Report on smart metering& control of transmission system
SMART METERING AND CONTROL OF TRANSMISSION SYSTEMS
Submitted in the fulfilment of the
Study Project EEE F266
M.SAI MANOBHIRAM 2012A3PS224H
G.DURGA RAO 2012A3PS255H
UNDER THE SUPERVISION OF
BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI
Writing and implementing this project was very rewarding for us. We are grateful to the
EEE Department for giving us the opportunity to work on this project. We would like to
thank our Instructor Ms T. Haripriya for the help and support offered. We are extremely
thankful to her for guiding us through the entire duration and patiently explaining all kinds
of doubts. We would like to thank her for her valuable inputs during the project and for the
help extended by her during the project.
This report focuses on the understanding of what a smart grid is and how it works. It also
concentrates about how it differs from the present grid (i.e., differences between smart grid
and present grid).
After getting an overview on smart grid we moved to Smart meter infrastructure where its
main components and its working are briefly explained. And also it explains how the
communication is implemented in the smart grid. And later what are the problems while
transferring the data in a safe mode i.e., a brief theory about cyber security is explained. A
brief description of self-healing and then how to integrate smart grid with renewable energy
sources is provided.
Table of contents
What is Smart Grid 5
Comparison of smart grid and present grid 6
Smart Grid Scope 7
Smart Meter Infrastructure (SMI) 9
Smart Meters 10
Smart Meter Communication 11
Communication Architecture 13
Meter Data Management System 14
Home Area Networks 15
Cyber Security 15
Smart Grid Renewable Energy System 23
Introduction to Smart Grid
Established electric power systems, which have developed over the past 70 years,
feed electrical power from large central generators up through generator transformers to a
high voltage interconnected network, known as the transmission grid. Each individual
generator unit, whether powered by hydropower, nuclear power or fossil fuelled, is large
with a rating of up to 1000 MW. The transmission grid is used to transport the electrical
power, sometimes over considerable distances, and this power is then extracted and passed
through a series of distribution transformers to final circuits for delivery to the end
The part of the power system supplying energy (the large generating units and the
transmission grid) has good communication links to ensure its effective operation, to enable
market transactions, to maintain the security of the system, and to facilitate the integrated
operation of the generators and the transmission circuits. This part of the power system has
some automatic behavior by the generators and the transmission network during major
The distribution system, feeding load, is very extensive but is almost entirely
passive with little communication and only limited local controls. Other than for the very
largest loads (for example, in a steelworks or in aluminum smelters), there is no real-time
monitoring of either the voltage being offered to a load or the current being drawn by it.
There is very little interaction between the loads and the power system other than the supply
of load energy whenever it is demanded.
The present revolution in communication systems, particularly stimulated by the
internet, offers the possibility of much greater monitoring and control throughout the power
system and hence more effective, flexible and lower cost operation. The Smart Grid is an
opportunity to use new ICTs (Information and Communication Technologies) to
revolutionize the electrical power system. However, due to the huge size of the power
system and the scale of investment that has been made in it over the years, any significant
change will be expensive and requires careful justification.
The consensus among climate scientists is clear that man-made greenhouse gases
are leading to dangerous climate change. Hence ways of using energy more effectively and
generating electricity without the production of CO2 must be found. The effective
management of loads and reduction of losses and wasted energy needs accurate information
while the use of large amounts of renewable generation requires the integration of the load
in the operation of the power system in order to help balance supply and demand. Smart
meters are an important element of the Smart Grid as they can provide information about
the loads and hence the power flows throughout the network. Once all the parts of the
power system are monitored, its state becomes observable and many possibilities for
What is the Smart Grid?
The Smart Grid concept combines a number of technologies, end-user solutions and
addresses a number of policy and regulatory drivers. It does not have a single clear
The European Technology Platform defines the Smart Grid as:
“A Smart Grid is an electricity network that can intelligently integrate the actions of all
users connected to it – generators, consumers and those that do both – in order to efficiently
deliver sustainable, economic and secure electricity supplies.”
According to the US Department of Energy:
“A smart grid uses digital technology to improve reliability, security, and efficiency (both
economic and energy) of the electric system from large generation, through the delivery
systems to electricity consumers and a growing number of distributed-generation and
In Smarter Grids: The Opportunity, the Smart Grid is defined as:
“A smart grid uses sensing, embedded processing and digital communications to enable
the electricity grid to be observable (able to be measured and visualized), controllable
(able to manipulated and optimized), automated (able to adapt and self-heal), fully
integrated (fully interoperable with existing systems and with the capacity to incorporate
a diverse set of energy sources).”
