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Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
Ee 444 electrical drives be(tx) 2012
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Ee 444 electrical drives be(tx) 2012

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ELECTRICAL LAB MANUAL

ELECTRICAL LAB MANUAL

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  • 1. PRACTICAL WORK BOOK For Academic Session 2012 ELECTRICAL DRIVES (EE-444) For BE (TX)Name:Roll Number:Class:Batch: Semester/Term :Department : Department of Electrical Engineering NED University of Engineering & Technology
  • 2. Electrical Drives Safety RulesNED University of Engineering and Technology Department of Electrical Engineering SAFETY RULES1. Please don t touch any live parts.2. Please don t work bare footed.3. Never use an electrical tool near water.4. Never use an electrical tool that has fallen into water.5. Don t carry unnecessary item with you during performance (like water bottle, bags etc.)6. Before connecting any leads/Connecting Wires make sure power is switch off.7. In case of emergency, push the nearby red color emergency switch of any panel or immediately call the laboratory staff.8. In case of electricity fire, never put water on it as it will further worse the condition; use the class C fire extinguisher.Fire is a chemical reaction involving rapid oxidation(combustion) of fuel. Three basic conditions when met,fire takes place. These are fuel, oxygen & heat, absenceof any one of the component will extinguish the fire. Figure: Fire Triangle A (think ashes): If there is a small electrical fire, be sure to use paper, wood etc. only a Class C or multipurpose (ABC) fire extinguisher, otherwise you might make the B(think barrels): problem worsen. flammable liquids The letters and symbols are explained in left C(think circuits): figure. Easy to remember words are also shown. electrical fires Don t play with electricity, Treat electricity with respect, it deserves
  • 3. Electrical Drives ContentsNED University of Engineering and Technology Department of Electrical Engineering CONTENTS Lab. List of Experiments Page Dated Remarks No. No. 01 Introduction SACED TECNEL. 01 Introduction to the devices : Diodes 02 SCR 03 IGBT s & MOSFET switches (a) AC/DC Single-phase Not- Controlled Half-wave Rectifier with 12 R load, RL Load. 03 (b) AC/DC Single-phase Not- Controlled Full wave Rectifier with R load and R-L load 17 To study the effect of Free Wheeling diode on the output of single phase Not-controlled 04 half-wave rectifier. 22 (a) AC/DC Three-Phase Not-Controlled Half-wave Rectifier with R load & 26 R-L load. 05 (b) AC/DC Three-Phase Not-Controlled Full-wave Rectifier with R load & 32 R-L load (a) AC/DC Single-phase Controlled Half-wave Rectifier with R load, 37 R-L load 06 (b) AC/DC Single Controlled Full- wave Rectifier with R load & R-L 43 load
  • 4. Electrical Drives ContentsNED University of Engineering and Technology Department of Electrical Engineering To study the effect of Free Wheeling diode 07 on the output of single phase controlled 49 half-wave rectifier. (a) AC/DC Three-phase Controlled Half-wave Rectifier with R load, 53 R-L load 08 (b) AC/DC Three-Phase Controlled Full-wave Rectifier with R load & 59 R-L load 09 DC/DC Chopper (BUCK). 64 To draw the Magnetization curve of self- 10 excited Dc shunt Generator (Open circuit 70 Characteristics O.C.C) To draw the load characteristics curve of 11 self-excited dc shunt generator 73 To draw the external and internal 12 characteristics of separately excited DC 76 generator Speed control of a DC shunt motor by flux 13 variation method 78 Speed control of a D.C. Shunt Motor by 14 armature rheostat control method 81 To observe the starting of three phase 15 Synchronous and Induction motor 83
  • 5. Electrical Drives Lab session 01NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 1Object:-Introduction to SACED TECNEL.Apparatus: SACED TECNEL (Software) TECNEL RCL3R Load moduleTheory: In electrical drives lab, we will use TECNEL/B hardware & RCL3R Load module.The front panel of Tecnel /B consists of: Diodes module: 6 diodes. Thyristors module: 6 Thyristors. IGBTS Module: 6 IGBTS. Capacitor module Sensors module: 4 Voltage sensors & 2 Current sensors. Power supply connections for Red Yellow Blue Phases (R, S, T), Neutral and Ground. Practices schemes. PROCESS DIAGRAM AND ELEMENTS ALLOCATION Page | - 1 -
  • 6. Electrical Drives Lab session 01NED University of Engineering and Technology Department of Electrical EngineeringRCL3R. Resistive, Inductive and Capacitive Loads Module:Our Resistive, Capacitive and Inductive Loads Module (RCL3R) offers single and Three-phaseresistances, inductances & capacitances.The values are as follows:Variable resistive loads: 3 x [150 (500 W)]Fixed resistive loads: 3 x [150 (500 W) + 150 x (500 W)]Inductive loads: 3 x [0, 33, 78, 140, 193, 236mH]. (230V /2 A)Capacitive loads: 3 x [4 x 7 µF]. (400V)Now load the TECNEL software in PC, the main screen will be look like this:And the Plot screen will be look like this: Page | - 2 -
  • 7. Electrical Drives Lab session 02NED University of Engineering and Technology Engineering Department of Electrical Engineering LAB SESSION 2Object:-Introduction to the devices devices: Diodes SCR IGBT s & MOSFET switchesTheory:- - 1. DIODE In electronics, a diode is a two terminal electronic component that conducts DIODE:- two-terminal electric current in only one direction. The most common function of a diode is to allow an electric current to pass in one direction (called the diodes forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be in thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extrac extract modulation from radio signals in radio receivers. Figure: (a) Construction of a semi conductor diode semi-conductor (b) symbol of diodeA diode is formed by joining two equivalently doped P Type and N-Type semiconductor. When P-Type N-Typethey are joined an interesting phenomenon takes place. The P Type semiconductor has excess P-Typeholes and is of positive charge. The N Type semiconductor has excess electrons. At the point of N-Typecontact of the P Type and N Type regions, the holes in the P Type attract electrons in the N Type P-Type N-Type P-Type N-Typematerial. Hence the electron diffuses and occupies the holes in the P Type material. Causing a aterial. P-Typesmall region of the N type near the junction to loose electrons and behaves like intrinsic N-typesemiconductor material, in the P type a small region gets filled up by holes and behaves like an P-typeintrinsic semiconductor semiconductor.This thin intrinsic region is called depletion layer, since it is depleted of charge (see diagram sabove) and hence offers high resistance. It s this depletion region that prevents the furtherdiffusion of majority carriers. In physical terms the size of the depletion layer is very thin. he Page | - 3 -
  • 8. Electrical Drives Lab session 02NED University of Engineering and Technology Engineering Department of Electrical EngineeringFigure: (a) Formation of depletion Layer. (b) Forward characteristics of diodeDue to formation this depletion layer the diode will not conduct until the depletion layer voltage isovercome, that is 0. V for Germanium and 0. V for silicon. An increase in the applied voltage , 0.3 0.7above that narrow depletion layer (0. V for Germanium and 0. V for silicon) results in rapid rise (0.3 0.7in the flow of current. Graphs depicting the current voltage relationship for forward biased PN of thejunction, for both silicon and germanium are called forward characteristics and shown below.Diode is mainly used to perform rectification, converting A.C into unidirectional D.C. In half mainly rectification, .wave rectification, either the positive or negative half of the AC wave is passed, while the other rectification,half is blocked. Because only one half of the input waveform reaches the output, it is veryinefficient if used for power transfer. Half wave rectification can be achieved with a single diode Half-wavein a one-phase supply, or with three diodes in a three-phase supply. phase phaseFigure:- Half wave rectification process in which negative half cycle is annulled by diodeReview A diode is an electrical component acting as a one way valve for current. one-way When voltage is applied across a diode in such a way that the diode allows current, the diode is said to be forward-biased biased. When voltage is applied across a diode in such a way that the diode prohibits current, the di diode is said to be reverse-biased biased. The voltage dropped across a conducting, forward forward-biased diode is called the forward voltage. voltage. Forward voltage for a diode varies only slightly for changes in forward current and temperature, and is fixed by the chemical composition of the P N junction. and P-N Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reverse bias voltage that a diode can withstand without breaking down is reverse-bias called the Peak Inverse Voltage or PIV rating. Voltage, Page | - 4 -
