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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 brought out for conducting laboratory experiment with legend printed for convenience. This is assembled in 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 earth connection.

These laboratory rectifiers are mainly used in electrical engineering laboratories for the purpose of conducting experiments in machines and DC circuits. This provides constant DC output. This provides 15A output for continuous operation. This rectifier provides suitable source for operating DC machines or any DC circuit. Suitable fuse protection is provided. The analog panel meters mounted on the front panel can monitor the output voltage and the current. This has a START and STOP push buttons. When start button is pressed, the DC voltage is available at the output terminals, as indicted by the meter reading. When stop button is pressed the output is reset to zero.

In the event of mains power failure or accidental break in the mains supply, the DC supply from this rectifier unit, is automatically disconnected. The output from this rectifier is available to the DC circuit, only when the mains power returns AND, the voltage setting Variac is brought to 0V position AND start push button is pressed. This facility provides the scope for investigating the reason for the failure, 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 other protective methods must be implemented, wherever required.

This is a 3-phase AC machine. This is mechanically coupled to a breakdrum to provide loading. The shaft of the machine is coupled a drum. In turn the drum is connected to mechanical weighing pan by means of a belt. Rotating the screws provided on either sides of the belt can adjust the belt tension. There by it is possible to load the shaft of the 3-phase motor with a defined tension. The difference in the scale reading, provides the tension, the shaft is subjected to. As a result 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 load characters of the motor can be evaluated.

This is an arrangement of a 3-phase induction motor, mechanically coupled to a DC generator.

This is a 3-phase AC machine. This is mechanically coupled to a breakdrum to provide loading. The shaft of the machine is coupled a drum. In turn the drum is connected to mechanical weighing pan by means of a belt. Rotating the screws provided on either sides of the belt can adjust the belt tension. There by it is possible to load the shaft of the 3-phase motor with a defined tension. The difference in the scale reading, provides the tension, the shaft is subjected to. As a result 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 load characters of the motor can be evaluated.

This is an arrangement of a 3-phase induction motor, mechanically coupled to a DC generator.

This is an AC 3 ? induction motor. This operates on 415V AC. This squirrel cage induction motor coupled to a 2KW shunt generator.

Specifications:

• Volts: 415V - 3?
  
• Power: 2.2KW
  
• Current : 4.8A
  
• RPM: 1440
  
• Frame: PM100L

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 STARTposition full resistance is included, and is reduced to zero ohms when the handle is moved to ON position, in discrete steps. The starter is held in ON position by an electromagnet. At this ON position the DC circuit gets its full current from the DC Rectifier unit. In the case of a DC motor, this is
connected in series with the armature circuit, to limit the starting current and eventually this resistance is CUTOUT, from the circuit. There by enabling the motor to run at it?s full armature current. Therefore this starter acts as a first order protection 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 DC motor. 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 a signal to the electromechanically held arm (handle) to release, and the starter is switched to OFF position, thereby providing safety to the system.

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

This is an AC 3 ? synchronous alternator with, square path, 4 poles, and rotor wound stator excited type. This is screen protected IP22, with drip proof enclosure.

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

Blocking 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 the current drawn to its full load value. At this reduced voltage, the core loss can be neglected but the effect of Xm has to be taken into account, as its value is small as 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 the rotor resistance, this test is conducted at a lower frequency and then the reactance values 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 each experiment are industrial grade. These instruments are housed in an elegant cabinet as a package. Range of instruments and accessories (standard format)

1. Squirrel cage induction motor 3HP 440V 1440rpm coupled with DC shunt generator 220V@1500rpm 2KW on a common base plate
2. DOL starter (ON line starter for 3? induction motor )
3. Suitable loading Rheostat single phase
4. Suitable Rheostat
5. Suitable Digital Voltmeter AC
6. Suitable Digital Ammeter AC
7. Suitable Wattmeter
8. Suitable Voltmeter DC
9. Suitable Digital Ammeter DC
10. Digital tachometer
11. 3? 6A capacity Variac 400V / 0-470V.

