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 the management of reactive power to improve the performance 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 the voltage fluctuation at a given terminal of transmission line.

Therefore the VAR compensation improves the stability of ac system by increasing the maximum active 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 sustains the electric and magnetic fields of alternating-current equipment. Reactive power must be supplied to most types of magnetic equipment, such as motors and transformers.

In an ac transmission, when the voltage and current go up and down at the same time, only real power is transmitted and when there is a time shift between voltage and current both active and reactive power 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 transmission

lines, capacitors and reactors.• Provides greater ability to transfer power between

controlled 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 controllerIt 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 controllerIt in which contains series and shunt elements

via a DC link for power exchange.

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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 simultaneously all three parameters of line power flow(voltage,current power).

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

1. STATCOM 2. SSSC• These two devices are two Voltage Source controller’s

(VSC’s) connected respectively in shunt with the transmission line through a shunt transformer and in series with the transmission line through a series transformer, connected to each other by a common dc link including a storage capacitor.

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

regulation at the point of connection injecting an opportune reactive power flow into the line and to balance the real power flow exchanged between the series inverter and the transmission line.

• The series converter (SSSC) can be used to control the real and reactive line power flow inserting an opportune voltage with controllable magnitude and phase in series with the transmission line.

• It’s also known as “unified” controller and require small amount of power for DC circuit exchange occurring between the shunt-series converters.

CIRCUIT DESCRIPTION• The basic configuration of a UPFC, which is installed

between the sending-end Vs and the receiving-end VR. the dc terminals of which are connected to a common dc 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!