Michael B. Marz CIGRE Grid of the Future October 12, 2015 Mackinac Back-to-Back Voltage Source Converter HVDC Interaction with Power Line Carrier and Automatic Meter Reading Communications Michael B. Marz CIGRE Grid of the Future October 12, 2015

Presentation Outline Mackinac Back-to-Back VSC HVDC Project Need: Flow Control in a Weak System (2013 CIGRE GOTF) Design: Hardware and Control (2014 CIGRE GOTF) Power Line Carrier Issue PLC Equipment Failure High Frequency Resonance Investigation Resolution Automatic Meter Reading Issue HVDC and AMR Interharmonic Interaction AMR Sensitivity to and HVDC Generation of Interharmonics Possible Resolutions Being Considered Conclusions

Mackinac VSC HVDC Flow Control Weak System Prevented Maintenance Outages System Split to Limit Flows In Service Summer 2014 MW Fully Controllable at any Short Circuit Level Independent Var Output STATCOM, Island and Blackstart Operation Oscillation Damping ACLE – No SPS/RAS

Two Level Converter Voltage Symmetrical Monopole Cascaded Two Level 200 MW Bi-Directional, +/- 100 Mvars per Terminal 71 kV DC/87 kV AC (9 Cells/Valve) 138 kV System Modular Multi-Level Like Voltage Two Level Converter Voltage Cascaded Two Level Converter Voltage

VSC HVDC Distortion and Filtering Two Level – Significant Distortion and Filtering Cascaded Two Level – Less Distortion and Filtering Modular Multilevel Converter – Smaller Voltage Steps so Very Little Harmonic Distortion and No Filters Needed IGBTs (Insulated Gate Bipolar Transistors) Allow High Speed Controls Necessary for VSC Stability Benefits, but Produce Interharmonics for all Three Designs Mackinac (Cascaded Two Level): Non-Integer Pulse Number to Prevent DC Cap Damage Low Level Interharmonics Not Harmful to Power System Equipment, but Can Affect Communications on Power Lines

Local Power Line Carrier Issue High Voltages in PLC Equipment due to High Frequency Resonance Local PLC Failed Soon After HVDC Energization Nearby PLC Equipment Eventually Failed Source Wide Band High Frequency (kHz) Signals IGBT Switching Transients (Also Exists for Thyristors) Normally Attenuated by Transformer or Distance Nothing (but PLC) at Transmission Voltages to Resonate High Frequency PSCAD Model of System and PLC Power System Looks Very Different at kHz Frequencies Models Approximate, but Phenomena Modeled Resonance Involved PLC Line Trap, CVT Capacitance, and PLC Drain Coil, Appearing on PLC Amplifier

PLC Issue Resolution Wide Spectrum Noise: Retuning the PLC Impractical Option 1: Alternate Communication Method (Rejected) Option 2: Filtering at Source (Most Practical Solution) Add High Pass Filter Concerns: Cost and Time Modify 5th and 30th Harmonic Filter (30th to High Pass) IEEE 519 Distortion Limits Met Components Not Stressed Implementation Quick and Low Cost at Both Terminals

Mackinac and AMR Interharmonics Interharmonics: Any Non-Integer Multiple of Fundamental, i.e. Measures Non-Periodic (at 60 Hz) Distortion VSC HVDC Interharmonics Due to IGBT Switching Benefits Previously Discussed Thyristors (LCC) HVDC Does Not Produce Interharmonics AMR Systems Using Power Line Communications Used on Both Sides of Mackinac (more intensely on one side) “Smart” Meters Report Energy Usage and Track Outages Distort Voltage and/or Current for Two-Way Communication Signal Processing Algorithms Extract Non-Periodic Signals Error Checking and Multiple Attempts increase Reliability AMR Issues have Been Seen Near Other Interharmonic Sources (Arc Furnaces, Type 4 Wind Turbines, etc.)

