Fault Current Detecting Circuit Surge Discrimination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing fault current detecting circuits in electric power systems suffer from delayed trip control and potential erroneous operations due to surge signals, leading to unnecessary power cutoffs and damage.
Innovation Solution
A fault current detecting circuit that includes a current detection unit, first and second comparing circuit units, and a trip determining unit, where the trip determining unit outputs a trip control signal only when specific output signals are maintained for a short period of 100 microseconds, and a third comparing circuit unit compares the current detection signal with a current detection limit reference value to differentiate between fault and surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the trip determining unit waits for a predetermined period (1 millisecond) before outputting the trip control signal, then the reliability of fault detection is improved, but the response time is delayed
Solution Approach 1:
The trip determining unit performs preliminary evaluation by checking whether the first and second output signals are simultaneously received before starting the timing measurement. This preliminary action allows the system to quickly identify obvious fault conditions without waiting for the full predetermined period, thereby reducing response time while maintaining reliability.
Solution Approach 2:
The timing mechanism is made dynamic by continuously monitoring the simultaneous reception of output signals during the predetermined period. If the signals remain simultaneous throughout the period, the trip control signal is output; otherwise, timing is stopped. This dynamic approach allows flexible response based on actual signal conditions.
2Speed
If the trip determining unit outputs the trip control signal when the first and second output signals are simultaneously received, then the response speed is improved, but erroneous operation due to surge signals increases
Solution Approach 1:
The system performs preliminary verification by checking whether the simultaneous reception of first and second output signals is maintained throughout the predetermined period before outputting the trip control signal. This preliminary action prevents erroneous operation by surge signals that may cause temporary simultaneous signal reception, while still enabling fast response to genuine faults.
Solution Approach 2:
The trip determining unit continuously monitors the status of output signals during the predetermined period and uses this feedback to determine whether to output the trip control signal. If the simultaneous signal condition is not maintained throughout the period, the system feedbacks to stop timing and prevents erroneous tripping.
3Reliability
If a predetermined period of 1 millisecond is used for timing, then the reliability of distinguishing fault from surge is improved, but the response time is excessively delayed
Solution Approach 1:
The trip determining unit performs preliminary evaluation of signal simultaneity before initiating the timing process. This preliminary action enables the system to quickly identify clear fault conditions and potentially complete the timing process faster than the full 1 millisecond, reducing delay while maintaining reliable discrimination capability.
Solution Approach 2:
The timing process is made dynamic and adaptive rather than fixed. The actual timing duration may be shorter than 1 millisecond if the simultaneous signal condition is clearly met, allowing the system to respond faster to genuine faults while maintaining the reliability threshold for fault-surge discrimination.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The fault current detecting circuit includes: a current detection unit (200) that outputs a current detection signal; a first comparing circuit unit (300) that compares the current detection signal with a predetermined reference current value and outputs a first output signal; a differentiator (400) that differentiates the current detection signal to output a change slope of the current detection signal; a second comparing circuit unit (500) that compares the change slope with a predetermined reference change slope value and outputs a second output signal; a third comparing circuit unit (700) that compares the current detection signal with a predetermined current detection limit reference value and outputs a third output signal; and a trip determining unit (600) that outputs a trip control signal only when the first output signal and the second output signal are maintained to be received and the third output signal is not received.