Module 4 : Voltage and Power Flow Control
Lecture 17 : Reactive Power and Voltage Control
Objectives
In this lecture you will learn the following
Means of voltage control in power systems.
Generator Excitation Systems and reactive power characteristics of power system components.
Since voltage magnitudes in a system are intimately related to the ability of various components to absorb or
supply reactive power, we shall begin by reviewing these characteristics.
Synchronous Generators: Can generate or absorb reactive power by control of field voltage. The
amount of reactive power which can be exchanged by a generator is given by the reactive power capability
curve (discussed in Module 2).
In rotating-type excitation
systems, field voltage is
obtained using separate
generators connected to
the same shaft as the main
generator. The excitation
for these excitation
generators themselves is
obtained by self-excitation
or permanent magnet
generators. Control is
achieved by controlled
rectification using thyristor
bridges.
A schematic of a brushless
rotating excitation system
is shown on the right.
Production and Absorption of Reactive Power
In static excitation systems, the field voltage is obtained directly by rectifying (using controlled rectifiers) the
output voltage of the main synchronous generator. Therefore in these systems, the generator is practically self
excited with some initial voltage being obtained temporarily using station batteries (called field flashing).
In static excitation systems, it is necessary to use slip rings to convey the field voltage (output of the
controlled rectifier) to the rotating field winding of the main generator.
Lecture 17 : Reactive Power and Voltage Control
Objectives
In this lecture you will learn the following
Means of voltage control in power systems.
Generator Excitation Systems and reactive power characteristics of power system components.
Since voltage magnitudes in a system are intimately related to the ability of various components to absorb or
supply reactive power, we shall begin by reviewing these characteristics.
Synchronous Generators: Can generate or absorb reactive power by control of field voltage. The
amount of reactive power which can be exchanged by a generator is given by the reactive power capability
curve (discussed in Module 2).
In rotating-type excitation
systems, field voltage is
obtained using separate
generators connected to
the same shaft as the main
generator. The excitation
for these excitation
generators themselves is
obtained by self-excitation
or permanent magnet
generators. Control is
achieved by controlled
rectification using thyristor
bridges.
A schematic of a brushless
rotating excitation system
is shown on the right.
Production and Absorption of Reactive Power
In static excitation systems, the field voltage is obtained directly by rectifying (using controlled rectifiers) the
output voltage of the main synchronous generator. Therefore in these systems, the generator is practically self
excited with some initial voltage being obtained temporarily using station batteries (called field flashing).
In static excitation systems, it is necessary to use slip rings to convey the field voltage (output of the
controlled rectifier) to the rotating field winding of the main generator.
