A

Seminar on

HVDC and FACTS for Improved

Power Delivery Through Long

Transmission Lines

Presented to: Presented By:

Prof. S.C.MITTAL RAJARAM CHANDRAMEENA

Prof. D.K.YADAV Roll no.-13/939

DEPARTMENT OF ELECTRICAL ENGINEERING, RTU, KOTA

CONTENTS

• Introduction of HVDC, and it’s Applications

• HVDC use in Long transmission lines

• Introduction of FACTS and it’s Advantages

• FACTS use in Long transmission lines

• Study of UPFC

• Power system analysis toolbox (PSAT)

• PSAT used in HVDC or UPFC line

• Conclusion

• References

Introduction of HVDC

• For long distance high power transmission by

overhead line & underground line.

• Requires converter stations at each end of the

line.

• It can interconnect different power systems.

• Frequency conversion-

(60 Hz to 50 Hz, 50Hz to 25 Hz).

COMPONENTS OF HVDC

TRANSMISSION SYSTEMS

Following component are used in DC system-

• Converters

• Smoothing reactors

• Reactive power supplies

• Harmonic filters

• Electrodes

• DC lines

• Circuit breaker

CONVERTERS

• Perform AC/DC (rectifier) and DC/AC

(inverter) conversion.

• They consist of bridges and transformers.

• The transformers are ungrounded such that

the DC system will be able to establish its

own reference to ground.

Multiple Bridge Converters

• Two or more bridges are

connected in series to obtain as

a high a direct voltage as

required.

• These bridges are series on the

DC side, parallel on the AC

side.

• The ratio of the transformers are

adjustable under load.

• Multiple bridge converters are

used in even numbers and

arranged in pairs for 12-pulse

arrangement .

SMOOTHING

REACTORS….

•They decrease harmonics in

voltages and currents in DC

lines.

•The availability of the

Smoothing inductors is to

control the pulses of

constant current flows into

the transformer’s secondary

windings.

•Prevent current from being

discontinuous for light

loads.

REACTIVE POWER SUPPLIES

Reactive power (VAR) compensation is defined as themanagement of reactive power to improve theperformance of ac systems. There are two aspects:-

1. Load Compensation – The main objectives are to:-

• Increase the power factor of the system.

• To balance the real power drawn from the system.

• Compensate voltage regulation.

• To eliminate current harmonics.

2.Voltage Support – The main purpose is to decrease thevoltage fluctuation at a given terminal of transmissionline.

Therefore the VAR compensation improves thestability of ac system by increasing the maximumactive power that can be transmitted.

Continue…

Power is referred as the product of voltage and current

i.e. power = V x I

The portion of electricity that establishes and sustainsthe electric and magnetic fields of alternating-currentequipment. Reactive power must be supplied to mosttypes of magnetic equipment, such as motors andtransformers.

In an ac transmission, when the voltage andcurrent go up and down at the same time, only realpower is transmitted and when there is a time shiftbetween voltage and current both active and reactivepower are transmitted.

AC HARMONIC FILTERS

• In the presence of system impendence of this

causes a non-sinusoidal voltage drop causing

voltage distortion at the load terminals known

as Harmonic Distortion.

• AC harmonic filters used to reduce

harmonics caused by converters which

generate harmonics in voltages and currents.

• These harmonics may cause overheating of

capacitors and nearby generators and

interference with telecommunication systems.

ELECTRODES• Used to provide connection to the earth for neutral.

DC LINES• They may be overhead lines or cables.

• DC lines are very similar to AC lines.

CIRCUIT BREAKERS• They used to clear faults in the transformer and for

taking the DC link out of service.

• They are not used for clearing DC faults.

• DC faults are cleared by converter control more rapidly(quickly).

ADVANTAGES OF HVDC

• Control of dc quantities (voltage, Current and Power).

• Loss is very less as no frequency reversals taken into

account.

• Improve line loading capacity & also increases the

efficiency of transmission.

• Requires less numbers of conductors for same power

transfer.

• Reduced in tower size (less clearance).

Continue...• More power can be transmitted more efficiently over

long distances by applying hvdc.

• Interconnection of two AC systems, where AC lines would not be possible due to stability problems or both systems having different nominal frequencies.

• Control of Reactive Power and control of AC Voltages.

• HVDC transmission is necessary for underwater power transfer if the cables are longer than 50km.

Introduction of FACTS

• FACTS as they are generally known, are new

devices that improve transmission systems.

• FACTS is a static equipment used for the AC

transmission of electrical energy.

• It is generally a power electronics based device.

• To enhance controllability and increase power

transfer capability.

Continue…

• Flexible AC Transmission System (Facts) is a

new integrated concept based on power

electronic switching converters and dynamic

controllers to enhance the system utilization and

power transfer capacity as well as the stability,

security, reliability and power quality of AC

system interconnections.

Benefits of FACTS

• Reduces the need for construction of new transmissionlines, capacitors and reactors.

• Provides greater ability to transfer power betweencontrolled areas.

