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

2. 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:

3. 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

4. 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

5. 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)

6. 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:

7. 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)

8. 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.

9. 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:

10. 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

11. 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

12. Arrowhead-Weston Transmission Line Project Dave Van House Minnesota Power

13. 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

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

17. 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.

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

21. 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

24. 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

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

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

28. 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

29. 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

30. 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

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

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

33. 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

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

35. Arrowhead Substation Noise

36. 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

38. 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

41. Common Utility Corridor

42. Visual Impact Of Crossing

43. Existing 161 kV H-Frame

44. 954 ACSR 2-Conductor Bundle with Shield Wire

45. Single 3M Composite Conductor

46. Post Permit Studies Equipment Specification
Construction Support Analysis
Operating studies

47. 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

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

50. 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

51. 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

52. 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.