1

A Smart Grid Application for Dynamic Reactive Power Compensation

A presentation by

G. Vamsi Krishna KartheekPRDC, Bangalore

Co-Author

SVN Jithin SunderBHEL, Hyderabad

2

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.

3

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 center

• Complete system automation

• Effective ICT

4

Technologies to be Effectively Deployed and Exploited

• Network operating condition monitoring

– Measuring devices to measure voltages, real power, reactive powers

– PMU technologies to measure voltage phase angle at all substations

• Network operating state visualization and Higher level control from a

centralized control center

– PRM 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.

5

Technologies to be Effectively Deployed and Exploited

• Automation of complete reactive power control

– Thyristor 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.

6

Technologies to be Effectively Deployed and Exploited

• Effective ICT

– Good 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.

7

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.

8

WAMS Architecture proposed by [2]

Dotted Line Indicates Data Flow

9

WAMS Architecture with PRM Control SystemDotted Line Indicates

Data FlowSolid Line Indicates

Control Flow

Primary Level Control

Secondary & Highest Level Control

10

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.

11

Types of Controls

Control Stations Types of Controllers

Generating Plant AVR, Governor, Transformer tap control, bus/line

switchable reactors (if any available)

EHV/UHV substations Transformer tap control, Switchable bus/line

reactors, switchable capacitors, FACTS

HVDC substation Converter control, Inverter control, switchable

capacitors, switchable reactors

Non-Conventional Energy

Sources

Switchable capacitors, switchable reactors,

transformer tap control, FACTS

12

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.

13

Equivalent South Indian Grid Model (EHV 24 Bus System)

14

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.

15

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.

16

Results of the Cases(1)

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

Maximum Network Loading Limit

Is 100% of Base Load

Network Voltages are between 0.82-1.10 p.u.

17

Results of the Cases(2)

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

Maximum Network Loading Limit

Is 110% of Base Load

Network Voltages are between 0.84-1.05 p.u.

18

Results of the Cases(3)

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

Maximum Network Loading Limit

Is 145% of Base Load

Network Voltages are between 0.95-1.05 p.u. upto 140% of Base Load

19

Eigen Value Analysis for Voltage Stability of the Three Cases

Most predominant Eigen value (distance from Y axia) Vs percentage of

base load

20

Real Power Losses of the Three Cases

Real Power losses(MW) Vs percentage of base load

21

Comparison of Three Cases

No Control Case Control without CSR

Control with CSR

Power Transmission Capacity

100% 115% 145%

Voltage Limits in p.u.

0.82-1.10 0.84-1.05 0.91-1.05(0.95-1.05 upto 140%)

Types of Controls No Controls AVG, Onload Tapchanger, Shunt Capacitors

AVG, Onload Tapchanger, Shunt Capacitors, CSR.

Real power loss at rated full load

70MW 60MW 55MW

This limit can be extended to 180%

with installed shunt capacitors

22

Case Study of Stability Maintenance under Disturbance Condition

• The studies are performed for two cases.

• The cases are

• Case(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.

23

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

0 20 40 60 80 1000.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Time (s)

Vol

tage

(V)

0 20 40 60 80 1000.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

Time (s)

Vol

tage

s (V

)

0 20 40 60 80 100-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Time (s)

Rot

or A

ngle

Syn 1

Syn 2

Syn 3

Syn 4

0 20 40 60 80 100-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Time (s)

Rot

or A

ngle

Syn 1

Syn 2

Syn 3

Syn 4

24

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.

25

• 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.

Explanation to the Case Study

26

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.

27

Intelligent Control Actions that can Save System from Collapse

• Intelligent switching of line, bus reactors, shunt capacitors and FACTS

devices

• Using optimum tap controls

• Intelligent and controlled switching of line circuit breakers

• Optimally setting the generator terminal voltage

• Optimal load dispatch under critical situations

28

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.

29

Thank you

Questions & Discussions