Super-capacitor Power Supply Circuit Ground Fault Protection
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Solution Overview
Problem
Existing power supply circuits for super-capacitor storage units in railway vehicles fail to effectively detect and break fault currents due to insulation losses to ground, leading to potential device damage or fire, as fuses are not suitable for currents within the operating threshold and may not immediately detect low but prolonged fault currents.
Innovation Solution
A power supply circuit that includes a high-speed circuit breaker and a differential relay connected in series along the negative bus between the super-capacitor storage unit's terminal and grounding point, allowing for automatic disconnection of the unit from the high voltage source upon detection of fault currents, with the differential relay generating an activation signal for the circuit breaker to manage both high and low current faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fuse is used on the negative bus to protect against fault currents, then the device structure is simple, but the fuse cannot detect and break fault currents of the same magnitude as operating current, allowing dangerous low-level faults to circulate indefinitely
Solution Approach 1:
The patent replaces the mechanical fuse system with an electronic protection system consisting of a differential relay and high-speed circuit breaker. The differential relay uses electrical measurement to detect ground leakage currents, and the circuit breaker uses electromagnetic actuation for rapid disconnection. This substitution enables detection and interruption of low-magnitude fault currents that would otherwise pass undetected through a fuse, directly resolving the reliability issue while accepting increased system complexity.
2Reliability
If a high-speed circuit breaker and differential relay are added to detect and break fault currents, then the reliability improves, but the device complexity and cost increase
Solution Approach 1:
The patent merges the functions of ground fault detection and circuit interruption into a coordinated system where the differential relay and high-speed circuit breaker work together as an integrated protection unit. The relay detects ground leakage on the negative bus and directly actuates the circuit breaker, creating a unified response mechanism. This merging optimizes the complexity-reliability tradeoff by using two specialized components in concert rather than multiple independent protection devices.
Solution Approach 2:
The differential relay serves as an intermediary between the fault condition and the circuit breaker actuation. It continuously monitors the negative bus for ground leakage currents, compares them against threshold values, and only triggers the high-speed circuit breaker when genuine fault conditions are detected. This intermediary function prevents spurious tripping while ensuring reliable fault interruption, managing the complexity by adding intelligent control logic.
3Object-affected harmful factors
If fuses are used for protection, then the cost is low, but they cannot detect prolonged low-level fault currents that cause overheating and potential fire
Solution Approach 1:
The differential relay implements continuous feedback monitoring of the negative bus for ground leakage currents. It maintains constant surveillance of the electrical state, comparing instantaneous current values against predetermined thresholds and immediately responding when fault conditions exceed safe levels. This feedback mechanism enables detection of prolonged low-level faults that would accumulate heat and cause damage, directly addressing the harmful factor of undetected overheating while managing the difficulty of detecting small currents through electronic measurement and comparison circuitry.
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
This configuration effectively prevents dangerous current circulation by detecting and isolating fault currents, reducing the risk of device damage or fire, and eliminates the need for a fuse and additional high-speed circuit breaker on the positive bus, while maintaining safety and moderate cost.
Implementation Method 1
differential relay which are connected in series along the negative bus... the differential relay being capable of generating an activation signal of the high speed circuit breaker in response to a fault current circulation
Implementation Method 2
high speed circuit breaker and a differential relay which are connected in series along the negative bus... means for disconnecting the super capacitor storage unit from the high voltage feeding source
Data Source
Figure 1
AI summary
A Power supply circuit for an on board energy source or storage device and particularly for a super-capacitor storage unit, the said super-capacitor storage unit consisting in a plurality of super-capacitors interconnected one to the other, the said super-capacitor storage unit having a first and a second terminal the circuit comprising a positive bus connecting the first terminal of the said super-capacitor storage unit to a positive pole of a DC high voltage feeding source and a negative bus connecting the said second terminal of the super-capacitor storage unit to a negative pole of the said DC high voltage feeding source, the negative bus being connected to the ground at a certain grounding point. According to the invention the said circuit further comprises means for disconnecting the super-capacitor storage unit from the high voltage feeding source in response to the detection of fault currents circulation due to insulation losses to ground of the super-capacitor storage unit and in which power supply circuit the said means for disconnecting the super capacitor storage unit from the high voltage feeding source consist in a high speed circuit breaker and a differential relay which are connected in series along the negative bus, between said second terminal and the said grounding point, the differential relay being capable of generating an activation signal of the high speed circuit breaker in response to a fault current circulation.