The Capacitive Load Problem Often Encountered By Diesel Generator Sets in Data Center

First of all, let's limit the scope of our discussion so that we don't get too loose. The generator discussed here refers to a brushless, three-phase AC synchronous generator, hereinafter referred to only as "generator".
This type of generator consists of at least the following three main parts, which will be mentioned in the following discussion:
Main generator, divided into main stator and main rotor; The main rotor provides the magnetic field, and the main stator generates electricity to supply the load. Exciter, exciter stator and rotor; The exciter stator provides a magnetic field, the rotor generates electricity, and after being rectified by a rotating commutator, it supplies power to the main rotor. The automatic voltage regulator (AVR) detects the output voltage of the main generator and controls the current of the exciter stator coil to stabilize the output voltage of the main stator.
AVR voltage regulation job description
The operation goal of AVR is to stabilize the generator output voltage, which is also called "regulator" in popular terms.
Its operation is: when the output voltage of the generator is lower than the set value, the exciter stator current is increased, which is equivalent to increasing the excitation current of the main rotor, so that the main generator voltage rises to the set value; Otherwise, the excitation current is reduced and the voltage drops. If the generator output voltage is equal to the set value, the AVR maintains the existing output without adjustment.
Then the load, according to the phase relationship between current and voltage classification, AC load can be divided into three categories:
Resistive loads where the current is in phase with the voltage applied to them; Inductive load, the current phase lags behind the voltage; Capacitive load, current phase ahead of voltage. The comparison of the characteristics of the three loads helps us to understand the capacitive load better.
For resistive loads, the larger the load, the greater the excitation current required for the main rotor (to stabilize the output voltage of the generator).
In the following discussion, we will take the excitation current required by the resistive load as a reference standard, that is, larger than it we call this larger; Anything smaller than that we call smaller.
When the load of the generator is inductive, the main rotor will need more exciting current to maintain a stable output voltage.
Capacitive load
When the generator encounters a capacitive load, the main rotor requires less exciting current, that is, the excitation current must be reduced in order to stabilize the output voltage of the generator.
Why does this happen?
We should also remember that the current on the capacitive load is ahead of the voltage, and these advanced currents (flowing through the main stator) will generate induced current on the main rotor, which is just in positive superposition with the exciting current, so that the main rotor magnetic field is enhanced. Therefore, the current from the exciter must be reduced to keep the output voltage of the generator stable.
The larger the capacitive load, the smaller the exciter output must be. When the capacitive load increases to a certain extent, the output of the exciter must be reduced to zero. The exciter output is zero, which is the limit of the generator; At this time, the output voltage of the generator will not be self-stabilized, and this power supply will not be qualified. This limitation is also called "underexcitation limitation".
The generator can only accept limited load capacity; (Of course, for a given generator, there are also size limits on resistive or inductive loads.)
If a project is troubled by capacitive loads, you can choose to use a less capacitive IT power supply per kilowatt of power, you can also use inductors to compensate, do not let the generator set work in the area near the "underexcitation limit".