  • 9. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical Engineering Figure: V-I characteristics of Diode THRYRISTOR (SCR):-A silicon-controlled rectifier is a four-layer semiconductor device that controls current. SCR consists of four layers of alternating P and N type semiconductor materials and it has three terminals called anode, cathode and gate. The SCR is uni-directional device, meaning it passes electron current only in one direction, from cathode to anode when positive gate signal is applied. It is named as controlled rectifier because it can control the amount of power flowing from source to load. It can be made to conduct for whole part of positive half cycle or for small part of positive half cycle. The SCR will turn on and conduct current when following two conditions are satisfied. 1. It has forward biased voltage across its anode and cathode of at least 0.7 Volts. Forward biased condition exists when anode is more positive than cathode. 2. It has a positive voltage applied across the gate. Figure: Thyristor Construction, schematic symbol, forward biasing for normal operationVolt-Ampere CharacteristicsFigure below illustrates the volt-ampere characteristics curve of an SCR. The vertical axis + Irepresent the device current, and the horizontal axis +V is the voltage applied across the device Page | - 5 -
  • 10. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical Engineeringanode to cathode. The parameter IF defines the RMS forward current that the SCR can carry in theON state, while VR defines the amount of voltage the unit can block in the OFF state. Figure:- V-I Characteristics of SCRBiasingThe application of an external voltage to a semiconductor is referred to as a bias.Forward Bias Operation A forward bias, shown above in figure as +V, will result when a positive potential is applied to the anode and negative to the cathode. Even after the application of a forward bias, the device remains non-conducting until the positive gate trigger voltage is applied. After the device is triggered ON it reverts to a low impedance state and current flows through the unit. The unit will remain conducting after the gate voltage has been removed. In the ON state (represented by +I), the current must be limited by the load, or damage to the SCR will result.Reverse Bias Operation The reverse bias condition is represented by -V. A reverse bias exists when the potential applied across the SCR results in the cathode being more positive than the anode. In this condition the SCR is non-conducting and the application of a trigger voltage will have no effect on the device. In the reverse bias mode, the knee of the curve is known as the Peak Inverse Voltage PIV (or Peak Reverse Voltage - PRV) and this value cannot be exceeded or the device will break-down and be destroyed. A good Rule-of -Thumb is to select a device with a PIV of at least three times the RMS value of the applied voltage Page | - 6 -
  • 11. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical EngineeringSCR Phase ControlIn SCR Phase Control, the firing angle, or point during the half-cycle at which the SCR istriggered, determines the amount of current which flows through the device. It acts as a high-speedswitch which is open for the first part of the cycle, and then closes to allow power flow after thetrigger pulse is applied. Figure two below shows an AC waveform being applied with a gatingpulse at 45 degrees. There are 360 electrical degrees in a cycle; 180 degrees in a half-cycle. Thenumber of degrees from the beginning of the cycle until the SCR is gated ON is referred to as thefiring angle, and the number of degrees that the SCR remains conducting is known as theconduction angle. The earlier in the cycle the SCR is gated ON, the greater will be the voltageapplied to the load. Figure Three shows a comparison between the average output voltages for anSCR being gated on at 30 degrees as compared with one which has a firing angle of 90 degrees.Note that the earlier the SCR is fired, the higher the output voltage applied to the load.Figure:- SCR output waveform (a) When forward biased (b) Triggering at different anglesThe voltage actually applied to the load is no longer sinusoidal, rather it is pulsating DC having asteep wave front which is high in harmonics. This waveform does not usually cause any problemson the driven equipment itself; in the case of motor loads, the waveform is smoothed by the circuitinductance.MOSFET (Metal oxide Semiconductor Field Effect Transistor):-The metal oxide semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is atransistor used for amplifying or switching electronic signals. It has three terminals gate, sourceand drain as shown below. Unlike the bipolar junction transistor (BJT), the metal-oxide-semiconductor field effect transistor (MOSFET) is composed of a bulk substrate of metal oxideions, which form n- and p-charged regions in order to amplify analog voltages across a circuit.Figure shows the basic of a MOSFET. Note the charged n-regions in the substrate and the four Page | - 7 -
  • 12. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical Engineeringterminals (3 active, 1 grounded). Furthermore, unlike the BJT, the operation of the MOSFET isdetermined by a voltage rather than a current. Gate Source Drain n+ n+ p Bulk (or substrate) Diagram of the composition of a MOSFETLike the bipolar junction transistors, the MOSFETs are composed of two different semiconductorregions, n and p. Instead of creating a current through the device by filling of holes in the pregion, the MOSFET forms a channel of the positively charged n layer between the two nsections, as shown in Figure 1. This channel forms when a voltage is applied across the gate,attracting the electrons in the n region nearer to the gate charge. The strength of the gate voltagedetermines the geometry of the channel and the current that passes through it. Figure below showsthe drain characteristic of the MOSFET, the relationship between the drain-source voltage and thedrain current. Like the collector characteristic of the BJT, the MOSFET drain characteristic usestwo voltages and the gate voltage to construct a series of characteristic curves for the device. Figure 1 Drain characteristic for a MOSFET Two voltages are keys to the operation of the MOSFET, the threshold voltage and the gatevoltage. The threshold voltage VT is the voltage at which the MOSFET begins to conduct theelectrons from the drain to the source. The difference between it and the gate voltage, VG ,determines the flow of the electrons through the channel. If the difference between the thresholdand the gate is negative, no current flows. If this difference is greater than zero, current flowsbetween the two terminals. Page | - 8 -
  • 13. Electrical Drives Lab session 02NED University of Engineering and Technology Engineering Department of Electrical EngineeringAt a certain point within the saturation region a pinch-off occurs. The pinch region, -off pinch-off means thatthe channel thins , not allowing electron flow between the two terminals. Generally, if the termidifference between the gate voltage and the threshold voltage is greater than or equal to thethreshold voltage, this pinch off occurs pinch-off Figure:- MOSFET schematic symbols Figure:IGBT (INSULATED GATE BIPOLAR TRANSISTOR):-A power transistor that has characteristics of both MOSFET and bipolar junction transistors(BJTs).is called IGBT. IGBT handles high current, a characteristic of BJTs, but enables fast isswitching with greater ease of control. IGBTs are found in home appliances, electric cars and electricdigital stereo power amplifiers The insulated gate bipolar transistor or IGBT is a three terminal three-terminalpower semiconductor device, noted for high efficiency and fast switching. It switches electricpower in many modern appliances: electric cars, trains, variable speed refrigerators, air air-conditioners and even stereo systems with switching amplifiers. Since it is designed to turn on andoff rapidly, amplifiers that use it often synthesize complex waveforms with pulse widthmodulation and low pass fi low-pass filters. The IGBT combines the simple gate drive characteristics of the gate-driveMOSFETs with the high current and low saturation voltage capability of bipolar transistors by high-current saturation-voltagecombining an isolated gate FET for the control input, and a bipolar power transistor as a switch, ina single device. The IGBT is used in medium- to high-power applications such as switched mode medium- power switched-modepower supply, traction motor control and induction heating. Large IGBT modules typically consistof many devices in parallel and can have very high current handling capabilities in the order of currenthundreds of amperes with blocking voltages of 6000 V, equating to hundreds of kilowatts. ,Figure:- Electronic symbol of IGBTIGBT switching characteristics: The switching characteristics of an IGBT are very much similar to GBT characteristics:-Thethat of a Power MOSFET. The major difference from Power MOSFET is that it has a tailingcollector current due to the stored charge in the N drift region. The tail current increases the turn N--drift turn-off loss and requires an increase in the dead time between the conduction of two devices in a half time half- Page | - 9 -
