Electric Power Grid

lettucestewElectronique - Appareils

21 nov. 2013 (il y a 4 années et 4 mois)

49 vue(s)



Electric Power Grid



by Anthony J Spurgin

Independent Consultant

San Diego, CA




Electric Power

Electric power is a useful and flexible form of power that
has allowed for the expansion of services to people,
such hospital services, lighting, trains, cooking and
heating capabilities as well as being used by industries
of various kinds

Energy and principally electric power has lead to the
development of nations and civilization

The grid is a method by which electric power can be
used for the benefit of many

The grid ensures that people are served with a reliable
and relatively inexpensive source of power



Electric Power Grid

The Grid is an integrated power distribution

It is made up Power generation elements (power
stations), power distribution lines (high voltage
lines) and household and commercial distribution
systems (low voltage lines), see Figure

It functions to ensure reliable power reaches end
state users

Issues to be considered are: reliability, and cost

Reliability is achieved by ensuring that power
outages are minimized, voltage and frequency
are controlled within narrow limits.

Costs are controlled by selection of power plants

There are also requirements for power shaping,
but this is not covered here



Electric Power Grid

from Wikipedia



Electric Power Grid

Cost is an issue, reliability could be enhanced by the
use of redundant power stations, power lines, etc, but
this has a cost.

Having standby systems maybe necessary but the
choice has to be prudent. What is enough?

To allow for variable power needs, some power
generators are kept at low loads, so
called spinning
reserve, the concern here is that running a unit at part
power can be expensive

By enhancing the reliability of power plant operations
one can also enhance the reliability of the grid, as a
whole. The same goes for power lines

Reliability of grid networks can be enhanced by
connection to other grids. Loads can flow into and out
of a given grid network, this is particularly useful when
dealing with localized disturbances



Electric Power Grid:

Control of Grid Frequency

Short term control of frequency is achieved by automatic
action associated with the power plants

Power stations generate electric power by the use of
alternators driven by steam or gas turbines

The rotational speed of the standard turbine is sensed by
governors and used as a proportional controller, so if the
grid frequency drops the controller opens the turbine
valves to admit more steam

In turn, power plant controllers sense the falling pressure
and increases power output (firing rate) to match the

The gain of the control maybe non
linear, different at
different power levels



Electric Power Grid:

Frequency Control

The objective of controlling the frequency is to try to
account for minute to minute load variations on the grid

Increasing load on the grid causes the frequency to drop
and voltage to change

Grid loads can vary in a number ways

Minute to minute load changes, washer/dryers turned on or off

daily variations to demand changes due to the activities of
people, such as lunch times from 12 to 1pm

Factory load requirements changing, production variations

Weather changes

For Daily and Yearly variations in power; see next figure



Electric Power Grid:

Load Variations

Daily and yearly power variations



Power Plants:

Characteristics affecting response
capabilities and cost

Power plants capabilities vary according to their
fuel, their design and their age

The above aspects influence their ability to fit
into the needs of the organization operating the

There are gas
fired power plants, coal
plants, nuclear plants, combined
cycle plants,
supercritical pressure plants and hydraulic dam
power units

There is an increased probability of solar, wind,
tidal plants to meet environmental imperatives



Power Plants:

Characteristics affecting response
capabilities and cost

Gas fired plants are very flexible and require less time to
build and license

Combined cycle plants are the most efficient fossil plants

Nuclear plants have low fuel costs

Coal plants are more expensive than both gas and
nuclear. They require extensive emission controls

Nuclear plants are less flexible than the others

Nuclear plants do not release carbon based gases

The size and cost of units depends on their
corresponding power density, fossil and nuclear plants
are compact, whereas solar, and wind plants spread out



Power Plants:

response and cost

From the point of view of the grid operator, one is
interested in having the most economic plants, match
load change requirements and are very reliable

So the cost per Megawatt sent
out is important, but
flexibility is important

Cost is also a function of the percent time that the plant
is at its most economical load

The grid operator has to supply power over the whole
year, so he has to factor daily, weekly, and yearly
variations. Periods of low demand maybe a good time to
maintain plants, but what reserves should be retained?

One can appreciate now why, it may be difficult to
incorporate solar and wind units into this mix.



Electric Power Grid:

Control Center

In addition to the plant control systems, the grid is also controlled by
the actions of the grid control center

The grid center sends instructions to the power plants to increase or
decrease power to meet predictions of upcoming load changes

The center has the responsibility of trying to predict large load
changes, correct grid frequency difference compared with standard,
and stabilize the grid during severe losses of load

The center monitors the power distribution to enhance the grid
security and optimize the cost of power

The cost of power depends on the type of power plant, fuel costs
and age of plant. The cost picture is broken up into cost of capital,
fuel cost and manpower costs

Government action can modify the cost picture by adding costs like
a carbon tax. Adding taxes for carbon increases cost of electricity,
maybe some reduction is likely if taxes levied results in higher
efficiency plants



Electric Power Grid:

Blackouts and Line losses

The main power lines are limited in number, controlled by cost and
politics, NIBY is an issue for both plants and lines. We want the
power, but not the power lines or plants!

If a line ceases to function, its load is redistributed among the
remaining lines

Each line has a load limit, determined by current limits which are
ensured by the use of breakers

One of the tasks of the control center is to monitor the health of the
grid and take action to protect the integrity of the grid

The grid controllers have to be aware of the potential for loss of
power plants and increases in loads It is the duty of the power plant
personnel to inform the center of actions that might lead to a loss of
a power plant or loss of load output



Electric Power Grid:

Grid Controllers

The grid controllers should have plans to step in
to maintain the grid, as a whole, by isolating part
of the grid

Once such an event has occurred, the grid
operations have to be recovered. This is not just
the case of closing breakers.

Depending on the power plants and the
customers’ equipment limitations, this may take
a while. In the case of nuclear power plants,
one has to factor in impact of xenon impacts on
the return to critical of the reactor



Grid Operations

The objective of the presentation is to inform the audience on some of the
complexities of the Grid

The Grid operations are a complex mixture of plant operations, reliability
considerations and cost implications

In moving to a Smart Grid all of the above needs to be considered, plus the
fact that Green technologies need to be integrated into the Grid functions,
so this increases the burdens on the Grid operations

The grid has been operating effectively for a large number of years, but as
the complexity of industry has increased the reliability of the grid has
decreased because of the increased burden being placed upon it

Steps have been taken to improve the reliability, but the move to the fully
Smart grid will take time and it appears that it will cost a lot of money

It will interesting to see how all of the requirements are going to be handled
and how the improvements will be factored into the system

This ends the first part of the three part series on the topic of Smart Grids
and Metering



Smart Grid



Although the grid has functioned in present form for some while;
technology has advanced in a number of ways and some of these
can help in increasing the reliability and cost of operations

Computer control systems allow for more predictive capabilities
along with better sensing devices to help mitigate or prevent line and
plant losses

Communication improvements by wireless can inform central
processes of sequential failures and the processes can step in to
prevent cascading events

Weather models tied into the central processes can be used to alert
for the need to bring units on line and select the most cost effective
way to do that

It is expected that SDG&E will tell us about their concepts related to
the SMART Grid and SMART Metering. I think that we are
wondering what are the implementation details, what is the process
of implementation, how long will it take and most importantly how
much will it cost?