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1UNIT-IIUNIT-IWELCOME TO THIS COURSE ENERGY EFFICIENCY IN
ELECTRICAL UTILITIESUNIT-IIIELECTRICAL SYSTEMELECTRIC
MOTORSCOMPRESSED AIR SYSTEMHVAC AND REFRIGERATION SYSTEMFANS AND
BLOWERSPUMPS AND PUMPING SYSTEMCOOLING TOWERDG SET SYSTEMSENERGY
EFFICIENT TECHNOLOGIES IN ELECTRICAL SYSTEMS
ENERGY EFFICIENCY IN ELECTRICAL UTILITIES
UNIT I2CHAPTER I
ELECTRICAL SYSTEM
3IntroductionElectricity is a general term encompassing a
variety of phenomena resulting from the presence and flow of
electric charge. Electric Power Supply System is an aggregate of
equipment used to transmit and distribute electricity from sources
to consumers. ClassificationElectrical Systems may be classified
by:type of current (direct and alternating)plant location (overhead
and cable)layout (circular and radial)normal operating mode (open
and closed)
UNIT IELECTRICAL SYSTEM44Generation, Transmission and
Distribution of ElectricityElectricity is generated in a number of
ways, the most prominent of all are thermal power plants,
hydroelectric power plants, nuclear power plants, etc. There are
other ways of producing electricity which are called
Non-Conventional Energy sources; which include windmill, solar
systems, tidal energy etc.The term transmission is used for the
process of transporting electricity at a very high voltage and the
transmission is in bulk amount. Transmission is a link between
Generation and Distribution.Distribution of electricity denotes
sending electricity from substations where it is transmitted and
received followed by its distribution to various points of
utilisation.
UNIT IELECTRICAL SYSTEM5
Important EquipmentUNIT IELECTRICAL SYSTEM6Electrical Load
Management and Maximum Demand ControlIn the utilisation of
electrical energy, there are three fundamental parameters which one
has to understand. They are:Load FactorDiversity FactorUtilisation
Factor
Maximum DemandMaximum Demand is measured during a prefixed time
duration of either 15 minutes or 30 minutes and then multiplied by
either four or two respectively to give kVAH per hour i.e. KVA.
Thus, at the end of each time cycle, the timer is reset and fresh
measurement starts.
Contracted Maximum Demand (CMD)Contracted Maximum Demand (CMD)
is the demand mutually agreed between the supply company and the
consumer by way of a signed contract.UNIT IELECTRICAL
SYSTEM7Connected LoadConnected load is the sum of the nameplate
ratings of all the equipment utilising electricity inside the
consumer installation.
Average load is energy consumption recorded divided by the
operating hours of the plant.Load Factor = (Average Load)/ (Maximum
Demand) always less than 1. Diversity Factor = (Connected Load)/
(Maximum Demand) always more than 1. Utilisation Factor=(Average
Load)/(Connected Load) always less than 1. Utilisation Factor =
(Load Factor) / (Diversity Factor)
Power FactorPower Factor is a ratio of kW to KVA which is always
less than or equal to unity. This is represented by a famous
triangular relation.UNIT IELECTRICAL SYSTEM8Leading and Lagging
Power Factor
Position of Power Factor Correction CapacitorsThe ideal location
for capacitors is to provide them as close to the point of
utilisation as possible. But there are certain practical
difficulties:Introduction of capacitors demands a cutting out
device which will disconnect them from the live circuit as soon as
the main equipment is switched off. If not done, this may result in
either the power factor going to the leading side but less than
unity again. Moreover it may also result in voltage surges which
may damage the installation.Hence installing capacitors for each
individual equipment becomes expensive and may work out to be
uneconomical.UNIT IELECTRICAL SYSTEM9Performance Assessment of
Power Factor Correction CapacitorsOnce the power factor capacitors
are installed, they continuously need to be monitored for their
performance. Their performance depends on voltage as well as
ambient temperature. The capacitor before failing totally, gives a
number of indications showing the deterioration of their
performance. This can be monitored by recording the daily reading
or hourly reading of the consumption and power factor by the user.
However specialised testing can be done by the manufacturer to know
the exact reason for the failure.TransformerThe transformer is one
of the most widely used electrical equipment. The main function of
the transformer is to either increase voltage or to reduce
voltage.
UNIT IELECTRICAL SYSTEM10Rating of the TransformerRating of the
transformer is calculated based on the connected load and applying
the diversity factor on the connected load, applicable to the
particular industry and arriving at the kVA rating of the
Transformer. The diversity factor is defined as the ratio of
overall maximum demand of the plant to the sum of individual
maximum demand of various equipment.
Location of the TransformerLocation of the transformer is very
important as far as distribution losses are concerned. A
transformer receives HT voltage from the grid and steps it down to
the required voltage. Transformers should be placed close to the
load centre, considering other features like optimisation needs for
centralised control, operational flexibility, etc. This brings down
distribution losses in cables.