Interharmonics in Standards IEC 61000-4-7 Defines 5 Hz “Bins,” Groups and Sub-Groups ATC Combines (RSS) 1st-16th Interharmonic Groups (TIHD) IEC “Reference” Levels: 0.2% Groups Below 50th, 0.3% for 200 Hz Bandwidths up to 9 kHz. To Allow Communications? IEEE 519: 0-120 Hz Flicker Based Limits. Otherwise: Due Consideration & Develop Appropriate Limits Case by Case 138 kV Harmonic Voltage Limits: 1.5% Individual, 2.5% Total

AMR Issues Near Mackinac Intermittent Communication Issues with a Minority, but Operationally Significant Number of Meters Issues at Both Terminals (More if Meters Used “Intensely”) Communication May Need to Wait for Reduced Distortion Issues Concentrated at Specific Stations and Meters Not Always Stations Closest to Mackinac Meter Age/Design (Technology) Feeder Voltage and Length Feeder Grounding No Other Interharmonic Issues (Light Flicker, Mechanical System Oscillation, Heating, CT Saturation, etc.) Levels Measured Not a Concern for Power Equipment

Local AMR Distortion Sensitivity AMR Filters Out Frequencies >1000 Hz (~16th Harmonic) Communication Issues Correlate to ~0.5% TIHVD AMR Sensitive to ~2% Cycle-to-Cycle Voltage Change Measured AMR ~0.25-0.4% Total Interharmonic Voltage Distortion Cycle-to-Cycle Change with 0.64% TIHVD (Measured Magnitudes, Assume Angle and Specific Frequency)

Individual Interharmonics at Three Locations HVDC Sustained AMR Short Duration Top: HVDC Inter-Harmonics Exceed AMR Interharmonics Middle: Similar HVDC and AMR Magnitudes Bottom: AMR Magnitude Exceeds HVDC

Mackinac MW, Mvar and TIHVD Data Blue TIHVD (%), Red HVDC MW/50. Green HVDC Mvars/50 One Month of 5 Minute Data (may not catch AMR data) TIHVD Relationship to HVDC MW? Mvars? Others?

TIHVD Relationship to HVDC Mvars (20 MW N) (Mvar/25)+0.6 - Varies with HVDC MW, Load, Reactive Resources (Caps, Reactors), Generation/System Strength, Failed IGBTs, etc. How? Why? Is HVDC Mvars Output Only Reflecting System Strength/Generation? Load? Reactive Resources? TIHVD has about a 0.3% Minimum when HVDC On

Interharmonics vs. MW Flow Two Day Plot – Orange MW/50, Grey Mvars/35 + 0.6, Blue Mackinac North TIHVD (%)

Distortion vs. Mvar Flow (30 MW North)

HVDC from STATCOM to 40 MW North TIHVD 0.95% to 0.7% When Leaving STATCOM Mode From 0.7% to 0.5% as MW & Mvars Adjust System Strength Unchanged (4 Second Data)

Interharmonics and Local Generation Top: TIHVD vs. HVDC MW Transferred (MW/100) Bottom: TIHVD vs. Local Generation MW (MW/30)

Interharmonics and Local Capacitor Status Nine Day Plot: Blue TIVD, Other Lines Cap Status More Caps Reduce Distortion? Filtering Effect? HVDC Mvar Reduction? At What MW Levels?

Interharmonics and Local Load Five Day Plot: Blue Local TIHVD, Dark Blue MW Load/7.5 +1, Orange HVDC MW N-S/10, Grey HVDC Status, Orange Line Status

Effect with One IGBT (of 1784) Failed 20 MW South Flow (Mvar Flow Varies) Average TIHVD Shown, Failed Phase Worse All Three Phases Worse than with No Failed IGBTs Left - No Failed IGBTs Right – One Failed IGBT Pack

AMR Issue Resolution Options Add Filtering At Source: Distortion Too Wide Band At Load: Interfere with AMR Operation? Modify HVDC Controls Loss of Functionality and Maintenance & Warranty Concerns. Is it Possible? A Research Project Modify System Strengthen System? Add Capacitors? Detune Resonances? Possible for All Conditions? Too Expensive? Modify HVDC Operation: Difficult Too Many System Conditions to Consider Reliability Top Priority Update AMR: Meters with Reduced Distortion Susceptibility. Available? Different Communication Medium (RF, Cellular, Microwave)

Conclusions Mackinac: Serving Its Purpose – Facilitating Maintenance Outages Occasionally Turned Off to Facilitate Meter Reading Long Term AMR Resolution Still Being Investigated Lessons Learned: Study High Frequency Issues – Especially if Power Line Carrier Installed Locally (High Pass Filter) Potential for VSC HVDC Interharmonics to Interfere with Power Line Communications The Same Problem Could Exist with Type 4 Wind Turbines Controls, Any IGBT Converter, Arc Furnaces, CFLs, etc. Industry Issue: Power Line Use for Communications

Questions?