15 August 2015 Delft University of Technology Electrical Power System Essentials ET2105 Electrical...

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



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



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)



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)



• 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





• Conclusion:• The voltage depends on the reactive power• The angle of transmission depends on the active power



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



The Primary Control• Speed governor control of a generating unit:

• Speed governor characteristics:



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



Voltage Control and Reactive Power (1)

Automatic voltage control




Tap-changing transformer




Capacitor banks

Courtesy of TenneT TSO B.V.



Reactive Power Injection

Current through a Thyristor Controlled Reactor

Static Var Compensator (SVC)



Controlling Active Power FlowsThe Phase Shifter

Phasor diagram of the phase shifter



Controlling Reactive Power Flows (1)A transmission line with a series capacitor



Controlling Reactive Power Flows (2)Thyristor-controlled series capacitor

TCSC reactance as a function of the Thyristor firing angle

15 August 2015 Delft University of Technology Electrical Power System Essentials ET2105 Electrical...

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