Calibrating an Ammeter is a broad statement, because the Ammeter can be AC or DC. The current ranges can be in uA, or mA, or Amp or a few hundred amperes. So there appears to be a wide variety of ranges in current measurement. Since the measurement philosophy is same for any current meter measurement, a DC ammeter is studied for experimental purpose in this experimental setup.

Any moving coil meter is a current meter. Normally it is designed to deflect the needle for 100 or 200?A FSD depending on the coil resistance used in the meter. This resistance can be called as INTERNAL RESISTANCE OF THE METER. However in reality any electrical or electronic circuits do provide much more current than 100 or 200?A in their circuits, typically anywhere between 1mA to a few Amperes. Therefore any current meter that we use in the laboratory do not have this capability. Therefore some extra elements are added to make it appear as though the current meter really reads what we see in the laboratory. Kirchoffs current law will yield better explanation how this is achieved.

Calibrating an ammeter is a two step approach. An ammeter is said, to have been calibrated, if it can be tested for

a) accuracy of the basic meter with 100?A FSD or
b) If it is calibrated and displayed on the scale of the meter, for functional applications, like displaying any other parameter with engineering units like A, RPM, Kg/Cm2 or 0C etc.

In this trainer, all the facilities required to calibrate an Ammeter is attempted. While doing so, the above tasks are studied for experimental purposes.

Specifications:
Analog Ammeter : Moving coil type
Range : 25mA DC FSD
Digital meter : 3-? digit digital Ammeter
Range : 20mA DC FSD
Input voltage source : 5 V DC Fixed
Load resistor : A continuously variable load resistance in the range of 100 to
5 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

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

(a) Energy meter ( WITH VISIBLE TRANSPARENT CASE FOR VIEWING ALL 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 energy meter.
(d) Stopwatch used to measure duration of energy consumed per Unit time.
(e) Necessary power supplies to conduct the experiment for the measurement of energy consumption per unit time. All assembled in a cabinet with all the terminals brought out for interconnecting and for the purpose of measurement.

By connecting an external variable lamp load and using stop watch, the energy consumed 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)

Voltmeter measures voltage across a known source of potential. This voltage measurement can be AC or DC voltage. In case of DC voltage measurement, another variety of the voltmeter is called as center Zero Voltmeter. The voltage referred on the scale of the voltmeter refers to full-scale deflection (FSD). The FSD indication is always on the right hand side of the instrument. It is necessary to study the name plate details of the voltmeter to identify the type of meter namely moving coil or moving iron type, in addition to FSD. The voltmeter under study is moving coil type AC Voltmeter.

Calibrating a voltmeter is a two step approach. A voltmeter is calibrated for
I. Accuracy of the basic meter or
(a) Calibrate and display on the scale of the meter, for functional applications, like displaying a parameter with engineering units like RPM, Kg/Cm2 or 0C etc.
Now there is a need to study how to accomplish the above-defined tasks. The scope of this instrument restricts to performing the above two tasks only.

This trainer has all the necessary facilities to carryout the experiment needed for calibration. This unit requires an external VARIAC, which can be adjusted in the range of 0 to 230V AC.

Specifications:
Voltmeter under study : Moving coil type
Range : 0 to 30 V AC
Digital meter : 3-? digit digital voltmeter
Range : 0 to 230 V AC
Potential spanider : Known values of Resistors of 1% for calculating the voltage applied
across the device under test.
An external VARIAC required. This is not in the scope of supply with basic experimental setup.

Study of calibration of WATT meter of 5 A capacity. This consists of calibration measurement of Known WATTmeter with unknown WATTmeter. Two WATT meters are supplied with this trainer. One of them is known to be calibrated and the other TO BE calibrated to determine % of deviation. By this method percentage deviation of an Unknown WATTmeter is studied.

