Current Transformer Fault Detection Using Differential Voltage Comparison
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Solution Overview
Problem
Existing relays in electric power systems take too long to determine faults, particularly arc faults within switchgear or electric power devices, leading to potential system, device, and personal damage due to delayed trip signal generation.
Innovation Solution
An apparatus and method that quickly determine faults by using a current transformer to detect current and generate differential voltages, comparing these with reference voltages to generate a trip signal within 0.125 to 0.25 cycles, and optionally incorporating an optical sensor to enhance fault detection speed and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the relay uses RMS value calculation for 0.5 to 1 cycle to determine fault occurrence, then the fault determination accuracy is improved, but the trip output time increases to about 30ms
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing differential voltage values (first-order and second-order derivatives) of the current waveform before fault occurrence. When a fault occurs, these pre-computed differential values are immediately compared with reference values, eliminating the need for time-consuming RMS calculations during the fault event. This allows the relay to determine arc faults within 0.125 to 0.25 cycles while maintaining high accuracy.
2Reliability
If the relay uses general protection elements with voltage, frequency and differentiation, then the protection coverage is improved, but the fault determination time cannot satisfy high-speed trip requirements
Solution Approach 1:
The patent extracts and isolates the differentiation function from the general protection elements, dedicating specific circuitry (first differentiator and second differentiator) solely for computing voltage derivatives. This specialized extraction allows the relay to focus computational resources on rapid arc fault detection through differential voltage comparison, achieving high-speed tripping while maintaining comprehensive protection coverage for various fault types.
3Reliability
If the relay waits for RMS value input of 0.5 to 1 cycle, then the fault detection reliability is improved, but the system cannot protect against arc faults occurring within the waiting period
Solution Approach 1:
The patent implements the skipping principle by bypassing the traditional RMS value waiting period entirely. Instead of sequentially waiting for complete cycle data before analysis, the system immediately computes differential voltages from available current data and performs real-time comparison with reference values. This rushing through the detection process enables the relay to identify and respond to arc faults within 0.125 to 0.25 cycles, preventing system, device, and personnel damage that would occur during conventional detection delays.
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 rapid fault detection and prevention of damage by generating a trip signal in less than 0.25 cycles, improving the speed and reliability of fault determination in electric power systems.
Implementation Method 1
a current transformer configured to detect current supplied to the electric power system and output a current detection voltage
Implementation Method 2
a first-order differential voltage of the current detection voltage and a second-order differential voltage of the current detection voltage
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An apparatus for quickly determining a fault in an electric power system includes a current transformer, a current determination unit and a fault determination unit. The current transformer detects current supplied to the electric power system and outputs a current detection voltage. The current determination unit respectively compares the current detection voltage, the first-order differential voltage of the current detection voltage and the second-order differential voltage of the current detection voltage with predetermined first, second and third reference voltages. The fault determination unit determines whether a fault occurs based on the compared result of the current determination unit and generates a trip signal when it is determined that the fault has occurred.