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    AC CONTROLLERS

    (EEL 744)

    Department of Electrical Engineering,Indian Institute of Technology, Delhi,

    Hauz Khas, New Delhi-10016, India- 110016email: [email protected], [email protected]

    Ph.:011-2659-1045

    Prof. Bhim Singh

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    Lecture - 4

    2

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    Three Phase AC VoltageController

    3

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    Three phase ac voltage controllers

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    These three controllers can be used for an inductionmotor as

    Soft starters;

    Energy saving controllers;

    Solid state speed controllers.

    Applications

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    Salient features as soft starter

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    Step less control of motor three phase voltage. Flexibility is more due low power control circuitry. Smooth acceleration and deceleration of the three phase motor.

    Easy implementation of current control. Simple protection against single phasing or

    unbalanced operation in three phase motors. Absence of current inrush.

    Low maintenance for applications requiringfrequent starting and stopping.

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    Soft start of three phase induction motors

    SIRIUS 3RW40 (Siemens) is the star among our standard soft starters. It is not just the only 2-phase-controlled soft starter in the world for use in the power range up to 250 kW (at 400V) respectively 300 hp (at 460V)

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    AC Voltage Controllers

    7

    Salient features as energy saver

    The motor losses primarily depend on three factors:

    o Loading on the motor

    o Magnitude of applied voltage and

    o Quality of motor construction.

    The most significant factor is motor loading.

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    Soft start and speed control ofprocess of Sugar mills

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    Material handling and conveyorequipment for Food Processing

    Industry

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    Soft start and speed control motorsused in Chemical Industry

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    In Cement and fertilizer industry the AC voltagecontrollers are used for soft starting and speed

    control

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    Applications 3- phase ac controller

    Gang ripsaws (1.63 kW saving for50 hp motor)

    12

    WoodworkingMachinery

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    Applications three phase ac controller

    Speed control of Drill presses13

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    Applications three phase ac controller

    Speed control of Cutoff saw used to cut metal pieces

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    Speed control of Lathe

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    Machine tools

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    On load transformer tap changer (OLTC)

    This is used to change the tapping of transformer without switching off the supply

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    High pressure Blowers

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    Speed control of High pressure Blowers

    Pressure blowers provide air for Burners,Furnaces, High pressure process applications,Water treatment plants, Dairy, Ceramic

    plants, Textile plants and many Conveyingsystem.

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    Three phase booster pumps

    Three phase booster pumps are used by firedepartments and sprinkler systems to control the

    pressure of liquid

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    A three phase booster pump is used for boosting thenormal system pressure. Used by fire departments, sprinkler systems, heatingsystems, fluid storage tanks, pools, dairies, food

    processing plants, commercial industries, industrial plants, aerospace, mining, etc.

    The fluid types that they pump range from wastewater,salt water, sewage, sludge, ash, liquid metal, gasoline, oillubricants, chemicals and coolants. The three phase

    booster is used on so many different types of applicationsincluding pumping uphill beyond the lift of another

    pump.

    Speed control of booster pumps

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    Three phase air compressor

    Three phase voltage controller controls themaximum tank pressure

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    Three phase air compressor

    The three phase air compressor has a closed loopcontrol on the maximum tank pressure using three

    phase voltage controller while the regulator sets the pressure to the air hose. There are thin metal valves thatopen and shut with air pressure. The cooling finsdissipate heat that is produced by any compression. Therate at which a three phase air compressor can deliver avolume of air is done in cubic feet per minute. Due tothe fact that atmospheric pressure plays a role in howfast air moves into the cylinder, the cubic feet per minute will vary.

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    Three phase conveyor belt

    The speed of the conveyor belt can be controlled by using three phase voltage controller

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    Speed control of conveyor belt

    using ac voltage controller A three phase conveyer belt consists of two or

    more pulleys. One or both of the pulleys are powered, moving the belt with the materialon the belt forward. The powered pulley iscalled the drive pulley and the non powered

    pulley is called the idler.

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    Temperature adjustment of kiln

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    Temperature adjustment of three phase kiln

    The three phase kiln was designed to dry,harden or burn materials during it's operation,depending on exactly what type of applicationyou are going for. Grains can be dried in a three

    phase kiln as timber can be dried to cure it. Clayis hardened through a three phase kiln whichactually turns it into ceramic as it changes thechemical composition of the clay. Wood can beturned into charcoal through the burning stageof the three phase kiln.

