VFD Maintenance L2 Weekly monthly yearly

VFD maintenance

1. AWI 106 Att. 8 Rev. 3 02 Jan. 2011
Date :
VFD Panel
Maintenance
FM-EL-VFD-L2-01
QC Department

2. Draft 03 April 2011/ Rev.32
Preface
ThiscourseintroducestoVariableFreqency
Drives.
Itwillenablethetechnicianstoobtainbasic
knowledgerequiredtoperformOperationaland
Maintenancetasks,classifiedasL1inElectrical
taskbook,forVFDMaintenance.

3. Draft 03 April 2011/ Rev.33
Background
Thiscourseisintendedtotechnicianswhohave
basicknowledgeandqualificationinthefieldof
Electrical.
Techniciansexperienceinsimilarfieldis
advantageous.

4. Draft 03 April 2011/ Rev.34
Topics / Tasks
TheFollowingTopicswillbecoveredduringthiscourse
I.WhatisVFD?
II.MaincomponentsofVFD?
IV.Cleantheroomandpanel,visualinspectionofall
componentsandcabletermination.(checkforany
looseconnections,chancesforheating&burning)
(FM-EL-TB#024)
V.Checktightnessofterminalsofconnections
includingearthconnections(Checkforanyloose
connections,chancesforheating&burning)(FM-EL-
TB#024)
VI.Question&Answers

5. Draft 03 April 2011/ Rev.35
What is VFD ?
Thesimplestandleastexpensivewaytocontrolthe
speedofaprocessorpieceofequipmentisto
operatealltheequipmentatfullspeed.
Manyapplicationsrequirethespeedofaprocessor
pieceofequipmenttobevaried.
Avariable-frequencydrive(VFD)isasystemto
controltherotationalspeedofanACmotorby
controllingthefrequencyoftheelectricalpower
suppliedtothemotor.

6. Draft 03 April 2011/ Rev.3
What is VFD ?
ACAdjustableSpeedDrivescanbethoughtofas
electricalcontroldevicesthatchangethe
operatingspeedofamotor.ASD’sareableto
varytheoperatingspeedofthemotorby
changingtheelectricalfrequencyinputtothe
motor.ThespeedanACinductionmotor
operatesisgivenbythefollowingequation:
Speed=120f
P
6

7. Draft 03 April 2011/ Rev.3
Variable Frequency Drive
Where:
f =Electrical frequency of the power supply in Hz.
P= Number of electrical poles in the motor stator.
Motors speed can be changed by altering the
electrical frequency, the # of poles, or both.
Motor speed can be changed by altering the # of
poles in a motor from 4 to 2:
4 pole motor operating on 60 hertz = 1800 rpm.
2 pole motor operating on 60 hertz = 3600 rpm.
7

8. Draft 03 April 2011/ Rev.3
Variable Frequency Drive
4polemotoroperatingon50hertz=1500rpm.
4polemotoroperatingon40hertz=1200rpm.
Byvaryingfrequency,wecanadjustthespeedovera
widerangeorvarythespeedpreciselyusingprecise
changesintheelectricalfrequencyinputtothemotor.
ManyASDsystemsmakeuseofabypassstarterin
parallelwiththedrivewhichallowsthedrivetobe
easilybypassedwhencriticalapplicationrequirea
back-upcontrolmeans.
8

9. Draft 03 April 2011/ Rev.3
Variable Frequency Drive
TheASDcanbebypassedinamatterofseconds
whereothertypesofspeedcontrolmaybedown
forhoursorevenweeks,whileitisbeingrepaired
ifthereisnotasparecontrol
SomeASD'scancontrolmultiplemotorsfromthe
samedrivewhichcanbeanadvantageoverother
typesofvariablespeedcontroldevices.
9

10. Draft 03 April 2011/ Rev.310
Parts of a Variable Frequency Drive (VFD)

11. Draft 03 April 2011/ Rev.3
Parts of a Drive
Parts of a Drive are
1.Rectifier
2 .Soft Charge Circuit
3 .Intermediate Circuit (DC Link)
4. Inverter
5. Control & Regulation Section
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12. Draft 03 April 2011/ Rev.3
Parts of a Drive
TheDriveisjustonepartofasystem.Inthe
diagramabove,noticethedisconnectswitch,
fuses,bypassswitch,thermaloverloads,BAS,
etc.allplayanimportantpartinmakingan
applicationworkcorrectly.
InsidetheVFDthereare4majorsections:
rectifier,intermediatecircuit(DCLink),inverter
andcontrol/regulation.Thisfourthsection,control
andregulation,interfaceswiththeother3
sections.
12

