Open Research and Future Standard Opportunities

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

Synchrophasor Considerations for Digital Secondary Systems Veselin Skendzic Schweitzer Engineering Laboratories

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

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

But Where Do We Stand Today? Limited deployment with multiple pilot projects Equipment availability is improving fast Vigorous standardization work: IEC 61850 series GOOSE, MMS, Time requirements and much more IEC 61850-9-2 Sampled Values IEC 61850-9-3 PTP Power Profile IEC 61869-6 Low Power Instrument Transformers IEC 61869-9 LPIT digital interface IEC 61869-13 Stand Alone Merging Units IEC 61869-16 IT Electronic Datasheet (TEDS)

DSS Standard Relationship IEC 60255-118-1

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

Key Mechanism Examples

IEC 61869-6 Frequency Response Mask

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

IEC 61869-9 Sampling Rates Rates are independent from power system frequency Preferred rates are integer multiples of 50 & 60 Hz

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

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

DSS Open Issues Synchrophasor applications need full time stamp (being added in IEC 61850-9-2) Automated exchange of IT calibration and nameplate data (IEC 61869-16 TEDS standard project) Higher sample rate support for emerging applications Cybersecurity

Difficulty with Frequency and ROCOF measurement Allen Goldstein NIST

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

Frequency and ROCOF are very important We have come a long way We need to trust the measurements IEC TC95 (255-187) 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, https://electronics.stackexchange.com/questions/326721/can-i-use-a-vfd-to-send-power-of-a-specific-frequency-to-a-frequency-meter/326728#326728

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

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

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

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

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.