Voltage and reactive power control

1. Voltage and reactive power
control
Presented by
Ahmed ALi
power system opration
Code: EEE 574

2.  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

3.  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

4. • 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

5.  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

6.  Reactive power formulas
Q =
V2
X
VAR
For heavy load condition s required
+ve var C- bank
For light load condition required
-ve var L –bank
Q α v2

7. Receive power Injection
Than Total reactive power in
receiving
QR = QS + QC
JQc
Ps+ JQs
PR+ J(QR +Qc )
LoadShunt compensation
Power sending
PR + JQR

8.  Methods of control voltage Reactive Power
Control 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

9.  Static sources or
fixed
• Shunt compensation
• Series compensation
• Static (VAR) compensators
• Static compensators
All these devices compensate reactive power using a similar
operating principle.

10. • 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

11. Figure 1 : Transmission line with shunt compensation

12.  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.

13. Figure 2 : Transmission line with series compensation
V Sending
X TL
V receiving
Xc serise

14. 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
 static VAR compensator

15. Figure 3 : static VAR compensator. use thyristor switched

16.  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

17.  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

18. 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

19.  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

20. 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,

21. 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

22. • 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
 autotransformer

23.  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

24.  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.

25. 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.

26.  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

27. Figure 6 : Three phase induction regulator Y_ Connected

28. • 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

29. figure 5 : Synchronous Condenser

30. 1 Reliability is very high.
2. No generation of harmonics.
3. Low maintenance and not affected by harmonics.
 Advantages

31.  Better efficiency of power generation, transmission and distribution
 Improvement in voltage
 Reduced KVA demand
 Reduced system losses.
 Benefit of reactive power and voltage controlled

32.  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

33. THANK YOU
FOR listening
any question

34. 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 -sauer@ece.uiuc.edu
3. www.google.com/ renewable academy
4. en.wikipedia.org