How do variables affect the sizing of a generator?

Analyzing the effect of voltage and frequency drops is indispensable for deciding which engines and alternators are more adequate for a generator.

Voltages are not a static phenomenon. They fluctuate resulting in peaks and drops during certain phases of the equipment’s functioning.

In fact, when we speak about circuits we distinguish between two types of situations:

  • The steady condition: It is the stationary situation of normal functioning in which the voltage ows in a balanced state according to the conditions determined by the network.
  • The transitional state: it occurs in certain periods of time in which the voltages and electrical intensities vary, before the circuit comes to its steady state and becomes stabilized.

The voltage variations occurring during these transitional periods are known as variables.

When do variables occur?

Logically, the normal situation in which variables occur is when we cause a circuit to pass from one condition to another, i.e. at the moment of connecting or disconnecting the equipment.

In fact, when we switch on and off a generator, short voltage peaks are triggered. Although they tend to end by themselves, we must not take them easily. Why is that? Because if the alternator and the engine happen not to be capable of coping with them, major functioning problems may ensue in the generator.

A matter of analysis

For this reason, in the process of designing and sizing a generator, it is indispensable to carry out a strict variable analysis.

This will provide the engineers with the necessary information for them to ensure that the engine and the alternator form a good tandem and are prepared to withstand the effects of the most usual voltage peaks and drops.

How is this analysis carried out?
  • Alternator: In order to decide which type of alternator is adequate for a generator according to the variables, we will have to calculate the apparent power (kVA) which our generator will need in order to ignite and start functioning. Once in possession of this data, we can choose the adequate alternator, given that the alternators have graphics which relate the apparent power at ignition with a blocked rotor to the drop in voltage.
  • Engine: in order to select the engine based on the variables, we need to calculate the active power (kW) upon ignition. Using this clear parameter, we will decide which engine is the adequate one. To do this, we must consult the graphics of frequency drops in the engine, bearing in mind that the adequate voltage drop caused by the load impact of the ignition power ranges between 5 and 7%.

In conclusion, sizing a generator is not something that we can do by “eyeballing”, but one must have the knowledge and the abilities necessary to calculate and analyze the phenomena that characterize the transitional state of a circuit. It is only in this way that we will be able to maintain the voltage variation under control and to guarantee that our equipment is 100% reliable.

At Genesal Energy we advise our clients and offer them the solution which best adapts to their project.

Contact us for more information at:
+34 900 730 124