The literature suggests the following attributes of the Smart Grid:
1. It enables demand response and demand side management through the integration
of smart meters, smart appliances and consumer loads, micro-generation, and
electricity storage (electric vehicles) and by providing customers with information
related to energy use and prices. It is anticipated that customers will be provided
with information and incentives to modify their consumption pattern to overcome
some of the constraints in the power system.
2. It accommodates and facilitates all renewable energy sources, distributed
generation, residential micro-generation, and storage options, thus reducing the
environmental impact of the whole electricity sector and also provides means of
aggregation. It will provide simplified interconnection similar to ‘plug-and-play’.
3. It optimizes and efficiently operates assets by intelligent operation of the delivery
system (rerouting power, working autonomously) and pursuing efficient asset
management. This includes utilizing asserts depending on what is needed and when
it is needed.
4. It assures and improves reliability and the security of supply by being resilient to
disturbances, attacks and natural disasters, anticipating and responding to system
disturbances (predictive maintenance and self-healing), and strengthening the
security of supply through enhanced transfer capabilities.
5. It maintains the power quality of the electricity supply to cater for sensitive
equipment that increases with the digital economy.
6. It opens access to the markets through increased transmission paths, aggregated
supply and demand response initiatives and ancillary service provisions
Comparison of Present Grid and Smart Grid:
Preferred Characteristics Today ’ s Grid Smart Grid
Consumers are uninformed
do not participate
consumers — demand
response and distributed
Accommodation of all
generation and storage
Dominated by central
generation — many obstacles
exist for distributed energy
Many distributed energy
resources with plug - and -
convenience focus on
New products, services, and
Limited, poorly integrated
wholesale markets; limited
opportunities for consumers
Mature, well - integrated
wholesale markets; growth of
new electricity markets for
Provision of power
quality for the digital
Focus on outages — slow
response to power quality
Power quality a priority with a
variety of quality/price
options — rapid resolution of
Optimization of assets
and operates efficiently
Little integration of
operational data with
business process silos
Greatly expanded data
acquisition of grid
parameters; focus on
minimizing impact to
Anticipating responses to
Responds to prevent further
damage; focus on protecting
assets following a fault
Automatically detects and
responds to problems; focus
impact to consumers
Resiliency against cyber
attack and natural disasters
Vulnerable to malicious acts of
terror and natural disasters;
Resilient to cyber-attack and
natural disasters; rapid
Smart grid scope:
The following areas arguably represent a reasonable partitioning of the electric system that
covers the scope of smart grid concerns. To describe the progress being made in moving
toward a smart grid, one must also consider the interfaces between elements within each
area and the systemic issues that transcend areas. The areas of the electric system that cover
the scope of a smart grid include the following:
• Area, regional and national coordination regimes: A series of interrelated,
hierarchical coordination functions exists for the economic and reliable operation
of the electric system. These include balancing areas, independent system operators
(ISOs), regional transmission operators (RTOs), electricity market operations, and
government emergency-operation centers. Smart-grid elements in this area include
collecting measurements from across the system to determine system state and
health, and coordinating actions to enhance economic efficiency, reliability,
environmental compliance, or response to disturbances.
• Distributed-energy resource technology: Arguably, the largest “new frontier” for
smart grid advancements, this area includes the integration of distributed-
generation, storage, and demand-side resources for participation in electric-system
operation. Consumer products such as smart appliances and electric vehicles are
expected to become important components of this area as are renewable-generation
components such as those derived from solar and wind sources. Aggregation
mechanisms of distributed-energy resources are also considered.
• Delivery (transmission and distribution [T&D]) infrastructure: T&D
represents the delivery part of the electric system. Smart-grid items at the
transmission level include substation automation, dynamic limits, relay
coordination, and the associated sensing, communication, and coordinated action.
Distribution-level items include distribution automation (such as feeder-load
balancing, capacitor switching, and restoration) and advanced metering (such as
meter reading, remote-service enabling and disabling, and demand-response
• Information networks and finance: Information technology and pervasive
communications are cornerstones of a smart grid. Though the information networks
requirements (capabilities and performance) will be different in different areas,
their attributes tend to transcend application areas. Examples include
interoperability and the ease of integration of automation components as well as
cyber-security concerns. Information technology related standards, methodologies,
and tools also fall into this area. In addition, the economic and investment
environment for procuring smart-gridrelated technology is an important part of the
discussion concerning implementation progress.
SMART METERING AND INFRASTRUCTURE OVERVIEW
SMI is the totality of the systems and networks that are used to measure, collect, store,
analyze, and use energy usage data. In other words, SMI includes smart meters and all
other infrastructure components—hardware, software, and communication networks that
are needed to offer advanced capabilities. SMI covers the infrastructure not only from
meters to the utility, but also from meters to customers, which enables every customer to
analyze and use the energy metering data. SMI also makes energy usage data available to
parties other than the utility in supporting the provision of demand response solutions.
