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A REPORT

ON

SMART METERING AND CONTROL OF TRANSMISSION SYSTEMS

Submitted in the fulfilment of the

Study Project EEE F266

BY

M.SAI MANOBHIRAM 2012A3PS224H

G.DURGA RAO 2012A3PS255H

D.MOHITH 2012A3PS166H

UNDER THE SUPERVISION OF

T. HARIPRIYA

Assistant professor

ELECTRICAL DEPARTMENT

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI

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ACKNOWLEDGEMENT

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.

ABSTRACT

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.

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Table of contents

Introduction 4

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

Self-Healing 20

Smart Grid Renewable Energy System 23

References 29

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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

customers.

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

disturbances.

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

control emerge.

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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

definition.

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

storage resources.”

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.

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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

Active Consumer

Participation

Consumers are uninformed

and

do not participate

Informed, involved

consumers — demand

response and distributed

energy resources

Accommodation of all

generation and storage

options

Dominated by central

generation — many obstacles

exist for distributed energy

resources interconnection

Many distributed energy

resources with plug - and -

play

convenience focus on

renewables

New products, services, and

markets

Limited, poorly integrated

wholesale markets; limited

opportunities for consumers

Mature, well - integrated

wholesale markets; growth of

new electricity markets for

consumers

Provision of power

quality for the digital

economy

Focus on outages — slow

response to power quality

issues

Power quality a priority with a

variety of quality/price

options — rapid resolution of

issues

Optimization of assets

and operates efficiently

Little integration of

operational data with

asset management—

business process silos

Greatly expanded data

acquisition of grid

parameters; focus on

prevention,

minimizing impact to

consumers

Anticipating responses to

system disturbances

(self- healing)

Responds to prevent further

damage; focus on protecting

assets following a fault

Automatically detects and

responds to problems; focus

on

prevention, minimizing

impact to consumers

Resiliency against cyber

attack and natural disasters

Vulnerable to malicious acts of

terror and natural disasters;

slow response

Resilient to cyber-attack and

natural disasters; rapid

restoration capabilities

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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.

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• 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

gateways).

• 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.

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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

AMR 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

pricing

Coverage limited to a small area or

a portion of a system

Whole-system coverage

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)

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Smart Meters

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

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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

customer sites

• 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

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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.

Wi-Fi

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.

PLCC

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

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.

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Communication Architecture

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

nodes themselves.

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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

this architecture.

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,

including:

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

premises.

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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

CYBER SECURITY

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 [2] . Smart grid

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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

message.

2. Integrity that the message arrives in time at the receiver in exactly the same way it was

sent.

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:

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Cyber Security can be provided by

Encryption and Decryption Methods…

Authentication

Digital Signature

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

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.

Transposition cipher

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.

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Authentication

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 [1].

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.

Digital signatures

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

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Cyber Security Concerns Associated with AMI

AMI is the convergence of the power grid, the communications infrastructure, and the

supporting information infrastructure [1]. 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.

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SELF HEALING

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

lost.

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

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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

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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.

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SMART GRID RENEWABLE ENERGY SYSTEM

INTRODUCTION:

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

energy generation.

• 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.

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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.

CENTRAL 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.

High efficiency.

Comparative ease of installation – a single unit in some scenarios.

Central inverter disadvantages

Size.

Noise.

A single potential point of entire system failure.

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STRING INVERTERS:

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.

High efficiency.

Robust.

3 phase variations available.

Low cost.

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.

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MICRO INVERTERS

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

entire array

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

inverters

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.

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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

Figure 1

Figure 2

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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

characteristic.

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) [4].

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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3. http://www.smartgridopinions.com

4. http://www.smartgrid.ieee.org

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Institution of Engineering and Technology, Stevenage.

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10. Applying Self-Healing Schemes to Modern Power Distribution Systems Julio

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