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Module #1Basic Electricity

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Module 1Learning Objectives

To gain an understanding of the following:

Basic Electricity (1A) Units of Measurement Energy and Power Ohm’s Law and Joule’s Law Electrical Losses, Parallel Paths AC and DC Frequency The Transformer Real and Reactive Power Power Factor Three Phase Power

Geography and History related to the Ontario power system (1B) History and Growth of Ontario’s Power System Functions performed by Ontario Hydro and where they now belong The world outside Ontario, the interconnected system NERC/NPCC

Module 1ABasic Electricity

Units of measurement

Voltage (volts) v (Kv)

Current (amps) I or A

Resistance (ohms)

Frequency (hertz) Hz

Power (watts) w (Mw)

Reactive Power var (Mvar)

Apparent Power va (Mva)

Basic Electricity

Units of measurement

Kilo (K) 1,000

Mega (M) 1,000,000

Giga (G) 1,000,000,000

Tera (T) 1,000,000,000,000

Typically

Volts in Kv eg 230 Kv

Watts in Mw eg 500 Mw

Current as is eg 100 A

Basic Electricity

Energy and Power

Basic Electricity Energy is the ability or capacity to do work.

Energy and work are measured in the same units: eg joules. There are two main types of energy viz;

Potential energy (stored energy, eg gravity, coal, oil, gas, the atom).

Kinetic energy (motion energy, eg electrical energy, wind, sound)

Energy can be neither created nor destroyed (law of conservation of matter and energy), but it can be changed from one form into another

From potential energy to mechanical energy to electrical energy (as is the case with a hydro electric facility)

From heat energy in coal to mechanical energy to electrical energy (as is the case of a fossil fired facility)

Basic ElectricityEnergy and Power

The basic energy unit is the Btu. This stands for British thermal unit. A Btu is defined as the amount of heat energy it takes to raise the temperature of one pound of water by one degree Fahrenheit, at sea level.

One Btu roughly equals:

An average candy bar One match

It takes, for example, about 2,000 Btus to make a pot of coffee.

1,056 joules = 1 Btu

In most countries (except for the USA) energy is measured in joules rather than Btus.

Basic Electricity Energy and Power

BTU Content of Common Energy Units

1 gallon (imp) of gasoline = 149,000 Btu

1 litre of gasoline = 33,000 Btu

1 gallon (imp) of diesel fuel = 167,000 Btu

1 litre of diesel fuel = 37,000 Btu

1 barrel(42 US gallons/ 34 imp gallons) of crude oil = 5,800,000 Btu

1 cubic foot of natural gas = 1,031 Btu

Power is a measure of how much work can be performed in a given amount of time or how rapidly a standard amount of work is done.

American cars for example are rated in "horsepower". In Europe many cars are rated in Kw. (1 horsepower = 0.746 Kw)

The power of a car's engine won't indicate how high a hill it can climb or how much weight it can tow, but it will indicate how fast it can climb a specific hill or tow a specific weight

Basic Electricity

Ohm’s Law and Joule’s law

Basic Electricity Ohm’s Law and Joule’s law

Water analogy for Voltage, Current and Resistance

Voltage (V)equivalent to water pressure

Current (I) equivalent to water flow

Resistance (R) equivalent to restrictions in pipes

Electrical energy is governed by Ohm’s Law and Joule’s law

I = V/R (Ohm’s law) where I is Current (amps), V is voltage

(volts) and R is resistance (ohms).

P = V*I (Joule’s law) where P is Power (watts)

Electrical energy is expressed in watt hours (power expended over a given amount of time)

Basic Electricity

Ohm’s Law and Joule’s law Example

Circuit must be complete for current to flow, if switch is open nothing happens.

Current (I) = 12/3= 4 amps

Power = 12 x 4 = 48 watts

Energy over an hour = 48 watt hours

The lamp will light 1 second after throwing the switch!

Now we can use these two formulae to show that :

P = V2/R

In other words power is proportional to the square of the voltage.

We can theoretically transfer four times the power if we double the voltage (important concept)

Basic Electricity

Electrical Losses and Parallel Paths

Basic Electricity

Electrical Losses and Parallel Paths

Power losses occur when current flows though a resistance

P = V x I (Joule’s Law)

But V = I x R (Ohm’s Law)

Therefore P = I2 x R or I2R

These losses appear as heat – example is the electric kettle

In a transmission line the resistance of the line causes losses based on this formula, the higher the resistance and the current the greater the power losses.

