Engineering, Polytechnic and Vocational Training Equipment-> Electrical Engineering Laboratory

1 2 [3] [«Back ]   Click to Enlarge NO LOAD TESTS ON A SYNCHRONOUS GENERATOR 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 See Enlarge Click to Enlarge HOPKINSON?S TEST 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 See Enlarge Click to Enlarge 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 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. See Enlarge Click to Enlarge 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 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 See Enlarge Click to Enlarge 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 actual circuit diagram. See Enlarge Click to Enlarge CALIBRATION OF ENERGY METER 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) See Enlarge Click to Enlarge CALIBRATION OF WATT METER 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) See Enlarge Click to Enlarge CALIBRATION OF VOLT METER 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 divider : 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. See Enlarge Click to Enlarge CALIBRATION OF AMMETER 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 See Enlarge Click to Enlarge STUDY OF B H CURVE 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. See Enlarge 1 2 [3] [«Back ] Go to Top