13. Draft 03 April 2011/ Rev.3
Rectifier Section
Powerfirstgoesintotherectifier,wherethe3-
phaseACisconvertedintoaripplingDCvoltage.
Theintermediatecircuitsthensmoothesandholds
theDCVoltageataconstantlevelorenergy
sourcefortheinverter.Thelastsection,the
inverter,usestheDCvoltagetopulsethemotor
withvaryinglevelsofvoltageandcurrent
dependinguponthecontrolcircuit.Thepatternof
thepulsesgoingtothemotormakesitappear
similartoanACsinusoidalwaveform.
13

14. Draft 03 April 2011/ Rev.3
Rectifier Section
14
Rectifier Section
Its function is to change 3-phase AC into DC

15. Draft 03 April 2011/ Rev.3
Rectifier Section
The3-phaseACvoltagegoesintotherectifiersection
whichismadeupofagroupofgateddiodes(silicon
rectifiersorSCRs).InmostVFDs,thesediodesareina
groupof6asdiagramedabove.
Inthistypeofcircuit,theDCvoltageis1.35timesthe
AClinevoltage.If240Vaciscomingin,324Vdcis
generated.
Becauseofline(powercomingin)andload(powerto
themotor)changes,theDCVoltagelevelisconstantly
movingaboveandbelowthisexpectedvalue.
15

16. Draft 03 April 2011/ Rev.3
Rectifier Section
This rectification
can generate a
considerable amount
of heat, so the SCRs
are mounted onto
a gold-colored
heatsink. fans
mounted across the
top of this VFD pull the
air across the
heatsink.
16
The Rectifier section contains
terminals for incoming
power, silicon rectifiers (SCR) and
heatsinks

17. Draft 03 April 2011/ Rev.3
Soft Charge Circuit
With this circuit, when
power is applied, the
inrush of current is
restricted going to the
large capacitors in the DC
Link, so that they may
charge up slowly (within a
couple of seconds). If this
circuit was absent, line
fuses would be blown
every time the VFD was
started.
17

18. Draft 03 April 2011/ Rev.3
Soft Charge Circuit
18

19. Draft 03 April 2011/ Rev.3
Intermediate Circuit (DC Link)
Using a large bank of
capacitors and DC
reactors the rippling
DC voltage becomes
more stable.
19

20. Draft 03 April 2011/ Rev.3
Intermediate Circuit (DC Link)
TherippledDCvoltagecominginhasnowbeen
filteredtoarelativelyconstantvoltage.Remember
thatthisDCLinkVoltageis1.35timestheinput
voltage.ThevalueoftheDCLinkvoltagecanbe
readfromthedisplayonthefrontofthedrive.
Wheneverworkingaroundthedrivealwaysbe
carefulandgiveitahealthyrespect.
Capacitorsbanks(blackonnewerunits)area
majorpartoftheDCLinkandstoreagreatdealof
energy.
20

21. Draft 03 April 2011/ Rev.3
Inverter Section
The Inverters take
the voltage from the
DC Bus and using
Pulse Width
Modulation (PWM)
sends a signal which
appears to the motor
as an AC signal
21

22. Draft 03 April 2011/ Rev.3
Inverter Section
Inverter section takes the DC
voltage from the intermediate
section and, with the help of the
control section, fires each set of
IGBT (Insulated Gate Bipolar
Transistors) to the U,V and W
terminals of the motor. This
firing of the IGBTs is known as
Pulse Width Modulation (PWM)
IGBTs
22
IGBTs

23. Draft 03 April 2011/ Rev.3
Control & Regulation
The control section
coordinates and
regulates signals
inside the drive.Here
numerous calculations
are completed to
properly switch the
IGBTs.This control
sectionseparates the
torque producing
current from the
magnetizing current.
23

24. Draft 03 April 2011/ Rev.3
Control & Regulation
The control section uses
the frequency (f), voltage
(V) and phase angle
(theta) to control the
inverter. The function of
all the parts of the drive,
Rectifier, DCLink, Inverter
and control/Regulation is
to make a clean
waveform to the motor.
24

25. Draft 03 April 2011/ Rev.3
Bypass System for VFD.
InCaseanyVFDfailurecomes,AStarDelta
starterhasbeenProvidedtoStartthemotor.
Itwillbypassthevariabledrivetorunthemotor
inratedfullspeed.
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26. Draft 03 April 2011/ Rev.3
PPM –Documents
26

27. Draft 03 April 2011/ Rev.327
Question & Answers
V.QUESTIONS????

28. Draft 03 April 2011/ Rev.328
However,thesecourseareclearinorderto
performmaintenanceofVariableFrequencyDrive
fortechniciansinthefieldofElectrical.
Conclusion ׃-