Basic ElectricitySeries Path

Total Resistance R = R1 + R2 = 11 ohms

Therefore I = V/R = 100/11 = 9.09 amps

Line Losses = I2 R1 = 82.6 x 1 = 82.6 watts

R1 = 1 Ohm

R2 = 10 Ohms

V = 100 Volts

I = 9.09 amps

Transmission Line

Load (Customer)

Basic ElectricityParallel Path

I/R1 = 1/RA +1/RB + 1/RC = 1/1 +1/1 +1/1 = 3/1

Therefore R1 = 1/3 ohm = 0.333 ohms

Therefore total Resistance = R1 + R2 = 10.333 ohms

Therefore I = V/R = 100/10.33 = 9.7 amps and line losses = I2 * R1 = 31 watts

V = 100 Volts

I =9.7 amps

R2 = 10 ohms

RA = 1 Ohm

RB = 1 ohm

RC = 1 ohm

Load (Customer)

Basic ElectricityCalculation: electrical voltage, current,

resistance, and power

Basic Electricity

Alternating Current and Direct Current

Basic Electricity Alternating Current and Direct Current

DC stands for "Direct Current," meaning voltage or current that maintains constant polarity and direction over time.

AC stands for "Alternating Current," meaning voltage or

current that changes polarity and direction over time.

Basic Electricity Alternating Current and Direct

Current

Basic Electricity Alternating Current and Direct Current

Basic Electricity

Alternating Current and Direct Current

Basic Electricity

Why Alternating Current (AC) is used and not Direct Current (DC)

The transformer's ability to step AC voltage up or down with ease gives AC an advantage unmatched by DC.

When transmitting electrical power over long distances, it is far more efficient to do so with stepped-up voltages and stepped-down currents, then step the voltage back down and the current back up for industry, business, or consumer use.

Cannot run induction motors with DC, most industrial motors are induction motors (simple and versatile).

DC is used to transmit power over very long distances but it is then converted back to AC for end use

Basic ElectricityHow AC Power is Produced

Magnetism and Electricity are completely intertwined

Electric current (moving electric charge) creates magnetism (discovered by Andre-Marie Ampere in the 1820’s)

Moving magnets create current in nearby conductors (discovered by Michael Faraday also in the 1820’s)

Basic Electricity How AC Power is Produced

Magnetism and Electricity are completely intertwined

If the magnet does not move there is no attraction

If the material is not a conductor there is no attraction

When the magnet is moved a current is induced in the coiled wire.

Magnet

Magnetic lines of force are stronger (more numerous) at the two poles of the magnet

When a rotating magnet passes a stationary conductor (wire) the induced current in the wire is greatest when each of the poles pass.

This is why we get a sine

The rotor of an AC generator is a rotating magnet(s).

The stator of an AC generator is a series of stationary windings and electric current is induced in them by the rotating magnet(s)

A rotor and stator for a hydro-electric generator (note the number of poles)

Basic Electricity

Frequency

Basic Electricity Frequency

Measured in cycles per second or Hertz.

60 Hertz in North America

50 Hertz in Europe

Time for 1 cycle = 1/60 = 16.66 milli secs

At what rotational speed must an AC generator spin at to produce a frequency of 60 Hz?

RPM = frequency x 120 divided by number of pole pairs, where

RPM = revolutions per minute f = frequency in hertz

Therefore the rotor of a machine with two pole pairs (typical fossil fired unit) rotates at 3600 RPM

Hydroelectric units rotate at much slower speeds, they have more pole pairs.

Frequency is the basic metric used to ensure that there is sufficient generation to meet customer demand.

Lower frequency (< 60 Hz) means customer demand not being fully met

Higher frequency (> 60 Hz) means that customer demand is being oversupplied

Basic Electricity

The Transformer

Basic Electricity The Transformer

Np x Ip = Ns x Is

Vp/Np = Vs/Ns

Basic Electricity Real and Reactive Power

The concepts of

Watts (real power)

Volt ampere reactive, Var (reactive power or imaginary power)

Reactive power is a concept used to describe the loss of power in a system arising from the production of electric and magnetic fields.

Although reactive loads such as inductors and capacitors dissipate no power, they drop voltage and draw current, which creates the impression that they actually do.

This “imaginary power” or “phantom power” is called reactive power. It is measured in a unit called Volt-Amps-Reactive (VAR).

The actual amount of power being used, or dissipated, is called true power, and is measured in the unit of watts.

The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current. Apparent power is measured in the unit of Volt-Amps (VA).

Power in a purely resistive AC circuit

All the power is positive

Power in a purely inductive AC circuit

Note that the power is pulsating, no power is absorbed by the load.

Power in an inductive and resistive AC circuit

Note that although most of the power is positive, there is a small pulsating component

In a purely resistive circuit, all circuit power is dissipated by the resistor(s). Voltage and current are in phase with each other.

In a purely reactive circuit, no circuit power is dissipated by the load(s). Rather, power is alternately absorbed from and returned to the AC source. Voltage and current are 90o out of phase with each other.

In a circuit consisting of resistance and reactance mixed, there will be more power dissipated by the load(s) than returned, but some power will definitely be dissipated and some will merely be absorbed and returned. Voltage and current in such a circuit will be out of phase by a value somewhere between 0o and 90o.

Basic Electricity Reactive Power

Power provided and maintained for the explicit purpose of ensuring continuous, steady voltage on transmission networks.

Reactive power must be produced for maintenance of the system and is not produced for end-use consumption.