A typical SMI network employs a two-way communication system and smart metering
technology. Instead of a monthly accumulated energy consumption recording, a smart
meter records the customer’s consumption at present intervals on a continuous basis. It
communicates the customer’s load profile data to a central location, where the data are
sorted and analyzed for a variety of purposes, such as customer billing, outage response,
and demand-side management. SMI also uses the same system equipment to send
information back through the network to meters to capture additional data, control the
meters, or update the meters’ firmware..
DIFFERENCE BETWEEN AMR AND SMI
Collection of registered readings from
a distant location
An infrastructure to collect, store, analyse,
and utilize remotely interval meter data
One-way communication Two-way communication
Monthly collection of data Variable data granularity supporting TOU
Coverage limited to a small area or
a portion of a system
MAJOR SYSTEM COMPONENTS OF SMI
A SMI system is comprised of a number of technologies and applications that have been
integrated into one solution. The four major SMI components are:
• Smart meters
• Communication system
• Meter data management systems (MDMS)
• Home area networks (HAN)
Conventional electromechanical meters have been used by utilities for residential customer
billing for many years. These meters simply record the total energy consumed over time
with an incremental energy counter. Although digital meters have been used for billing in
the last two decades, they are also mainly used to record accumulated energy (there may
be some limited records of megawatt [MW] demand). The measurements from both
electromechanical meters and non-smart digital meters are collected manually by physical
site visits and, thus, record only the readings at the time of the visit. Smart meters are
intelligent, solid-state, programmable devices that can perform many functions beyond
energy consumption recordings. By using built-in memories, smart meters can record and
store readings at present intervals (e.g., 15 min, 30 min, or hourly) and prescheduled times.
With built-in communication modules, they can connect to a two-way communication
system, not only to send readings from meters to the data centre but also to deliver
information or control orders from the data centre to meters
The two-way communication functionality supports on-demand reading, which enables
verification of customer energy consumption in time, remote connection and
disconnection, and detection of tampering or out-of-range voltage conditions. These
functions also make TOU rate or real-time pricing and demand management programs
possible. Most of the smart meters available on the market can also send out a “last gasp”
message when loss of power is detected and a “first breath” message when power service
is restored. Such information provides significant benefits for outage location and response.
An example of a smart meter is shown in Figure
A smart meter can also work as a gateway for utilities to communicate with the customer’s
HAN, which enables customers to view their near real-time consumption information and
receive price signals from utilities. Depending on customers’ willingness, smart meters can
relay load control commands from the utility to customers’ appliances for emergency load
control or demand response programs.
Typical smart meter functionalities include the following:
• Record interval (daily, hourly, or sub hourly) energy consumption and demand data
• Support demand read capability
• Provide bidirectional metering, which will accommodate distributed generations at
• Provide notification on loss of power and service restoration
• Provide tamper alarms and enable theft detection
• Provide voltage measurement, voltage alarms, and power quality monitoring
• Be remotely programmed and firmware upgraded over the air
• Support remote time synchronizing
• Enable TOU rate billing
• Enable remote connection and disconnection service
• Limit loads for purposes of demand response
• Communicate and interact with intelligent appliances or devices in a customer’s HAN
• Protect meter data security
Smart Meter Communications
Smart Meter communicates with the base station or the control centre on a bi-
directional mode. It is accomplished through a module piggybacked to the meter through a
channel which can be chosen based on the analysis in Indian context. Some of the important
channels that are available in India for communication are: GSM, Wi-Fi, PLCC, PSTN.
The type of communication available depends severely on the geographic location
especially in India where not every specific mode is available throughout. A new
communication topology all over the country is a costly option. Thus the communication
mode used should be a combination of available options. Here we present a brief
description of technology and viability in Indian context.
GSM (2G, 3G)
It is a second generation digital-type wireless telephone technology which can be
broadly divided into two categories based on the type of multiplexing used namely TDMA
and COMA. TDMA involves allocation of time slots to the users sharing the frequency
channel on a rotational method while COMA generates a unique code for each transaction
and spreads it over the available frequencies in the common spectrum. 2G uses digital
encryption offering better security of the transmission content than its earlier versions. 2G
engages various Compression Decompression (CO DE C) algorithms for abridging and
multiplexing the data. 2G supports
GPRS abbreviated as General Packet Radio Service, is based on the phenomenon
of packet switching which involves transmission of data in the form of packets. It supports
TCP/IP protocol enabling transmission of data over internet.