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    Three Phase Chain Hoist

    Three phase chainhoists are used onlarger industrial

    equipment that is being moved

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    Speed control of Chain Hoist

    Three phase chain hoists are sometimes equippedwith an electric trolley as well. This makes itmuch easier when trying to move heavy

    loads. Most three phase chain hoists are used onlarger industrial equipment that is beingmoved. Three phase chain hoists improveefficiency in the most severe work environments.

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    Three Phase Grain Mixer

    Speed control of Grain Mixer which

    mixes food grains

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    Speed control of Grain Mixer

    The three phase grain mixer is used to mixand blend uniformly, particles of grains of different sizes, moisture content and bulk density. Mixing grains requires motion of the

    particles, which is what the three phase grainmixer does. This is done with mechanical

    forces from the three phase grain mixer withaugers, reels, chains and drums.

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    Applications three phase ac controller

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    Thyristor controlled reactor

    A

    B

    C ic

    i b

    ia

    T4T1

    T6

    T3

    T2T5

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    Applications three phase ac controller

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    Thyristor switched capacitors

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    Speed control and soft start of motors inPrinting machine

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    Three phase full wave controllers ACVoltage controller

    34

    Load

    VAN

    VBN

    VCN

    Van

    V bn

    Vcn

    R R

    R

    ia

    i b

    ic

    T1

    T4

    T3

    T6

    T5

    T2

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    Instantaneous input phase voltages

    the instantaneous input line voltages

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    2 sin

    22 sin( )3

    42 sin( )

    3

    AN s

    BN s

    CN s

    v V t

    v V t

    v V t

    6 sin( )6

    6 sin( )27

    6 sin( )6

    AB s

    BC s

    CA s

    v V t

    v V t

    v V t

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    Three phase full wave controllers AC Voltage controller

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    For 0 60 before the T 1 conducts two thyristors conduct.

    Once T 1 is fired, three thyristors conduct. A thyristor turns offwhen its current attempts to reverse. The conditionsalternate between the two and three thyristors.

    For 60 90 , only two thyristors conduct at any time.

    For 90 150 , although two thyristors conduct at anytime, there are periods when no thyristor conducts.

    For 150 , there is no period for two conducting thyristorsand the output voltage becomes zero at = 150

    37

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    1/22 2

    o 0

    2 2/3 /2

    /4

    1/22 2 22 /3 /2

    /3 /2 2 /3

    1/2

    1V ( )

    2

    2 sin sin6 ( ) ( )2 3 4

    0

    sin sin sin( ) ( ) ( )

    3 4 3

    1 sin

    60

    26

    6 4 8

    an

    s

    s

    F

    v d t

    t t V

    o

    d t d t

    t t t d t d t d t

    V

    r

    For 1/22 25 /6 /3 5 /6 /3

    o /2 /3 /2 /3

    1/2

    o

    2 sin sinV 6 ( ) ( )2 4 4

    1 3sin 2 3 cos 26

    60 90

    12 16 1

    6

    s

    s

    t t V d t d t

    V

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    2 21/2

    /2 /3 /2 /3

    1/2

    2 sin sin6 ( ) ( )

    2 4 4

    1 5 sin 2

    90 1

    3cos26

    24 4 1 16

    50

    6

    o s

    s

    For

    t t V V d t d t

    V

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    In the absence of a neutral connection, two thyristorsappear effectively in series with the load across thesupply.

    Therefore, for current to flow through the load, at least

    two thyristors must conduct simultaneously. Pulses are applied at intervals of 60 to various

    thyristors in sequence the same as that of the supplyvoltage

    For triggering angles exceeding 90 each thyristor isswitched on by both the leading and delayed pulses,thereby conducting twice in each cycle

    Three-phase star connected load

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    Voltage waveforms for 3-wire star connected load firing angle =041

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    Voltage waveforms for 3-wire star connected load at =30=3042

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    Voltage waveforms for 3-wire star connected load =60 43

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    Voltage waveforms for 3-wire star connected load =12044

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    The firing angles between zero and 60 the mode ofoperation in which either two or three lines conduct isreferred to as 2/3.

