EE Tech in Electrical Systems

8/6/2019 EE Tech in Electrical Systems

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ENERGY EFFICIENTENERGY EFFICIENTTECHNOLOGIES INTECHNOLOGIES IN

ELECTRICAL SYSTEMSELECTRICAL SYSTEMS


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ENERGY EFFICIENT TECHNOLOGIES INENERGY EFFICIENT TECHNOLOGIES IN

ELECTRICAL SYSTEMSELECTRICAL SYSTEMS

SyllabusSy

llabus

Maximum demand controllers,Maximum demand controllers,

Automatic power factor controllersAutomatic power factor controllers,,

Energy efficient motors,Energy efficient motors,

Soft starters with energy saver,Soft starters with energy saver,

Variable speed drives,Variable speed drives,

Energy efficient transformers,Energy efficient transformers,

Electronic ballast,Electronic ballast,

Occupancy sensors,Occupancy sensors,

Energy efficient lighting controlsEnergy efficient lighting controls


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MAXIMUM DEMAND CONTROLLERSMAXIMUM DEMAND CONTROLLERS

Maximum Demand Controller is a device designed

to meet the need of industries conscious of thevalue of load management.

Alarm is sounded when demand approaches a presetvalue.

If corrective action is not taken, the controllerswitches off non-essential loads in a logicalsequence.

This sequence is predetermined by the user and isprogrammed jointly by the user and the supplier ofthe device. The plant equipments selected for the

load management are stopped and restarted as per thedesired load profile. Demand control scheme isimplemented by using suitable control contactors.Audio and visual annunciations could also be used.


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AUTOMATIC POWER FACTOR CONTROLLERAUTOMATIC POWER FACTOR CONTROLLER

Various types of automatic controls are available with

relay / microprocessor logic. Two of the most commoncontrols are: Voltage Control and KVAR Control

Voltage Control

Voltage is used as a source of intelligence.

capacitors are applied at point where the circuitvoltage decreases as circuit load increases.

Generally, used where the applied the voltagedecrease as circuit load increases and the drop involtage is around 4 5 % with increasing load.

This type of control is independent of load cycle. During light load time and low source voltage, this

may give leading PF at the S/S, which is to betaken note of.


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KILOVAR Control

Kilovar sensitive controls are used at locations wherethe voltage level is closely regulated and notavailable as a control variable. The capacitors can be switched to respond to adecreasing power factor as a result of change in system

loading. This type of control can also be used to avoid penaltyon low power factor by adding capacitors in steps asthe system power factor begins to lag behind the

desired value.

Kilovar control requires two inputs - current andvoltage from the incoming feeder, which are fed to thePF correction mechanism, either the microprocessor or therelay.


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Automatic PF Control Relay

APFCR is installed to switch ON & switch OFFcapacitors for PF correction. Different types of APFCR are available:

Same rating Capacitor switching

Appropriate rating Capacitor switching

Static VAR Control switching


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ENERGY EFFICIENT MOTORSENERGY EFFICIENT MOTORS

1.Why is improving Motor efficiency important?

Induction Motors consume 70% of total electrical

energy

80% of motors are less than 15kW where efficiencies

are generally lower with good scope for improvement

Energy efficiency should be a major consideration

when you purchase or rewind a motor

Loading of motors also plays important role inselecting appropriate rated efficiency.


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Watts Loss Area Efficiency Improvement

1. Iron Use of thinner gauge, lower loss core steel reduceseddy current losses. Longer core adds more steel tothe design, which reduces losses due to loweroperating flux densities.

2. Stator I 2 R Use of more copper and larger conductors increases

cross sectional area of stator windings. This lowersresistance (R) of the windings and reduces lossesdue to current flow (I).

3. Rotor I 2 R Use of larger rotor conductor bars increases size ofcross section, lowering conductor resistance (R) and

losses due to current flow (I).

