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Facts 15-11-2011




Prof. M.V. Aware Electrical Engg. Dept. VNIT , NAGPUR MVA-VNIT MVA-VNIT NAGPUR 1 Simple illustration of the power transmission system MVA-VNIT MVA-VNIT NAGPUR 2 Simple illustration of the power transmission system MVA-VNIT MVA-VNIT NAGPUR 2 Power system structure PCompensation  Pi = PGenerator + PLoad + PCompensation S = P + jQ  Qi = QGenerator + QLoad + QCompensation MVA-VNIT MVA-VNIT NAGPUR 3 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. There is only a few percent margin for such a self regulation MVA-VNIT NAGPUR 4 Apparent Complex Power: Real Power: P V  S = P + jQ 2  X   sin    Reactive Power: Q  V    I   sin(   / 2)  V  2  X   (1  cos   ) V voltage X reactance   phase angle I current MVA-VNIT NAGPUR 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 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, capacity and flexibility of power transmission systems. MVA-VNIT NAGPUR 8 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 FACTS solutions enable power grid owners to increase existing transmission network capacity while maintaining or improving the operating margins necessary for grid stability. As a result, more power can reach consumers with a minimum impact on the environment, after substantially shorter project implementation times, and at lower investment costs - all compared to the alternative of building new transmission lines or power generation facilities. The two main reasons for incorporating FACTS devices in electric power systems are: - Raising dynamic stability limits - Provide better power flow control MVA-VNIT NAGPUR 11 MVA-VNIT NAGPUR 12 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. MVA-VNIT NAGPUR 13 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 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) - Unified Power Flow Controllers (UPFC) MVA-VNIT NAGPUR 16 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 SVC Configurations: Thyristor controlled Reactor (TCR) or Thyristor Switched Capacitor (TSC) Or Combination of both. Other combination of SVC Fixed Capacitor-TCR (FC-TCR) Or TCR-Mechanically Switched Capacitor (TCR-MSC) MVA-VNIT NAGPUR 19 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 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. 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