transient enhancement technique

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  2. 2. Transient stabilityTransient stability is the ability of thepower grid system to maintain synchronismwhen subjected to severe disturbances.Short circuit on transmission line. removal of large transmission loads,cascaded failure operations,
  3. 3. Swing Equation22 = = = 12M=Inertia constant (if speed constant depend onsize)= Power angle of the machine in rad=Accelerating powerPm=Mechanical input to synchronous gen.Pe=Electrical output of synchronous gen.E=Generator voltageV=Bus voltageX12=Reactance of the line
  4. 4. Transient stability improvementmethod:Rotor size and transfer reactance of line Dynamic braking resistorIndependent-pole operation of circuitbreakerSingle- pole switchingFast excitation ControlFast governor action
  5. 5. Cont.Generator tripping (For large systems)Load TrippingRegulated shunt compensationSCR (Short Circuit Ratio)HVDC
  6. 6. Effect of MAn increase in the value of inertiaconstant M reduces the angle throughwhich the rotor swings farther during afault. However, this is not a practicalpropositionIncreasing M meansIncreasing the dimensions of the machine,which is uneconomical.Note: Not feasible
  7. 7. Effect of X12Reduction of transfer reactanceUse of parallel lines instead of single lineuse of bundle conductors.
  8. 8. Dynamic braking resistor
  9. 9. Dynamic Braking resistorIt is one of the most efficient and widely used externalcontrol method.BR is a artificial (dummy) load added at the terminalof the synchronous generators for short duration oftime to reduce the generator speed and then removefrom the system so as to maintain synchronism.It open under fault condition and absorb theaccelerating energy during fault condition.Control can be done by power electronics switch.
  10. 10. Dynamic braking resistorShunt resistor energy dissipated VoltageSeries resistor energy dissipated CurrentNote:Preferred in hydro station due remotelocation from load Centre
  11. 11. Independent- pole operation ofcircuit breakerUse of separate mechanism for eachphase .Each phase open and close individually.Fault of any phase will not affect theother phase.Relaying system is normally arrange totrip all the pole for any type of fault.
  12. 12. Single pole switchingUse of separate mechanism for eachphase.For single line to ground fault relaydesign to trip only fault phaseReclosing operation followed after certaintime.Used where single line connect agenerator connected to rest of systems.
  13. 13. Fast excitation ControlGenerator excitation controls are a basicstability control. provide powerful andeconomical means to ensure stability for largedisturbances.Automatic voltage regulators Detect the decrease in the voltage Response by increase in excitation voltagePower system stabilizer Fast excitation due to transient lead to degrading of damping oflocal plant mode oscillations It produce the damping torque component
  14. 14. Fast governor actionChange in power angle during disturbancecan be mitigated by varying the prime moveroutput with the help of fast acting governorAcceleration energy of rotor can be controlledIt operate after about 15 cycle (i.e.0.30sec for50Hz system). Which can cause stabilityproblem with severity of the faults.It is not adequate for hydro power station dueto difficulty in control of water flow.
  15. 15. Generator tripping(For large systems)Tripping of generator units for severetransmission system.Power transferred reduced over thetransmission line.Generator can be tripped rapidlySo accelerating energy greatly reduced tomaintain the synchronismNote: Due to tripping of generator powertransferred is reduced and available energy keptin idle state.
  16. 16. Load TrippingSimilar to generator trippingTripping at load end To reduce the decelerating of receiving end generation Tripping of some part of system rather than large system
  17. 17. Regulated shunt compensationSynchronous condenser Synchronous machine without mechanical load. It can operate in leading, unity and lagging on requirement. Control the lagging and leading reactive power.Static VAR compensator Shunt connected generator or absorber with control device. Its output can be varied to control the specific parameter ofelectrical power system. It is static means no moving parts.
  19. 19. Static VAR devices (FACTs Device)Saturated reactorThyristor control reactor(TCR)Thyristor switched capacitor(TSC)Thyristor switched reactor (TSC)
  20. 20. HVDCThyristor control employed.DC link is asynchronous No synchronization is required Power transfer can be easily controlled No risk of a fault in one system causing loss of stability in theother system.Note: high cost of converter and inverter.
  21. 21. ReferencesPower system stability and control by PrbhaKundur.Power system analysis by Prof. P.S.R.Murthy.Power system engineering by D.P.Kothariand I.J.Nagrath.Power system analysis operation and controlby Abhijit Chakrabarti and Sunita Halder.
  22. 22. Thank You
  23. 23. SCR (Short Circuit Ratio)Ratio of the field current required for therated voltage at open circuit to the fieldcurrent required for rated armature currentat short circuit.SCR=SCR=1..
  24. 24. Cont.Lower the SCR ratioReduction machine air gapSaving machine mmf, size weight andcostReduction in size of rotor reduce inertiaconstant lowering thereby stability margin


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