In an ideal conditions, complete input power to induction motor get converted into output power; there are no losses & system works on 100% efficiency But in actual conditions losses exists Which makes the efficiency fall.
In an Induction motor; in actual conditions; several types of losses occurs. A power flow diagram is shown below with such type of losses.
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| Power flow diagram of Induction Motor |
There are two types of losses in the winding, One is Core loss & another one is Copper loss. Core losses are fixed losses which does not depend upon the loading percentage/current. These losses includes hysteresis loss & eddy current loss Which are occurring on silicon steel stamping which does not depend upon the current. On the other hand, Copper losses are variable losses; depend upon the loading percentage as copper loss also known as I²R loss depends upon current square.
At first, Power is connected as an input to the stator winding. There; both the losses takes place core & copper, After then rest remaining power links to rotor's stamping known as Air gap power.
Similarly on rotor's stamping both the losses core & copper takes place. At last, Output power which is the shaft power get delivered after windage loss & friction loss.
Pin= Stator core loss+ Stator I²R loss+ Rotor core loss+ Rotor I²R loss+ Windage loss+ Friction Loss+ shaft output power
NO LOAD TEST OF INDUCTION MOTOR
No load test on induction motor as name implies been performed without any type of load by connecting the motor with rated voltage & rated frequency. This test is performed to know about the constant losses such as core, windage & friction losses.
In this test, Motor run without any type of load that's why A minor current been drawn by the motor. Copper loss is much lower than the core losses that's why copper loss is neglected in no load test.
Loading test on low rating induction motor is simple & easy But it is difficult for high rating induction motors. That's Why no load test is performed on high rating motors to know about the important parameters.
With this test; Noise & vibration level can also be observed. By observing the current on all three Phases; We can also conclude winding coils are symmetrically balanced or not.
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| Power meter connected across induction motor | No load test of Induction Motor |
CIRCUIT FOR NO LOAD TEST
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| Circuit diagram | No load test of Induction motor |
PRACTICAL
* For Power monitoring, We are using
Power Meter 3510PHW by MECOHAVING
Rated Voltage = 400Volts
Rated Current = 7.9Amps
Rated frequency = 50Hz
Winding connections in STAR
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| Power Meter 3510PHW by MECO |
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| Power measuring of 3 phase induction motor with Power meter 3510PHW |
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| Motor's terminals connected in STAR |
OBSERVATIONS
(All the parameters are no load parameters )
(All parameters been recorded through Power Meter 3510PHW by MECO)
Observed Values
- Line to Line Voltage, Vl= 398 Volts
- Volte/phase, Vp= 229.8
- No Line Current, I0= 4.15 Amps
- No load Power, P= 0.88KW
1. No load P.f (cosΦ)
cosΦ= P/(√3*Vl*I0)
= 880/(√3*398*4.15)
= 0.3
2. Energy component of no load current, Ie
Ie= I0*cosΦ
= 4.15*0.3
= 1.2Amps
3. Magnetising component of no load current, Im
Im= √(I0²-Ie²)
= √(4.15)²-(1.2)²
= 3.96Amps
4. No load impedance, Z0
Z0= Vp/I0 = 229.8/4.15
= 55.37 ohm
5. Resistance, R
R= cosΦ*Z0
= 0.3*55.37
= 16.6 ohm
CONCLUSION
- This test is performed without any load.
- It is performed to know about the constant losses such as core, windage & friction losses.
- Due to no load, A minor current been drawn by the motor. Copper loss is much lower than the Core loss that's why copper loss is neglected in no load test.
- Noise & vibration level can be observed.
- At no load by observing the current on all three Phases; we can also conclude winding coils are symmetrically balanced or not.
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