Reactive Power Management and Voltage Control in RE rich Regime

Reactive Power Management and Voltage Control in RE rich Regime

Location: JaipurDate: Sep 13, 2017Location: JaipurDate: Sep 13, 2017

Renewable Integration & Sustainable Energy Initiativeunder Greening the Grid (GTG) ProgramA Joint initiative of USAID and Ministry of Power

Renewable Integration & Sustainable Energy Initiativeunder Greening the Grid (GTG) ProgramA Joint initiative of USAID and Ministry of Power

9/13/2017 2

Organization of the talk

• Introduction

• Pro-active planning requirement

• Understanding reactive power

• Reactive power control devices

• Case Studies

• Conclusions

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Wind Power: Installed Capacity & Potential

Source: NIWE Indian Wind Atlas 2015, IWTMA

7870

5429

4752

4280

3775

3611

2498

101

11900

8800

7600

8600

6200

8100

6200

2000

33800

84431

45394

18770

55857

44229

10484

4244

0 10000 20000 30000 40000 50000 60000 70000 80000 90000

Tamilnadu

Gujarat

Maharashtra

Rajasthan

Karnataka

Andhra

Madhya

Telangana

State wise Wind Utilized (as on 31st March 2017)

Wind Power potential at 100m

Target for 2022

Wind Installed Capacity

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Solar Power: Installed Capacity & Potential

Source: MRRE

2023

1262

1117

3658

1261

1697

5762

8020

5675

11834

5697

8884

142310

35770

61660

58440

24700

17670

0 20000 40000 60000 80000 100000 120000 140000 160000

Rajasthan

Gujarat

Madhya Pradesh

Andhra&Telangana

Karnataka

Tamilnadu

State wise Wind Utilized (as on 31st Jul 2017)

Solar Power potential

Target for 2022

Solar Installed Capacity

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Introduction - Challenges

Renewable sectors are facing the interconnection and scheduling issues world wide

At times, the generation is backed off due to network congestion or in-adequacy of the evacuation at up-stream.

New interconnections are delayed

When problem still persists in the sector, there is lot of push from policy makers to enhance the renewable energy foot print.

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Existing Problems

Construction of new transmission facility

Acquisition of linear property rights to establish rights-of-way

Environmental impacts and disruption of communities,

Require major capital investments

Usually require many years to site, license, design, and construct,

New transmission lines must, by necessity, typically be planned to accommodate long-term use instead of just the immediate needs.

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Proactive Plans – What it means

State Policy

Problems

Planning

• Electrification• Industrialization• Urbanization• Renewable energy

policy

Addition of• Lines• Substations• Dynamic

compensations

• Poor voltage• Over loading of

lines• Network

congestion• High losses• System security

Proactive

9/13/2017 8

Probable Solutions

While pure merchant-based transmission infrastructure may not soon materialize in India, transmission infrastructure construction by non-utility entities is still possible under existing rules and legislation.

Regulations are required to ensure cost recovery for transmission projects that relieve congestion, regardless of ownership.

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What should be done?

STUs or any other state body should

undertake efforts to address

interconnection needs so as to expedite matters for those

facilities.

They should have major interest in

resolving the delays in the interconnection

process for all resources, especially

with regard to renewables.

As new renewable energy policies are

being coined in, proactive measures are required by all

concerned agencies to address the

interconnection issues and arrive at plans

that can be implemented in stage

wise.

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Environmental Requirements

Emerging environmental requirements also raise

uncertainty, especially with regard to the costs to

comply with such requirements.

Construction of new right of way is always an issue

The existing corridors to be better utilized by dynamic compensation, loading the

lines to thermal limits without compromising on

the system security.

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What is needed?

To come out with a comprehensive plan covering at least 10 years horizon period

Revisit the plan year on year

Have both short term measures to overcome uncertainties and long term measures to accommodate State policies.

Always look for the technical feasibility and grid security.

Economic viability may not be seen in all projects

Prioritize the projects into those economically viable and less viable.

However, there can be special incentives or tariff mechanism to accommodate state policies.

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Renewable Integration Study

Each state utility should conduct a Renewable Integration Study to address the statewide effects of additional renewable generation interconnected to the grid

The study should consider both normal growth scenario (business as usual) and high growth scenarios for atleast 5-10 years.

The analysis should consider impacts on power system operations, system planning and the need for transmission system augmentation.

