Gautam Buddha University Electrical Exp.

Pandit Experiment no.-1 Objective: Study of CRO Apparatus Required: 1. CRO

1. CRO Cathode ray oscilloscope, CRO: - Scope, is a versatile electronic instrument used in many fields of basic and applied .research to measure time-dependent voltage signals. A CRO consists of a cathode ray tube, CRT (similar to a television picture tube), and associated circuits. Because an oscilloscope has very high resistance inputs (like a voltmeter), it draws very little current and thus usually does not disturb the circuit being studied. Block Diagram:

Components The principle parts of the tube are: 1. Filament-heats the cathode with a current of a few amperes. 2. Cathode-A metal surface coated with a metallic oxide which emits electrons when it is heated; emission currents of a few mA are typical. 3. Control Grid-controls the electron current and consequently the brightness of the image. The potential applied to it can be varied by adjusting the INTENSITY control. By the time the electron beam reaches the screen, it is reduced to a few μA Do not make the spot brighter than necessary as this may damage the screen. If the spot has a halo around it, turn down the intensity; the intensity required for a spot is less than that required for a line. 4. Focusing Anode-permits sharpening the image. Focus is controlled by the FOCUS knob. 5. Acceleration Anode-accelerates the electrons toward the screen so that they strike it with enough energy, several kV, to give off light. There is no external control to adjust this voltage. 6. Vertical Deflection Plates-two horizontal plates parallel to the beam. The beam can be deflected by a potential difference between these plates, usually derived from the amplified signal being studied. The VERTICAL POSITION control applies a DC voltage to offset or centre the beam vertically. 7. Horizontal Deflection Plates-analogous to the vertical deflection plates. A sweep voltage is usually applied to these plates to cause the electron beam to sweep across the screen at a controlled rate, and then rapidly return to its starting position. The sweep rate is controlled by the TIME/DIV switch. A >DIV= is generally a cm marking on the screen. The TIME/DIV often varies from 1 sec down to 1 μs. The HORIZONTAL POSITION control is used to offset the beam horizontally, usually so that the sweep starts at the left hand edge of the scale.

8. Fluorescent Screen-the screen has a phosphor coating which produces light when struck by a charged particle. A grid is marked on the outside of the screen, usually with cm spacing and small marks every 2 mm.

Fig: Diagram of CRT. Principle of Operation: The operation of the tube depends on the fact that charged particles such as electrons can be deflected, accelerated, and focused by suitably applied electric fields. Because the electron has little inertia, it can be deflected quickly, making possible the study of high frequency and transient effects. The filament heats the cathode which emits electrons; these are focused into a beam by an electric field; the beam strikes a fluorescent screen at the end of the tube and causes the screen to emit light. Before it hits the screen, the beam is deflected by the electric fields on the plates. This deflection causes the beam to move vertically and/or horizontally across the face of the screen. (Television tubes use magnetic deflection. This permits greater deflection in a shorter distance, thus larger screens, but gives up response time. Observation: S.NO.

Waveform

Voltage(Vp-p)

Frequency (f) , Hz

Results: 1. Examination of waveforms.............................................. 2. Voltage measurement (Vp-p)............................................. 3. Frequency measurement (f)..............................................

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Will continue to glow even if starter is withdrawn. The ionization in the tube will produce ultra- violet (UV) radiation is converted to visible spectrum by the fluorescent coating on tube. Testing: we can test the performance of tube light with help of “Series test lamp”. We perform following test: 1. For starter: Connect the starter in series with the lamp and to the supply. If the lamp fluctuates continuously than the starter is OK otherwise it is faulty. 2. For Tube: Connect one end of lamp and one electrode point to the supply. If the glow of lamp is: a.

Dim: The filament is ok.

b.

Full: The filament is short.

c.

Not Glow: It is open.

3.

For Choke: Connect the choke in series with the lamp and supply.

a.

If glow is Dimmer, it is ok.

b.

If glow is bright, it is short

c.

If not glow, it is open.

Testing of Capacitor: Connect both terminal of capacitor in the supply foe 2-3 sec. and then short them. If spark appear between the terminals, than the Capacitor is Ok. Otherwise is open ckt or short ckt. Earth Test: Connect one terminal of lamp in the supply and other the body of fan. If the bulb glows than there is earth fault and it can be removed by isolating the shorted part.

2. The Electric Iron An iron is a small appliance used in ironing to remove wrinkles from fabric. Ironing works by loosening the ties between the long chains of molecules that exist in polymer fibre materials. With the heat and the weight of the ironing plate, the fibres are stretched and the fabric maintains its new shape when cool. Some materials such as cotton require the use of water to loosen the intermolecular bonds. Many materials developed in the twentieth century are advertised as needing little or no ironing.

Parts of an Electric Iron

1. Sole Plate: The sole plate is the thick, triangular-shaped slab of iron that forms the base over which the electric iron is built up. The bottom surface and edges are heavily chromium plated, to prevent it from rusting. The base plate should hold the iron pressure plate and cover plate in position. For this purpose we can see two or sometimes three studs in the base plate. These studs aid in holding the position of cover plate and pressure plate. 2. Pressure Plate: This plate is generally called the top plate as it follows the shape of sole plate. The pressure plate has some holes through which the studs form the base plate passes through. We should tighten the nuts on the studs in such a way that the pressure plate and sole plate are pressed tight against each other. In some iron the pressure plate is heavy and made of cast iron while in some other cases, it is a thin sheet of steel, about ¼ cm thick. In automatic type of electric iron, the pressure plate has a rectangular or circular hole for locating the thermostat.

Fig: component of electric iron. 3. The Heating Element: The heating element is present between the sole plate and pressure plate. It is pressed hard between the two plates. The heating element consists of nichrome wire wound around a sheet of mica. The two ends of the nichrome wire are connected to the contact strips. The contact strips are connected to the terminals of the iron. There are two reasons for which mica is chosen in the heating material. Mica is a very good insulating material. Besides that mica can also withstand very high temperatures. The entire assembly of mica sheet, nichrome wire and Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 5

contact strips are riveted together resulting in a mechanically sound and robust construction. There is an asbestos sheet, which separates and thermally insulates the top plate from the heating element.

