Electrical Drives Lab

Diploma

VIth Semester

Electrical & Electronics Engineering

List of Experiments

1. To Study 1-phase Half & Full Controlled Converter. 2. To study Characteristics of 1-phase Cycloconverter. 3. To study the construction of a three phase induction motor with the help of a

model. 4. To study about the starters of three phase induction motors. 5. To study about the power modulator & control unit.

6. To perform the Speed control of DC shunt Motor by Armature control.

7. To Start DC shunt motor by using three point starter.

8. To obtain the Speed control of DC shunt Motor by Field control.

9. To study about the detailed structure of wind power station.

EXPERIMENT NO. 1

AIM:-TO STUDY SINGLE PHASE HALF & FULL CONTROLLED CONVERTER.

APPARATUS REQUIRED:-

1. Power Thyristors

2. Rheostat

3. CRO

4. Transformer (1-phase) 230V/24V

5. Connection wires

THEORY:-

A semi converter uses two diodes and two thyristors and there is a limited control over the level of dc output voltage. A semi converter is one quadrant converter. A one-

quadrant converter has same polarity of dc output voltage and current at its output terminals and it is always positive. It is also known as two-pulse converter.

Vout=(√2Vs)(1+Cosα)/π

A fully controlled converter or full converter uses thyristors only and there is a wider

control over the level of dc output voltage. With pure resistive load, it is single quadrant

converter. Here, both the output voltage and output current are positive. With RL- load it

becomes a two-quadrant converter. Here, output voltage is either positive or negative but

output current is always positive. Figure shows the quadrant operation of fully controlled

bridge rectifier with R-load.

Vout= (2Vs) (Cosα)/π & Iavg=Vavg/R

CIRCUIT DIAGRAM:-

Fig-Half-Controlled Converter

Fig-Fully-Controlled Converter

OUTPUT WAVEFORM:-

Fig-Waveform for Half-Controlled

Fig-Waveform for Fully-Controlled

OBSERVATION TABLE:-

PROCEDURE:-

Procedure for Half-Controlled:

1. Make the connections as per the circuit diagram.

2. Connect CRO and voltmeter across the load.

3. Keep the potentiometer at the minimum position.

4. Switch on the step down ac source.

5. Check the gate pulses at G1-K1 & G2-K2, respectively. 6. Observe the wave form on CRO and note the triggering angle ‘α’ and 7. Note the corresponding reading of the voltmeter. Also note the value of Maximum amplitude Vm from the waveform. 8. Set the potentiometer at different positions and follow the step given in (6) for every position. 9. Tabulate the readings in the observation column.

Procedure for Fully-Controlled:

1. Single Phase Fully Controlled Bridge Rectifier

2. Make the connections as per the circuit diagram.

3. Connect CRO and multimeter (in dc) across the load. 4. Keep the potentiometer (Ramp control) at the minimum position (maximum resistance). 5. Switch on the step down ac source.

6. Check the gate pulses at G1-K1, G2-K2,G3-K3,& G4-K4 respectively. 7. Observe the waveform on CRO and note the triggering angle ‘α’ and note the corresponding reading of the multimeter. Also note the value of maximum amplitude Vm from the waveform. 8. Set the potentiometer at different positions and follow the step given in (6) for every position. 9. Tabulate the readings in observation column.

10. Draw the waveforms observed on CRO.

PRECAUCATION:-

1. Follow the entire recommended dimension.

2. Properly connect all the equipment.

3. Check the insulation between the probes.

4. Shoes must be part of attire while doing the lab.

5. Before giving the supply check all the connections once again.

RESULT:-

Thus the operation of single phase half controlled converter using R and RL load has been studied and the output waveforms has been observed.

EXPERIMENT NO. 2

AIM:-TO STUDY CHARACTERISTICS OF SINGLE-PHASE CYCLOCONVERTER.

APPARATUS REQUIRED:-

1. Power Electronics Trainer Kit

2. Firing Circuit

3. CRO

THEORY:-

Cyclo converter is a circuit which converts the input voltage at one frequency to the Output voltage at different frequecy.

