3 three ph ac voltage controller.doc

7/27/2019 3 Three Ph AC Voltage Controller.doc

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THREE PHASE AC VOLTAGE CONTROLLER

INTRODUCTION:

Three phase AC voltage controller consists of a power module and a firing unit.

Power module is the combination of six SCRs in anti-parallel. In addition short circuit

protection is provided b! fast fuses for SCRs. The th!ristors are mounted on individual heat

sin"s and protected b! fast fuses.

terminals for connection purposes.

#iring unit generates six line s!nchroni$ed firing pulses to trigger th!ristors of three

phase ac voltage controller power circuit. #iring circuit is based on %C& pulse generator pulseamplification ' pulse triggering method. (ate pulses are ta"en out through isolation pulse

transformer. #iring angle can be varied from minium to maximum b! the control "nob provided

on the front panel. #iring circuit testing points are ta"en out to front panel. All the terminals are

brought out to front panel with )TI-*+ terminals.

Individual devices of the power module must be interconnected externall! to form three

phase ac voltage controller power circuit. (ate pulses must be given to gate and cathode of

respective th!ristors from firing unit ' firing angle must be varied to get variable load voltage.

#or convenience of experimentation isolation of mains must be provided. Power input is

to be given through an isolation transformer of suitable rating for the power circuit while

conducting experiment. ,xternal load must be connected while doing experiment.

This unit can be used with R R- ' motor loads.

A well designed snubber circuit is provided for dvdt

protection. All the terminals of the power module are brought out to front panel through )TI-*+

*



SPECIFICATIONS/

POWER CIRCUIT/

1. SCRs 0mar"ed as A C ' (1 / 2 nos

Sl.3o.*

4

5

6

2. Fuses:

+A replaceable fuses are provided on 7#-48 soc"ets at the bac" side of the

instrument.

3. Maxiu a!!"#a$!e i%&u' ("!'a)e: - 658 9 AC

Parameters9RR7

9&R7

ITR7S

ITA9 0*:8 Conduction1

Ratings

*488 9

*488 9

4+ Amps

*2 Amps

FIRING CIRCUIT/

S!. N"

*

4

5

6

+

Pa*ae'e*s

Input power suppl!/

;utput/(ate drive current/

#iring angle/

Test points/

Pa*'i+u!a*s

#rom three phase mains suppl!

Six isolated gate signals for th!ristors

488 mA.

7inimum to 7aximum for load voltagecontrol.

Provided for the stud! of different waveforms.

FRONT PANEL DETAILS:

POWER MODULE:

*. Six SCRS are placed inside and the terminals are brought to front panel and mar"ed with

their s!mbols.4. A three phase 7C) is provided with this unit.

4



FIRING UNIT:

*. Power onoff switch with ,& indicator.

4. + to : test points are provided b! RS-4 terminals to stud! the different wave forms at the

different points of firing circuit.

5. 7inimum to 7aximum firing angle control is provided b! potentiometer.

6. Six isolated gate pulses are connected to the )TI-*+ terminals on the front panel and

mar"ed as gate ' cathode.

E,PERIMENTAL

RECOMMENDED FOR E,PERIMENT:

Nae "- 'e e/ui&e%' S&e+i-i+a'i"%s 0ua%'i'

Three phase 6*+9+8<$ input ' suitable*. I3P=T 0S;=RC,1/Isolation Transformer output to suit the load ratings.

Input/ 6*+9 line to line Star connected

;utput/ Re>uired rating to suit load

re>uirements

4. C;3TR; 7;&=,S/ *. Three phase AC 9oltage power 7odule

4. Three phase AC 9oltage controller firing

unit.

5. ;=TP=T 0;A&1/ *. Resistance ? Suitable load for given power

4. A.C. motor. 0;ptional1

6. 7,AS=RI3(

I3STR=7,3TS/

? *no.

? *no.

? *no.

? *no.

? *no.

? *no.;scilloscope

#or connection purposes+. C;33,CTI3( @IR,S/

5



HOW TO CONDUCT E,PERIMENT:

AIM:

To construct a three phase AC voltage controller ' to control the speed of the AC motor

APPARAT=S/ 6*+9 input suitable output isolation transformer power module firing unit

suitable R7otor load connecting wires etc.

THEOR: AC voltage controller converts fixed AC suppl! to variable AC suppl!. @ith

th!ristor variable AC suppl! 89 to maximum can be obtained from a fixed AC source b!

triggering 0turning ;31 th!ristor i.e. b! appl!ing gate current to the th!ristor at an! desired

instant when the th!ristor is applied with positive voltage to anode. =nli"e diode th!ristor can

bloc" the forward voltage when gate current is not supplied.

