www.eit.edu.au
Electrical Power
System
Fundamentals for
Non-Electrical
Engineers
by
Steve Mackay
www.eit.edu.auEIT Micro-Course
Series
• Every two weeks we present a 35 to 45 minute interactive course
• Practical, useful with Q & A throughout
• PID loop Tuning / Arc Flash Protection, Functional Safety, Troubleshooting conveyors presented so far
• Upcoming:
– Electrical Troubleshooting and much much more…..
• Go to
http://www.eit.edu.au/free-courses
• You get the recording and slides
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Overall Presentation
The focus of this session is the building
blocks of electrical engineering, the
fundamentals of electrical design and
integrating electrical engineering
know-how into the other disciplines
within an organisation.
Objectives
• The basics • Design rules • Selection, installation and commissioning of electrical systemswww.eit.edu.au
Topics
1. Generation, Transmission & Distribution 2. Transformers 3. Earthing/grounding 4. Power Quality 5. Protection www.eit.edu.au1.0Electrical Power
Generation, Transmission &
Distribution
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Energy Conversion
¾ Process of transforming one form of energy
into another
¾ In physics and engineering, energy
transformation is often referred to as energy conversion
¾ Energy of fossil fuels, solar radiation, or
nuclear fuels can be converted into other energy forms
¾ Such as electrical, propulsive, or heating
that are more useful to us.
Electrical Energy
¾ Electrical energy is undoubtedly the primary
source of energy consumption in any modern household.
¾ Most electrical energy is supplied by
commercial power plants.
¾ The most common sources of power plants
are:
• Fuel energy
• Hydro-potential energy
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Turbine
¾ Rotary engine that extracts energy from a
fluid flow
¾ Has a number of blades, like a windmill
¾ Blades rotate when a liquid or gas (steam) is
forced through it under pressure.
¾ The rotating turbine is connected to a
generator
which produces alternating current electricity
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Electrical Generator
¾ Device that converts kinetic energy to
electrical energy, using electromagnetic induction.
¾ Reverse conversion of electrical energy into
mechanical energy is done by a motor
¾ The source of mechanical energy may be
•A turbine steam engine,
•Water falling through a turbine or waterwheel,
•An internal combustion engine,
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Electrical Generator
(contd…)
¾ The generators are the key to getting
electricity
¾ These are very large containing magnets
and wires
¾ Power lines are connected to the generator
to carry electricity.
www.loc.gov www.terragalleria.com
Electrical Generator
(contd…)
¾ A metal shaft connected to a
turbine is being turned by falling water or steam.
¾ As the turbine rotates, the
shaft coupled to the generator also rotates
¾ Therefore the generator
components also rotate and produces electricity.
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Coal-Fired Power Plant
www.tva.gov
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Combustion Turbine Power
Plant
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Hydroelectric Power Plant
¾ Hydro-electric power plants convert the
kinetic energy contained in falling water into electricity.
¾ There are two types: ¾ Hydroelectric dam ¾ Pump-storage plant
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Modern Power Station
Overview
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Alternative Energy Sources
¾ Renewable energy sources are the
alternative sources to generate electricity
• Solar energy
• Geothermal energy
• Biomass energy
• Ocean energy
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Transmission of Electric
Power
¾ Generated electricity at power plant is sent
out over a power grid through transmission lines.
¾ Transmission – Transporting high-voltage
electricity using a giant network of cables (the National Grid)
¾ Power transmission is between power
station and substation.
¾ Transmission is carried out by bare
overhead conductors strung between tall steel towers.
Transmission
(contd…)
¾ When electricity leaves the power station, it
is transformed upwards to 400,000 volts (400kV)
¾ Transmission takes place at very high
voltages to minimise losses.
¾ Super Grid is a giant network of overhead
lines and underground cables
¾ It transports the electricity to substations
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Transmission Losses
¾ Lightning strokes cause huge current flow,
therefore produces I2R losses.
¾ Tree limbs falling across the power lines
cause short circuits.
¾ Due to the interference of the
communication cables losses occur.
¾ Accumulation of ice on the conductors in
cold countries cause damage to the conductors.
¾ Environmental conditions also effect the
transmission efficiency.
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Distribution of Power
¾ Taking electricity to homes, industries and
schools in towns and cities in different areas.
¾ Then supplied to homes at 230V,50Hz or
110V, 60Hz by local distribution
¾ Power is transformed down from the ultra
high transmission voltages to lower voltages by series of substations
¾ When higher voltages (132kV) are used, this
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Distribution
(contd…)
¾ Typical distribution voltages vary from
34,500/19,920 volts to 4,160/2400 volts.
¾ The end point of this supply is a "Zone"
Sub-station
¾ Here the electricity is transformed down to
11kV or 22kV for distribution to the immediate vicinity of customers.
¾ Power is carried through overhead wires or
through underground cables.
Distribution
(contd…)
¾ For supply to residential consumers -- the
voltage has to be transformed down again to 415/240 volts
¾ This occurs at local sub-stations which are
located close to customers.
