A Smart Grid Application for Dynamic Reactive Power Compens

A Smart Grid Application for Dynamic Reactive Power Compensation

A presentation byG. Vamsi Krishna KartheekPRDC, BangaloreCo-AuthorSVN Jithin SunderBHEL, Hyderabad

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Requirement of Automatic Coordinated Control

Modern power system are distributed over a wide geographical region. Voltage levels are 33kV, 132kV, 220kV, 400kV, 765kV and even 1200kV.Both conventional and non-conventional sources are present. Voltage controls are like AVR, Online tap change transformers, FACTS, HVDC, Switchable capacitors and reactors, etc.All these controls to be coordinated through centralized control to achieve optimization at higher level.Automation is to implement effective control in real time.

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Steps to Implement Automatic Coordinated Control

Network operating condition to be monitored Network operating state to be visualized Higher level control from a centralized control centerComplete system automationEffective ICT

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Technologies to be Effectively Deployed and Exploited

Network operating condition monitoring Measuring devices to measure voltages, real power, reactive powersPMU technologies to measure voltage phase angle at all substationsNetwork operating state visualization and Higher level control from a centralized control centerPRM control system for visualization and control in real time to optimize the reactive power dispatch from time to time. Additionally various system stability analysis algorithms (non real time) can run in back ground for visualization and analysis of operator.

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Technologies to be Effectively Deployed and Exploited

Automation of complete reactive power controlThyristor switched reactors in place of fixed shunt reactors where ever possible.Dynamic reactive power support devices like SVC, STATCOM, CSR, etc. Relay protection and circuit breaker control be centralized in all substations and be monitorable/controllable from control center. Complete automation of substations where reactive power control is present.Any substation/power plant monitoring and control system will be centralized in itself and controllable from control center.

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Technologies to be Effectively Deployed and Exploited

Effective ICTGood communication channels for communication between control centers and entire network. Full-fledged SCADA system with hierarchal control system. Substation wise control be primary level control PRM control system at control center will be secondary level control. State of art technology hardware and software.

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Phasor Relativity based Mathematical Control System

The PRM control system will not predict any voltage collapse.The control system will always try to bind the system operation within the optimum region of operation through optimum reactive power dispatch. So this will enhance the voltage stability from time to time. The computations will be from the local measurements.We are proposing PRM control system for online real time control based on the studies performed.

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WAMS Architecture proposed by [2]

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Dotted Line Indicates

Data Flow

WAMS Architecture with PRM Control System

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Dotted Line Indicates

Data Flow

Solid Line Indicates

Control Flow

Primary Level Control

Secondary & Highest Level Control

WAMS Architecture with PRM Control System

Any disturbance will lead to change in operating state.New optimum reactive power dispatch will be generated for the new state.Incase of system islanding each island will operate as separate region.So the respective PRM control system in the island will be the central control.Any time the controller at NLDC will be the supreme.Effective reactive power management helps to neutralize the post disturbance uncertainties. Ultimately helps in mitigating blackout.No alarm will be generated to indicate voltage collapse.Alarms can be generated to indicate the exhausted reserves.

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Types of Controls

Control StationsTypes of ControllersGenerating PlantAVR, Governor, Transformer tap control, bus/line switchable reactors (if any available)EHV/UHV substationsTransformer tap control, Switchable bus/line reactors, switchable capacitors, FACTSHVDC substationConverter control, Inverter control, switchable capacitors, switchable reactorsNon-Conventional Energy SourcesSwitchable capacitors, switchable reactors, transformer tap control, FACTS

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Case Studies Performed

Two case studies are performed, model analysis and time domain simulation.All devices are assumed to be centrally controlled. System operating state data comes from SCADA using PMU in WAMS In Model analysis performing load flow, the same data is assumed to be reaching the PRM control system.The simulation demonstrates the performance of PRM control system for functional behavior of the system. In the time domain simulation also similar consideration is assumed.

