Because in the case of large motors. It is difficult to dissipate the large amount of heat generated at the brake. The load test can be conducted by using a belt brake or rope brake. For a constant applied voltage, the field current is constant for a D.C. Shunt motor.
Why the brake or load test is not suitable for large size machines?
Explanation: From Hopkinson’s test both machines are not loaded equally and this crucial in small machines. … Explanation: A large variation of field currents is required for small machines, the full-load set speed is usually higher than the rated speed and the speed varies with load.
Why brake test is performed with small machine only?
This test is performed on small motors only. In case of large motors, it is difficult to dissipate the large amount of heat generated at the brake. The drawback of the brake test is we cannot determine unavoidable errors occurring in spring balance.
Why the break test is not recommended for the machines with higher hp rating?
Disadvantages of Brake Test:
1) The Spring Balance Readings are not stable rather it fluctuates. 2) Output power is wasted. 3) The frictional torque at a particular setting of Hand wheel H1 and H2 do not remain constant.
Why Swinburne’s test is preferred instead of brake test in a dc machine?
The main advantages of this test are: This test is very convenient and economical as it is required very less power from supply to perform the test. Since constant losses are known, efficiency of Swinburne’s test can be pre-determined at any load.
Which motor has the poorest speed control?
Which of the following DC motor has the poorest speed control? Explanation: DC series motor at no load condition gives infinite speed ideally. Practically it will damage all the armature circuit. Thus, as the load is reduced speed of the motor will go on increasing rapidly.
What will be the efficiency of the motor at no load?
a) at no load efficiency is zero (as output is zero).
How can the speed of a DC motor be controlled?
Thus, the speed of a DC motor can control in three ways: By varying the flux, and by varying the current through field winding. By varying the armature voltage, and the armature resistance. Through the supply voltage.
How much torque does a 1 hp motor have?
The 3600 RPM, 1HP motor produces 1.5 ft. lbs. of torque at 3600 RPM. So if your 1HP pump was operating at 1800 RPM, the 1800 RPM motor would be producing 3 ft.