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

1. 27 April 2024
Delft
University of
Technology
Electrical Power System Essentials
ET2105 Electrical Power System Essentials
Prof. Lou van der Sluis
The Transmission of Electric Energy

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Electrical Power System Essentials
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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Introduction (2)
Rated voltage for AC – power system

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Introduction (3)
Voltage levels in the Dutch Power System

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The Dutch High-Voltage Network
Introduction (4)

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Network Structures
Radial structure Loop structure Multi-loop structure

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Substations (1)
Open-air substation
Courtesy of TenneT TSO B.V.

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Substations (2)
High-Voltage Circuit Breakers and Pantograph
Disconnector
Courtesy of TenneT TSO B.V.

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Substations (3)
SF6-insulated substation
Courtesy of Eaton Holec

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Substations (4)
Bus system
Single bus system
Double bus system

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The Transformer
The ideal transformer

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Electrical Power System Essentials
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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The Transformer Model (2)
Copper losses
Leakage reactance
Iron losses (core) Magnetizing susceptance
Efficiency = Pout / Pin = 1 – Ploss / Pin

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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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Three-Phase Transformer (2)
Single-phase equivalent

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Three-Phase Transformer (3)
Out of the tank
Courtesy of TenneT TSO B.V.

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The Yy-4 Transformer

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The Yd-11 Transformer

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The Magnetization Current
The magnetization current contains a third harmonic

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Overhead Transmission Lines (1)
380 kV River crossing
Courtesy of TenneT TSO B.V.

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

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Overhead Transmission Lines (3)
150kV transmission line tower

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Transmission Line Conductors (1)
• Material
• Al
• Cu
• ACSR (Aluminum Conductor Steel Reinforced)

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Transmission Line Conductors (2)
Courtesy of TenneT TSO B.V.

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

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Galloping Lines
• Counter measures

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Shield Wires

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Transposition (1)
• Unbalanced system
• Solution: transposition

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Transposition (2)

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High-Voltage Cable
Courtesy of Prysmian Cable Holding B.V.
• 6/10 kV cable • 220/380 kV cable

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Transmission of Power
Poynting Vector: S = E x H
V
H
H
H
E
E
E
S
S
S
E
S
S
H
H
E
S
S

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

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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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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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Line Models
• Short
(<80 km)
• Medium
(80 km..240 km)
• Long
(>240 km)
VR
IR
IS
VS
Z
IR
IS
VS
Y/2
Y/2 VR
Z
IR
IS
VS
VR
/km
H/km
F/km

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Short Line
VR
IR
IS
VS
R+jX
Vr
Vs
jIrX
Ir
IrR
Vr
Vs
jIrX
Ir
IrR
Vr
Vs jIrX
Ir
IrR

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Series-Compensation
• Z = R + jX
= R + j (L - 1/C)
Hydro-Quebec / 735 kV

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Long Line: Distributed Elements
zx
yx V(x)
x
V(x+x)
I(x)
I(x+x)

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Equivalent Circuits of Lines
• Short
• Medium
• Long
VR
IR
IS
VS
Z
IR
IS
VS
Z
Y/
2
Y/2 VR
IR
IS
VS
Z'
Y'/
2
Y'/
2
VR