Losses and Efficiency of a TransformerThe efficiency varies
anywhere between 96 to 99 percent. The efficiency of transformers
not only depends on the design, but also, on the effective
operating load.Transformer losses consist of two parts:No-load
lossLoad lossUNIT IELECTRICAL SYSTEM11Control Used for Voltage
FluctuationThe control of voltage in a transformer is important due
to frequent changes in the supply voltage level. Voltage regulation
in transformers is done by altering the voltage transformation
ratio with the help of tapping.
The Parallel Operation of TransformersWhenever two transformers
are operating in parallel, both should be technically identical in
all aspects and more importantly should have the same impedance
level. This minimises the circulating current between
transformers.Where the load is fluctuating in nature, it is
preferable to have more than one transformer running in parallel,
so that the load can be optimised by sharing it between
transformers. The transformers can be operated close to the maximum
efficiency range by this operation.
UNIT IELECTRICAL SYSTEM12CHAPTER II
ELECTRIC MOTORS
13IntroductionMotors convert electrical energy into mechanical
energy by the interaction between the magnetic fields set up in the
stator and rotor windings. Electric motors are undoubtedly the
largest prime movers used. Industrial electric motors can be
broadly classified as:induction motorsdirect current
motorssynchronous motors
All motor types have the same four operating components which
are:stator (stationary windings)rotor (rotating
windings)bearingsframe (enclosure)
Types of MotorsThere are two main types of motors:DC MotorsAC
Motors
UNIT IELECTRIC MOTORS14Industrial Classification of
MotorsIndustrial electric motors are generally classified as:direct
current motors (DC motors)synchronous motors (AC motors)induction
motors (induced magnetic field)
UNIT IELECTRIC MOTORS15Direct Current Motors (DC Motors)DC
motors have a stationary field winding housed in a stator and
rotating armature called rotor. The rotor winding rotate in front
of alternating rotor poles, north and south poles. This tries to
reverse the current in the winding. To overcome this problem, a
commutator and brush arrangement is provided.
Depending on the field and armature connections, the motors are
classified into different categories:Separately Excited Motor Self
excited motor
Advantages of DC MotorsThe main advantage of DC motors is speed
control, which does not affect the quality of power supply. It can
be controlled by adjusting:the armature voltage increasing the
armature voltage will increase the speedthe field current reducing
the field current will increase the speed
UNIT IELECTRIC MOTORS16
Disadvantages of DC MotorsThe disadvantages of these motors are
mainly their initial cost and maintenance of brushes and the
commutator. Moreover they require a separate cooling
arrangement.UNIT IELECTRIC MOTORS17Synchronous/AC MotorsIn these
motors, the stator is given a three phase A.C. supply. The Rotor is
given a DC supply through brushes and slip rings. The stator
produces a rotating magnetic field and the rotor field is locked
into the synchronism of the rotating magnetic field.
The main advantage of this motor was that by controlling the
rotor excitation, the power factor of the motor could be controlled
and the motor could be made to operate with a leading power
factor.
The evident disadvantages of this motor were:the slip ring and
brush maintenance and provision for the prime mover..the initial
cost of these motors also was high. But these days nobody opts to
use these motors.
UNIT IELECTRIC MOTORS18Induction MotorsInduction motors are the
most commonly used prime mover for various equipment in industrial
applications. In induction motors, the induced magnetic field of
the stator winding induces a current in the rotor. This induced
rotor current produces a second magnetic field, which tries to
oppose the stator magnetic field, and this causes the rotor to
rotate.
There are two types of Induction Motors:The slip ring induction
motor: In this motor, the stator is given a three phase A.C.
supply. The rotor is shorted outside through slip rings and
brushes. The squirrel cage induction motor: A squirrel cage rotor
is the rotating part used in the most common form of AC induction
motor. An electric motor with a squirrel cage rotor is termed a
squirrel cage motor. UNIT IELECTRIC MOTORS19The Power FactorThe
power factor of the motor is given as: Power factor = Cos =
kW/kVA
Name Plate Parameters of a Motor
UNIT IELECTRIC MOTORS20Motor LoadBecause the efficiency of a
motor is difficult to assess under normal operating conditions, the
motor load can be measured as an indicator of the motors
efficiency. As loading increases, the power factor and the motor
efficiency increase to an optimum value at around full load.Motor
Efficiency and its LossesIf power output is measured in Watt (W),
efficiency can be expressed as:m = Pout / PinWherem = motor
efficiency..Pout = shaft power out (Watt, W)..Pin = electric power
in to the motor (Watt, W)
The losses can be generally classified into two categories:Fixed
losses are those which occur in the motor irrespective of the
quantum of load. These are also called no load losses.Variable
losses are those which are dependent on the quantum of the load.
UNIT IELECTRIC MOTORS21Factors Affecting Motor PerformanceMotor
performance depends on: Partial load operationCorrect Application
of the drive to suit the applicationApplication of rated voltage
and frequency
Rewinding and Motor Replacement IssuesMany a times during the
maintenance of motors, one has to encounter rewinding of motors.
The rewound motors seldom give the same performance as original
motors. Due to this every time a motor is rewound, its useful life
is affected and the next rewinding is advanced. Hence motors
rewound must be checked thoroughly before loading them to the
original loading pattern.Energy Saving Opportunities with Energy
Efficient Motors
UNIT IELECTRIC MOTORS22CHAPTER III
COMPRESSED AIR SYSTEM
23IntroductionAir compressors account for significant amount of
electricity used in Indian industries. Compressed air is an
essential but costly utility and its use must be made wisely.
