best presentation on vfd
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Application of VFD in
Power Plants.........AN OVERVIEW
by
Amit KulshreshthaAGM(PE-Mech.)
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Why to Use VFD
1. Energy savings on most pump and fanapplications.
2. Better process control and regulation.3. Speeding up or slowing down a machine or
process.4. Inherent power-factor correction5. Protection from high in-rush currents6. Safe Acceleration and braking
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Electric & Power Basics
All VFDs must:
Run a machine or process at adesired speed.
Produce adequate torque tohandle the load.
Use power efficiently to producethe necessary torque at a givenspeed.
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Electric & Power Basics
The typical waveform consists of thefrequency portion (time based) ofthe wave and the amplitude portion
(the magnitude). This wave isactually in sine-wave form,commonly referred to as the
fundamental.
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Electric & Power Basics
Sinusoidal Waveform With Frequency& Amplitude Components
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AC-Induction-Motor Theory
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AC Induction Motor Theory
AC Induction Motor Squirrel Cage Design
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AC Induction Motor Theory
Three-phasemotor operation.
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AC Induction Motor Theory
How a motor shaft rotates?
Torque is produced as the induction motorgenerates flux in its rotating field.
As shaft torque load increases, the slip
increases and more flux lines cut the rotorwindings, which in turn increases rotorcurrent, which increases the rotormagnetic field and consequently the rotortorque.
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AC Induction Motor Theory
Typical speedversus torquecurve for aNEMA design Bmotor.
% Synchronous Speed
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AC Induction Motor Issues
Starting Induction Motors The starting current is very high, between 3 to 8
times the full load current. Depending on the sizeof the motor, this can result in voltage sags inthe power system.
The full torque is applied instantly at starting andthe mechanical shock can eventually damage thedrive system, particularly with materials handlingequipment, such as conveyors.
In spite of the high starting current, for some
applications the starting torque may be relativelylow, only 1.0 to 2.5 times full load torque.
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AC Induction Motor Theory
The speed of the rotating electric fieldwithin the induction motor.
Synchronous Speed = 120 x frequencyNo. of motor poles
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AC Induction Motor Theory
AC motor speed change can beaccomplished in three ways:
1. Change the number of poles in the motor; thismeans separate windings
2. Change the slip characteristics of the motor;this is done with varying resistors, such as isdone with a wound-rotor motor or by varyingthe stator voltage; or
3. Change the frequency of the power supplied tothe motor. This can be achieved by VFD .
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VFD Basics
The main objective of the VFD is to vary the speedof the motor while providing the closest
approximation to a sine wave for current (whilepulsing DC voltage to the motor).
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Components of VFD System1.Operator Interface2.Variable Frequency Controller
3.AC Motor
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VFD Controller
The variable frequency drive controlleris a solid state power electronicsconversion system consisting of threedistinct sub-systems
1. A rectifier bridge converter
2. A direct current (DC) link and
3. An inverter
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Rectifier bridge converter
All VFDs need a power section that converts ACpower into DC power.
This is called the Rectifier bridge.
The Rectifieris commonly a three-phase, full-wave-diode bridge.
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Direct current (DC) link
The DC link may consist of a capacitor/inductorwhich smoothes out the converter's DC outputripple and provides a stiff input to the inverter. Ifnot, this distortion will show up in the output tothe motor.
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Inverter
The inverter section is made up of modules that consist of atransistor and diode in combination with each other whichinverts the DC energy back to AC.
The power semi-conductors in the inverter section act asswitches, switches of the DC bus, and therefore, arepulsingthe motor with some voltage.
By switching the inverter-transistor devices on and offmany times per half cycle, a
pseudo - sinusoidal currentwaveform is approximated.
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VFD Types
Voltage-source inverter (VSI) drive The DC output of the diode-bridge converter stores energy in
the capacitor bus to supply stiff voltage input to the inverter.The vast majority of drives are VSI type with PWM voltageoutput.