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Requirement for Grid Friendly RE Integration

Voltage/Var control and regulation

Fault ride through

Active power

control, ramping

and curtailment

Primary frequency regulation

Inertial response

Short circuit current control

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Reactive Power

• Arises due to inductance and capacitancein the electrical circuit.

• Ideal situation is to compensate at thesource or sink so that through out thesystem unity power factor is maintained.

• Any deviation from the ideal situationcauses the voltage variation and increasedlosses in the system.

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Device, Current and Voltage Drop

• Inductive current flowing inthe inductor

• Capacitive current flowing inthe inductor

• Inductive current flowing inthe capacitor

• Capacitive current flowing inthe capacitor

� Voltage drop in the direction ofcurrent flow

� Voltage drop in the direction ofcurrent flow

� Voltage raise in the direction ofcurrent flow

� Voltage raise in the direction ofcurrent flow

9/13/2017 16

Reactive Power Management

• Reactive power planning

• System operations planning

• Reactive power dispatch andcontrol

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Reactive Power Planning

• Reactive power planning isconcerned with the installationor removal of reactive powerequipment in a power system.

• System conditions for the futuresystem is studied and reactivepower planning is done inadvance

• More crucial, when the systemload increases and more andmore EHV lines are added to thesystem.

Where Q?When Q?What quantum Q?

G

LGRID

9/13/2017 18

System Operations Planning

G

LGRID

• This is concerned withthe improvement inoperating practicesutilizing existing reactivepower equipment.

• This planning isperformed for systemconditions anticipated tooccur a few days to ayear into the future. How to operate Q

When to operate Q

9/13/2017 19

Reactive Power Dispatch & Control

G

LGRID

• This determines the actualequipment operations.

• Associated analysis isperformed seconds to hoursprior to its implementation

• Reactive power optimizationprogram running in the loaddispatch center helps in thereactive power dispatch andcontrol.

What Tap?What excitation?Q on or off?FACTS control at what value?

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Reactive Power Control – Utility Objectives

• Utility objectives are two fold

1. Security

2. Economics

• Reactive power and voltage problems generally lead tosecurity problem.

• A power system is stated to be secure if it is able toundergo a disturbance without violating any of its loadand operating limits.

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Reactive Power –Transmission Line

Voltage kV 400 220 110 66

Line type Twin Moose Zebra Panther Wolf

R ohm/km 0.029 0.07 0.162 0.257

X ohm/km 0.308 0.398 0.386 0.432

B mho/km 3.76E-06 2.91E-06 2.93E-06 2.66E-06

Line loading and Base MVA 500 200 80 25

Typical line length km 300 150 50 25

R pu for entire line length 0.0271875 0.043388 0.053554 0.036874

X pu for entire line length 0.28875 0.246694 0.127603 0.061983

B pu for entire line length 3.61E-01 1.06E-01 2.21E-02 1.16E-02

Line charging Mvar - 100 km at rated

voltage 60.16 14.10 3.54 1.16

Line charging Mvar entire line length at

rated voltage 180.48 21.16 1.77 0.29

Reactive power loss in Mvar at 100%

loading at rated voltage 144.375 49.33884 10.20826 1.549587

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Effect of Source Impedance on Voltage

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Effect of Shunt and Series Compensation

50% series compensation at sending end or 63 MVAR reactor at receiving end – Same voltage

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Effect of Shunt and Series Compensation

Reactor deteriorates the performance when loaded!!!!

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Effect of Shunt and Series Compensation

* Double circuit line each carrying 500 MW* Outage of one circuit calls for building the 3rd circuit* Just for contingency, build the 3rd circuit or provide series and shunt compensation

9/13/2017 26

Case Study - Economics

• Double circuit 400 kV, 300 km twin moose line carrying 1000 MW

• One circuit trips, second circuit can not deliver the full power, as voltage collapses

• Option 1: Build 3rd circuit – Cost Rs. 210 Cr.

• Option 2: 150 Mvar SVC and 50% series compensation of both the circuit – Cost Rs. 106 Cr.

• Option 1: Right of way problem and problem still persists in terms of steady state and dynamic performance

• Option 2: Enhanced steady state and dynamic performance of the system

DeviceRs. Lakhs/MVAR

Shunt Capacitor 4.32Shunt Reactor 10.0Series cpacitor 10.8SVC only TCR 21.6SVC with capacitor 25.92STATCOM 27

400 kV S/C line - Rs. 70 lakhs/km

9/13/2017 27

Reactive Power Control – Control Devices

•Conventional – Series capacitor, Shunt reactors, Shunt capacitors, Transformer taps, Generator excitation system voltage

•Advanced – Flexible AC Transmission System (FACTS)

9/13/2017 28

Reactive Power Control – FACTS Devices

• Flexible AC Transmission Systems (FACTS) are the name given to the application of power electronics devices to control the power flows and other quantities in power systems.