Fig: Heating element 4. The Cover Plate: The cover plate is made of thin sheet of iron. It is placed on top of the base plate and it covers all the internal parts of the iron. The handle and connector are only attached to the cover plate. 5. Handle: The handle can be made either with wood or with plastic. The handle is attached to the cover plate with the aid of screws. Studs can also be used for this purpose. 6. Pilot Lamp: The pilot lamp is housed in the cover plate of the electric iron. One end of the pilot lamp is connected to supply, while the other end is connected to the heating element. A shunt resistance is provided across the pilot lamp which assists in providing a voltage drop. The shunt is designed to provide a voltage drop of 2-5 volts

Fig: Circuit diagram of electric iron. 7. Thermostat: When it comes to an automatic electric iron, the thermostat is the most important item. It uses a bimetallic strip to operate the switch which is connected in series with the resistance (or) heating element. The bimetallic strip is a simple element which converts a temperature change into mechanical displacement. A bimetallic strip consists of two different metals bonded together. The two metals should have a different coefficient of expansion. If such a strip is heated, it starts to curve towards the metal having the lower co-efficient of expansion. On cooling, it straightens and comes back to the normal position. The bimetallic strip is attached to a contact spring through small pins. The contact point between the strip and contact points remains closed. When the temperature rises significantly, the unusual expansion causes the strip to curve and the contact between strip and contact spring opens. Thus the supply to heating element is temporarily stopped (until the temperature goes down to normal). A special device called the cam is placed is placed near the contact spring, with which we specify the amount of curving of bimetallic strip required to separate the contact. Thus using bimetallic strip the temperature is kept constant within certain limits

Fig: Diagram of Thermostat Working: When a current is passed through the heating element which is placed between the sole plate and pressure plate, the element gets heated up and transfers its heat to the sole plate through conduction and in-turn the sole plate also gets heated up. Now to remove the wrinkles in clothing, we Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 7

should apply heat and pressure. Heat is formed due to the coil and when we press the clothes with iron, the wrinkles are removed. For maintaining the optimum temperature, a thermostat is used along with pilot lamp which serves as an indicator

3. Ceiling Fan: The electric fans are most popular devices for providing the cooling in industry and homes. The motors in ceiling fans single-phase AC, squirrel cage, permanent capacitor type motors. These motors are used where the motor starts practically at zero loads. The main winding generally has low resistance while starting winding has high resistance. Thus, the two winding have different phase angles and consequently the current in two winding are not in phase, giving effectively a two-phase operation. • The winding are physically displaced by 90° electrical degrees from each other. • The direction of rotation can be reversed by interchanging the connection to the supply of either winding. Main part of ceiling fan: The main parts of can be divided into two categories: 3.a.i.a.i.a. Electrical parts: The major parts are follows: 1. Motor: The single phase AC squirrel cage motor is most important part the ceiling fan. The motor consists of two major units. i). Stator: This is the stationary part of the fan and consists of two windings: 3.a.i.b) Starting winding: It is also called the auxiliary winding of the fan. It is placed in the top slot of stator. This winding has high resistance and low reactance. 3.a.i.c) Running winding: This is the main winding of the fan and is placed in the bottom slots the stator to increase the reactance. It has low resistance and high reactance. ii). Rotor: The rotor is made of steel and is laminated to reduce eddy currents. Copper or aluminium bars are embedded into the laminations short circuited at both ends for flowing of current due to induced voltage. 1. Starting capacitor: The capacitor is connected in series with the starting winding to increase the starting torque. The value of the capacitor is generally in the range of 2 to 4 microfarad, but is generally kept at about 2.5 microfarad. 2. Regulator: The regulator is used to control the speed of the fan. The regulator can be resistance type or electronic type. 2. Mechanical parts: The main mechanical parts are as follows: (i) Motor enclosure: The motor is enclosed in a heavy enclosure to protect the windings and reduce the starting jerk due to high inertia. (ii) Blades: A ceiling fan has got 3 or 4 blades, which are slightly twisted for circulating the air.

(iii) Suspension Rod: It is used to suspend the fan from the ceiling. The length of the rod depends on the position of the fan with respect to the ceiling. The rod is fixed to the ceiling hook by means of a bolt and a suspension bush. (iv) Bearings: The fans consist of two bearing one which is fixed on the stator and other on the rotor. (v) Canopy: Two canopies are used at two ends of the rod to cover the capacitor and the hook.

Circuit diagram:

Working: Main and auxiliary winding are spaces displaced by 90° electrical. The time displacement between the currents in the main and auxiliary winding is achieved by connecting a capacitor in series with auxiliary winding. By using capacitor of proper value, the current in auxiliary winding (I a) can be made to lead the current (Im) in main winding by approx 85° at standstill. So, torque at stand still (T=KIaImsinα) increased due to increase in angle α°. Both the capacitor and auxiliary winding are designed for short time duty so auxiliary winding is disconnected by centrifugal switch when the motor has reached 75% of speed. A high starting torque is an outstanding feature of this motor. Typical application is large fans, compressors and high-inertia loads. Testing of windings: The windings are tested for the following faults: 1. Open circuit 2. Short circuit 3. Earth fault The leads of the testing board are connected to the two ends of the winding (running or starting) to be tested. If the lamp glows dimly the winding is good. If the lamp does not glow it shows open circuit and if it glows brightly it shows short circuit. To test for earth fault one lead of the test board is connected to the winding terminal and other lead to the body of the fan. If the lamp glows it shows earth fault in the winding. A) Testing of capacitor: The capacitor is generally tested for by charging the capacitor and then observing the strength of discharge. The two leads of the test board are connected to the two leads of the capacitor for a short time. Then the test board leads are removed and the two leads are shorted with the help of a shorting wire. The capacitor gets discharged with a cracking sound. The strength of the spark indicates the strength of the capacitor. (The capacitor can also be checked with the help of the multimeter.) B) Testing of regulator: The resistance type regulator is tested for continuity by connecting the test board leads to its two ends and turning the knob to different positions. The bulb should glow at all positions. A non glowing bulb indicates open circuit. (The resistance can also be checked with the help of the multimeter.) C)

Connecting & Running: 1. Connect the fan with supply. 2. Run the fan and change speed with regulator. 3. Disconnect starting winding. Switch on supply. If fan does not start, rotate it by hand in either direction and observe the result. 4. Now reconnect starting winding and running winding. If fan does not start, rotate it by hand in either direction and observe the result. 5. Reverse the connection of running winding and observe the result. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 9

Precautions at the time of testing: 1. Do not touch any naked wire unless you are sure that the supply is switched off. 2. Insulate yourself from earth by means of wood or rubber. 3. Always use the test board bulb in series with the supply to prevent accidental short circuit. 4. Make sure that the capacitor has been discharged at the end of the experiment. It should not be left in charged state. 5. Switch off all supplies at the end of the experiment.