Compressed air is generated from compressors which are largely
driven by electricity. If efficiency is calculated, only 10% useful
energy reaches the end point through compressed air. Thus there is
a vast scope for energy saving through proper understanding of the
functions of this utility and avoiding its wastage.
Classification of CompressorsCompressors are broadly classified
as :- Positive Displacement CompressorsDynamic (Centrifugal)
Compressors
UNIT ICOMPRESSED AIR SYSTEM24Positive displacement
compressorsThe compressors which increase the pressure of the gas
by reducing the volume are called positive displacement
compressors. These compressors are further classified
into:reciprocating compressorsrotary compressors
Dynamic compressorsDynamic compressors increase the air
velocity, which is then converted to increased pressure at the
outlet. They are basically centrifugal compressors and are further
divided into:radial typeaxial flow type
Compressor CapacityCapacity of a compressor is the full rated
volume of flow of gas compressed and delivered at conditions of
total temperature, total pressure, and composition existing at the
compressor inlet. UNIT ICOMPRESSED AIR SYSTEM25Compressed Air
System ComponentsUNIT ICOMPRESSED AIR SYSTEM26Prerequisites for
Efficient Operation of CompressorThere are a number of issues to be
considered right at the stage of project planning and also during
operation. Few of them are listed below:Compressor LocationCool Air
IntakeDust free air intakeDry AirAppropriate AltitudeOptimum
pressure settingsFactors Affecting Performance and
EfficiencyFollowing are a few factors affecting the performance and
efficiency of compressors:Lack of general awarenessWrong
application and extensions of existing pipelinesWrong choice of
system (distributive/ centralised )
UNIT ICOMPRESSED AIR SYSTEM27
ENERGY EFFICIENCY IN ELECTRICAL UTILITIES
UNIT II28
29CHAPTER I
HVAC AND REFRIGERATION SYSTEMIntroductionThe Heating,
Ventilation, and Air Conditioning (HVAC) and refrigeration systems
transfer heat energy from one environment to the other. HVAC
includes the bi-directional flow of heat, in the sense that when
earth's atmospheric temperature is too low, then the requirements
of a closed atmosphere are to be maintained. Heat is injected into
the closed atmosphere.Refrigeration on the other hand, has a
unidirectional flow of heat. It always extracts heat from the
closed atmosphere with the help of a low boiling point refrigerant
and dispels it into the open atmosphere of the earth.
UNIT IIHVAC AND REFRIGERATION SYSTEM30Air-Conditioning
SystemsDepending on applications, there are several options /
combinations, which are available for use as given below:Air
Conditioning (for comfort / machine)Split air conditioners Fan coil
units in a larger systemAir handling units in a larger system
UNIT IIHVAC AND REFRIGERATION SYSTEM31Refrigeration Systems (for
processes)Small capacity modular units of direct expansion type
similar to domestic refrigerators, small capacity refrigeration
units.Centralised chilled water plants with chilled water as a
secondary coolant for temperature range over 50C typically. They
can also be used for ice bank formation.Brine plants, which use
brines as lower temperature, secondary coolant, for typically sub
zero temperature applications, which come as modular unit
capacities as well as large centralised plant capacities.
UNIT IIHVAC AND REFRIGERATION SYSTEM32Types of Refrigeration
SystemsThe two principle types of refrigeration plants found in
industry include:Vapour Compression Refrigeration (VCR)Vapour
Absorption Refrigeration (VAR)
VCR uses mechanical energy as the driving force for
refrigeration, while VAR uses thermal energy as the driving force
for refrigeration.
UNIT IIHVAC AND REFRIGERATION SYSTEM33
EvaporatorThe refrigerant (water) evaporates at around 400C
under a high vacuum condition of 754mmHg in the evaporator.Chilled
water goes through heat exchanger tubes in the evaporator and
transfers heat to the evaporated refrigerant.The evaporated
refrigerant (vapour) turns into liquid again, while the latent heat
from this vaporization process cools the chilled water. The chilled
water is then used for cooling purposes.
AbsorberIn order to keep evaporating, the refrigerant vapour
must be discharged from the evaporator and refrigerant (water) must
be supplied. The refrigerant vapour is absorbed into lithium
bromide solution, which is convenient to absorb the refrigerant
vapour in the absorber. The heat generated in the absorption
process is continuously removed from the system by cooling water.
The absorption also maintains the vacuum inside the evaporatorUNIT
IIHVAC AND REFRIGERATION SYSTEM3434High Pressure GeneratorAs
lithium bromide solution is diluted, the ability to absorb the
refrigerant vapour reduces. In order to keep the absorption process
going, the diluted lithium bromide solution must be concentrated
again.An absorption chiller is provided with a solution
concentrating system, called a generator. Heating media such as
steam, hot water, gas or oil perform the function of concentrating
solutions.The concentrated solution is returned to the absorber to
absorb refrigerant vapour again.