• As per IEEE definition

–FACTS: AC transmission systems incorporating the power electronic-based and other static controllers to enhance controllability and increase power transfer capability.

–FACTS Controllers: A power electronic based system & other static equipment that provide control of one or more AC transmission parameters.

9/13/2017 29

Reactive Power Control – FACTS Devices

• Benefits of FACTS Technology

– To increase the power transfer capability of transmission networks and

– To provide direct control of power flow over designated transmission routes.

• Further it offers following opportunities

– The use of control of the power flow may be to follow a contract, meet the utilities’ own needs, ensure optimum power flow,

– Increase the loading capability of lines to their thermal capabilities, including short-term and seasonal.

– Increase the system security and damping electromechanical oscillations.

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FACTS - Opportunities

–Provide secure tie line connections to neighboring utilities and regions thereby decreasing overall generation reserve requirements on both sides.

–Damping of power oscillation,

–Preventing cascading outages by limiting the impacts of faults and equipment failures.

–Provide greater flexibility in sitting new generation.

–Reduce reactive power flows, thus allowing the lines to carry more active power.

–Reduce loop flows.

– Increase utilization of lowest cost generation.

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FACTS - Controllers

• Static Var Compensator (SVC)

– It has been used for reactive power compensation since the mid 1970s.

– Presently about 300 SVCs of 40000 Mvar are in service worldwide.

– Main advantages

• Voltage support

• Transient stability improvement and

• Power system oscillation damping.

9/13/2017 32

FACTS - Controllers

• Static Compensator (STATCOM)

– It is superior than SVC.

– Reduction in outdoor area requirement as it reduces voluminous capacitor/ Reactors.

– Improves performance at low voltage

– Reduces need of filters.

– Improves dynamic performance and enhances stability.

(a)VSC STATCOM

(b)CSC STATCOM

(a) (b)

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Reactive Power Control in RE regime – Indian Context

• CEA report “Large Scale Grid Integration of Renewable Energy Sources – Way Forward” dated November, 2013 emphasizes the installation of SVC/STACOM at renewable energy pooling stations for supporting dynamic voltage control to manage the reactive power flows.

• LVRT regulation insists that the RE plant should continue to get connected to the grid, as per the guidelines and support the system with reactive power

Vt: Bus voltageVn: Nominal system voltage

9/13/2017 34

Case Study 1: Integrating Wind Energy to the Grid

with Advance Control Techniques

9/13/2017 35

Problem Definition

The present system has a unique problem in which with 70% of wind generation, the voltage at some buses going beyond 1.1 PU; though the loading on the network are within the limits.

In order to understand the issues detailed measurements were undertaken. The details of system considered for the study and measurement are presented here.

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9/13/2017 37

Measurement at 132 kV Voltage at 132 kV Line (M1)

134

136

138

140

142

144

146

148

150

152

11:5

412

:17

12:4

013

:03

13:2

613

:49

14:1

214

:35

14:5

815

:21

15:4

416

:07

16:3

016

:53

17:1

617

:39

18:0

218

:25

18:4

819

:11

19:3

419

:57

20:2

020

:43

Time in Hours

Vo

ltag

e in

kV

Voltage at 132 kV Line (M1)

134

136

138

140

142

144

146

148

150

152

11:5

412

:17

12:4

013

:03

13:2

613

:49

14:1

214

:35

14:5

815

:21

15:4

416

:07

16:3

016

:53

17:1

617

:39

18:0

218

:25

18:4

819

:11

19:3

419

:57

20:2

020

:43

Time in Hours

Vo

ltag

e in

kV

The measurement at 132 kV indicates the voltage and power generation from wind generator of 147MW capacity.

During the measurement, the wind generation varies from 0 MW to 105MW.

Figure reveals that when wind generation is almost zero (with line flow zero) the voltage oscillates between 142kV to 144kV

However, as the wind generation increases (as shown in the line flow, the voltage at bus 22 increases to about 150kV and oscillates between 142kV to 150kV.

9/13/2017 38

Measurement at 220 kV

The measurement at the interconnecting line of 220kV, for evacuation of power to the grid which also connects to wind generator of 110MW capacity.

