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Why prefer DC Generators instead of AC Generators?

DC GENSET AC GENSET
1)  For N+1 redundancy, peak load demand,    and site expansion, multiple DC generators can be operated at the same time and power outputs can be paralleled. It is impractical to parallel small AC generators due to the issues of sinking the frequency; therefore they must be over-sized for peak load demands and future expansion.
2)  DC generator backs up not only the utility power, but the rectifier and the battery bank as well. AC generators only backup utility power. If the rectifier or battery fails, the site is down.
3)  The DC generator’s variable speed feature reduces “wet stacking”. In the hybrid system at low power levels the DC generator is off and the battery supplies the power to load. Small loads can cause the engine to "wet stack”. Frequently electrical dummy loads are placed on the AC generator to reduce wet stacking at the expense of increased fuel consumption.
4)  For Prime power, the DC generator connects directly to the battery simplifying the system and reducing fuel consumption. Reliability is also greatly increased. Battery Chargers / rectifiers add considerable to the CAPEX and lowers reliability. In addition the power losses in the conversion from AC to DC increases fuel consumption
5) The variable speed feature automatically adjusts engine RPM to help optimize engine efficiency with electrical loads thereby providing a large savings in fuel cost. Engine must run at fixed speeds in order to maintain 60 or 50Hz frequency. Engine is not able to run at peak fuel efficiencies with either 2 or 4 pole alternators.
6)   For prime power or extended power outages the DC generator can be cycled on and off allowing the battery to power the minimum electrical needs. The DC generator will recharge the battery and power the peak loads. This allows the DC generator to operate at its peak efficiency to reduce maintenance and conserve fuel. The design of an AC Generator with cumbersome transfer switch/rectifier systems, warn up cycles, and lower charging capacity makes cycling charging undesirable. The AC generator uses more fuel and produces a lower charging current than the DC generator.
7)  The lightweight and compact size of Intelux DC generator is ideal for rooftop or mountain top installations. Our DC generator has significantly more current available than a comparable AC generator and is generally less than half the weight. AC generator systems are more difficult to install due to their increased weight and cumbersome size. Helicopter and crane installation are good reasons to consider DC over AC generators.
8)  With Intelux high efficiency alternator we are able to use smaller horsepower engines. The DC alternator allows us to operate within the engine’s peak torque range allowing the use of smaller engine. Combined with the rectifier power losses and current surges from the air conditioning during startup, the engines and alternators on AC generators require over sizing the engines in order to assist in output frequency regulation.
9)  For Backup, a DC generator can "come on line” much faster than an AC generator which allows the customer to reduce the size of the installed battery bank lowering both procurement and replacement costs. Telecomm experience have shown that larger battery banks are required when using AC generator backup systems
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