Current-source inverter (CSI) drive
The DC output of the SCR-bridge converter stores energy inseries-reactor connection to supply stiff current input to theinverter. CSI drives can be operated with either PWM or six-step waveform output.
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VFD Types Cont.. Six-step inverter drive
The DC output of the SCR-bridge converter is smoothed viacapacitor bus and series-reactor connection to supply viaDarlington Pair or IGBT inverter quasi-sinusoidal, six-stepvoltage or current input to an induction motor.
Load commutated inverter (LCI) drive The DC output of the SCR-bridge converter stores energy via
DC link inductor circuit to supply stiff quasi-sinusoidal six-stepcurrent output of a second SCR-bridge's inverter and an over-excited synchronous machine.
Cycloconverter or matrix converter (MC) Cyclo converters and MCs are AC-AC converters that have no
intermediate DC link for energy storage.
Doubly fed slip recovery system A doubly fed slip recovery system feeds rectified slip power to
a smoothing reactor to supply power to the AC supply networkvia an inverter, the speed of the motor being controlled byadjusting the DC current.
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Pulse Width Modulation
Pulse-width modulation (PWM), or pulse-durationmodulation (PDM), is a commonly used technique forcontrolling power to electrical devices.
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Pulse-width-modulated voltage and
current waveforms.
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VFD Motor Selection issues
The switching of insulated-gate bipolar transistors(IGBTs) to accomplish PWM on the output of aVFD creates voltage spikes on the line out to themotor.
These spikes are amplified over distance and, intime, break down the insulation of a motor,shortening the motors life.
For VFD applications, Class F or higher insulation
should be selected when possible.
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VFD Motor Selection issues Cont..
In constant power applications, for higher torque,the speed would be low.
Reduced speed may affect the cooling of the
motor windings for high torque applications. When a VFD applies high-frequency pulses to a
motor, the parasitic capacitance between statorand rotor generates voltage on the motor shaft.
This creates discharge arcing and shaft current,which may damage the shaft and bearingsurfaces.
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Sample PWM-Equivalent Circuit
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Application in Power
Plants
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VFD APPLICATION TO CEP/ID fan(for Energy Savings)
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Variable speed control is the most energy efficient control method
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7 10
7
10
12
H
Q
Flow
HeadHow VFD Saves Energy ?
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VFD for CEP
P saving= 161.7 KW
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CEP/ID Fan
There is a gap between design pointand the rated operating point.
Design margins are to take care of
extreme operating conditions. VFD ensures energy savings by
reducing speed at the operating
point. Margin to take care of operation at
47.5Hz. is not needed.
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VFD APPLICATION TO COMPRESSOR
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VFD in Compressors
Instead of loading and unloading in a cyclicmanner, the compressor is start/stop as perdesired duty requirement to maintain the setpressure.
System saves energy as the motor does not runin idle mode.
VFD in compressor allows frequent start/stop of
motor as per duty requirement. Lower maintenance of the system due to smooth
start.
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Coal Conveyors
Coal conveyors are subjected to frequentstart/stop.
Idle running of motor during stop bydisengaging the hydraulic coupling causes
energy loss. Only 2 starts/hour are permissible. Conveyors have to be designed to start
while fully loaded, i.e. high torque.
Generally motors are run at part load. VFD can provide ideal solution for
Conveyors.
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REELING DRUM APPLICATIONcont. The present scheme
Cables reeling drum provided with brake motor The brake motor stops and holds the drum, as
and when the paddle-feeder or stacker-re-claimer stops moving
It protects the cable from slackness. The brake is released on restart and motor
rotates the drum to maintain safe tension inthe cable.
The motor with conical rotor with spring loaded
brake and brake-shoe arrangement are proneto high maintenance. Many times causes unreeling of cable resulting
in snapping or damage of it.
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REELING DRUM APPLICATION
VFD Alternative Scheme The arrangement is an innovative solution
of brake motor. The VFD maintains constant torque on the
cable reeling drum continuously even atzero speed (i.e. stop condition).
