1. Open Research and Future Standard Opportunities

2. Outline Digital Secondary Systems
Frequency and ROCOF Measurement Challenge
Total Vector Error vs. Magnitude and Phase Error
Overview—self explanitory.

3. Synchrophasor Considerations for Digital Secondary Systems
Veselin Skendzic
Schweitzer Engineering Laboratories

4. Remember When… The World Used to be Analog?
People answered the phone
Vinyl records ruled the world
Tape recorders were cool
Amplifiers were linear
Movies were not compressed

5. Digital Secondary Systems
Promise to:
Consolidate large amounts of data over a few fibers
Reduce expensive copper connections
Improve substation EMC performance
Improve accuracy (reduced CT burden)
Improve safety (fiber based LPITs)
Reduce operating cost

6. But Where Do We Stand Today?
Limited deployment with multiple pilot projects
Equipment availability is improving fast
Vigorous standardization work:
IEC series GOOSE, MMS, Time requirements and much more
IEC Sampled Values
IEC PTP Power Profile
IEC Low Power Instrument Transformers
IEC LPIT digital interface
IEC Stand Alone Merging Units
IEC IT Electronic Datasheet (TEDS)

7. DSS Standard Relationship
IEC

8. Synchrophasors and Digital Secondary Systems
DSS system standards are built with Synchrophasors in mind
Synchrophasors inspired key DSS concepts (precise time synchronization, group delay compensation)
Network based (terrestrial) time distribution improves system reliability

9. Key Mechanism Examples

10. IEC 61869-6 Frequency Response Mask

11. Anti-Aliasing Filter Attenuation Requirements
Accuracy Class
Filter Attenuation ( f  fs-fr )
Protection
 20 dB 1
0.5
0.2
 28 dB
0.1
 34 dB

12. IEC Sampling Rates
Rates are independent from power system frequency
Preferred rates are integer multiples of 50 & 60 Hz

13. IEC 61869-9 Maximum Processing Delay Time
Application
Maximum Processing Delay
High Bandwidth DC (closed loop control)
25 s
Time-critical low bandwidth DC control
100 s
Protection
2 ms
Quality Metering
10 ms
Merging Unit is responsible for compensating the data acquisition chain Group Delay

14. IEC 61869-13 Dynamic Response Requirements
Fully offset fault waveform passing through a linear system with 1Hz corner frequency (no saturation)

15. DSS Open Issues
Synchrophasor applications need full time stamp (being added in IEC )
Automated exchange of IT calibration and nameplate data (IEC TEDS standard project)
Higher sample rate support for emerging applications
Cybersecurity

16. Difficulty with Frequency and ROCOF measurement
Allen Goldstein
NIST

17. Frequency and ROCOF Many ways to measure:
Zero Crossing
Peak detection
Hilbert Transform
Fourier techniques
Derivative of estimated phase
etc.
All for these have issues when measuring power system F and dF:
Harmonics, interharmonics and noise shift the zero crossing times
Discrete Fourier transform leakage
Error and noise in phase estimation
Non-ideal filtering and aliasing

18. Frequency and ROCOF are very important
We have come a long way
We need to trust the measurements
IEC TC95 ( ) and ANSI 81 are protection devices
standards to not include requirements performance frequency measurement output
Compliant PMUs can be trusted
Vibrating Reed Frequency Meter
Source: StackExchange,

19. Total Vector Error vs. Magnitude and Phase Error
Allen Goldstein
NIST

20. TVE vs ME and PE
TVE is a SCALAR value equal to the MAGNITUDE of the difference between the PMU reported synchrophasor (a vector) and a REFERENCE synchrophasor (another vector)
The difference between two vectors is, of course another vector and TVE is the magnitude of that vector
TVE is a very convenient term to calculate, state, and to compare against requirements.
However it makes no sense to add or subtract two TVE values because the vector ANGLE information has been lost.
Also, when trying to analyze PMU error causes, TVE is not very helpful

21. Magnitude Error and Phase Error
𝑀𝐸= 𝑋 𝑚 𝑡 𝑛 − 𝑋 𝑚 𝑡 𝑛 2
Phase Error
𝑃𝐸= ∅ 𝑡 𝑛 - ∅ 𝑡 𝑛
TVE 𝑇𝑉𝐸= 2(1+𝑀𝐸)(1− cos 𝑃𝐸 + 𝑀𝐸 2

22. Chinese PMU Standard
Source: NASPI: Chinese PMU Standard, Dynamic Testing and Future Applications, Tianshu Bi et al

23. Understanding PMU errors
Magnitude Error
Exposes issues with scaling
A/D Scaling
A/D Linearity
Input Gain
PMU filter gain/rolloff
Noise
Phase Error
Exposes issues with timing
Timing offset
Jitter
Exposes issues with PMU Filter phase shift
Filters have group delay that the PMU must correct for.