PowerNex Associates Inc.
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Transcript of PowerNex Associates Inc.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Pow
erN
ex Associates
Inc.
Module #1Basic Electricity
www.pnxa.com
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Energy and Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Energy and Power
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Energy and Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Energy and Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Energy and Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Energy and Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Ohm’s Law and Joule’s law
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Ohm’s Law and Joule’s law
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Ohm’s Law and Joule’s law
The lamp will light 1 second after throwing the switch!
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Ohm’s Law and Joule’s law
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Electrical Losses and Parallel Paths
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
R1
Load (Customer)
Lines
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic ElectricityCalculation: electrical voltage, current,
resistance, and power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Alternating Current and Direct Current
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Alternating Current and Direct
Current
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Alternating Current and Direct Current
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Alternating Current and Direct Current
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
When the magnet is moved a current is induced in the coiled wire.
Magnet
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
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
wave
N S
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity How AC Power is Produced
A rotor and stator for a hydro-electric generator (note the number of poles)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Frequency
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Frequency
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Frequency
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
The Transformer
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity The Transformer
Np x Ip = Ns x Is
Vp/Np = Vs/Ns
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity The Transformer
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity The Transformer
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
The concepts of
Watts (real power)
Volt ampere reactive, Var (reactive power or imaginary power)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive 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).
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
Power in a purely resistive AC circuit
All the power is positive
V =
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
Power in a purely inductive AC circuit
Note that the power is pulsating, no power is absorbed by the load.
V =
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
Power in an inductive and resistive AC circuit
Note that although most of the power is positive, there is a small pulsating component
V =
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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)
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Real and Reactive Power
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Power Factor
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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).
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Three Phase Power
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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.
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity Three Phase Power
Each phase is 1200 apart
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Double circuit transmission line
Each line has 3 phases
Phase Voltage is Phase to Phase
Line Voltage is Line to ground
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
Perspectives
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
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
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PowerNex Associates Inc.Power System Operation/Electricity Market Operation Overview
Basic Electricity
The End