Experiment 2 AC Machines


Published on

uncomplete report and got many errors

Published in: Education, Business
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Experiment 2 AC Machines

  2. 2. OBJECTIVES 1. To demonstrate the operating characteristics of a three-phase induction motor using the four pole squirrel cage induction motor. 2. To record the load characteristics N, I, cos 0, P2, s, and n as a function of torque, (t) of a three-phase induction motor with squirrel-cage rotor for star and delta connections. 3. To examine its performance characteristics. LIST OF REQUIREMENTS Equipment 1. Voltage supply 2. Three-phase induction motor with squirrel cage rotor 3. Power factor meter 4. Watt meter 5. Ammeter 6. Voltmeter 7. Pendulum machine 8. Display panel 9. Coupling cover 10.Control unit 11.Shaft and cover 12.Connection mask(code:3125651)
  3. 3. THEORY AC motor An AC motor is an electric motor that is driven by an alternating current. It consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field. There are two types of AC motors, depending on the type of rotor used. The first is the synchronous motor, which rotates exactly at the supply frequency or a submultiples of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. The second type is the induction motor, which turns slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current. DEVICE 2 POLES
  4. 4. Three-phase AC induction motors Three phase AC induction motors rated 746 W (1.000 hp) and 25 W (left), with smaller motors from CD player, toy and CD/DVD drive reader head traverse (9 V battery shown, at bottom center, for size comparison). Squirrel-cage rotors Most common AC motors use the squirrel cage rotor, which will be found in virtually all domestic and light industrial alternating current motors. The squirrel cage refers to the rotating exercise cage for pet animals. The motor takes its name from the shape of its rotor "windings"- a ring at either end of the rotor, with bars connecting the rings running the length of the rotor. It is typically cast aluminum or copper poured between the iron laminates of the rotor, and usually only the end rings will be visible. The vast majority of the rotor currents will flow through the bars rather than the higher-resistance and usually varnished laminates. Very low voltages at very high currents are typical in the bars and end rings; high efficiency motors will often use cast copper in order to reduce the resistance in the rotor.
  5. 5. In operation, the squirrel cage motor may be viewed as a transformer with a rotating secondary. When the rotor is not rotating in sync with the magnetic field, large rotor currents are induced; the large rotor currents magnetize the rotor and interact with the stator's magnetic fields to bring the rotor almost into synchronization with the stator's field. An unloaded squirrel cage motor at rated no-load speed will consume electrical power only to maintain rotor speed against friction and resistance losses; as the mechanical load increases, so will the electrical load - the electrical load is inherently related to the mechanical load. This is similar to a transformer, where the primary's electrical load is related to the secondary's electrical load. This is why, for example, a squirrel cage blower motor may cause the lights in a home to dim as it starts, but doesn't dim the lights on startup when its fan belt (and therefore mechanical load) is removed. Furthermore, a stalled squirrel cage motor (overloaded or with a jammed shaft) will consume current limited only by circuit resistance as it attempts to start. Unless something else limits the current (or cuts it off completely) overheating and destruction of the winding insulation is the likely outcome. In order to prevent the currents induced in the squirrel cage from superimposing itself back onto the supply, the squirrel cage is generally constructed with a prime number of bars, or at least a small multiple of a prime number (rarely more than 2). There is an optimum number of bars in any design, and increasing the number of bars beyond that point merely serves to increase the losses of the motor particularly when starting. Virtually every washing machine, dishwasher, standalone fan, record player, etc. uses some variant of a squirrel cage motor. Slip If the rotor of a squirrel runs at high speed, the flux in the rotor at any given place on the rotor would not change, and no current would be created in the squirrel cage. For this reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed, even at no load. Because the rotating field (or equivalent pulsating field) actually or effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The difference between synchronous speed and
