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Instruments and Equipments Used in Electrical Laboratory

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    INSTRUMENTS AND EQUIPMENTS USED IN ELECTRICAL LABORATORY .

    Single phase double wound copper transformer having primary 230VAC and secondary

    115V AC with a rated capacity of 1KVA. The primary and secondary terminals are broughtout for conducting laboratory experiment with legend printed for convenience. This is assembledin a powder coated MS metal box.Specifications:

    Primary : 230 V AC Secondary with tappings at 86.6% and at 50% of primary voltage.

    Rated capacity: 1KVA

    Terminations: Separate 4mm Banana terminals at input and outputs

    Enclosure: Powder coated MS metal cabinet, with separate screw terminal for earthconnection.

    PORTABLE VARIAC

    This is a variable auto transformer. This is also called as Dimmer-stat. This isused to vary the output voltage by rotating a knob placed above this instrument.The output voltage can be varied from 0 to 270V AC, when its input terminals are

    connected to 230V AC. It can deliver 6A of current at its peak rated voltage. Theentire instrument is assembled in a sheet rolled powder coated MS metal box withseparate screw terminal for earth connection.

    Specifications:

    Input: 230 V AC Output: Variable in the range of 0 to 270V AC.

    Rated capacity: 6A

    LOADING CAPACITOR

    Loading capacitor, is a capacitor bank with step variation. This is requiredwhen experimenting to determine the output characteristics of devices like atransformer etc. More particularly while experimenting to determine the powerfactor measurements in single-phase electrical circuits.

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    This is a loading capacitor, where by the capacitance in a load circuit can bevaried in the range of 2uF to 16uF @ 230V AC, in 8 steps. The variation incapacitance can be obtained by suitable patch cord mechanism. This is suitablyprotected with necessary fuse arrangement. The terminals are suitably brought out

    on a 4mm Banana sockets for easy interconnections.

    3 POINT DC STARTER

    3 point DC starter is a unit intended to limit the starting current in a DC

    circuit. This starter is a must for any DC motor applications. This starter has

    three functions.

    (a) To provide series resistance in a DC circuit when this starter is in START

    position. I.e. In START position full resistance is included, and is reduced to zeroohms when the handle is moved to ON position, in discrete steps. The starter isheld in ON position by an electromagnet. At this ON position the DC circuit getsits full current from the DC Rectifier unit. In the case of a DC motor, this isconnected in series with the armature circuit, to limit the starting current andeventually this resistance is CUTOUT, from the circuit. There by enabling themotor to run at its full armature current. Therefore this starter acts as a first orderprotection circuit, in between a DC rectifier unit and the DC circuit.

    (b) No Volt Coil (NVC) This is normally connected to Field circuit in a DCmotor. In case of a failure in current in this circuit, for any reason, namely

    accidental tripping, or unintentional break in field circuit, this coil will provide asignal to the electromechanically held arm (handle) to release, and the starter isswitched to OFF position, thereby providing safety to the system.

    (c) Over Load (OL) release switch This is connected in series with the armaturecircuit. In case of current beyond the rated current of this coil in the circuit, thisautomatically trips the electromagnet, which is holding the handle in ON position.Thereby tripping the starter from being over loaded

    METERSVarieties of meters are available for making suitable measurements of electricalparameters. These meters are available for use in single phase and three phasecircuits. The meters are available in tabletop models and panel mountingarrangements. Normally these meters are used in Electrical engineeringlaboratories for various measurements. The meters available are

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    1. Volt meters- analog /digital2. Ammeters analog / digital3. Watt-meters analog / digital4. Phase sequence indicators

    5. Tacho meters contact type and photo reflective type6. Reed type frequency meters7. Phase meters.8. Power factor meters.

    MEASUREMENT STATION

    This is an AC measuring digital instrument station. This is a typical laboratoryinstrument station. This has 3 meters. It measures the

    a. frequency in the range of 0 to 99Hz,b. Voltage in the range of 0 to 500V AC, andc. Current in the range of 0 to 5A AC.The entire instrument is assembled in a compact and sleek looking cabinet forconvenience.

    MACHINES LABORATORY. DC MOTOR

    This DC motor is integral, internally mounted cooling fan on the shaft. When themotor is running at rated speed the, fan provides the necessary cooling to give theassigned rating. When motors are required to start from zero speed and smoothlyaccelerate to the rated speed, these motors can be selected. If motors are to runbelow rated speed for long duration, either they have to be de-rated or can beforced cooled. The DC Generators are normally continuously rated and have torun at rated speeds only.