Experiment no.-3 Objective: Assembly and working of DC Motor. Apparatus Required: 1. Cut section of DC Motor Diagram:

INTRODUCTION: The world machine is commonly used to explain features that are common to both the generator and motor. In the rotating machines an electromechanical energy conversion takes place. There are two types of rotating energy conversion machines. (i) Direct current(DC) machine (ii) Alternating current(AC) machine • All DC machines can be operated as either a motor or a generator without taking any modifications. • A rotating machine converting electrical energy into mechanical energy is called motor. • A rotating machine converting mechanical energy into electrical energy is called generator. Construction of DC motor: 1. YOKE: (a) Functions: 1. It serves the purpose of outermost cover of the Dc machine, so that the insulating materials get harmful atmospheric elements like moisture, dust and various gases like so2, acidic fumes, etc. 2. It provides mechanical support to the poles. 3. It forms a part of the magnetic circuit. It provides a path of low reluctance for magnetic flux. The low reluctance path is important to avoid wastage of power to provide same flux. Large current and hence the power is necessary if has high reluctance, to produce the same flux. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 11

2.

POLES: Each pole is divided into two parts namely,(1) pole core and (2) pole shoe.

Fig: Pole structure Functions of pole core and pole shoe: i. Pole core basically carries a field winding which is necessary to produce the flux ii. It directs the flux produced through air gap to armature core, to the next pole. iii. Pole shoe enlarges the area of armature core to come across the flux, producing better induced emf shape. To achieve this, pole shoe has been given a particular shape. 3. FIELD WINDING: it is made up of magnetic material like cast iron or cast steel. As it requires a definite shape and size, laminated construction is used. The laminations of required size and shape are stamped together to get a pole which is then bolted to the yoke. (a) Functions: Field winding carries a D.C. current due to which a stationary pole and necessary flux are produced. 4. ARMATURE: It is further divided in two parts, namely, i) Armature core ii) Armature winding (i) Armature core: Armature core is cylindrical in shape and is mounded on shaft. It consists of slots and teeth on its periphery and the air ducts to permit the air flow through armature which serves cooling purpose. (a) Functions: i. Armature core provides house for armature winding. ii. To provide a path of low reluctance to the magnetic flux produced by field winding. (ii) Armature winding: Armature winding is nothing but the interconnection of the armature conductors, placed in slots provided on the armature core periphery. When the armature is rotated, the magnetic flux gets cut by armature conductors and emf gets induced in them. (a)Functions: i. Generation of the emf takes place in the armature winding in case of generator and emf is also induced in case motor but it is called back emf. ii. Armature winding carry the supplied current by source in case in case of motor and drawn out current in case of generator. iii. To do the useful work in the external circuit. 5. Commutator: We have seen earlier that the basic nature of emf induced in the armature conductors is alternating. This needs rectification in case of DC generator, which is possible by a device called commutator. (a)

(a)

Functions: i. To facilitate the collection of current from the armature conductors. ii. To change internally developed alternating emf to unidirectional (DC) emf. iii. To produce unidirectional torque in case of motor. 6. Brushes and Brush Gear: Brushes are stationary and resting on the surface of the commutator. (a) Function: To collect current from commutator and make it available to this stationary external circuit. 7. Bearing: Ball-bearings are usually used as they are more reliable. For heavy duty machines, roller bearings are preferred.

Fig: Working diagram of DC motor. WORKING PRINCIPLE OF DC MOTOR: When a electric current (supplying electrical energy) passes through a coil in a magnetic field, then these conductors experience a force. Direction of force is governed by FLH Rule. Direction of the force is upward and in conductor ab force is downward. So due to these couple of magnetic forces a torque is produced (T=F×L) which turns the rotor. For rotating the motor in one direction the torque should be unidirectional. The conductor that comes under the South Pole should experience a force always upward or downward and the conductor that comes under the North Pole should experience a force always downward or upward. The commutator reverses the current in each half cycle revolution to keep the torque in the same direction.

1. To study & verify the connection of Energy Meter, MCB and Consumer Unit (CU) Equipments Needed: Connecting leads AC Supply

Circuit Diagram: Procedure 1. First of all make sure that the earthling of your laboratory is proper and connected to the terminal provided on back side of the panel. 2. Connect terminal of ground to terminal of ground points for grounding all ground points as shown in figure. 3. Make sure that the AC Mains and the MCB of your trainer is at ‘Off’ position. 4. Connect Red and Black terminals of Mains Supply to the Input terminals of Energy Meter. 5. Connect Output terminals of Energy Meter to the Input terminals of MCB. 6. Connect the Output terminals of MCB to L and N terminal of CU. When all three connections are complete then switch ON the supply.

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Note: Procedure of experiment 1 is common for all experiments, so before start any experiment first follow the procedure of experiment 1 and then starts other experiments. 2. To study & verify the connection procedure for Tube Light wiring section Equipments Needed: Connecting leads AC Supply Tube Light Starter

Circuit

Diagram:

Procedure:

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1. First connect the tube light on tube light connectors and starter in starter holder provided on the panel. 2. Connect terminal 1 of Ballast to terminal L of Tube Light section and terminal 2 to terminal 3 of Tube Light. 3. Connect terminal 4 to terminal 5 and terminal 6 to terminal 7. 4. Connect terminal 8 to terminal N of Tube Light section. 5. Now connect L and N terminals of Tube Light section to L and N terminals of CU as shown in figure 6. Now switch ON the MCB, so tube light will turn ON and after then switch ON the LCD switch provided on right side of LCD.

3. To study & verify the connection procedure for Two-Way Switch wiring section Equipments Needed: Connecting leads AC Supply Bulb Circuit Diagram:

Fig: Circuit diagram of two way switch( stair case) wiring

Two-Way Light Switch A two-way switch refers to a pair of switches that control the same circuit. In a two way switch, electricity can flow if both switches are turned to the "up" position or both switches are turned to the down position. If one switch is up and the other is down, however, the circuit will not light. This system is very useful in homes, particularly on stairs. You can turn on the light at the bottom to walk up the stairs in the evening, then turn the light back off again at the top. Two-Way Light Switch Wiring

Have you ever wonder how a lamp that is used to light up the stairs of a building is connected to the two switches that control it from either end? These two way switches have a single pole double throw (SPDT) configuration. Each has a common terminal (COM) with a pole that can be switched between position L1 or L2.

