Characteristic of Smart Grid

Characteristics of smart grids

Characteristic Description

Enables informed participation  by customers

Consumers help balance supply and demand, and ensure reliability by modifying

the way they use and purchase electricity. These modifications come as a result of

consumers having choices that motivate different purchasing patterns and behaviour.

These choices involve new technologies, new information about their electricity use, and

new forms of electricity pricing and incentives.

Accommodates all generation and storage options

A smart grid accommodates not only large, centralised power plants, but also the

growing array of customer-sited distributed energy resources. Integration of these

resources – including renewables, small-scale combined heat and power, and energy

storage – will increase rapidly all along the value chain, from suppliers to marketers to

customers.

Enables new products, services and markets

Correctly designed and operated markets efficiently create an opportunity for

consumers to choose among competing services. Some of the independent grid

variables that must be explicitly managed are energy, capacity, location, time, rate of

change and quality. Markets can play a major role in the management of these variables.

Regulators, owners/operators and consumers need the flexibility to modify the rules of

business to suit operating and market conditions.

Provides the power quality for the range of needs

Not all commercial enterprises, and certainly not all residential customers, need the

same quality of power. A smart grid supplies varying grades (and prices) of power.

The cost of premium power-quality features can be included in the electrical service

contract. Advanced control methods monitor essential components, enabling rapid

diagnosis and solutions to events that impact power quality, such as lightning,

switching surges, line faults and harmonic sources.

Optimises asset utilisation and operating efficiency

A smart grid applies the latest technologies to optimise the use of its assets. For

example, optimised capacity can be attainable with dynamic ratings, which allow

assets to be used at greater loads by continuously sensing and rating their capacities.

Maintenance efficiency can be optimised with condition-based maintenance, which

signals the need for equipment maintenance at precisely the right time. System-control

devices can be adjusted to reduce losses and eliminate congestion. Operating efficiency

increases when selecting the least-cost energy-delivery system available through these

types of system-control devices.

Provides resiliency to disturbances, attacks and natural disasters

Resiliency refers to the ability of a system to react to unexpected events by isolating

problematic elements while the rest of the system is restored to normal operation. These

self-healing actions result in reduced interruption of service to consumers and help

service providers better manage the delivery infrastructure.

Source: Adapted from DOE, 2009.

smart grid

Introduction of smart Grid

There is a pressing need to accelerate the

development of low-carbon energy technologies

in order to address the global challenges of

energy security, climate change and economic

growth. Smart grids are particularly important

as they enable several other low-carbon energy

technologies, including electric vehicles, variable

renewable energy sources and demand response.

This roadmap provides a consensus view on the

current status of smart grid technologies, and maps

out a global path for expanded use of smart grids,

together with milestones and recommendations for

action for technology and policy development.

What are smart grids?

A smart grid is an electricity network that uses

digital and other advanced technologies to

monitor and manage the transport of electricity

from all generation sources to meet the varying

electricity demands of end-users. Smart grids

co-ordinate the needs and capabilities of all

generators, grid operators, end-users and

electricity market stakeholders to operate all parts

of the system as efficiently as possible, minimising

costs and environmental impacts while maximising

system reliability, resilience and stability.

For the purposes of this roadmap, smart grids

include electricity networks (transmission

and distribution systems) and interfaces with

generation, storage and end-users.1 While

many regions have already begun to “smarten”

their electricity system, all regions will require

significant additional investment and planning

to achieve a smarter grid. Smart grids are an

evolving set of technologies that will be deployed

at different rates in a variety of settings around

the world, depending on local commercial

attractiveness, compatibility with existing

technologies, regulatory developments and

investment frameworks.

Rationale for smart grid technology

The world’s electricity systems face a number

of challenges, including ageing infrastructure,

continued growth in demand, the integration of

increasing numbers of variable renewable energy

sources and electric vehicles, the need to improve

the security of supply and the need to lower carbon

emissions. Smart grid technologies offer ways not

just to meet these challenges but also to develop a

cleaner energy supply that is more energy efficient,

more affordable and more sustainable.