    This requires DC rectifier source for its operation. The DC source to this isprovided through a 3-4 point DC starter unit. Using this, several experiments onDC motor can be conducted. Depending on the experiment, you need appropriatemeters, rheostats, switchgear are required. These motors are screen protected, withIP21/IP22 enclosures.

    Specifications:

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    Voltage: 220V Amps: 6.8

    RPM: 1500

    KW: 1.5

    Rating-CMR

    INS Class-B/.

    Extn type: Shunt

    220V, 0.5A

    DC MACHINE WITH LOADING ARRANGEMENT

    This is a DC motor with the above specifications. The shaft of this motor iscoupled mechanically to a break drum. A belt moving over this break drumprovides necessary torque to the shaft of the motor, and in turn loads the shaft witha finite torque. Two calibrated spring balances are connected to either side of thebelt, which is moving over the break drum. This is a method to load the shaft ofthe motor with a loading arrangement. By taking reading on these spring balancereadings, the loading value may be calculated.

    IDENTICAL MACHINES

    This is a typical setup for conducting experiments on two identical machines,which are mechanically coupled. This requires DC rectifier source of 15 A, for itsoperation. The DC source to this is provided through a 3-4 point DC starter unit.The coupled DC machine to this DC motor is used as generator. This generatormay be loaded by drawing sufficient current using an external Loading rheostat.There by loading the DC motor. It is possible to evaluate the performance of thisidentical machines setup in several ways, for varied parameters.

    Specifications:

    DC machines: Two identical machines. Voltage: 220V

    Amps: 6.8

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    RPM: 1500

    KW: 1.5

    Rating-CMR

    INS Class-B/. Extn type: Shunt

    220V, 0.5A

    ALTERNATOR

    This is an AC 3phase synchronous alternator with, square path, 4 poles, and rotorwound stator excited type. This is screen protected IP22, with drip proofenclosure.Specifications:

    Voltage: 415V Amps: 4.2A

    RPM: 1500

    KVA-3

    Rating-CMR

    Phases-3,Hz-50

    ENCL-S.P,PF-0.8

    Extn VOLTS-220

    Winding-Y

    Amps-1.4A

    SYNCHRONOUS ALTERNATOR

    This is a synchronous alternator generator experimental setup. Both aremechanically coupled. This setup is used to perform experiments onsynchronization. A DC motor is used as prime mover. This experiment is betterunderstood when connected to a synchronizing panel.

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    SYNCHRONIZATION PANEL

    This is a synchronization panel. This panel is used to study the synchronization ofan alternator with main bus bar voltages. While performing this experiment, it isrequired to study the dark / bright lamp method for synchronization. In order tofacilitate this, the panel is provided with two voltmeters, two frequency meters,one synchro-scope, 6 lamps, phase sequence indicator and a selector switchprovides for synchronization. 3 sets of 4mm terminals are provided for makingnecessary RYB connections.

    3 PHASE INDUCTION MOTOR

    This is an AC 3phase induction motor. This operates on 415V AC. This squirrelcage induction motor coupled to a 2KW shunt generator.Specifications:

    Volts: 415V - 3 Power: 2.2KW

    Current : 4.8A RPM: 1440

    Frame: PM100L

    http://www.interlabs-india.com/synchronization-panel-2962.htmlhttp://www.interlabs-india.com/3-phase-induction-motor-2963.htmlhttp://www.interlabs-india.com/synchronization-panel-2962.htmlhttp://www.interlabs-india.com/3-phase-induction-motor-2963.html
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    3 PHASE AC MACHINE WITH LOADING ARRANGEMENT

    This is a 3-phase AC machine. This is mechanically coupled to a breakdrum toprovide loading. The shaft of the machine is coupled a drum. In turn the drum isconnected to mechanical weighing pan by means of a belt. Rotating the screwsprovided on either sides of the belt can adjust the belt tension. There by it ispossible to load the shaft of the 3-phase motor with a defined tension. Thedifference in the scale reading, provides the tension, the shaft is subjected to. As aresult of this the current in the windings are varied. By noting the readings of theassociated meters and the difference in the weighing pan readings, the loadcharacters of the motor can be evaluated.This is an arrangement of a 3-phase induction motor, mechanically coupled to aDC generator.

