The power supply voltage is rectified and filtered before being used by the AVR monitoring transistor. This principle ensures that regulation is not affected by distortions generated by the load. This excitation system consists of a "PMG" (permanent magnet generator). This is fitted at the rear of the machine and connected to the R438 AVR. The PMG supplies the AVR with constant voltage which is independent of the main alternator winding. As a result the machine has a short-circuit current capacity and good immunity to distortions generated by the load. The AVR monitors and corrects the alternator output voltage by adjusting the excitation current. - 50/60 Hz selection via the ST3 jumper.    

The LAM system is integrated in the R438 AVR as standard. Role of the "LAM" (Load Adjustment Module) On application of a load, the rotation speed of the generator set decreases. When it passes below the preset frequency threshold, the LAM causes the voltage to  drop by approximately 13% or 25% and consequently the amount of active load applied is reduced by approximately 25% to 50%, until the speed reaches its rated value again.

Hence the LAM can be used either to reduce the speed variation (frequency) and its duration for a given applied load, or to increase the applied load possible for one speed variation (turbo-charged engine). To avoid voltage oscillations, the trip threshold for the LAM function should be set approximately 2 Hz below the lowest frequency in steady state. During load impacts, the function helps the genset to return to its rated speed faster thanks to a gradual increase in voltage according to the principle:

If the speed drops between 46 and 50 Hz, the rated voltage follows a fast gradient as it is restored. If the speed drops below 46 Hz, since the engine needs more help, the voltage follows a slow gradient as it returns to the reference value.

General Characteristics