CondenserTo complete the refrigeration cycle, and thereby
ensuring the refrigeration takes place continuously, the following
two functions are required:To concentrate and liquefy the
evaporated refrigerant vapour, which is generated in the high
pressure generator.To supply the condensed water to the evaporator
as refrigerant (water).
UNIT IIHVAC AND REFRIGERATION SYSTEM35Types of Compressors used
in Cooling SystemsCentrifugal CompressorsCentrifugal compressors
are the most efficient types , when they operate near full load.
Their efficiency advantage is the greatest in large sizes and they
offer considerable economy of scale, so they dominate the market
for large chillers.
Reciprocating CompressorsThe maximum efficiency of reciprocating
compressors is lower than that of centrifugal and screw
compressors. Efficiency is reduced by the clearance volume (the
compressed gas volume that is left at the top of the piston
stroke), throttling losses at the intake and discharge valves,
abrupt changes in gas flow, and friction.
Screw CompressorsScrew compressors, sometimes called helical
rotary compressors, compress the refrigerant by trapping it in the
threads of a rotating screw-shaped rotor.
Scroll CompressorsThe gas is compressed between two
scroll-shaped vanes. One of the vanes is fixed, and the other moves
within it. The moving vane does not rotate, but its centre revolves
with respect to the centre of the fixed vane.UNIT IIHVAC AND
REFRIGERATION SYSTEM36Selection of a Suitable Refrigeration SystemA
clear understanding of the cooling load to be met is the first and
most important part of designing/selecting the components of a
refrigeration system. Important factors to be considered in
quantifying the load are the actual cooling need, heat (cool)
leaks, and internal heat sources (from all heat generating
equipment). Consideration should also be given to process changes
and/or changes in ambient conditions that might affect the load in
the future.
UNIT IIHVAC AND REFRIGERATION SYSTEM37Factors Affecting
Performance and Energy Efficiency of Refrigeration PlantsThe
various factors which affect the performance and energy efficiency
of refrigeration plants are as follows:The Design of Process Heat
ExchangersMaintenance of Heat Exchanger SurfacesMulti-staging for
EfficiencyMatching Capacity to System LoadCapacity Control and
Energy Efficiency
Energy Saving OpportunitiesCold InsulationInsulate all cold
lines / vessels using economic insulation thickness to minimise
heat gains; and to choose appropriate (correct) insulation.Building
EnvelopeOptimise air conditioning volumes by measures such as use
of false ceiling and segregation of critical areas for air
conditioning by air curtains.Building Heat Loads Minimisation
Cold InsulationUNIT IIHVAC AND REFRIGERATION SYSTEM38
39CHAPTER II
FANS AND BLOWERSIntroductionFans and blowers provide air for
ventilation and industrial process requirements. Fans generate a
pressure to move air (or gases) against a resistance caused by
ducts, dampers, or other components in a fan system. The fan rotor
receives energy from a rotating shaft and transmits it to the air.
Industrial FansIndustrial fans and blowers are machines whose
primary function is to provide a large flow of air or gas to
various processes of many industries. This is achieved by rotating
a number of blades, connected to a hub and shaft and driven by a
motor or turbine.
UNIT IIFANS AND BLOWERS40Types of FansFans are divided into two
general categories:Centrifugal flowIn centrifugal flow, airflow
changes direction twice once when entering and secondly, while
leaving (forward curved, backward curved or inclined, radial)
Axial flowIn axial flow, air enters and leaves the fan with no
change in direction (propeller, tube axial, vane axial)
Centrifugal FlowAxial FlowUNIT IIFANS AND BLOWERS41Types of
BlowersBlowers can achieve much higher pressures than fans, as high
as 1.20 kg/cm2. They are also used to produce negative pressures
for industrial vacuum systems. Major types of blowers
are:Centrifugal BlowersCentrifugal blowers look more like
centrifugal pumps compared to fans. In multi-stage blowers, air is
accelerated as it passes through each impeller. In a single-stage
blower, air does not take many turns, and hence it is more
efficient.
Positive-Displacement BlowersPositive-displacement blowers have
rotors, which "trap" air and push it through the housing.
Positive-displacement blowers provide a constant volume of air even
if the system pressure varies.
Centrifugal BlowerPositive-Displacement BlowerUNIT IIFANS AND
BLOWERS42System CharacteristicsThe term system resistance is used
while referring to the static pressure. The system resistance is
the sum of static pressure losses in the system.The system
resistance varies with the square of the volume of air flowing
through the system. System resistance increases substantially as
the volume of air flowing through the system increases; square of
air flow. Conversely, resistance decreases as flow decreases.
System CharacteristicsUNIT IIFANS AND BLOWERS43Fan
CharacteristicsThe fan curve is a performance curve for the
particular fan under a specific set of conditions. The fan curve is
a graphical representation of a number of interrelated
parameters.Typically, a curve will be developed for a given set of
conditions usually including fan volume, system static pressure,
fan speed and brake horsepower required to drive the fan under the
stated conditions.
UNIT IIFANS AND BLOWERS44Fan LawsThe fans operate under a
predictable set of laws concerning speed, power and pressure. A
change in speed (rpm) of any fan will predictably change the
pressure rise and power necessary to operate it at the new RPM.
