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8/8/2019 2.Basics of Energy and Its Various Forms
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Basics of Energy and itsvarious forms
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Syllabus
Basics of Energy and its various forms:
Electricity basics - DC & AC currents, Electricity tariff,
Load management and maximum demand control, Power
factor. Thermal Basics -Fuels, Thermal energy contents offuel, Temperature & Pressure, Heat capacity, sensible and
latent heat, evaporation, condensation, steam, moist air and
humidity & heat transfer, units and conversion.
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Various forms of energy
Potential energy Chemical
Nuclear
Mechanical stored energy
Gravitational
Kinetic Radiant Thermal
Motion Sound
Electrical
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Oil burns to generate heat -->
Heat boils water -->
Water turns to steam -->
Steam pressure turns a turbine -->
Turbine turns an electric generator -->
Generator produces electricity -->
Electricity powers light bulbs -->
Light bulbs give off light and heat
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High and Low grade energy
High grade energy is concentrated
Energy Examples are Light energy, chemical
energy, electricity
Low grade energy rapidly dissipates(molecules are more randomly
distributed) Example: heat energy
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Direct current and Alternating current
Direct current: Non-varying unidirectionalcurrent
Current produced by batteries
Alternating Current: Reverses in regular
recurring intervals with alternate +ve and vevalues at specified number of times per second
In 50 cycle AC, current reverses direction 100 times
a second (twice in one cycle
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Current, Voltage, Resistance & Frequency
Current or Ampere is rate of flow of electricity current which produces a specified force between two
parallel wires, which are 1 metre apart in vacuum
Voltage is measure of electric potential orelectromotive force A potential of one volt appears across a resistance of one
ohm when a current of one ampere flows through thatresistance.
Resistance = Volts / Current and denoted asOhms
Frequency is cycles at which alternating currentchanges Unit is Hertz which is number of cycles per second
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KVA, KVAR, KW & PF KVA = Kilovolts (KV) x Amperes(A)
Also called as as Apparent power
Measures the electrical load of system
Single phase = V x A/1000
Three phase = 1.732 x V x A /1000
KVAR is reactive power i.e. portion of apparent
power that does no work KW is real power or work producing part of power
Single phase = V x A x PF/1000
Three phase = 1.732 x V x A x PF /1000 KWH is energy consumed by 1000 Watts in 1 hour
Power Factor (PF) is ratio of real power to apparentpower PF = KW/KVA or KW/(KW2 + KVAR2)
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Electrical Tariff
Billing demand is highest KVA recordedduring 1-demand interval(30 minutes) in onemonth-measured by digital tri-vector meter
Maximum demand is maximum KVA or KWover one billing cycle
Contract demand is amount of electric power(KVA or KW) demanded by consumer frompower utility
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Connected Load, Demand factorand Load factor
Connected Load is name plate readings(in KVA or KW) of all equipment in aindustry
Demand factor = maximum demand/connected load
Load factor = average load/ maximumload
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Time of Day (TOD)
Utilities prefer flat demand curve
Encourage users to draw power duringoff-peak hours (i.e. Night time) Utilities have TOD offer or incentives or
disincentives Separate energy meters to record peak
and off-peak power consumption
Opportunity for user as off-peak powertariff is usually lower
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TOD charges for different time zone for one electric utility
A-Zone:
22 hrs to
6 hrs
B-Zone:
6 hrs to 9
hrs & 12
hrs to 18
hrs
C-Zone:
9 hrs to
12 hrs
D-Zone:
18 hrs to
22 hrs
205
280330
370
0
50
100
150
200
250
300
350
400
Paise
TOD charges for different time zones for one of the Indian electric
utility
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Example:
3 phase power measurement
A 3-phase AC induction motor (20 kW capacity) is usedfor pumping operation. Electrical parameter such as
current, volt and power factor were measured with power analyzer. Find energy consumption of motor inone hour? (line volts. = 440 V, line current = 25 amps
and PF = 0.90).Power = 3 x V x I x Cos
Measured energy consumption =
3 x 0.440 x 25 x 0.90 x 1 = 17.15 kWh
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Example
Motor loading calculationIn nameplate details of motor, kW or HP indicates the outputof the motor
at full load .The other parameters such as volt, amps, pf are the input
condition of motor at full load
A 10 kW motor has the name plate details as 415 V, 18.2 amps and 0.9
PF. Actual input measurement shows 415 V, 12 amps and 0.7 PF
which was measured with power analyzer during motor running.. What
is motor loading?