The circuit diagram of a three phase full-wave controller is shown in figure with a

connected resistive load. The firing se>uence of th!ristor is T* T4 T5 T6 T+ T2.

LOAD VOLTAGES:

# o r 8 B α B 2 8 8/

Immediatel! before the firing of T* two th!ristors conduct. ;nce T* is fired three

th!ristors conduct. A th!ristor turns off when its current attempts to reverse. The condition

alternate between two and three conducting th!ristors.

#or 288BαB88/

;nl! two th!ristors conduct at an! time.

#or 88BαB*+88/

Although two th!ristors conduct at an! time there are period when no th!ristors are on.

F o r α D * + 8 8/

There is no period for two conducting thyristors and the output voltagebecome zero at αE *+88.

PROCEDURE:

N"'es:

*. &o not conduct the experiment without three phase isolation transformer. If !ou tr! to

conduct experiment without isolation transformer the instrument ma! be damaged due to

6



short circuit exists between single phase ' three phase suppl! while ma"ing

measurement using CR;.

4. &o not attempt to observe line to line voltage and input voltage simultaneousl! if does

so input voltage terminal directl! connected to load terminals due to the isolation of both

channels of the CR;.

5. Conduct experiment b! "eeping input AC voltage suitable low value to get proper wave

form on CR; screen using resistive load.

6. It is recommended to =se power scope.

THREE PHASE AC VOLTAGE CONTROLLER WITH R LOAD.

T*

C

TC66

*

*

3Ψ IS;ATI;3

TRA3S#;R7,R R R

(6

T

R

5(5

CT

5

9R

93

9R3 CR;

3Ψ7C)

)

3

C 22

)

3

(29

T+(+

CT

C44 +

)3

C;33,CTI;3 )

T

3R)

#IRI3( =3IT

T

T

T

T

T

*

6

5

2

+

4

(4

#ig T<R,, P<AS, AC 9;TA(,

C;3TR;,R

+



*. The connections are made as shown in the circuit of three phase AC voltage controller

with R loads using Isolation transformer and rheostates 05 nos of same resistance value1.

4. Connect output terminals R ' ) of isolation transformer 0star connected1 to respective

terminals R ' ) of power module ' firing unit.

5. The gate cathode terminals of the 2 SCRFs are connected to the respective points on the

firing unit.

6. Chec" all the connections and conform connections made are correct before

switching on the instrument.

+. Geep firing angle "nob at minimum position.

2. Switch on three phase suppl! power unit as well as firing unit.

H. The output wave forms are seen on a CR;.

H



:. The firing angle is varied and AC output voltage is noted.

. Tabulate values in the table. 0refer given table1.

*8. A graph of 9ac 0line to line1 verses firing angle is plotted.

THREE PHASE AC VOLTAGE CONTROLLER WITH MOTOR LOAD.

T* (*C*

TC6

(6

T (5

C5TC2

(2

T (+

C+T

C4

4

2

6

3ШIS;ATI;3TRA3S#;R7,R

R R

R

R

)

AC

I3P=T

5

3Ш

7C )

3Ш

I3&=CTI;37;T;R

)

3

)

+ C;33,CTI;3

)

T

3R)

#IRI3( =3IT

T

T

T

TT

*

6

5

2

+

4

(4

#ig T<R,, P<AS, AC 9;TA(,

C;3TR;,R @IT< 7;T;R ;A&

*. The connections are made as shown in the circuit of three phase AC voltage controller

with 7otor load using Isolation transformer.

4. Connect output terminals R ' ) of isolation transformer 0star connected1 to respective

terminals R ' ) of power module ' firing unit.

5. The gate cathode terminals of the 2 SCRFs are connected to the respective points on the

firing unit.

6. Chec" all the connections and conform connections made are correct before

switching on the instrument.

:



+. Geep firing angle "nob at minimum position.

2. Switch on three phase suppl! power unit as well as firing unit.

H. The output wave forms are seen on a CR;.

:. The firing angle is varied and AC output voltage is noted.

. Tabulate values in the table. 0refer given table1.

*8. A graph of speed verses firing angle is plotted.

E,PERIMENTAL OSERVATIONS:

FOR R LOAD.

Sl. 3o.

#iring anglein degrees

oad voltage0line to line1 9AC

in volts

FOR MOTOR LOAD.

Sl. 3o.

#iring anglein degrees

Speed in rpm

RESULT: Three phase AC voltage controller is constructed ' studied.

3 three ph ac voltage controller.doc

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