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

2. 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

3. 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

4. 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

5. 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

6. 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

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

8. 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

9. 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

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

11. 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

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

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

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

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

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

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

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