signals and current signals at multiple positions on each phase feeder (61), and determining the corresponding transient voltage signals and transient current signals according to the extraction of the voltage signals and the current signals (62); when the change in the transient voltage signals and the transient current signals exceeds a preset threshold (63), synchronously picking up the voltage signals and current signals at multiple positions on a three-phase feeder (64); calculating corresponding zero-sequence voltages and zero-sequence currents according to the voltage signals and current signals synchronously picked up at multiple positions on the three-phase feeder (65), and then extracting the steady-state signal and transient signal of the zero-sequence voltage and zero-sequence current at each position on the three-phase feeder (66); and determining a specific fault location on a faulty line according to the steady-state signal and the transient signal (67). The method effectively detects and displays a single-phase ground fault on a low current grounded power-distribution network.