(a) ANALOG PORTABLE WATT METER ? 2 Nos
(b) Digital voltmeter to monitor the incoming line voltage,
(c) Digital Ammeter to measure the amount of current passing thought the energy meter.

Necessary power supplies to conduct the experiment for the measurement of power consumed. All assembled in a cabinet with all the terminals brought out for interconnecting and for the purpose of measurement.

By connecting an external variable lamp load power consumed (KWH) can be measured.

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

Open Circuit Test
Objective: To obtain the magnetization characteristic and therefrom determine the 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, the number of conductors and speed. This EMF depends on speed and flux. As the flux increases the EMF increases beyond a point the flux gets saturated. The BH curve 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 fixed excitation and variable speed, as the speed reduces the OCC proportionally slides down so that the no load voltage reduces. At a particular speed, called the critical speed, the OCC is tangential to the Rf line and as a result the generator fails to excite.

Preview :
With the fixed excitation and variable speed, as the speed reduces the OCC proportionally slides down so that the no load voltage reduces. At a particular speed, 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 each experiment 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 2HP 1500rpm.
2. 3-4 point DC Starter for the above
3. Suitable Loading rheostat
4. Digital tachometer
5. Suitable Double tube rheostat
6. Suitable Single tube rheostat
7. Suitable Digital Voltmeter DC
8. Suitable Digital Voltmeter DC
9. Suitable Digital Ammeter DC
10. Rectifier Unit 0-240V DC @ 1.5KVA with power failure protection.

Distribution panels are intended to provide necessary AC or DC supplies to the AC or DC machines. There are two different distribution panels available. These are 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 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 the rectifier unit respectively, through these panels only. I.e. the supply for each machine is routed through this distribution panel. The supply to each machine is suitably switched ON / OFF through a suitably protected MCB. This provides protection to each machine. Routing supply through these panels allow you to switch ON or OFF using respective switch gear, there by power can be saved, permitting you to switch ON the machines which are required for experimentation, 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 meter indicates the overall DC voltage available to the DC circuits. There will be line drop at the respective machines, when measured near the machine. This is due to line loss. The current meter indicates the total current drawn by the whole DC circuit through this panel.
4. Switches: 12 different DC circuits can be connected through this panel. Each circuit is protected with an independent MCB. In addition to this a master switch controls the complete DC circuit. When this is in OFF position, the DC supply to all the DC circuits are switched OFF.
5. A lamp indicator is used to display the status of power supply. This is illuminated when the power is ON.
6. Separate earth connection is provided to the panel. This must be securely connected 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 DC rectifier unit.

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

All the electrical engineering experiments will have broadly the following objectives while performing relevant experiments. The scope of the supply does not include, hardware like DOL starters, Mains switches, wiring from the mains supply to the experimental tables, HRC fuse assemblies, Circuit breakers, ELCBs, civil structures etc. However these are required to be installed or constructed or assembled and wired, prior to connecting necessary experimental setups.

Objectives of experimental setups.

a. Activity Sequence
b. Study of nameplate details
c. Identifying measuring instruments and support accessories required for conducting the experiment
d. Preview
e. Record Circuit Diagram and connection diagrams
f. Model graph and expected outcome
g. Data processing and calculations and
h. Inference

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

?Separate wires and neutral wires using standard 7-20 SWG, must be drawn from MCBs on the distribution panel to the respective Motor ? Generator / Alternator sets.
?Mains trip switch (Isolators) for DC and 3 ?, to be provided near every equipment MG Set of each experimental setup for safety purpose.
?Neutral must be terminated with 30A black color banana terminal, at each and every 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 earth wire.
?Isolators must be fitted as shown in the diagram near each and every MG set.

UNENDING DEBATE:
How do you distinguish and qualify a component, or a machine or an experimental setup, suitable for Electrical engineering laboratory and why?

