Brake Test On DC Shunt Motor
In this article, we are going to discuss brake test on d.c. motor.Brake test is also a method of finding the efficiency of dc motors.We took dc shunt motor as running machine. Brake test also called for direct loading test of testing the motor. Because loading will be applied directly to the shaft of the motor by means of a belt and pulley arrangement.
How to conduct brake test on dc shunt motors?
1. DC shunt motor
2. Water-cooled pulley
3. Spring balance
The procedure of Brake Test On DC Shunt Motor
1. By adjusting the handle of the pulley takes different readings of the spring balance.
2. The tension in the belt can be adjusted using the handle. The tension in kg can be obtained from the spring balance readings.
3. Adjusting the load step by step till full load, the number of readings can be obtained.By increasing the load is slowly, adjust to get rated load current.
4. The power developed gets wasted against the friction between belt and shaft. Due to the braking action of the belt the test is called brake test.
5. The speed can be measured by a tachometer. Thus all the motor characteristics can be plotted.
You can refer figure for the experimental setup for performing brake test on a d.c. shunt motor, belt & pulley arrangement mounted on the shaft of the motor.
Calculation Of Brake Test On DC Shunt Motor
Let R (or) r= Radius of the pulley in meters
N = Speed in r.p.m.
W1 = Spring balance reading on the tight side in kg
W2 = Spring balance reading on the slack side in kg
So net pull on the belt due to friction at the pulley is the difference between the two spring balance readings.
Net pull on the rope = (W – S) kg = (W – S) X 9.81 newtons……(1)
As radius R and speed N are known, the shaft torque developed can be obtained as,
Tsh = Net pull X R=(W – S) X 9.81 X R …..(2)
Hence the output power can be obtained as, Say speed of the pulley is N r.p.m., then, The above equation shows the output power of dc shunt motor in brake test.
Now let, V = Voltage applied in volts
I = Total line current drawn in amps.
As we know V,I am input parameters of dc motors in brake test.then,
Pin=V.I Watts …..(3)
We have output and input.Then why late go and find the efficiency of dc shunt motor.
Efficiency (η)=Output/Input [No units]