Working: The method is as shown in the figure. In this configuration, the L1 of both SW1 and SW2 are connected together. Similarly, the L2 of both SW1 and SW2 are connected together. The LIVE of the AC Source is connected to COM of SW1 and one side of the load is connected to COM of SW2. The other side of the load is then connected to the NEUTRAL of the AC Source. With this configuration, the lamp will be turned ON when one switch is ON and the other is also ON. If both switches are in different position, the lamp will be OFF. Procedure: 1. First connect bulb in bulb holder. 2. Connect terminals L1, Com and L2 of SW1 to terminals L1, Com and L2 of SW2 respectively as shown in figure. 3. Connect terminal L2 of SW2 to terminal L2 of bulb. 4. Connect L and N terminals of CU to terminal L1 of SW1 and terminal N of bulb respectively and switch on the MCB after then switch ON the LCD switch provided on right side of LCD. 5. With this configuration, the lamp will be turned ON when one switch is at ON position and the other is at OFF position. If both switches are in the same position, the lamp will be OFF.

4. To study of Short Circuit Fault and verify the connection procedure for short circuit fault section Equipments Needed: Connecting leads AC Supply Circuit Diagram:

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Procedure: 1. First connect L and N terminals of Short Circuit Fault section to L and N terminals of CU as shown in figure 13 and switch ON the main MCB. 2. Again Connect L terminal of Short Circuit Fault section to lower terminal of MCB. 3. Now switch ON the MCB and connect upper terminal of MCB to terminal N of Short Circuit Fault section. Note: When upper terminal of MCB is connected to terminal N, the short circuit occurs in that circuit and the MCB will trip (turned OFF).

5. To study of switch board wiring Equipments Needed: * Connecting lead *AC Supply Circuit Diagram:

Procedure: 1. Make sure that switches of load section and main MCB are at OFF position. 2. First Connect terminal S1 and N1 to L and N terminals of CU as shown in figure 3. Connect terminal S2 to terminal L1 and terminal G1 to one terminal of ground points. 4. Now connect terminal S3 and N2 to L and N terminal of CU. 5. Connect terminal S4 to terminal L2 and terminal G2 to one terminal of ground points. 6. Switch ON the MCB after then switch ON the LCD switch provided on right side of LCD.

Note: Sockets with Switch provided in Load Section, we can connect load on panel through sockets.

6.

To study the connection of Fan with switch and regulator

Equipments Needed:  Connecting leads  AC Supply  Ceiling Fan Circuit Diagram: Procedure: 1. Make sure that switch and regulator of Fan section and main MCB is at OFF position. 2. Connect running winding terminals of fan to terminals R1 and R2 provided on panel. 3. Connect Starting winding terminals of fan to terminals S1 and S2 provided on panel. 4. Connect capacitor terminals of fan to terminals C1 and C2 provided on panel. 5. Connect terminal S6 to terminal Re1 and terminal Re2 to terminal R1. 6. Connect terminal R1 to terminal C1 and terminal C2 to terminal S1. 7. Connect terminal S2 to terminal R2. 8. Connect L and N terminals of CU to terminals S5 and R2 respectively as shown in figure. 9. Switch ON the MCB after then switch ON the LCD switch provided on right side of LCD.

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10. Now switch ON the switch of fan section and slowly increase regulator to increase speed of fan, when regulator is at its maximum position fan moves at its higher speed. So we can control the speed of fan through regulator.

7.

To study and verify the behaviour of current and voltage in series circuit

Equipments Needed: Connecting leads AC Supply Four 100 watt Bulbs Circuit Diagram:

Procedure: 1. First connect bulbs in bulb holders. 2. Connect terminal L to ammeter terminals A1. 3. Connect ammeter terminal A2 to terminal B1. 4. Connect terminal B2 to terminal B3 and terminal B4 to terminal B6. 5. Connect terminal B5 to B8 and terminal B7 to terminal N. 6. Connect L and N terminals of series-parallel operation section to L and N terminals of CU as shown in figure. 7. Now switch ON the MCB after then switch ON the LCD switch provided on right side of LCD and take readings of current and voltage on LCD screen.

Note: In a series circuit, the current through each of the components is the same, and the voltage across the components is the sum of the voltages across each component. So we can measure the voltage across each bulb by connecting voltmeter terminals V1 and V2 across each bulb.

8.

To study and verify the behaviour of current and voltage in parallel circuit

Equipments Needed: Connecting leads AC Supply Four 100 watt Bulbs Circuit Diagram:

Procedure: 1. First connect bulbs in bulb holder. 2. Connect L and N terminals of series-parallel operation section to voltage terminals V1 and V2 respectively. 3. Connect voltmeter terminal V1 to terminal A1 and terminal V2 to terminal B2 respectively as shown in figure. 4. Connect ammeter terminal A2 to terminal B1. 5. Connect terminals B1 to B3, B3 to B5 and B5 to B8 respectively. 6. Connect terminals B2 to B4, B4 to B6 and B6 to B7 respectively. 7. Now all bulbs are connected in parallel, so Connect L and N terminals of series parallel operation section to L and N terminals of CU. 8. Now switch ON the MCB after then switch ON the LCD switch provided on right side of LCD and take readings of current and voltage on LCD screen. Note: In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. So we can measure current flowing in the circuit by connecting ammeter terminals A1 and A2 between to two bulbs in series.

b. Connect positive of DC power supply to other end of ammeter 3. Switch ‘On’ the trainer board. 4. Set the multimeter to the appropriate range and measure the current flowing through the resistance. Record this value of current in the table. Note: when current is to be measure we have to connect ammeter (multimeter) In series. 5. Now disconnect the above setup and connect the new circuit as shown in figure 6.2. a. Connect a resister across the DC power supply. b. Connect a voltmeter across the resistance. 6. Now measure the voltage across the resistor (Note that voltage is to be measure in parallel). 7. Record the corresponding voltages/current in table for different resistors. You can start with the lower values of resistors. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 21

8. Draw graph between current (vertical axis) and resistance (horizontal axis). It is clear that current is inversely proportional to resistance. 9. Now you can compare the values of V/R with current. According to the ohm’s law current is given by ratio of voltage to the resistance. OBSERVATION TABLE: Resistance ( Ω )

Current (A)

Voltage ( V )

Voltage/Resistanc e

RESULTS: PRECAUTIONS: i. Avoid loose connections in the circuit. ii. Reading should be taken without parallax error.