    3 PHASE AC MACHINE WITH LOADING ARRANGEMENT

    This is a 3-phase AC machine. This is mechanically coupled to a breakdrum toprovide loading. The shaft of the machine is coupled a drum. In turn the drum isconnected to mechanical weighing pan by means of a belt. Rotating the screwsprovided on either sides of the belt can adjust the belt tension. There by it ispossible to load the shaft of the 3-phase motor with a defined tension. Thedifference in the scale reading, provides the tension, the shaft is subjected to. As aresult of this the current in the windings are varied. By noting the readings of the

    associated meters and the difference in the weighing pan readings, the loadcharacters of the motor can be evaluated.This is an arrangement of a 3-phase induction motor, mechanically coupled to aDC generator.

    PATCH PANELS

    Patch panels are the connector panels, used to interconnect various machines to meters,rheostats, Variac and others, which are used in a machines lab. This is only another way, toincrease the safety for the personnel, conducting the experiments. The connections from eachmachine are terminated on this connector panel. The necessary wirings from the machine tothese panels are to be securely made, prior to, conducting lab experiment. Each panel isdiagrammatically represented to reflect various terminals of a machine, and they are printedabove the terminals. All the necessary terminals of the machine are terminated on a 4mm patchcord terminal, suitable to make interconnections with other associated circuitry. Each connector

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    panel differs from the other panel in terms of drawings used for different machines. We supplythese, as part of a turnkey project, while setting up the machines lab.The pictures shown here, describe how each panel is represented. These are the panels, whichare placed on the experimental table. The 4mm terminals from these are used forinterconnecting with other associated circuitry.

    LABORATORY RECTIFIER UNITThese laboratory rectifiers are mainly used in electrical engineering laboratoriesfor the purpose of conducting experiments in machines and DC circuits. This isservo controlled to provide constant DC output. This provides 100A output forcontinuous operation. This rectifier provides suitable source for operating DCmachines.

    System Description:

    This rectifier works with 3 phase 415V AC as its mains supply voltage. Theripple factor is less than 5% at its peak load. The DC output from this unit iscontinuously variable by a potentiometer, in the range of 200 to 240 DC. A servocontrol motor circuit ensures constant DC output voltage. A digital voltmeter andSuitable HRC fuses are provided at AC input and DC output stages forprotection. The rating of the mains transformer is designed to provide upto 200VDC, while the series transformer provides 40V DC, suitably arranged to providethe correction required. The series transformer is controlled by a three phasemotorized dimmerstat. The rectifier circuit is generously rated with suitable heatsink and hole storage suppression.

    This unit has a START and STOP push buttons. Pressing Start push buttonmakes, the output to set at the voltage shown by the panel meter, and the output isavailable at the terminals at this time. Pressing stop push button, the output isreset to 0V. In the event of mains power failure or accidental break in the mainssupply, the DC supply from this rectifier unit, is automatically disconnected. Theoutput from this rectifier is available to the DC circuit, only when the mainspower returns AND start push button is pressed. This facility provides the scopefor investigating the reason for the failure, and also protecting the assets.The entire rectifier unit is assembled in a rugged sheet steel material with suitablereinforcements wherever required. The entire unit is assembled on suitable casterwheels, to provide mobility for unit.

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    15A LABORATORY RECTIFIER

    These laboratory rectifiers are mainly used in electrical engineering laboratoriesfor the purpose of conducting experiments in machines and DC circuits. Thisprovides constant DC output. This provides 15A output for continuous operation.This rectifier provides suitable source for operating DC machines or any DCcircuit. Suitable fuse protection is provided. The analog panel meters mounted onthe front panel can monitor the output voltage and the current. This has a STARTand STOP push buttons. When start button is pressed, the DC voltage is availableat the output terminals, as indicted by the meter reading. When stop button ispressed the output is reset to zero.In the event of mains power failure or accidental break in the mains supply, theDC supply from this rectifier unit, is automatically disconnected. The output from

    this rectifier is available to the DC circuit, only when the mains power returnsAND, the voltage setting Variac is brought to 0V position AND start push buttonis pressed. This facility provides the scope for investigating the reason for thefailure, and also protecting the assets.Specifications:

    Input : 230 V AC single phase Output : 230 V DC continuously variable from 0 to 230V with suitable

    START

    Interlock.