During the positive half cycle Thyristors P1, N2 are forward biased and Thyristors P2 and N1 are reverse biased. The circuit is designed for step down cyclo converter for a output frequency of = 3 .To get the desired frequency the Thyristors are triggered accordingly.

During the first positive half cycle P1 and N2 are forward biased and to get the positive

output voltage, P1 is triggered at an angle of (π+α). During the next positive half cycle

P2 and N1 are forward biased, to get required output voltage thyristor P2 is triggered.

In the next half cycle P1 is triggered next N1, N2 and again N1 are triggered

accordingly. This process repeats.

CIRCUIT DIAGRAM:-

Fig-Single-Phase Step-Down Cyclo-Converter

OUTPUT WAVEFORM

Fig-Waveform for Single-Phase Step-Down Cyclo-Converter

PROCEDURE:-

1. Connect the circuit as shown in the circuit diagram.

2. Give the firing pulses accordingly at a suitable firing angle from the firing circuit.

3. Observe the load voltage on the CRO and note down the firing angle.

PRECAUCATION:-

1. Follow the entire recommended dimension.

2. Properly connect all the equipment.

3. Check the insulation between the probes.

4. Shoes must be part of attire while doing the lab.

5. Before giving the supply check all the connections once again.

RESULT:-

Thus the operation of single phase Cyclo-converter using R load has studied and the output waveforms has been observed.

EXPERIMENT NO. 3

AIM: - TO STUDY THE CONSTRUCTION OF A THREE PHASE INDUCTION MOTOR WITH THE

HELP OF A MODEL.

Theory: The induction motor essentially consists of two parts:

· Stator

· Rotor.

The supply is connected to the stator and the rotor received power by induction caused

by the stator rotating flux, hence the motor obtains its name –induction motor.

The stator consists of a cylindrical laminated & slotted core placed in a frame of rolled

or cast steel. The frame provides mechanical protection and carries the terminal box

and the end covers with bearings. In the slots of a 3-phase winding of insulated copper

wire is distributed which can be wound for 2,4,6 etc. poles.

The rotor consists of a laminated and slotted core tightly pressed on the shaft.

There are two general types of rotors:

· The squirrel-cage rotor,

· The wound (or slip ring) rotor.

In the squirrel-cage rotor, the rotor winding consists of single copper or aluminium

bars placed in the slots and short-circuited by end-rings on both sides of the rotor.

In the wound rotor, an insulated 3-phasewinding similar to the stator winding and for

the same number of poles is placed in the rotor slots. The ends of the star-connected

rotor winding are brought to three slip rings on the shaft so that connection can be

made to it for starting or speed control.

Procedure:

1) Design the rotor according to the define ratings of the machine with proper

lamination & skewing slots. 2) Make sure the rotor must be closed with end rings ifit is a squirrel cage rotor. 3) Properly design the 3-phase rotor winding as similar to the stator with each

phase 120 mechanically apart if it is a slip ring rotor. 4) Design the stator periphery with internal slots. 5) Make sure the construction of stator & rotor are in such a way that there must be

an air gap between the stator & rotor for the rotation of RMF.

Precaution:

Make sure there must be proper lamination in all the part & also in the winding in

order to reduce the losses.

Result: We studied the construction of three-phase induction motor.

EXPERIMENT NO. 4

AIM: -TO STUDY ABOUT THE STARTERS OF THREE PHASE INDUCTION MOTORS.

Theory: The most usual methods of starting 3-phase induction motors are:

1. For slip-ring motors

- Rotor resistance starting

2. For squirrel-cage motors

- Direct-on -line starting

- Star-Delta starting

- Autotransformer starting.

There are two important factors to be considered in starting of induction motors:

-The starting current drawn from the supply, and

-The starting torque.

The starting current should be kept low to avoid overheating of motor and excessive

voltage drops in the supply network. The starting torque must be about 50 to 100%

more than the expected load torque t ensure that the motor runs up in a reasonably

short time.

a. Rotor resistance starting

By adding eternal resistance to the rotor circuit any starting torque up to the maximum

torque can be achieved; and by gradually cutting out the resistance a high torque can

be maintained throughout the starting period. The added resistance also reduces the

starting current, so that a starting torque in the range of 2 to 2.5 times the full load

torque can be obtained at a starting current of 1 to 1.5 times the full load current.

b. Direct-on-line starting

This is the most simple and inexpensive method of starting a squirrel cage induction

motor. The motor is switched on directly to full supply voltage. The initial starting

current is large, normally about 5 to 7 times the rated current but the starting torque is

likely to be 0.75 to 2 times the full load torque. To avoid excessive supply voltage

drops because of large starting currents the method is restricted to small motors only.