  • 14. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical Engineeringbridge circuit. The Figure shows a test circuit for switching characteristics and the Figure 9 showsthe corresponding current and voltage turn-on and turn-off waveforms. IXYS IGBTs are testedwith a gate voltage switched from +15V to 0V. To reduce switching losses, it is recommended toswitch off the gate with a negative voltage (-15V).The turn-off speed of an IGBT is limited by the lifetime of the stored charge or minority carriers inthe N--drift region which is the base of the parasitic PNP transistor. The base is not accessiblephysically thus the external means cannot be applied to sweep out the stored charge from the N--drift region to improve the switching time. The only way the stored charge can be removed is byrecombination within the IGBT. Traditional lifetime killing techniques or an N+ buffer layer tocollect the minority charges at turn-off are commonly used to speed-up recombination time. Page | - 10 -
  • 15. Electrical Drives Lab session 02NED University of Engineering and Technology Department of Electrical EngineeringThe main advantages of IGBT over a Power MOSFET and a BJT are:1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-statecurrent density. So smaller chip size is possible and the cost can be reduced.2. Low driving power and a simple drive circuit due to the input MOS gate structure. It can beeasily controlled as compared to current controlled devices (Thyristor, BJT) in high voltage andhigh current applications.3. Wide SOA. It has superior current conduction capability compared with the bipolar transistor. Italso has excellent forward and reverse blocking capabilities.The main drawbacks are:1. Switching speed is inferior to that of a Power MOSFET and superior to that of a BJT. Thecollector current tailing due to the minority carrier causes the turn off speed to be slow.2. There is a possibility of latch up due to the internal PNPN Thyristor structure. Page | - 11 -
  • 16. Electrical Drives Lab Session 03 (a)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 3 (a)Object:AC/DC Single phase Not Controlled Half-wave Rectifier with R load, RL Load. Single-phase Not-Controlled wave load,Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Single-phase half wave not controlled rectifiers: phase half-wave not-controlledNot-controlled rectifiers are constituted by diodes that, a controlled actsas not-controlled elements, provide a dependent output controlledvoltage of fixed magnitude. In half wave rectifiers, diodeconducts only in half cycle of the input, otherwise open.From a theoretical point of view, they may be considered asswitches that are opened or closed depending on the direction of the voltage applied. That is with a voltagepositive voltage between anode (A) and cathode (K) the switch is closed, and it is opened if thevoltage is negative.The behavior of the rectifier will depend considerably on the used load type, so we may have:Pure resistive load (R) where the voltage is annulled when its direction changes. (R):Inductive load (R L), where the conduction continues until the moment when the current in the (R-L),coil is annulled, although the output voltage inverts its polarity.Circuit Diagram Diagram: E1UK ModelProcedure: 1. Carry out the assembly E1UK shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. Page | - 12 -
  • 17. Electrical Drives Lab Session 03 (a)NED University of Engineering and Technology Department of Electrical Engineering And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure) Figure: Uncontrolled Half Wave Rectifier R Load For different values of R the RMS voltage will vary across the load, which can be calculated using multi meter. S. No Load Resistance V rms Voltage Across Diode 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage Across Diode 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure) Page | - 13 -
  • 18. Electrical Drives Lab Session 03 (a)NED University of Engineering and Technology Department of Electrical Engineering Figure: Uncontrolled Half Wave Rectifier RL Load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Single-phase Not-Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.Question:Define the following terms:1. Ripple Factors:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. Harmonics:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________3. Fundamental Frequency:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 14 -
  • 19. Electrical Drives Lab Session 03 (a)NED University of Engineering and Technology Department of Electrical Engineering4. Power Factor:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________5. Rectifiers:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Waveforms: R LOAD Fig: Input Voltage Fig: Output Voltage across R Load Fig: Load Current IL Fig: Output Voltage across Diode Page | - 15 -
  • 20. Electrical Drives Lab Session 03 (a)NED University of Engineering and Technology Department of Electrical Engineering R-L LOAD Fig: Input Voltage Fig: Output Voltage across RL Load Fig: Load Current IL Fig: Output Voltage across Diode D1 Page | - 16 -
  • 21. Electrical Drives Lab Session 03 (b)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 3 (b)Object:AC/DC Single-phase Not-Controlled Full wave Rectifier with R load and R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Single-phase full-wave not-controlled rectifiers:By the use of four diodes, rectifier circuit performance can be greatly improved. The entire supplyvoltage wave is utilized to impress current through the load. Figure: Single-phase, full-wave diode rectifier: (a) Circuit diagram and (b) load voltage and current waveforms for R load.The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RLLoad.Circuit Diagram: B2U Model Page | - 17 -
  • 22. Electrical Drives Lab Session 03 (b)NED University of Engineering and Technology Department of Electrical Engineering Table 1: Single-Phase Diode Rectifier Circuits with Resistive LoadProcedure: 1. Carry out the assembly B2U shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure) Figure: Uncontrolled Full Wave Rectifier with R load Page | - 18 -
  • 23. Electrical Drives Lab Session 03 (b)NED University of Engineering and Technology Department of Electrical Engineering And measure the following quantities S. No Load Resistance V rms Voltage Across D1 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage Across Diode 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure) Figure: Uncontrolled Full Wave Rectifier with RL load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Single-phase Not-Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment. Page | - 19 -
  • 24. Electrical Drives Lab Session 03 (b)NED University of Engineering and Technology Department of Electrical EngineeringWaveforms: R LOAD Fig: Input Voltage Fig: Output Voltage across R Load Fig: Load Current IL Fig: Supply Current IS Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3 Page | - 20 -
  • 25. Electrical Drives Lab Session 03 (b)NED University of Engineering and Technology Department of Electrical Engineering R-L LOAD Fig: Input Voltage Fig: Output Voltage across RL Load Fig: Load Current IL Fig: Supply Current IS Fig: Output Voltage across Diode D1 Fig: Output Voltage across Diode D3 Page | - 21 -
  • 26. Electrical Drives Lab Session 04NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 4Object:To study the effect of Free Wheeling diode on the output of single phase Not-controlled half-waverectifier.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Freewheeling diode:-The behavior of the rectifier will depend considerably on the used load type, so we may have:when using a load with inductive character, the following effects appear: when the input voltage is inverted, a peak of negative voltage appears in the output, and it is not annulled until the current becomes zero. In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.These two effects may be eliminated, as well as the reduction of the harmonic content, with theintroduction in parallel with the load of a diode called Freewheeling Diode (FWD) or FlyingDiode.When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil isinverted. It begins to act as a generator, forcing the conduction of the FWD and the load currentgoing through it, annulling the peak of negative voltage, as we can see in the following. Page | - 22 -
