Transmission Line Faulted Phase Detection With Lumped Voltage Compensation
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Solution Overview
Problem
Existing faulted phase detection methods in AC power systems face sensitivity issues due to System Impedance Ratio (SIR) variations, particularly when the SIR is close to zero, leading to inaccurate fault detection and increased costs with higher sampling rates for accurate calculations.
Innovation Solution
A faulted phase detection method based on a time domain lumped parameter differential equation, utilizing a low sampling rate (1 kHz to 4 kHz), which compensates for voltage variations and effectively identifies faulted phases by analyzing instantaneous voltage values in phase-phase/phase-ground loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage compensation based on distributed parameter and travelling wave transmitting formula is used, then sensitivity for faulted phase detection is improved, but sampling rate requirement increases to 1 kHz or higher, increasing cost and technical challenge
Solution Approach 1:
The patent changes the mathematical model from distributed parameter travelling wave formula to lumped parameter differential equation, allowing accurate faulted phase detection at lower sampling rates (500 Hz or below) while maintaining sensitivity. This parameter change in the calculation model resolves the contradiction between detection sensitivity and sampling rate requirements.
Solution Approach 2:
The patent adopts a simpler lumped parameter model that requires lower sampling rates and less computational resources, effectively replacing the complex distributed parameter model with a more economical solution that achieves the same detection accuracy at reduced cost and technical complexity.
2Ease of manufacture
If faulted phase detection is based on fault component phase voltages, then the method is simple to implement, but sensitivity fails when SIR is close to zero, leading to inaccurate detection
Solution Approach 1:
The patent performs preliminary voltage compensation calculation using the lumped parameter differential equation before faulted phase detection. This preliminary action compensates for the effect of system impedance ratio, ensuring accurate detection even when SIR is close to zero, while maintaining the simplicity of the overall implementation.
Solution Approach 2:
The patent introduces voltage compensation as an intermediary step that mediates between the simple fault component voltage comparison method and the accurate faulted phase detection requirement. The compensation calculation serves as a bridge that maintains detection accuracy without complicating the overall system.
3Ease of manufacture
If lumped parameter voltage compensation method is used, then implementation is simple and widely applicable, but it is not suitable for time-domain protections
Solution Approach 1:
The patent transforms the static lumped parameter voltage compensation method into a dynamic time-domain applicable method by using differential equations that operate on instantaneous values. This makes the simple lumped parameter approach suitable for time-domain protection while maintaining its implementation simplicity.
Data Source
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AI summary
Provided are a method and a control system for detecting faulted phases of transmission lines in an AC power system and a protective relay using the same. The method includes sampling electric signals at one end of the transmission lines at a series of time points; computing instantaneous voltage values of electric signals at compensated points on the transmission lines from the values of the sampled electric signals based on a time domain lumped parameter differential equation for the transmission lines for the series of time points; recording the computed instantaneous voltage values of the electric signals; computing fault component or sudden-change of the instantaneous voltage values of the electrical signals; detecting the faulted phases or fault types by comparing the calculated fault component of the instantaneous voltage values at the preset compensated points; and generating signals indicating the faulted phases or fault types.