Introduction of Electricity

February, 2010 Mohammad Shoeb Siddiqui
Sr. Shift Supervisor
Saba Power Company
Introduction to Electricity

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Introduction to Electricity
Basic Electricity
How Central Power Grids Work
Electricity Generation

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Part 1: Electricity Concepts
What is Electricity?
Electrons, atoms, negative charge
Conductors (example?)
Insulators (example?)
Electrical energy
Magnet

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In September of 1831,
Michael Faraday made the
discovery of
Electromagnetic Induction.

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What does copper wire and magnets have to do with
Electricity?
Faraday attached two
wires to a disc and
rotated the disc between
the opposing poles of a
horseshoe magnet
creating an electric
current.

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Electric current generation - whether from fossil fuels, nuclear,
renewable fuels, or other sources is usually based on the:

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How does a generator work?
A generator is simply a
device that moves a
magnet to create a steady
flow of electrons.
What moves the magnet?
Water, or high pressure
steam or gas drive
turbine blades.

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Process of Generation

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Electrical Units
Three basic units of measurement:
Voltage (volts)
Current (amps)
Resistance (ohms)

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Water Analogy
Voltage ~ water
pressure
Current ~ flow rate
Resistance ~ pipe size

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Key Concept
Let’s say you have a tank of pressurized water
connected to a hose that you use to water your
vegetable garden. If you increase the pressure in the
tank, more water comes out of the hose. Same for
electrical systems: increase the voltage: you get a
higher current of electrons.
OR if you increase the size of the hose more water
can flow out. This is like reducing resistance in an
electrical system, so you get more current.

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Basic Electrical Circuit
All circuits have basic components: a
source of electricity (such as a battery), a
load (a light or motor) and two wires to
carry electricity between the two. Electrons
move from the source, through the load,
and back to the source.
These moving electrons have what we call
energy. As they move they can do work.

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Key Concept
In an electrical system, increasing either the
current (i) or the voltage (V) will increase
power output (P).
Increase resistance in the wires, voltage
drops, current drops > power output drops.

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Electrical Circuits
Battery is a simple electrical circuit and
source
When you load a battery into an electronic
device, the negatively charged electrons will
travel to the portion of the battery with a
positive charge - much like water flowing
down a stream and being forced to turn a
water wheel.

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How to calculate electricity consumption
In a light bulb, electrical
energy creates heat in the
bulb, and the heat then
creates light.
How much power in
kilowatt-hours does a 100-
watt lightbulb use in a year?
0.1 kW x 8,760 hours in a
year (24 x 365) or 876
kilowatt-hours (kWh)

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Household Electricity Consumption
In Pakistan, the power outlets in
the wall deliver 220 volts each.
The frequency or the current is 50
cycles per second.
If you know the amps and volts,
you can determine the amount of
electricity consumed, which is
measured in watts.
Most appliances are rated in
watts. Say your appliance
consumes 1,200 watts or 1.2
kilowatts. If you leave the
appliance on for one hour the
amount of electrical energy
consumed is 1.2 kilowatts per
hour.

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Your Electricity Bill
Power is measured in watts (voltage x
current)
Consumption is measured in kilowatt-hours
How much does the power company charge
you for electricity?

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Electrical Current
Direct Current (DC)
Batteries (and solar cells) produce DC. The
positive and negative terminals of a battery
are always positive and negative. Current
always flows in the same direction between
the two terminals.

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Electrical Current
Alternating Current (AC)
Power from a power plant is AC. The
direction of the current reverses or
alternates.
In Pakistan, AC moves at 50 cycles per
second.
Power from a wall socket is 220 volts, 50-
cycle single-phase AC power.

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Key Concept
There is an advantage in using less current to
make the same amount of power. The
resistance in electrical wires consumes power;
as current increases, more power consumed.
Using a higher voltage to reduce the current
makes electrical system more efficient.

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Part 2: How Central Power Systems Work

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The Power Plant
This is where electrical power begins. In most
cases, the plant consists of a spinning
electrical generator. Something – some kind
of force or pressure - has to make the
generator spin. It might be a turbine in a
hydroelectric dam, a large diesel engine, or a
gas turbine. Often a steam turbine is used to
spin the generator. The steam is created by
burning coal, oil or natural gas. Or the steam
may be generated in a nuclear station.

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Power Plants Generate 3-phase AC Power
Commercial generators
of any size generate
what is called 3-phase
AC power.
There are 4 wires
coming out of every
power plant – the three
phases plus a ground.

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Transmission Substation
3-phase power leaves the
generator and enters a
transmission substation at the
power plant. This substation uses
large transformers to convert the
generator’s voltage (thousands of
volts) up to extremely high
voltages for long distance
transmission on the grid.
In Saba Power generation voltage
is 15.5 kv, a step-up power
transformer covert 15.5 kv to
132 kv.

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Transmission Lines
Typical voltages for long
distance transmission range
from 132 to 765 kilovolts (1
kilo is 1000)
In Pakistan transmission
range is 132 to 500 kv.
A typical long distance
transmission is under 500
kilometres.