Where, Q flow; SP Static Pressure, kW Power; N speed (RPM)UNIT
IIFANS AND BLOWERS45Fan Design and Selection CriteriaFollowing are
some important points to remember before selecting a particular
fan:Precise determination of air-flow and required outlet pressure
System pressure requirementGood judgement on magnitudes of the
required flow and static pressureFan Performance and
EfficiencyForward curved fans have large hub-to-tip ratios compared
to backward curved fans and produce lower pressure.Radial fans can
be made with different heel-to-tip ratios to produce different
pressures.At both design and off-design points, backward-curved
fans provide the most stable operation. Centrifugal fans are
suitable for low to moderate flow at high pressures, while
axial-flow fans are suitable for low to high flows at low
pressures.
UNIT IIFANS AND BLOWERS46Flow Control StrategiesVarious ways to
achieve a change in flow are:Pulley ChangeDamper ControlsVariable
Speed DrivesSeries and Parallel OperationAir flow MeasurementThe
components of air flow management are:Static Pressure: It is the
potential energy put into the system by the fan. Velocity Pressure:
It is the pressure along the line of the flow that results from the
air flowing through the duct. Total Pressure: Sum of Static and
Velocity pressuresEnergy Saving OpportunitiesFollowing are a few
ways to save energy with respect to fan/blower usage:Minimising
demand on the fanMinimising excess air level in combustion systems
to reduce FD fan and ID fan loadMinimising air in-leaks in the hot
flue gas path to reduce the ID fan load, especially in case of
kilns, boiler plants, furnaces, etc. In-leaks / out-leaks in air
conditioning systems also have a major impact on energy efficiency
and fan power consumption and need to be minimised.UNIT IIFANS AND
BLOWERS47
48CHAPTER III
PUMPS AND PUMPING SYSTEMIntroductionA pump is a device used to
move fluids, such as liquids, gases or slurries. A pump displaces a
volume of fluid by physical or mechanical action. Major Groups of
PumpsDirect lift pumpsDisplacement pumpsVelocity pumpsBuoyancy
pumpsGravity pumpsMain Purpose of PumpsPumps have two main
purposes:transfer of liquid from one place to another place
circulate liquid around a system
UNIT IIPUMPS AND PUMPING SYSTEM
49Types of PumpsPumps have a variety of sizes for a wide range
of applications. They can be classified according to their basic
operating principles as:Dynamic pumps: Dynamic pumps are
characterised by their mode of operation; a rotating impeller
converts kinetic energy into pressure or velocity that is needed to
pump the fluid.
Positive-displacement pumps: In these pumps, liquid is taken
from one end and positively discharged at the other end for every
revolution.
UNIT IIPUMPS AND PUMPING SYSTEM50Centrifugal PumpThe two main
parts of the centrifugal pump are:The impeller, which is the only
moving part, is attached to a shaft and driven by a motor.
Impellers are generally made of bronze, polycarbonate, cast iron,
stainless steel as well as other materials.The diffuser (also
called volute) houses the impeller and captures and directs the
water off the impeller.
WorkingWater enters the centre (eye) of the impeller and exits
the impeller with the help of centrifugal force. As water leaves
the eye of the impeller, a low-pressure area is created, causing
more water to flow into the eye. Velocity is developed as the water
flows through the impeller spinning at high speed.UNIT IIPUMPS AND
PUMPING SYSTEM51System CharacteristicsIn a pumping system, the
objective, in most cases, is either to transfer a liquid from a
source to a required destination, e.g. Filling a high level
reservoir or to circulate liquid around a system.Pressure is needed
to make the liquid flow at the required rate and this must overcome
head losses' in the system.
Losses are of two types: Static Head: The static head is simply
the difference in the height of the supply and destination
reservoirsFriction Head: The friction head (sometimes called
dynamic head loss) is the friction loss on the liquid being moved,
in pipes, valves and equipment in the system.
UNIT IIPUMPS AND PUMPING SYSTEM52Factors Affecting Pump
PerformanceFactors which affect the performance of the pump
are:Matching Pump and System Head-flow CharacteristicsEffect of
Over Sizing the PumpEnergy Loss in ThrottlingEfficient Pumping
System OperationTo understand a pumping system, one must realise
that all of its components are interdependent. While examining or
designing a pump system, the process demands must be established
first and the most energy efficient solution should be introduced.
Following points would be helpful:Target the end-use Good water
conservation measures Optimise flow requirements
UNIT IIPUMPS AND PUMPING SYSTEM53Flow Control
StrategiesDifferent strategies to control flow are:Pump Control by
Varying SpeedPumps in Parallel Switched to Meet DemandStop/Start
ControlFlow Control ValveBy-pass ControlSteps for Energy Efficiency
in Pumping SystemFollowing are a few steps towards achieving energy
efficiency in pumps:Ensure availability of basic instruments at
pumps like pressure gauges, flow meters. Operate pumps near the
best efficiency pointAdapt to wide load variation with variable
speed drives or sequenced control of multiple unitsUse booster
pumps for small loads requiring higher pressuresIn multiple pump
operations, carefully combine the operation of pumps to avoid
throttlingReplace old pumps by energy efficient pumps
UNIT IIPUMPS AND PUMPING SYSTEM54
ENERGY EFFICIENCY IN ELECTRICAL UTILITIES
UNIT III55
56CHAPTER I
COOLING TOWERIntroductionThe primary task of a cooling tower is
to reject heat into the atmosphere. They represent a relatively
inexpensive and dependable means of removing low-grade heat from
cooling water.
