understanding electrical engineering and safety for non-electricians
DESCRIPTION
Electrical engineering is often considered to be a mysterious science, because electricity cannot be seen. However, we are all aware of its existence and usefulness in our daily lives. This workshop aims to take the mystery out of electrical engineering and give a good understanding of the fundamental principles of electricity. While many of us work on electrical systems, we do not fully appreciate the dangers, which we get exposed to when doing so. All it takes is a few simple precautions to avoid getting hurt. This workshop teaches you all about the dangers of careless handling of electrical appliances and prevention of electrical accidents. This workshop is not meant for electrical engineers and other qualified technicians. It is for those who are not formally trained as electricians but often have to handle and maintain electrical appliances in the course of their work. The participants will have an opportunity to understand how the appliances they see everyday actually function. This workshop will deal with the subject with a minimum of theory while emphasising on the practical, hands-on approach. WHO SHOULD ATTEND? Civil, mechanical, chemical, mining engineers, technologists and technicians Managers who are involved with or work with staff and projects in electrical engineering Non-electrical engineers and technicians Non-electrical personnel who want to understand the broader picture Plant and facility engineers Procurement and buying staff Project managers Sales engineers MORE INFORMATION: http://www.idc-online.com/content/understanding-electrical-engineering-and-safety-non-electricians-24TRANSCRIPT
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Understanding Electrical
Engineering and Safety for Non-
electricians
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What is Electric current? An electric current is a movement or flow of charge
similarly like the flow of water moving through the tube (wire).
Flow of charges in a wire
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Charge / Quantity
Charge is of two types
• Positive charge
• Negative charge
Charge is carried by tiny particles called Electrons.
Coulomb = litre current = litre/second
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What is Electricity? Flow of current that is used to power lights, motors, tools,
and many other devices.
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How are charges moved? An amount of energy is needed to
move.
POTENTIAL DIFFERENCE or VOLTAGE is that energy or electric force which causes charges to move.
10 Volts sends more current than 1 Volt.
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PRESSURE Water pressure results from the head of water, e.g. a dam
and is regulated to the customer Electricity comes from a power station, regulated along
the way Different pressures and capacities necessitate different
sized pipes at different sections of the route Differing voltages and current carrying requirements
require varying size conductors and cable insulation
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Electric Cell There should be an energy source to provide this energy
or voltage.
ELECTRIC CELL is one such source.
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A Simple Circuit A battery connected by conductors (copper wire) to
electrical components (bulb).
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Charges moving in a circuit
Voltage from energy source causes current
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Electrical current is defined as
electrons flowing between two points having a difference in voltage potential.
Current is measured in amperes or amps (A).
Litres per Second - Ampere Water cycle via evaporation and rain Closed loop of electron flow. Either via “Earth” or dedicated conductor
Electric Current
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Resistance
Resistance is a property that slows the flow of electrons––the current.
Resistance causes an opposition to the flow of electricity in a circuit. It is measured in OHMS ().
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Resistance Resistance to flow increases with decreasing size
of pipe/conductor Resistance creates losses/Heat Losses proportional to square of current Doubling voltage halves current, reduces losses to
one quarter.
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Pressure Drop Loss incurred overcoming resistance reduces
pressure Same effect water and electricity Equipment requires a minimum pressure to work
efficiently Pressure/voltage drop must be controlled
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Ohm’s Law Ohm's Law is a mathematical equation explaining the
relationship of voltage (V), current (I), and resistance (R)
It is defined as:
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We notice static electricity when the air is very dry.
When the air is more humid, the water in the air helps electrons move off you more quickly, so you can not build up as big a charge.
Static Electricity
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Direct current (DC) and Alternating current (AC)
Flow of current can be DIRECT Current (DC) or ALTERNATING Current (AC)
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Direct current is a continuous current (I) per unit time
Alternating current is current (I) that reverses multiple times per second
In AC-- currents are sinusoidal function of time.
DC and AC Currents
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V
TIME0
1
0.5
Direct Current (DC)
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Cycle (degree)
V
0 90 180 270 360-1
-0.5
0.5
1
0
Alternating Current (AC)
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Electric Energy or Electric Work Energy is defined as ‘the ability to do work’ --as measured
by the capability of doing work (potential energy) or the conversion of this capability to motion (kinetic energy).
Electrical energy is usually measured in watt-hours.
Electric work is said to be done when an electric charge flows through a conductor.
The SI unit of electrical energy is the joule.
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Electric power Defined as the amount of work
done by an electric current per unit time.
The unit of power is WATT
For a resistor in a D C Circuit the power is given by the product of applied voltage and the electric current
Power = Voltage x Current
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Relationship Power is the rate at which electrical energy is
transmitted
Power is energy per unit time
=Electrical power
Electric work (or energy)
Time in seconds
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Single phase AC
A single-phase system is one where there is only one AC voltage source (one source voltage waveform).
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Frequency Measurement of the number of occurrences of a
repeated event per unit of time (for example, 1Hz means an even repeats once per second. 2 Hz is twice per second, and so on.)
Measure the time between two consecutive occurrences of the event (the Time period T)
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Frequency Compute frequency as
f=1/T
SI Units is measured in hertz (Hz) named after the German physicist Heinrich Hertz.
Frequency was originally called cycle per second (cps), which is still sometimes used. Other units used to measure frequency include revolutions per minute (rpm).
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The generation of AC electric power is commonly three phase.
In Three phase AC, the waveforms of three supply conductors are offset from one another by 120°.
Standard frequency is 60 Hz.
Three Phase AC
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Three Phase Waveform
V12 V23 V31
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Advantages of Three Phase 3 phase power is typically 150% more efficient than
single phase in the same power range.
The power delivered to the load is the same at any instant.
Also, in 3 phase the conductors need only be 75% the size of conductors for single phase for the same power output.
Takes more load than Single Phase.
In a single phase unit the power falls to zero three times during each cycle, in 3 phase it never drops to zero.
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Phase Sequence Phase rotation, or phase sequence, is the order in which
the voltage waveforms of a Three phase AC source reach their respective peaks.
For a three-phase system, there are only two possible phase sequences: 1-2-3 and 3-2-1, corresponding to the two possible directions of alternator rotation.
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1-2-3 rotation: 1-2-3-1-2-3-1-2-3-1-2-3-1-2-3 . . .
3-2-1 rotation: 3-2-1-3-2-1-3-2-1-3-2-1-3-2-1 . . .
Phase Sequence
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