Distance Protection Relay Transient Decay Detection
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Solution Overview
Problem
Distance protection relays using capacitive voltage transformers (CVTs) face challenges with transient transition effects during faults, leading to delayed fault location determination and increased computing power requirements for compensation, while inductive voltage converters become uneconomical at higher voltages.
Innovation Solution
Assigning change vector amounts between successive time steps and determining a change limit value to assess the decay of transient effects, allowing for reliable fault location determination before effects subside, using the last line impedance value for tripping when a predetermined number of change amounts meet the limit, and focusing on the reactance component to minimize offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If capacitive voltage transformers (CVTs) are used for voltage measurement above 100 kV, then the economic feasibility is improved, but the transient transition effects during faults worsen the fault location determination accuracy
Solution Approach 1:
The patent applies preliminary action by continuously monitoring the amount of change in line impedance values before a fault occurs and establishing a baseline of transient behavior. This pre-established understanding of transient characteristics enables the system to quickly distinguish between normal transient effects and actual fault conditions immediately upon fault occurrence, without requiring waiting periods or complex real-time compensation calculations.
Solution Approach 2:
The patent changes the parameter being monitored from raw line impedance values to the amount of change in these values over time. By focusing on the rate of change rather than absolute values, the method naturally filters out transient effects which manifest as temporary variations, while genuine faults produce sustained changes in the amount of change parameter, enabling accurate fault detection despite using CVTs.
2Measurement precision
If a fixed predefined period is waited for transient effects to decay, then the fault location determination accuracy is improved, but the tripping time is increased
Solution Approach 1:
The patent implements feedback by continuously calculating the amount of change in line impedance values and comparing it against predetermined thresholds during the fault event. This real-time feedback mechanism allows the system to immediately identify when transient effects have sufficiently decayed based on actual observed behavior rather than waiting for a predetermined time period, enabling rapid and accurate fault location determination.
Solution Approach 2:
The patent applies dynamics by making the waiting period dynamic rather than fixed. Instead of waiting for a predetermined time period, the system adaptively determines when transients have decayed by monitoring the amount of change in impedance values in real-time. This dynamic approach allows the tripping decision to be made as soon as the transient effects naturally subside, minimizing loss of time while ensuring accuracy.
3Measurement precision
If recursive filters are used to compensate for transient effects, then the fault location determination accuracy is improved, but the computing power requirements and settling time are increased
Solution Approach 1:
The patent employs a simple, computationally inexpensive approach by directly measuring and comparing the amount of change in line impedance values against predetermined thresholds, rather than using complex recursive filters. This 'cheap' method requires minimal computing power and provides sufficient accuracy for fault location determination, eliminating the need for resource-intensive compensation algorithms.
4Measurement precision
If inverse transmission functions are used to improve transmission behavior, then the measurement precision is improved, but the device complexity and requirement for precise mathematical models are increased
Solution Approach 1:
The patent extracts only the essential information needed for fault detection by focusing solely on the amount of change in line impedance values. Rather than applying complex inverse transmission functions that require precise mathematical models of the CVT and impedance determination methods, the invention extracts the critical transient behavior characteristic and uses simple threshold comparison, significantly reducing device complexity while maintaining measurement precision.
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 early and reliable generation of trip signals independent of voltage transformer type, reducing computing power needs and ensuring accurate fault location within the monitored zone, even near the zone boundary, with minimal parameters and rapid arc detection.
Implementation Method 1
a line impedance value is determined in predetermined time steps
Implementation Method 2
each time step is assigned the amount of change of a change vector between the line impedance value determined for the respective time step and the one for the preceding time step
Data Source
Figure 1
Figure 2~3
AI summary
A method for triggering a distance protection relay monitoring a zone is described, in which a line impedance value is determined at predetermined time steps.In order to enable reliable fault location despite the use of voltage transformers with unfavorable transmission characteristics, even before transient transition effects have decayed, it is proposed that each time step be assigned the change magnitude of a change vector between the line impedance value determined for the respective time step and the value of the preceding time step, as well as a change magnitude limit value (10) determined from the line impedance value determined for the respective time step and a zone limit impedance value, and, if a predetermined number of change magnitudes assigned to each time step are below the change magnitude limit value (10) assigned to the respective time step, the line impedance value of the last time step is output to generate a trip signal (8) as a function of the zone limit impedance value.