¾ “Padmount Transformers” are transformers
which supply small voltages at this local sub-station.
¾ From here power is carried directly to the
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Distribution
(contd…)
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Distribution
(contd…)
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AC Power
¾ AC power flow has the three components:
– Real power (P)
•It is in phase with the applied voltage (V)
•Also known as the active component.
•Measured in watts (W)
– Reactive power (Q)
•It is not in phase with the applied voltage (V)
•Also known as Idle or wattless power
•Measured in reactive volt-amperes (VAr)
Power Factor
¾ It is the ratio of the real power to the
apparent power.
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Fig.1 Fig.2
Fig.3
Power Factor
(Contd…)
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Transformers
• A transformer efficiently raises or
lowers AC voltages
• It cannot increase power so that if the
voltage is raised, the current is
proportionally lowered and vice versa
• For an Ideal Transformer
– The voltage ratio is equal to the turns ratio
– Power In is equal to Power Out
Transformers
• Internal losses reduce the power Out
Vs Vp Ns Np = Pp = VpIp = VsIs= Ps
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Large power transformers
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Distribution Boards
• Serve as the point at which electricity
is distributed within a building.
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3.0
Earthing/Grounding
Need for Earthing
• The primary goal of earthing system is SAFETY.
• Secondary goals are effective lightning protection, diminishing electromagnetic coupling (EMC), and the protection against electromagnetic pulses (EMP).
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• Earthing reduce the risks of fires and personnel injuries.
• To provide a low impedance route for high frequency leakage currents.
Need for Earthing
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Electric shock (Direct and
indirect)
• An electric shock occurs when electric current passes through human body
• Two categories of electric shocks are: • Direct contact shock
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Direct contact shock
• A direct contact shock occurs when conductors that are meant to be live such as bare wire or terminals are touched.
Indirect contact shock
• Indirect contact shock is touching an exposed conductive part that has become live under fault conditions.
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Effects of electrical shock
The effects depend upon the following: • The amount of current
• The path of the current
• The length of time the body remains in contact with the circuit
• The frequency of the current
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• Muscular contractions “freeze” the body – when the amount of current flowing through the body reaches a level at which person cannot let go
– increases length of exposure
– current flow causes blisters, reduces surface resistance to current flow, increases current flow, causes severe injury or death
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• Extensor muscles “fling” the body
• “Jerk” reaction results in falls, cuts, bruises, bone fractures, and even death
Effects of electrical shock
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of Ground-Potential
Gradients
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• The use of insulated equipment can protect employees handling grounded equipment, and conductors.
• Restricting employees from areas where hazardous step or touch potentials could arise can protect employees not directly involved in the operation being performed
Protection From the Hazards
of Ground-Potential
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Earth conductors and
Electrodes
• There are two main types of earth
conductor, "bonding" conductors and earth electrodes.
• Bonding and Protective Conductors are two types:
¾Circuit Protective Conductor (CPC) ¾Bonding Conductors
Bonding Conductors
• These ensure that exposed conductive parts remain at the same potential during
electrical fault conditions.
• The two forms of bonding conductor
are:-¾ Main equipotential bonding
conductors
¾ Supplementary bonding conductors
Earth conductors and
Electrodes
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Bonding Conductors
• The conductor size is capable of dealing with anticipated fault current.
• If a fault develops, the whole of the fault current may flow through via the earth conductor through to the "in ground" electrode system.
• Once there, it will normally be split up between the various electrodes.
Earth conductors and
Electrodes
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Earth Electrodes
• Direct contact with the ground provides a means of releasing or collecting any
earth leakage currents.
• Earthed systems requires to carry quite a large fault current for a short period of time and,
• It has a cross-sectional area large enough to carry fault current safely.
Earth conductors and
Electrodes
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• Electrodes must have adequate mechanical and electrical properties.
• To meet demand for long period of time. • During which actual testing or inspection is
difficult.
• The material should have good electrical conductivity and should not corrode in a wide range of soil conditions.
Earth conductors and
Electrodes
• Materials used include copper,
galvanized steel, stainless steel and cast iron.
• Copper is generally the preferred material
• Aluminium is sometimes used for ground “bonding”.
• The corrosive product an oxide layer -is non-conductive.
• Corrosive product reduce the
Earth conductors and
Electrodes
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4.0 Power
Quality
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Power Quality
It is defined with respect to three primary components
¾ Continuity ¾ Quality ¾ Efficiency
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Causes of Power Quality
Problems
¾ Voltage fluctuations (flicker) ¾ Voltage dips and interruptions ¾ Voltage Imbalance (unbalance) ¾ Power frequency variations ¾ Harmonics
Voltage Variations
¾ Short duration (sag, swell) ¾ Long duration
• Undervoltage
• Overvoltage
¾ Voltage Imbalance ¾ Voltage Fluctuations.
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Voltage Sags (dips):
Causes:
• Decrease between 0.1 and 0.9 p.u. in rms voltage or current at the power
frequency for duration from 0.5 cycles to 1 min.