    Capacitry : 15A Meter : Voltmeter and current meter indicators.

    Switches : START and STOP switches.

    Output control : DC Mains ON/OFF switch.

    NOTE: You must connect ELCBs, earth connections, fuse switch gear, all otherprotective methods must be implemented, wherever required.

    DISTRIBUTION PANELS

    Distribution panels are intended to provide necessary AC or DC supplies to theAC or DC machines. There are two different distribution panels available. Theseare classified as AC distribution panel or DC distribution panel. The AC supply(three phase) to an AC machine is routed through AC panel, and while DC supply

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    is routed through DC panel. This is similar to a distribution board, in function.Each machine gets its AC or DC supply either from the mains or from therectifier unit respectively, through these panels only. I.e. the supply for eachmachine is routed through this distribution panel. The supply to each machine issuitably switched ON / OFF through a suitably protected MCB. This provides

    protection to each machine. Routing supply through these panels allow you toswitch ON or OFF using respective switch gear, there by power can be saved,permitting you to switch ON the machines which are required forexperimentation, and switching OFF the remaining machines.

    Specifications:

    1. DC Distribution Panel:

    1. Input: DC voltage input 230V DC from the 100A rectifier unit.2. Output: 230V DC to respective machines

    3. Meters: DC Voltmeter and DC current meters are used. The DC meterindicates the overall DC voltage available to the DC circuits. There will be linedrop at the respective machines, when measured near the machine. This is due toline loss. The current meter indicates the total current drawn by the whole DCcircuit through this panel.

    4. Switches: 12 different DC circuits can be connected through this panel. Eachcircuit is protected with an independent MCB. In addition to this a master switchcontrols the complete DC circuit. When this is in OFF position, the DC supply toall the DC circuits are switched OFF.

    5. A lamp indicator is used to display the status of power supply. This isilluminated when the power is ON.6. Separate earth connection is provided to the panel. This must be securelyconnected to the Earth.

    7. Enclosure: This is assembled in a sturdy cabinet, using sheet steel.8. Assembly: This has to be assembled on a rigid foundation next to the DCrectifier unit.

    NOTE: You must connect ELCBs, earth connections, fuse switchgear, all otherprotective methods must be implemented, wherever required.

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    EXPERIMENTS IN ELECTRICAL ENGINEERINGAll the electrical engineering experiments will have broadly the followingobjectives while performing relevant experiments. The scope of the supply doesnot include, hardware like DOL starters, Mains switches, wiring from the mainssupply to the experimental tables, HRC fuse assemblies, Circuit breakers,ELCBs, civil structures etc. However these are required to be installed orconstructed or assembled and wired, prior to connecting necessary experimentalsetups.

    Objectives of experimental setups.

    a. Activity Sequenceb. Study of nameplate detailsc. Identifying measuring instruments and support accessories required forconducting the experiment

    d. Previewe. Record Circuit Diagram and connection diagramsf. Model graph and expected outcomeg. Data processing and calculations andh. Inference

    While establishing the electrical laboratory, the following recommendations maybe adhered at the experimental tables, as a precautionary measure.

    Separate wires and neutral wires using standard 7-20 SWG, must be drawn fromMCBs on the distribution panel to the respective Motor Generator / Alternator

    sets.Mains trip switch (Isolators) for DC and 3 ?, to be provided near everyequipment MG Set of each experimental setup for safety purpose.Neutral must be terminated with 30A black color banana terminal, at each andevery experimental work table

    Earth wire using 8 SWG copper wire must be made available at every MG set.At least two bolts on the base assembly of MG set must be connected to this earthwire.Isolators must be fitted as shown in the diagram near each and every MG set.

    EXPERIMENTS ON TRANSFORMER SINGLE PHASE

    TRANSFORMER (OPEN CIRCUIT AND SHORT CIRCUIT TEST)

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    SUMPNERS TEST EXPERIMENT

    Objective: To perform Sumpners test. Predetermination of performancecharacteristics and equivalent circuit of single-phase transformer.