There was a growing concern expressed by various learned faculty members, that power-handling capabilities of the machines recommended for laboratory experiments should reflect, close to qualify for true Electrical engineering laboratories. This is partly because, true electrical characteristics of systems will be better observed and more pronounced in higher power handling ranges, than in the machines working at few hundred watts. This remained always a point of discussion and debate, with differing views by many learned faculty members. For example, one faculty member says it is sufficient if rudiments of electrical engineering are explained to the students at graduate level, so that we need not invest big money. The other faculty member differs, stating that, it is something like teaching swimming without a swimming pool to a trainee / student. Further, he goes on to say that, the student / trainee cannot feel the strain and pain without actual swimming in the pool. So it looks, the characteristics of an electrical machine, will look more pronounced and meaningful, if it is atleast close to a KW region. The arguments and counter arguments are unending. It looks, power handling capabilities, probably appears to be the point in argument, to qualify a component or machine or a setup to be used in electrical engineering laboratories. Atleast this appears to be the consensus by various faculty members in electrical engineering.

For example, a transformer used in an electronic measuring instrument can be anywhere between a few watts to say hundred watts. When such a transformer is used in electrical engineering experiment, no doubt, it is sufficient to explain the rudiments of a transformer. But when it comes to electrical engineering labs, a KW appears to be a normal parameter, while it is a few tens of watts or at the best say 300 watts, when used by an electronics engineer. This is because an electrical engineer is tuned to handling power systems or must be trained to handle large power. Hence the power handling capabilities of the machines appear to be the necessary evil.

Experimental setups made in modular style, looks small and compact. They are economical, but the power handling capabilities of such systems, will not exceed more than say 250Watts. At such low power handling, true electrical experimental characteristics can be realised,

Experimental setup required for popular experiments are listed below. This is not a comprehensive list. There is ample scope for listing plenty of experiments. These are minimum requirements, listed in various university syllabi. specific request. It is very important for you to incorporate all the necessary safety features against accidents that may occur during the experiments.

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

Preview:
Swinburn?s test is a no-load test on a dc machine. The machine is started and run as a dc motor with shaft decoupled from any load. In this regard the test is very easy to carry out for a machine of any size, particularly convenient for a large machine.
The input to motor at no-load comprises of:
Iron losses (Pi)

Mechanical, friction and windage loss (Pwf)
Field Copper Loss (Pshf)

Armature Copper Loss
(Armature resistance is measured by drop test and corrected to operating temperature 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) can be predetermined either as motor or generator.

Equipment Required: All the measuring instruments associated with each experiment are industrial grade. These instruments are housed in an elegant cabinet 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 armature
4. 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.

Transformer is the very first electrical that is required in making any electrical equipment. This component in turn provides the overall power required, for any system to operate successfully, after necessary isolation, step/up or step/down conditions, as required in the final system. Hence this is the most critical and useful part of any electrical equipment. Therefore it is important to study, understand and experiment, a process, for evaluating its operating characteristics. This knowledge will be utilized, when an engineer is required to design, troubleshot and maintain any electrical system.

Suitable HRC fuses are provided at AC input and DC output stages for protection. The rating of the mains transformer is designed to provide upto 200V DC, while the series transformer provides 40V DC, suitably arranged to provide the correction required. The series transformer is controlled by a three phase motorized dimmerstat. The rectifier circuit is generously rated with suitable heat sink and hole storage suppression.

Objective: Determine the parameters of the equivalent circuit of a single-phase transformer, and to predetermine the performance characteristics and verify the specifications by open circuit and short circuit tests.

1. Study of nameplate ratings of the transformer under test.
2. Determination of Voltage ratio (Turns ratio) test
3. Performing an Open Circuit (OC) Test
4. Performing Short Circuit (SC) Test
5. Determination of Efficiency of the transformer.
6. Draw a graph of performance at UPF and at 0.8p.f.lag.
7. Predetermination of Regulation of Transformer

Scope for inference
As the transformer is inductive load, it takes large in rush current. Select proper fuse rating. Prefer OC test on LV side and SC test on HV side for personnel safety and meter range. On No load, the p.f. of the transformer will be very low. Hence for better results choose LPF wattmeter. During SC test, low voltage is applied, the LV side is shorted by an insulated wire, use proper connection and proper wire. Always switch OFF the supply after taking readings and then start calculations. Do not increase the input voltage beyond the voltage rating of the transformer.