  • 27. Electrical Drives Lab Session 04NED University of Engineering and Technology Department of Electrical EngineeringWe may see here that from 10ms the waveform of the current load (graph in previous page) is anexponential one, that proves the discharge of the coil for the resistance through the FWD. This iscorroborated by the input current, ceasing at 10ms.Circuit Di Diagram:- Figure:- E1UK Model Figure:Procedure: 1. Carry out the assembly E1UK shown in the above figure 2. Now connect a diode in anti-Parallel manner with the First diode as shown below anti 3. Connect the respective RL load to its terminal. For RL Load with FWD Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , mH) R=37 measuring with the voltmeter the average output voltage. Voltage Across Diode S. No Load Impedance V rms D1 D2 1. 300 + 75 + 140mH 140 2. 300 + 75 + 236mH 23 Observe how the output current varies for different L values with R=375 . R=3 And sample the following parameters: sample Input voltage V2, Output voltage V1, Output current I2, Diode voltage V3 (as shown in figure) Page | - 23 -
  • 28. Electrical Drives Lab Session 04NED University of Engineering and Technology Department of Electrical Engineering Figure: Uncontrolled single phase Half Wave Rectifier RL Load & FWD. 4. Load the SACED TECNEL program in PC and the window corresponding to this practice 5. Select Practice Option 6. AC/DC Single-phase Not-Controlled Half wave Rectifier option 7. Select the respective sample sensors 8. Check the connections and switch on the equipment. 9. Press the Data Capture button. 10. Visualize the parameters measured and save them in the corresponding file.Switch off the equipmentQuestion:Define the following terms:1. Free Wheeling Diode________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. Effect of FWD on RL Load Output________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 24 -
  • 29. Electrical Drives Lab Session 04NED University of Engineering and Technology Department of Electrical Engineering3. Fundamental Frequency:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________5. Rectifiers:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Waveforms:- R-L LOAD WITH FWD Fig: Input Voltage Fig: Output Voltage across R-L Load Fig: Load Current IL Fig: Diode Voltage Page | - 25 -
  • 30. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 5 (a)Object:AC/DC Three-Phase Not-Controlled Half-wave Rectifier with R load& R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Three-phase half-wave not-controlled rectifiers:Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is foundthat the use of a three-phase rectifier system, in comparison with a single-phase system, providessmoother output voltage and higher rectifier efficiency. Also, the utilization of any supplytransformers and associated equipment is better with poly-phase circuits. If it is necessary to usean output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier. Figure: Three-phase, half-wave diode rectifier with resistive load: (a) circuit connection, (b) phase voltages at the supply, (c) load current. Page | - 26 -
  • 31. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering Table: Three Phase Uncontrolled Rectifier with Ideal SupplyCircuit Diagram: M3UK ModelProcedure: 1. Carry out the assembly M3UK shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as shown in figure) Page | - 27 -
  • 32. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering Figure: Uncontrolled Three Phase Full Wave Rectifier with R load Also measure the following quantities using multi-meter. S. No Load Resistance V rms Voltage Across D1 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage Across Diode 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltages (V2, V3, V4), Output voltage V1, Output current I1, Diode voltage V5 (as shown in figure) Page | - 28 -
  • 33. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering Figure: Uncontrolled Three Phase Full Wave Rectifier with RL load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Three-phase Not-Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment. Here you can also study and visualize what will be the effect of inverting the polarization of the three diodes. Secondly suppose that, due to an over-voltage, one of the diodes is in open circuit. Study and visualize what effect provokes the output voltage. Page | - 29 -
  • 34. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering Waveforms: R LOAD Fig: Input Voltages R,S,T Fig: Output Voltage across R Load Fig: Load Current IL Fig: Output Voltage across Diode R-L LOAD Fig: Input Voltages R,S,T Fig: Output Voltage across R Load Page | - 30 -
  • 35. Electrical Drives Lab Session 05(a)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL Fig: Output Voltage across Diode Page | - 31 -
  • 36. Electrical Drives Lab Session 05 (b)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 5 (b)Object:AC/DC Three-Phase Not-Controlled Full-wave Rectifier with R load& R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Three-phase full-wave not-controlled rectifiers:The basic full wave uncontrolled (diode) rectifier circuit is shown in the following figure. Thediodes D1, D3, D5 are sometimes referred to as the upper half of the bridge, while diodes D2, D4and D6 constitute the lower half of the bridge. As with the half wave operation the voltages at theanode of the diode valves vary periodically as the supply voltages undergo cyclic excursions.Commutation or switch off of a conducting diode is therefore accomplished by natural cycling ofthe supply voltages and is known as natural commutation. The load current IL is nowunidirectional but the supply currents are bi-directional. In order to permit load current to flow, atleast one diode must conduct in each half of the bridge. When this happens the appropriate line toline supply point voltage is applied across the load. In comparison with the half wave bridge, inwhich supply phase voltage is applied across the load, the full wave bridge has immediateadvantage that peak load voltage is 3 times as great.Circuit Diagram: B6U ModelProcedure: 1. Carry out the assembly B6U shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Page | - 32 -
  • 37. Electrical Drives Lab Session 05 (b)NED University of Engineering and Technology Department of Electrical Engineering Input voltage V4, Output voltage V1, Output current I1, Diode voltage V3 (as shown in figure) Figure:- Three phase not controlled full wave rectifier with R load Also measure following quantities using multi-meter S. No Load Resistance V rms Voltage across D1 1 300 + 75 2 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. V av = S. No Load Impedance V rms Voltage across D1 1 300 + 75 + 140 m H 2 300 + 120 + 236mH Observe how the output current varies for different L values with R=375. Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Diode voltage V3, Output current (load) I1 (as shown in figure) Page | - 33 -
  • 38. Electrical Drives Lab Session 05 (b)NED University of Engineering and Technology Department of Electrical Engineering Figure:- three phase not controlled full wave rectifier with RL load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Three-phase Not-Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment. Page | - 34 -
  • 39. Electrical Drives Lab Session 05 (b)NED University of Engineering and Technology Department of Electrical EngineeringWaveforms: R LOAD Fig: Input Voltage Fig: Output Voltage across R Load Fig: Load Current IL Fig: Output Voltage across Diode R-L LOAD Fig: Input Voltage Fig: Output Voltage across R Load Page | - 35 -
  • 40. Electrical Drives Lab Session 05 (b)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL with L=140mH Fig: Load Current IL with L=236mH Fig: Output Voltage across diode Page | - 36 -
  • 41. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 6 (a)Object:AC/DC Single-phase Controlled Half-wave Rectifier with R load, R-L load and R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Single-phase half-wave controlled rectifiers:The controlled rectifiers are constituted by Thyristors. The Thyristoris basically a diode controlled by positive voltage among gate (G)and anode (A).The main difference between controlled rectifiers and not controlledRectifiers is based on the fact that the Thyristor conduction and non-conductionstates can be controlled externally.Figure:- single phase half wave controlled rectifier a) circuit connections b) output voltage waveformThe Thyristors can be made to conduct during the whole part of positive cycle or for some part ofpositive cycle, in this way we can control the amount of power flowing from source to load incontrolled rectifiers.In this lab session we will deal with rectifiers which are capable to decide the moment when wemay trigger the Thyristor by using PC.The behaviour of controlled rectifier will depend, to a great extent, on the load type used.Pure resistive load (R): where the voltage is annulled when its direction changes. The averageoutput voltage for resistive load will be : V average = [1 + cos ] V/2Inductive load (R-L), where the conduction continues until the moment when the current in thecoil is annulled, although the output voltage inverts its polarity.The average output voltage for RL load will be : Page | - 37 -