    Preview: In OC and SC tests a transformer is subjected to either core loss orcopper loss and so these tests cannot as such be used for heat-run for heat-run-test. A heat-run test can be conducted on two identical transformers byconnecting them back-to-back. Wherein, their secondaries are connected in phaseopposition. So the secondaries will behave open-circuited when the primaries areexcited, the current drawn from V1 source being 2I0 providing core losses (2P0)of the two transformers. A low-voltage variable source V2, is connected in thesecondary circuit which causes circulating current in the secondaries with

    primaries acting as short circuit for this source (use superposition theorem). Thiscirculating current can be adjusted to full-load value. The power injected by thissource is 2PC, the full-load copper loss of both transformers, while theimpedance seen by it is 2Zeq. Both the transformers in this test are thus subjectedto full load core and copper losses by phantom loading, while drawing only coreloss power from source V1 and only copper loss power from source V2. In somesense this test has similarity with the Hopkinsons test on two identical dcmachines.

    Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegant

    cabinet as a package. Range of instruments and accessories (standard format)1. Transformer 1 1KVA Capacity, Primary: 230V Secondary: 115V Twonumbers2. Suitable Variac3. Suitable digital ammeters of different ratings AC4. Suitable digital voltmeters of different ratings AC5. Suitable digital wattmeter

    SCOTT CONNECTION EXPERIMENT

    Objective: To obtain Two-phase supply from Three-phase and to conduct loadtest.

    Preview:

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    The concept of 3phase to 2-phase connection follows from the voltage phasordiagram of balanced 3-phase supply. If the point M midway on Vbc could belocated then VAM leads Vbc by 900. A 2-phase supply could be thus obtained bymeans of two transformers; one connected across AM, called the teaser

    transformer and the other connected across the lines B &C. Since VAM =3Vbc/2, the transformer primaries musthave 3N1/2 (teaser) and N1 turns;this would mean equal voltage / turn in eachtransformer. A balanced two phase supply could then be easily obtained byhaving both secondaries with equal number of turns N2. The point M is locatedmidway on the primary of the transformer connected across the lines B & C. Theconnection of two such transformers, known as the Scott Connection, is shown inFig with its phasor diagram of two phase supply in the secondary.Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)

    1. Transformer 1 1KVA Capacity, Primary: 230V(tapings at 86.6%,50%),Secondary: 115V Two numbers2. Suitable Loading rheostat for the above single phase two numbers3. Suitable Variac three phase4. Suitable digital ammeters of different ratings AC5. Suitable digital voltmeters of different ratings AC6. Suitable digital wattmeter

    EXPERIMENTS IN MACHINES LAB NO LOAD TESTS ON A DC

    SHUNT MOTOR (SWINBOURNS TEST)

    Objective:To determine the performance of the given DC shunt machine in bothgenerator and motor modes of operation

    Preview:

    Swinburns test is a no-load test on a dc machine. The machine is started and runas a dc motor with shaft decoupled from any load. In this regard the test is veryeasy to carry out for a machine of any size, particularly convenient for a largemachine.

    The input to motor at no-load comprises of:Iron losses (Pi)Mechanical, friction and windage loss (Pwf)

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    Field Copper Loss (Pshf)

    Armature Copper Loss

    (Armature resistance is measured by drop test and corrected to operatingtemperature of about 750C)

    Stray load losses are estimated to be 1% of kW rating of the machine at full load and considered proportional to square of armature current.With the above data the machine performance at any load (or a set of loads) canbe predetermined either as motor or generator.

    Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. 2HP DC Motor 220V 2HP 1500rpm with standard screen protected/drip proof(IP21)2. 3-4 Point DC starters with protectors.3. Suitable Digital Voltmeter DC to measure voltage across armature4. Suitable Digital Ammeter DC to measure filed current.5. Suitable Digital Ammeter DC to measure armature current.6. Suitable Digital Tachometer to read RPM of the motor.7. Suitable Rheostat for Armature circuit.8. Suitable Rheostat for field circuit.9. Rectifier Unit 0-240V DC @ 1.5KVA with power failure protection.

    SPEED CONTROL OF DC MOTOR BY ARMATURE & FIELD

    CONTROL

    Objective: obtain the speed control characteristics of a dc motor at no load.Preview: The dc motors are in general much more adaptable speed drives than acmotors. The speed of dc motors depends upon the following relation. Since the

    speed is proportional to the ratio between the back EMF and the flux per pole.The back EMF can be varied by varying the armature applied voltage (called asarmature control). The flux per pole can be varied by varying the field current(called field control).Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. 2HP DC Motor 220V 2HP 1500rpm with standard screen protected/drip proof

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    (IP21)2. 3-4 Point DC starters with protectors.3. Suitable Digital Voltmeter DC to measure voltage across armature4. Suitable Digital Ammeter DC to measure filed current.5. Suitable Digital Ammeter DC to measure armature current.

