voltage and reactive power control
TRANSCRIPT
Voltage and reactive
power control
Presented byAhmed ALi
Instructor : Asst .Prof .Dr. Ahmed METE VURAL
power system opration
Code: EEE 574
the lamp characteristics are very sensitive to changes of voltage.
the life of the lamp may be reduced by 50%
Also the power load consisting of induction motors, the voltage
variations may cause stray operation.
Too wide variations of voltage cause excessive heating of electrical
device such as distribution transformers
Importance of Voltage and reactive power Control
both utility and customer equipment designed to operate at certain
voltage rating, Long time operation outside allowable range could
cause them damage
System stability is satisfactory
voltage levels and reactive power control have significant impact on
stability
The reactive power flow is minimized so as to reduce I 2R and I 2X
losses to a practical minimum that
ensures transmission system operates efficiently
• Reactive power does not travel very far Usually necessary to produce it
close to the location where it is needed A supplier/source close to the
location of the need is in a much better position to provide reactive
power
• Reactive power generated by the ac power source is stored in a capacitor
or a reactor during a quarter of a cycle and in the next quarter of the cycle
it is sent back to the power source. Therefore the reactive power oscillates
between the ac source and the capacitor or reactor So to avoid the
circulation between the load and source it needs to be control
Reactive power generated
alternator synchronous impedance
Transmission line
transformer impedance
feeders
These voltage variations are undesirable and must be kept within
the limits
When the load on the system increases,
the voltage drop increased in
Reactive power formulas
Q = VAR
For heavy load condition s required
+ve var C- bank
For light load condition required
-ve var L –bank
Q α
Receive power Injection
Than Total reactive power in receiving
QR = QS + QC
JQc
Ps+ JQs
PR+ J(QR +Qc )
Load Shunt compensation
Power sending
PR + JQR
Methods of control voltage Reactive PowerControl of voltage levels is accomplished by controlling the production,
and absorption, of reactive power flow at all levels in the system
Generating units provide the basic means of voltage control
Additional devices to control voltage:
o Static sources or sinks of reactive power
o Voltage regulating such as tap transformers,
o Dynamic source such as Synchronous motor
Static sources or fixed
• Shunt compensation
• Series compensation
• Static (VAR) compensators
• Static compensators
All these devices compensate reactive power using a similar operating principle.
• The device that is connected in parallel with the transmission line is
called the shunt compensator.
• A shunt compensator is widely used in transmission system to
regulate the voltage magnitude. It can be provided by either a
current source ,or voltage source
• The Shunt connected reactors are used to reduce the line over
voltages by consuming the reactive power,
• The shunt connected capacitors are used to maintain the voltage
levels by compensating the reactive power to transmission line.
Shunt compensators
Figure 1 : Transmission line with shunt compensation
Series compensators
When a device is connected in series with the transmission line or
feeder it is called a series compensator.
A series compensator can be connected anywhere in the transmission
It works as a controllable voltage source.
Series inductance exists in all AC transmission lines.
when a large current flows, this causes a large voltage drop. To
compensate, series capacitors are connected, to decreasing the
effect of the inductance.
Figure 2 : Transmission line with series compensation
V Sending
X TL
V receiving
Xc serise
A static VAR compensator (or SVC) is an electrical device for providing reactive
power
The term static is used to denote that there are no moving or rotating components
The SVC designed to bring the system closer to unity power factor. (usually use
thyristor to Controlled Reactors and capacitor)
• If the power system's reactive load is capacitive (leading),
the SVC will use reactors lowering the system voltage.
• also Under inductive (lagging) conditions,
the capacitor banks are automatically switched to providing a higher
system voltage.
static VAR compensator
Figure 3 : static VAR compensator. use thyristor switched
Advantage and disadvantage a) They are more reliable .
b) Faster in operation .
c) Smoother control and more
flexibility can be provided with
the help of thyristors.
Disadvantage
Need a transformers steps the
transmission voltage down to a much
lower level
the size and number of components.
more expansive compered with
shunt capacitive
Static Compensator
The devices use synchronous voltage sources for generating or absorbing
reactive power.
A synchronous voltage source (SVS) is constructed using a voltage source
converter (VSC).