Experiment: 6 Objective: Verification of Kirchhoff’s current law Equipments Needed: 1. NV6513 Trainer Board 2. 2mm patch cords. Theory: Kirchhoff's Current Law: The first rule, the junction theorem, states that the sum of the currents into a specific junction in the circuit equals the sum of the currents out of the same junction. Electric charge is conserved: it does not suddenly appear or disappear; it does not pile up at one point and thins out at another. Specifically, the law states that: “The algebraic sum of current into any junction is zero”.

Σ I into node = Σ I away from node Or, I1 = I2 + I3 Or, I1- I2 – I3 = 0 Circuit diagram:

Procedure: 1. Connect inbuilt +12V DC power supply to the indicated position on the trainer circuit. 2. Connect 2mm patch cords between test points 1 & 2, 3 & 4, 5 & 6, 7 & 8, 9 & 10, 11 & 12, 13 & 14, 15 & 16. 3. Switch ‘ON’ the power supply. 4. To test KCL at node B 5. Measure incoming current I in between test points 1 & 2 by replacing 2mm patch cord with an inbuilt DC Ammeter. For this, connect the test point 1 to positive terminal and test point 2 to negative terminal of the DC Ammeter section. 6. Reconnect the patch cord between test points 1 & 2. 7. Now measure the outgoing current I1 between test points 7 & 8 by replacing 2mm patch cord with an in-built DC Ammeter. For this connect test point 7 to positive terminal and test point 8 to negative terminal of the DC Ammeter section. 8. Reconnect patch cord between test points 7 & 8. 9. Measure outgoing current I2 between test points 3 & 4 by replacing 2mm patch cord with an in-built DC Ammeter. For this connect test point 3 to positive terminal and test point 4 to negative terminal of the DC Ammeter section. 10. Reconnect patch cord between test points 3 & 4. 11. Check whether the sum of incoming current/currents is equal to the sum of outgoing current/currents. 12. Repeat above procedure for junction point C, D, G, H, I and there corresponding incoming and outgoing current/currents.

Observation:

S.No.

Iin

I1

I2

I3

I4

I5

I6

Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 23

I0ut

Calculation:

Results: Precautions: i. Avoid loose connections in the circuit.

Objective: Verification of Kirchhoff’s voltage low Equipments Needed: 1. NV6513 Trainer Board 2. 2mm patch cords. Kirchhoff’s Voltage Law: The second rule, the loop equation, states that around each loop in an electric circuit the sum of the emfs (electromotive forces, or voltages, of energy sources such as batteries and generators) is equal to the sum of the potential drops, or voltages across each of the resistances, in the same loop.

Circuit diagram:

Procedure: 1. Connect inbuilt +12V DC power supply to the indicated position on trainer circuit. 2. Connect 2mm patch cord between test points 1 & 2, 3 & 4, 5 & 6, 7 & 8, 9 & 10, 11 & 12, 13 & 14, 15 & 16. 3. Switch ‘on’ the power supply. 4. To test KVL in loop ABIJ. 5. Measure current I in flowing through resistor of 330E with the help of inbuilt Ammeter by replacing 2mm patch cord between test point 1 & 2 with Ammeter. 6. Reconnect patch cord between test point 1 & 2. 7. Measure current I1 flowing through resistor of 100E with the help of inbuilt Ammeter by replacing 2mm patch cord between test point 7 & 8 with Ammeter. 8. Reconnect patch cord between test point 7 & 8. 9. Measure current I out flowing through resistor of 100E with the help of inbuilt Ammeter by replacing 2mm patch cord between test point 15 & 16 with Ammeter. 10. Reconnect patch cord between test point 15 & 16. 11. Calculate different IR drop in the selected loop (Check that the sign of IR drop should be given after considering direction on current). 12. Measure the sum of IR drop with their sign. 13. Equate the sum of all IR drop with there sign and sum of the source voltage of that particular loop. 14. In case of no voltage source in loop take the sum of all voltage sources equal to zero. 15. Repeat above procedure for loop BCHI, CDGH, DEFG ……………. by measuring current (with inbuilt Ammeter) flowing through different resistor in the loop.

Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 25

Observation: S.No.

Iin

I1

I2

I3

I4

I5

I6

I0ut

Calculation: Results:

Precautions: i.

Avoid loose connections in the circuit.

Experiment No. -7 Objective: To verify Thevenin’s Theorem Equipments Needed: 1. NV6509 Trainer Board 2. 2mm patch cords. Theory: Statement of Thevenin’s Theorem: Thevnin’s theorem states that any two terminal liner network containing energy sources (voltage or current) and impedance or resistances can be replaced with an equivalent circuit consisting of a voltage source ( V th) and a series resistance or impedance( R th or Zth) connected to laod.

Circuit diagram:

Procedure: 1. Connect +12V, DC power supplies at their indicated position using patch cords. 2. Find the Thevenin resistance (Rth) by removing all power sources in the original circuit and then calculate total resistance between the open connection points. 3. Practical value measured by multimeter and compare. 4. Find the Thevenin source voltage (Vth) by removing, the load resistor from the original circuit and calculate the voltage across the open connection point where the load resistor used to be. 5. Practical value of Thevenin voltage measured by voltmeter and compare. 6. Draw the Thevenin equivalent circuit, with the V th in series with Rth. The load resistor reattaches between the two open points of the equivalent circuit. 7. Measure value of IL in both circuit and compare. Observation: S.No.

Rth (Ω)

Theoretic al

%Error

Practica l

Vth (mv)

%Error

IL (ma)

Theoretic al

Practic al

%Error

Theoretic al

Practic al

1.

Calculation:

Result: 1. Theoretical value of Thevenin’s equivalent voltage VTH = 2. Practical value of Thevenin’s equivalent voltage VTH = 3. % Error = 4. Theoretical value of Thevenin’s equivalent resistance RTH = 5. Practical value of Thevenin's equivalent resistance RTH = Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 27

6. %Error = 7. The value of current flowing through the load in linear circuit = 8. The value of current flowing through the equivalent circuit = 9. %Error = (Error = Theoretical value –Measured value). Objective: To verify Norton’s Theorem Equipments Needed: 1. NV6509 Trainer Board 2. 2mm patch cords, Theory Norton’s Theorem: Norton’s theorem states that any two terminal networks containing energy sources and resistance or impedances can be replaced by an equivalent circuit having a current source (I N) and parallel resistance or impedance connected to load.

