Electric Relay Protection for Fluctuating IDMT Trip Timing
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Solution Overview
Problem
Inverse definite minimum time (IDMT) relays in electric systems face challenges in accurately predicting operating times due to strongly fluctuating signal levels, making it difficult to determine when a trip condition exists.
Innovation Solution
A method and apparatus that monitor a signal's magnitude and count the time it exceeds a threshold, calculating an operate time based on the signal's magnitude and comparing it to the counted time to determine if a trip condition is met, using a time counter and calculation means to simplify and accurately implement protection in electric systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an integrating timer is used to calculate operating time based on signal magnitude and duration, then the protection can respond to variable signal levels, but it becomes very difficult to predict the resulting operating time in advance
Solution Approach 1:
The patent segments the operating time calculation into discrete time intervals (e.g., 1ms, 10ms, 100ms) and uses separate counters for each interval. This allows the system to accumulate time in predictable increments while still responding to variable signal levels, resolving the contradiction between adaptability and predictability.
Solution Approach 2:
The patent pre-calculates and stores operating time values in lookup tables before operation. These tables contain pre-computed time values for different signal magnitudes and time intervals, allowing the system to quickly retrieve predictable operating times without complex real-time calculations, thus maintaining both adaptability and prediction accuracy.
2Speed
If the relay operates as an inverse time relay with operating time inversely proportional to current magnitude, then the protection responds faster to higher currents, but it becomes difficult to accurately calculate theoretical operating time when signal levels fluctuate strongly
Solution Approach 1:
The patent implements dynamic time interval adjustment where the counter increment rate changes based on the measured signal magnitude. For higher currents, the system uses shorter time intervals (faster counting), while for lower currents, it uses longer intervals. This dynamic adaptation maintains inverse-time characteristics while enabling accurate tracking even with fluctuating signals.
Solution Approach 2:
The patent replaces complex continuous mathematical integration with discrete digital counting mechanisms. Instead of continuously integrating variable current signals to determine operating time, the system uses digital counters that increment based on pre-defined time intervals, substituting mechanical/continuous calculation with digital/discrete measurement for greater precision and predictability.
3Measurement precision
If the relay acts as a definite time relay with predefined operating time, then the operation time is predictable and fixed, but it cannot adapt to different current magnitudes and their varying impact on fault severity
Solution Approach 1:
The patent creates a universal protection mechanism that can operate in multiple modes (inverse-time, definite-time, or hybrid) depending on configuration and fault conditions. The same hardware and software infrastructure supports different time-characteristic curves, making the system universally applicable to various protection requirements while maintaining both predictability and adaptability.
Solution Approach 2:
The patent allows dynamic adjustment of operating time parameters based on the measured signal characteristics. The system can modify the time interval, counter increment rate, and threshold values in real-time based on the magnitude and duration of the monitored quantity, enabling the same device to provide both fixed and adaptive time responses as needed.
Data Source
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AI summary
A method and apparatus for protection in an electric system, the apparatus (30) being configured to monitor a signal indicative of a characteristic quantity in the electric system (10, 20, F1, F2, F3), count, by a time counter, a time during which a magnitude of the monitored signal exceeds a first threshold value, in response to the magnitude of the monitored signal being equal to or smaller than a second threshold value, calculate an operate time on the basis of the magnitude of the monitored signal, and in response to the magnitude of the monitored signal being greater than the second threshold value, calculate the operate time on the basis of the second threshold value, and in response to the time counted by the time counter being equal to or exceeding the calculated operate time, signal a trip condition.