4. Friction & Windage Use of low loss fan design reduces losses due to airmovement.

5. Stray Load Loss Use of optimized design and strict quality control

procedures minimizes stray load losses.


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What efficiency values should I use when comparing motors?

IS-325 allows variation in efficiency, IS-12615 does not allowvariation

Efficiencies must be brought to common specification forcomparison

When should I consider buying energy efficient motors? For all new installations/modifications Instead of rewinding old standard efficiency motors To replace over sized under loaded motors As a part of energy conservation program considering motors

that work in excess of 2000 hours per annum and ratings less

than 37 kW

Rewinding reduces efficiency by 1% to 2% or more if it is a veryold motor. Better to replace with EE motor if rewinding cost


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SOFT STARTERSSOFT STARTERS

Usually the load starting torque is near zero, an

induction motor will develop far too much torque whenconnected directly to the supply. So, At the instant ofstart-up, there is an un-necessary heavy power surge onboth the electrical supply and the mechanical drivecomponents.

The sudden impact at start up on the load, followed bythe rapid acceleration to full speed causes excessivewear on :-

1. Belts and pulleys

2. Gears and chains

3. Couplings and bearings and :-

4. Cavitation in pumps etc........


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Is based upon the silicon controlled rectifier or

thyristor.

By pulsing a thyristor, it switches from off to on until

the current stops flowing though it - which occurs

every half cycle in an AC. supply. By controlling electronically the thyristor turn on point,

it is possible to regulate the energy passing through

it.


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By starting with a large delay angle (firing angle of

SCR) and gradually reducing it , the motor terminalvoltage is increased from a low value to full voltage,

giving a smooth, step less, start.

Starting methods:

Voltage ramp (with & without kick-start)

Current limit (with & without kick-start)

Stopping methods

Soft stop with voltageramp

Smart motor braking

SMB

Special Controls

Preset slow speed

Slow speed with braking


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SOFT STARTERS - ADVANTAGESSOFT STARTERS - ADVANTAGES

Optimising continuously, improves the part-load

efficiency by reducing the degree of over-fluxing ofthe stator in the motor

The part load PF of the motor is improved.

This produces a significant reduction in kVAr andkVA, as well as a useful reduction in kW.

Electrical losses in the stator and feed cables are also

reduced.

Motor performance is not impaired.

The life of frequently-started drives and of reversing

drives is considerably extended by the soft start

action.


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BY installing Variable speed drives

Substantial energy saving can be achieved in addition to the other benefits such as

smooth variation in flow / pressure

increased motor life

precise output control.

Classification:

Fluid coupling Eddy current drives

Electronic control systems

Slip-power recovery systems

VARIABLE SPEED DRIVESVARIABLE SPEED DRIVES


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Basic laws of fluid mechanics

Flow is proportional to Speed

Head is proportional to (Speed)2

Power is proportional to(Speed)

3

Theoritically--------

If a pump is overdesigned for 30% flow

with 100 kW power drawn, thenoptimising speed to required flow can

P=(0.7)3* 100 kW

=65% of original power



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Earlier technologies used Wound rotor controllers with resistors

Constant potential DC motors with

armature series resistance control Variable speed clutches

MG sets

Gears/Pulleys

Variable speed fluid coupling

Rotary or static frequency converters



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Solid State Electronic Control MethodsVoltage Control

25 kW, 20-100%

Cycloconverter75 kW, X 30-50% ofSupply frequency

Voltage source invertor750 kW, 100 : 1

Current source inverter25 kW, 100:1

Pulse width modulation750 kW, 100:1

Slip power recovery500 kW50 100% (Kramer)50 150% (Scherbius)

Simple: low cost

Can operate down to zerospeed, High torquecapability

Good efficiency; simplecircuit design

Regenerative braking;simple circuit design

Good power factor; lowdistortion

VSD power rating lessthan motor rating

Harmonic; low torque; low efficiency;limited speed range.