Circuit diagram:

Procedure: 1. Connect a 2mm patch cord between +5V supply and terminal 1, and ground to ground of the circuit as shown in figure. 2. Find the Norton source current (IN) by removing the load resistor from the original circuit and starting the open terminal. This short circuit current is INorton. 3. Find the Norton resistance (RN=Rth) by removing all energy sources and calculate total resistance between the open connection point after removing load. 4. Draw the Norton’s equivalent circuit with the Norton’s current source in parallel with the Norton’s resistance. The load resistor reattaches between the open points of equivalent circuit.

Observation: S.No.

RN (Ω)

Theoretic al

%Error

Practica l

IN (ma)

%Error

IL (ma)

Theoretic al

Practic al

%Error

Theoretic al

Practic al

1.

Calculation:

Result: Theoretical value of Norton’s equivalent current IN = ………….. Practical value of Norton’s equivalent current IN =……………... Theoretical value of Norton’s equivalent resistance RN =……… Practical value of Norton's equivalent resistance RN = …………. ..... (Yes/No), the value of current flowing through the load resistance in both of the cases is approximately equal. Hence Norton’s theorem is verified.

Experiment no.8 Objective: To study and verify Superposition Theorem. Equipments Needed: 1. NV6509 Trainer Board 2. 2mm patch cords Theory Superposition Theorem: This theorem states that in a linear network, containing more than one independent energy source, then the complete response (voltage or current) in any branch of the network is equal to the sum of the response due to each independent source acting one at a time with all other ideal independent sources are made inactive (short the voltage source and open the current source). Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 29

Circuit diagram: Procedure: 1. 2. 3. 4.

Take any one independent source in the circuit. Make all other independent sources inactive. Dependent sources will not be disturbed. Determine the magnitude and direction of response (voltage or current) in desired branch by a single source selected. 5. Now take another independent source and calculate the response in desired branch using step 1 to 4. 6. Add all the component of responses in the desired branch. Algebraic addition is to be done for Dc networks and phasor addition for Ac network. Observation: S.No.

Current in CD branch (ma) 1.

%Error

5V

12 V

Current in EF branch (ma) Bot h

%Error

5V

12 V

Bot h

Result: ................(Yes/No), the sum of current flowing through branches in case of individual sources is nearly equals to the amount of current flowing through the same branch in case of both of the sources.

Experiment No.9 Objective: To study and Verify Maximum Power Transfer Theorem. Equipments Needed: 1. NV6509/NV6510 Trainer Board 2. 2mm patch cords Theory Maximum Power Transfer Theorem: This theorem that the maximum amount of power will be dissipated by a load resistance when that load resistance is equal toThevenin/ Norton resistance of the

network supplying the power. If the load resistance is lower or higher than the R th or RN, its dissipated power will be less than maximum. Proof: For a DC network.

Power delivered to load RL is PL PL=IL2RL = To find the value of RL that absorbs a maximum power from the given practical source, we differentiate with respect to RL. dpL Equate derivative to zero.

A network delivers the maximum power to a load resistance R when r is equal to the Thevnin equivalent (or source) resistance of the network. Procedure: 1. Set a value of load resistance R L at some lower value (say 400Ω). For this connect multimeter between terminals 6 and 7 and set the resistance. 2. Now remove multimeter and connect +5V supply to terminal 5 and Gnd to Gnd. 3. Connect the onboard DC Ammeter between terminals 6 & 7, for this connect terminal 6 to + terminal of Ammeter and 7 to its –ve terminal. 4. Observe the reading of DC Ammeter, this will give the load current IL. 5. Determine the product of I²LRL, the power dissipated for this value of load resistance. 6. Record the value of load resistor RL, current flowing through load resistance IL, and power dissipated PL in an observation table. 7. Now repeat same steps for different values of resistances like 450Ω, 500Ω, 550Ωetc. Observations: S. No .

Load Resistance RL

Load Current IL

Power dissipated PL

Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 31

1.

400 Ω

2.

450 Ω

3.

500 Ω

4.

550 Ω

5.

600 Ω

6.

650 Ω

7.

680 Ω

8.

750 Ω

8. Observe for what value of resistance the power transferred is maximum. This resistance must be equal to the Thevenin resistance or internal resistance of the circuit. Result: ............... (Yes/No), the maximum amount of power will be dissipated by a load resistance, when that load resistance is equal to the Thevenin resistance of the network supplying the power and the value of Maximum power dissipated is found equal to..................

Experiment No.-10 Objective: To understand Woking of a 1-, transformer and to determine its transformation ratio. Equipments Needed: · Single phase transformer lab. Theory Transformer: A transformer is a static (or stationary) piece of apparatus by means of electric power in one circuit is transformed into electric power of the same frequency in another circuit. It can rise or lower the voltage in a circuit but with a corresponding decrease or increase in current. The physical basis of a transformer is mutual induction between two circuit linked by common magnetic flux. In brief, a transformer is a device that 1. Transfers electric power from one circuit to another 2. it does so without a change of frequency 3. it accomplishes this by electromagnetic induction and 4. Where the two electric circuits are in mutual inductive influence of each other. Step-up transformers A "step-up transformer" allows a device that requires a high voltage power supply to operate from a lower voltage source. The transformer takes in the low voltage at a high current and puts out the high voltage at a low current. The secondary has more turns than the primary.

Step-down transformers A "step-down transformer" allows a device that requires a low voltage power supply to operate from a higher voltage. The transformer takes in the high voltage at a low current and puts out a low voltage at a high current. The secondary has less turns than the primary.

Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 33

Isolation transformers An "isolation transformer" does not raise or lower a voltage; whatever voltage comes in is what goes out. An isolation transformer prevents current from flowing directly from one side to the other. This usually serves as a safety device to prevent electrocution. The secondary has got equal turns than the primary.

Variable auto-transformers A "variable auto-transformer" (variac) can act like a step-up transformer or step-down transformer. It has a big knob on top that allows you to dial in whatever output voltage you want. Working of transformer: The principle of the transformer is illustrated by consideration of a hypothetical ideal transformer. In this case, the core requires negligible Magneto-Motive Force to sustain flux, and all flux linking the primary winding also links the secondary winding. The hypothetical ideal transformer has no resistance in its coils. A simple transformer consists of two electrical conductors called the primary winding and the secondary winding. Energy is coupled between the windings by the time varying magnetic flux that passes through (links) both primary and secondary windings. Whenever the amount of current in a coil changes, a voltage is induced in the neighbouring coil the effect, called mutual inductance, is an example of electromagnetic induction.

