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Electrical machines and drives practical, Lab Reports of Electrical and Electronics Engineering

Lab file with explainations to experiments

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2020/2021

Uploaded on 06/08/2021

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Submission by SRISHTI MITTAL 101805029 3EIC2
Experiment 1 : Single Phase AC to DC Power Converter (Fully Controlled).
Objective: To verify experimentally the operation of single phase full Converter
Apparatus: : (1) Converter Trainer kit (2) Load Resistance (3) C.R.O.
(4) Single phase Variac (5) Isolation Transformer
Theory/Working:
Here there are 4 thyristors used in the circuit. So it is called fully controlled converter.In half
controlled converter , there 2 diodes and 2 thyristors used.DC voltage(input to motor and it
is output after converting AC->DC) is used to control speed of motor(DC). To control DC input
voltage, we have to control AC input voltage or we can directly control DC output BY use of
thyristors.
In positive half cycle , thyristor 1 and 4 will work and in negative half cycle thyristor 2 and 3
will be on.So In both cases the voltage across load will be positive as current is moving in same
direction from +ve to -ve.Current will be unidirectional. It is the reason why 1st and 4th
quadrant operation will work here.The SCR will not turn ON if anode to cathode voltage is
+ve.It will turn ON if gate current is applied.
Gate current we can give at a firing angle from 0 to 180 degree.So duration of the on period
of thyristor can be controlled.To increase the output voltage , firing angle should be less. As
ON period is more . So speed will be more at lesser firing angle.
To measure firing angle - 1 division value is 18 degree.so according with 2 divisions the firing
angle wil be 72 degree.
T1,T4 will conduct from alpha to (pi+alpha). Only for 180 degree.After that T2 and T3 will
conduct from pi+alpha. During the time period [0 to alpha] and [pi to pi+alpha] the thyristor
is forward biased but not in conductive state.
So output voltage during that time period will be 0 and current will be linearly decreasing.It
is important that the thyristors completely turn off before turning on the next thyristor,
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12

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Submission by SRISHTI MITTAL 101805029 3EIC

Experiment 1 : Single Phase AC to DC Power Converter (Fully Controlled). Objective: To verify experimentally the operation of single phase full Converter Apparatus: : (1) Converter Trainer kit (2) Load Resistance (3) C.R.O. (4) Single phase Variac (5) Isolation Transformer Theory/Working: Here there are 4 thyristors used in the circuit. So it is called fully controlled converter.In half controlled converter , there 2 diodes and 2 thyristors used.DC voltage(input to motor and it is output after converting AC->DC) is used to control speed of motor(DC). To control DC input voltage, we have to control AC input voltage or we can directly control DC output BY use of thyristors. In positive half cycle , thyristor 1 and 4 will work and in negative half cycle thyristor 2 and 3 will be on.So In both cases the voltage across load will be positive as current is moving in same direction from +ve to -ve.Current will be unidirectional. It is the reason why 1st^ and 4th quadrant operation will work here.The SCR will not turn ON if anode to cathode voltage is +ve.It will turn ON if gate current is applied. Gate current we can give at a firing angle from 0 to 180 degree.So duration of the on period of thyristor can be controlled.To increase the output voltage , firing angle should be less. As ON period is more. So speed will be more at lesser firing angle. To measure firing angle - 1 division value is 18 degree.so according with 2 divisions the firing angle wil be 72 degree. T1,T4 will conduct from alpha to (pi+alpha). Only for 180 degree.After that T2 and T3 will conduct from pi+alpha. During the time period [0 to alpha] and [pi to pi+alpha] the thyristor is forward biased but not in conductive state. So output voltage during that time period will be 0 and current will be linearly decreasing.It is important that the thyristors completely turn off before turning on the next thyristor,

because then the circuit will be damaged if all the thyristors are in working mode.So between pi to pi+alpha , no thyristor is working.Two thyristors are gradually getting turned off and the other ones is not triggered yet. Observation Table: S. No. Firing Angle Average Output (v) Load current(A) Speed (rpm)