Complex circuit Design; poor powerfactor at low speeds

No regenerative braking; problems alow speed (10%)

Poor power factor; poor performanceat low speed

No regenerative Braking; slightly lessefficient than VSD

Can use only with slip-ring inductionmotor

Speed Control Alternatives for AC Induction Motors

VSD Advantages Disadvantages



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Eddy current clutch mechanism is used.

Primary member connected to shaft-and freely

revolving secondary member is connected to load

shaft which is excited by varying DC to induce eddycurrents in shaft.

The interaction of two fluxes gives rise to a torque

at load shaft which can be varied .

Poor efficiency

Eddy Current drives


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More efficient alternative speed control mechanism for

use with slip-ring motors.

By varying rotor voltage to control speed & dissipating

power through resistors, the excess power is

collected from the slip rings and returned asmechanical power to the shaft or as electrical power

back to the supply line.

Tends to be economical only in relatively high power

applications and where the motor speed range is 1:5or less.

Slip Power Recovery Systems


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Role of Fluid Coupling

Smaller Motor for Running Duty

Reduced Current Demand DuringStarting

Reduced Heating in Motor

Over Load Protection

Fluid Coupling


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ENERGY EFFCIENT TRANSFORMERSENERGY EFFCIENT TRANSFORMERS

Dry-type transformers, for a variety of reasons, have

largely replaced oil-filled units within industrial,commercial and institutional buildings.

But first cost is not the last cost of any transformer.

Complete life-cycle costs must be carefully examinedalong with the economics of high-efficiency dry-type

transformers.


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ENERGY EFFCIENT TRANSFORMERSENERGY EFFCIENT TRANSFORMERS

Advantages

Fire Safe. Zero Maintenance

No monitoring

Environment friendly

Clean & compact installation

Reduced civil costs.

Disadvantages

High capital cost

Limitations in Harmonicenvironment

Replacement/repair cost high


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Ballasts for Fluorescent Lamps

Magnetic

supply frequency

(50Hz) operation

May produce audiblehum

May produce

noticeable lamp flicker

Less efficient lampoperation

Electronic

High frequency (20 to

50 kHz) operation

Quiet No noticeable lamp

flicker

More efficient lamp

operation


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Ballasts for Fluorescent Lamps

Electronic Ballast Types

Instant start

Most efficient

May sacrifice lamp life if frequently switched Cannot be dimmed

Rapid start and Programmed start

Generally consumes an additional 2 watts More gentle starting for frequent switching

Can be dimmed (if a dimming ballast is selected)


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ENERGY EFFCIENT LIGHTINGENERGY EFFCIENT LIGHTING

Compact Fluorescent Lamp:

The new low energy and highly cost effectivecompact fluorescent lamp is a recent addition to

modern lighting technology and is an attractive

alternative to incandescent lamps.

Energy Cost Comparison

Lamp WattageW

EfficacyLM/W

AverageLife (Hrs)

EnergySaving %

Incandescent 60 12 1000 -

CompactFluorescent

9 67 7500 80


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ENERGY EFFCIENT LIGHTING CONTROLENERGY EFFCIENT LIGHTING CONTROL

Timers& Timed Switches

Sensors & Photocells


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Timers can be effectively utilized for basic on/off

operation of lighting fixtures. By utilizing low voltagerelays, large numbers of fixtures can be controlled by

a single timer, thereby making it very cost effective.

Timed Switches are switches that incorporate a timed

function, to ensure that the fixtures are turned off after

a preset interval of time, typically one to two hours.


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Sensors

Three Types of Occupancy Sensors:

Passive Infrared

Ultrasonic Dual-Technology

(a combination of

PIR and Ultrasonic)


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Ultrasonic Occupancy Sensors

Emit an inaudible sound wave.

Triggered by changes

in the reflected sound.

Provides coverage

without gaps.


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NATURAL LIGHTING

Use of natural lightingsaves tremendousamount of lightingenergy.

One has to integratenatural lighting alongwith bay lighting inindustrial workshops.

Documents

EE Tech in Electrical Systems