Voltage Built Up; Parallel Operation With Two Or More Generators; Protections; U/F Protection - WEG WRGA-02 Manual De Instalación, Operación Y Mantenimiento

12.3 VOLTAGE BUILT UP

WRGA02 - The excitation starts through the residual voltage of the generator. When the generator output voltage is very low,
the control supplies all the input field voltage. When the output voltage reaches an acceptable value the PI control starts
actuating. If the residual voltage is not enough, it becomes necessary to apply voltage to the generator field, in order to increase
the output voltage to supply the regulator
WRGA02/D – The PMG voltage is used for supplying the power, therefore it does not depend on the residual voltage to start the
excitation. The ramp up and field flashing characteristics are similar to the WRGA02 model.

12.4 PARALLEL OPERATION WITH TWO OR MORE GENERATORS

The reagent compensation system adopted is named phase diagram composition (see Figure 12.4.1). In this kind of system, the
generator output voltage signal is taken and the composition with the generator current signal it's made. The result of this
interaction introduces a sensing error in the real voltage signal, causing a increase or decrease in the generator voltage,
keeping the reactive power between the generators (sharing) inside of acceptable values. The adjustment of this compensation
is made by droop adjustment trimpot.
According to the phase diagram, the feedback voltage suffers an influence from the S phase current, which is add to the R and
T phase voltage. The influence is small in module and big in phase, which means that there is a good compensation for reactive
loads and a small influence of active loads. The current transformer for reactive compensation shall be in S phase of the
generator, and the sensing signal in R and T phases.
To certify that the compensation is in the proper direction, proceed as follows:
Start the generator in island mode (isolated from the grid) and apply a resistive load of about 20% of its capacity
After turning the droop adjustment trimpot completely clockwise, this process will cause a voltage dropl in the generator.
Turning back the trimpot in the anti-clockwise direction, the voltage must increase. If it doesn't happen, the CT (Current
Transformer) polarity should be inverted. When several machines are connected in parallel, these steps are necessary in each
machine to make sure that all the CT's are polarized the in the same way.
13.

PROTECTIONS

13.1 U/F PROTECTION

On figure 13.1.1 a graph is shown with the generator voltage variation as a function of the frequency variation. For rated
operating frequency the U/F is disabled. In the case of rotation slowdown (when shutting down, for example), excitation
diminishes, reducing the output voltage of the generator. For the case shown on 13.1.1, the U/F adjustment was done on the
limit of the rated frequency.
S
IS
R
RT
Figure 12.1 - Phasor diagram.
Automatic Voltage Regulator – GRT7-TH4-R2
T
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