Parallel Operation Of Two Or More Generators; Analog Input - WEG GRT7-TH4-R2 Manual De Instalación, Operación Y Mantenimiento

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4.4 PARALLEL OPERATION OF TWO OR MORE GENERATORS

The reactive compensation method applied is called phasorial composition (see Figura 4.4.1). On this system, the generator
output voltage is taken and then the composition with the generator current is processed. The result of this interaction
introduces a sensing error in real voltage signal, causing an increase or a decrease in the generator voltage, so maintaining the
reactive between the generators within acceptable values. The adjustment of this compensation is made through trimpot Drp.
According to the diagram shown above, the sensing voltage suffers an influence caused by the current coming from phase S,
which is added to voltage of phases R and T. The influence in module is small and is large in phase. This means that there is
good compensation for reactive loads and a small influence with active loads. The current transformer for reactive
compensation must be in phase S of the generator, and the voltage feedback must be in phases R and T.
To make sure the compensation is in the correct sense, proceed as follows:
Operate the generator in stand alone mode (isolated from the system/grid) and apply a resistive load with about 20% of the
generator capacity;
Then rotate the trimpot Drp completely CW. Under this condition, the generator voltage should decrease.
Returning the trimpot completely CCW again, generator voltage should then increase; If this occur, the CT polarity is correct.
Otherwise the CT should be reverted. This procedure is required in each machine, when several machines are connected in
parallel so as to ensure that all CT's are equally polarized. Some parallel CT characteristics are as follows:
Accuracy Class: 0,6C12,5;
Window or bar type;
Transformer current ratio will be In/5A or In/1A, where In/xA is the Current ratio primary/secondary for example: 100/5A,
150/5A, 100/1A;
Current of the secondary from 5A to regulator PAR/5 and 1A for regulator PAR/1;
The primary current of the CT must be 20% higher than the nominal current of the generator
The working frequency of the CT must be equal to the generator frequency;
The isolation voltage class of the CT must be higher than the output voltage of the generator;
Should withstand 1.2 x In load.

4.5 ANALOG INPUT

The analog inputs of the GRT7-TH4 R2 AVRs have the following characteristics:
Can be –9Vcc to +9Vcc (E9) or 0Vdc to 10Vdc (E10) according to the customer specification.
They are isolated by optocouplers.
Maximum current consumption: 10mA.
16 l Automatic Voltage Regulator – GRT7-TH4-R2
Figure 4.5 - Phasorial Composition of the generator