Cooling Tower TypesCooling towers fall into two main
categories:Natural draft: Natural draft towers use very large
concrete chimneys to introduce air through the media. These types
of towers are used only by utility power stations.
Mechanical draft: Mechanical draft towers utilise large fans to
force or suck air through circulated water. The water falls
downward over fill surfaces, which helps to increase the contact
time between the water and the air - this helps to maximise heat
transfer between the two.UNIT IIICOOLING TOWER57Components of a
Cooling TowerThe basic components of an evaporative tower are as
follows:Frame and casingFillCold water basinDrift eliminatorsAir
inletLouversNozzlesFansTower MaterialsFollowing are a few of the
materials used in the construction of cooling towers:Galvanized
SteelStainless steel ConcreteGlass Fibre
UNIT IIICOOLING TOWER58Performance ParametersRange is the
difference between the cooling tower water inlet and outlet
temperature.
Approach is the difference between the cooling tower outlet cold
water temperature and the ambient wet bulb temperature.
Cooling tower effectiveness (in percentage) is the ratio of
range, to the ideal range, i.e., difference between cooling water
inlet temperature and ambient wet bulb temperature, or in other
words it is = Range / (Range + Approach).
Cooling capacity is the heat rejected in kCal/hour, given as a
product of the mass flow rate of water, specific heat and
temperature difference.
Evaporation loss is the water quantity evaporated for cooling
duty.
UNIT IIICOOLING TOWER59Factors Affecting Cooling Tower
PerformanceCapacityRangeWet Bulb TemperatureWet bulb temperature is
an important factor in the performance of evaporative water cooling
equipment. It is a controlling factor from the aspect of the
minimum cold water temperature to which water can be cooled by the
evaporative method. Thus, the wet bulb temperature of the air
entering the cooling tower determines the operating temperature
levels throughout the plant, process, or system.Range, Flow and
Heat LoadRange is a direct function of the quantity of water
circulated and the heat load. Increasing the range as a result of
added heat load does require an increase in the tower size. If the
cold water temperature is not changed and the range is increased
with a higher hot water temperature, the driving force between the
wet bulb temperature of the air entering the tower and the hot
water temperature is increased, the higher level heat is economical
to dissipate.UNIT IIICOOLING TOWER60Choosing a Cooling TowerThe
counter-flow and cross flows are two basic designs of cooling
towers based on the fundamentals of heat exchange.Cross-flow
cooling towers are provided with splash fill of concrete, wood or
perforated PVC. Counter-flow cooling towers are provided with both
film fill and splash fill.Counter flow heat exchange is more
effective as compared to cross flow or parallel flow heat
exchange.Efficient System OperationSystem efficiency can be
improved by employing the following methods:Cooling Water
TreatmentAvoiding Drift Loss in the Cooling TowersUsing Cooling
Tower FansPerformance Assessment of Cooling Towers
UNIT IIICOOLING TOWER61Flow Control StrategiesControl of tower
air flow can be done by varying methods: Starting and stopping
(On-off) of fansUse of two or three-speed fan motorsUse of
automatically adjustable pitch fansUse of variable speed fans.
Energy Saving Opportunities in Cooling TowersFollowing are a few
tips on saving energy while operating Cooling Towers:Follow the
manufacturer's recommended clearances around cooling towers and
relocate or modify structures that interfere with the air intake or
exhaust.Optimise cooling tower fan blade angle on a seasonal and/or
load basis.Periodically clean plugged cooling tower distribution
nozzles.Correct excessive and/or uneven fan blade tip clearance and
poor fan balance. UNIT IIICOOLING TOWER62
63CHAPTER II
LIGHTING SYSTEMIntroductionLighting is an essential service in
all the industries. Innovation and continuous improvement in the
field of lighting, has given rise to tremendous energy saving
opportunities in this area.Lighting is an area which provides a
major scope to achieve energy efficiency at the design stage, by
the incorporation of modern energy efficient lamps, luminaries and
gears, apart from good operational practices.Types of
LampsIncandescent Lamps Reflector LampsGas Discharge Lamps
UNIT IIILIGHTING SYSTEM64Other Lighting EquipmentLuminaire: The
luminaire is a device that distributes, filters or transforms the
light emitted from one or more lamps. Luminaires include all the
parts necessary for fixing and protecting the lamps, except the
lamps themselves.
Ballast: A current limiting device, to counter the negative
resistance characteristics of any discharge lamp. In case of
fluorescent lamps, it aids the initial voltage build up, required
for starting.
Ignitors: These are used for starting high intensity Metal
Halide and Sodium vapour lamps.Lighting TerminologyIlluminance:
This is the quotient of the luminous flux incident on an element of
the surface at a point of surface containing the point, by the area
of that element.