Objective:
To conduct Hopkinson’s test on the given pair of identical dc machines and obtains item performance characteristics

Preview:
Swinburne’s test on a dc machine is a non-loading test. The machine performance can 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 it particularly for a heat-run test where the machine is fully loaded for a long period to determine its steady state temperature rise. Such a test may not be feasible for machines of even moderate size and such load test even where feasible is highly wasteful of energy for the heat-run test.

In a manufacturing concern a number of identical machines may be on production line. Two such machines can be put on a test and coupled mechanically. These machines can then be tested by the Hopkinson’s test where these two machines are connected in parallel across the supply. By adjusting their excitations both of them can be simultaneously loaded (to any extent) where one machine (motoring) feeds mechanical power to the other machine (generating), while the generating machine feeds electrical power to the motoring machine. The only power drawn from the mains is the losses of both the machines. Load test and heat-run test could thus be conducted with very little energy consumption while the machines carry full load current at rated voltage.

Equipment Required: All the measuring instruments associated with each experiment 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 2HP 1500rpm.
2. 3-4 point DC Starter for the above
3. Suitable Loading rheostats
4. Digital tachometer
5. Suitable double tube rheostat
6. Suitable single tube rheostat
7. Suitable digital Voltmeters DC
8. Suitable digital ammeters DC.
9. Suitable DC source –Rectifier unit

Objective: To conduct Hopkinson?s test on the given pair of identical dc machines and obtains item performance characteristics

Preview:
Swinburne?s test on a dc machine is a non-loading test. The machine performance can 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 it particularly for a heat-run test where the machine is fully loaded for a long period to determine its steady state temperature rise. Such a test may not be feasible for machines of even moderate size and such load test even where feasible is highly wasteful of energy for the heat-run test.

In a manufacturing concern a number of identical machines may be on production line. Two such machines can be put on a test and coupled mechanically. These machines can then be tested by the Hopkinson?s test where these two machines are connected in parallel across the supply. By adjusting their excitations both of them can be simultaneously loaded (to any extent) where one machine (motoring) feeds mechanical power to the other machine (generating), while the generating machine feeds electrical power to the motoring machine. The only power drawn from the mains is the losses of both the machines. Load test and heat-run test could thus be conducted with very little energy consumption while the machines carry full load current at rated voltage.

Equipment Required: All the measuring instruments associated with each experiment 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 2HP 1500rpm.
2. 3-4 point DC Starter for the above
3. Suitable Loading rheostats
4. Digital tachometer
5. Suitable double tube rheostat
6. Suitable single tube rheostat
7. Suitable digital Voltmeters DC
8. Suitable digital ammeters DC.
9. Suitable DC source ?Rectifier unit

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 its operation. 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 generator may 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 this identical machines setup in several ways, for varied parameters.

Specifications:

• DC machines: Two identical machines.
  
• Voltage: 220V
  
• Amps: 6.8
  
• RPM: 1500
  
• KW: 1.5
  
• Rating-CMR
  
• INS Class-B/.
  
• Extn type: Shunt
  
• 220V, 0.5A

These laboratory rectifiers are mainly used in electrical engineering laboratories for the purpose of conducting experiments in machines and DC circuits. This is servo controlled to provide constant DC output. This provides 100A output for continuous operation. This rectifier provides suitable source for operating DC machines.