Isolation Transformer

Procedure: First of all make sure that the earthing of your laboratory is proper and connected to the terminal provided on back side of the panel. Isolation Transformer 1. First of all make sure that the AC Mains is off and knob of variac is at zero position. 2. Now connect terminal 1 to 8 and 2 to 9. 3. Connect 8 to 10 and 9 to 13. 4. Short terminals 11 and 12 similarly on secondary side short 15 and 16. 5. Connect terminals 14 to 18 and 17 to 19. 6. Now insert voltmeters, for this connect terminals 8 and 9 to Vp1 and Vp2. 7. Similarly on the secondary side connect terminals 18 and 19 to Vs3 and Vs4. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 35

8. Switch on the Mains Supply. 9. Record reading of primary Voltmeter as Vp and that of secondary as Vs into the observation table. 10. Switch off the mains supply

Step Down Transformer Procedure: 1. First of all make sure that the AC Mains is off and knob of variac is at zero position. 2. Now connect terminal 1 to 8 and 2 to 9. 3. Connect 8 to 10 and 9 to 13. 4. Short terminals 11 and 12 of primary. 5. Connect terminals 14 to 18 and 15 to 19. 6. Now insert voltmeters, for this connect terminals 8 and 9 to Vp1 and Vp2. 7. Similarly on the secondary side connect terminals 18 and 19 to Vs3 and Vs4. 8. Switch on the Mains Supply. 9. Record reading of primary Voltmeter as Vp and that of secondary as Vs into the observation table. 10. Switch off the mains supply.

Step Up Transformer Procedure: 1. First of all make sure that the AC Mains is off and knob of variac is at 0position. 2. Now connect terminal 1 to 8 and 2 to 9. 3. Connect 8 to 10 and 9 to 11. 4. Short terminals on secondary side 15 and 16. 5. Connect terminals 14 to 18 and 17 to 19. 6. Now insert voltmeters, for this connect terminals 8 and 9 to Vp1 and Vp2. 7. Similarly on the secondary side connect terminals 18 and 19 to Vs3 and Vs4. 8. Switch on the Mains Supply. 9. Record reading of primary Voltmeter as Vp and that of secondary as Vs into the observation table. 10. Switch off the mains supply. Observation Table: Transformer

Vp

Vs

K

Isolation

Step Up

Step Down

Calculations: Transformation Ratio of transformer is given by:

Where, Vp and Vs are voltages across primary and secondary, Np and Ns are the number of turns in the primary and secondary, respectively Results: Transformation Ratio of Isolation Transformer is__________ Transformation Ratio of Step up Transformer is___________ Transformation Ratio of Step down Transformer is________ Precautions: 1. Avoid loose connections in the circuit. 2. Reading should be taken without parallax error.

Experiment 11 Objective: To perform Open Circuit and short circuit Test on Single-Phase Transformer. Equipments Needed: · Single phase transformer lab.

Theory: The purpose of this test is to determine the (i) Shunt branch parameters (Rc, Xø), (ii) No load power factor and (iii) core losses of a transformer. • Secondary side open CKT, that is why the ammeter (A) reads a no load current I 0 which is usually 2 to 6% of the rated current. • Wattmeter reads a total loss of a transformer at no load. W= Pcore+ Poh = + Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 37

0

I is very low hence (Pcore) is further low and negligible in comparison to core loss (P oh) no load = (.04 to .36) % of rated copper loss hence the wattmeter indicates practically only core loss at no load. • At no load wattmeter indicates only core loss (P h + Pe) and the core loss depends on the voltage if the frequency is constant. • So for getting rated or complete core loss we have to apply a rated voltage. • Hence, Open CKT test perform on rated voltage. • We will perform the O.C. test at LV side because at LV side apparatus of low voltage rating (voltage) is easily available and availability of supply easily made available.

Open Circuit test:

Procedure: First of all make sure that the earthing of your laboratory is proper and connected to the terminal provided on back side of the panel. · Open circuit test 1. First make sure that the mains supply is off and the knob of variac is at zero position. 2. Connect terminal 1 to 3 and 2 to 6. 3. Now connect 4 to 5 and connect 7 to 8. 4. Connect 6 to 9. 5. Connect 8 to 10 and 9 to 11. (Since Open Circuit Test is performed on low voltage side so low voltage winding is selected). 6. Connect 15 to 16, and secondary terminals 14 and 17 to 25 and 26 respectively (Opened).

7. Now insert meters at their corresponding positions, to insert ammeter connect terminals 3 and 4 to Ap3 and Ap4 (Since No load current is very low hence low range meter is used). 8. Now insert wattmeter, for this connect Wp1, Wp2 and Wp3 to 5, 7 and 6 respectively. 9. Now connect voltmeter by connecting terminals 8 and 9 to terminals Vp1 and Vp2. 10. Now switch on the mains supply. 11. Note the readings of Voltmeter, Ammeter and Wattmeter into the observation table as V0, I0 and W0 respectively. 12. Switch off the supply. Observation Table: S. N o

Voltmeter readings V0 in volt

Ammeter readings I0 in ampere

Wattmeter readings W0 in watt

1.

2.

3.

Calculation: Applied rated voltage on low voltage side = V1 Exciting current or no load current = I0 Wattmeter reading, W0/ Iron loss, Pc = V0I0Cosø0 No load power factor, Cosø0 = Pc/V0I0 Working component, Ic Magnetizing component, Iø

= I0Cosø0 = I0Sinø0

Core loss resistance, Rc

= PcI2c = V1/Ic =V1/ I0Cosø0

Magnetising reactance, Xø

= V1/Iø = V1/ I0Sinø0

Results: NO load loss& core loss=....... Rc=..........&Xø=........ Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 39

Precautions: 1. Avoid loose connections in the circuit. 2. Reading should be taken without parallax error. Short circuit Test: Theory: • • • •

As secondary is shorted, it may draw a very large current at rated voltage and transformer may burn out. So, this is not performed at rated voltage. For getting full load or rated ohmic, this test is performed at rated current. Rated current may be drawn at only 2 to 10% of rated voltage. So, reading of the voltmeter is 2 to 10% of rated voltage. It is convenient to connect high voltage side to supply ratio current at HV side is low, so we can solve our purpose with low rating ammeter.