Rated output at full load = 10 kW
Rated input at full load = 1.732 x 0.415 x 18.2 x 0.9 = 11.8 kW
The rated efficiency of motor at full load = 10/11.8 = 85%
Measured (Actual) input power = 1.732x 0.415 x 12x 0.7 = 6.0 kW
Motor loading = Measured KW/Rated KW = 6.0/11.8 x 100 = 51.2%
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Thermal Energy Basics
Temperature is denoted in Fahrenheit (F) to Celsius(C)
Calorie is unit of heat: 1 kilocalorie can raise 1000 kgof water by 1oC
Specific heat is amount of heat required to raise 1 kg
of water by 1oC Heat quantity = mass x specific heat x rise in
temperature
Latent heat of fusion is amount of heat applied tosolid to change its state to liquid
Latent heat of vapourisation is amount of heatapplied to liquid to change its state to vapour
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Thermal Energy Basics:
Superheat is heating of vapour to a temperaturehigher than its boiling point at existing pressure
Moisture content in air is humidity Actual weight of water vapour mixed in 1 kg of dry air
Humidity factor is kg of water vapour per kg of dry air
Relative humidity is degree of saturation of air at any drybulb temperature ( given as % of actual water content of airdivided by moisture content of air at exiting temperature
RH = Percentage (%) at temperature (oC
Dew point is temperature at which condensation ofwater vapour from the air begins as the temperatureof the air-water vapour mixture falls
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Thermal energy basics
Dry bulb Temperature is an indication of the sensibleheat content of air-water vapour mixtures
Wet bulb Temperature is a measure of total heatcontent or enthalpy. It is the temperatureapproached by the dry bulb and the dew point assaturation occurs
Specific gravity is density of fuel relative to water Viscosity is measure of internal resistance to flow
Calorific value is measure of heat content in organic
matter Gross or high calorific value and Net or low calorific value
d
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Units and Conversion
1 MW 1,000 kW
1 kW 1,000 Watts
1 kWh 3,412 Btu
1 kWh 1.340 Hp hours
1,000 Btu 0.293 kWh
1 Therm 100,000 Btu (British Thermal Units)1 Million Btu 293.1 Kilowatt hours
100,000 Btu 1 Therm
1 Watt 3.412 Btu per hour
1 Horsepower 746 Watts or 0.746 Kilo Watts1 Horsepower hr. 2,545 Btu
1 kJ 0.239005 Kilocalories
1 Calorie 4.184 Joules
1 kcal/Kg 1.8 Btus/lb.
1 Million Btu 252 Mega calories1 Btu 252 Calories
1 Btu 1,055 Joules
1 Btu/lb. 2.3260000 kJ/kg
1 Btu/lb. 0.5559 Kilocalories/kg
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Units of energy
1 Joule (J) = 0.2390057 calorie (cal) = 9.47817210-4 Britishthermal unit (Btu)
1 cal = 4.184 J = 3.96566710
-3
Btu 1 Btu = 1055.056 J = 252.1644 cal = 2.93071110-4 kilowatt-hour (kWh)
1 kWh = 3.6 Megajoule (MJ) = 0.8604207 Mcal = 3412.142 Btu
Power (Energy Rate) Equivalents
1 kilowatt (kW) 1 kilo joule /second (kJ/s)
1 kilowatt (kW) 3413 BTU/hour (Btu/hr.)1 horsepower (hp) 746 watts (0.746 kW)
1 Ton of refrigeration 12000 Btu/hr.
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Units for Pressure
Gauge pressure is defined relative to atmosphericpressure
Absolute pressure = Gauge pressure + Atmosphericpressure
Units of measure of pressure:Metric (SI) : kilopascals (kPa)
Imperial : pounds per square inch (psi)
1 pascal (Pa) = 1 Newton/m2 (N/m2 )
1 physical atmosphere (atm) = 101325 Pa = 760 mm of mercury
(mm Hg) = 14.69 lb-force/in2 (psi)
1 technical atmosphere (ata) = 1 kilogram-force/cm2 (kg/cm2 )=9.806650104 Pa
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Fuel to KWH Conversions
Natural gas
LPG (propane)
Coal
CokeGas oil
Light fuel oil
Medium fuel oilHeavy fuel oil
M3 x 10.6
Ft3 x 0.3
therms x 29.3
m3 x 25
kg x 8.05
kg x 10.0litres x 12.5
litres x 12.9
litres x 13.1litres x 13.3
kWh
kWh
kWh
kWh
kWh
kWhkWh
kWh
kWhkWh
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Energy Conversions
To: TJ Gcal Mtoe MBtu GWh
From: Multiply by: . . . .TJ 1 238.82.388 x 10-5 947.8 0.2778
Gcal 4.1868 x 10-3 1 10-7 3.968 1.163 x 10-3
Mtoe 4.1868 x 104 107 1 3.968 x 107 11630
MBtu 1.0551 x 10-3 0.252 2.52 x 10-8 1 2.931 x 10-4
GWh 3.6 860 8.6 x 10-5 3412 1
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Mass conversions
To: kg t lt st lb
From: multiply by: . . ..
kilogram (kg) 1 0.001 9.84 x 10-4 1.102 x 10-32.2046
tonne (t) 1000 1 0.984 1.1023
2204.6
long ton (lt) 1016 1.016 1 1.1202240.0
short ton (st) 907.2 0.9072 0.893 1 2000.0
pound (lb) 0.454 4.54 x 10-44.46 x 10-4 5.0 x 10-41
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Volume conversions
To: gal U.S. gal U.K. bbl ft3 lm3
From: multiply by: . . . .
.
U.S. gallon (gal) 1 0.8327 0.02381 0.1337 3.7850.0038
U.K. gallon (gal) 1.201 1 0.02859 0.1605 4.5460.0045
Barrel (bbl) 42.0 34.97 1 5.615 159.00.159
Cubic foot (ft3
) 7.48 6.229 0.1781 1 28.30.0283
Litre (l) 0.2642 0.220 0.0063 0.0353 10.001
Cubic metre (m3) 264.2 220.0 6.289 35.31471000.0 1
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End