Transmission Lines EE 4501 S.R.Norr and D. Van House

First Long Transmission Line The first Trans-Atlantic Telegraph Cable, installed in 1858, identified the need to accurately model transmission lines. Oliver Heaviside developed the model that still exists today:

T-Line Model: Components Rdx – Series Resistance per unit length Ldx – Series Inductance per unit length Gdx – Leakage Conductance in the insulation between conductors Cdx – Mutual Capacitance between conductors

50/60 Hz T-Lines Wavelength at 60 Hz: λ = c/f = 186 k-mi/60 λ = 3100 miles; λ/4 = 775 miles Skin Effect: Alternating Current produces a counter-emf in the conductor, forcing current flow to the outer perimeter of the conductor 63% within δ (skin) δ is about 8mm in 60 Hz conductors wikipedia.org

50/60 Hz Lines Ferranti Effect: Voltage RISE along long T-Line (lightly loaded or open ckt at one end) The longer the T-Line, the higher the rise Concentric cables even worse (higher mutual capacitance)

Short and Medium T-Lines If Line Length is small relative to the 60 Hz quarter-wavelength: (750 mi) Short Line: < 50 Miles: Dominated by Inductive Reactance Medium Line: < 150 Miles:

Medium Length Lines Engineering Calculations on lines of medium length can be expedited using the 2-Port Network concept: V1 = AV2 + BI2, I1 = CV2 + DI2 A = D = ( ZY/2 ) + 1 ; B = Z ; C = Y(1 + ZY/4)

Longer Lines Lines above 150 miles in length require more exact modeling to account for phase shift, etc The differential equations used to describe the line voltages and currents are of second order, with sinusoidal forcing functions. The solutions are complex exponentials that can be mapped to the Hyperbolic Plane in order to reduce the complexity.

Longer Lines (cont’d) At any point on the line: d2V/dt2 = YZV, d2I/dt2 = YZI Using hyperbolic trig, the solutions lead to a more general PI model:

Characteristic Impedance The characteristic impedance of a T-Line is: Zc = sqrt(Z/Y) Sometimes called the Surge Impedance More accurately, Surge Impedance is: Zsi = sqrt(L/C) [lossless line] Used for assessing impact of fast transients, such as a lightning strike

Surge Impedance Loading Under normal power delivery conditions, most T-Lines are a net capacitive entity. Provide leading VARs to grid Achieve a Ferranti voltage rise profile If a T-Line is terminated in a pure resistive load equal to its Zsi, that is considered its Surge Impedance Load (SIL): SIL = | Vline|2 / Zsi watts Beyond SIL, the line is a net inductive entity, consuming VARs and subject to voltage collapse

Arrowhead-Weston Transmission Line Project Dave Van House Minnesota Power

Description & Overview 220 mile 345,000 volt electric transmission line Approved by the Minnesota and Wisconsin regulators in 2001 Construction Began in Minnesota February 2004 Construction to Begin in Wisconsin Fall 2004 Construction scheduled to be completed in 2008

Why was it proposed? Reliability!! Improves Regional System Security Provides Maintenance & Operational Flexibility Allows Customers Greater Access to Generation Sources

Minnesota Minnesota’s electric network is tied to neighboring states. If Wisconsin has a problem, Minnesota has a problem. Minnesota Power customers have been knocked off line by electric system disturbances related to the weak Minnesota- Wisconsin connection. www.powerupwisconsin.com

Recent Regional Problems June 11, 1997 June 25, 1998 June 10, 1999

IMPACT OF June 25, 1998 DISTURBANCE IN MAPP 60+ TRANSMISSION LINES TRIPPED 4,000+ MW OF GENERATION LOST More Than 39,000+ CUSTOMERS AFFECTED IN NW ONTARIO BLACK OUT TO 113,000 CUSTOMERS 650 MW OF LOAD LOST 270 MW OF Generation Lost

Wisconsin Actions 1997 events raise concerns about electric supply reliability in Wisconsin Wisconsin utilities and regulators form Wisconsin Reliability Assessment Organization (WRAO) WRAO forms engineering group to study alternatives - WIRES group

PERFORMANCE EVALUATION DETAILED POWER FLOWS SIMULATION GENERATOR RESPONSE DYNAMIC STABILITY VOLTAGE STABILITY IMPACT ON MAPP CONSTRUCTION COSTS LOSS EVALUATION

Power Flow Analysis Reactive Voltage Support Requirements Steady State Maximum Transfer capability Sensitivity to Modeling Assumptions Transmission System Loss Analysis

Generator Response Mechanical Stress on Weston Generator Shaft Large Phase Angle Across MAPP MAIN Interface Eau Claire Arpin Line Switching Instanteous change in Power output

Dynamic Stability Ability of Systems Generators to remain synchronized and recover from Major System Disturbance MAPP WUMS Disturbances Loss of New Facilities Impact on Existing Limiting Conditions Dynamic Reactive Support Requirements

Voltage Stability Ability of the System to Maintain Adequate Voltage Following a Disturbance Without Adequate Voltage Support System can Experience Increased Current Demand (P = VI) Slowly Declining Voltage Loss of Voltage Sensitive Loads Voltage Collapse

Engineering to Support Permitting Calculation of; AUDIBLE NOISE ELECTRIC FIELD MAGNETIC FIELD Analysis of Potential Farm Impacts Stray Voltage Earth Currents

EMF Issues Magnetic Field Electric Field Spark Discharge Multiple Routes Multiple Structures Multiple Circuits Multiple Flows Future Years

Transmission Line Noise Due to Corona Discharge Electric Field at surface of the conductor exceeds the breakdown strength of air Generates light, audible noise, radio noise and energy losses Mitigation Increase Conductor Surface area Larger Conductors Multiple conductors

Substation Noise Monitoring Long Term Short Term Existing Equipment Impact of Additions

Arrowhead Substation Noise

Other Engineering Issues Differential GPS Interference (Precision Farming) Electric & Magnetic Field Impacts on Pacemakers and implantable Defibulators Impacts on Railroad, Pipeline and AM Radio Transmitter sites

Opposition to the project: Save Our Unique Lands Citizens Utility Board Wisconsin Environmental Decade North American Water Office Hillside Dairy World Organization of Landowner Freedom

Common Utility Corridor

Visual Impact Of Crossing

Existing 161 kV H-Frame

954 ACSR 2-Conductor Bundle with Shield Wire

Single 3M Composite Conductor

Post Permit Studies Equipment Specification Construction Support Analysis Operating studies

Equipment Specifications Transient studies Breaker Switching Duties Shunt Reactor Shunt Capacitor 345 & 230 kV line breakers Capacitor Bank Switching Issues Voltage Magnification Insulation Coordination Surge Arrester rating & placement Equipment BIL requirements Line Insulation

Construction Impact Studies Constructability Line outage concerns Maintenance issues Ownership Issues Increased Cost Landowner Opposition

Operating Studies Determination of Operating Limits Reactive Support Requirements Shunt Capacitor location optimization Line Loadability Issues System Intact and Post Contingency Phase Shifter Requirements Line load sharing optimization Post Contingency requirements New Flow-Gate Limits

Summary Operating experience has shown there is a significant risk to electrical reliability in the upper Midwest and Wisconsin Engineering study commissioned through Assembly Act 204 WRAO recommendation Arrowhead Weston 345 kV Line

Summary The Arrowhead-Weston Project will substantially alleviate the reliability problems being experienced due to the weak electrical tie between the upper Midwest and Wisconsin. It will also provide import capability for Wisconsin to meet its emergency power supply requirements.