Grid integration issues and solutions

GRID CONNECTIVITY OF RENEWABLE
ENERGY SOURCES ISSUES & SOLUTION
Swathi venugopal
Semester; 8
Electrical & Electronics
RIT, Kottayam
Date; 22/02/13

More than 400
cities
50 million people
globally
Major icons went
dark
Seminar
Series-4,
2013
GRID CONNECTIVITY OF RENEWABLE ENERGY SOURCES ISSUES & SOLUTION

Effect Of Combustion Of Fossil Fuels?
Increasing oil
prizes
Exhaustible sources
Increasing co2
Releases
GH gases
SO2+NOX+H2O+O2=ACID RAIN
NITROGEN OXIDE + VOC = SMOG
Global warming
Seminar
Series-4,
2013

Reasons for Renewable Energy in India why
and why now??
 Declining Fossil Fuel Supplies
 Environmental Concerns
 Increasing Cost of Fossil Fuels
 Business Opportunities
 Energy Security
 Energy independence
“1 MW of wind plant in one year can displace 1500 tons of
CO2, 6.5 tons of SO2 and 3.2 tons of NOx. (REPP report,
Washington July 2003)”
Seminar
Series-4,
2013

The vision of Indian renewable energy program
“To develop new and renewable energy technologies,
processes, materials, components, sub-systems,
products and services at par with international
specifications, standards and performance parameters
in order to make the country a net foreign exchange
earner in the sector and deploy such indigenously
developed and/or manufactured products and services
in furtherance of the national goal of energy
security”.
Seminar
Series-4,
2013

Features And Structures Of Electrical
Power Systems
Generating units
Transmission
network
Distribution
network
Consumers
Seminar
Series-4,
2013

Features And Structures Of Electrical
Power Systems
 Electricity Demand (Inc. Losses) Is Varying .
.  Minimum at night and increasing to a peak during working hours.
 During working days and weekends/holidays
 seasonal variations
.
 Generators Must Be Scheduled To Match These
Variations Throughout The Year
 To maintain an AC power system at its nominal
frequency ,
 “Instantaneous Power Supplied = Demand .”
 Done by control of generation regulation/ load following
 Controlled automatically or by a central electricity system operator
Seminar
Series-4,
2013

Grid connectivity renewable energy issues and solutions .
Renewable Energy Generation
Characteristics
Grid
Connectivity
RE
Issues And
Solutions .

Comparison
Seminar
Series-4,
2013

CHALLENGES WITH INTEGRATING INTO
ELECTRICAL POWER SYSTEMS
 Most RE resources are location specific.
• Renewable-generated electricity may need to be
transported over considerable distances.
• Beneficial combinations of renewable sources may
not always be practicable.
 Lack of flexibility
• Balancing supply and demand
• Uncertainty in predicted out-put.
Seminar
Series-4,
2013

Transmission
Generators
Transmission Network
Distribution Network
Distribution Generators
Consumers
Transmission
Generators
DISTRIBUTED GENERATORS
Seminar
Series-4,
2013

What is an efficient grid connection ?
 Respect the power quality of the grid
 Respect the grid protection plan
 Allow control and clear monitoring
Seminar
Series-4,
2013

Lack of standerds
1. Central Electricity Authority
2. Central Electricity Regulatory
Commission
3. State Electricity Regulatory
Commissions
.
 Exist only for connecting
voltage levels of 33 kv &
above to the grid
“ Viable standards of grid connectivity to be framed ”

INTEGRATING INTO ELECTRICAL POWER
SYSTEMS ISSUES & SOLUTIONS
Voltage fluctuation and regulation
 Extended under voltage causes “brownouts”
 Extended overvoltage decreases the life of
equipment's.
 DG systems are not only affected by voltage
fluctuations, but can cause voltage fluctuations
themselves
Seminar
Series-4,
2013

1. Grid-derived voltage fluctuations
 Inverters - ‘voltage-following’
 Disconnect DG when the grid voltage moves outside set parameters.
 Ensure suitable power quality
 Antislanding.
 Automatic disconnection will cause overloading of other generators
• Avoid this happening, Low Voltage Ride-through Techniques
(LVRT) could be incorporated into inverter design
 Inverters -‘voltage-regulating’ mode
 inject reactive power during voltage sags
 Reduce network voltage by drawing reactive power during voltage
rise.
 provide current that is out of phase with the grid voltage so provide
power factor correction.
Seminar
Series-4,
2013

