Ward-Leonard system is used where an unusually wide (upto 10:1) and very sensitive speed control is required.
This system is used to supply variable to the motor. M1 is the main motor whose speed control is required. A d.c. generator G is mechanically coupled with either a d.c. shunt motor or an a.c. motor M2. The motor M2 runs at an approximately constant speed. The field winding of the d.c. generator is connected to a constant voltage d.c. supply line through a field regulator. The d.c. motor M1 is fed from the generator G and its field connected directly to a d.c. supply line.
The voltage of the generator can be varied from zero upto its maximum value by means of its field regulator. By reversing the direction of the field current of generator G by means of the reversing switch, generated voltage can be reversed and hence the direction of rotation of motor M1 . The direction rotation of the generator – motor set is changed.
- The speed and direction of rotation both can be controlled very accurately.
- The capital investment in this method is very high as two extra machines (generator G and Motor M2) are required.
- A large output machine must be used for the motor generator set.
- This system has a low overall efficiency especially at light loads.
Ward-Leonard system is extensively used for in followings :
- Steel rolling mills
- Paper mills
- Diesel-electric propulsions etc.