This constant torque maintains safetension on the cable.
Power consumption at zero speed is equalto no load and part consumption duringmovements, as and when the drumrotates.
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VFD APPLICATION TO BOILER AREA
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VFD APPLICATION TO BOILER AREA
Axial blade pitch control and VFD control give thesame level of efficiency in power consumption atpart load operations
VFD control for PA fan, ID fan, Coal Feeder andFuel Oil motors can be implemented for old210MW units.
VFD control for ID fans, Coal Feeder and Fuel Oilmotors can be implemented for old 500 MW units
New units should have VFD for coal feeder speedcontrol as against eddy current clutch control
Sipat-I coal feeder motors already have VFD
controls.
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VFD APPLICATION TO BFP(for smooth start)
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Advantages of Using VFD
Increased motor life due to the lowerthermal and mechanical stressed inview of the absence of starting inrushcurrents and reduced speed operation
No limitation on the number of starts No contribution to fault current.
One VFD can be used to start all the
MDBFPs One more VFD can be kept as standby
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OPTION-A OPTION-B OPTION-C
2 x50% TD+1x50%MD(hydrauliccoupling)
2 x50% TD+1x50%MD (VFD)
3x50% MDBFP (VFD)
VFDs 0 2 ( 1+1standby) 9 (8+1standby)
Turbines 8 8 0Motor 4 4 12
Hydraulic couplings 4 0 0
Flexibility of layout Negative Negative Positive
Space requirement Negative Negative Positive
Maintenance Negative Negative PositiveStartup time Negative Positive Positive
Motor startup Negative Positive Positive
Supply side Harmonics Neutral Neutral Neutral
System Cost Low High Neutral
VFD solution may be cheaper than the conventional one with other advantages as bonus
VFD APPLICATION TO BFP4 UNITS
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BFP for 660MW Units- OPTION-B
The BFP motor rating for 660MW (2x50%
TDBFP+1x50% MDBFP) unit is 18MW andthus causes high electrical and mechanicalstress on the system during starting.
Instead of 1x50%, it was proposed to use2x30% rating BFP for 660 & 800 MW units.However with VFD it can be retained as
1x50%. The size of each VFD for 18MW motor shall
be approximately 5MVA equal to no loadMVA rating.
Ad t f U i VFD ith OPTION C
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Advantages of Using VFD with OPTION-C
BFPs can be placed at 0.0 M El. Saving in Plant Cost due to lowering of
De-aerator Elevation Absence of Associated Steam and
Condensate piping
Flexibility of Layout and Space Saving Absence of voltage dip problems This option is ruled out now because new
CERC regulation permits only 2%
additional aux. power on account of BFP,whereas BFP power consumption will be4% in supercritical unit.
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PRICE OF VFDfor BFP Motors cont.
