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Buying a Power Generator: Size Issues and Why They Matter

Generators are basically the lifeblood of significant outdoor projects ranging from construction to social events and more. And when buying one, there is typically no other question that comes before, does size actually count? 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.

However, remember that for high efficiency motors being specified today, inrush currents could be nearly 100% higher. This resulted in the common practice of using motor and transformer starting kVA requirements as a gauge for determining generator size.

This method often means generators are being sized too large for the motor running load, instead of being based on the application’s actual needs. Furthermore, it rules out other key factors that must be considered, like harmonics due to sequential starting of motors. With a poorly sized generator, starting motors or transformers can also produce big voltage and frequency dips.

On top of that, any particularly sensitive loads connected to the generator output can cause issues. Fortunately, many generators nowadays can be equipped with solutions that neutralize the excess excitation systems needed in the alternator.

There are usually two options: permanent magnet and auxiliary winding. Both give the generator thrice their basic current to handle inrush peaks coming from the electrical motor, for a minimum period of ten seconds, through an excess 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 comes in handy for magnetizing step up transformers for medium-voltage installations. As a result, there’s no more need to spend on a bigger generator for the sake of managing the initial electrical surge when starting. 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’re buying several generators, also check if you can stack them on top of each other for reduced footprint and access issues. These things can make a huge difference in both your operational and carbon costs.

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