  • 42. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical Engineering V average = [ cos {cos( + )}] V/2In order to separate the output voltage and the load type, we may use the freewheeling diode(FWD), which avoids the inversion of polarization in the output voltage.Circuit Diagram: E1CK ModelProcedure: 1. Carry out the assembly E1CK shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300 ohms plus variable resistance in series. And sample the following parameters: Input voltage V2, Output voltage V1, Output current I2, Thyristor voltage V3 (as shown in figure) Figure: Controlled Half Wave Rectifier with R Load Page | - 38 -
  • 43. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical Engineering For different values of R the RMS voltage will vary across the load, which can be calculated using multi meter. S. No Load Resistance V rms Voltage Across Thyristor 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage Across Thyristor 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V2, Output voltage V1, Thyristor voltage V3, Output current (load) I2 (as shown in figure) Figure: Controlled Half Wave Rectifier RL Load Page | - 39 -
  • 44. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical Engineering 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Single-phase Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.Question:Define the following terms:1. Ripple Factors:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. Harmonics:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________3. Fundamental Frequency:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________4. Power Factor:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________5. Rectifiers:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 40 -
  • 45. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical EngineeringWaveforms: R LOAD Fig: Input Voltage Fig: Output Voltage across R load Fig: Load Current IL Fig: Output Voltage across Thyristor R-L LOAD Fig: Input Voltage Fig: Output Voltage across R-L load Page | - 41 -
  • 46. Electrical Drives Lab Session 06 (a)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL Fig: Output Voltage across Thyristor Th 1 Page | - 42 -
  • 47. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 06 (b)Object:AC/DC Single-phase Controlled Full wave Rectifier with R load and R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module WiresTheory:Single-phase full wave controlled rectifiers:By the use of four Thyristor, rectifier circuit performance can be greatly improved. In full controlsingle phase rectifier the Thyristor are divided into the two group, one with common anodes andother with common cathodes as shown below in the figure. Figure: Single-phase, full-wave controlled rectifier: (a) circuit diagram and (b) load voltage and current waveforms for R load. Thyristor Th 1 and Th 4 will conduct when input voltage is positive. Thyristor Th 2 and Th 3 will conduct when input voltage is negative.The average output voltage for R load will be: V average = (1 + cos ) V/The average output voltage for RL load will be: V average = ( cos ) 2V/The behavior of the rectifier will depend considerably on the used load type, i.e. R Load or RLLoad. Page | - 43 -
  • 48. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical EngineeringCircuit Diagram: B2C Model Table 1: Single-Phase Controlled Rectifier Circuits with Resistive LoadProcedure: 1. Carry out the assembly B2C shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I2, Thyristor voltage (V2 , V3) as shown in figure Page | - 44 -
  • 49. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical Engineering Figure: Controlled Full Wave Rectifier with R load And measure the following quantities S. No Load Resistance V rms Voltage Across Thyristor 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage Across Thyristor 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1,Thyristor voltage (V2, V3), Output current (load) I2, Supply current I1 , as shown in figure Page | - 45 -
  • 50. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical Engineering Figure: Controlled Full Wave Rectifier with RL load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Single-phase Controlled full wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment.Waveforms: R LOAD Fig: Input Voltage Fig: Output Voltage across R load Page | - 46 -
  • 51. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL Fig: Supply Current IS Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3 R-L LOAD Fig: Input Voltage Fig: Output Voltage across R-L load Page | - 47 -
  • 52. Electrical Drives Lab Session 06 (b)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL Fig: Supply Current IS Fig: Output Voltage across Thyristor Th 1 Fig: Output Voltage across Thyristor Th 3 Page | - 48 -
  • 53. Electrical Drives Lab Session 07NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 07Object:To study the effect of Free Wheeling diode on the output of single phase controlled half-waverectifier.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Freewheeling diode:-The behavior of the rectifier will depend considerably on the used load type, so we may have:when using a load with inductive character, the following effects appear: when the input voltage is inverted, a peak of negative voltage appears in the output, and it is not annulled until the current becomes zero. In a part of the cycle, the current is interrupted, that is, the conduction is discontinuous.These two effects may be eliminated, as well as the reduction of the harmonic content, with theintroduction in parallel with the load of a diode called Freewheeling Diode (FWD) or FlyingDiode.When the input voltage is annulled at the end of the positive semi cycle, the voltage in the coil isinverted. It begins to act as a generator, forcing the conduction of the FWD and the load currentgoing through it, annulling the peak of negative voltage, as we can see in the following.Consider the above figure which shows the assembly of Thyristor and Free Wheeling diode. Figure:- Controlled Half wave rectifier with FWD Page | - 49 -
  • 54. Electrical Drives Lab Session 07NED University of Engineering and Technology Department of Electrical EngineeringThe circuit works as follows:In the positive semi cycle, during the interval in which the Thyristor is switched on, the inputvoltage appears in the output with no changes. When the input voltage is annulled at the end of thepositive semi cycle, the voltage in the coil is inverted, thus, the coil works as a generator. As aconsequence, the freewheeling diode is directly polarized, and the load current circulates through.The negative peak of the output voltage that took place in the previous paragraph is annulled. Thismay be betterappreciated in the following graphsCircuit Diagram:-Procedure: 1. Carry out the assembly E1CK shown in the above figure 2. Now connect a diode in anti-Parallel manner with the Thyristor as shown below 3. Connect the respective RL load to its terminal . For RL Load with FWD Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. Voltage Across S. No Load Impedance V rms Thyristor Th 1 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Page | - 50 -
  • 55. Electrical Drives Lab Session 07NED University of Engineering and Technology Department of Electrical Engineering Observe how the output current varies for different L values with R=375 . And sample the following parameters: Input voltage V2, Output voltage V1, Output current I1, Thyristor Voltage V3 Figure: Controlled Half Wave Rectifier RL Load with FWD 4. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Single-phase Controlled Half wave Rectifier option 5. Select the respective sample sensors 6. Check the connections and switch on the equipment. 7. Press the Data Capture button. 8. Visualize the parameters measured and save them in the corresponding file. 9. Switch off the equipment.Question:Define the following terms:1. Free Wheeling Diode________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. Effect of FWD on RL Load Output________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 51 -
  • 56. Electrical Drives Lab Session 07NED University of Engineering and Technology Department of Electrical Engineering3. Fundamental Frequency:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________5. Rectifiers:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Waveforms:- R-L LOAD WITH FWD Fig: Input Voltage Fig: Output Voltage across R-L load Fig: Load Current IL Fig: Thyristor voltage Page | - 52 -