Lux (lx): This is the illuminance produced by a luminous flux of
one lumen, uniformly distributed over a surface area of one square
metre. One lux is equal to one lumen per square metre. UNIT
IIILIGHTING SYSTEM6565A step-by-step approach for assessing the
energy efficiency of the lighting system is as stated:Inventorise
the lighting system elements and transformers in the facility.With
the aid of a lux meter, measure and document the lux levels at
various plant locations at the working level, as day time lux and
night time lux values alongside the number of lamps ON during
measurement.With the aid of a portable load analyser, measure and
document the voltage, current, power factor and power consumption
at various input points.Compare the measured lux values with
standard values as reference and identify locations as under lit
and over lit areas.Collect and analyse the failure rates of lamps,
ballasts and the actual life expectancy levels from past data.Bring
about improvements after proper assessment.Methodology of Lighting
System Energy Efficiency Study
UNIT IIILIGHTING SYSTEM66Some Good Practices in
LightingInstallation of Compact Fluorescent Lamps (CFL's) in Place
of Incandescent Lamps
Installation of Metal Halide Lamps in Place of Mercury/Sodium
Vapour Lamps
Installation of High Pressure Sodium Vapour (HPSV) Lamps for
Applications where Colour Rendering is not Critical
Installation of LED Panel Indicator Lamps in Place of Filament
Lamps
Optimum usage of day lighting
UNIT IIILIGHTING SYSTEM67
68CHAPTER III
DG SET SYSTEMSIntroductionThe Diesel engine is a prime mover,
which drives an alternator to produce electrical energy. In the
diesel engine, air is drawn into the cylinder and is compressed to
a high ratio (14:1 to 25:1). During this compression, the air is
heated to a temperature of 700 9000C. A metered quantity of diesel
fuel is then injected into the cylinder, which ignites
spontaneously because of the high temperature. Hence, the diesel
engine is also known as the compression ignition (CI)
engine.Classification of Diesel Generating SetsDiesel generating
(DG) sets can be classified according to cycle types as:Two
strokeFour Stroke
A bulk of the CI engines use the four-stroke cycle.
UNIT IIIDG SET SYSTEMS69
The Four Stroke Diesel EngineThe 4 stroke operations in a diesel
engine are: Induction strokeCompression strokeIgnition and power
stroke Exhaust stroke
UNIT IIIDG SET SYSTEMS70The DG Set as a SystemA diesel
generating set should be considered as a system since its
successful operation depends on the well-matched performance of the
following components:The diesel engine and its accessoriesThe ac
generator The control systems and switchgear. The foundation and
power house civil works The connected load with its own components
like heating, motor drives, lighting etc.It is necessary to select
components with the highest efficiency and operate them at their
optimum efficiency levels to conserve energy in this
system.Selection ConsiderationsTo make a decision on the type of
engine which is most suitable for a specific application, several
factors need to be considered. The two most important factors are:
Power of the engine: The power requirement is determined by the
maximum load.Speed of the engine: Speed is measured at the output
shaft and given in revolutions per minute (RPM).
UNIT IIIDG SET SYSTEMS71Diesel Generator Captive Power
PlantsDiesel engine power plants are most frequently used in small
power (captive non-utility) systems. The main reason for their
extensive use is the higher efficiency of the diesel engines
compared to gas turbines and small steam turbines in the output
range considered.Advantages of adopting Diesel Power PlantsLow
installation costShort delivery and installation periods Higher
efficiency (as high as 43 -45 %)More efficient plant performance
under part loadsSuitable for different types of fuels such as low
sulphur heavy stock and heavy fuel oil in case of large
capacities.Minimum cooling water requirements
UNIT IIIDG SET SYSTEMS72Selection and Installation FactorsSizing
of a GensetHigh Speed Engine or Slow/Medium Speed EngineCapacity
CombinationsAir Cooling Vs. Water CoolingSafety FeaturesParallel
Operation with GridSite Condition Effects on Performance
DeratingUnbalanced Load EffectsOperational FactorsLoad Pattern and
DG Set CapacitySequencing of LoadsLoad PatternLoad
CharacteristicsGenset
UNIT IIIDG SET SYSTEMS73Load CharacteristicsSome of the load
characteristics influence the efficient use of a D.G.set. These
characteristics are entirely load dependent and cannot be
controlled by the D.G.set. Some of these characteristics
are:Unbalanced Load: Unbalanced loads on the A.C. generator lead to
an unbalanced set of voltages and additional heating in the A.C.
generator. Transient Loading: On many occasions, to contain the
transient voltage dip arising due to the transient load
application, a specially designed generator may have to be
selected.Special Loads: Special loads like the rectifier loads,
welding loads, furnace loads need an application check.Energy
Performance Assessment of DG SetsRoutine energy efficiency
assessment of DG sets on the shop floor involves the following
typical steps:Ensure reliability of all instruments used for
trial.Collect technical literature, characteristics, and
specifications of the plant.Conduct a 2 hour trial on the DG set,
ensuring a steady load. The fuel oil/diesel analysis is referred to
from an oil company data.Analysis of trial data.UNIT IIIDG SET
SYSTEMS74Energy Saving Measures for DG SetsFollowing are a few
energy saving measures for DG sets:Ensure steady load conditions on
the DG set, and provide cold, dust free air at the intake (use of
air washers for large sets, in case of dry, hot weather, can be
considered).Ensure fuel oil storage, handling and preparation as
per manufacturers' guidelines/oil company data.Improve air
filtration. Calibrate fuel injection pumps frequently. Ensure
compliance with the maintenance checklist.
