Diesel-driven vs. electrical equipment

Diesel-driven vs. electrical equipment

The equipment used in quarries may be diesel operated or electrically operated. Machines which have to move frequently from place to place are operated by diesel engines e.g. bulldozers, scrapers, graders, dumpers, tractors dozers. But the equipment which has to 'work from one site over long periods in a shift may be electrically operated or diesel operated e.g. dipper shovels, draglines, compressors, well hole drills, bucket wheel excavators. Permanent or semi-permanent machines are always powered electrically e.g. large centrally located compressors, pumps, etc.

An electric shovel avoids fuelling problem, is comparatively quiet, simple and maintenance cost is cheaper than for the diesel one. In electric shovel motors can be placed so as to eliminate complex gear trains and chain drives, and controls are esay to operate. Initial cost of electric shovel is however higher than for a diesel unit. Ward-Leonard system is the standard method of drive and control on large H.P.

 shovels and draglines. Dipper shovels of smaller size (upto 3.5 m³) are usually diesel driven, but electric drive is preferred for larger machines. The electric shovel, due to limited length of the trailing cable, operates only within a restricted area and. the trailing cable being heavy needs men to handle it during movement from one place to another. Some shovels are diesel-electric. In this type of drive a diesel engine mounted on the shovel itself drives a generator that supplies electricity to motors which do the heavy work of the machine and the various controls on the shovel. Such drive is found in medium large shovels.

The voltage of small machines is usually medium, 400 or 500, though H.T. voltage (3300-6600) is often essential for large machines like dipper shovels which have to move very little during a shift. The bucket wheel excavators at Neyveli are supplied power at 11 kV through T.R.S. cables and transformers in the machine step down the -voltage to 3.3 kV for some motors and to 400 V for some other motors. Overhead power transmission lines bring the power to a convenient point near the quarry and from there the pliable armoured cables which are sufficiently flexible carry it to the machines. In mechanised quarries it is difficult to construct the power lines entirely outside the blasting zone as trailing cable lengths are restricted by the Electricity Rules and such overhead lines and the insulators sometimes break due to flying stones of blasting.