VFD dismantaling

8/18/2019 VFD dismantaling

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VFD dismantaling

Frequently used Induction motors had constant speed, thus using these kind of

motors not useful at all. But induction motor can be control under useful manner

to perform industrial work. For that Variable speed drive used. Induction motors

are used at conveyor belts ,mills,etc .hus need to control the speed or use

multi!speeds during the operation.

"e were assigned to tear down a damaged VFD Before going to program a

VFD.In the tear down process in the very #rst we were removed capacitor bank

and outer plastic casing .It$s screwed and bolted to the heat sink of the

VFD."hen after removed the casing ,we were #gured some electronic cards .%ne

card contains some input terminals and its mounted to the bottom card by some

screws.It connect to the bottom card by a cables.Bottom card$s upper layer was

#lled with black thin insulation layer and it also have some terminals

.%nly recti#er diode bridge can easily #gure without removing the layer. hus we

were identi#ed the upper card as control card and bottom card as power card

.in between the power card and the heat sink there was another module which

were enclosed by a sealed bo&. "e were removed the heat sink and removed

those enclosed bo&.here were some white layer witched applied between the

module and the heat sink. It known as 'igh!Density (olysynthetic )ilver hermal

*ompound

.It +sed for increase thermal conductivity of the heat sink.It was very hard to

remove the casing of the module because it was sealed by pressing .Inside of

the module there was the IB module.it covered by some special kind of

gel.he IBs are not welded they were assembled with the aid of the gel."hen

we were removed the gel some sensitive conductors in the module weredamaged. "e are unable to replaced those equipment. Igbts module consist

some freewheeling diodes to protect the module from back emf. -nd also ther

were dc bus which previously removed as capacitor bank, other than that there

were terminals for breaking resistors.

During the inspection "e were #gured that vfd control motor speed

by using two methods. +nder VF method or Vector /ethod .)o the VFD is

basically consist 0ecti#er Bridge and inverter module .-s follows the (ower

electronics circuit.

-ccording to the VF method VFD rectify -* input voltage which at 12 '3 in to D*

voltage and invert back to -* voltage of desire output voltage."hen the

frequency of the output voltage signal changed and thus %utput voltage will

changed.

%utput(ower InverterD* bus0ecti#er


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"hen we installing a VFD very #rst we needed to consider some parameters,there were

4ame plate of motor connected to vfd

*ode name and name plate details of the VFD,

-t the very #rst we should consider about name plate details of the motor.-ctually we used motors for convert electrical energy into kinetic 5rotational6energy. hus VFD will used to supply power to motor at e7ective manner. -nd wemust not select vfd which has lower power rating than rated power of motor .Ifwe used vfd lower than motor rated power, VFD will destroyed. -nd also we musttake care about the terminals of the vfd ."e must not connect power inputterminals in to the power output terminals of the VFD. it will destroy the VFD.Butdue to the freewheeling diodes VFD could be protect but damaged it.

"e know that motor consist some thermal limits due to its insulations. )owe must take care about its rated speed .If we trying to increase the speedbeyond the thermal limit of the motor will damaged./odel of the VFD formedaccording to following reason

"hen we using a VFD we must refer the manual before using it. -ctually VFDparameter codes will changed from brand to brand and also version to version.

hus needed to refer basic parameters very #rst. If we used a brand new VFD itwill already at the no parameters set. But if we use used one it will programedearlier thus needed to reset before using it. If we didn$t consider that, it willdamaged our motors and other equipment.-fter resetting the VFD, basic parameters should be set. -s basic parametersthere areBase frequency,%perating frequency,Frequency upper limit


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Frequency lower limit,%verload setting,-cceleration and deceleration time etc.

"e could connect some e&tra equipment into the control card, such like limitswitches, push buttons potentiometers etc. -ccording to the requirement wecould connect those kind of equipment. -nd also we could connect to the(rogrammable 8ogic *ontroller to the VFD.

"hen we using a VFD we needed to consider the protection of notonly the human but also the equipment. here was a minimum clearance to bemaintain to have good ventilation system. here e&ist some cooling fan inside ofthe VFD. Blocking the fan means damaged to the drive. -nd also we mustconnect 0**B and according to the situation /*B or /**B to the power input ofthe drive.

)ervo motor drive

here were two frequently used motors in industry they were )tepper motors

and servo motors. -ccording to the )tator and rotor both motors are very similar

but both of them used at di7erent applications.

)ervo motor applications9!*4* machines, :ero )peed torque requirements

)tepper /otor9 ! 'ard disc, *D rom

)ervo motor consist of encoder which could be used for get feedback signal. )o

position ,direction, speed could easily monitors it could be used at *4*

machine .If we used a stepper motor instead of servo we were unable to #gure

the wear of the tool .thus the design will not smooth .-nd also formed chips will

damage the tool. But if we used a servo it will sense the position of the tool and

used the feedback to complete the task .)o stepper motor only used for torque

less process. It doesn$t need feedbacks because its very accurate by its inside

coils of stator energised by the appropriately applied pulses.

he servo motor feedback could be used for 3ero speed torques. hus motor will

not rotate but output was the torque .)o such kind of situation we could use

servo motors. -ccording the motor speci#cation we could control stepper motor

using -0D+I4o +no circuit board, But when we using a servo we were needed to

use servo drive like as VFD.)ervo drive very di7erent rather than the VFD .If wewant to use a servo drive for speci#c servo motor #rst we must select a drive

according to the motor code. /otor code should support to the servo drive

supporting motors. hen we should enter parameter 2 known as password .If we

were not entered parameter 2 properly we are unable to change the

parameters .-t that kind of situation we could only monitor the parameters .If we

were entered correct password then we could change parameters .Its basicaly

needed to enter motor code as ne&t parameter .If we were entered wrong code

motor will not run perfectly .In )ervo drive there e&ist stored memory according

to the supporting motors. Driver model type is formed according to following,


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In the industry there are numerous control circuits that done by logical

thinking .But when we are used contactors for the logics it was limited the area

of usage .hus there were more controlling logics that could be used for that.

hey were (neumatics valves logics or (rogrammable logics *ontrollers.

-s a big factory *amso loadstar used both of the controlling logics .But widely

used the (8* due to its compactness. If we used (neumatic valve it needs air line

of speci#c pressure .hus it increased the cost of the circuit.

"hen we want to use a plc we use speci#c (8* according to our requirement. But

it is good to think about the number of speci#c inputs and outputs of the (8*.

)ome of the (8* only have digital inputs and outputs. )ome of them consist both

digital and analog inputs and outputs. hus needed to consider about our need

before using them. )ometimes the output may be signals to the relays .In relays

there are normally open or normally closed contacts ."e could use them to

control. he desired output. "e could enter the logic into the (8* using (8*

programming software ."e enter a ladder logic into the plc according to the

inputs and output codes.

Inputs may be limit switches, push buttons etc. -ccording to the

input signal ladder logic will run .hus the %utput will be signals to the relays or

other equipment .he normally open and normally closed points at relays are

used to control circuits.

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VFD dismantaling