Siemens quote for VFD of 300kW Air Compressormotor: Rs. 4 million
Siemens quote for VFD of 4000kW ID Fan
induction motor: Rs. 45 million
ABB quote for VFD of 4000kW ID Fan inductionmotor: Rs. 28.8 million
Expected Price of VFD of 10MW rating along withmotor Rs. 80 millions
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VFD WITH REMOTE RF CONTROLFOR
EOT CRANES
INTRODUCTION
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INTRODUCTION
USE :
LIFTING / LOWERINGLOADS
CARRYING LOADSALONG /ACROSS THERAILS
MOTORS : MAIN HOIST/ CREEP MOTOR AUXILIARY HOIST / CREEP
MOTOR
CROSS TRAVEL / CREEPMOTOR
LONG TRAVEL / CREEPMOTOR
RANGE OF EOT CRANESIN NTPC:
( 7.5 T 105 T )
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CONVENTIONAL PRACTICE
SLIP-RING INDUCTIONMOTOR EMPLOYINGRESISTANCE CUT-IN/
CUT-OUT FOR SPEEDCONTROL
CABIN /PENDENTCONTROL
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VFD SYSTEM
SQUIRREL CAGEINDUCTION MOTOR INPLACE OF SLIP RING IM
SPEED CONTROL BYVARIABLE VOLTAGEVARIABLE REQUENCYDRIVE
RADIO REMOTEFREQUENCY CONTROL
UNIT
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COMPONENTS & WORKINGPHILOSOPHY
A) VARIABLE FREQUENCY DRIVE
B) RADIO FREQUENCY REMOTE
CONTROLLERTransmitter unitEncoderReceiverDecoderInterface panelCoupling systemControl gearBattery
FEATURES
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SALIENTFEATURES
A) VFD SYSTEM
SQ.CAGE INDUCTION MOTOR WITH VPI INSULATION AND INSULATEDNDE BEARING
CHOICE OF MOTION CONTROL FROM OPERATORS CABIN OR REMOTE
CONTROLLER
STARTING TORQUE UPTO 400% WITH STARTING CURRENT LIMITEDTO 150%
VFD CAPABLE OF WITHSTANDING UPTO 50C
HARMONIC REDUCTION DEVICES
SPEED CONTROL WITH 6 PULSE DESIGN
PROTECTIONS: O/L , O/V , E/F , O/ S Ckt., I/P LOSS , LOAD LOSS, I/PTRANSIENT PROTECTION
SALIENT FEATURES CONTINUED..
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B)RADIO FREQUENCY REMOTE UNIT
WIRELESS CONTROL WITH DOUBLE JOYSTIC MOVEMENTTYPE STEPPED CONTROL WITH SPRING RETURN
TRANSMITTER & RECEIVER HAVE A UNIQUE FREQUENCY &
ADDRESS CODE TO AVOID INTERFERENCE
CAN COMMUNICATE UPTO 100 m DISTANCE
CRANE OPERATION IS LOCKED IN CASE OFCOMMUNICATION FAILURE
CHOICE OF TANDEM/SLAVE/SINGLE OPERATION
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TECHNICAL ADVANTAGES
VFD SYSTEM
No slip ring related maintenance
Creep motor not required
Gear box not required
Electrical braking before mechanical breaking-break life is more
On line fault display- hence less down time
Starting current is less than dol starting
Smooth starting and stopping offers jerk less operation longer life due
to less mechanical fatigue
Wide speed range- step less speed control
100% holding torque available at standstill
More energy efficient
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TECHNICAL ADVANTAGES
RF CONTROL
EASE IN HANDLING
UNRESTRICTED OPERATOR MOBILITY
NO ROUTINE MAINTENANCE REQUIRED
WIRELESS OPERATION
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COST ANALYSIS
A) VFD SYSTEM IN 105T EOT CRANE IS COSTLIER BY Rs 1,39,750ie 0.7% OF COST OF ONE EOT CRANE (Approx. 2 crore)
B) RF REMOTE CONTROLLER COSTS 1.15 Lacs WHICH IS 0.57% OFCOST OF ONE EOT CRANE
BOTTOM LINE:
A) + B) COMBINED TOGETHER SUMS UP TO BE 1.27%
COSTLIER THAN THE PRESENT SYSTEM
The 1.27% extra cost is insignificant, in lieu ofbenefits on energy savings, reduction in man powerand low maintenance.
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AIR CONDITIONING
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Limitations of Centralized AC
Higher space requirement for installation ofequipment. AC plant room is required.
Not suitable for frequent load variation.
Not efficient at part load operation. Difficult to retrofit.
Operators intervention is required to control/vary inside conditions.
Water Cooled systems although are veryefficient, require large quantity of make-upwater.
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Limitations of Localized AC system
Envisaged normally for small buildings.
Available upto 15 TR capacity as a single unit.
No humidity control.
No arrangement for fresh air supply. Distance of out door unit can not be more
than 10M.
Part load operation is not possible.