Another option, Wi-Fi by Wi-Fi alliance uses IEEE 802.11 family of standards
operating in the unlicensed 2.4GHz ISM band. It involves broadcast and reception of data
through radio signals in an encrypted format. It works on the OFDM (Orthogonal
Frequency-Division Multiplexing) or Direct Sequence Spread Spectrum transmission
scheme. It offers great bandwidths unmatched with many other wireless technologies. It
uses Wireless Protected Access (WPA) as an encryption standard but it fails to offer
reliability over the system. This is the present trend of communication being implemented
and deployed in many parts of the country. It cuts the cost of the cables to be run to
particular houses. The establishment of this mode requires good amount of capital to make
it into a full-fledged network connecting the smart meters.
Power Line Carrier Communication associates the use of power conductors for
communication by imposing a modulated carrier frequency signal over them. They are
operational in many parts in Europe and are the prime mode of communication between
sub stations in the power sector. These involve special infrastructure to be built to handle
and ensure safe communication without affecting the power transmission. The carrier
signal degrades gradually along the length of the line, so PLCC repeaters are used which
improve the strength of the signal by demodulation and re-modulating it back on a new
carrier frequency and injecting it back into the power line. It has been implemented for
many applications like home automation, BPL (Broadband over Power Line) etc.
Zigbee is a wireless technology using low-power digital radios developed as an
open standard to meet the requirements of short distance data transmission with minimal
cost. It operates in the unlicensed or ISM band of 2.4GHz under the IEEE 802.1S.4 standard
of physical radio specification which defines the Physical and MAC protocol layers. Zigbee
offers enough bandwidths required for the implementation of AMI and home automation.
It supports good amount of network topologies like point to point, point to multipoint and
mesh architecture. Its low power consumption eliminates to change for a new battery or
frequent charging thereby offering good reliability. It involves Direct Sequence Spread
Spectrum modulation technique. It has very low start-on latency enabling faster response.
It supports bandwidths up to 2S0Kbps. Its typical range is around 7Sm and even high
(IS00m) for specially designed Zigbee devices (Zigbee Pro). The Zigbee device can be
made to work in three modes.
In this we propose the communication architecture based on the analysis presented
in the previous section. As shown in the figure 7 nodes 1-7 represent the customers to
whom the electricity is supplied through the distribution transformer shown in picture. E
ach meter is a node, equipped with a communication module to enable two way
acknowledgements and data transfer between the control centre and the user.
The nodes or meters are connected to a main module placed at distribution
transformer through Zigbee in a wireless mesh network topology using the concept of
multi-hop routing methods thereby economizing the infrastructure and improving the
reliability. Employing 2G connectivity for each node is an expensive solution which can
be inferred from the following analysis. An ordinary energy meter transmits data of nearly
34MB per month and according to the prevalent data charges it amounts to nearly Rs.50.
Installing Zigbee module eliminates these running costs which involves only one time
installation of its module whose worth is around 300-500 INR. The distance between the
distribution transformer and the nearest residential customer ranges from 10-50 m which
falls well in the range of Zigbee and hence it can be installed to use without loss of
connectivity. The data collected at various distribution transformers is relayed to its parent
substation through GSM network as the distance between the two varies from 1-10 km.
Thus optimal utilization of free and paid communications bands occurs. Thus the module
at distribution transformer works as a coordinator and those at the meters as routers and
The module at the distribution transformer needs to be designed such that it accumulates
data from the smart meters in and around. This data is used to mitigate power theft by
designing a differential type algorithm which compares the power flow in and data reported
by smart meters over ZigBee network. Thus power theft detection is an added feature of
The distribution transformers update the information to the substation through GSM
network which can communicate over long ranges. Thus the module at distribution
transformer is equipped with both Zigbee and GSM communication capabilities. In
addition, the device at distribution transformers can be devised so as to include other Smart
Grid features like self- healing, automatic fault detection and isolation, automated
transformer protection etc.
The data received at various substations is fed to a main control centre through a data
concentrator for analysis. PLCC provides the best solution for transmission of this data
collected to control centre. The existing communication channels between substations can
be revamped for the data transfer.
METER DATA MANAGEMENT SYSTEM:
MDMS is a database software application with analytical tools that interfaces with the SMI
data collection system to process, store, and analyze meter readings. Many important
features of SM rely on the successful collection of meter data and manipulation of alarm
signals within MDMS. In order to gain operational efficiencies provided by SMI, utilities
should build interactions of MDMS with other information systems or applications,
Consumer information system (CIS), billing systems, and utility’s websites
Demand response management system
Distribution management system (DMS)/energy management system
Outage management system
Reliability data management system
Power quality management system and load forecasting system
Mobile workforce management system
Geographic information system (GIS)
Transformer load management system
Distribution automation and other operation applications
One of the primary functions of an MDMS is to perform validation, editing, and estimation
on the SMI data to ensure that the collected data flowing to the systems described above
are complete and accurate despite disruptions in communication networks or at customer
HOME AREA NETWORKS
HAN has become a popular term in recent years. One important component of HAN
is the in home display (IHD) device, which is also called the in-premise device. IHD is a
device located inside a customer’s home. It receives the customer’s metering measurement
and utility pricing information in near real time, and displays the information to the
customer. A HAN interfaces with a consumer portal (HAN gateway) to link the smart
meter to controllable electrical devices within the customer’s home to allow the customer
to actively participate in demand response programs.