2. Voltage imbalance
 Voltage imbalance is when the amplitude of each
phase voltage is different in a three-phase system or
the phase difference is not exactly 120°.
 High RE penetrations, the cumulative size of all
systems connected to each phase should be as equal
as possible.
3. Power output fluctuation
 Short-term fluctuations
 Geographical dispersal
 Forecasting
 Storage
 Affect power quality
 Continuous tap-changing and capacitor switching
 increased number of switching surge
 Long-term fluctuations
 Require back-up generation to maintain power
supply.
Seminar
Series-4,
2013

4. Voltage rise and reverse power flow
Voltage
Substation
max
min
Overhead line
Seminar
Series-4,
2013

 To minimize voltage rise and reverse power flow
 Ensuring PV systems are smaller than the daytime load,
 Use dynamically controlled inverter (DCI) to gradually reduce PV
output
 Use of a minimum import relay (MIR) to disconnect the RE system,
 Use of a reverse power relay (RPR) to disconnect the system on
low voltage and reverse power flow
 Decreasing the network’s series impedance , to reduce voltage
drop.
 Requiring customer loads to operate at improved power factor
 Requiring customers with large loads to incorporate some form of
load-shedding scheme,
 The use of storage units
Seminar
Series-4,
2013

Grid connectivity renewable energy issues and solutions .
Power factor correction
 Poor power factor -increases line losses & makes voltage
regulation more difficult.
 voltage-following have unity power factor
 voltage-regulating mode provide power factor correction.
Unintentional islanding
 Occurs when DG delivers power to the
network even after circuit breakers have
disconnected from main grid.
 grid inverter technology has developed to
include anti-islanding features as per local
regulations and standards
Seminar
Series-4,
2013

Frequency variation and regulation
 Unbalanced supply-demand lead to frequency fluctuation
 High penetration of intermittent energy make control more
difficult.
 DG inverters can provide frequency control in milliseconds,
Only when they can inject power into the network
 DG linked to thermal plant are restricted in their ability to
provide frequency regulation because of their thermal loads.
 Inverters disconnect from the grid when the frequency moves
outside set limits (as a form of islanding detection),
 Ability to provide frequency support may be compromised.
 All DG will also disconnect, exacerbating the power imbalance
 Leads to complete system shutdown
.
“New frequency ride through systems that do not interfere with the anti-islanding
protection systems will need to be developed”
Seminar
Series-4,
2013

Harmonics
Transformers
• Overheating leads to insulation
failure
• Reverse power flow capability?
Switchgear
failure
Cables
failure
Seminar
Series-4,
2013

Harmonics
 HARMONIC REDUCTION
 voltage-source inverters can provide the harmonic
support but do so at an energy cost
 There are a variety of harmonic compensators that are
likely to be cheaper.
Seminar
Series-4,
2013

Generalization
1. Very low penetration (typically 5-10% of connected load)
 Can be tolerated without significant problems
2. Moderate level penetration (10-20% of connected load)
 More significant issues arise .
 More DG may be accommodated by making changes to
the network
• Minimizing VAr flows, power factor correction, increased
voltage regulation and careful consideration of protection.
3. High levels of penetration, (Network dependent)
 Require significant overall design and communications
infrastructure changes – for coordinated protection and power flow
control.
 Under research and development
Seminar
Series-4,
2013

What are the other key barriers ?
 No market
 Utility culture & framework
 Lack of expertise
 Limited role for private sector
 Capital costs vs. variable energy costs
 Transmission access & strength of grid
Seminar
Series-4,
2013

What are the Strategies to overcome
barriers ?
 Promote market development
 Support utility RE procurement
 Encourage private investment
 Provide long-term contracts
 Value RE attributes
 Facilitate access to Electricity grid
 Train RE designers and operators
Seminar
Series-4,
2013

GUIDE LINES
Seminar
Series-4,
2013

1. CONNECTION OF REPS TO THE GRID
Seminar
Series-4,
2013

2. SAFETY CONSIDERATIONS
 Incorporate an anti islanding function
 Install a lockable switch at an easily accessible position –
manually isolate REPS from grid
 Update circuit diagram regularly and display at
appropriate locations
 Establish a direct communication channel between owner
and utility
Seminar
Series-4,
2013

