08-05-2012, 04:21 PM
LOAD TEST ON DC SHUNT MOTOR
FORMULAE
1. Torque T = (S1~S2) × (R+t/2) × 9.81 in N-m.
Where R- Radius of the Break drum in m.
t- Thickness of the Belt in m.
S1,S2- Spring balance reading in Kg.
2. Input power = VL × IL in Watts.
Where VL – Load Voltage in Volts.
IL- Load current in Amps.
3. Output power = 2NT/60 in Watts.
Where N- Speed of the armature in rpm.
T- Torque in N-m.
4. Percentage of Efficiency = (Output power/Input power) × 100
PRECAUTION
• The motor field rheostat should be kept at minimum resistance position.
• At the time of starting, the motor should be in no load condition.
• The motor should be run in anticlockwise direction.
PROCEDURE
• Connections are given as per the circuit diagram.
• Using the three-point starter the motor is started to run at the rated speed by adjusting the
field rheostat if necessary.
• The meter readings are noted at no load condition.
• By using the Break drum with spring balance arrangement the motor is loaded and the
corresponding readings are noted up to the rated current.
• After the observation of all the readings the load is released gradually.
• The motor is switched off by using the DPIC switch.
GRAPH
The graphs are drawn as
• Output power Vs Efficiency
• Output power Vs Armature current
• Output power Vs Torque
• Output power Vs Speed
• Torque Vs Speed
• Torque Vs Armature current
• Speed Vs Armature current