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Examoogle • User • info@examoogle.com • EE-2024-8821
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Ward-Leonard controlled D.C. drives are generally used for _______________ excavators
Light duty
Medium duty
Heavy duty
All of these
Heavy duty
Quick Summary: Ward-Leonard controlled D.C. drives are used for heavy-duty excavators because they provide precise, wide-range speed control and high starting torque capabilities. This system allows for smooth acceleration, deceleration, and frequent reversals, which are essential operational requirements for large-scale earthmoving machinery.
Ward-Leonard controlled D.C. drives are used for heavy-duty excavators because they provide precise, wide-range speed control and high starting torque capabilities. This system allows for smooth acceleration, deceleration, and frequent reversals, which are essential operational requirements for large-scale earthmoving machinery.
Eg=kgΦgωg — Generated EMF proportional to field flux and speed
T=kmΦmIa — Electromagnetic torque developed by the motor
The system employs a motor-generator (M-G) set where a constant-speed AC motor drives a DC generator. The generator's output voltage is controlled by varying its field excitation, which is then fed to the armature of the DC motor driving the load. By controlling the generator field current, the motor speed can be varied smoothly from zero to rated speed in both directions without using large power-wasting resistors.
Provides extremely smooth speed control over a wide range.
Enables regenerative braking capabilities, allowing energy to be returned to the supply.
Highly suitable for applications requiring frequent starting, stopping, and reversing.
Essential for high-inertia loads like excavators, rolling mills, and hoists.
Precise speed control in both directions.
High torque capacity at low speeds.
Smooth and fast acceleration/deceleration.
Easy and inherent regenerative braking.
High initial cost due to M-G set (three machines required).
Low overall efficiency compared to modern solid-state drives.
Requires significant floor space and maintenance for rotating components.
High noise and vibration levels.
Heavy-duty excavators
Mine hoists
Rolling mills
Large printing presses
Modern excavators have largely shifted to AC drives or solid-state PWM-controlled DC drives, but the Ward-Leonard system remains the classic benchmark for high-torque industrial control.
Option A and B are incorrect as the high cost and maintenance of the M-G set are not justified for light or medium-duty applications where simpler controllers suffice.
C is correct — The Ward-Leonard system provides the high torque, precise control, and robust performance required for the heavy-duty cycles of excavators.
Always relate the drive selection to the nature of the load; high-inertia loads (like excavators) with frequent speed changes demand systems with inherent regenerative capabilities.