It is seen from the figure, the voltage variation is from 236kV to 248kV for variation in the wind generation.

Voltage at 220kV Line (M4)

232

234

236

238

240

242

244

246

248

250

1:36

1:48

2:00

2:12

2:24

2:36

2:48

3:00

3:12

3:24

3:36

3:48

4:00

4:12

4:24

4:36

4:48

5:00

5:12

5:24

5:36

5:48

6:00

6:12

6:24

6:36

Time in Hours

Vo

ltag

e in

kV

Voltage at 220kV Line (M4)

232

234

236

238

240

242

244

246

248

250

1:36

1:48

2:00

2:12

2:24

2:36

2:48

3:00

3:12

3:24

3:36

3:48

4:00

4:12

4:24

4:36

4:48

5:00

5:12

5:24

5:36

5:48

6:00

6:12

6:24

6:36

Time in Hours

Vo

ltag

e in

kV

Voltage profile from load flow

Voltage in PU at wind farm buses and at other buses

Wind generation

Bus10

Bus21

Bus28

Bus29

Bus41

Bus42

Bus43

Bus44

0% 1.098 1.101 1.046 1.031 1.101 1.101 1.094 1.098

10% 1.108 1.114 1.049 1.033 1.114 1.112 1.110 1.109

20% 1.114 1.122 1.048 1.032 1.123 1.119 1.103 1.116

30% 1.115 1.125 1.044 1.028 1.126 1.121 1.101 1.118

40% 1.112 1.124 1.037 1.020 1.125 1.118 1.095 1.115

50% 1.103 1.117 1.025 1.009 1.118 1.109 1.085 1.107

60% 1.088 1.103 1.008 0.993 1.104 1.094 1.068 1.092

70% 1.063 1.079 0.983 0.971 1.080 1.068 1.042 1.068

80% 1.022 1.038 0.944 0.936 1.039 1.026 1.001 1.027

90% 0.992 1.011 0.920 0.914 1.012 0.998 0.981 0.997

95% 0.982 1.004 0.914 0.908 1.004 0.989 0.978 0.987

96% 0.980 1.002 0.913 0.907 1.002 0.987 0.977 0.985

97% 0.970 0.992 0.905 0.899 0.992 0.977 0.968 0.975

98% 0.951 0.972 0.888 0.885 0.972 0.957 0.950 0.955

99% 0.904 0.924 0.851 0.8530.924 0.908 0.908 0.909

Dynamic Compensation System

Studies revealed that with dynamic

compensation the system it is possible to evacuate full generation and also the voltages at all the buses are within

acceptable range.

The simulation results show the need for

dynamic compensation with reactive power requirement varying from -37.02 MVAr

(inductive) to +6.59 MVAr (capacitive).

Block diagram of SVC for Simulation Studies

BL: Inductive Compensation, BC: Capacitive Compensation, BSVC: Effective Compensation.

Dynamic simulation with SVC

9/13/2017 43

Case Study 2: Dynamic Analysis of a Wind farm

Terms of Reference

Analysis of Disturbance data in a particular wind farm and observing the voltage variation

Dynamic Analysis of wind farm

Location and sizing of Dynamic reactive power compensation

Preparation of technical specification for the dynamic reactive power compensation

Root cause

Weak grid at the PCC for existing network configuration as a result under-voltage and overvoltage disturbance occurs

Possibility of failure of tripping logic co-ordination at the individual WTG.

Asynchronous (constant speed) Generator used wherein• A squirrel cage induction generator always consumes reactive power. In

most cases, this is undesirable, particularly in case of large turbines and weak grids.

• Reactive power consumption of the squirrel cage induction generator is nearly always partly or fully compensated by capacitors in order to achieve a power factor close to one

Voltage variation and turbine trippings at the Pooling point

Turbine trippings due to disturbance - undervoltage

Tripping details consolidated from sample 8 tripping details- feeder wise

0

5

10

15

20

25

30

35

40

45

feeder 1 feeder 2 feeder 3 feeder 4 feeder 5 feeder 6 feeder 7 feeder 8 feeder 9 feeder 10 feeder 11 feeder 12

Asymmetry

undervoltage

overvoltage

Data considered for study

33kV line layout (SLD) for 209.85MW Akal Wf

Disturbance recorder data at the 220kV pooling point

Reactor / generation data in wind farm region

Induction generator equivalent parameters from site

OLTC transformer name plate (33/220kV)

Turbine level disturbance recorded data

Date wise turbine tripped details

System Analysis

Steady state analysis:

