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19 April 2023
DelftUniversity ofTechnology
Electrical Power System Essentials
ET2105 Electrical Power System EssentialsProf. Lou van der Sluis
Power System Control
25. Power System Control | 18
Electrical Power System Essentials ET2105
Introduction (1)
• The customer expects electrical power at constant frequency and voltage
• The system load changes continuously
• Electricity can not be stored in large quantities
• Maintaining the balance between generation and consumption
35. Power System Control | 18
Electrical Power System Essentials ET2105
Introduction (2)
• The active power balance is controlled by generators
• Another method is load shedding
• The reactive power balance is controlled by generators and static components
• The synchronous generator plays an important role
45. Power System Control | 18
Electrical Power System Essentials ET2105
Increase of Active Power Consumption
• Kinetic energy in the rotating parts of the generator and turbine are 200 MJ
• Suddenly a 10 MW load is connected. What happens to the frequency?• In 1 second the load consumes 10 MJ more active power P• The frequency will drop to 48.7 Hz
f1 = 50 Hz (3000 RPM)
55. Power System Control | 18
Electrical Power System Essentials ET2105
10 kV system:P = 2 MW; cos φ = 0.9Xgen = 3 Ω
This results in:I = 128 A ∠-26°Q = 969 kvar
• Suddenly the load consumes Q = 1.5 Mvar and P remains at 2 MW. What happens?• The power factor drops to 0.8• The current becomes I = 146 ∠-37°• The terminal voltage drops with 100 V
Increase of Reactive Power Consumption (1)
65. Power System Control | 18
Electrical Power System Essentials ET2105
• P remains 2 MW• Q increases from 969 kvar 1.5 Mvar• I increases from 128 A ∠-26° 147 A ∠-37°• V drops with 100 V
Increase of Reactive Power Consumption (2)
75. Power System Control | 18
Electrical Power System Essentials ET2105
Increase of Reactive Power Consumption (3)
85. Power System Control | 18
Electrical Power System Essentials ET2105
Increase of Reactive Power Consumption (4)
• Conclusion:• The voltage depends on the reactive power• The angle of transmission depends on the active power
95. Power System Control | 18
Electrical Power System Essentials ET2105
Some Important Conclusions
• The frequency is a common parameter throughout the system
• The voltage is controlled locally
• The control mechanism for P (rotor angle) and Q (voltage amplitude) operate more or less separately
105. Power System Control | 18
Electrical Power System Essentials ET2105
The Primary Control• Speed governor control of a generating unit:
• Speed governor characteristics:
115. Power System Control | 18
Electrical Power System Essentials ET2105
The Secondary Control or Load Frequency Control
Power exchange between three control areas
a) The original (scheduled) situationb) Incremental generation after losing 400 MW of generation in
control area B
125. Power System Control | 18
Electrical Power System Essentials ET2105
Voltage Control and Reactive Power (1)
Automatic voltage control
135. Power System Control | 18
Electrical Power System Essentials ET2105
Voltage Control and Reactive Power (2)
Tap-changing transformer
145. Power System Control | 18
Electrical Power System Essentials ET2105
Voltage Control and Reactive Power (3)
Capacitor banks
Courtesy of TenneT TSO B.V.
155. Power System Control | 18
Electrical Power System Essentials ET2105
Reactive Power Injection
Current through a Thyristor Controlled Reactor
Static Var Compensator (SVC)
165. Power System Control | 18
Electrical Power System Essentials ET2105
Controlling Active Power FlowsThe Phase Shifter
Phasor diagram of the phase shifter
175. Power System Control | 18
Electrical Power System Essentials ET2105
Controlling Reactive Power Flows (1)A transmission line with a series capacitor