System Description:

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

This unit has a START and STOP push buttons. Pressing Start push button makes, the output to set at the voltage shown by the panel meter, and the output is available at the terminals at this time. Pressing stop push button, the output is reset to 0V. In the event of mains power failure or accidental break in the mains supply, the DC supply from this rectifier unit, is automatically disconnected. The output from this rectifier is available to the DC circuit, only when the mains power returns AND start push button is pressed. This facility provides the scope for investigating the reason for the failure, and also protecting the assets.

The entire rectifier unit is assembled in a rugged sheet steel material with suitable reinforcements wherever required. The entire unit is assembled on suitable caster wheels, to provide mobility for unit.

Objective: To obtain external characteristics of a dc shunt generator

Preview:
The self excited DC shunt Generator is coupled to a DC motor, which acts as prime mover. Two characteristics are more important. The internal or total characteristic that gives the relation between the emf actually induced in the armature and the armature current. This is of interest mainly to the designer. The external characteristics called performance characteristics (also voltage regulating curve) which give the relation between the terminal voltage and load current. This curve lies below the internal characteristics due to armature drop. This is important in judging the suitability of a generator for a particular purpose. These characteristics can be obtained by a load test with total field resistance remaining fixed as the speed is to be kept constant.

Equipment Required: All the measuring instruments associated with each experiment 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 2HP 1500rpm.
2. 3-4 point DC Starter for the above
3. Suitable Loading rheostats
4. Digital tachometer
5. Suitable double tube rheostat
6. Suitable single tube rheostat
7. Suitable digital Voltmeters DC
8. Suitable digital ammeters DC.
9. Suitable DC source ?Rectifier unit

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 it slowly 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 at about 80% of rated load and then starts decreasing. One of the methods of loading an induction motor is to couple it to a dc machine, which is run as a dynamometer or with the help of a brake drum arrangement.

Objective:
To start and synchronise the synchronous machine (SM) to the Bus Bars.
To conduct load test on the SM as a motor
To 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 is made to run at a speed close to synchronous speed. The two fields get locked in each other and the rotor must run at a speed equal to synchronous speed. The torque developed is proportional to Sin A. The power angle A is the angle between 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 the rotor field leads (in the direction of the rotor) the resultant air gap field by an angle delta. The electrical power flows out of the machine to the load or to the bus bar, as the case may be, while the mechanical power flows into it throughout the 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 field then begins to lag behind the resultant air gap field by an angle delta. The electrical power is now drawn from the mains while the mechanical power goes out 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 motor the matching of the two fields is lost and the machine is said to lose synchronism or fall out of step. In such a condition the machine must be electrically disconnected from the bus and the input to the prime mover must be immediately brought down. This loss of synchronism can occur at values of delta much less than 900 in conditions of electrical or mechanical shock to the machine. So in practical operation of synchronous machine, value of delta is about 300.

A per phase circuit model of the machine with dc field excitation is drawn in Fig.1. Xs is the synchronous reactance of the machine and Ef is the excitation emf due to the rotor alone. In generating operation Ef leads V by angle delta while in motoring operation it lags. In any given load condition if the dc field excitation is changed the excitation emf changes accordingly and thus results in change in power factor of the current being fed by the generator or drawn by the motor. While the machine is run at synchronous speed the excitation gives a simple control over the power factor of its operation. Of course if the field excitation is excessively reduced it reduces the maximum torque (power capability 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 properly synchronized. 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 to the bus bar at the exact moment when the machine voltage phasor and the bus bars 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 is required and control over power factor helps in improving the power factor of the total plant. It is to be pointed out here that when the motor field is over ?excited it draws 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 is duly coupled to a dc machine. It can either act as a generator or as a motor. It also of course helps in synchronizing the machine to the bus bar. Such a set up in our laboratory will be used for synchronous machine tests.