Grid side analysis• Existing network scenario• With immediate future transmission line scenario and • With generation in the vicinity commissioned

Turbine level analysis

Transient analysis:• Existing network scenario• With immediate future transmission line scenario and• With generation in the vicinity commissioned

Steady state analysis observation at the wind turbine level

Voltage variation for undervoltage and overvoltage disturbance

Voltage profile

For undervoltage disturbance of 0.85pu For overvoltage disturbance of 1.15pu

Without SVC

With SVCWithout

SVC

With SVC

±20MVAr ±30MVAr ±40MVAr ±50MVAr ±20MVAr ±30MVAr ±40MVAr ±50MVAr

220kV pooling point

0.853 0.8783 0.8895 0.9000 0.95 1.158 1.1371 1.1260 1.1180 1.11

33kV pooling point

0.830 0.8687 0.8871 0.9047 0.92 1.159 0.1258 1.1080 1.0935 1.08

Minimum voltage at

wind turbine (690V)

0.809 0.8481 0.8661 0.8833 0.90 1.1314 1.0985 1.0813 1.0670 1.05

Maximum voltage at

wind turbines (690V)

0.835 0.8751 0.8937 0.9114 0.93 1.1628 1.129 1.1113 1.0966 1.08

Impact of network strengthening

0.8

0.9

1

Voltage profile at WTG side during different stages for Under-Voltage Scenario[Steady State Analysis]

Existing Network ConfigurationExisting Network Configuration with Lines commissionedExisting Network Configuration with 400kV Lines and Generation commissioned

Dynamic Study Results with SVC

Feeder No.Without SVC With SVC

Minimum voltage (pu)

Maximum voltage (pu)

Minimum voltage (pu)

Maximum voltage (pu)

220 kV pooling point 0.88 1.025 0.93 1.00

33 kV pooling point 0.84 1.00 0.93 0.95

Conclusion & Observation

Based on the detailed steady state and transient analysis for the existing network, it is observed that to control the voltage variations at the WTG. It is required to provide +/- 50MVAr SVC at the 33kV pooling station

The proposed ±50MVAr SVC rating for existing network configuration could be made with two (2) numbers of ±25MVAr SVC, so that one of the ±25MVAr SVC can be utilized.

Similarly for the immediate future network, by conducting the detailed system analysis, it is observed that to control the voltage within the limits, it is required to provide +/- 25MVAr SVC at the 33kV pooling station

And for the future network(with lines and generation), it is observed that the voltage variation will be within the allowable limits and hence there might not be the requirement for Dynamic compensation

Comparison TableWith Dynamic compensation

With Hybrid Dynamic compensation

With Switchable capacitor banks at 690v

Unbalance faults √ √ X

Asymmetry √ √ X

Balance faults √ √ (MAJOR CASES) X

Close-in faults √ √ (MAJOR CASES) X

Slow voltage variation √ √ √

Faster voltage variations √ √ X

Reliability √ √ X

Response time 1 cycle 1 cycle + Fewcycles (fixed)

Few cycles (>150ms)

Stress due to transients Low Moderate High

Risk Low Low High

Conclusions

• Reactive power control and management is an important aspect in the operation and control of power system

• A proper mix of excitation system control, transformer tap control and switchable var source control will achieve the objective of reactive power control.

• Advance in technology in the SCADA & EMS in addition to FACTS devices will enable better reactive power control.

• With more and more RE penetration, judicious applications of FACTS devices will enable the system security, voltage control and better management of the grid.

References

[1] Reactive Power Control in Electric Systems, T.J.E. Miller, General Electric Company, John Wiley & Sons.

[2] Power System Stability and Control, Prabha Kundur, Tata McGraw Hill Education.

[3] Narain G. Hingorani and Laszlo Gyugi “Understanding FACTS Concepts and Technology of Flexible AC Transmission systems” IEEE publications2000.

[4] M.H.Haque “Determination of Steady State Voltage Stability limit of a power system in the presence of SVC, IEEE Porto Power Tech Conference, Sept. 2001.

[5] P. Pourbeik, ABB Inc. “Integration of Large Wind Farms into Utility Grids (Part 2 – Performance Issues)”.

9/13/2017 59

Contact

Monali Zeya HazraSenior Clean Energy SpecialistUSAID/India

Email: mhazra@usaid.gov

Shubhranshu PatnaikChief of PartyUSAID GTG-RISE Initiative

Email: spatnaik@gtg-india.com