Generators are basically the lifeblood of significant outdoor projects ranging from construction to social events and more. And when purchasing one, the first question usually is, does size really mater? Without a doubt, the answer is yes, and what makes the biggest difference here is the high inrush current needed for starting electric motors and transformers, which is generally six times the full load current.
But take note that inrush currents for high efficiency motors specified nowadays can be even almost twice that amount. This led to motor and transformer starting kVA requirements becoming a measure for sizing a generator.
This typically results in generators being too big for what is actually needed by the application. Furthermore, it rules out other key factors that must be considered, like harmonics due to sequential starting of motors. As well, starting motors or transformers can produce considerable dips in voltage and frequency with an incorrectly sized generator.
And if there are loads connected to the generator output that are extremely sensitive, a new set of challenges could ensue. Fortunately, many generators nowadays can be equipped with solutions that neutralize the excess excitation systems needed in the alternator.
Auxiliary winding and permanent magnet are the two general options offered. Either provides the generator with three times their minimum current to take care of inrush peaks emanating from the electrical motor, for at least a tenth of a minute, via a leftover excitation current. Sometimes, other more advanced options are available, such as digital automatic voltage designed for inrush currents, allowing users to lessen the generator requirement and improve the management of power transient behavior.
A “Close Before Excitation” system is another option that deactivates the breaker the moment the engine starts. This allows the excitation to step up bit by bit along with the engine’s speed, which means loads connected to the generator can start softly. This is particularly helpful for installations where medium voltage is required and step up transformers are magnetized. In effect, you no longer have to get a bigger generation simply to cope with the start-up electrical surge. And with smart control of the generator’s voltage, fuel and maintenance costs are lessened as lifetimes are stretched.
In terms of transportation, you should be able to load the generator on a truck or tow it, and it must have lifting eyes and other useful features. If you plan to get more than one generator, see to it that you can stack them on top of each other so you have minimal footprint and access issues. These things can have an impact on your total operation expenditure and efforts to drive down carbon costs.