21 April 2023

DelftUniversity ofTechnology

Electrical Power System Essentials

ET2105 Electrical Power System Essentials

Prof. Lou van der Sluis

The Transmission of Electric Energy

23. The Transmission of Electric Energy | 39

Electrical Power System Essentials ET2105

Introduction (1)

• Transmission and Distribution• Advantages of interconnected systems

• Better reliability• Smaller frequency deviations• Better overall system efficiency• Facilitates power exchange

• Disadvantages of interconnected systems• Limitations to interconnection transport capacity• Power losses because of energy exchange• Unwanted parallel power flows• More complex system operation

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Electrical Power System Essentials ET2105

Introduction (2)Rated voltage for AC – power system

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Electrical Power System Essentials ET2105

Introduction (3)Voltage levels in the Dutch Power System

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Electrical Power System Essentials ET2105

The Dutch High-Voltage Network

Introduction (4)

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Electrical Power System Essentials ET2105

Network Structures

Radial structure Loop structure Multi-loop structure

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Electrical Power System Essentials ET2105

Substations (1)Open-air substation

Courtesy of TenneT TSO B.V.

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Electrical Power System Essentials ET2105

Substations (2)High-Voltage Circuit Breakers and Pantograph Disconnector

Courtesy of TenneT TSO B.V.

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Electrical Power System Essentials ET2105

Substations (3)SF6-insulated substation

Courtesy of Eaton Holec

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Electrical Power System Essentials ET2105

Substations (4)Bus system

Single bus system

Double bus system

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Electrical Power System Essentials ET2105

The TransformerThe ideal transformer

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Electrical Power System Essentials ET2105

The Transformer Model (1)

• Not ideal• Permeability is not infinity

• Finite self inductance

• Leakage flux• Winding losses (copper losses)• Core losses

• Hysteresis

• Eddy-current losses

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Electrical Power System Essentials ET2105

The Transformer Model (2)

Copper lossesLeakage reactance

Iron losses (core) Magnetizing susceptance

Efficiency = Pout / Pin = 1 – Ploss / Pin

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Electrical Power System Essentials ET2105

Three-Phase Transformer (1)

• Three single-phase transformers

• Three phase transformer

• Complex turns ratio 1 : a*ej

• Amplitude• Phase shift: multiple of 30°

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Electrical Power System Essentials ET2105

Three-Phase Transformer (2)Single-phase equivalent

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Electrical Power System Essentials ET2105

Three-Phase Transformer (3)Out of the tank

Courtesy of TenneT TSO B.V.

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Electrical Power System Essentials ET2105

The Yy-4 Transformer

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Electrical Power System Essentials ET2105

The Yd-11 Transformer

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Electrical Power System Essentials ET2105

The Magnetization CurrentThe magnetization current contains a third harmonic

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Electrical Power System Essentials ET2105

Overhead Transmission Lines (1)380 kV River crossing

Courtesy of TenneT TSO B.V.

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Electrical Power System Essentials ET2105

Overhead Transmission Lines (2)The power carriers in the Dutch power system

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Electrical Power System Essentials ET2105

Overhead Transmission Lines (3)150kV transmission line tower

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Electrical Power System Essentials ET2105

Transmission Line Conductors (1)

• Material• Al• Cu

• ACSR (Aluminum Conductor Steel Reinforced)

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Electrical Power System Essentials ET2105

Transmission Line Conductors (2)

Courtesy of TenneT TSO B.V.

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Electrical Power System Essentials ET2105

Transmission Line Conductors (3)Advantages and disadvantages of bundled conductors

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Electrical Power System Essentials ET2105

Galloping Lines

• Counter measures

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Electrical Power System Essentials ET2105

Shield Wires

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Electrical Power System Essentials ET2105

Transposition (1)

• Unbalanced system

• Solution: transposition

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Electrical Power System Essentials ET2105

Transposition (2)

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Electrical Power System Essentials ET2105

High-Voltage Cable

Courtesy of Prysmian Cable Holding B.V.

• 6/10 kV cable • 220/380 kV cable

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Electrical Power System Essentials ET2105

Transmission of PowerPoynting Vector: S = E x H

VV

HH

HH

HHEE

EE

EE

SS

SS

SS

EE

SS

SS

HH

HHEE

SS

SS

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Electrical Power System Essentials ET2105

Conductor Modeling

• L : H-field• C : E-field• R : Ohmic losses• G : Insulator and corona losses

RL

G C

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Electrical Power System Essentials ET2105

Line / Cable

• Line, 150 kV• R = 0.125 /km• XL = 0.425 /km

• C = 7.7 nF/km• Sth = 130 MVA

• Cable, 150 kV• R = 0.12 /km• XL = 0.166 /km

• C = 210 nF/km• Sth = 135 MVA

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Electrical Power System Essentials ET2105

1 km Line / Cable

• Line, 132 kV• R = 0.178 • XL = j0.40 • XC = -j350 k• I = 450 A

• Cable, 400 kV• R = 9 m• L = 0.4 mH• C = 0.38 µF• I = 1.9 kA

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Electrical Power System Essentials ET2105

Line Models

• Short(<80 km)

• Medium(80 km..240 km)

• Long(>240 km)

VR

IRIS

VS

Z

IRIS

VS Y/2Y/2 VR

Z

IRIS

VS VR

/kmH/kmF/km

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Electrical Power System Essentials ET2105

Short Line

VR

IRIS

VS

R+jX

Vr

Vs

jIrX

IrIrR

Vr

VsjIrX

IrIrR

Vr

Vs jIrX

Ir

IrR

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Electrical Power System Essentials ET2105

Series-Compensation

• Z = R + jX = R + j (L - 1/C)

Hydro-Quebec / 735 kV

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Electrical Power System Essentials ET2105

Long Line: Distributed Elements

zx

yx V(x)

x

V(x+x)

I(x)I(x+x)

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Electrical Power System Essentials ET2105

Equivalent Circuits of Lines

• Short

• Medium

• Long

VR

IRIS

VS

Z

IRIS

VS

Z

Y/2

Y/2 VR

IRIS

VS

Z'

Y'/2

Y'/2 VR