How to perform load test on induction three phase induction motor ? | How to perform break test on induction three phase induction motor?

Brake test is basically a load test or direct load test of induction motor. This test is called a type test.

Note that applying brake on pulley mounted on shaft of any motor increases loading on it. This is generally done in case of small motors only.

In case of large motors, other methods have been developed to load a motor, like coupling the motor with a generator and putting electrical load (say, lamps) on the generator. This is a much easier job as compared to providing mechanical load on the motor.

In a brake test, a mechanical brake (by a friction belt) is applied on the motor shaft gradually. Increase in load is indicated by corresponding increase in motor current. Readings are taken for motor current, speed, electrical power input and brake load. The brake load is increased in steps till the full load current is reached.

Based upon the readings taken, load characteristics i.e. speed, power input, efficiency, power factor is plotted against motor current.

Content :

Perform load test on induction three phase induction motor.
How to find efficiency of three induction motor by brake test
How to find break down torque of three phase induction motor

Perform load test on induction three phase induction motor :

Instruments and Tools :

MI Voltmeter (0 - 500 V) - 1 No
Mi Ammeter (0 - 10 A) - 1 No.
Watt meter dynamo meter type 500 V, 10 A, 3000 W - 2 Nos.
Spring balance 10 kg - 1 No

Equipment/Machines

3-phase squirrel cage induction motor 415 V, 3 HP 50 Hz - 1 No.
Brake loading arrangement DOL starter 415 V AC 3-phase,50 Hz, 10 A - 1 No.
Connecting cables - as required.
ICTP switch 16 A, 415 V - 1 No

Diagram :

Procedure :

Calculate the torque

Measure the diameter of the drum and thickness of the rope/belt

Drum radius ‘R’ = _meter. Rope/belt thickness ‘t’ __meter

Collect motor data from motor name plate

Connect Voltmeter, Ammeter and watt meter as shown in diagram.

Set spring balance in spring balances in slack condition

Switch ‘ON’ ICTP and start motor on No load.

Measure the speed and record in Table

Tight the belt until the motor take 1\4 of full load current

Reading of the spring balances (Tension side ST, slack side SS) and record in Table

Reading of the voltmeter, ammeter and watt meter readings in Table

Measure the speed of the motor at this loaded condition and record in Table

Repeat the steps 6 to 9 for different load currents,for 1/4 , 1/2, 3/4 and full load

Calculation :

Torque:

T = (ST - SS) x (R + t) Kg

where (R + t) is in metre, (ST - SS) is in Kg. Record the torque and output

note down in table

Output :

Output = 1.027 NT watt

where N - revolutions per minute, T - torque in Kg m

Input :

Input = (W 1 + W 2) watt

Efficiency:

Efficiency = Output/Input

Observation table:

Table 1

Table 2

How to find break down torque of three phase induction motor:

The maximum torque point C that the motor is capable of developing.after maximum torque or break down torque if we increase the load torque decreases rapidly.

This is my view on How to perform load test on induction three phase induction motor ? How to perform break test on induction three phase induction motor.

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