1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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.)

9. Interharmonics in Standards
IEC 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: Hz Flicker Based Limits. Otherwise: Due Consideration & Develop Appropriate Limits Case by Case
138 kV Harmonic Voltage Limits: 1.5% Individual, 2.5% Total

10. 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

11. 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 ~ % Total Interharmonic Voltage Distortion
Cycle-to-Cycle Change with 0.64% TIHVD (Measured Magnitudes, Assume Angle and Specific Frequency)

12. 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

13. 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?

14. TIHVD Relationship to HVDC Mvars (20 MW N)
(Mvar/25) 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

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

16. Distortion vs. Mvar Flow (30 MW North)

17. 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)

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

19. 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?

20. 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

21. 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

22. 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)

23. 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

24. Questions?