iec61850-9-2 process bus implementation on ieds · 2015. 9. 21. · 1 iec61850-9-2 process bus...
TRANSCRIPT
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IEC61850-9-2 Process Bus
Implementation on IEDs
Author: Roberto Cimadevilla
Co-authors: Iñigo Ferrero, José Miguel Yarza
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Overview
• Conventional / Process Bus Substations
• SV time alignment
• Sampling frequency change
• Frequency tracking
• Estimation of lost SV
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Conventional Substation
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Process Bus Substation
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• Currents and Voltages can be measured by several MU
• Each SV has a Sample Counter (smpCnt) used by the IED
that receives the frames to make the alignment:
• 50 Hz: 0 – 3999
• 60 Hz: 0 - 4799
• MU are synchronized (IRIG-B, PPS, IEEE1588). Reception
on PPS signal forces the sample number 0, the rest are based
on the internal MU clock
• SV from different MU can arrive at different times. Delays
due to:
• MU processing time
• Communication network
SV Alignment
MU works with 80samples/cycle
2ms delay considered
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SV Alignment
Sampling Frequency Change
• Two option to convert a conventional IED:
• Adapt the filters to work with the new sampling frequency
• Change the sample frequency and use the same filters
• Resampling was chosen to maintain the sampling rate of the conventional IED converted into a SV based IED so:
• The same digital filters and protection algorithms can be used
• Resampling algorithm is also required for the frequency tracking
Newton third order polynomial
interpolation algorithm based on the
divided differences
MU: 80 s/c
IED: 32 s/c
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Frequency Tracking
• Sampling frequency of the MU is fixed (80 samples per 50 / 60 Hz cycle) without changing with the frequency
• Resampling is used for frequency tracking, if SV are directly used, errors during off-nominal frequencies will appear.
• Frequency is measured based on zero-crossings
• Low pass filter and phase-shift filtering is used
• α Clarke transformation is used to obtain a voltage involving the three phases
• A third order polynomial interpolation is used to obtain 32 samples spanning exactly one cycle.
Frequency tracking: algorithm that modifies the time between
samples based on the frequency measurement to make the DFT
window expand exactly one cycle
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Resampling for 51 Hz
Sinusoidal voltage waveform with a rated RMS value and 51Hz
Same results with
direct sampling and
resampling
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ABSOLUTE ERROR
RELATIVE ERROR
Resampling for 50 Hz: 1st, 2nd and 3rd order pol.
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Harmonic Influence THD=20%
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Estimation of Lost SV
• SV can be lost
• Lost SV can generate phasor errors during one cycle
• Blocking will delay the operation for too long
Estimation on SV
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Estimation of Lost SV
• SV is consider as lost:
• Delay time
• Quality invalid
• Synchronized flag FALSE
• Estimation. Replaced by:
• Zeros
• Value of last SV
• New SV after lost SV
• Estimation of lost SV based on polynomial interpolation
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Estimation of 10 Lost SV
ERROR P1=-1.613%
ERROR P2=-0.063%
ERROR P3=-0.044%
ERROR P1=-0.022%
ERROR P2=-0.0086%
ERROR P3=-0.0061%
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Harmonic Influence with 5 Lost SV THD=20%
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• A time delay of 2 ms has been considered when time alignment is performed
• Changing from the MU sampling rate to the conventional relay sampling rate allows maintaining the digital filters and protection algorithms
• The resampling is done with a Newton third order polynomial interpolation: results have shown a very good accuracy even in the presence of harmonics
• Frequency tracking is needed because of the fixed sampling rate of the MU. Resampling is used
• Estimation of lost SV is based on the polynomial interpolation: results have shown a good accuracy for up to 5 consecutive lost SV in the presence of harmonics
Conclusions
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Thank you