In an Induction motor; in actual conditions; several types of losses occurs from input to output.
There are two types of losses in the winding, One is ‘Core loss’ & second one is ‘Copper loss’.
- Core losses are fixed losses which do not depend upon the loading percentage/current. These losses includes hysteresis loss & eddy current loss. These are occurring on silicon steel stamping which does not depend upon the current.
- Copper losses are variable losses; depend upon the loading percentage. Copper loss is also known as I²R Which depends upon current square.
A power flow diagram is shown below Which completely reflects the power flow from input to output !
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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
Induction motors never operate at 100% efficiency because various electrical and mechanical losses occur during operation. To evaluate these losses without applying mechanical load, the No Load Test is performed.
The no load test is one of the most important practical tests used to determine:
- Core (iron) losses
- Friction and windage losses
- Magnetizing current
- No-load power factor
This test is widely used for performance analysis of medium and high-capacity induction motors, where direct loading is difficult.
NO LOAD TEST OF INDUCTION MOTOR
“No load test on Induction motor as name implies been performed without any type of load on motor by connecting the motor with rated voltage & rated frequency. This test is performed to calculate the constant losses such as core, windage & friction losses. “
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Advantages of No Load Test of Induction Motor
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Simple and easy to perform
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Does not require mechanical loading of the motor
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Suitable for testing large capacity motors
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Helps determine constant losses such as core loss, friction and windage loss
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Requires minimum equipment and power
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Useful for estimating motor efficiency and performance
- Helps in identifying abnormal conditions like excessive no-load current or core issues
CIRCUIT FOR NO LOAD TEST
A DOL starter can be used to run the Induction motor. A voltmeter is connected across the two phases Which shows the line voltage. An Ammeter or clamp meter is placed across one of the line Which shows the line current. A power meter is connected across the circuit to observe the power consumption.
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PRACTICAL FOR NO LOAD TEST
- Rated Voltage = 400Volts
- Rated Current = 7.9Amps
- Rated frequency = 50Hz
- Winding connections in STAR
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OBSERVATIONS
- Line Voltage, Vl= 398 Volts
- Volte/phase, Vp= 229.8
- No load Line Current, I0= 4.15 Amps
- No load Power, P= 0.88KW
FAQs – No Load Test of Induction Motor
Q1. What is the no load test of an induction motor?
The no load test is performed by running the induction motor at rated voltage and frequency without any mechanical load to determine its constant losses and no-load characteristics.
Q2. What is the purpose of the no load test?
The main purpose is to determine core loss, friction and windage loss, magnetizing current, and no-load power factor of the motor.
Q3. Why is copper loss neglected in the no load test?
At no load, the motor draws a very small current. Therefore, the stator copper loss (I²R loss) is very small compared to core and mechanical losses and is usually neglected.
Q4. What instruments are required for the no load test?
A voltmeter, ammeter (or clamp meter), and a wattmeter are required to measure voltage, current, and input power.
Q5. What is the typical power factor during no load condition?
The power factor at no load is low, usually between 0.2 and 0.4 lagging.
Q6. Why is the no load test important for large motors?
Direct loading of large motors is difficult and costly, so the no load test helps evaluate performance without applying mechanical load.
SUM UP
- 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 also be observed.
- At no load; by observing the current on all three Phases; We can also conclude winding coils are symmetrically balanced or not.