Parallel Operation For Two Or More Generators¹ - WEG GRT7-TH4 Manual De Instalación, Operación Y Mantenimiento

9.5 PARALLEL OPERATION FOR TWO OR MORE GENERATORS¹
The reactive compensation method applied is called a phasor diagram (see fig. 02). Through this diagram, the generator output
voltage signal is measured and compared with the generator current voltage. The result of this interaction introduces a sensing
error of the actual voltage signal, causing an increase or a decrease in the generator voltage, thus maintaining the reactive
between the generators within acceptable values. The adjustment of this compensation is made through trimpot P2.
According to the phasor diagram, the sensing voltage is influenced by the current coming from phase S, which is added to the
voltage of phases R and T. The influence is small in module and large in phase, which means that there is good compensation
for reactive loads and a small influence with active loads.
The current transformer (CT) for reactive compensation must be in phase S of the generator, and the voltage sensing signal
must be in phases R and T.
To make sure the compensation is in the proper direction, proceed as follows:
Operate the generator by itself (isolated from the grid) and apply a resistive load with about 20% of the generator capacity;
After completely rotating the P2 trimpot clock wise (CW), the generator voltage should decrease.
Rotating back the trimpot completely CCW, generator voltage should then increase; If this occurs, the CT polarity is correct.
Otherwise the CT should be inverted.
When several generators are connected in parallel, this procedure is required to ensure that all the CT's are properly polarized.
The current transformer for compensation of reactive must be in phase S of the generator and the feeding signal in the phase R.
To ensure the correct polarization of TC, Inductive Resistive loads must be applied and the system checked for good response
as below.
Resistive Loads: It will not present compensation with resistive load, keeping the excitation current and generator voltage
constant in the value adjusted via trimpot Vad. In case of compensation, it indicates that TC is in the wrong phase.
Inductive Loads: With inductive load application, it shall present negative compensation, decreasing the excitation current
corresponding to the gain adjusted in the trimpot droop (0 to 15% voltage adjusted in the Vad). If the compensation is positive, it
indicates the TC is inverted.
Capacitive Loads: With application of capacitive loads, it will present a positive compensation, increasing the excitation current
corresponding to the gain adjusted in the trimpot droop (0 to 15% voltage adjusted in the Vad). If the compensation is positive, it
indicates the TC is inverted.
Accuracy class of 0,6C12,5;
Window or bar type;
Transformer ratio will be In/5A or In/1A, where In/xA is the ratio of the TC primary. Ex.: 100/5A, 150/5A, 100/1A;
5A secondary current for regulator PAR/5 and 1A for regulator PAR/1;
The current in TC primary must be 20% bigger than the nominal current of the machine;
The TC operation frequency must be equal to the generator frequency;
The TC isolation voltage class must be bigger than the generator output voltage;
It must support 1.2 x In.
S
IS
R RT
¹ Only for models TH4.
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