  • 57. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 08 (a)Object:AC/DC Three phase Controlled Half-wave Rectifier with R load & R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module WiresTheory:Three-phase half-wave controlled rectifiers:Three-phase electricity supplies with balanced, sinusoidal voltages are widely available. It is foundthat the use of a three-phase rectifier system, in comparison with a single-phase system, providessmoother output voltage and higher rectifier efficiency. Also, the utilization of any supplytransformers and associated equipment is better with poly-phase circuits. If it is necessary to usean output filter this can be realized in a simpler and cheaper way with a poly-phase rectifier. Figure: Three-phase, half-wave controlled rectifier with resistive load: (a) circuit connection, (b) phase voltages at the supply, output voltage, output current. Page | - 53 -
  • 58. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering Table: Three Phase Controlled Rectifier with Ideal SupplyCircuit Diagram: B6C ModelProcedure: 1. Carry out the assembly B6C shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as shown in the above figure. Page | - 54 -
  • 59. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering Figure: Controlled Three Phase Full Wave Rectifier with R load Also measure the following quantities using multi-meter. S. No Load Resistance V rms Voltage across Th 1 1. 300 + 75 2. 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0 to 236mH) with R=375 , measuring with the voltmeter the average output voltage. S. No Load Impedance V rms Voltage across Th 1 1. 300 + 75 + 140mH 2. 300 + 75 + 236mH Observe how the output current varies for different L values with R=375 . Save the different samples. And sample the following parameters: Input voltage (V2,V3, V4), Output voltage V1, Output current I1, Thyristor voltage V5 as shown in the above figure. Page | - 55 -
  • 60. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering Figure: Controlled Three Phase Full Wave Rectifier with RL load 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Three Phase Controlled Half wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment. Here you can also study and visualize what will be the effect of inverting the polarization of the three Thyristor. Secondly suppose that, due to an over-voltage, one of the Thyristor is in open circuit. Study and visualize what effect provokes the output voltage. Page | - 56 -
  • 61. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering Waveforms: R LOAD Fig: Input Voltages R,S,T Fig: Output Voltage across R Load Fig: Load Current IL Fig: Output Voltage across Thyristor R-L LOAD Fig: Input Voltages R,S,T Fig: Output Voltage across R Load Page | - 57 -
  • 62. Electrical Drives Lab Session 08 (a)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL Fig: Output Voltage across Thyristor Page | - 58 -
  • 63. Electrical Drives Lab Session 08 (b)NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 08 (b)Object:AC/DC Three-Phase Controlled Full-wave Rectifier with R load& R-L load.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:Three phase controlled full wave rectifier:-Three phase controlled full wave rectifier is just like assembly of two controlled, three phase halfwave rectifiers. One with common anodes and other with common cathodes as shown below. Figure:- Three Phase controlled full wave rectifier with resistive load a) Circuit connections with load b) load voltage and load current waveforms. Th 1, Th 2, Th 3, conduct when the voltages Vr, Vs, Vt respectively are most positive provided that the Thyristor have been triggered. Th 4, Th 5, Th 6, conduct when the voltages Vr, Vs, Vt respectively are most negative provided that the Thyristor have been triggered. The average output voltage for R load will be: 60 (direct conduction ) V average = (cos wt) 3 3V/ 60 (discontinuous conduction) V average = (1 - 3/2 sin + 1/2 cos )3 3V/ The average output voltage for RL load will be: Page | - 59 -
  • 64. Electrical Drives Lab Session 08 (b)NED University of Engineering and Technology Department of Electrical Engineering 60 (direct conduction ) V average = (cos ) 3 3V/ 60 (discontinuous conduction) V average = (sin wt - 3/2 sin + 1/2 cos )3 3V/ Circuit Diagram:- B6C Model Procedure: 1. Carry out the assembly B6C shown in the above figure 2. Connect the respective load to its terminals one by one. For R Load Use Fixed R= 300ohms plus variable resistance in series. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I1, Thyristor voltage V3 (as shown in figure) Figure:- Three Phase controlled full wave rectifier with R load. Page | - 60 -
  • 65. Electrical Drives Lab Session 08 (b)NED University of Engineering and Technology Department of Electrical Engineering Also measure the following quantities using multi meter. S. No Load Resistance V rms Voltage across D1 1 300 + 75 2 300 + 120 For RL Load Observe how the conduction angle increases as we increase L (0to 236mH) with R=375 , measuring with the voltmeter the average output voltage. V av = S. No Load Impedance V rms Voltage across D1 1 300 + 75 + 140 m H 2 300 + 120 + 236mH Observe how the output current varies for different L values with R=375. Save the different samples. And sample the following parameters: Input voltage V4, Output voltage V1, Output current I1, Thyristor voltage V3 (as shown in figure) Figure:- Three Phase controlled full wave rectifier with RL load. 3. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC Three-Phase Controlled Full-wave Rectifier option 4. Select the respective sample sensors 5. Check the connections and switch on the equipment. 6. Press the Data Capture button. 7. Visualize the parameters measured and save them in the corresponding file. 8. Switch off the equipment. Page | - 61 -
  • 66. Electrical Drives Lab Session 08 (b)NED University of Engineering and Technology Department of Electrical EngineeringWaveforms: R LOAD Fig: Input Voltage R, S, T Fig: Output Voltage across R Load Fig: Load Current IL Fig: Output Voltage across Thyristor R-L LOAD Fig: Input Voltage R , S , T Fig: Output Voltage across RL load Page | - 62 -
  • 67. Electrical Drives Lab Session 08 (b)NED University of Engineering and Technology Department of Electrical Engineering Fig: Load Current IL with L=140mH Fig: Load Current IL with L=236mH Fig: output voltage across Thyristor Page | - 63 -
  • 68. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 09Object:-DC/DC Chopper.Apparatus: SACED TECNEL TECNEL or TECNEL/B RCL3R Load module Connecting WiresTheory:-Chopper is used to convert the unregulated DC input to a controlled DC output with a desiredvoltage level. It is a static device which gives variable dc voltage from a constant dc voltagesource. Chopper is also known as dc-to-dc converter.There are basically two types of the chopper: 1. Step down chopper (BUCK) :- In step down chopper output voltage is less than input voltage. 2. Step up chopper (BOOST) :- In step up chopper output voltage is more than input voltage.Basically, we may obtain a variable voltage from a fixed direct voltage by way of connecting anddisconnecting the source from the load by using a switch, so the average value of the outputvoltage may depend on the opening and closing rhythm of the controllable switch. In this case itwill be an IGBT. They are, thus, called Commuted Direct Current Converters.The input voltage chopping to obtain a lower average value is the Chopper operation principle.The average value of this voltage will depend on the ratio of the T on time (conduction time) andthe period T, called work cycle.The average value of voltage is given by above formula;Therefore, the variation of the average output voltage can be made in three ways: Page | - 64 -
  • 69. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical Engineering By closing the switch at a fixed frequency (1/T) and delaying its opening (varying the work cycle using Ton). By acting on the switch with a variable frequency, but always leaving the switch closed at the same time (fixed Ton). By acting on the switch in a mixed way, that is, acting the same as in the latter case only with a variable conduction time.The most general sketch for this type of converters is the following one: Figure:- BUCK chopper The function of the output filter is to cut down the output intensity. The freewheeling diodeprevents any dangerous over voltages that may damage the switch, since the current in the loadcirculates through it as soon as it is annulled, and there is no abrupt variation of the current inLout. The source possesses internal impedance Rg, and Lin and Cin constitute the input filter,which has a double function: Limiting the over voltages that will take place in Lg when the switch is opened. To cut down the intensity supplied by the source, and consequently the curling of its output voltage.There are two ways of operation of a chopper which are given as under :Direct conduction modeThe intensity that circulates through the load fluctuates between maximum and minimum values,never to the point of being annulled. As it will be seen later on, it is caused by the ratio of theperiod of time that the switch is closed and the time that the coil needs to discharge all its energypreviously stored. This is also called direct current regime.Discontinuous conduction modeThe intensity for the load is annulled at a certain moment during the Toff period (time duringwhich the switch is opened). The time during which the switch is opened is bigger than the one Page | - 65 -