    6. Suitable Digital Tachometer to read RPM of the motor.7. Suitable Rheostat for Armature circuit.8. Suitable Rheostat for field circuit.

    DC SHUNT GENERATOR NO LOAD TESTS ON DC SHUNT

    GENERATOR

    Open Circuit Test

    Objective: To obtain the magnetization characteristic and therefrom determinethe critical field resistance and critical speed of the given dc shunt generator.

    Preview:

    The EMF induced in a DC machine is proportional to the flux per pole, thenumber of conductors and speed. This EMF depends on speed and flux. As theflux increases the EMF increases beyond a point the flux gets saturated. The BHcurve of the core depicts the magnetization curve of the machine.(A) Critical Speed of a DC Shunt Generator

    Objective: To determine the critical speed of a dc shunt generator. With the fixedexcitation and variable speed, as the speed reduces the OCC proportionally slidesdown so that the no load voltage reduces. At a particular speed, called the criticalspeed, the OCC is tangential to the Rf line and as a result the generator fails toexcite.

    Preview

    With the fixed excitation and variable speed, as the speed reduces the OCCproportionally slides down so that the no load voltage reduces. At a particularspeed, called the critical speed, the OCC is tangential to the Rf line and as a result

    the generator fails to excite.Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. 2HP Shunt machines mechanically coupled both are identical 220V 2HP1500rpm.2. 3-4 point DC Starter for the above3. Suitable Loading rheostat

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    4. Digital tachometer5. Suitable Double tube rheostat6. Suitable Single tube rheostat7. Suitable Digital Voltmeter DC8. Suitable Digital Voltmeter DC

    9. Suitable Digital Ammeter DC10. Rectifier Unit 0-240V DC @ 1.5KVA with power failure protection.

    LOAD TEST ON A DC SHUNT GENERATOR

    Objective: To obtain external characteristics of a dc shunt generatorPreview:The self excited DC shunt Generator is coupled to a DC motor, which acts asprime mover. Two characteristics are more important. The internal or totalcharacteristic that gives the relation between the emf actually induced in thearmature and the armature current. This is of interest mainly to the designer. Theexternal characteristics called performance characteristics (also voltage regulatingcurve) which give the relation between the terminal voltage and load current.This curve lies below the internal characteristics due to armature drop. This isimportant in judging the suitability of a generator for a particular purpose. Thesecharacteristics can be obtained by a load test with total field resistance remainingfixed as the speed is to be kept constant.

    Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. 2HP Shunt machines mechanically coupled both are identical 220V 2HP1500rpm.2. 3-4 point DC Starter for the above3. Suitable Loading rheostats4. Digital tachometer5. Suitable double tube rheostat6. Suitable single tube rheostat

    7. Suitable digital Voltmeters DC8. Suitable digital ammeters DC.9. Suitable DC source Rectifier unit

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    HOPKINSONS TESTObjective:

    To conduct Hopkinsons test on the given pair of identical dc machines and

    obtains item performance characteristicsPreview:

    Swinburnes test on a dc machine is a non-loading test. The machine performancecan be computed from the data obtained from this test without actually loading it.In certain situations a dc machine has to be tested by actually loading itparticularly for a heat-run test where the machine is fully loaded for a long periodto determine its steady state temperature rise. Such a test may not be feasible formachines of even moderate size and such load test even where feasible is highlywasteful of energy for the heat-run test.In a manufacturing concern a number of identical machines may be on productionline. Two such machines can be put on a test and coupled mechanically. These

    machines can then be tested by the Hopkinsons test where these two machinesare connected in parallel across the supply. By adjusting their excitations both ofthem can be simultaneously loaded (to any extent) where one machine (motoring)feeds mechanical power to the other machine (generating), while the generatingmachine feeds electrical power to the motoring machine. The only power drawnfrom the mains is the losses of both the machines. Load test and heat-run testcould thus be conducted with very little energy consumption while the machinescarry full load current at rated voltage.

    Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegant

    cabinet as a package. Range of instruments and accessories (standard format)1. 2HP Shunt machines mechanically coupled both are identical 220V 2HP1500rpm.2. 3-4 point DC Starter for the above3. Suitable Loading rheostats4. Digital tachometer5. Suitable double tube rheostat6. Suitable single tube rheostat7. Suitable digital Voltmeters DC8. Suitable digital ammeters DC.9. Suitable DC source Rectifier unit

    THREE PHASE INDUCTION MOTOR NO LOAD TEST ON A THREE

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    PHASE INDUCTION MOTOR

    No-Load Test: At no-load the machine runs at very small slip sufficient toprovide power for windage and friction loss, core loss and also a certain amountof stator copper loss, which has to be, accounted for because of the large no loadcurrent.

    With low slip, the following approximation will hold good.R2(1/s-1) is very highR2/s>>X2With these approximations the necessary formulae for finding out Xm will begiven while conducting the no-load test.

    BLOCKED ROTOR TESTBlocking the rotor from rotating is equivalent to making s=1 so that R2(1/s-1)=0.This test is conducted by applying a low voltage to the stator so as to limit thecurrent drawn to its full load value. At this reduced voltage, the core loss can beneglected but the effect of Xm has to be taken into account, as its value is smallas compared to that of the transformer.The slip of induction motor during normal operating conditions is low (2 to 8%).This leads to lower rotor frequency. So for obtaining more accurate value of therotor resistance, this test is conducted at a lower frequency and then the reactancevalues are scaled upto 50Hz. Such kind of a test at low frequency is not necessary

    for motors of less than 25kw.Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. Squirrel cage induction motor 3HP 440V 1440rpm coupled with DC shuntgenerator 220V@1500rpm 2KW on a common base plate2. DOL starter (ON line starter for 3? induction motor )3. Suitable loading Rheostat single phase4. Suitable Rheostat5. Suitable Digital Voltmeter AC6. Suitable Digital Ammeter AC

    7. Suitable Wattmeter8. Suitable Voltmeter DC9. Suitable Digital Ammeter DC10. Digital tachometer11. 3? 6A capacity Variac 400V / 0-470V.

    NO LOAD TESTS ON A SYNCHRONOUS GENERATOR

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    LOAD TEST ON A THREE PHASE INDUCTION MOTOR

    Objective: To obtain the performance characteristic of 3-phase induction motor

    by load test and by loss summation method.

    Preview : On no load, the power factor of an induction motor is very low and itslowly improves with load and attains a value around 0.85 on full load.Efficiency starts from zero on no load; increases with load, reaches a maximum atabout 80% of rated load and then starts decreasing. One of the methods ofloading an induction motor is to couple it to a dc machine, which is run as adynamometer or with the help of a brake drum arrangement.

    LOAD TESTS ON A SYNCHRONOUS GENERATOR

    Objective:

    To start and synchronise the synchronous machine (SM) to the Bus Bars.To conduct load test on the SM as a motorTo conduct load test on the SM as a generator

    Preview:

    A synchronous machine has a three-phase stator winding which carries three-

    phase balanced currents producing rotating field at synchronous speed(ns=120f/p). The rotor is dc excited and produces fixed poles when the rotor ismade to run at a speed close to synchronous speed. The two fields get locked ineach other and the rotor must run at a speed equal to synchronous speed. Thetorque developed is proportional to Sin A. The power angle A is the anglebetween the rotor field axis and resultant air-gap field.

    When the power is put into the machine by a prime mover coupled to it, then therotor field leads (in the direction of the rotor) the resultant air gap field by anangle delta. The electrical power flows out of the machine to the load or to thebus bar, as the case may be, while the mechanical power flows into it throughoutthe shaft from the prime mover. This is generating operation of the machine.If instead a mechanical load is placed on the shaft of the machine the rotor fieldthen begins to lag behind the resultant air gap field by an angle delta. Theelectrical power is now drawn from the mains while the mechanical power goesout of the shaft into the load. This is the motoring operation of the machine.

    If the electrical load on the generating machine is the maximum load of the motorthe matching of the two fields is lost and the machine is said to lose synchronism

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    or fall out of step. In such a condition the machine must be electricallydisconnected from the bus and the input to the prime mover must be immediatelybrought down. This loss of synchronism can occur at values of delta much lessthan 900 in conditions of electrical or mechanical shock to the machine. So inpractical operation of synchronous machine, value of delta is about 300.