Noise in operation
VRV (Variable Refrigerant
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VRV (Variable Refrigerant
Volume) Based on limitation of the above two
systems a need was felt for anintermediate of the above two
systems. VRV system has beendeveloped to overcome thelimitations imposed by centralisedand localised systems.
The Variable Refrigerant Volume(VRV) system is also Known asVariable refrigerant Flow (VRF)
system.
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Schematic diagram of VRVsystem
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VRV (Variable Refrigerant Volume) System
Similar to split type of air conditioning. VRV comprises of no. of indoor units which share a common
refrigerant circuit, served from a common outdoor unitcomprises of multiple compressors of varying capacity.
The refrigerant flow is varied by using inverter controlledvariable speed compressor to respond to changes in thecooling or heating requirement.
By the combination with the inverter compressor and theconstant speed compressor, the comfortable room conditionwill be obtained by changing the compressor operationcondition.
VRV conditions air for each room individually as per loadrequirement.
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Layout of VRV system
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Freely Selectable Operation of
Indoor UnitsUnitsOthers System VRF
ON ONOFF OFF
Partial Load implies 40 to 70%less energy consumption
Not Possible
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VRV/VRF
VRV system can work as centralisedsystem.
VRV system can work as localised system.
Operating cost of the system is minimisedby use of varaible refrigerant flowconcept.
Make up water is not required.
VRV system can operate at part load. Total Piping length from outdoor to indoor
unit can be as maximum as 150M.
VRV/VRF
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VRV/VRF
(Comparison with chillers)
S.No. Features VRV System Water cooled Chiller
system
Benefits of
VRF System
1. Type of System Completely Air-
cooled system
with three basic
parts- Outdoor,indoor units &
controllers
Water cooled
system with many
component chilling
machines, AHUs,Cooling tower,
Chilled Water
pumps, Condensate
water pumps, many
types valves,
Electricals &controls etc.
Minimum partsthus very
simple VRF
systems
2. Energy
Consumption
Overall 25%-
35% power
saving on
average basis
Only efficient at
certain load
conditions
Constant
saving by
optimal
running
VRV/VRF
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VRV/VRF
(Comparison with chillers)
S.No. Features VRV System Water cooled
Chiller system
Benefits of
VRV System
3. Distribution
Piping
Network
Smaller
copper piping
Bigger MS piping Shaft/ floor
space not
required
4. Interiors,
Ceiling height
Different type
of Indoor
options to fit
into different
construction,interiors
Only Ducted
Systems possible.
Flexibility in
layout.
5. Standby
Function
Inbuilt
Standby -
Multi tier
To be added at
extra cost
Ensured
Operation all
Times
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Conclusion VFD Can be used in CEP for future projects for
energy saving.
For All old stations, VFD can be installed in CEPbased on techno-economics.
For Large size units, VFD in BFP Motor offers anumber of advantages and can be considered infuture.
VFD can be useful for conveyor motors, compressorand reeling drum motors.
Boiler Auxiliaries such as PA fan , ID fan ,Coal Feederand Fuel Oil motors can be upgraded with VFDcontrol, for old 210 MW and 500MW units.
New units of all sizes should have VFD for coal feederspeed control.
VFD is becoming popular for VRV air-conditioning ,Hoists, Lifts and EOT Cranes
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THANK YOU
Speed & Motor Ratings - Major SG Auxiliaries
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Aux\MW 210 500 660
FD fan575 KW
1480 RPM1225 KW900 RPM
1950 KW990 RPM
PA fan1600 KW1480 RPM
2850 KW1490 RPM
3350 KW1490 RPM
ID fan1650 KW
120-580 RPM3895 KW
AT 545 RPM5250 KW590 RPM
Coal Feeder5.5 KW
1500 RPM5.5 KW
1500 RPM5.5 KW
VFD
Coal Mill
425 KW
589 RPM
525 KW
985 RPM
690 KW
986 RPM
BCW pump NA365 KW
1455 RPM545 KW
2930 RPM
37 KW 90 KW 75 KW
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