To decrease the starting current cage motors of medium and larger sizes are started at a

reduced supply voltage. The reduced supply voltage starting is applied in the next two

methods.

c. Star-Delta starting

This is applicable to motors designed for delta connection in normal running

conditions. Both ends of each phase of the stator winding are brought out and

connected to a 3-phase change -over switch. For starting, the stator windings are

connected in star and when the machine is running the switch is thrown quickly to the

running position, thus connecting the motor in delta for normal operation. The phase

voltages & the phase currents of the motor in star connection are reduced to 1/Ö3 of

the direct -on -line values in delta. The line current is 1/3 of the value in delta.

A disadvantage of this method is that the starting torque (which is proportional to the

square of the applied voltage) is also reduced to 1/3 of its delta value.

d. Auto-transformer starting

This method also reduces the initial voltage applied to the motor and therefore the

starting current and torque. The motor, which can be connected permanently in delta or

in star, is switched first on reduced voltage from a 3-phase tapped auto -transformer

and when it has accelerated sufficiently, it is switched to the running (full voltage)

position. The principle is similar to star/delta starting and has similar limitations. The

advantage of the method is that the current and torque can be adjusted to the required

value, by taking the correct tapping on the autotransformer. This method is more

expensive because of the additional autotransformer.

Reversing:

Reversing the connections to any two of the three motor terminals can reverse the

direction of rotation of 3-phase induction motor

Procedure

1. For rotor resistance starting, connect the slip-ring motor as shown in FIG.1. Start the

motor with full starting resistance and then decrease the resistance in steps down to

zero. Take observations of the stator & rotor currents 2. For direct-on -line starting , connect the cage motor as shown in FIG.2 3. For star-delta starting , connect the cage motor to the terminals of the stardeltaswitch

(FIG.3) 4. For autotransformer starting, connect the cage motor as shown in FIG.4. Take care

at starting that the "Run" switch is open and that it is not closed before the "Start"

switch is opened.

5. In each case observe the starting currents by quickly reading the maximum

indication of the ammeters in the stator circuit. 6. Reverse the direction of rotation of the motor by reversing of two phases at the

terminal box. The reversal has to be made when the motor is stopped and the supply

switched off.

Result:

We studied the different starting methods& how to revere the direction of rotation of a

3-phase induction motor.

EXPERIMENT NO. 5

AIM: - TO START DC SHUNT MOTOR BY USING THREE POINT STARTER.

Apparatus: DC power supply, DC motor, Connection wires, Starter.

Theory: At starting, Eb =0 because speed of motor is zero. Armature current of motor is equal to, Ia = V- Eb / Ra so Ia =V/ Ra (Eb = 0) Since Ra is very small so motor will draw large armature current. To limit the armature current in safe value we add some external resistance in armature circuit. A mechanism which adds resistance during starting only is known as starter. There are two types of starters which are commonly used for d.c. shunt motor

1. 3-point starter

2. 4 - point starter

3- point starter

Three point starter is shown in the figure 1, when motor is started, starting arm is moved slowly towards the ON position 1)As soon as arm touches the stud no. 1 full starting resistance get connected in the armature circuit.

1) Field current receives supply directly The starting armature current is equal to,

Ia = V / (Ra + Rst) 2) The arm is moved against the spring force towards the ON position. 3) When the arm travels towards ON position , the starting resistance is gradually removed from

armature circuit . since motor takes full speed, motor develops full back E.M.F. the starting arm carries a soft iron piece which is held by attraction of the hold on coil. starter remains in ON position because the electromagnetism formed by NO VOLT COIL

Function of hold on (no volt coil)

1) In case of supply failure NO VOLT COIL gets de-energized and the starting arm will be released to OFF position. This is automatically done by spring action.