The management functions of HAN include:
• Updated and continuous in-home energy consumption and pricing signal
displays so that consumers always know how much energy is being used and what
it is costing
• Response to price signals based on consumer-entered preferences
• Set points that limit utility or local control actions to a consumer-specified band
• Control of loads without consumer’s continuing involvement
• Consumer override capability
The backbone of the Smart Grid will be its network. This network will connect the different
components of the Smart Grid together, and allow two-way communication between them.
Net- working the components together will introduce security risks into the system, but it
is required to implement many of the main functionalities of the Smart Grid. Networking
the different com- ponents together will increase the complexity of the electrical power
grid, which will then increase the number of opportunities for new security vulnerabilities.
Also, the number of entry points that can be used to gain access to the electrical power
system will increase when all of the components are networked together.
And there comes CYBER SECURITY
Cyber security is a critical priority of smart grid development. However, the cyber security
requirements for the smart grid are in a considerable state of flux. Cyber security includes
measures to ensure the confidentiality, integrity, and availability of the electronic
information communication systems necessary for the management and protection of the
smart grid’s energy, information technology, and telecommunications infrastructure.
Cyber security is defined as security from threats conveyed by computer or computer
terminals and the protection of other physical assets from modification or damage from
accidental or malicious misuse of computer - based control facilities  . Smart grid
security protocols contain elements of deterrence, prevention, detection, response, and
mitigation; a mature smart grid will be capable of thwarting multiple, coordinated attacks
over a span of time. Enhanced security will reduce the impact of abnormal events on grid
stability and integrity, ensuring the safety of society and the economy.
Security measures should ensure the following:
1. Privacy that only the sender and intended receiver(s) can understand the content of a
2. Integrity that the message arrives in time at the receiver in exactly the same way it was
3. Message authentication that the receiver can be sure of the sender’s identity and that
the message does not come from an imposter.
4. Non-repudiation that a receiver is able to prove that a message came from a specific
sender and the sender is unable to deny sending the message
The following picture depicts smart grid architecture with different security needs:
Cyber Security can be provided by
Encryption and Decryption Methods…
Encryption and Decryption Methods
Cryptography has been the most widely used technique to protect information from
adversaries, a message to be protected is transformed using a Key that is only known to the
Sender and Receiver. The process of transformation is called encryption and the message
to be encrypted is called Plain text. The transformed or encrypted message is called Cipher
text. At the Receiver, the encrypted message is decrypted.
Substitution cipher was an early approach based on symmetric Key encryption. In this
process, each character is replaced by another character. An example of a mapping in a
substitution cipher system is
Plain text A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher text W Y A C Q G I K M O E S U X Z B D F H J L N P R T V
The encryption of message or plain text HELLO THERE will produce KQSSZ JKQFQ as
Cipher text. Since a given character is replaced by another fixed character, this system is
called a mono-alphabetic substitution. The Key here is the string of 26-characters
corresponding to the full alphabet. Substitution cipher systems disguise the characters in
the Plain text but preserve the order of characters in the Plain text.
In a transposition cipher the characters in the Plain text are transposed to create the Cipher
text. Transposition can be achieved by organizing the Plain text into a two-dimensional
array and interchanging columns according to a rule defined by a Key. An example of
transposition cipher is shown in Figure. As can be seen, Plain text is first assigned to an
array having the same number of columns as the Key. Any unused columns are filled with
the letter ‘a’. Then each row in the array is rearranged in the alphabetical order of the Key.
Authentication is required to verify the identities of communicating parties to avoid
imposters gaining access to information. When user A receives a communication from user
B, A needs to verify that it is actually B, but not someone else masquerading as B, who is
talking to him. Detailed descriptions of authentication methods can be found in .
a) A indicates to B that it wishes to communicate with B and sends his identity with a
large random number (NA) in Plain text.
b) B encrypts NA using a secret Key known to A and B and sends Cipher text (EKAB
(NA)) together with another large random number (NB) to A as Plain text.
c) A decrypts the Cipher text received to check whether it gets the same number (NA)
that he sent to B and encrypts the number NB using a shared secret Key and sends the
Cipher text to B.
d) B decrypts the received Cipher text using a shared secret Key and checks whether
he gets the same number (NB) as that he sent.
A digital signature allows the signing of digital messages by the Sender in such a way that:
1. The Receiver can verify the claimed identity of the Sender (authentication).
2. The Receiver can prove and the Sender cannot deny that the message has been sent by
the specific user (non-repudiation).
