FLEXIBLE AC TRANSMISSION SYSTEM

PRESENTED BY:-

MONIK ADROJA

GOVT. POLYTECHNICHJUNAGADH

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..

The first FACTS installation was at the C. J. Slatt Substation in Northern Oregon. This is a 500 kV, 3-phase 60 Hz substation, and was developed by EPRI, the Bonneville Power Administration and General Electric Company.

History

Series Compensation

In series compensation, the FACTS is connected in series with the power system. It works as a controllable voltage source.

Series inductance exists in all AC transmission lines.

Shunt Compensation

In shunt compensation, power system is connected in Shunt (parallel) with the FACTS. It works as a controllable current source.

Types Of Shunt Compensation

Shunt capacitive compensation

This method is used to improve the power factor. Whenever an inductive load is connected to the transmission line, power factor lags because of lagging load current.

This method is used either when charging the transmission line, or, when there is very low load at the receiving end. Due to very low, or no load – very low current flows through the transmission line.

Shunt Inductive Compensation

What are FACTS devices?

FACTS devices are used for the dynamic control of voltage, impedance and phase angle of high voltage AC transmission lines.

Types of FACTS devices

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Static var compensators.

Statcoms.

Thyristor controlled series compensators.

4 Unified power flow controller.

Static var compensators.

The most important FACTS devices, have been used for a number of years to improve transmission line economics by resolving dynamic voltage problems.

The accuracy, availability and fast response enable svc’s to provide high Performance steady state and transient voltage control compared with classical shuntCompensation.

Svc’s are also used to dampen power swings, improve transient stability, and Reduce system losses by optimized reactive power control.

Statcoms.

Statcoms are GTO (gate turn-off type thyristor) based svc’s. Compared with conventional svc’s (see above) they don’t require large inductive and capacitive components to provide inductive or capacitive reactive power to high voltage transmission systems.

An additional advantage is the higher reactive output at low system voltages where a STATCOM can be considered as a current source independent from the system voltage

Statcoms have been in operation for approximately 5 years.

Thyristor Controlled Series Compensators.

Thyristor controlled series compensators are an extension of conventional series capacitors through adding a thyristor-controlled reactor.

Placing a controlled reactor in parallel with a series capacitor enables a continuous and rapidly variable series compensation system.

The main benefits of tcscs are increased energy transfer, dampening of power oscillations, dampening of sub synchronous resonances, and control of line power flow.

Unified power flow controller.

UPFC Connecting a STATCOM, which is a shunt connected device, with a series branch in the transmission line via its DC circuit results in a UPFC.

This device is comparable to a phase shifting transformer but can apply a series voltage of the required phase angle instead of a voltage with a fixed phase angle.

The UPFC combines the benefits of a STATCOM and a TCSC.

Benefits of FACTS devices

Better utilization of existing transmission system assets

Increased transmission system reliability and availability

Increased dynamic and transient grid stability and reduction of loop flows

Increased quality of supply for sensitive industries.

Environmental benefits better utilization of existing transmission system assets

Financial Benefits Of FACTS Devices

Additional sales due to increased transmission capability.

Additional wheeling charges due to increased transmission capability.

Avoiding or delaying of investments in new high voltage transmission lines or even new power generation.

Maintenance Of FACTS Devices

The amount of maintenance ranges from 150 to 250 man-hours per year and depends upon the size of the installation and the local ambient (pollution) conditions.

Maintenance of FACTS devices is minimal and similar to that required for shunt capacitors, reactors and transformers

It can be performed by normal substation personnel with no special procedures.

Identification Of FACTS Projects

Conduct a detailed network study to investigate the critical conditions of a grid or grids’ connections

For a stable grid, the optimized utilization of the transmission lines

If there is a potential for improving the transmission system, either through enhanced stability or energy transfer capability, the appropriate FACTS device and its required rating can be determined.

Future Developments In FACTS

Future developments will include the combination of existing devices.Like Combining STATCOM with a TSC to extend the operational range.

Developments in superconductor technology open the door to new devices like SCCL (super conducting current limiter) andSMES (super conducting magnetic energy storage).

CONCLUSION

Compensators can be effectively applied in power transmission systems to solve the problems of poor dynamic performance and voltage regulation in a 115 kv and 230 kv transmission system.

Transmission SVCS and other FACTS controllers will continue to be applied with more frequency as their benefits make the network “flexible” and directed towards an “open access” structure.

Since SVC is a proven FACTS controller, it is likely that utilities will continue to use the Svc’s ability to resolve voltage regulation and voltage stability problems.

SVCS also provide an environmentally-friendly alternative to the installation of costly and often un-popular new transmission lines.

Dynamic performance and voltage control analyses will continue to be a very importantProcess to identify system problems and demonstrate the effectiveness of possible solutions.