Electric motors, electromagnetic generators and alternators used for creating alternating current are all components of the energy delivery chain which require reactive power.

Losses incurred in transmission from heat and electromagnetic emissions are included in total reactive power.

This power is supplied for many purposes by generators, condensers, capacitors and similar devices which can react to changes in current flow by releasing energy to normalize this flow.

Basic Electricity Reactive Power

Why do we need Reactive Power?

To Maintain and Control the voltage balance on the power system

To avoid damage to the

Transmission system Generation plant Other connected parties

The provision of Reactive Power by all generating units for voltage support is vital in maintaining a secure and stable Transmission System

Basic Electricity

Reactive Power – an analogy (sort of!)

Consider walking across a trampoline.

There is an up and down motion required to traverse the trampoline.

This up and down motion is analgous to reactive power (required but not useful work)

Basic Electricity Impedance

R = Resistance (ohms)

XL = Inductive Reactance (ohms)

XC = Capacitive Reactance (ohms)

X = XL - XC (ohms)

Ohm’s Law still applies only now it’s

I = V/Z

Power dissipated by a load is referred to as true power. True power is symbolized by the letter P and is measured in the unit of Watts (W).

Power merely absorbed and returned in load due to its reactive properties is referred to as reactive power. Reactive power is symbolized by the letter Q and is measured in the unit of Volt-Amps-Reactive (VAR).

Total power in an AC circuit, both dissipated and absorbed/returned is referred to as apparent power. Apparent power is symbolized by the letter S and is measured in the unit of Volt-Amps (VA).

These three types of power are trigonometrically related to one another. In a right triangle, P = adjacent length, Q = opposite length, and S = hypotenuse length. The opposite angle is equal to the circuit's impedance (Z) phase angle

True, Reactive, and Apparent power

Good paper on Reactive Power Supply can be found at:

http://www.ferc.gov/EventCalendar/Files/20050310144430-02-04-05-reactive-power.pdf

Basic Electricity

Good explanations of reactive power requirements in a power system

http://www.ferc.gov/EventCalendar/Files/20050310144430-02-04-05-reactive-power.pdf

http://www.ornl.gov/sci/btc/apps/Restructuring/con453.pdf

Basic Electricity

Power Factor

Basic Electricity Power Factor

When expressed as a fraction, the ratio between true power and apparent power is called the power factor.

Because true power and apparent power form the adjacent and hypotenuse sides of a right angle triangle, respectively, the power factor ratio is also equal to the cosine of that phase angle

If the cosine of the angle is 0.9 then the angle is ~ 25 degrees

Basic Electricity

Power Factor

For the purely resistive circuit, the power factor is 1 (perfect), because the reactive power equals zero. Here, the power triangle would look like a horizontal line, because the opposite (reactive power) side would have zero length.

For the purely inductive circuit, the power factor is zero, because true power equals zero. Here, the power triangle would look like a vertical line, because the adjacent (true power) side would have zero length.

The same could be said for a purely capacitive circuit. If there are no dissipative (resistive) components in the circuit, then the true power must be equal to zero, making any power in the circuit purely reactive. The power triangle for a purely capacitive circuit would again be a vertical line (pointing down instead of up as it was for the purely inductive circuit).

Basic Electricity

Customer loads are generally a combination of resistive and inductive, hence the aggregate load on the power system is net inductive, ie customer loads absorb VARs.

At off peak times lightly loaded transmission lines can have a large capacitive effect.

Hence during on peak periods generators have to produce VARs and at off peak times have to absorb VARs

Generators are required to be able to provide full Mw output at 0.9 power factor lagging and 0.95 power factor leading

Basic Electricity

Three Phase Power

Basic Electricity Three Phase Power

Single phase versus three phase generator

Could be any number of phases but standardized at three phase

Can be compared to the number of cylinders in your car

Industry uses all three phases, households normally only one.

Basic Electricity Three Phase Power

Each phase is 1200 apart

Basic Electricity

Three phase power

All transmission lines are three phase

Some distribution lines (very low voltage) are single phase

Loads on each phase normally balanced

Basic Electricity

Double circuit transmission line

Each line has 3 phases

Phase Voltage is Phase to Phase

Line Voltage is Line to ground

Basic Electricity

Perspectives

Basic Electricity

Typical household load is about 10 to 20 kw

And about 10 Mwh per year

Total Ontario electrical energy in the year ~ 150,000,000 Mwh or 150 Twh

Basic ElectricitySome every day examples of power

Desktop Computer 80 w

One sq meter solar panel 120 w

Human brain 30 w

Electric kettle 1 Kw

A 200 horsepower car 150 Kw

Av electric power useage/capita in world 2.2 Kw (in USA 12 Kw)

Diesel locomotive 3 Mw

Aircraft carrier 190 Mw

Three Gorges power station (China) 18 Gw

Peak load in Ontario 26.5 Gw

Hurricane 50 to 200 Tw

Basic Electricity

The End

PowerNex Associates Inc.

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