    Mode2/2 and mode 0/2 describe the operation of thecircuit for firing angles ranging from 60 to 90 and from90 to 150 respectively

    Due to the different switching patterns, the load voltagesfor the three modes are also different. Let the supplyvoltages be

    U is the unit vector

    2 sin

    2 sin( 2 / 3)

    2 sin( 2 / 3)

    A

    B

    C

    v V t

    v V t

    v V t

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    exp

    ( ) ( / 3)1

    ( / 3

    2 / 3

    ) ( / 3 )2

    ( / 3 ) ( 2 / 3)

    1( 2 / 3) ( 2 / 3 )

    2( 2 / 3 ) ( )

    (0 / 3)

    a A

    AB

    A

    AB

    A

    Theload voltageover the first half

    period maybe ressed as

    v v U t U t

    v U t U t

    v U t U t

    v U t U t

    v U t t

    Mode

    U

    Modes of operation with 3-phasestar connected load

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    01

    1

    2 2

    2

    0 0

    2

    0

    2

    0

    / 2 sin( )

    tan

    1

    1cos( )

    1sin( )

    a n nn

    nn

    n

    n n n

    a

    n a

    n a

    v a c n t

    awhereb

    c a b

    a v d t

    a v n t d t

    b v n t d t

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    0

    1

    1

    2

    2

    0

    1 2 3 sin21 3

    2 3 cos sin2 2

    ' ' . 2 ,

    int0

    0

    n n

    k

    k

    a

    a

    b

    Furthermore it can be shown that for even valuesof n coefficients a and b are zero Putting n k

    where k is is any positive eger a

    b

    Fourier analysis

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    2 1

    2 1

    , 2 1cos cos

    1 ( 1) sin / 62 ( 1)

    sin sin 1 ( 1) sin / 62 ( 1)

    in3 , .

    k k

    k k

    For odd values of n that is n k n

    a nk k

    nb nk k

    no triplen harmoniccurrents can exist the linesof wire balanced load The highest orders of harmo 1, 5, 7nics are found tobe n n n as

    shown in next slide

    Fourier analysis contd..

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    Load and line current harmonics of thyristor controller with3-wire resistive load

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    0

    1( ) ( / 3)

    2 / 2

    21

    ( / 3) ( 2 / 3)

    ( / 3 / 2)

    2

    exp

    0

    a AB

    AC

    Theload voltageover theone half period is givenby

    v v U t U t

    v U t U t

    Fourier coefficients for the above ressionare fou

    Mode

    nd tobe

    a

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    1

    1

    2

    2

    3 3 2 3cos sin

    4 2 3 2

    3 3 2 3cos cos

    4 2 3 2

    00

    k

    k

    a

    b

    ab

    Fourier analysis contd..

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    2 1

    2 1

    3 (2 1)cos

    6

    sin / 3sin 2 / 3

    sin( 1) / 3sin 2( 1) / 3

    13 (2 1)

    cos6

    sin / 3cos 2 / 3

    sin( 1) / 3cos 2( 1) / 3

    1

    k

    k

    k a

    k k k

    k k

    k k

    b

    k k k

    k k

    k

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    0

    1

    sup exp

    1( ) ( / 3)

    2

    1 ( / 3) ( 2 / 3)2

    mod

    0

    0 / 2 ( / 2 5 / 6)

    3 52

    4 3

    a AB

    AC

    The load voltageover the first half

    period of the ply cycle may be ressed as

    v v U t U t

    v U t U t

    The Fourier coefficients pertaining to this e are

    a

    a

    Mode

    3 1sin cos

    2 2

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    1

    2 2

    2 1

    2 1

    3 5 3 32 cos sin

    4 3 2 2

    0 ; 0

    3 (2 1)cos

    2 6

    cos 1 / 3 cos( / 3) cos1 ( 1)

    3 (2 1)cos 6

    sin 1 / 3 sin( / 3) sin1 ( 1)

    k k

    k

    k

    b

    a b

    k a

    k k nxk k k k

    k b

    k k nxk k k k

    Th h f ll t ll ith diff t

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    Three phase full wave controllers with differentloads

    56

    Load

    A

    B

    C

    N

    A1

    A2B1

    B2C1

    C2

    N

    Z1

    Z2 Z3

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    Three phase full wave controller with inductive load

