This was a good experiment in terms of it was to show us the direct result of the effect of increasing the load current on the motor power factor. It showed that the higher the current the better the power factor. The Electrical Supply Board desire a high power factor for installations within Ireland and penalise those which do not meet required standards as they see poor power factor as a wasteful loss of energy. It also showed that there are two ways in which the rotating magnetic field could be used to provide the rotating motion.
AIM :
To determine the performance characteristics of 3-phase squirrel cage induction motor by direct loading.
APPARATUS REQUIRED:
SI NO
APPARATUS REQUIRED
TYPE
RANGE
QUANTITY
NAME PLATE DETAILS :
FUSE RATING CALCULATION :
125% of rated current.
No-load test - 25% of rated current.
THEORY :
The load test on 3-phase induction motor is performed to obtain its various characteristics including efficiency. A belt and brake drum arrangement as shown in the circuit diagram can load the motor. If S1 and S2 are the tensions provided at the two sides of the belt, then the load torque is given by
T = (S1 - S2) * 9.81 * R N-m.
Where R is the radius of the brake drum in metre. The mechanical output of the motor is given by
Pm = 2 * 3.14 * N * T Watt
60
Where N is the speed of the motor in RPM. The power input to the motor
Pi = VLIL watt
The efficiency of the motor is given by
Efficiency = Pm / Pi
FORMULA :
Torque,
T = (S1 - S2) * 9.81 * r (Nm)
Input power
(Pi) = (W1 + W2) (Watt)
Output power
(Po) = 2 P NT / 60 (Watt)
Efficiency
h = Po X 100
Pi
Cos f = W/(31/2 VLIL)
Slip = (Ns - N) / Ns *100
PRECAUTION:
1. TPST switch should be at open position.
2. 3-phase autotransformer should be at minimum voltage position.
3. There should be no-load at the time of starting(Loosen the belt on the brake drum)
4. Brake drum should be filled with water.
PROCEDURE:
1. The connections are made as per the circuit diagram.
2. Power supply is obtained from the control panel.
3. The TPST switch is closed.
4. Rated voltage of 3-phase induction motor, is applied by adjusting autotransformer
5. The initial readings of ammeter, voltmeter and wattmeter are noted.
6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter
7. Step1 to 6 is repeated till the ammeter shows the rated current of 3-phase induction motor.
8. Decrease the load, bring auto-transformer to its minimum voltage position.
9. Switch off the supply.
CIRCUIT DIAGRAM
LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR:
(0 - 10) A, MI
M L R
R C V
TPST
( 0 -600)V,MI
Y B
415V,50Hz, 3f SUPPLY
STATORY
M L
C V
N
OBSERVATION TABLE :
S.NO
V (volt)
I (A)
Speed (rpm)
Spring Balance
S1(Kg) S2(Kg)
Torque
=((S1 - S2) *
9.81 * R)
N-m
I/P
(V*IL)
watt
O/P
2 P NT
60 (watt)
Efficiency = Output Power
Input Power
100
%h
%
slip
RESULT :
By coupling a dynamo meter to output shaft of the motor. By means of dynamo meter, you can create mechanical load which can be easily adjustable. Just Google search "dynamometer" for getting information.
Eddy current (EC) dynamometers, regenerative induction motor dynamometers, water dynamometers are some of the types of dynamometers, which can be used for testing the motors.
usually you just need to read the name plate only the manufacturer needs to test to come up with numbers on the nameplate most common load for testing motors is a water brake dynamometer
The ratio is between 30% to 40 %
The current flowing through a transformer's secondary is the current drawn by the load, so it will be exactly the same as the current flowing through your induction motor -assuming that is the load. Don't really understand the point of your question!
The slip is proportional to the load torque in an induction motor. This can also be seen as a reduction in speed causing extra current to be induced in the rotor to supply the increased torque.
if a motor blows fuses and it didnt before disconnect the coupling try to turn the machine and the motor by hand first with the coupling disconnected see if the motor runs ok chances are the trouble is in the machine the motor can have bad bearings very basic troubleshooting
When you do a load test on a 3-phase induction motor you are checking the power factor, viz slip, and efficiency of the motor. You can test various loads with this test.
yes
That indicates a fault in the induction motor.
Induction motor by design is inductive load. Hence the PF tends to be lower
1. Induction Motor has an air-gap but transformer has no air gap rather it is mutually link. 2. Induction Motor has high no-load current than transformer. 3. Induction Motor is a dynamic device. 4. Induction Motor has high power factor.
90/3=30ma
Doing a No Load test of a 3-phase induction motor involves the measuring of current, voltage, torque etc with no load on the rotor shaft, meaning that it is free to turn but is not driving anything else. Similarly a Locked Rotor test involves the measuring of current, voltage, torque etc with the rotor shaft "locked" i.e. prevented from turning, which is the worst loading condition the motor would ever have to contend with.
no load means the motor is acting like a coil
It is maximum at about 75% to 100% of the motor rated load. Efficiency is maximum at unity power factor , when R=X and when variable losses Is equal to constant losses at rated load.
usually you just need to read the name plate only the manufacturer needs to test to come up with numbers on the nameplate most common load for testing motors is a water brake dynamometer
As the load increases, the speed reduces to deliver the increased torque required.
The ratio is between 30% to 40 %