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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
9/13/2017 3
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
9/13/2017 4
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
9/13/2017 5
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.
9/13/2017 6
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.
9/13/2017 7
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.
9/13/2017 9
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.
9/13/2017 10
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.
9/13/2017 11
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.
9/13/2017 12
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.
9/13/2017 13
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
9/13/2017 14
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.
9/13/2017 15
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
9/13/2017 17
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?
9/13/2017 20
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.
9/13/2017 21
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
9/13/2017 22
Effect of Source Impedance on Voltage
9/13/2017 23
Effect of Shunt and Series Compensation
50% series compensation at sending end or 63 MVAR reactor at receiving end – Same voltage
9/13/2017 24
Effect of Shunt and Series Compensation
Reactor deteriorates the performance when loaded!!!!
9/13/2017 25
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.
9/13/2017 30
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.
9/13/2017 31
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)
9/13/2017 33
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.
9/13/2017 36
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: [email protected]
Shubhranshu PatnaikChief of PartyUSAID GTG-RISE Initiative
Email: [email protected]