A d.c,machine is a highly versversatile energy conversion device.In normal dc machines, stator pole is not laminated,armature core is always laminated to reduce eddy -current losses d.c.machines used in control systems These d.c machines mainly consists of two types .i.e generators & motors, In the year1821 Michael faraday invented these machines i.e.generators&motors basing on his laws of magnetic induction.
The DC generator system is designed and optimized to deliver the high currents at low voltages required for battery charging and operating DC loads. No battery chargers or power supplies are required. DC generators do not require a transfer switch. Transfer switches lower system reliability. In prime power applications the DC generator lowers the overall cost of the system. Certain AC generators and switch mode power supplies are incompatible. These AC generators have voltage regulators that cannot regulate voltage due to the current pulsing load of the switch mode power supplies.
Polar's DC generators when connected to a battery do not suffer this incompatibility. DC generators are more fuel-efficient. Site operators want the longest run time with the least amountof fuel on site. Polar's DC generators are simpler in design, have considerably less maintenance and are more reliable than AC generators. Propane carburetion and electronic speed governors require frequent calibration and testing. If the propane carburetion, ignition system, or governor speed control should develop a problem, alternator voltage regulation and frequency control will fail. Some equipment powered by the generator will be damaged, other equipment may survive.
Polar's DC generators have a current limit control to prevent the alternator from overheating and the engine from stalling during shorts or overloads. This feature is extremely important in battery charging because a battery in a low state of charge can demand more power than the generator or battery charger can manage. Polar's DC generators will continues to supply power under current limit control, allowing the battery to increase its charge and drop its current demand. The AC generator uses a fuse or circuit breaker to protect against shorts and over current so the battery fails to get charged if it is overly discharged. The additional problem is that for remote sites a person is required to visit the site to replace or reset the fuse or circuit breaker and devise a means where the batteries can be brought to a state of charge where the batteries can take over.
Polar's DC generators can be connected in parallel and load share. Paralleling these small AC generators is not practical. In many projects there are concerns about future site expansion and given load estimates are sometimes understated. DC generators use smaller engines that can be lifted by hand and transported to a shop for repair. The high-level generator mechanics are not required, or their expensive travel time to the site.
AC generators are typically oversized to handle starting currents of motors and to provide light enough engine loads to facilitate speed regulation. Engines that are lightly loaded build up carbon around the valves and exhaust lines (wet stacking) this creates additional engine maintenance.
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