  • 70. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical Engineeringrequired by the coil to give away all its energy, therefore when the following period starts theintensity will be zero. Also called regime of discontinuous current.To study the circuit operation, we will analyze the two states that the switch may present (openedor closed). when switch is closed as , as shown in figure the diode is reversed biased . switch conducts the inductor current , this results in positive voltage across inductor. when switch is opened , as shown in figure the current iL continues to flow. The diode is forward biased and current now flows (free-wheeling) through the diode Page | - 66 -
  • 71. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical EngineeringCIRCUIT DIAGRAM:- Figure:- BUCK modelPROCEDURE:- 1. Carry out the assembly BUCK as shown in the above figure. 2. Connect the respective load to its terminal . 3. Select the following sensors. Input Voltage (V1), Output Voltage (V2), Input Current (I1) and Output current (I2) 4. Introduce 500 Hz as frequency and 50% as duty cycle. 5. Obtain and analyze the output voltage, determine its average value and check it with voltmeter, analyze how R variations effect the voltage 6. Obtain and analyze output current and determine its average value. Analyze how variations of R effect the maximum and average value.For RL LoadS. No Load Impedance Input Voltage (V1) Output Voltage (V2) V av 1. 600 +236mH 2. 600 + 472mH Page | - 67 -
  • 72. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical Engineering S. No Load Impedance Input Current (I1) Output Current(I2) 1. 600 +236mH 2. 600 +472mH Figure:- Circuit Diagram of DC/DC Chopper with RL Load. 7. Load the SACED TECNEL program in PC and the window corresponding to this practice Select Practice Option AC/DC CHOPPER option 8. Select the respective sample sensors 9. Check the connections and switch on the equipment. 10. Press the Data Capture button. 11. Visualize the parameters measured and save them in the corresponding file. Switch off the equipment. Page | - 68 -
  • 73. Electrical Drives Lab Session 09NED University of Engineering and Technology Department of Electrical Engineering Waveforms:- Fig: Input Voltage Fig: Output Voltage across load Fig: Load Current Fig: Input Current Page | - 69 -
  • 74. Electrical Drives Lab Session 10NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 10OBJECT To draw the magnetization curve of self-exited DC shunt generator (open circuitcharacteristics curve O.C.C).APPARATUS 1. Bench 10-ES/EV or Bench 14-ES/EV 2. DC multi-range ammeter 3. DC multi-range voltmeterCIRCUIT DIAGRAMTHEORY The magnetization characteristics, also known as No load or Open circuitcharacteristics, is the relation between emf generated and field current at a given speed. Due to residual magnetism in the poles, some emf is generated even when filed current iszero. Hence the curve starts a little way up. It is seen that the first part of the curve is practicallystraight. This is due the fact that at low flux densities reluctance of iron path is being negligible,total reluctance is given by air gap reluctance which is constant. Hence the flux and consequentlythe generated emf is directly proportional to exciting current. However at high flux densities iron Page | - 70 -
  • 75. Electrical Drives Lab Session 10NED University of Engineering and Technology Department of Electrical Engineeringpath reluctance is being appreciable and straight relation between emf and field current no longerholds good. In other words saturation of poles starts.PROCEDURE 1. Connect the shunt field to armature terminal through the ammeter, switch and rheostat. 2. Connect the multi-range voltmeter across the terminals of armature. 3. Press yellow switch on and increase AC voltage of induction motor (prime mover) by the help of 3-phase autotransformer until it reaches at normal speed. 4. Note the reading of voltmeter which indicates the voltage due to residual magnetism. 5. Close field switch and excite the field at low current. 6. Increase the field current in steps and note the voltage each time. 7. Take at least 11-12 readings. 8. Tabulate the reading and draw the curve between armature induced emf and exciting currentOBSERVATIONS S. No. FIELD CURRENT TERMINAL VOLTAGE IF (A) VT (volts) 1 2 3 4 5 6 7 8 9 10 11 12 Page | - 71 -
  • 76. Electrical Drives Lab Session 10NED University of Engineering and Technology Department of Electrical EngineeringRESULT 1. The curve starts somewhat above the origin. The voltage at zero excitation is due to residual magnetism of the field, which is necessary for building up the voltage of self- excitation generator. 2. The voltage increases rapidly at first and then changes a little in value at higher excitations indicating the effect of the poles saturation.EXERCISE:Answer the following questions:What do you understand by Self Excited ? If this is a self-excited machine then why there is aneed of supplying voltage to the auto transformer?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 72 -
  • 77. Electrical Drives Lab Session 11NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 11OBJECT To draw the load characteristic curve of self-excited D.C shunt generator.APPARATUS 1. Bench 10-ES/EV or Bench 14-ES/EV 2. DC multi-range ammeter 3. DC multi-range voltmeterCIRCUIT DIAGRAMTHEORY Load characteristic curve is the graphical representation which shows change in terminalvoltage with respect to change in load. After building up of voltage, if a shunt generator is loadedthen terminal voltage drops with increase in load current. There are three main reasons for thedrop of terminal voltage for a shunt generator under load. Page | - 73 -
  • 78. Electrical Drives Lab Session 11NED University of Engineering and Technology Department of Electrical Engineeringi) Armature Reaction Armature reaction is the effect of magnetic field set up by the armature current on thedistribution of flux under main poles of a generator. Due to demagnetizing effect of armaturereaction, pole flux is weakened and so induced emf in the armature is decreased.ii) Armature Resistance As the load current increases, more voltage is consumed in ohmic resistance of armaturecircuit. Hence the terminal voltage (Vt = E IaRa) is decreased where E is the emf induced inarmature under load condition.iii) Drop In Terminal Voltage The drop in terminal voltage (Vt) due to armature resistance and armature reaction resultsin decreased field current, which further reduces emf induced. For a shunt generator Ia = IL+ If E = Vt + IaRaPROCEDURE 1. Make the connections as shown in circuit diagram. 2. Press yellow switch on and increase AC voltage of induction motor (prime mover) by the help of 3-phase autotransformer until it reaches at normal speed. 3. When motor reaches rated speed, close the shunt field switch. 4. Increase field current by changing the field resistance until the terminal voltage reaches to 220 volt. 5. Close the switch of load and vary the load current by means of load rheostat. 6. Note down the meter readings from all meters carefully. Page | - 74 -
  • 79. Electrical Drives Lab Session 11NED University of Engineering and Technology Department of Electrical EngineeringOBSERVATIONS Vd=IaRa S. No If(A) IL(A) VT(V) Ia=If+IL Ra=0. 5 ohm 1 2 3 4 5 6 7 8RESULTThe terminal voltage of a D.C. generator is maximum at no load, which decreases with increasingload. Page | - 75 -
  • 80. Electrical Drives Lab Session 12NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 12OBJECT To draw the external and internal characteristics of separately excited DC generator.APPARATUS 1. Bench 10-ES/EV or Bench 14-ES/EV 2. DC multi-range ammeter 3. DC multi-range voltmeterCIRCUIT DIAGRAM Figure: Separately Excited DC generatorTHEORY The load or external characteristic of a generator is the relation between the terminalvoltage and load current. The characteristic expressed the manner in which the voltage across theload varies with I, the value of load current. The internal or total characteristic of a generator is therelation between the emf actually induced in the generator Ea and the armature current Ia Theinternal characteristic of the generator, which is separately excited, can be obtained as below:Let: Vt= Terminal voltage, Ia = Armature current, Ra = Armature resistanceThen, Ea = Vt + IaRa I a = ILTherefore if we add drop of armature (IaRa) to terminal voltage Vt we get actually induced emf(Ea). Page | - 76 -