2) It hold the plunger in ON position 3) It gives the protection against field failure

Function of overload coil

Overload coil is a electromagnet connected in series with armature. when current exceeds beyond certain predetermined value the electromagnet will become strong and it attracts plunger. Due to this voltage across NO VOLT COIL becomes zero. this will make hold on coil de – energized due to which arm gets to OFF position and motor gets disconnected from supply.

Limitations of three point starter

1) When motor is in ON position the starting resistance gets remove form armature circuit at the same time it gets attached to field circuit, which is dangerous to the motor.

2) When we control speed of motor by field control method, resistance in field circuit reduces field current which increases the speed of motor at the same time there is chance under ON condition motor could disconnect from supply due to de energisation of HOLD ON COIL, due to less field

current. 3) 4- Point starter

4- point starter with brass arc covers limitations of 3- point starter; using brass arc covers first limitation. Making field circuit path independent of hold coil circuit by making forth point in addition with 3-point circuit covers second limitation.

When field current is reduced while controlling speed of motor will not effect on magnetic field of

hold on coil because circuit of hold coil is separate than field coil circuit as shown in the fig.2.

Figure-Three point starter

Reversal of direction of Rotation of D.C. shunt motor.

It means changing the direction of rotation of motor either in clockwise or anticlockwise

direction. This is achieved by changing the field connections or armature connections.

EQUIPMENTS:

D.C. Motor rating …………….V, ………………A, ………………KW

Three point starter.

CIRCUIT DIAGRAM

PROCEDURE :

1. Make the connection as per circuit diagram.

2. Switch on the D.C.Supply and start the motor by moving arm of the three point starter.

3. Observe the direction of rotation.

4. Switch off the supply.

5. Change the the field winding connections as per Fig.2 and by switching on the supply

observe the direction of rotation of rotation of the motor.

6. Change the armature winding connections as per Fig.3 and by switching on the supply

observe the direction of rotation of rotation of the motor.

OBSERVATIONS :

1. Table of readings for connections as shown in Fig.1.

Direction of rotation of Sr.No. Position of the observer motor

2. Table of readings for connections as shown in Fig.2.

Direction of rotation of Sr.No. Position of the observer motor

Table of readings for connections as shown in

3. Fig.3.

Direction of rotation of Sr.No. Position of the observer motor

CONCLUSION:

a. When field winding and armature windings are connected normally to the supply terminals The

D.C.motor rotates in ……………………Direction.

b. When Field winding and armature windings are connected as shown in Fig.2 to the supply

terminals the D.C.motor rotates in ……………………Direction.

c. When Field winding and armature windings are connected as shown in Fig.3 to the supply

terminals the D.C.motor rotates in ……………………Direction

EXPERIMENT NO. 6

AIM:-TO OBTAIN THE SPEED CONTROL OF DC SHUNT MOTOR BY ARMATURE

CONTROL.

Name Plate Details:

Power = 5.0 hp Speed =1500 rpm

Armature voltage = 220 volts Field voltage =220 volts

Armature current = 19.0 amps Field current =1.0 amps

Field Winding = shunt

Apparatus:

S.No. Name Range Quantity

1 DC Voltmeter 0-300V 1

2 DC Ammeter 0-20A 1

3 DC Ammeter 0-2A 1

4 Variable rheostat 0-150Ω 1

5 Variable rheostat 0-200Ω 1

6 Speed Indicator 0-2000rpm 1

Theory:

Any D.C. motor can be made to have smooth and effective control of speed over a wide range. The shunt motor runs at a speed defined by the expressions.

E NPZ 60A & E V I R

b

b a a

Where N is the speed, V is applied voltage, Ia is the armature current, and Ra is the armature resistance and Φ is the field flux. Speed control methods of shunt motor: 1. Applied voltage control.

2. Armature rheostat control.

3. Field flux control.

Applied voltage control: In the past, Ward -Leonard method is used for Voltage control method. At present, variable voltage is achieved by SCR controlled AC to DC converter unit is used to control the speed of a motor. In this method, speed control is possible from rated speed to low speeds. Armature rheostat control:

Speed control is achieved by adding an external resistance in the armature circuit. This method is used where a fixed voltage is available. In this method, a high current rating rheostat is required. Disadvantages: 1. Large amount of power is lost as heat in the rheostat. Hence, the efficiency is low.