HVDC

Why High Voltage Direct Current ?

High Voltage Direct Current (HVDC) History

The transmission and distribution of

electrical energy started with direct

current. In 1882, a 50-km-long 2-kV DC

transmission line was built between

Miesbach and Munich in Germany.

At that time, conversion between

reasonable consumer voltages and

higher DC transmission voltages could

only be realized by means of rotating

DC machines.

In an AC system, voltage conversion is

simple. An AC transformer allows high

power levels and high insulation levels

within one unit, and has low losses. It is

a relatively simple device, which requires

little maintenance. Further, a three-phase

synchronous generator is superior to a

DC generator in every respect. For these

reasons, AC technology was introduced

at a very early stage in the development

of electrical power systems. It was soon

accepted as the only feasible technology

for generation, transmission and distribution

of electrical energy.

However, high-voltage AC transmission

links have disadvantages, which may

compel a change to DC technology:

• Inductive and capacitive elements of

overhead lines and cables put limits

to the transmission capacity and the

transmission distance of AC transmission

links.

• This limitation is of particular significance

for cables. Depending on the

required transmission capacity, the

system frequency and the loss evaluation,

the achievable transmission

distance for an AC cable will be in the

range of 40 to 100 km. It will mainly

be limited by the charging current.

• Direct connection between two AC

systems with different frequencies is

not possible.

• Direct connection between two AC

systems with the same frequency or

a new connection within a meshed

grid may be impossible because of

system instability, too high short-circuit

levels or undesirable power flow

scenarios.

Engineers were therefore engaged over

generations in the development of a

technology for DC transmissions as a

supplement to the AC transmissions.

1 Technical Merits of HVDC

The advantages of a DC link over an AC

link are:

• A DC link allows power transmission

between AC networks with different

frequencies or networks, which can

not be synchronized, for other reasons.

• Inductive and capacitive parameters

do not limit the transmission capacity

or the maximum length of a DC

overhead line or cable. The conductor

cross section is fully utilized because

there is no skin effect.

For a long cable connection, e.g. beyond

40 km, HVDC will in most cases offer

the only technical solution because of

the high charging current of an AC cable.

This is of particular interest for transmission

across open sea or into large

cities where a DC cable may provide the

only possible solution.

• A digital control system provides

accurate and fast control of the active

power flow.

• Fast modulation of DC transmission

power can be used to damp power

oscillations in an AC grid and thus

improve the system stability.

1.3

Economic Considerations

For a given transmission task, feasibility

studies are carried out before the final

decision on implementation of an HVAC

or HVDC system can be taken

considering:

• AC vs. DC station terminal costs

• AC vs. DC line costs

• AC vs. DC capitalised value of losses

The DC curve is not as steep as the AC

curve because of considerably lower line

costs per kilometre. For long AC lines

the cost of intermediate reactive power

compensation has to be taken into

account.

The break-even distance is in the range

of 500 to 800 km depending on a number

of other factors, like country-specific cost

elements, interest rates for project

financing, loss evaluation, cost of right

of way etc.

1.4

Environmental Issues

An HVDC transmission system is basically

environment-friendly because

improved energy transmission possibilities

contribute to a more efficient

utilization of existing power plants.

The land coverage and the associated

right-of-way cost for an HVDC overhead

transmission line is not as high as that

of an AC line. This reduces the visual

impact and saves land compensation for

new projects. It is also possible to increase

the power transmission capacity

for existing rights of way. A comparison

between a DC and an AC overhead line

is shown in Fig. 1-2.

There are, however, some environmental

issues which must be considered for the

converter stations. The most important

ones are:

• Audible noise

• Visual impact

• Electromagnetic compatibility

• Use of ground or sea return path

in monopolar operation

In general, it can be said that an HVDC

system is highly compatible with any

environment and can be integrated into

it without the need to compromise on

any environmentally important issues of

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