• Improves the transient stability of the system.

• Controls real and reactive power flow in the line

independently.

• Increase quality of supply for sensitive industries.

• Increase transmission system reliability and availability.

Types of FACTS

• (a) Series controller

• (b) Shunt controller

• (c) Combined series-series controller

• (d) Combined series-shunt controller

•Series controller

It is designed to vary the impedance of the line

by presenting to the line circuit series

equivalents of capacitor, reactor or a variable

source. Voltage is injected in series from this

controller to vary the reactive power

compensation.

• Shunt controller .

It varies the shunt impedance connected to the

line by current injection. It can supply or

absorb variable reactive power.

Combined series-series controller

• It is use in multi-line transmission system. It

provides series reactive power compensation

for each line (3-phase) for real power to be

transferred via the interconnection. Another

term used for this controller is Interline Power

Flow Controller (IPFC), which is able to

balance both the real and reactive power flow.

It also contains a DC link like capacitor or

“battery” that provides energy storage.

•Combined series-shunt controller

It in which contains series and shunt elements

via a DC link for power exchange.

22

Efficient Installations: Easily installed in transmission lines.

Increased System Capacity: Maximum operational efficiency of

existing transmission lines and other equipment.

System Reliability: Provide greater voltage stability and power

flow control, which improves system reliability and security.

Improved System Controllability: Intelligence built into the

grid, ability to instantaneously respond to disturbances & redirect

power flows.

Investment: Less expensive than new transmission lines.

Greater flexibility as compare to hvdc line.

Improving real power transfer capability.

Advantage of FACTS Devices

STUTY OF UPFC

• The UPFC is a device which can control simultaneouslyall three parameters of line power flow(voltage,currentpower).

• Such "new" FACTS device combines together thefeatures of two "old" FACTS devices:

1. STATCOM2. SSSC

• These two devices are two Voltage Source controller’s(VSC’s) connected respectively in shunt with thetransmission line through a shunt transformer and inseries with the transmission line through a seriestransformer, connected to each other by a common dclink including a storage capacitor.

Continue…• The shunt converter (STATCOM) is used for

voltage regulation at the point of connectioninjecting an opportune reactive power flow intothe line and to balance the real power flowexchanged between the series inverter and thetransmission line.

• The series converter (SSSC) can be used to controlthe real and reactive line power flow inserting anopportune voltage with controllable magnitudeand phase in series with the transmission line.

• It’s also known as “unified” controller andrequire small amount of power for DC circuitexchange occurring between the shunt-seriesconverters.

CIRCUIT DESCRIPTION

• The basic configuration of a UPFC, which is installedbetween the sending-end Vs and the receiving-end VR.the dc terminals of which are connected to a commondc link capacitor.

Fig1: Basic configuration of UPFC

Power System Analysis Toolbox (PSAT)

• PSAT is a Matlab toolbox for static and dynamic

analysis and control of electric power systems.

• All operations can be assessed by means of graphical

user interfaces (GUIs) and a Simulink based library

provides an user friendly tool for network design.

• In order to perform accurate power system analysis,

PSAT supports a variety of static and dynamic

component models.

• A HVDC system is implemented in PSAT,

representing two AC/DC converters connected by a

DC line.

VSC HVDC in a DC line circuit with fault and

load and its back- to-back converter

(rectifier and inverter)

PSAT used in HVDC or UPFC line

a. The fundamental values of using lesser command lines for power simulation can be investigated and differences of power enhancement by applying HVDC or UPFC in a line can be reviewed critically.

b. Three phase generator is connected with a fault at the remote end bus (receiving end bus), which is the inverter. Normal power flow simulation is conducted using toolbox with discrete time in Matlab .

c. Fault is introduced at the inverter end or rectifier end, then clearing time is very low.

Results…

d. PSAT in general is more suitable for

fundamental power flow and is more

graphical user interface based simulation.

e. There are adequate types of FACTS model and

as well with latest power devices for

continuous or optimal power flow studies in

for a given network.

e. PSAT is found to be more user friendly toolset.

CONCLUSION• The advantages of HVDC in promoting damping of lines

power oscillation were shown in the case study to be more efficient than UPFC.

• HVDC can be very useful for long transmission lines.

• It is more recommended in networks or interconnected lines that have high variation of power demands and complicated network connections with different power frequencies.

• the cost for installing HVDC is 85 percent greater than FACTS devices.

• UPFC in general is good for promoting line load-ability and pool through interconnected network buses more effectively.

REFERENCES• IEEE guide for commissioning High-Voltage Direct-

Current (HVDC) converter stations and associated transmission systems.

• N.G. Hingorani & L. Gyugyi, "Understanding FACTS," New York.

• A. Edris, “Technology Developments Applications of power electronics-Based controller on transmission grid”.

• E.M. Yap, M. Al-Dabbagh, “Applications of FACTS Controller for Improving Power Transmission Capability”.

• F. Milano, “Power System Analysis Toolbox documentation (PSAT)”.

Thank you!