atcllc.com

Mackinac HVDC Construction and Testing

Michael B. Marz

MIPSYCON

November 5, 2014

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• Back-to-Back VSC

• Controls Flow between

Michigan Peninsulas to

Allow Maintenance Outages

• Control Challenges: Weak

System and No RAS/SPS

• Compressed Schedule

• Operational Summer 2014

• Design, Construction,

Testing and Operation

Mackinac HVDC

The Need for Flow Control

• Weak UP & LP Systems

Carry Some W-E Bias Flow

• Thermal & Voltage Issues

• Fix by Splitting System

(Re-dispatch Impractical)

• Once Rare Later Common

• Split Deferred Maintenance

• Upgrading System Too

Expensive and Not Timely

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• Requirements – Control Power Flows

– Operate Under Weak System Conditions

– Not Exacerbate (Mitigate?) Area Voltage Issues

• Concerns – Cost, Losses and Maintenance Outages

– Operation During Faults and Outages

– Robustness – System Changes Can’t Make Obsolete

– No SPS, Only Use Local Measurements to Protect

Equipment and Maintain Stability

Project Requirements & Concerns

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Technology Selection

• Alternatives Considered – Series Reactors

– Phase Shifting/Variable Frequency Transformers

– Line Commutated/Voltage Source Converter HVDC

• Advantages of VSC HVDC – Can Operate Under Minimal Short Circuit Level

– Can Control Flow Regardless of System Changes

– Provides Dynamic Vars Independently at Each Terminal

– With Terminals Disconnected Can Act as Two STATCOMs

– Fast Real & Reactive Power Response to Contingencies

– Can Help Damp System Oscillations

– Islanded Operation and Blackstart Capability

– Eliminate Need for Special Protection System?

• 200 MW Bi-Directional, +/- 100 Mvars per Terminal

• Symmetrical Monopole Cascaded 2 Level Design

• Doubly Tuned 5th and 30th Harmonic filters

• 138 kV AC, 71 kV DC

Project Design – Equipment

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Two Level & Cascaded Two Level Topology

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• Voltage Like Modular Multi-Level Converter rather than

Two Level Converter

Two Level Converter Voltage

Cascaded Two Level Converter Voltage

Cascaded Two Level Design

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SVC Design Distortion

• Two Level – Significant Distortion and Filtering

• Cascaded Two Level – Less Distortion and Less

Filtering Required

• Modular Multilevel Converter – Smaller Voltage

Steps so Very Little Distortion and No Filtering

Interharmonics

• High Speed Controls Necessary for VSC Stability

Benefits Produce Interharmonics for all 3 Designs

• Non-Harmonic Switching (Mackinac 3.37 pulse)

VSC HVDC Distortion and Filtering

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• South Converter – Vector Current Control – Instantaneous P & Q Controlled Independently

– Fast Inner Control Loop Decouples Current (q & d)

– Outer Loop uses d for P or DC voltage and q for Q or AC

voltage control

• North (Weak System) Converter – Phasor Voltage Control – Direct Control of Converter’s Internal AC Voltage Magnitude

and Phase

– Magnitude Control Extended to PCC by Impedance Correction

– Phase Control Extended by Frequency Droop and Phase Angle

Offset to Adjust Synchronizing Power

– Damping Controller – Responds to Small, Continuous

Frequency Changes – Real Power Flow Varies From Set Value

Control Design – Normal Operation

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• Automatically Detect and Switch to Islanded Operation – Fixed Frequency and Voltage Mode with Droop settings

– Can Operate in Island Mode Indefinitely

• Post Contingency Quasi-Islanding Control – HVDC and a Single 69 kV line Serving Eastern UP

– Goal: Maintain Voltage and Angular Stability Using Only Local

Measurements (No RAS/SPS)

• AC Line Emulation (ACLE) – Triggered by Large Network Change (Angle Across HVDC)

– Power Order Recalculated to More Stable Level

• Maintains Voltage and Angular Stability

• Prevents Lines from Overloading

Control Design – Contingency Operation

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• Automatic Runback

• Phase Shifter Emulation?