  1. 72 152 0.2 A 1504
  2. 90 135 0.25 A^1334
  3. 108 110 0.19A 1058 Electrical input power = V*I , If voltage is decreasing then input power supplied to motor also decreases. Because of this motor speed decreases. This experiment works in 2 quadrant operation.1st^ and 4th. In 1st^ voltage and current is positive and in 4th^ quadrant , current is positive and voltage is negative. So power is positive and negative respectively.When it is positive power , it is called forward motoring and when it is negative power , it is called reverse regenerative braking. Questions:
  4. What is one quadrant and two quadrant operations of phase controlled Rectifier? Ans: One quadrant operation is when the voltage and current are positive and they cannot be negative.Half controlled converter works on 1st^ quadrant whereas fully controlled Converter works on 1st^ and 4th^ quadrant.
  5. Why is it important to use absolutely matched SCRs in the circuit? Ans: For high current applications , SCRs must be connected in parallel with each other to increase their common current capability.If the SCRs rating are not matched perfecting they will carry unequal current.Eg SCR1 will carry I1 and SCR2 will carry I2.But I1 will be much less than its rated current.
  6. Mention the applications of single phase fully controlled converter? Ans: Speed control of DC motor, Battary Charging

Observation Table: S. No. Firing Angle Average Output (v) Load current(A)

  1. 0 149.2^ 0.
  2. 18 144 0.
  3. 36 130 0.
  4. 54 110 0.
  5. 72 83 0.
  6. 90 60 0.
  7. 108 36 0. Electrical input power = V*I , If voltage is decreasing then input power supplied to motor also decreases. Because of this motor speed decreases. This experiment works in 1 quadrant operation.1st^ quadrant only. In 1st^ voltage and current is positive. So power is positive. Questions:
  8. Mention the applications of single phase half controlled converter? Ans: Speed control of DC motor, Battary Charging

Experiment 3: Three Phase fully controlled converter to control DC Drive. Apparatus Required: Sr. No. Apparatus Specification

  1. Three phase Bridge Converter Kit Fully controlled
  2. Three phase Firing circuit Three phase
  3. C.R.O Normal
  4. D.C Shunt Motor .37 kW, 230 V
  5. Tachometer Contact Type For 120 degree mode of conduction , two thyrsitors will work at a time , for a period of 60 degree.so in 360 degree , 6 pulses will be generated.[T1,T6],[T1,T2],[T2,T3],[T3,T4],[T4,T5],[T5,T6] like this thyristors will conduct. Every thyristor conducts for 120 degree.Free wheeling diode has to be connected across the load.It is for prevention of development of high voltage across switches. When the inductive circuit is switched off, this diode gives a short circuit path for the flow of inductor decay current and hence dissipation of stored energy in the inductor. This diode is also called Flywheel or Fly-back diode.

Experiment 4: Three Phase half controlled Converter to control DC Drive. Apparatus Required: Sr. No. Apparatus Specification

  1. Three phase Bridge Converter Kit Half controlled
  2. Three phase Firing circuit Three phase
  3. C.R.O Normal
  4. D.C Shunt Motor .37 kW, 230 V
  5. Tachometer Contact Type Circuit diagram: This consists of 3 thyristors T1,T3 and T5 And 3 diodes D2,D4 and D6. A free-wheeling diode FD is connected in parallel with the load, which is connected across the o/p terminals of half converter.So when the circuit is not conducting , that when it is ints off circuit time , the current stored in the load gets a path through the free wheeling diode , as the circuit becomes shorted. Observation table: S. No. Firing Angle Average output Speed (rpm)
  6. 6.7 197 1286
  7. 13.4 194 1260
  8. 20.1 190 1246
  9. 26.8 184 1216

Experiment-5: SPIM - Single phase Induction Motor variable speed Drive. Apparatus Required: S.NO Apparatus Specification

  1. SPIM Trainer Kit Trainer Module
  2. Induction Motor 0.37 KW ,230V
  3. AC voltmeter 0 - 300 v
  4. C.R.O Double Beam
  5. Tachometer Digital Circuit Diagram THEORY: Basic working of single phase inductor - If we apply ac supply , its magnitude is changing of sinusoidal voltage. Flux is changing.So emf will be induced .E=Nd(phi)/dt.Because of closed path , current will flow and when current carrying conductor is placed in a magnetic field , it will start experiencing a force and start moving. Speed control of single-phase induction motors is desirable in most motor control applications since it not only provides variable speed but also reduces energy consumption
    1. 61 1800 30.
    1. 61 1900 32.
    1. 62 1990 34.

