Differential Protection Time Alignment for Process Bus Delay Errors
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Solution Overview
Problem
In power line differential protection systems, the use of satellite positioning module-generated PPS signals as reference time for time alignment can result in significant errors due to transmission delays and interference in substation automation systems employing process buses, leading to potential safety risks during faults.
Innovation Solution
A time alignment method involving resampling current sampled values based on the satellite positioning module's PPS signal generation moments and performing Fourier transforms to align current Fourier values, considering the transmission delay and using the PPS signal generation moments as reference for accurate time alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the differential protection device uses the PPS signal generated by its own satellite positioning module as the reference time for time alignment, then the device complexity is reduced and ease of operation is improved, but the measurement precision of time alignment deteriorates due to transmission delays in process bus communications
Solution Approach 1:
The patent introduces an intermediary mechanism by using the PPS signal generation moment from the merging unit (which receives current from the current transformer) as the reference time, rather than using the PPS signal from the differential protection device itself. This intermediary reference point eliminates the transmission delay variable in the process bus communication, thereby improving time alignment precision while maintaining operational simplicity.
2Adaptability or versatility
If the differential protection device receives current sampled value packets from the merging unit via the process bus, then the substation automation system evolves to a more advanced architecture, but the reliability of time alignment deteriorates due to large errors in transmission delays
Solution Approach 1:
The patent applies preliminary action by capturing the PPS signal generation moment at the source (merging unit) before the current sampled values are transmitted through the process bus. By recording this reference time moment in advance and using it for time alignment, the system eliminates the uncertainty introduced by variable transmission delays, thereby maintaining reliability in the advanced process bus architecture.
3Device complexity
If the differential protection device uses its own PPS signal as reference time, then the device can operate independently without complex synchronization, but the accuracy of differential current calculation deteriorates during rapid current changes such as faults
Solution Approach 1:
The patent uses an intermediary reference time source from the merging unit's PPS signal generation moment, which is closer to the current transformer and less affected by process bus transmission delays. This intermediary reference improves the accuracy of differential current calculation during rapid current changes while keeping the device complexity manageable by leveraging existing infrastructure.
4Adaptability or versatility
If the system uses process bus communication for current sampled values, then the substation automation system achieves better integration and communication capabilities, but the time alignment accuracy deteriorates due to transmission delays and interference
Solution Approach 1:
The patent implements preliminary action by recording the PPS signal generation moment at the merging unit before the current sampled values undergo transmission through the process bus. This pre-captured reference time allows the system to maintain high measurement precision despite the benefits of integrated process bus communication, as the reference point is established before transmission delays can affect it.
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
This method improves the accuracy of time alignment and reliability of differential current calculations, reducing the likelihood of incorrect protection decisions during rapid current changes, such as faults, by accounting for transmission delays in process bus communications.
Implementation Method 1
a sampling moment of a current sampled value whose count value is a first value in the plurality of current sampled values is a moment of generation of a PPS signal of a satellite positioning module of the merging unit
Implementation Method 2
performing Fourier transform on the plurality of current resampled values to obtain a plurality of temporally arranged current Fourier values
Data Source
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AI summary
A time alignment method for a differential protection device, the differential protection device (402, 404) and a differential protection system are disclosed. The time alignment method includes obtaining, from a merging unit, a plurality of current sampled values and a count value of each current sampled values (S510); resampling the plurality of current sampled values with sampling frequency of J points/cycle to obtain a plurality of current resampled values (S520); and performing Fourier transform on the plurality of current resampled values to obtain a plurality of temporally arranged current Fourier values, the plurality of current Fourier values includes a reference current Fourier value corresponding to the sampling moment of the current sampled value whose count value is the first value in the plurality of current sampled values, and the reference current Fourier value is determined based on the reference current resampled value and the J-1 current resampled values that temporally arranged before the reference current resampled value (S530). Fig. 5