  6. 6. actual speed is called slip, and loading the motor increases the amount of slip as the motor slows down slightly. The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation: Ns = 120F / p where Ns = Synchronous speed, in revolutions per minute F = AC power frequency p = Number of poles per phase winding Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip, that increases with the torque produced. With no load, the speed will be very close to synchronous. The slip of the AC motor is calculated by: S = (Ns − Nr) / Ns where Nr = Rotational speed, in revolutions per minute. S = Normalised Slip, 0 to 1. As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800 RPM.
  7. 7. PROCEDURES PART A (WYE)-CONNECTION 1. Established the connections for recording the load characteristics in star (Y) connection according to the current diagram shown in the figure 2.3. 2. Before that, we must adjusted the operating elements of the control units as shown in table 2.1. Operating elaments Value Type of Power 1000 W Operating switch On position Off Switch “ N const. const.” position const Switch “torque range”position 10 Nm Switch”speed range” position 3000 3. The control unit with master switch was switch on. The reset button then pressed. Note that the red LED light should not be alight anymore. Otherwise the mistake might had occurred during the set-up. Check or the following: I. The coupling hoop guard is missing. II. The hoop guard for the shaft and cover is missing. III. The jack plug for the motor temperature control has not been plugging. IV. The motor is too hot.
  8. 8. 4. The motor was started by increasing the voltage supply gradually until it was reached its rated voltage. Measured the require quantities at no load. Enter the measured value into Table 2.2. switch the function selector from “off” to Nconstant , The corresponding greed LED light up. ( the speed of the pendulum machine automatically adjusted to the motor frequency). Then adjusted the given load at the control units of the pendulum machines by pressing the down button. When exceeding the selected value, press the up button. Read the corresponding values measured. Enter the measured values into the Table 2.2. Measurements was continued with other values. 5. Used those equations to calculated the values of: The power output, = =(2 x N)/60 The apparent power,S=1.732(V/ ) The efficiency, =( )x100% The slip,s=[( ]x 100% 6. Plotted the graph showing N,I, cos , , and torque in star (Y) connection in Graph 2.4. PART B: (DELTA) CONNECTION 1. The motor was connected in delta connection. Connected terminals U1- W2, V1-U2 and W1-V2. 2. Conducted the experiment as in a Part A, under procedure 3 and 4. The calculated and measured value was recorded in Tables 2.3. 3. Plotted a graph showing N,I, cos , , and torque in delta ( connection in Graph 2.5. Indicated the rated torque clearly.
  9. 9. Result Part A Parameter Measured Value Torque, (Nm) 0.0 0.5 1.0 1.5 2.0 2.5 Voltage (V) 400 400 400 400 400 400 Current, (A) 1.8 1.8 1.8 1.8 1.8 1.8 Power factor (cos ) 78.46 75.52 72.54 69.51 66.42 63.26 Speed, N (rpm) 1495 1494 1490 1487 1480 1480 Power input, (W) 80 100 120 140 160 190 Calculated value Apparent power, S(VA) 1.247k 1.247k 1.247k 1.247k 1.247k 1.247k Power output, (W) 0.00 78.23 156.0 233.6 310.0 387.5 Efficiency, (%) 0.00 78 130 167 194 204 Slip, s 0.3 0.4 0.67 0.87 1.3 1.3 Table 2.2 Part B Parameter Measured Value Torque, (Nm) 0.0 0.5 1.5 2.0 2.5 2.5 Voltage (V) 230 230 230 230 230 230 Current, (A) 2.8 2.8 2.8 2.8 2.8 2.8 Power factor (cos ) 78.46 75.52 72.54 69.51 66.42 60 Speed, N (rpm) 1496 1493 1490 1487 1482 1480 Power input, (W) 80 100 120 140 180 190 Calculated value Apparent power, S(VA) 1.115k 1.115k 1.115k 1.115k 1.115k 1.115k Power output, (W) 0.00 78.2 156.0 233.6 310.4 387.5 Efficiency, (%) 0.00 78 130 167 172 204 Slip, s 0.27 0.47 0.67 0.87 1.2 1.3 Table 2.3
  10. 10. REFERENCES D.F. Warne,(2000). Newnes Electrical Engineer’s Handbook, Newnes. Rusnani Ariffin and Mohd Aminudin Murad, (2010).Laboratory Manual Electrical Engineering Laboratory 2 EEE 240.University Publication Centre (UPENA). Stevenson, William D., Jr. (1975). Elements of Power Systems Analysis. McGraw- Hill electrical and electronic engineering series (3rd Ed.). New York: McGraw Hill. Paul E. Tippens, (2007). Physics (7 th Ed.).McGraw Hill International Edition. http://www.tpub.com/neets/book1/chapter1/1g.htm retrieved on 18 march 2013
  11. 11. TABLE OF CONTENT Topic Page Introduction Objectives and Equipments Procedure Result Discussion Conclusion Reference