• Uses Equivalent AC Line Flow – With Artificial Impedance

and Pre-Contingency Equivalent Phase Shift

• Dynamic Characteristics of a Large Synchronous

Machine

ACLE – AC Line Emulation

)sin( 2121

, X

VVP ACLEref

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• Relocate Existing Lines – Substation uses existing ROW

– 138 kV Lines (1 North, 2 South) Pass through Mackinac

• Build New AC Station – North and South Sides with HVDC Bypass

– South Sides Include New Reactors for Cables

• Build New DC Station – ATC Provided Roughly Graded Site

– Turnkey Project to Design, Fabricate, Furnish, Deliver,

Construct, Install, Test and Commission

– Controlled and Monitored Remotely.

– Local First Response Troubleshooting and Inspection

Project Components

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• Aggressive Because of Project Need

• Challenging Due to Project Uniqueness

Project Schedule

February 2012 HVdc Contract Signed

Spring 2012 Start Line & AC Station Construction

August 2012 Start DC Underground Construction

April 2013 AC Substation & Lines Completed

June 2013 Start DC Overhead Construction

August 2013 Dynamic Studies & Factory Tests Complete

September 2013 Converter Building Completed

October 2013 Major Equipment Arrives

May 2014 Commissioning Completed

July 2014 Station Turnover to ATC

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• Not Unusual, No Unexpected Challenges

• Long Lead Time Reactors Not Needed Until HVDC On

Line Moves and AC Station

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• 300’ Long, 130’ Wide, 45’ High

• Four Valve Halls, Two on Each Floor

• Reactor Halls on Ends

HVDC Building

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HVDC Building

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Mackinac AC and HVDC Substations

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Valve Hall

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Reactor Hall

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• Studies and Factory Tests Completion Scheduled Only

One Month Before Major Equipment Arrival – Control Changes Made via Software not Hardware

• Equipment in October Commissioning Completed in May – Much Work Done in Winter Outdoors (Trenches, Wiring, etc.)

– July Completion to Give 60 Days for 30 Day Run

Project Schedule Issues

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• Confirm All Equipment Meets Specifications

• Confirm Control System Operates as Designed – Confirm RTDS Simulations and Tests

– Allow some Control Tweaking

• PQ Capability Testing – HVDC Connected Radially – Circulate 200 MW in Bypass

– Prevent Voltage Collapse by Accidental 200 MW Throughput

Commissioning Tests

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Control System Tests

• Tests Included: Power Order, Active Power Control,

Reactive Power Control (both terminals independently &

Simultaneously), AC Voltage Control, High Power

Transfer, Black Start, By-Pass, etc.

• Islanding Test – Match DC Power to that of Small Part of UP

– Isolate that Small Part of UP

– Wait (45 Seconds) for Shift to Island Mode

– Successful Test

• No ACLE Disturbance Test (Manually Triggered ACLE)

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• High Frequency Resonance in Local Power Line

Carrier Equipment

• May 28th Short Circuit in Valve Hall

• July 16th Power Deviation (Loss of Voltage Signal)

• August 27th HVDC Response to a Remote Fault

• Power System Communications Issues

Issues During (and After) Commissioning Tests

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• Local PLC Equipment Failed Soon After HVDC Energization

• High Voltage in High Frequency Resonant Circuit

• No Remote Failures, but Excessive Voltages Measured

• Source Wide Band High Frequency (kHz) Signals – Normally Attenuated by Transformer or Distance – Nothing (but PLC) at Transmission Voltages to Resonate

• Doubly Tuned (5th and 30th) Harmonic Filter Ineffective

• Option: Alternate Communication Method (Rejected)

• Solution: Add High Pass Filter – Concerns: Cost and Time to Implement

Local Power Line Carrier Issues

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• Modify Existing Filter

(Bypass Reactor)

• Convert 30th Harmonic

to High Pass

• Project Harmonic

Distortion Limits Met

• Filter Components Not

Over Stressed

• Implemented Quickly

at Low Cost on Both

Terminals

PLC Issue Solution

R3C2 L2

C1

L1

C1

C2 L2 R3

Original Modified

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• HVDC Tripped When 7 IGBTs in One Switch Indicated

they were Short Circuited

• No Other Indication of Fault and IGBTs Tested OK

• Incorrectly Installed Cable to Corona Shield Touched

Frame of IGBT Module at a Different Potential

Short Circuit in the Valve Hall - Problem

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• Insulation Breakdown Caused Short Circuit

