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Indian Institute of Technology, Gandhinagar Department of Electrical Engineering
EE 311 Electrical Machines and Power Electronics Lab. B. Tech.: Electrical, Sem. : VI
EXPERIMENT 2: A)OCC AND THE LOAD TEST ON THE THREE PHASE ALTERNATOR
LAB REPORT Batch No: 2
GROUP NO : 2
NAME: PATEL TANAY SOMNATH ROLL NO: 10002038 LAB PARTNER: DHARM RATNA BAUDH ROLL NO: 10002036
DATE OF EXPERIMENT: 14 / 08 / 2012 DATE OF SUBMISSION: 21 / 08 / 2012
EXPERIMENT 2: A)OCC AND THE LOAD TEST ON THE THREE PHASE ALTERNATOR AIM: 1. Determination of the OCC characteristics of the given Alternator 2. To determine the percentage regulation and percentage efficiency of the given three phase alternator by conducting load test.
APPARATUS REQUIRED Sl. No. 1.
Apparatus
Specification
Qty
Rotating Machines from The machines from the Test Bench are to be Test bench
configured for running the Synchronous machine
1
as Alternator with the DC machine as its prime mover. 2
Extension Panel
Panel that facilitates having terminals extended from rotating machinery, power supplies, Load
1
banks and panel meters.
THEORY Alternator is an alternating current generator. It works on the principle of electromagnetic Induction. Alternators according to construction are divided into two categories.
Revolving Field type
Revolving Armature Type Most alternators are of the revolving field type in which the revolving field structure or Rotor has slip rings and brushes to supply the excitation current from an outside DC source. The Armature coils are placed in slots in a laminated core, called stator. When the rotor rotates, the stator conductors are cut by the magnetic flux, hence they induce emf in them. Because the magnetic poles are N and S an alternating emf is produced in the stator conductors whose frequency depends on the number of N and S poles moving past a conductor in one second whose direction is given by Flemings Right Hand Rule. For a machine with P poles that rotates at N rpm the frequency and the Induced EMF will be
As the Field current of the alternator is increased, its terminal voltage is increases as in DC generators. With the alternator terminals open, the voltage output vs Field current characteristics is known as OCC characteristics of the Alternator.
As the load on the alternator is varied, its terminal voltage is found to vary with load current. This variation in terminal voltage is due to the following reasons. 1. Voltage drop due to armature resistance R a 2. Voltage drop due to leakage reactance X L. 3. Voltage drop or rise due to armature reaction.
CIRCUIT DIAGRAM – OCC AND LOAD CHARACTERISTICS
A _ Variable DC Power Supply
A _ A F
V _ A _
FF
LOAD
V _
R
M _ AA
B
Y
F
FF
A _ V _
V _ l o r t n o C
Variable DC Power Supply
Sensors T&S Display T/I
1 φ Supply
Variable DC Power Supply
C o n t r o l
1 φ Supply
PROCEDURE - Open Circuit Characteristics 1. configure the Synchronous Machine in generating mode and the DC machine in Motoring mode. Keep the Field of Synchronous Machine at minimum. Keep the field of The DC machine at rated value. Ensure Mechanical coupling between Synchronous machine and the DC machine. 2. Keep the synchronous machine field off/Minimum. Start the DC machine as motor by gradually applying the armature voltage. Once the synchronous machine is kept running at rated speed of the alternator speed, the field of the Alternator is switched on. 3. Now with the Field current of the alternator zero the generated voltage is noted. This is the voltage induced due to the residual magnetism and the first point in the OCC characteristics. Now the field is gradually applied and corresponding voltage at the open circuit terminal of the alternator is recorded. Gradually increase the Field current in steps
of 0.05 A and note down the generated emf against each field current. Take the readings till the generated emf reaches the rated voltage of 420 Volts 4. Plot the open circuit characteristics of E G vs If TABULATION Sr. No
If in A
EG in V
1.
0
20.04
2.
0.05
63.5
3.
0.1
109.1
4.
0.15
155.2
5.
0.2
188.3
6.
0.25
227
7.
0.3
262.6
8.
0.35
286
9.
0.4
315
10.
0.45
338
11.
0.5
360
12.
0.55
373
13.
0.6
390
14.
0.65
406
15.
0.7
410
16.
0.72
416
17.
Open Circuit Characteristics of an alternator 450 400 350 ) g 300 E ( e g a t 250 l o v l a 200 n i m r e t 150
Eg(V)
100 50 0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Field current (I)
PROCEDURE – Load Characteristics 1. The Alternator is kept at rated voltage output and made to run at rated rpm from the DC motor. 2. The Three phase resistive load is connected to the Alternator output terminals with the load switches in off condition. . 3. Vary the load in steps and note down the corresponding load current and terminal voltage. While doing so, maintain the speed of the DC Motor constant by adjusting the Armature voltage. 4. Also note down the Torque and speed of the DC Machine 5. Repeat the steps till the rated current alternator is reached.
TABULATION
DC Motor
Torque (T)
Alternator
Speed (N) RPM
Input
VL
IL Amp.
Volt
I1 , I 2 , I 3
% Output % Efficien Load in KW Regulation cy
V1, V2, V3 5.5 9.8 13.5 16.2
1511 1511 1510 1512
869.832333 1549.88307 2133.63 2563.7472
407 394 379 359
1.01 1.99 2.89 3.68
711.97324 1357.99192 1897.07692 2288.17984
No load torque: 0.9 N.m No load speed: 1509 RPM No load Voltage: 416 V Graph: Regulation 16 14 12 n o 10 i t a l u 8 g e r %
6
% reg
4 2 0 350
360
370
380
390
400
410
terminal voltage
Efficiency 90 89 88 ) 87 % ( y 86 c n e i 85 c i f f e 84
%effic
83 82 81 0
1
2 load current
3
4
2.16346154 5.28846154 8.89423077 13.7019231
81.852 87.619 88.913 89.251
CALCULATION
% Efficiency
Output of the DC Motor
:
(This is equal to Alternator input)
Alternator output
:
( or)
: W1+W2 (wattmeter reading if wattmeters are used). Alternator Efficiency
: (output/Input) X 100
% Regulation
No load Terminal voltage
: VNL volts (Rated value)
Load Voltage
: VL volts
The % Regulation
:
RESULT AND INFERENCE Open Circuit Characteristics
As the Field current of the alternator is increased, terminal voltage of an alternator is increases.
For the given speed terminal voltage is maximum at no load.
Load Characteristics
Terminal voltage of an alternator is decreased with increasing in load.
Efficiency of an alternator increase with increasing in load.