    A per phase circuit model of the machine with dc field excitation is drawn inFig.1. Xs is the synchronous reactance of the machine and Ef is the excitationemf due to the rotor alone. In generating operation Ef leads V by angle deltawhile in motoring operation it lags. In any given load condition if the dc fieldexcitation is changed the excitation emf changes accordingly and thus results inchange in power factor of the current being fed by the generator or drawn by themotor. While the machine is run at synchronous speed the excitation gives asimple control over the power factor of its operation. Of course if the fieldexcitation is excessively reduced it reduces the maximum torque (powercapability of the machine) and it may lose

    Synchronism (fall out of step).

    In order to connect synchronous machine to the bus bars, it has to be properlysynchronized. i.e. the rotor is brought to a speed close to synchronous speed,adjusted to give rated voltage at its terminals and the machine is switched over tothe bus bar at the exact moment when the machine voltage phasor and the busbars voltage phasor are coincident. This process is known as synchronization.Practically all generating stations small or large use synchronous generators.Synchronous motor is used in special applications where constancy of speed isrequired and control over power factor helps in improving the power factor of thetotal plant. It is to be pointed out here that when the motor field is over excited itdraws a lagging power factor current (inducted behavior). At a certain load,excitation is called normal, when the power factor is unity.In order to conduct experimental test on a synchronous machine the machine isduly coupled to a dc machine. It can either act as a generator or as a motor. It alsoof course helps in synchronizing the machine to the bus bar. Such a set up in ourlaboratory will be used for synchronous machine tests.

    Equipment Required: All the measuring instruments associated with eachexperiment are industrial grade. These instruments are housed in an elegantcabinet as a package. Range of instruments and accessories (standard format)1. Three Phase 400V 3KVA 1500rpm synchronous alternator coupled with 5HPDC shunt motor 220V 1500rpm on a common base plate2. 3/4point DC starter3. synchronizing panel consisting of 2frequency meters, 2voltmeters,1synchronscope, 1set of bulbs for dark and bright method, complete with ON /OFF switch and a knife switch for synchronizing4. Suitable Digital Ammeter AC5. Suitable Digital Wattmeter6. Suitable Digital Voltmeter DC7. Suitable Digital Ammeter DC

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    8. Suitable Loading rheostat 39. Suitable Single tube rheostat10. Suitable Double tube rheostat11. Suitable DC Rectifier unit12. Phase sequence indicator

    TYPICAL CONNECTION DIAGRAM

    The following is a representative connection diagram shown in the manuals.Diagrams like this will be available for each experiment, in addition to the actualcircuit diagram.

    CALIBRATION OF ENERGY METER

    Study of calibration of Single phase Energy meter of 5 A capacity with 750revolutions / KWH with unity power factor. This consists of calibrationmeasurement of Known energy meter with unknown energy meter. Two energymeters are supplied with this trainer. One of them is known to be calibrated andthe other TO BE calibrated to determine % of deviation. By this methodpercentage deviation of an Unknown energy meter is studied.

    (a) Energy meter ( WITH VISIBLE TRANSPARENT CASE FOR VIEWINGALL THE MOVING PARTS) 2 Nos(b) Digital voltmeter to monitor the incoming line voltage,(c) Digital Ammeter to measure the amount of current passing thought the energymeter.(d) Stopwatch used to measure duration of energy consumed per Unit time.(e) Necessary power supplies to conduct the experiment for the measurement ofenergy consumption per unit time. All assembled in a cabinet with all theterminals brought out for interconnecting and for the purpose of measurement.By connecting an external variable lamp load and using stop watch, the energyconsumed per unit time (KWH) can be measured.

    Lamp load capable of providing 5A OR resistive load of 10A.(Specify the type of load required at the time of placing your purchase order)

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    Specifications:

    Analog Ammeter : Moving coil typeRange : 25mA DC FSDDigital meter : 3- digit digital AmmeterRange : 20mA DC FSD

    Input voltage source : 5 V DC FixedLoad resistor : A continuously variable load resistance in the range of 100 to5 K Ohms using potentiometer method.Shunt resistor : 10K Ohm shunt resistor will be supplied.Power supply : Necessary built-in power supplies operating at 230V AC mains.Cabinet : An ergonomically designed cabinet

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