ET2105 Electrical Power System Essentials Power System Control ET2105 Electrical Power System Essentials Prof. Lou van der Sluis Electrical Power System Essentials

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 Electrical Power System Essentials

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 Electrical Power System Essentials

Increase of Active Power Consumption f1 = 50 Hz (3000 RPM) 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 Electrical Power System Essentials

Increase of Reactive Power Consumption (1) 10 kV system: P = 2 MW; cos φ = 0.9 Xgen = 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 Electrical Power System Essentials

Increase of Reactive Power Consumption (2) 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 Electrical Power System Essentials

Increase of Reactive Power Consumption (3) Electrical Power System Essentials

Increase of Reactive Power Consumption (4) Conclusion: The voltage depends on the reactive power The angle of transmission depends on the active power Electrical Power System Essentials

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 Electrical Power System Essentials

The Primary Control Speed governor control of a generating unit: Speed governor characteristics: Electrical Power System Essentials

The Secondary Control or Load Frequency Control Power exchange between three control areas The original (scheduled) situation Incremental generation after losing 400 MW of generation in control area B Electrical Power System Essentials

Voltage Control and Reactive Power (1) Automatic voltage control Electrical Power System Essentials

Voltage Control and Reactive Power (2) Tap-changing transformer Electrical Power System Essentials

Voltage Control and Reactive Power (3) Capacitor banks Courtesy of TenneT TSO B.V. Electrical Power System Essentials

Reactive Power Injection Static Var Compensator (SVC) Current through a Thyristor Controlled Reactor Electrical Power System Essentials

Controlling Active Power Flows The Phase Shifter Phasor diagram of the phase shifter Electrical Power System Essentials

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

Controlling Reactive Power Flows (2) Thyristor-controlled series capacitor TCSC reactance as a function of the Thyristor firing angle Electrical Power System Essentials