Transcript Power System Control ET2105 Electrical Power System Essentials 24 May 2016

Power System Control
ET2105 Electrical Power System Essentials
Prof. Lou van der Sluis
24 May 2016
Delft
University of
Technology
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
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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
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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
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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
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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
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Increase of Reactive Power
Consumption (3)
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Increase of Reactive Power
Consumption (4)
• Conclusion:
• The voltage depends on the reactive power
• The angle of transmission depends on the active power
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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
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The Primary Control
• Speed governor control of a generating unit:
• Speed governor characteristics:
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The Secondary Control or
Load Frequency Control
Power exchange between three control areas
a) The original (scheduled) situation
b) Incremental generation after losing 400 MW of generation in control
area B
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Voltage Control and Reactive Power (1)
Automatic voltage control
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Voltage Control and Reactive Power (2)
Tap-changing transformer
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Voltage Control and Reactive Power (3)
Capacitor banks
Courtesy of TenneT TSO B.V.
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Reactive Power Injection
Static Var Compensator (SVC)
Current through a Thyristor Controlled Reactor
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Controlling Active Power Flows
The Phase Shifter
Phasor diagram of the phase shifter
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Controlling Reactive Power Flows (1)
A transmission line with a series capacitor
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Controlling Reactive Power Flows (2)
Thyristor-controlled series capacitor
TCSC reactance as a function of the Thyristor firing angle
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