3. The Receiver cannot modify the message and claim that the modified message is the one
that was received from the Sender
Cyber Security Concerns Associated with AMI
AMI is the convergence of the power grid, the communications infrastructure, and the
supporting information infrastructure . This system of systems is constituted by a
collection of software, hardware, operators, and information and has applications to billing,
customer service and support, and electrical distribution. These applications each have
associated cyber security concerns as summarized in Table. The development of the
security domain for AMI systems is addressed in Reference 1 and a security domain model
was developed to bound the complexity of specifying the security required to implement a
robust, secure AMI solution and to guide utilities in applying the security requirements to
their AMI implementation. The services shown in Table are descriptions of each of the six
security domains. Each utility’s AMI implementation will vary based on the specific
technologies selected, the policies of the utility, and the deployment environment.
SELF-HEALING of power delivery systems is a concept that enables the identification
and isolation of faulted system components and the restoration of service to customers supplied by
healthy elements. This activity may be conducted with little or no human intervention and has the
objective of minimizing interruptions of service and avoiding further deterioration of system
reliability. Self-healing of power distribution systems is conducted via Distribution Automation
(DA), specifically through smart protective and switching devices that minimize the number of
interrupted customers during contingency conditions by automatically isolating faulted
components and transferring customers to an optional source when their normal supply has been
Distribution Automation (DA) is a set of technologies that enable an electric utility to
remotely monitor, coordinate, and operate distribution components in a real-time mode from
remote locations. DA includes substation, feeder and customer automation. DA driving forces are:
a) addressing the needs of the smart grid pertaining to service reliability and power quality, b)
regulatory incentives and penalties, and c) pressure to cut costs and optimize operations. DA
benefits can be classified in functional and monetary and they are a function of the specific
application to be deployed. One of the most popular DA applications is Fault Location, Isolation
and Service Restoration (FLISR).
SELF-HEALING OF A SMART GRID
Self-healing or self-restoration ranges from conventional approaches such as automatic
load transfer and loop sectionalizing to more advanced agent-based restoration schemes, including
DER intentional islanding. Self-restoration can be implemented by utilizing only switches (no fault
current detection or interrupting capability), only reclosers or a combination of both. The
advantages of using switches for conducting self-restoration is that it avoids dealing with issues
pertaining to protection coordination that may occur when power flow through a device is reversed
due to transferring load to a neighbour feeder. If not properly taken into account this situation may
lead to miscoordination and/or nuisance tripping of reclosers. However, modern remote-controlled
reclosers allow overcoming this issue, being the drawback the need to calculate and program
different overcurrent protection settings depending on the potential feeder configurations. This can
be overcome by the implementation of adaptive protection systems.
The concept of self-restoration in distribution systems seems more suitable for urban and
suburban feeders where open ties and alternative supply routes are available, but not to rural
feeders where radial distribution is predominant. However, even in the latter case, the
implementation of microgrids and intentional islanding of DG and DES may help minimize
reliability impacts, successful experiences in this regard have been reported in the literature.
Furthermore, in the case of urban and suburban distribution feeders, alternatives such as close-
loop operation of medium-voltage feeders may also be implemented in the context of
selfrestoration while attaining other benefits such as improved system efficiency. It is worth noting
that there are a series of difficulties to implement such operation.
A key aspect of self-restoration when applied to distribution systems is the need to identify
fault locations and if possible anticipate fault occurrence. Numerous proposals and commercial
products are available in this area, and different levels of fault location capabilities are becoming
available not only on field level devices such as modern microprocessor based relays and reclosers,
but also on Distribution Management Systems. This includes either fault or outage location. Fault
location aims at pinpointing faulted feeder components (pole, distribution line, etc), while outage
location has the goal of identifying the protective device that has operated to isolate the fault. Here
it is worth remembering that not all protective devices are monitored in real-time, thus outage
location is aimed at assisting the distribution system operator in detecting the operation of this type
of devices and confirming the operation of those that are supervised in realtime.
The proliferation of distribution equipment with monitoring capabilities, such as modern
reclosers and switches, Intelligent Electronic Devices (IED) such as voltage and current sensors,
faulted circuit indicators, DER, and the growing utilization of SCADA and Advanced Metering
Infrastructure (AMI), is helping utilities overcome the traditional real-time supervision limitations
of distribution systems and allowing the implementation and increased accuracy of fault location
algorithms. Moreover, the growing interest in applying Phasor Measurement Units (PMU) to
distribution systems is expected to provide with an additional high-definition data source that could
be used for conducting not only more accurate state estimation and fault location.
