FLEXIBLE AC TRANSMISSION SYSTEMS (FACTS) Prof. M.V. Aware Electrical Engg. Dept. VNIT , NAGPUR MVA-VNIT NAGPUR 1 Simple illustration of the power transmission system MVA-VNIT NAGPUR 2 Power system structure S = P + jQ Pi = PGenerator + PLoad + PCompensation Qi = QGenerator + QLoad + QCompensation MVA-VNIT NAGPUR 3 There is only a few percent margin for such a self regulation MVA-VNIT NAGPUR 4 .FLOW OF POWER IN AN AC SYSTEM Many transmission facilities confronts one or more limiting network parameters plus inability to direct flow at will Electrical systems are self regulating: If generation is less than load---the voltage and frequency drop The load goes down to equal the generation minus the transmission losses. Apparent Complex Power: S = P + jQ Real Power: V2 P sin X Reactive Power: V2 Q V I sin( / 2) (1 cos ) X MVA-VNIT NAGPUR V voltage X reactance phase angle I current 5 . Power Transfer Capacity Limiting Factors : •Thermal Limit •Steady State Stability Limit •System Damping Steady-state-stability Limit (MW) Thermal Limit (MW) Transient-stability Limit (MW) Electrical Damping Limit (MW) Different limits on power flow in transmission systems MVA-VNIT NAGPUR 6 . Power flow in parallel paths MVA-VNIT NAGPUR 7 . capacity and flexibility of power transmission systems. MVA-VNIT NAGPUR 8 .Applying Flexibility to the Electric Power System The power industry term FACTS (Flexible AC Transmission Systems) covers a number of technologies that enhance the security. FACTS are defined as “Alternating current transmission systems incorporating power-electronic based and other static controllers to enhance controllability and increase power transfer capability” MVA-VNIT NAGPUR 9 . FACTS are utilised for: •Increase/control of power transmission capacity in a line and for preventing loop flows •Improvement of system transient stability limits •Enhancement of system damping •Mitigation of sub-synchronous resonance •Alleviation of voltage stability •Limiting short circuit currents •Improvement of HVDC converter terminal performance •Grid Integration of Wind Power Generation Systems MVA-VNIT NAGPUR 10 . more power can reach consumers with a minimum impact on the environment.all compared to the alternative of building new transmission lines or power generation facilities. and at lower investment costs .Raising dynamic stability limits .Provide better power flow control MVA-VNIT NAGPUR 11 . after substantially shorter project implementation times. As a result.FACTS solutions enable power grid owners to increase existing transmission network capacity while maintaining or improving the operating margins necessary for grid stability. The two main reasons for incorporating FACTS devices in electric power systems are: . MVA-VNIT NAGPUR 12 . MVA-VNIT NAGPUR 13 .Possibilities of power flow control: • Control of line impedance X • Angle controls the active power • Injecting the voltage in series with line •Combination of the line impedance control with a series controller and voltage regulation with a shunt controller Can also provide a cost effective means to control both the active and reactive power flow between TWO systems. BASIC TYPES OF FACTS CONTROLLERS •Series Controllers •Shunt Controllers •Combined series-series Controllers •Combined series-shunt controllers MVA-VNIT NAGPUR 14 . TYPES OF FACTS DEVICES MVA-VNIT NAGPUR 15 . Unified Power Flow Controllers (UPFC) MVA-VNIT NAGPUR 16 .FACTS controllers are classified into two types: 1) Thyristor based FACTS controllers -Static Var Compensator (SVC) -Thyristor controlled Series Compensator (TCSC) 2) Voltage Source Converters (VSC) Based Controllers -Static Synchronous Compensator (STATCOM) -Static Synchronous Series Compensator (SSSC) . STATIC VAR COMPENSATOR (SVC) It is a shunt-connected static var generator or absorber It adjust the exchange of capacitive or inductive current to maintain or control specific parameters of the electrical power system (Typically bus voltage) MVA-VNIT NAGPUR 17 . MVA-VNIT NAGPUR 18 . Other combination of SVC Fixed Capacitor-TCR (FC-TCR) Or TCR-Mechanically Switched Capacitor (TCR-MSC) MVA-VNIT NAGPUR 19 .SVC Configurations: Thyristor controlled Reactor (TCR) or Thyristor Switched Capacitor (TSC) Or Combination of both. The dynamic V-I characteristics of the SVC Linear range of control over which SVC terminal Voltage varies linearly with SVC current (Capacitive to inductive range) MVA-VNIT NAGPUR 20 . THYRISTOR CONTROLLED SERIES CAPACITORS (TCSC) Control of capacitive reactance of the line Provides continuous control of power on ac line over a wide range The basic principle of variable series compensation from the system viewpoint is to simply increase the fundamental frequency voltage across a fixed capacitor in a series compensated line through appropriate variation of the firing angle MVA-VNIT NAGPUR 21 . MVA-VNIT NAGPUR 22 . STATIC SYNCHRONOUS COMPENSATOR (STATCOM) It is a controlled reactive power source It provides desired reactive power generation as well as absorption By processing voltage and current waveforms in a -Voltage Source Converter (VSC) MVA-VNIT NAGPUR 23 . STATCOM CONTROL Reactive power exchange between the converter and the ac system can be controlled by varying the amplitude of the converter MVA-VNIT NAGPUR 24 . MVA-VNIT NAGPUR 25 . V-I Characteristics of a STATCOM MVA-VNIT NAGPUR 26 . STATIC SYNCHRONOUS SERIES COMPENSATOR (SSSC) Series connected synchronous voltage source Effective impedance variation by injecting a voltage with appropriate phase angle in relation to the line current power Capable of real and reactive power exchange with the transmission system MVA-VNIT NAGPUR 27 . MVA-VNIT NAGPUR 28 . MVA-VNIT NAGPUR 29 .UNIFIED POWER FLOW CONTROLLER (UPFC) -Voltage regulation -Series compensation -Phase shifting It can independently control both the real and reactive power flow in Transmission line with extremely rapid speed. MVA-VNIT NAGPUR 30 . MVA-VNIT NAGPUR 31 . MVA-VNIT NAGPUR 32 . MVA-VNIT NAGPUR 33 . ' ' % !&# . ' ' % !&# .