Experiment 6: Performance Analysis of AC Servomotor Drive. Apparatus Required: S.NO Apparatus Specification

  1. AC Servo motor drive Seimens

  2. Induction Motor 3H.P, 3 Phase, 400V

  3. Tachometer Non Contact type Circuit Diagram Theory: Components used in AC servo motor 3 phase supply RYB is given. Selector switch for selection of R,Y,B. Isolators - source isolated with load during off load condition. MCB is used for protecting heavy current to load during load condition. Fuse wires - to protect heavy current from affecting load.Circuit Breakers. Application in high power application like inverter , refrigerator. In servo motors , speed control is done by using resistance drop.By varing resistance, voltage drop across it happens just like voltage regulator in fans , uses the variac resistances. It is highly non linear circuit because of highly inductive nature of motor , because of windings. Magnetic field is non-linear. Air gap length is also responsible for non-linear characteristic.

Experiment 7: Performance Analysis of DC Digital Master Drive. Apparatus Required: S. NO Apparatus Specification

  1. DC digital Master Drive kit Siemens
  2. DC motor 3 H.P, 400V
  3. C.R.O Normal
    1. Tachometer Non Contact type Theory: DC motor drives means speed of the motor should be within the control. DC motor works on DC supply. Types of motor: 1.Seperately excited There is a Armature conductor. Inductance is developed in this winding and Back emf developed in the armature. Currents passing through the armature conductor. Other part which is the field winding is magnetising the circuit .So armature carrying conductor is placed near magnetic field and this is why it is called separately excited DC. Current carrying conductor placed in a magnetic field experiences force and starts moving. Field winding separately excites the armature winding.

To control speed of motor we can apply DC to DC chopper based on the duty cycle.Or just control the field winding current by inserting some variable resistance. 2.Shunt Motor Field winding excited by same source and in parallel with armature , it is called shunt Current is flowing through armature.Same current (because in parallel) magnetises the field winding. In magnetic field, current carrying conductor is placed.But the resistance of field winding is more than armature, so that the current doesnot bypass armature - it passes through it.The field winding shouldnot saturate- the magnetic flux should not reach maximum, so less amount current should pass through field winding. If magnetic field gets saturated , It is of no use to us.Also if very little goes to field winding, flux produced will be less and motor will not move. 3.Series Motor Field winding is in series with armature. Magnetic field current equal to armature current.It is called DC series motor and used for high power application - locomotives because of its high starting torque. 4.Cumulatively compound Motor Use of S1, S2 - is for control of flux. Flux developed by field winding and S1S2 may get added or subtracted to decrease or increase flux. There are two methods of joining the S1S2 BY Differential and additive method.Net flux will reduce and increase respectively. 2 terminal is series motors and 4 terminal is separately excited -> 2 of field and 2 of armature. Some components : Motor blower - for heat dissipation. To run that blower 3 phase suppy is required, so used just for cooling purposes.Field winding at bottom.Connectors - just to give the path.Switches to give supply to IC.Thyristor protection is imp , from thermal protection , voltage overload. Speed control can be from armature or field winding. Direction of motor can be reversed. Speed vary through pot.HRC fuse is used.Motor rpm is 1500 , Voltage-220 V. In this experiment , DC shunt motor was used.Speed control is done with resistance method by armature winding-current going into armature is controlled by changing the value of resistance. Field gets supply and armature voltage is controlled by pot .If field was controlled by pot , then field current would have been measured. So there is a variac resistance between armature and supply. Observation: S.NO Voltage to Motor Speed

  1. (^60 )
  2. (^160 )
  3. (^190 )
  4. 260 1372
  5. (^340 )

the same time if we decrease voltage flux will also decease causing no change in flux and hence it remains constant keeping the ratio of V/f as constant. Hence its name is V/ f method. For controlling the speed of three phase induction motor by V/f method we have to supply variable voltage and frequency which is easily obtained by using converter and inverter set. Observation: S. NO Output Voltage Speed Output frequency V/f

  1. 60 285 9.53 6.
  2. 160 570 .5 19.11 8.
  3. 240 853.5 28. 84 8.
  4. 300 1136 3 8.82 7.
  5. 400 1468 49.52 8.

Experiment 9: Speed Control of 3 phase induction motor by pole changing method Apparatus Required: Sr No. Apparatus

  1. 3 phase induction motor
  2. AC Ammeter
  3. DC Voltmeter Theory: By pole changing method , we can control the speed of the motor by changing the number of stator poles.As frequency is constant , the synchronous speed will be Ns=120f/P Where Ns = Synchronous speed ,P=no of poles and F= frequency