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Equivalent South Indian Grid Model (EHV 24 Bus System)

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Case Study 1

Model analysis is performed for three cases. The cases are as below.Case(1):- This case is with fixed shunt reactors and no control in the system. Case(2):- This case is with fixed shunt reactors but PRM control system is implemented with controls limited to generators, tap change transformer and switched shunt capacitors. Case(3):- In this case along with all the controllers in the case(2) CSR is also installed in the PRM control system.

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Studies Performed on the EHV 24 Bus System

Load is varied from 40% of the base load to the maximum permissible limit in each case.For every 10% of load variation a snapshot is collected.Control calculations are performed manually according to the algorithm.The voltages are plotted for the three cases for all the snapshots. Voltage stability indices plot and loss plot are drawn separately for all the three cases. MATPOWER and PSAT software are used.

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Results of the Cases(1)

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Voltage profile(

p.u.) Vs percentage of base load

Maximum Network Loading LimitIs 100% of Base Load

Network Voltages are

between 0.82-1.10 p.u.

Results of the Cases(2)

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Voltage profile(p.u.) Vs percentage of base load

Maximum Network

Loading LimitIs 110% of Base Load

Network Voltages are

between 0.84-1.05 p.u.

Results of the Cases(3)

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Voltage profile(p.u.) Vs percentage of base load

Maximum Network

Loading LimitIs 145% of Base Load

Network Voltages are between

0.95-1.05 p.u. upto 140% of Base Load

Eigen Value Analysis for Voltage Stability of the Three Cases

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Most predominant Eigen value (distance from Y

axia

) Vs percentage of base load

Real Power Losses of the Three Cases

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Real Power losses(MW) Vs percentage of base load

Comparison of Three Cases

No Control CaseControl without CSRControl with CSRPower Transmission Capacity100%115%145% Voltage Limits in p.u.0.82-1.10 0.84-1.050.91-1.05(0.95-1.05 upto 140%)Types of Controls No ControlsAVG, Onload Tapchanger, Shunt CapacitorsAVG, Onload Tapchanger, Shunt Capacitors, CSR.Real power loss at rated full load70MW60MW55MW

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This limit can be extended to 180% with installed shunt capacitors

Case Study of Stability Maintenance under Disturbance Condition

The studies are performed for two cases.The cases areCase(A):- The reactors are fixed reactors.Case(B):- The reactors are switched reactors and PRM control system is implemented.Branch between buses 23-24 is tripped at 10s.Voltages, rotor angles and powers are plotted for the two cases.

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Voltage and rotor angle plots of two casesCase(A) Case(B)

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Explanation to the Case Study

The network with reactors connected wont satisfy n-1 contingency means in Alert state. When any fault occurs it goes to emergency or extremis case.

Network with reactors disconnected satisfies n-1 contingency so its in normal state.When any fault occurs it goes to alert state.

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When the reactors are suddenly switched the system that’s in alert state will stay in alert state for some more time.This time gap may be of order of 20s to 5mins. Some control action should taken to bring the system back to normal state.If not again blackout may occur or load shedding is to be performed. The operator or the control system has to make advantage of this time gap to secure the system.

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Explanation to the Case

Study

Significance of PRM Control System and CSR

System security will be improved with increased reactive power reserve.Reduction in dynamic over voltage limit as its no more required to limit the reactive compensation to 60%.The faster response of CSR (10ms) will be primary control and PRM control system will be secondary control with response time of 10-20s. System security is improved with CSR. (as system satisfies n-1 contingency)Coordinated control can avoid blackouts. Reduces the installation cost and the maintenance cost in a significant manner.

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Intelligent Control Actions that can Save System from Collapse

Intelligent switching of line, bus reactors, shunt capacitors and FACTS devicesUsing optimum tap controlsIntelligent and controlled switching of line circuit breakers Optimally setting the generator terminal voltageOptimal load dispatch under critical situations

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Conclusion & Future Work

In the studies performed, the local controls are not considered as it is difficult to simulate local automatic control.However the future work is to simulate local automatic control at each substation and centralized control in RTDS. PMUs to be present at main substations and where control is available.WAMS system present at control centers.

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Thank you

Questions & Discussions

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