3. EQUIPMENT PROTECTION
 Carry out assessments on the new fault levels due
to connection of REPS
 Incorporate the following features
 auto switching & auto reclosing
 facility to isolate REPS from DS when fault occur
 protection facilities against transient abnormalities in the grid
 stable and fast responding voltage & frequency regulators
 Protection facilities to avoid unsynchronized connections
 4 pole CB to provide complete isolation from DS when REPS
is not in service.
 Automatic reconnection facility after the fault is removed
Seminar
Series-4,
2013

3. POWER QUALITY
 Design REPS with three phase inverter or three
identical single phase inverter to supply current Which
is balanced over the three phases to the grid –
minimize voltage & current unbalance
 Install the following features
 inverter with power conditioning feature to control THD & PF
 Isolation transformer on the output side of inverter to avoid the
injection of DC to DS
 Fast responding frequency and voltage regulator.
Seminar
Series-4,
2013

What is the the need for government
involvement?
 Policy implementation & enforcement
 Renewable energy market promotion
 Pricing of electricity
 Cost sharing
Seminar
Series-4,
2013

YESTERDAY
Centralized power
Seminar
Series-4,
2013
Price of non renewable energy source is increasing
day by day , where as the availability is reducing day
by day.
It is mandatory that we have to depend on renewable
energy sources

Centralized power Off grid power
plant
TODAY
Seminar
Series-4,
2013
 High initial capital costs
 Electricity production is dependent on availability of
source
 Electricity production may not match when household
requires .
 Electricity requiring either batteries to store electricity
(especially if there is no grid connection and/or an
agreement with your electricity retailer to purchase
surplus electricity from you).

TOM0RROW
GRID TIED SYSTEM
Seminar
Series-4,
2013

DECENTRALIZED GENERATION / FUTURE
INTEGRATION
 Additional energy supply systems (esp using RE)
in the medium and low voltage level is highly visible
 Configuration of an intelligent distributed electricity
system as the most important alteration.
 In Europe it is called “decentralized generation”.
 Aims at generating the energy where it is
required
Seminar
Series-4,
2013

 Should avoid interferences and overcharge in
circuits
 storage facilities
 Accumulator systems.
 capacitors
 compressed-air stores
 Energy management
 interactions between different electricity levels.
 communication,
 information, control, metering, services, planning,
optimization
 forecast
Seminar
Series-4,
2013

4
7
Central Generating
Station
Step-Up
Transformer
Distribution
Substation
Receiving
Station
Distribution
Substation
Distribution
Substation
Commercial
Industrial Commercial
Gas
Turbine
Diesel
Engine
Cogeneration
Cogeneration
Turbine
Fuel
cell
Micro-turbine
Wind Power
Storage
Residential
Photovoltaic systems
Control Center
Operators,
Planners & Engineers
2. Communications and Information Infrastructure

CONCLUSION
Seminar
Series-4,
2013
 Wind energy , tidal energy ,and solar PV are not
dispatchable unlike NRE
 Integrating this RE to power system is a difficult process
 Grid tied system is becoming a must
 New Technologies will need to be developed.
 Promote off – grid (mainly solar pv ) for sustainable
economy
Advantages of grid tied system is predominating over
disadvantages
 Save energy save environment

REFERENCE
 Integration of Renewable Energy into Present and Future Energy
Systems-Ralph Sims (New Zealand), Pedro Mercado (Argentina),
Wolfram Krewitt †(Germany)
 Vergnet S.A. Integration Of A Wind Farm Into The Utility Grid
Eric ANDRIEU, Electric Al Design Département Manager Pierre
PESNEL,Export Manager
 Grid integration of renewable energy sources
GermanP. Kammer, A. Kober BTU Cottbus Cottbus, y
 Renewable Energy Sources (RES) Grid Integration: Key Issues
and Challenges Bharat Singh
Seminar
Series-4,
2013

 Addressing Grid-interconnection Issues With Variable Renewable
Energy Sources Summary Document Report for Asia Pacific
Economic Cooperation (APEC)
 Renewable Energy Technologies Solutions Grid Connected Systems
IRENA Workshop
 Grid connection of Renewable Energy CHALMERS ENERGY
CONFERENCE 2012 Peter Konings – SEIAPI / APEG
 Renewable Energy in India: Progress, Vision and Strategy
Ministry of New and Renewable Energy Government of India
 Fractional Order Modeling & Control Strategies for Grid-
Connected Renewable Energy SourcesMajor Professor : Dr. Chen
 Renewable Energy Grid Connection Dave Fleming
Seminar
Series-4,
2013

Grid integration issues and solutions

Grid integration issues and solutions

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