• Damaged Cable Replaced

• All Four Valve Halls Inspected

• No Similar Problems Found

• Protection and Control Worked as Designed

Short Circuit in the Valve Hall - Resolution

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• Power Increased Twice from 40 MW to 130 & 110 MW for just Under 2 Seconds Each Time

• Reactive Power, Voltage and Frequency Affected

• No System Events at the Time

Unexpected Power Deviation - Event

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• Technician in Control Panel Looking for Measurement Connection

• Touched Loose CCVT Phase and Neutral Wire Connection Changed Ambient Noise (Touched Again to Confirm)

• One Phase Voltage Measurement Lost

• “A” System Voltage Lost, “B” System and Others OK

• System Protection Responded as it Should Have

• 200 milliseconds from Tripping HVDC

• “Do Not Touch” Order Until Connections Re-examined

Unexpected Power Deviation - Resolution

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• 345 kV Tower on Line Bringing Power from WI to UP

Knocked Down by a Logging Truck on a Clear Day

• HVDC Temporarily Increased Power into the UP

• Increased Mvars Temporarily South, Permanently North

HVDC Response to a Remote Fault

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• ACLE Not in Service – Waiting Operations Study Completion

– If in Service Power would have Changed Permanently

– Operators Manually Increased Flow from 40 to 65 MW

• PSSE Dynamic and PSCAD Transient Simulations – PSSE a Simplification of PSCAD’s Detailed Control Model

– PSSE Showed Better Response – Due to Delay Lost in

Model Conversion

– To Improve System Response Delay Removed from

PSCAD and Real System

HVDC Response to a Remote Fault

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• VSC HVDC Uses 3.37th Harmonic Switching Frequency

• IGBT Switching Capabilities to improve Stability by

Continuously Adjusting its Operating Point

• This Creates Non-Repetitive (Interharmonic) Distortion

• Smart Meters Report Energy Usage and Track Outages

• Smart Meters Communicate by Transiently Distorting

System Voltage or Current (or Both)

• Information Extracted by Subtracting Consecutive 60 Hz

• Effective with Error Checking and Multiple Attempts

• Unaffected by Harmonic Distortion – Susceptible to Non-

repetitive Interference (Arc Furnaces, etc.)

Power System Communications Issue

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• One Distribution Company with 40,000+ Smart Meters

Communicating Over Power Lines Near Mackinac

• A Significant Minority of Meters Near Mackinac “Affected”

• Mackinac Interharmonics with HVDC Off and On:

Mackinac HVDC and Smart Meters

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• How Does Each Interharmonic Affect Communications?

Interharmonics Change with HVDC and

System Changes

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Interharmonics at Three Locations

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• Exist only for Flicker (<120 Hz)

• IEEE 519-2014 “develop on a case-by-case basis”

• IEC 61000-2-2 suggests 0.2 to 0.3% Individual – Seems Designed to Allow Some Communication

• Over a Decade Ago IEEE Working Group on

Interharmonics Looked at Limits Based on Equipment – Similar to Harmonic Voltage Limits (1.5% Individual, 2.5%

THD at 138 kV)

– Almost an Order of Magnitude Higher than IEC

– Never Made it into any IEEE Standard

• Should Power Lines be Used for Communications?

Interharmonic Limits

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For Now:

• HVDC is in Service for Its Primary Purpose – Facilitating Deferred Maintenance Outages

• HVDC is Taken Out of Service to Facilitate Periodic Meter Reading and When Storms Approach

Future:

• Investigating HVDC-Smart Meter Interaction

• Key HVDC Functionality Produces Some Interharmonics

• Can HVDC be Modified or Operated to Decrease Interharmoncs to and Acceptable Level?

• Expect Some Meter Fixes and New Communication Path for Some Substations

Interharmonic Issue Resolution

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• Mackinac HVDC Met its Goals Economically and Timely

• Any Project using New Technology in a Unique Part of the

System will have Implementation Issues

Two Key Lessons Learned

• The Need to Study High Frequency Issues – Especially if

Power Line Carrier Installed Locally (High Pass Filter)

• Potential for VSC HVDC Interharmonics to Interfere with

Smart Grid Power Line Communications – The Same Problem Could Exist with Type 4 Wind Turbines

Controls which use IGBTs (arc furnaces, CFLs, etc.)

Conclusions

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Questions?