    57

    Load

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    Three phase full wave controller with motor load

    58

    Load

    I M

    Line controlled delta connected load

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    A

    B

    C

    A 1

    A 2

    B 1

    B 2

    C 1

    C 2

    Z 1 Z 3

    Z 2

    a

    b

    c

    Line controlled delta connected load

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    Voltage waveforms for thyristor controller with line controlleddelta connected resistive load =30

    60

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    Voltage waveforms for thyristor controller with line controlleddelta connected resistive load =60

    61

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    Voltage waveforms for thyristor controller with line controlled

    delta connected resistive load =90 62

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    Voltage waveforms for thyristor controller with line controlled

    delta connected resistive load =120 63

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    exp

    ( ) ( 2 / 3)

    ( 2 / 3) ( 2 / 3 )2

    ( 2 / 3 ) ( )

    2 / 3(0 / 3

    ( ) (

    )

    )2

    ab AB

    AC

    AB

    CB

    Theload voltageover the first half

    period may be ressed as

    v v U t U t

    vU t U t

    v U t U t v

    U t U

    M e

    t

    od

    Fourier analysis

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    0

    2

    2

    03 3 2 3

    cos 2 sin 24 3 2 6

    3 3 2 13 sin 2 cos 2

    4 2 63

    int0

    0

    n

    n

    k

    k

    The Fourier coefficients are found tobe

    a

    a

    b

    for any positive eger k a

    b

    Fourier analysis

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    F i l i d

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    2 1 3 cos(2 1) / 3 2cos 2 / 32* cos(2 1) / 3 cos 2 (2 1) / 3

    3cos(2 1) / 3 2cos 2( 1) / 3

    2( 1)

    * cos(2 1) / 3 cos 2( 1) (2 1) / 3

    k b k k kxk k k

    k k k

    k k k

    Fourier analysis contd..

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    mod

    ( ) ( / 3)

    ( / 3) ( 2 / 3)2

    2 / 2( / 3 / 2

    ( 2 / 3) ( )2

    )

    ab AB

    AC

    CB

    Theload voltage for this eof operationis

    v v U t U t

    v U t U t

    vU t

    Mode

    U t

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    A

    B

    C

    For small motors anti-parallel thyristor pairs can bereplaced by a triac.

    Three phase ac voltage controllers

    Three phase ac voltage controllers

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    A

    B

    C

    N 0 p

    pwt

    VAN IA

    gHold offAngle

    Three phase ac voltage controllers

    Three phase ac voltage controllers for speed

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    A

    B

    C

    InductionMotor

    A

    B

    C

    C

    A

    p g preversal using static state devices

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    A

    B

    C

    InductionMotor

    A

    B

    C

    Three phase ac voltage controllers for speedreversal with contactors

    Three phase bidirectional delta connected controllers with

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    resistive load

    73

    A B C

    ici bia

    T 4

    T 1

    T 6

    T 3

    T 2

    T 5

    iab

    ica i bc

    b

    ac

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    Waveforms of three phase bidirectional delta connected

    controllers 74

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    Three phase bidirectional delta connected controllers withinductive load

    75

    A

    B

    C ic

    i b

    ia

    T4T1

    T6

    T3

    T2T5

    A 3 h t t d t ll ith i t l d h

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    A 3-phase star connected ac controller with resistance load has

    power dissipation of 10 kW at 30 firing angle, ac mains 415V,

    50Hz. Compute (i) value of resistance in each phase, (ii) supplyrms, and fundamental currents and (iii) power factor.

    0in 0

    S

    12

    00 S

    12

    0

    Solution: 3-ph Y-connected, V =415V, 50Hz, P =10kW at =30

    415i) V /phase= =239.6V

    3

    1 sin2V = 6*V - + for 0<

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    2

    3

    S

    2 2s1

    0

    (234.361)Resistance/phase = = 16.4775

    1 *10*103

    V /phase 234.361ii) Supply rms current = = =14.22Aresistance/phase 16.4775

    Fundamental current =

    VI = 2 3 sin + 2 3 cos 3sin2 R =14.02A

    P /piii) p.f=

    3

    ph ph

    1 *10*10hase 3= =0.978V *I 239.6*14.22

    A three-phase bidirectional delta connected controller (back-to-back connected

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    A three-phase bidirectional delta connected controller (back-to-back connected

    thyristors in series with load) has resistive load of R=20 ohms and fed from

    415V rms line voltage at 50 Hz. If output power of 10 kW is desired then,

    calculate (i) firing angle of thyristors, (ii) the rms output voltage, (iii) rms phase

    current, (iv) rms line current, and (v) input power factor.