UNIT IIIDG SET SYSTEMS75
76CHAPTER IV
ENERGY EFFICIENT TECHNOLOGIES IN ELECTRICAL SYSTEMS Maximum
Demand ControllersHigh-tension (HT) consumers have to pay a maximum
demand charge in addition to the usual charge for the number of
units consumed. This charge is usually based on the highest amount
of power used during some period (say 30 minutes) during the
metering month.The Maximum Demand Controller is a device designed
to meet the need of industries conscious of the value of load
management. An alarm is sounded when demand approaches a preset
value.
UNIT IIIENERGY EFFICIENT TECHNOLOGIES IN ELECTRICAL SYSTEMS
77Automatic Power Factor ControllersVarious types of automatic
power factor controls are available with relay / microprocessor
logic. Two of the most common controls are:Voltage Control: Voltage
alone can be used as a source of intelligence when the switched
capacitors are applied at a point where the circuit voltage
decreases as circuit load increases.Kilovar Control: Kilovar
sensitive controls are used at locations where the voltage level is
closely regulated and not available as a control variable.Energy
Efficient MotorsEnergy-efficient electric motors reduce energy
losses through an improved design, better material, and improved
manufacturing techniques. Improvement in motor efficiency is
possible from reducing the Watt losses. Following are a few ways to
do that:Use of thinner gauge, lower loss core steel reduces eddy
current losses. Use of more copper and larger conductors increases
cross sectional area of stator windings. Use of low loss fan design
reduces losses due to air movement. UNIT IIIENERGY EFFICIENT
TECHNOLOGIES IN ELECTRICAL SYSTEMS 78Soft StarterWhen starting, an
AC Induction motor develops more torque than is required at full
speed. This stress is transferred to the mechanical transmission
system resulting in excessive wear and the premature failure of
chains, belts, gears, mechanical seals, etc.The soft starter
provides a reliable and economical solution to these problems by
delivering a controlled release of power to the motor, thereby
providing smooth acceleration and deceleration.
Advantages of Soft StartLess mechanical stressImproved power
factorLower maximum demandLess mechanical maintenanceUNIT IIIENERGY
EFFICIENT TECHNOLOGIES IN ELECTRICAL SYSTEMS 79Speed Control of
Induction MotorsThe induction motor is the workhorse of the
industry. It is cheap rugged and provides high power to weight
ratio. On account of high cost-implications and limitations of the
D.C. System, induction motors are preferred for variable speed
applications, the speed of which can be varied by changing the
supply frequency.The Variable Frequency DriveThe rotational speed
of an AC induction motor depends on the number of poles in that
stator and the frequency of the applied AC power. Although the
number of poles in an induction motor cannot be altered easily,
variable speed can be achieved through a variation in the
frequency.
Eddy Current DrivesThis method employs an eddy-current clutch to
vary the output speed. The clutch consists of a primary member
coupled to the shaft of the motor and a freely revolving secondary
member coupled to the load shaft.UNIT IIIENERGY EFFICIENT
TECHNOLOGIES IN ELECTRICAL SYSTEMS 80Energy Efficient
TransformersThe iron loss of any transformer depends on the type of
core used in the transformer. The expected reduction in energy loss
over conventional (Si Fe core) transformers is roughly around 70%,
which is quite significant. By using an amorphous core with unique
physical and magnetic properties, these new types of transformers
have increased efficiencies even at low loads - 98.5% efficiency at
35% load.Electronic BallastIn an electric circuit, the ballast acts
as a stabiliser. Since the fluorescent lamps cannot produce light
by direct connection to the power source, they need an ancillary
circuit and device to get started and remain illuminated. The
auxillary circuit housed in a casing is known as the ballast.
UNIT IIIENERGY EFFICIENT TECHNOLOGIES IN ELECTRICAL SYSTEMS
81Energy Efficient Lighting Controls
Occupancy SensorsOccupancy-linked control can be achieved using
infra-red, acoustic, ultrasonic or microwave sensors, which detect
either movement or noise in room spaces. These sensors switch
lighting on when occupancy is detected, and off again after a set
time period, when no occupancy movements are detected.
Timed Based ControlTimed-turn off switches are the least
expensive type of automatic lighting control. In some cases, their
low cost and ease of installation makes it desirable to use them
where more efficient controls would be too expensive.
Daylight Linked ControlPhotoelectric cells can be used either
simply to switch lighting on and off, or for dimming. By using an
internally mounted photoelectric dimming control system, it is
possible to ensure that the sum of daylight and electric lighting
always reaches the design level by sensing the total light in the
controlled area and adjusting the output of the electric lighting
accordingly.UNIT IIIENERGY EFFICIENT TECHNOLOGIES IN ELECTRICAL
SYSTEMS 82