A STATCOM usually contains an ( SVS) A synchronous voltage source
that is driven from a dc storage capacitor and the (SVS) is connected to
the ac system bus through an interface transformer. The transformer
steps the ac system voltage down
Figure 4 : STATCOM Static synchronous Compensator
The STATCOM can be operated in two different modes:
When the feeder voltage is lower than the voltage of the converter
the STATCOM generates reactive power.
When the converter voltage is higher than the feeder voltage,
the STATCOM absorbs reactive power
Voltage regulating tap changing transformers
Auto transformer
In this method, a number of tapping's are provided on the secondary
of the transformer.
The tap selection may be made on automatic or manual tap
changer mechanism.
the number of tapping have been provided a variation voltage on
the secondary.
When the position of the tap is varied, the number of secondary
turns is varied the voltage varied
Tap Changing transformer
Tap/changing transformer works when the movable arm makes contact with lower positions such as 1, the
secondary voltage is minimum
• this during the period of light inductive load
When the movable arm contact with higher position such as 5 ,the
secondary voltage is maximum
• This during the period of high inductive load,
During high system load conditions, network voltages are kept at
highest practical level to
• minimize reactive power requirements
• increase effectiveness of shunt capacitors to compensated reactive
power
During light load conditions, it is usually required to lower network
voltages
• avoid under excited operation of generators
Advantage of tap changing transformer
• autotransformer has a single winding with two end terminals, one or
more terminals at intermediate tap points,
• The primary voltage is applied across two of the terminals,
• the secondary voltage taken from two terminals,
• always having one terminal is common with the primary and
secondary
• the current flows directly from the input to the output, and only
smaller part inductively
• Autotransformers are frequently used in power transmission and
distribution
autotransformer
In a step down transformer the source is usually connected across
the full winding while the load is connected by a tap across the
desired voltage
In a step up transformer, the source is connected to a tap across
desired voltage ,while load is attached across the full winding
common autotransformer
Induction Regulators
There are two types of induction regulators single phase and 3 phase.
The construction it is similar to a induction motor except that the rotor is
not allowed to rotate continuously but can be adjusted in any position
either manually or by a small motor.
The adjustable output voltage by varying the inductive coupling between a
rotor and a stator winding
induction Regulators are used for voltage control of distribution primary
feeders.
Figure 5 :single induction Regulators
Single phase induction regulator.
The primary winding terminals of the stator and is connected across
the supply line.
The secondary winding is for rotor is connected in series with the line
whose voltage is to be controlled.
The primary windings either in star or delta are wound of the stator and
are connected across the supply.
The secondary windings are wound of the rotor and the six terminals are
connected in series with the line whose voltage is to be controlled.
Three phase induction regulators are used to regulate the voltage of
feeders and connection with high voltage
Three phase induction regulator
Figure 6 : Three phase induction regulator Y_ Connected
• A synchronous machine running without a prime mover or a mechanical
load
• the reactive power control depending on field excitation, Started as an
induction motor ,
• the main function is the improvement of p.f of the electrical system is
known as the synchronous condenser.
• It is installed at the receiving end of the line .
Synchronous Condenser dynamic Compensators
figure 5 : Synchronous Condenser
1 Reliability is very high.
2. No generation of harmonics.
3. Low maintenance and not affected by harmonics.
Advantages
Better efficiency of power generation, transmission and distribution
Improvement in voltage
Reduced KVA demand
Reduced system losses.
Benefit of reactive power and voltage controlled
why capacitors are used as reactive power compensation device?
A capacitor is said to be generator of reactive power. When a
capacitor is connected across a load, it provides reactive power to
the load. Its cheep type of compensation
By reactive power compensation we can control the power factor
and stability of voltage and reduce the consumption of electricity.
Summary of reactive power compaction
THANK YOU
FOR listening
any question
Reference
1. The raja Electrical Technology chapter 15 voltage controlled of
Twenty Third edition
2. REACTIVE POWER AND VOLTAGE CONTROL ISSUES IN ELECTRIC
POWER SYSTEMS Peter W. Sauer University of Illinois at Urbana-
Champaign [email protected]
3. www.google.com/ renewable academy
4. en.wikipedia.org