Circuit diagram:

Procedure: First of all make sure that the earthing of your laboratory is proper and connected to the terminal provided on back side of the panel. 1. First of all make sure that the Mains are off and the knob of Variac is at zero position. 2. Connect terminal 1 to 3 and 2 to 6. 3. Now connect 4 to 5. 4. Connect terminal 7 to 8 and 6 to 9. 5. Connect 8 to 10 and 9 to 13, short terminals 11 and 12 of primary of transformer. (Since Short Circuit Test is performed on high voltage side, hence high voltage winding is selected). 6. On the secondary side, connect terminal 14 to 25, 15 to 26 and then short terminals 25 and 26. 7. Now insert meters in the circuit. To insert ammeter connect terminals 3 to As1 and 4 to As2. 8. To insert wattmeter, connect terminals 5 to Ws2, 7 to Ws1 and 6 to Ws3. 9. Now connect voltmeter in the circuit, for this connects terminal 8 to Vs1 and 9 to Vs2. 10. Switch on AC supply.

11. Now gradually increase the input voltage so that the reading of ammeter reaches its maximum value (5A). 12. Record the Ammeter, Voltmeter, Wattmeter readings as Isc, Vsc and Wsc in the observation table. 13. Switch off the supply. Observation Table: S. No

Voltmeter reading VSC in volt

Ammeter reading ISC in ampere

Wattmeter reading WSC in watts

1.

2.

3.

4.

Calculations: Hence, WSC = VSC ISC CosФSC. CosФSC = WSC/VSC ISC. Once these factors known we can determine the circuit parameter Re1 = WSC / I² Ze1 = VSC / ISC = = Knowing the transformation ratio K, equivalent circuit parameters referred to Secondary also can be determined. Here, VSC = Reading of Voltmeter. ISC = Short circuit current of the transformer. WSC = (PCU) F.L. = full load copper loss of the transformer.(reading of Wattmeter) Re1 = Equivalent resistance of the transformer at primary side. Xe1 = Equivalent reactance of the transformer at primary side. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 41

Ze1 = Equivalent impedance of the transformer at primary side. CosФSC = Short circuit power factor.

Results: Find equivalent impedance =................ Cu loss at full load =................. Total voltage drop in the transformer =..............

Precautions: 1. Avoid loose connections in the circuit. 2. Reading should be taken without parallax error 3. System should not remain ON for more than 5 min. in this test (in short condition), otherwise the transformer may burn.

Experiment:-12 Objective: Speed control of DC shunt motor. Apparatus Required: i. Advanced DC Shunt Motor Lab. ii. Connecting leads.

iii. Tachometer Theory: Speed Control of DC Motor: Speed of the DC motor is given by the relation:

Where, N = Speed of the DC motor. V = Applied voltage in DC motor. Ф = Flux per pole of DC motor. IA = Armature current in DC motor. RA = Armature resistance of DC motor. From the above equation it is clear that the speed of DC motor can be controlled: By varying flux per pole this is known as flux or field control method. By varying the armature drop that is by varying the resistance of the armature circuit this is known as armature controlled method. By varying the applied voltage this is known as voltage controlled method. 1. Field Control Method : The flux produced by the shunt winding depend upon the current flowing through it, when a variable resistance is connected in series with the field winding the shunt field current is reduced and hence the flux consequently the motor run at the speed higher than the normal speed. The amount of increase in speed depends of the variable resistance. This method is more economical as very little power is wasted in the shunt field variable resistance due to relatively small current. 2. Armature Control Method : In a shunt motor flux is constant when the applied voltage and shunt field resistance are constant therefore the speed of the motor is directly proportional to the induced emf the value of induced emf depend upon the drop in armature circuit when additional resistance is connected in series with the armature circuit induced emf is reduced and hence the speed thus the motor runs at a speed lesser than the normal speed. This method is not economical as large power is wasted in the control resistance since it carries full armature current. 3. Voltage Controlled Method : In this motor the voltage across the motor can be changed by connecting them in series or in parallel. This is widely used in electric traction. When the motor are connected in series low speed are obtained and when they are connected in parallel high speed (nearly 4 times to that of the first case) are obtained.

Speed and Armature Current Characteristic:

It is the curve drawn between the speed and armature current, known as speed characteristic. If the armature drop is negligible the speed of the motor will remain constant for all the value of load as shown by the dotted line AB but as the armature current increase due to increase of load armature drop increase and speed of the motor decreases as shown by the line AC. Moreover the characteristic curve does not start from zero because a small armature current called no load current is necessary to maintain rotation of the motor at no load. Since there is no appreciable change in the speed of the DC motor from no load to full load as it is considered to be the constant speed motor this motor is best suited where almost speed constant is required. Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 43

To perform Load characteristics of separately excited DC Shunt Motor and Draw N-Ia Graph Equipments Needed: · Connecting Leads. · Techometer. Circuit Diagram: Procedure: 1. First of all make sure that the earthing of your laboratory is proper and it is connected to the terminal provided on back side of the panel. 2. Make sure that the supply is off and knob of Variac is at 0 positions. 3. Also make sure that the belt is loose so that motor can run at normal speed. 4. Connect + terminals of Fixed DC supply to the field terminal F of DC motor section provided on panel and - terminal of Fixed DC supply to field terminal FF of DC motor section provided on panel. 5. Connect field terminal FF of DC motor section provided on panel to terminal A3. 6. Connect + terminals of Variable DC supply to the armature terminal A of DC motor section provided on panel and - terminal of Variable DC supply to armature terminal AA of DC motor section provided on panel. 7. Connect armature terminal AA of DC motor section provided on panel to terminal A1. 8. Connect motor to the panel for this connect armature terminal A of DC motor section provided on panel to terminal A of motor and AA terminal of motor to terminal A2 provided on panel as shown in figure 17.

9. Similarly connect field terminal F of DC motor section provided on panel to terminal FF of motor and FF terminal of motor to terminal A4 provided on panel as shown in figure. 10. Switch ON the supply and Switch ON the mains Switch provided on the panel. 11. Now slowly vary the variac of variable DC supply to its maximum position and note no load speed of motor and also note the readings displayed on Screen. 12. Now slowly tight the belt and record Speed for different armature currents. 13. Record your observations into the observation table. 14. Take number of readings and draw graph between Armature Current and Motor Speed. 15. Switch off the Supply. Note: While performing the experiment make sure that armature current should not exceed 3A because after 3A drive will trip and red neon lamp will blow. Observation Table: S. No.

Armature Voltage (Va),in volt

Armature Current Ia (Amp.)

Load ( Kg )

Speed (RPM)

1.

2.

3.

4.

5.

6.

Results:

Deptt. Of electrical engineering, SOE, GBU, Greater Noida (U.P.) 201308 Page 45