Equipment Required: All the measuring instruments associated with each experiment are industrial grade. These instruments are housed in an elegant cabinet as a package. Range of instruments and accessories (standard format)

1. Three Phase 400V 3KVA 1500rpm synchronous alternator coupled with 5HP DC shunt motor 220V 1500rpm on a common base plate
2. 3/4point DC starter
3. 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 synchronizing
4. Suitable Digital Ammeter AC
5. Suitable Digital Wattmeter
6. Suitable Digital Voltmeter DC
7. Suitable Digital Ammeter DC
8. Suitable Loading rheostat 3?
9. Suitable Single tube rheostat
10. Suitable Double tube rheostat
11. Suitable DC Rectifier unit
12. Phase sequence indicator

Loading capacitor, is a capacitor bank with step variation. This is required when experimenting to determine the output characteristics of devices like a transformer etc. More particularly while experimenting to determine the power factor measurements in single-phase electrical circuits.

This is a loading capacitor, where by the capacitance in a load circuit can be varied in the range of 2uF to 16uF @ 230V AC, in 8 steps. The variation in capacitance can be obtained by suitable patch cord mechanism. This is suitably protected with necessary fuse arrangement. The terminals are suitably brought out on a 4mm Banana sockets for easy interconnections.

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

This requires DC rectifier source for its operation. The DC source to this is provided through a 3-4 point DC starter unit. Using this, several experiments on DC motor can be conducted. Depending on the experiment, you need appropriate meters, rheostats, switchgear are required. These motors are screen protected, with IP21/IP22 enclosures.

Specifications:

• Voltage: 220V
  
• Amps: 6.8
  
• RPM: 1500
  
• KW: 1.5
  
• Rating-CMR
  
• INS Class-B/.
  
• Extn type: Shunt
  
• 220V, 0.5A

Varieties of meters are available for making suitable measurements of electrical parameters. These meters are available for use in single phase and three phase circuits. The meters are available in tabletop models and panel mounting arrangements. Normally these meters are used in Electrical engineering laboratories for various measurements. The meters available are

1. Volt meters- analog /digital
2. Ammeters – analog / digital
3. Watt-meters – analog / digital
4. Phase sequence indicators
5. Tacho meters – contact type and photo reflective type
6. Reed type frequency meters
7. Phase meters.
8. Power factor metes.

Objective: To determine the equivalent circuit parameters of synchronous machine and hence to predetermine the percentage regulation at different power factors.

Open Circuit Test:
The machine is run (as generator) at synchronous speed with armature terminals open. The plot of Vocl Vs If is the OCC (open circuit characteristic) which indeed is the magnetization characteristic of the machine. It exhibits the saturation effects.

Short Circuit Test:

The armature terminals are shorted. The machine is run at synchronous speed while If is gradually increased starting from zero value. The field current needed for ISCL = IFL (rated) is very small. The plot of ISCL Vs If is SCC (short circuit characteristic). The field current being very small this operates in linear region. So SCC is straight line, only one point on SCC corresponding to ISCL = IFL need be determined experimentally.

Measurement of Armature Resistance
Using a dc source, voltmeter and ammeter take a few readings across two terminals of Stator by adjusting the series resistance

Equipment Required: All the measuring instruments associated with each experiment are industrial grade. These instruments are housed in an elegant cabinet as a package. Range of instruments and accessories (standard format)

1. Three Phase 400V 3KVA 1500rpm synchronous alternator coupled with 5HP DC shunt motor 220V 1500rpm on a common base plate
2. 3/4point DC starter
3. 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 synchronizing
4. Suitable Digital Ammeter AC
5. Suitable Digital Wattmeter
6. Suitable Digital Voltmeter DC
7. Suitable Digital Ammeter DC
8. Suitable Loading rheostat 3?
9. Suitable Single tube rheostat
10. Suitable Double tube rheostat
11. Suitable DC Rectifier unit
12. Phase sequence indicator

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, to increase the safety for the personnel, conducting the experiments. The connections from each machine are terminated on this connector panel. The necessary wirings from the machine to these panels are to be securely made, prior to, conducting lab experiment. Each panel is diagrammatically represented to reflect various terminals of a machine, and they are printed above the terminals. All the necessary terminals of the machine are terminated on a 4mm patch cord terminal, suitable to make interconnections with other associated circuitry. Each connector panel differs from the other panel in terms of drawings used for different machines. We supply these, 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, which are placed on the experimental table. The 4mm terminals from these are used for interconnecting with other associated circuitry.

