To find the full load speed of the motor, we can use the following formula:
Full load speed = (No load speed x (1 - (Armature current / Full load current) x (Armature resistance / (Total resistance - Armature resistance))))
Where:
- No load speed is the speed of the motor at no load
- Armature current is the current flowing through the armature at full load
- Full load current is the current flowing through the motor at full load
- Armature resistance is the resistance of the armature
- Total resistance is the total resistance of the motor, including armature resistance and field resistance
- First, we need to find the total resistance of the motor:
- Total resistance = armature resistance + field resistance
Given that armature resistance is 0.20 Ohm, and the armature reaction weakens the field by 40% on full load, the field resistance is:
Field resistance = armature resistance x (1 + (40/100)) = 0.2 x 1.4 = 0.28 Ohm
Therefore, the total resistance is:
Total resistance = armature resistance + field resistance = 0.20 + 0.28 = 0.48 Ohm
No load speed of the motor is given as N0.
Now, we can plug in the values into the formula and get:
Full load speed = (N0 x (1 - (122 / 122 + 7) x (0.20 / (0.48 - 0.20))))
Given that the contact drop/brush is 1V and is neglected in the calculation.
We can now calculate the full load speed of the motor, which is the final answer.
Please be noticed that this is a very specific question, and the answer assumes that you have all the information and data needed.