FAULT LOCATION, IDENTIFICATION, AND SERVICE RESTORATION (FLISR):
The smart grid concept is driving the implementation of series of self-restoration schemes in the
form of D applications. The most popular of these is FLISR, which consists of the utilization of
advanced protective and switching devices to automatically locate and isolate faulted feeder
sections and restore the maximum number of customers possible located on healthy sections. There
is a growing trend in the industry for implementing
FLISR as well as other DA schemes. This is due to several reasons such as the access to incentives
provided through government-funded programs the maturity of DA technologies and the
availability of a variety of communication technologies that facilitate its implementation.
FLISR benefits include
a. Functional benefits:
• Improve SAIDI, SAIFI, and other reliability statistics
• Reduce “energy not supplied” (kWh)
• Provide “premium quality” service
• Reduce fault investigation time
b. Monetary benefits:
• Increase revenue (sell more energy)
• Reduce customer cost of outage
• Additional revenue from “premium quality” customers
• Labor/vehicle savings
• Achieve regulatory incentives (when available)
Figure shows the advantages of implementing FLISR versus conventional operation for a typical
distribution feeder. When conventional operation (without FLISR) is used, there is a need for
investigating the specific fault location and conducting manual switching to isolate the faulted area
and restore service to customers located on healthy feeder sections. In this case customer trouble
calls may play an important role, and human intervention, either for fault location or switching
operations to restore service, is vital. FLISR on the other side allows detecting faults and restoring
affected customers faster and with limited human intervention. When FLISR is used power is
quickly restored to customers located on healthy sections of a feeder. Moreover, the faulted area
is delimited by the FLISR scheme, this reduces the time required for fault investigation and
patrolling. Moreover, if FLISR switching and protective devices are monitored in real-time then
there is no need to wait for customer trouble calls to dispatch crews. Therefore, besides its obvious
reliability benefits FLISR also has a direct impact on reducing operators and crews’ workload,
which increases efficiency and reduces operation costs.
SMART GRID RENEWABLE ENERGY SYSTEM
Smart grid provides quality power that meet 21st century demand which cooperative generation
and storage options that fulfills needs considering the changes and the challenges. The key goal of
smart grid is to promote active customer participation and decision making as well as to create the
operation environment in which both utilities and electricity users influence each other. In smart
grids, users can influence utilities by adding distributed generation sources such as photovoltaic
(PV) modules or energy storage at the point of use, and reacting pricing signals. Utilities can
improve reliability through the demand response programs, adding distributed generation or
energy storage at substations, and providing automated control to the grid.
Renewable energy sources are being developed in many countries to reduce CO2 emissions and
provide sustainable electrical power. The balance of particular technologies and their scale changes
from country to country. However, hydro, wind, biomass (solid biomass, bio liquids and biogas),
tidal stream, and photovoltaic (PV) are common choices.
Variable speed turbines are used for wind, small hydro and tidal power generation. These generally
use–DC–AC power conversion where the turbine is arranged to rotate at optimum speed to extract
the maximum power from the fluid flow or minimize mechanical loads on the turbine. The variable
frequency power output from the generator is first converted to DC. A second converter is used to
convert DC into 50/60 Hz AC.
The output of a PV system is DC and therefore a DC–AC converter is essential for grid connection.
SMART GRID CONNECTIONS TO RENEWABLE RESOURCES:
As harnessing the natural and renewable energies of the sun, wind, hydro, geothermal, and biomass
improves the sustainability of energy production and delivers benefits to the environment, their
grid integration is the driver for smart grid which has the following features:
• Smart grid technologies and concepts reduce barriers to the integration of renewable resources
and allow power grids to support a greater percentage of variable renewable resources.
• Enabling smart grid technology, such as distributed storage, demand response, advanced sensing,
control software, information infrastructure, and market signals, increases the ability to influence
and balance supply and demand.
• With smart grid technology, grid operators can better coordinate and control the system in
response to grid conditions, thus allowing integration of increasingly greater levels of renewable
resources more effectively and at lower cost.
• Advanced Metering Instrument (AMI) and internet-based services engage demand response and
distributed storage to accommodate higher penetration and cost-effective integration of renewable
• Smart grid technologies that support the integration of renewable resources at the distribution
level include AMI, distributed storage, demand response, and distribution automation.
• Advanced and automated integration systems, such as inverters and converters with
communications software interfaces, enable distributed management and application integration
for renewable generation.
SOLAR PV DESIGN FOR SMART GRID INTEGRATION:
For seamless gird tied PV interconnections, a typical solar PV should provide two-way flows of
power and communication between the smart grid and the solar PV system. At the heart of this
intelligent system is the inverter.
Three solar PV inverters are available which are the string, the central and the newly developed
micro inverter, known also as integrated AC module inverter.
The conventional solar PV installations feed DC voltage to a central inverter for conditioning and
distribution locally or across the power grid. Furthermore, the DC voltage carried through the array
to the central inverter may have significant fire and safety hazards, leading to increased costs for
cabling and, in turn, higher costs for installation and maintenance. Therefore, to mitigate individual
panel effects, solar PV designers have moved power conversion to each individual string, or set of
series-connected panels in a large array.