    0

    30

    30

    0

    Solution: 3-ph -connected, = 415V, 50Hz, =10KW, R=201/ = *10*10 =3333.33W3

    1ii) Rms output voltage = / *10*10 *20 =258.19V3

    1 sin 2firing angle of thyristors:2

    in

    S

    V P P phase

    V phase

    V V

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    0

    3

    0

    1 sin 2258.19 415*

    2

    1801.75 ' 1.75* 100.27

    258.19rms phase current ; 12.909

    20rms line current: 3 *12.909 22.359

    1 *10*10/ 3input power factor: .* 415*12.909

    ph

    rms

    ph ph

    I A

    I A

    P phase p f

    V I 0.622

    A three-phase six-pulse 50 kVAR TCR (thyristor controlled reactor consisting

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    A three phase, six pulse 50 kVAR TCR (thyristor controlled reactor consisting

    back-to-back connected thyristors with pure inductor) has an input line-line

    voltage of 415V, 50Hz, AC supply and a set of three inductances, which are

    connected in delta. Calculate (i) inductance rating, (ii) rms inductor current, (iii)

    maximum THD of phase current and its value and corresponding delay angle.

    2

    2

    3-ph, 6-pulse, TCR, =415V, 50Hz, -connected inductors

    inductance rating: /

    50000 41510.335

    3

    L = = 32.89mH

    iii)maximum THD of phase current and corresponding delay angle:

    maximum TH

    in

    L

    L L

    L

    V

    V Q phase

    X

    X X

    X

    D can be obtained by making 0nd

    I d

    hich gi es cos * cos 0n

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    0

    2

    which gives cos * cos 0making cos =0; in the phase winding of deltaconnected inductor 3rd harmonic is most dominant

    one. i.e n=3, which gives =30rms inductor current

    sin 212 sin2

    s

    rms

    n

    V I

    L

    2

    2

    2

    =11.81A

    2 sin 21 =11.102A

    2 *11.81

    1 36.3%11.102

    s F

    s

    V I

    L

    THD

    A three-phase bidirectional delta connected controller (back-to-back connected

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    thyristors in series with load) has resistive load of R=10 ohms and fed from 415V

    rms line voltage at 50 Hz. If firing angle of thyristors is 30 then, calculate (i) output

    active power, (ii) the rms output voltage, (iii) rms phase current, (iv) rms line

    current, and (v) input power factor. [20]

    oin

    0

    0

    2 20

    ph

    Solution: 3-ph -connected, V = 415V, 50 Hz, R=10 ,=30

    1 sin2V =415* -+ 2

    (ii) V =408.97V

    (i) output power = 3V /R=3x408.97 /10=50.176kW

    408.97(iii) rms phase current ; I = =40.8A10(iv) ph

    rms

    So taking rms line current = 3 * I

    rms line current:I =70.25A (simulation results)

    aThe rms line current i =

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    2

    2

    ab s ca s

    22

    s2

    22 2s

    2

    1= ( ) .

    1 .

    4where v = 2 V sin , v = 2 V sin -

    3

    2 V 4sin sin - .3

    2V 4sin sin -

    3

    ab ca

    ab ca

    i i d

    v v d R R

    d R

    R

    2s2

    s L

    42sin *sin -

    3

    2V 3 13 cos(2 120) sin ( 240)

    2 2

    50.176k (v) input power factor: p.f = =0.985

    3*V *I

    d

    R

    R f

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    References

    W. Shepard Thyristor control of AC circuits BradfordUniversity Press, London M. H. Rashid, Power Electronics, circuits, Devices and

    Applications, Second Edition, Prentice-Hall, 1995, India,ISBN 81-203-0869-7.

    G. K. Dubey, S. R. Doradla, A. Joshi and R. M. K. Sinha,Thyristorised Power Controllers, Willey Eastern, 1986,New Delhi, ISBN 0-85226-190-X.