Electrical Engineering Principles (EET 211) Laboratory Module
EXPERIMENT 6
Principle of a Three-Phase Synchronous Generator and No- load Characteristic
Objective:
To understand the principle of a 3-phase generator used to supply 3-phase power and its no-load characteristic.
Introduction:
The 3-phase synchronous generator or known as alternator, produces most of the electrical power used. Its structure is made of two main items as shown in Figure 1.
Figure 1: Structure of a synchronous generator
In a 3-phase synchronous generator, the stator coils are displaced to each other by 120 apart. The coils are normally named as a, b and c and direct identification of 3 phases. The basic wiring circuit of the rotor and stator is given as in Figure 2 below.
Figure 2: Basic wiring circuit
The rotor is normally a rotating coil which a DC current is supplied through it to create the rotating magnetic field. The rotor could be a single pole or number of poles and the relation of the frequency produced by the generator with respect to the speed is given by,
Frequency,
where is speed of rotor in rpm and is no. of pole pairs.
The amplitude of induced voltage output from the generator is also a function of rotational speed of the rotor.
Induced voltage per phase,
where is the frequency, is no. of turn per phase and is flux per pole (Wb).
Equipment and Parts:
1) Field Rheostat Module (NO-5301)………………………………………….…..1 set
2) DC/AC Meter Load Module (NO-5303)……………….…………………….…. 1 set
3) 3-phase load module (NO-5304)………….…………………………………….1 set
4) Power Supply Module (NO-5306)………………………….……………………1 set
5) AC Volt/Ampere Meter Module (NO-5308) …………………………………... 1 set
6) AC/DC Machine Field Frame Module (NO-5310) ………………………….….1 set
7) Auto Driving Unit Module (NO-5311) …………………………………………...1 set
8) 3-phase machine graphic board (NO-5314)………………………….………….1 ea
9) Two-arctic Rotor/Armature (A03) …………………………….,…………………..1 ea
10) Wide Pole Piece for Coils (A10) ……….…………………………….……………3 ea
11) Field Winding/300 turns (A13)……………………………………….…………….3 ea
12) A type Brush Holder Set (A16) ……………………………………………..…….1 set
13) Incandescent Lamp 6V (A19) …………………………………..…………………3 ea
14) Shaft of Rotors (A20) ……………………………………………..………………..1 ea
15) Shaft of Pole Piece (A21) …………………………………………………….……3 ea
16) Locking Bolt (A22) …………………………..………………………………………4 ea
17) Drive Belt (A23) ……………………………………………………………..………1 ea
18) 8mm Spanner (A24) …………………………………………………………..……1 ea
19) Oscilloscope (option) ……………….…………………………………………….. 1 set
20) Digital Tacho Meter (option)………..………………………………...... 1 set
Figure 3: Connection diagram of the 3-phase synchronous generator.
Figure 4: Assembly diagram of the 3-phase generator
Procedure:
1) Assemble and set-up all related parts and equipment as shown in Figure 3 and 4 above. Ensure you use the correct items with their respective parts’ numbers.
2) Wiring up your set-up accordingly. Before turning on the power, perform these steps:
i) Adjust the speed control knob of the Auto Driving unit to the position of MIN.
ii) Set the switch direction of the driving unit to CCW.
iii) Set the VR of field rheostat to the position of max. resistance 100.
iv) Ensure you use the 8.4V DC supply terminals of the Power Supply Module (No 5306) to supply the field rotor coil.
3) Request your instructor to confirm on your work before turning on the set-up.
4) Switch on the Power Supply Module (No-5306) and the Auto Driving unit.
5) Increase slowly the speed control knob of the Auto Driving unit until the speed of your synchronous rotor is around 1200rpm. Confirm the actual speed using a tachometer targets on the synchronous rotor, not on the prime mover of Auto Driving unit.
6) Adjust the field rheostat clockwise to increase the field current and you will notice the lamps begin to light up.
7) Then remove the lamps from the holder unit and let the generator runs in no-load condition.
8) Using the oscilloscope, sketch the output waveforms of all of the 3-phase output voltages on the same graph. Indicate their respective phase: a, b and c on the sketch and state the phase difference (in degrees) between each other.
9) Theoretically calculate the frequency of the output voltage. Confirm your calculated frequency with the actual measured value. State whether the values are similar.
10) While still maintaining the speed as in (5), turn slowly the field rheostat knob clockwise to increase the field current, in sequence of 0.1A, 0.2A,…, 0.8..,Max. Record the data as shown in Table 1.0.
11) Upon completion, turn off all the power switches.
12) Draw a graph of generated voltage vs field current using data from Table 1.0.
13) Observe the graph. Is the synchronous generator output voltage () zero when the field current () is zero? Briefly explain why.
14) Briefly explain why the relation between the synchronous generator output voltage and field current is either non-linear or linear (depends on your results) for higher values of field current?
15) Now turn on all the power switches. Set your field current to 0.8A. Adjust the speed of the Auto Driving unit in steps of 300, 500, 900, 1200 and 1500rpm. Record your data accordingly as in Table 2.0.
16) Upon completion, turn off all the power switches. Draw a graph of generated voltage vs actual speed using the data from Table 2.0.
17) Describe how the synchronous generator output voltage varies with respect to speed in reference to your graph.
18) How do the amplitude and frequency of the voltage waveforms vary when the speed of the synchronous generator is decreased? Briefly explain why.
19) Does varying the speed of the synchronous generator significantly affect the phase shift between the voltage waveforms? Comment on the observation.
20) At the end of your lab session, dismantle all parts and equipment from the machine trainer rack and keep them in their proper places.
EXPERIMENT 6
Principle of a Three-Phase Synchronous Generator and No-load Characteristic
Name: ______Matric No: ______
Group: ______Date: ______
Answers:
Q.8 Sketch waveforms
Q.9 Theoretically calculate frequency and compare.
Q.10 Actual speed = ______rpm
Table 1.0
Q.12 Draw a graph generated voltage () vs field current ().
Q.13
Q.14
Q.15 Field Current = ______A
Table 2.0
Speed(RPM) / Generated voltage
(V)
Target / Actual
300
600
900
1200
1500
Q.16 Draw a graph of generated voltage vs actual speed.
Q.17
Q.18
Q.19
Conclusion:
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UNIVERSITI MALAYSIA PERLIS (UniMAP) – Exp.6 (Revision 2)