This is a variable auto transformer. This is also called as Dimmer-stat. This is used 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. The entire instrument is assembled in a sheet rolled powder coated MS metal box with separate screw terminal for earth connection.

Specifications:

• Input: 230 V AC
  
• Output: Variable in the range of 0 to 270V AC.
  
• Rated capacity: 6A

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

Preview:
The concept of 3phase to 2-phase connection follows from the voltage phasor diagram of balanced 3-phase supply. If the point M midway on Vbc could be located then VAM leads Vbc by 900. A 2-phase supply could be thus obtained by means 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 must

have ?3N1/2 (teaser) and N1 turns;this would mean equal voltage / turn in each transformer. A balanced two phase supply could then be easily obtained by having both secondaries with equal number of turns N2. The point M is located midway on the primary of the transformer connected across the lines B & C. The connection of two such transformers, known as the Scott Connection, is shown in Fig with its phasor diagram of two phase supply in the secondary.

Equipment Required: All the measuring instruments associated with each experiment 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(tapings at 86.6%,50%), Secondary: 115V ? Two numbers
2. Suitable Loading rheostat for the above single phase ? two numbers
3. Suitable Variac ? three phase
4. Suitable digital ammeters of different ratings AC
5. Suitable digital voltmeters of different ratings AC
6. Suitable digital wattmeter

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 ac motors. 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 as armature control). The flux per pole can be varied by varying the field current (called field control).

Equipment Required: All the measuring instruments associated with each experiment are industrial grade. These instruments are housed in an elegant cabinet 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 armature
4. 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.

In a magnetic circuit, the medium of transformation of induced voltages and current plays a vital role in study of Hysteresis. It is necessary to study the Hysteresis to evaluate the performance of this media for electrical characteristics. Often the transformation media in electrical circuit is a transformer either for step-up or step-down purposes. The magneto-motive force “H” is a direct function of the exciting current and the flux density “B”. It is integral of the applied voltage.

In this trainer, it is attempted to study and demonstrate the above mentioned principles. This trainer permits to view the BH curve on the oscilloscope for various currents. This trainer has necessary components to like transformer under study, Isolation transformers, passive components, Ammeter and Voltmeter. An external Variac, continuously variable in the range of 0 to 270V @ 3A is necessary.

NOTE: Since low power transformer is used in this trainer, large power measurements beyond 10W cannot be made.

Objective: To perform Sumpner?s test. Predetermination of performance characteristics and equivalent circuit of single-phase transformer.

Preview: In OC and SC tests a transformer is subjected to either core loss or copper 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 by connecting them back-to-back. Wherein, their secondaries are connected in phase opposition. So the secondaries will behave open-circuited when the primaries are excited, 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 the secondary circuit which causes circulating current in the secondaries with primaries acting as short circuit for this source (use superposition theorem). This circulating current can be adjusted to full-load value. The power injected by this source is 2PC, the full-load copper loss of both transformers, while the impedance seen by it is 2Zeq. Both the transformers in this test are thus subjected to full load core and copper losses by phantom loading, while drawing only core loss power from source V1 and only copper loss power from source V2. In some sense this test has similarity with the Hopkinson?s test on two identical dc machines.

Equipment Required: All the measuring instruments associated with each experiment 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 ? Two numbers
2. Suitable Variac
3. Suitable digital ammeters of different ratings AC
4. Suitable digital voltmeters of different ratings AC
5. Suitable digital wattmeter

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

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

With low slip, the following approximation will hold good.
R2?(1/s-1) is very high
R2?/s>>X2?
With these approximations the necessary formulae for finding out Xm will be given while conducting the no-load test.