• Local and remote faults.
Short Duration Voltage
Variations
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(contd…)
Impacts:
¾ Dropouts of sensitive customer equipment
such as
•Computer crashes
•Bulbs glow dim
•Fan speed reduces
•Effect on motor speed
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Voltage Swells (surges):
Causes:
• Increase to between 1.1 and 1.8 p.u in the rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.
• Single-line-to-ground faults.
• Equipment over voltage.
(contd…)
¾ Impacts:
• Electronic equipments such as
television, computers will mis-operate
• Small fuses in electronic equipment will blow off
• Bulbs of low power rating will blow off
• Failure of MOVs forced into conduction etc.
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Overvoltage:
Causes:
• Increase in the rms ac voltage greater than 110 percent at the power frequency for a duration longer than 1 min.
• Load switching off
• Capacitor switching on
• System voltage regulation.
Long Duration Voltage variations
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(contd…)
¾ Impacts:
•Electronic devices will burn
•Refrigerator will blow off
•Winding of motors of fan mixers and grinders will burn
•Over heating of equipment
•Bulbs will blow off
•Fuses will blow off
•Causes short circuits which will result sparks in the circuit etc.
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Under Voltage (Brown out)
Causes:
• Decrease in the rms ac voltage to less than 90 percent at the power frequency for a duration longer than 1 min.
• Load switching on
• Capacitor switching off
• System voltage regulation.
(contd…)
¾ Impacts:
• Video on the TV will not appear but one can still hear the audio
• Mixers and grinders may not start
• Computer crashes
• Filament bulbs will glow dim but fluorescent bulbs may not glow.
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Variation of frequency
¾ The deviation of the power system
fundamental frequency from its specified nominal value (e.g. 50 or 60 Hz).
www.ackadia.com/computer/images/ups_power_sag.gif
www.eit.edu.au ¾ Causes:
•Poor speed regulations of local generation
•Faults on the bulk power system
•Large block of load being disconnected
•Disconnecting a large source of generation.
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(contd…)
¾ Impacts:
•Equipment Failure
•Black outs
•Transformers will blow off
•Motor windings will burn due to over heating.
•Motors in mixers, grinders, fans will burn.
Interruptions
Momentary Interruption: 1/2 - 3secs
Temporary Interruption: 3 - 60 secs Long-Term interruption (outage): >1 min
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(contd…)
¾ Causes:
• Temporary faults.
• Lightning stroke.
• Tree limbs falling across conductors.
¾ Impacts: • Operation interruption. • Production losses. • Revenue losses. www.eit.edu.au
Surge
¾ An unexpected increase in voltage i.e. a
increase of 110% of normal voltage for
more than three nanoseconds is considered a surge.
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Surge Protector
¾ A device that shields electronic devices from surges in electrical power, or transient voltage, that flow from the power supply.
Switching Surges
¾ A transient disturbance caused due to
switching on/off of reactive load.
• Load switching
• Oscillatory switching
• Capacitor switching
• Multiple re-strike switching
• Power system switching
• Arcing faults
• Fault clearing
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Lightning Surges
¾ A high voltage transient in an electric circuit
due to lightning.
www.leonardo-energy.org
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¾
Lightning surges in electrical systems
can in general be classified according
to their origin as follows:
• Direct flashes to overhead lines
• Induced over voltages on overhead lines
• Over voltages caused by coupling from other systems.
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Effects of Surges
¾ Electronic devices may operate erratically.
Equipment could lock up or produced garbled results.
¾ Electronic devices may operate at
decreased efficiencies.
¾ Integrated circuits may fail immediately or
fail prematurely. Most of the time, the failure is attributed to "age of the equipment".
(contd…)
¾ Motors will run at high temperatures
resulting in motor vibration, noise,
excessive heat, winding insulation is lost.
¾ Degrade the contacting surfaces of
switches, disconnects, and circuit breakers.
¾ Electrical and electronic appliances will
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Lightning Arrestors
¾ A device that protects from lightning surges.
Lightning arrestors
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5.0 Protection of
Electrical Systems
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Incipient faults
• A fault that takes a long time to
develop into a breakdown of
insulation caused by:
– Partial discharge currents
– Normally become solid faults in
time.
Breakdown of Insulation
Solid fault
• Immediate, complete breakdown of
insulation causing:
– High fault currents / energy
– Danger to personnel
– High stressing of all network
equipment due to heating and
electromechanical forces and
possibility of combustion
– Dips on the network voltage
affecting other parties
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Need for protection
• Protection is also needed to avoid
– Electric shocks
– Electrical burns
– Arc blast injuries
– Fire
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THANK YOU FOR ATTENDING
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Practical online Certificate, Advanced Diploma and Graduate Certificate programs:
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If you are interested in further training in the area
Electrical Power System Fundamentals for Non-Electrical Engineers
UK
Manchester 3 & 4 November Birmingham 7 & 8 November
London 10 & 11 November
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Johannesburg 8 & 9 September
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