2. Speed above the rated speed is not possible. The motor can be run from its rated speed to low speeds.

Procedure:

1. Voltage Control Method: Make the connections as per the given circuit diagram.

Keep the External resistances in the Armature and Fields circuits at minimum

resistance (zero) position.

Switch on the supply and increase the voltage gradually to its rated voltage i.e. 220V.

Gradually decrease the voltage and note down the speed at different supply voltages.

2. External Resistance Control in the Armature Circuit:

Make the connections as shown in the circuit diagram. Keep the External Resistances in the Armature and field circuit at minimum resistance position.

Gradually, increase the voltage till the motor attains the rated voltage.

Increase the External resistance in the Armature circuit and record the speed at various armature currents.

3. External Resistance Control in the Field Circuit:

Make the connections as shown in the circuit diagram. Keep the External Resistances in the Armature and field circuit at minimum resistance position.

Gradually, increase the voltage till the motor attains the rated voltage. Increase the External resistance in the Field circuit and record the speed at various field currents.

Do not exceed the speed above 1800rpm.

Observations:

Voltage Control Method:

Field current = A

S.No Applied Voltage Armature Current Speed

1

2

3

4

5

Resistance control in the armature circuit:

Applied voltage = V.

Field current = A.

S. No. Supply Armature Armature Speed(Rpm) External

Voltage Voltage Current Resistance(Ohms)

1

2

3

Conclusions:

Armature Rheostat control method and voltage control methods are useful to obtain the speed less than the rated speed.

Among the above two methods voltage control method is preferable than Armature Rheostat control since large amount of power is wasted in the external resistance. Field control or Flux control method is used to obtain the speed more than the rated speed.

EXPERIMENT NO.7

AIM:-TO OBTAIN THE SPEED CONTROL OF DC SHUNT MOTOR

BY ARMATURE

CONTROL.

Name Plate Details:

Power = 5.0 hp Speed =1500 rpm

Armature voltage = 220 volts Field voltage =220 volts

Armature current = 19.0 amps Field current =1.0 amps

Field Winding = shunt

Apparatus:

S.No. Name Range Quantity

1 DC Voltmeter 0-300V 1

2 DC Ammeter 0-20A 1

3 DC Ammeter 0-2A 1

4 Variable rheostat 0-150Ω 1

5 Variable rheostat 0-200Ω 1

6 Speed Indicator 0-2000rpm 1

Theory:

Any D.C. motor can be made to have smooth and effective control of speed over a wide range. The shunt motor runs at a speed defined by the expressions.

E NPZ 60A & E V I R

b

b a a

Where N is the speed, V is applied voltage, Ia is the armature current, and Ra is the armature resistance and Φ is the field flux. Speed control methods of shunt motor: 4. Applied voltage control.

5. Armature rheostat control.

6. Field flux control.

Applied voltage control: In the past, Ward -Leonard method is used for Voltage control method. At present, variable voltage is achieved by SCR controlled AC to DC converter unit is used to control the speed of a motor. In this method, speed control is possible from rated speed to low speeds.

Field flux control:

Speed control by adjusting the air gap flux is achieved by means of adjusting the field current i.e., by adding an external resistance in the field circuit. The disadvantage of this method is that at low field

flux, the armature current will be high for the same load. This method is used to run the motor above its rated speed only.

Procedure:

4. Voltage Control Method: Make the connections as per the given circuit diagram.

Keep the External resistances in the Armature and Fields circuits at minimum

resistance (zero) position.

Switch on the supply and increase the voltage gradually to its rated voltage i.e. 220V.

Gradually decrease the voltage and note down the speed at different supply voltages.5. External Resistance Control in the Armature Circuit:

Make the connections as shown in the circuit diagram. Keep the External Resistances in the Armature and field circuit at minimum resistance position.

Gradually, increase the voltage till the motor attains the rated voltage.

Increase the External resistance in the Armature circuit and record the speed at various armature currents.

6. External Resistance Control in the Field Circuit:

Make the connections as shown in the circuit diagram. Keep the External Resistances in the Armature and field circuit at minimum resistance position.

