• A single-speed three-phase squirrel-cage induction motor (the drive motor) is connected to the three-phase supply and mechanically coupled to a d.c. generator.
• The d.c. generator armature is connected directly to the armature of the d.c. winch motor (the two armatures are connected in series, forming a closed loop).
• The field winding of the d.c. generator is supplied from a d.c. exciter (or from a controlled rectifier) through a field rheostat / reversing switch.
• The field winding of the d.c. winch motor is separately excited from the same d.c. source (constant field).
• The induction motor runs continuously at constant speed, driving the d.c. generator. By controlling the generator field current, the generator e.m.f. and hence the voltage applied to the winch motor armature is varied, giving smooth speed control of the winch motor from zero to full speed in either direction.
• The circuit: 3-phase supply -> squirrel cage motor -> d.c. generator (armature) -> d.c. winch motor (armature) -> back to generator. Generator field circuit with reversing switch; motor field circuit separately excited.

• The direction of rotation of a d.c. motor depends on the relative direction of the armature current and the field flux. In the Ward Leonard system the winch motor field is kept constant, so reversal is achieved by reversing the direction of the armature current.
• This is done by reversing the polarity of the generator field current using a reversing switch (or by reversing the generator field connections). Reversing the generator field reverses the polarity of the generated e.m.f., which reverses the direction of current in the armature loop, and hence reverses the direction of rotation of the winch motor.
• Because the generator field is a low-power circuit, reversal is easy and can be done smoothly. The motor can also be brought to rest and reversed by reducing the generator field to zero and then building it up in the opposite direction, giving smooth, controlled reversal without large current surges.

• Very smooth, stepless speed control from zero to full speed in both directions.
• Excellent speed regulation and high torque at low speed, ideal for winches and windlasses.
• Easy reversal with low-power control circuits.
• Regenerative braking is possible (the motor can act as a generator and return power to the system).
• High starting torque with controlled current.

Disadvantages:

• Low overall efficiency because power is converted three times (electrical to mechanical in the drive motor, mechanical to electrical in the generator, electrical to mechanical in the winch motor).
• High initial cost and large physical size (three machines plus exciter).
• Requires more maintenance (commutators and brushes on two d.c. machines).
• The drive motor runs continuously even when the winch is idle, wasting power.
• Slow response compared to modern thyristor/static drives.