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Power Substation
The power substation does 2 or 3
things:
transformers bring down the
voltage to distribution voltages.
a busbar splits the distribution
power off in multiple directions.
circuit breakers and switches to
allow the substation to be
disconnected from the
transmission grid or separate
distribution lines.

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Electricity Distribution
To use power in homes
and markets, power
from the transmission
grid must be stepped
down to the distribution
grid.
Conversion from
transmission voltage to
standard line voltage 11
kV (kilovolts)

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Distribution Line to End Users
The transformer steps down
electricity from 11 kilovolts to
3Ф400/230 volts for normal
household electrical service.
The 3 phase 400 or single phase
230 volts enters your house
through a typical watt-hour
meter.
The meter allows the power
company to charge you (the end
user) the cost of putting up all
these wires and consuming
electricity delivered to your
house, office, factory, etc.

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Key Concept
AC power has one big
advantage: voltage
can be changed (up or
down) using a device
called a transformer.
Power companies save
money using very high
voltages to transmit
power over long
distances.

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Part 3: Electricity Generation
Generation Technologies
Steam turbines
Gas turbines
Wind turbines
Hydro/hydraulic turbines
Combined cycle plants
Cogeneration
Microturbines
Solar photovoltaics (DC power)

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Fossil Fuel Plants Use Steam Turbines

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Saba Power Plant Arial View

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Nuclear Reactors use steam turbines

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Biomass Generation

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Biomass Gasifier Power Plant

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Combined Cycle Power Plants
use gas & steam turbines

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Combined Cycle Plants
use gas turbine and steam turbine

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Solar Photovoltaics

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Solar: On-Grid/Off-Grid Technology

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Characteristics of Generating Plants
Size, generating capacity
Energy/fuel source
Efficiency – conversion to electrical energy
Type of use
Availability

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Generation: Capacity
Depends on size of the
hydraulic turbine, the
electric generator and
the height of the water
(head).
The volume of water
behind the dam affects
the maximum amount
of energy that may be
generated in a given
period of time.

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Power Plant – Size (Capacity)
Range from a few kilowatts to >1,000 MW
Microturbines are the smallest

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Generation: Efficiency
The efficiency of a generating unit is a
measure of the amount of electrical energy
produced per unit of energy input.
For thermal plants (plants burning fuel),
the energy input is fuel and the way
efficiency is measured is called the heat
rate.
The more fuel that has to be burned to
produce electricity, the lower the thermal
efficiency.

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Comparing Plant Efficiency
Newer combined cycle plants have near 50
percent thermal efficiency compared to
simple cycle or nuclear plants which can
only convert 30 percent of their fuel into
electrical energy (the rest is released into
the atmosphere as waste heat).

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Type of Use: Base, Intermediate, Peak Load
In a central power system, power plants are
designed and operated for: base load,
intermediate load, and peak load.
Base load – usually large units with low operating
costs. Usually operated at full capacity during
most of the hours they are available. Designed to
operate for long periods of time at or near
maximum dependable capacity. Low operating
costs refer to low cost of the fuel they use.

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Intermediate Load
Power plants used to respond to variations
in customer demand which occur during
the day. Plants designed for change in
output levels.

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Type of Use: Peak Load
Peak load – power plant is called upon to supply
customer demand during peak (= highest) load
hours of a given day, month, season or year.
Combustion turbines and small hydro units –
usually less than 150 MW, capable of achieving
full load operation within 10 minutes. They may
also be used to replace capacity of other units that
have suddenly been taken off the system due to
forced outages. While steam power units usually
takes 20 to 30 minutes to achieve load from
minimum to maximum or vise versa.

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Plant Availability & Dispatch
System operators are concerned about availability
of each power plant to supply the grid.
System operators (NTDC) dispatch power plants
according to their availability (and operating
cost).
On a day to day and hour to hour basis there
must sufficient generation synchronized to the
grid to meet all load requirements and respond to
short-term variations in customer load, as well as
cover for the loss of another generator.

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Availability vs Outages
Unavailability of a generating unit due to
component failure is called a forced outage.
Various components of generating units
must be removed from service on a regular
basis for preventive maintenance or to
replace components before a forced outage
results – this is called a planned outage.

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Power System Reliability
80 to 90 percent of power
disruption in power
systems today are caused
by transmission grid, not
generation.
Voltage dips in major
transmission line > other
transmission lines within
the system pick up
additional load and may
require central utility to
redispatch generation
>instability, overloading,
blackouts.

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Reserve Capacity
Central power systems designed to meet demand
plus a reserve capacity, over and above the
expected peak load obligation of the power plant
(15 to 45 %).
Today big questions within the industry: should
the amount of installed generating capacity
should be a design requirement (set by
government) or should be determined by the
market; who should pay for transmission?
[MORE TOMORROW].

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END: Introduction to Electricity

Introduction of Electricity

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