Central inverter advantages
Low capital price per watt.
Comparative ease of installation – a single unit in some scenarios.
Central inverter disadvantages
A single potential point of entire system failure.
String converters provide DC-DC conversion to enhance the power delivered to the central inverter
by each string. As with string converters, string inverters offer incremental improvement in the
overall array efficiency compared to conventional central inverter installations, yet still permit a
single degraded panel to have an unduly large impact on overall output. This approach reduces the
impact of a single poorly-performing panel to its string rather than the entire array. Therefore,
string inverters eliminate the need for a central inverter by providing DC-AC conversion at the
output of each string.
By eliminating the central inverter and its potential as a single point of failure, this approach
improves system robustness. However, such installations still need to contend with the hazards
and costs associated with DC voltage transmission.
String inverter advantages
Allows for high design flexibility.
3 phase variations available.
Well supported (if buying trusted brands).
Remote system monitoring capabilities.
String inverter disadvantages
No panel level MPPT.
No panel level monitoring.
High voltage levels present a potential safety hazard.
Recent researches focus on micro inverters which take the concept of string inverters to the next
level - providing DC-AC conversion from each individual panel rather than an entire string.
Micro inverter advantages:
Panel level MPPT (Maximum Power Point Tracking)
Increase system availability – a single malfunctioning panel will not have such an impact on the
Panel level monitoring
Lower DC voltage, increasing safety. No need for ~ 600 V DC cabling requiring conduits
Allows for increased design flexibility, modules can be oriented in different directions
Increased yield from sites that suffer from overshadowing, as one shadowed module doesn’t drag
down a whole string
No need to calculate string lengths – simpler to design systems
Ability to use different makes/models of modules in one system, particularly when repairing or
updating older systems
Micro inverter disadvantages
Higher costs in terms of dollars per watt, currently up to double the cost compared to string
Increased complexity in installation
Given their positioning in an installation, some micro-inverters may have issues in extreme heat
Increased maintenance costs due to there being multiple units in an array.
Power electronics in pv cell integration:
Figure 1 shows the main elements of a grid-connected domestic PV system. It typically consists
of: (1) a DC–DC converter for Maximum Power Point Tracking (MPPT) and to increase the
voltage; (2) a single phase DC–AC inverter; (3) an output filter and sometimes a transformer; and
(4) a controller
The PV module contains a number of photovoltaic cells connected in series and in parallel.
Figure2 shows the current versus voltage and the power versus voltage characteristics of a PV
module. The maximum power output of the module is obtained near the knee of its voltage/current
Different configurations of DC–DC converters are used, for example, boost, push–pull, full bridge,
and fly back converter. The DC voltage on the inverter side of the DC–DC converter is normally
maintained to be constant by the inverter control. The MPPT algorithm is used to find continually
a PV array DC voltage which extracts the most power from the PV array while the cell
temperatures and operating conditions of the module change.
As it is easy to implement in a digital controller, the most widely used MPPT algorithm is ‘perturb
and observe’ sometime known as ‘hill climbing’. In this method, the terminal voltage of the PV
array is perturbed in one direction and if the power from the PV array increases, then the operating
voltage is further perturbed in the same direction. Otherwise if the power from the PV array
decreases, then the operating voltage is perturbed in the reverse direction. Another technique more
easily implemented with analogue electronics is incremental conductance. This is based on the fact
that at maximum power point, (di/dv) + (i/v) of the PV array is zero (derived from dP/dv = 0) .
This equation suggests that the voltage corresponding to the maximum power can be found by
measuring the incremental conductance (di/dv) and instantaneous conductance (i/v).
The DC voltage obtained from the DC–DC converter is inverted to 50/60 Hz AC. A voltage source
inverter is widely used. This normally uses a pulse width modulation switching technique to
minimize harmonic distortion. Finally, a filter is placed at the output to minimize harmonics fed
into the power system. In some designs a transformer is also employed at the output of the inverter
to ensure no DC is injected into the grid.
Benefits and barrier of smart grid renewable energy
The benefits of smart grid renewable energy system are summarized as follows:
First, enabling renewable energy resources to accommodate higher penetration with cost
effective while improving power quality and reliability.
Second, integrating consumers as active players in the electricity system; savings, achieved
by reducing peaks in demand and improving energy efficiency, as well as cutting
greenhouse gas emissions.
Finally, voltage regulation and load following enables reducing cost of operations based
on marginal production costs.
The barrier to smart grid technology adoption is justifying the value preposition by the service
provider and the customer, followed by regulatory constraints and technology standard that
obstruct the smart grid technologies.
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