Gradually, increase the voltage till the motor attains the rated voltage. Increase the External resistance in the Field circuit and record the speed at various field currents.

Do not exceed the speed above 1800rpm.

Observations:

Voltage Control Method:

Field current = A

S.No Applied Voltage Armature Current Speed

1

2

3

4

5

Flux Control Method:

Rext = Ω,

Va = V.

S. No. Field current If (amp) Armature current If (amp) Speed (rpm)

1

2

3

4

5

Conclusions:

Armature Rheostat control method and voltage control methods are useful to obtain the speed less

than the rated speed.

Among the above two methods voltage control method is preferable than Armature Rheostat control since large amount of power is wasted in the external resistance. Field control or Flux control method is used to obtain the speed more than the rated speed.

EXPERIMENT NO.8

AIM:-TO STUDY ABOUT THE POWER MODULATOR & CONTROL UNIT.

APPARATUS REQUIRED:-

Power Converter (Modulator) Model

THEORY:-A modern electrical drive system has the following components

1. Electrical Machines & Loads

2. Power Modulator or Processor

3. Sources 4. Control Unit

5. Sensing Unit

Whenever the term electric motor or electrical generator is used, we tend to think that the speed of rotation of

these machines is totally controlled only by the applied voltage and frequency of the source current. But the speed of rotation of an electrical machine can be controlled precisely also by implementing the concept of drive. The main advantage of this concept is, the motion control is easily optimized with the help of drive. In very simple words, the systems which control the motion of the electrical machines, are known as electrical drives. A typical drive system is assembled with a electric motor (may be several) and a sophisticated control system that controls the rotation of the motor shaft. Now days, this control can be done easily with the help of software. So, the controlling becomes more and more accurate and this concept of drive also provides the ease of use.

BLOCK DIAGRAM OF ELECTRIC DRIVES:-

CIRCUIT DIAGRAM OF POWER CONVERTERS (MODULATORS):-

Fig-Half-Controlled Converter

Fig-Fully-Controlled Converter

BLOCK DIAGRAM OF DIFFERENT CONTROL UNITS:-

PROCEDURE:-

1. Study about the construction of electric drives briefly

2. Study about Different motor terminology 3. Then go for detailed study of power modulator & control unit 4. Also need to aware about the type of supply

PRECAUCATION:-

1. Follow the entire recommended dimension.

2. Properly connect all the equipment.

3. Check the insulation between the probes. 4. Shoes must be part of attire while doing the lab.

5. Before giving the supply check all the connections once again.

RESULT:-

Thus we studied about the Power Modulator & Control Unit.

EXPERIMENT NO.9

AIM:-TO STUDY ABOUT THE DETAILED STRUCTURE OF WIND POWER STATION.

THEORY: -

Wind power is the use of air flow through wind turbines to mechanically power generators for electric power. Wind power, as an alternative to burning fossil fuels, is plentiful, renewable, widely distributed, clean, produces no greenhouse gas emissions during operation, consumes no water, and uses little

land.[2]

The net effects on the environment are far less problematic than those of nonrenewable power

sources.

Wind farms consist of many individual wind turbines which are connected to the electric power

transmission network. Onshore wind is an inexpensive source of electric power, competitive with or in

many places cheaper than coal or gas plants. Offshore wind is steadier and stronger than on land, and

offshore farms have less visual impact, but construction and maintenance costs are considerably higher.

Small onshore wind farms can feed some energy into the grid or provide electric power to isolated off-

grid locations. In 2014, global wind power capacity expanded 16% to 369,553 MW

Synchronized Wind Power Station :-

Wind Turbine:-

PROCEDURE:-

5. Selection of site.

6. Selection of Generator.

7. Selection of wind turbine either Vertical or Horizontal.

8. Then most importantly synchronization of Wind Mill with the Grid.

PRECAUCATION:-

1. Follow the entire recommended dimension.

2. Properly connect all the equipment.

3. Check the insulation between the Generating station & Grid.

4. Shoes must be part of attire while doing the lab.

5. Before starting the Power Generation check all the generation constraints once again.

RESULT:- Thus we studied about the detailed structure of wind power station.