  • 81. Electrical Drives Lab Session 12NED University of Engineering and Technology Department of Electrical EngineeringPROCEDURE 1. Make the circuit as shown in circuit diagram. 2. Press yellow switch on and increase AC voltage of induction motor (prime mover) by the help of 3-phase autotransformer until it reaches at normal speed. 3. When motor reaches rated speed, close the shunt field switch. 4. Increase field current by changing the field resistance until the terminal voltage reaches to 220 volt. 5. Close the switch of load and vary the load current by means of load rheostat. 6. Note down the meter readings from all meters carefully.OBSERVATIONS S. No IL(A) If(A) VT(V) Ea = Vt + IaRa (V) 1 2 3 4 5 6 7 8 RESULT From the graph it is observed that the terminal voltage across generator decreases as the load increases. Page | - 77 -
  • 82. Electrical Drives Lab Session 13NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 13OBJECTSpeed control of a DC shunt motor by flux variation method.APPARATUS 1. Bench 13-ES/EV or Bench 15-ES/EV 2. DC multi-range ammeter 3. DC multi range voltmeters 4. Digital tachometerCIRCUIT DIAGRAM Fig: DC Shunt MotorTHEORY This method is used to increase speed of DC motor above base speed. To understand whathappens when the field resistance of dc motor is changed, assume that the field resistance isincreased then the following sequence of cause and effect will take place 1. Increasing Rf causes If to decrease 2. Decreasing If Decreases 3. Decreasing lowers Ea 4. Decreasing Ea Increases Ia 5. Increasing Ia increases Tind 6. Increasing Tind makes Tind>Tload, hence speed increases. 7. Increasing speed increases Ea Page | - 78 -
  • 83. Electrical Drives Lab Session 13NED University of Engineering and Technology Department of Electrical Engineering 8. Increasing Ea decreases Ia 9. Decreasing Ia decrease Tind until Tind= Tload at higher speed. Naturally decreasing Rf would reverse the whole process and speed of motor will decrease.It is important to bear in mind, changing field resistance does not affect torque induced, at the endits magnitude remains same but at higher or lower speed depending upon change in resistance.PROCEDURE 1. Make connections as shown in the circuit. 2. Keep the motor starting rheostat at its maximum position and field rheostat at its minimum position while starting motor. 3. Start the motor by pressing yellow switch "ON" without load. 4. Adjust the motor start rheostat to its minimum value. 5. Decrease field current by the help of field rheostat step by step and take readings of field current and speed from digital tachometer at every step. Adjust the field rheostat to give maximum speed at which it is safe to operate the motor.OBSERVATIONS Field Current Speed S. No If(A) N (RPM) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.RESULT Speed increases as the field excitation decreases. Page | - 79 -
  • 84. Electrical Drives Lab Session 13NED University of Engineering and Technology Department of Electrical EngineeringEXERCISE:Answer the following questions:Why do we set the armature rheostat at maximum and field rheostat at minimum?__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________After starting motor, why do we set the Ra to its minimum?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 80 -
  • 85. Electrical Drives Lab Session 14NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 14OBJECTSpeed control of a D.C. Shunt Motor by armature rheostat control method.APPARATUS 1. Bench 13-ES/EV or Bench 15-ES/EV 2. DC multi-range ammeter 3. Voltmeters 4. Digital tachometerCIRCUIT DIAGRAM Fig: DC Shunt MotorTHEORY This method is used to decrease speed of DC motor below base speed. To understand whathappens when the armature resistance of DC motor is changed, assume that the armatureresistance is increased then the following sequence of cause and effect will take place 1. Increasing Ra causes Ia to decrease 2. Decreasing Ia decreases Tind 3. Decreasing Tind makes Tind<Tload, hence speed decreases. Page | - 81 -
  • 86. Electrical Drives Lab Session 14NED University of Engineering and Technology Department of Electrical Engineering 4. Decreasing speed decreases Ea 5. Decreasing Ea increases Ia again. 6. Increasing Ia increases Tind until Tind = Tload at lower speed. Naturally decreasing Ra would reverse the whole process and speed of motor will increase.It is important to bear in mind, changing armature resistance does not effect torque induced ,at theend its magnitude remains same but at higher or lower speed depending upon change in resistance.PROCEDURE 1. Make connections as shown in the circuit. 2. Keep the motor starting rheostat at its maximum position and field rheostat at its minimum position while starting motor. 3. Start the motor by pressing yellow switch "ON" without load. 4. Adjust the motor start rheostat to its minimum value. 5. Increase the value of starting resistance by the help of motor start rheostat step by step and take readings of voltage across armature and speed from digital tachometer at every step.OBSERVATIONS Armature Voltage Speed S. No Va (V) N (RPM) 1. 2. 3. 4. 5. 6. 7. 8.RESULT Speed is very nearly proportional to the applied voltage in the case of armature control method. Page | - 82 -
  • 87. Electrical Drives Lab Session 15NED University of Engineering and Technology Department of Electrical Engineering LAB SESSION 15OBJECTTo observe the starting of three phase Synchronous and Induction motorAPPARATUS 1. 3- Synchronous motor 2. 3- Induction motor 3. Variable 3 AC supply 3- 4. DC Supply 5. TachometerTHEORY RY To understand how the induction motor works, apply the three phase ac supply on stator ofIM. The application of three phase ac power causes a rotating magnetic field to be set up around he three-phasethe rotor. The voltages are induced on the rotor bars(short circuited at both ends), developing itsown field. Both fields interact with each other causing the rotor to move at speed less than the .synchronous speed. The reversal of any two applied phases causes the rotating magnetic field to rotatingrotate in opposite direction (w.r.t. to previous one). In this fashion an Induction motor works Figure: Induction Motor Page | - 83 -
  • 88. Electrical Drives Lab Session 15NED University of Engineering and Technology Department of Electrical Engineering To understand how the synchronous motor works, assume that the application of three-phase ac power to the stator causes a rotating magnetic field to be set up around the rotor. Therotor is energized with dc (it acts like a bar magnet). The strong rotating magnetic field attracts thestrong rotor field activated by the dc. This results in a strong turning force on the rotor shaft. Therotor is therefore able to turn a load as it rotates in step with the rotating magnetic field. It worksthis way once it s started. Figure: Synchronous Motor However, one of the disadvantages of a synchronous motor is that it cannot be started froma standstill by applying three-phase ac power to the stator and dc to its rotor. When ac is applied tothe stator, a high-speed rotating magnetic field appears immediately. This rotating field rushes pastthe rotor poles so quickly that the rotor does not have a chance to get started. In effect, the rotor isrepelled first in one direction and then the other. A synchronous motor in its purest form has nostarting torque. It has torque only when it is running at synchronous speed. A squirrel-cage type ofwinding is added to the rotor of a synchronous motor to cause it to start. The squirrel cage isshown as the outer part of the rotor in figure. It is so named because it is shaped and lookssomething like a turn able squirrel cage. Simply, the windings are heavy copper bars shorted. Hence, three phase synchronous motor is not self-started. At the starting time, it behaves asinduction motor and gets accelerated. Once it approaches speed near to synchronous speed, itsrotor winding is excited then synchronous motor start rotating at synchronous speed. If we havegiven rotor supply at start, motor will just produce humming sound.PROCEDURE For Induction Motor: 1. Make the circuit and switch on three phase ac supply and observe the performance. 2. Now reverse any of the two phases and verify double field revolving theory. Page | - 84 -
  • 89. Electrical Drives Lab Session 15NED University of Engineering and Technology Department of Electrical Engineering For Synchronous Motor: 1. Make the circuit and switch on both ac and dc supply and observe the performance. 2. Disconnect dc supply, switch on ac supply and observe the performance. 3. When motor run near to synchronous speed, which already calculated, switch on dc supply also and observe the behavior.OBSERVATIONS:Speed of Induction Motor: rpm Calculate: Slip speed = Slip =Speed of Synchronous Motor =rpmEXERCISE:Answer the following questions:Why Induction motors have high starting current?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________Write three differences between Induction & Synchronous motor._________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Page | - 85 -

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